Chapter Notes: Fundus

Table of Contents
1. Anatomy of Retina
2. Microscopic Structure of Retina (Out to In)
3. Methods for Assessing Macular Disease
4. Fluorescein Angiography (FA)
5. Diabetic Retinopathy
6. Central Retinal Vein Occlusion
7. Central Retinal Artery Occlusion (CRAO)
8. Hypertensive Retinopathy
9. Toxaemia of Pregnancy
10. Retinitis Pigmentosa
11. Retinal Degenerations
12. Bull's Eye Maculopathy
13. Myopic Maculopathy
14. Eales' Disease (Periphlebitis Retinae)
15. Choroidal Neovascularization: Overview and Treatment
16. Understanding Retinopathy of Prematurity (ROP)
17. Persistent Hyperplastic Primary Vitreous (PHPV)
18. Photoreceptor Dystrophies
19. Dystrophies of the Retinal Pigment Epithelium (RPE)
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Anatomy of Retina

• The retina, which is the eye's innermost layer, is thin and transparent.
• It extends from the optic disc to the ora serrata and is divided into three main parts:
  • Optic Disc:
  • The optic disc, measuring 1.5 mm across, is where nerve fibers exit the eye.
• Macula:
  • Located at the back of the eyeball, the macula is 5.5 mm wide and corresponds to 15° of the visual field.
  • It plays a crucial role in photopic (daylight) vision and color vision.
  • The macula contains the macula lutea, a 3 mm area that appears yellow.
• Fovea Centralis:
  • The fovea centralis, the most sensitive part of the retina, provides the highest visual acuity and maximum light sensitivity.
  • It is the central depressed area of the macula, measuring 1.85 mm in diameter and covering 5° of the visual field.
  • Within the fovea, there is a central area called the foveola, which is 0.35 mm across.
• Foveal Avascular Zone (FAZ):
  • The FAZ is an area inside the fovea but outside the foveola, characterized by a lack of blood vessels.
• Foveola:
  • The foveola, measuring 0.35 mm in diameter, is located 2 disc diameters away from the temporal edge of the optic disc.
  • It is primarily composed of cone photoreceptors, which are essential for sharp vision.
• Umbo:
  • The umbo is a small depression at the center of the foveola, often observed as a foveal reflex.
• Peripheral Retina:
  • The peripheral retina is divided into four sections:
    • Near periphery
    • Mid periphery
    • Far periphery
    • Ora serrata, which is the serrated edge of the retina
• Thickness of Retina:
  • At the posterior pole: 0.5 mm
  • At the equator: 0.2 mm
  • At the ora serrata: 0.1 mm
• Artery to Vein (A:V) Ratio:
  • The normal A:V ratio is 2:3.
  • This ratio can increase in certain conditions:
    • Hypertensive Retinopathy: The ratio may become 1:3 due to arteriolar narrowing.
    • Papilloedema: The ratio can rise to 2:4 or higher because of vein dilation.

Blood Supply of the Retina

• The choriocapillaris supplies the outer four layers of the retina.
• The central retinal artery nourishes the inner six layers.
• The area around the optic disc receives blood from the Circle of Haller and Zinn, which connects short posterior ciliary arteries.

Microscopic Structure of Retina (Out to In)

• RPE (Retinal Pigment Epithelium): The outermost layer of the retina, consisting of pigmented cells that play a crucial role in supporting the photoreceptors.
• Rods and Cones: The photoreceptor cells responsible for capturing light and converting it into neural signals. Rods are sensitive to dim light, while cones are responsible for color vision and function best in bright light.
• External Limiting Membrane:. thin barrier that helps maintain the integrity of the outer retinal layers.
• Outer Nuclear Layer: Contains the cell bodies of the photoreceptor cells (rods and cones).
• Outer Plexiform Layer: The layer where the synapses between photoreceptors and bipolar cells, as well as horizontal cells, occur.
• Inner Nuclear Layer: Contains the cell bodies of bipolar cells, horizontal cells, and amacrine cells.
• Inner Plexiform Layer: The layer where synapses between bipolar cells, amacrine cells, and ganglion cells take place.
• Ganglion Cell Layer: Contains the cell bodies of ganglion cells, which receive signals from bipolar and amacrine cells.
• Nerve Fiber Layer: Contains the axons of ganglion cells, which form the optic nerve and transmit visual information to the brain.
• Internal Limiting Membrane: The innermost layer of the retina, serving as a boundary between the retinal tissue and the vitreous body.

Rhodopsin (Visual Purple)

• Rhodopsin is a light-sensitive pigment located in the discs of the outer segments of rod photoreceptors in the retina.
• It consists of a protein called opsin (specifically scotopsin. and a carotenoid known as retinal.
• Rhodopsin is a complex molecule tightly bound within the cell membrane, playing a crucial role in vision.
• The average molecular weight of human rhodopsin is approximately 40-45 kDa.
• When light strikes the retina, it is absorbed by the pigments in the rods and cones, initiating a series of chemical changes.
• These photochemical changes generate electrical signals, kickstarting the process of vision.
• Such changes occur in the outer segments of both rods and cones.

Visual Cycle

• Rhodopsin and Light Energy: Rhodopsin is a light-sensitive protein in the retina that plays a crucial role in vision. When exposed to light, it undergoes a series of transformations.
• Bacteriorhodopsin (in nanoseconds): This is a type of rhodopsin found in certain bacteria, and it changes very quickly, in nanoseconds, when it absorbs light.
• Lumirhodopsin (in microseconds): This is an intermediate stage in the visual cycle that occurs after rhodopsin absorbs light, and it lasts for microseconds.
• Metarhodopsin-I (in milliseconds): This is another intermediate stage that occurs after lumirhodopsin, and it lasts for milliseconds.
• Metarhodopsin-II (in seconds): This is a further stage in the visual cycle that lasts for seconds and is crucial for the regeneration of rhodopsin.
• 11-cis-retinal and All-trans-retinal: These are different forms of retinal, a molecule that is part of rhodopsin. 11-cis-retinal is the form that is present in the dark, while all-trans-retinal is produced when rhodopsin absorbs light.
• Isomerase: This is an enzyme that helps convert all-trans-retinal back to 11-cis-retinal, which is necessary for the regeneration of rhodopsin.
• NADH and NAD: These are molecules involved in the energy production and metabolism in cells. NADH is the reduced form of NAD, and they play a role in the regeneration of rhodopsin.
• OPSIN: OPSIN is a protein that, along with retinal, forms rhodopsin and is essential for the visual cycle.
• Dietary Vitamin A: Vitamin A is essential for the production of rhodopsin and is obtained from the diet. Carotenoids from plant sources can be converted into retinol in the body, while retinol is found in animal foods.
• Digestion and Absorption: Vitamin A is digested and absorbed from food in the intestines and transported in intestinal lymphatics.
• Storage in Liver: Vitamin A is stored in liver cells as retinol.
• Production of Retinol-Binding Protein: The liver produces retinol-binding protein, which carries retinol to other parts of the body.
• Transport of Retinol: Retinol is transported in the body bound to retinol-binding protein.
• Formation of Rhodopsin: Retinol is used to form rhodopsin, which is essential for night vision.
• Maintenance of Epithelial Cells: Vitamin A is also important for maintaining healthy corneal and conjunctival epithelial cells.

In rods, the following changes occur:

• Rhodopsin Bleaching: When exposed to light, rhodopsin undergoes bleaching, where the retinal molecule changes from the 11-cis form to the all-trans form, leading to the activation of the phototransduction cascade.
• Rhodopsin Regeneration: After bleaching, the all-trans-retinal is converted back to 11-cis-retinal through a series of enzymatic reactions, and then it binds to opsin again to regenerate rhodopsin.
• Visual Cycle: The visual cycle refers to the continuous process of rhodopsin bleaching and regeneration, which is crucial for maintaining the sensitivity of rod photoreceptors to light.

Cone Pigments:  

• Similarity to Rhodopsin: Cone pigments are similar to rhodopsin in that they consist of a protein component called opsin and a retinal molecule. However, in cone pigments, the retinal is in the 11-cis form, and the protein component is slightly different.
• Opsin Variants: The opsin protein in cone pigments is called photopsin, and it differs from scotopsin, which is the opsin protein in rhodopsin. This difference in opsin protein is what makes cone pigments sensitive to different wavelengths of light.
• Classes of Cone Pigments: There are three classes of cone pigments, each sensitive to different colors of light:
• Red-Sensitive (Erythrolabe): This pigment is sensitive to red light and is found in the long-wavelength cones.
• Green-Sensitive (Chlorolabe): This pigment is sensitive to green light and is found in the medium-wavelength cones.
• Blue-Sensitive (Cyanolabe): This pigment is sensitive to blue light and is found in the short-wavelength cones.

Photoreceptor Cells

The process of phototransduction in photoreceptor cells involves several steps:

• When light hits, Rhodopsin is activated.
• All-trans Retinal is converted to Metarhodopsin II.
• Opsin then activates transduction.
• This activation leads to the activation of Phosphodiesterase.
• As a result, levels of cGMP decrease.
• The decrease in cGMP causes Na+ channels to close.
• This closing of channels results in hyperpolarization of the cell.
• Following hyperpolarization, the release of synaptic transmitters decreases, which in turn affects bipolar cells and other neural elements.

Bipolar Cells

• Bipolar cells are the first-order neurons in the visual pathway.
• They are responsible for processing the signals from photoreceptors.
• The dendrites of bipolar cells are activated by the hyperpolarization of photoreceptors caused by light.
• Depending on the type of bipolar cell, they may depolarize or hyperpolarize in response to photoreceptor stimulation.
• This variation occurs because some bipolar cells receive input directly from photoreceptors, while others get input indirectly through horizontal cells.
• The interaction between bipolar cells creates a mechanism for lateral inhibition, which is important for spatial information processing in the visual system.

Muller Cells

• Muller cells are a type of supportive cell found in the retina. They play a crucial role in maintaining the health and function of retinal neurons.

Retinal Astrocytes

• Astrocytes are a kind of neuroglial cell, which are non-neuronal cells located in the central nervous system. They have numerous branches, and their footplates rest on capillaries within the nervous tissue.
• Astrocytes serve both nutritive and structural functions, providing essential support to neurons.

Amacrine Cells

• Amacrine cells are involved in processing information at the synapse between the axon of a bipolar cell and the dendrites of a ganglion cell.
• They play a role in making temporal adjustments to the signals being sent from bipolar cells to ganglion cells.
• By modulating the response projected onto the ganglion cell, amacrine cells help refine and adjust the visual information being transmitted to the brain.

Horizontal Cells

• Horizontal cells are responsible for transmitting signals horizontally in the outer plexiform layer of the retina, relaying information from rods and cones to bipolar cells.
• Their primary function is to enhance visual contrast through a mechanism known as lateral inhibition.
• When a small spot of light strikes the retina, the central region is excited, while the surrounding area is inhibited by the horizontal cells.
• This process is crucial for maintaining high visual accuracy by effectively conveying the contrast between different portions of the visual image.

Ganglion Cells

• The electrical signals generated by bipolar cells are transmitted to ganglion cells.
• These signals may be altered by amacrine cells before reaching the ganglion cells.
• Ganglion cells then send these modified signals to the brain in the form of action potentials.

Types of Ganglion Cells:

Ganglion cells in the retina can be categorized into different types based on their response to light and their specific functions in vision.

• On-center and Off-center cells: These cells have opposite responses to light. On-center cells increase their activity when they are illuminated, while Off-center cells decrease their activity under the same conditions.
• W, X, and Y cells: These are specific types of ganglion cells with distinct characteristics and functions.

W-ganglion cells

• Size: These cells are small in size.
• Dendritic Branching: W-ganglion cells have widely branching dendrites, which allows them to cover a larger area of the visual field.
• Function: These cells are responsible for rod vision, which is important for seeing in low light conditions. They are also sensitive to directional movement, making them crucial for detecting movement in the visual field.

X-ganglion cells

• Size: X-ganglion cells are medium-sized.
• Receptive Field: These cells have a very small receptive field because their dendrites do not spread out widely.
• Function: X-ganglion cells are responsible for colour vision, helping to differentiate between different colours in the visual field.

Y-ganglion cells

• Size: Y-ganglion cells are the largest of the ganglion cells.
• Dendritic Field: These cells have a very broad dendritic field, allowing them to capture a wide range of visual information.
• Function: Y-ganglion cells respond to rapid changes in visual stimuli, including fast movement and quick shifts in light intensity. This makes them important for detecting dynamic changes in the visual environment.

Methods for Assessing Macular Disease

A. Clinical Evaluation

• Patients with macular disease may experience distortion of images, which can manifest as wavy lines, blurred areas, or blank spots in their vision.
• A positive scotoma may be present, indicating areas of vision loss.
• Metamorphopsia, a condition where straight lines appear bent or distorted, is often reported.
• Patients might also experience micropsia, where objects appear smaller than they are.
• Visual acuity is typically reduced in macular disorders.
• The pupillary light reaction remains normal in eyes with macular disorders.
• Colour vision is usually not significantly affected.

B. Amsler Grid Test

• The Amsler Grid Test is used to assess a 10° visual field around the fixation point.
• The Amsler grid consists of a 10 cm square divided into smaller 5 mm squares.
• When viewed from a distance of one third of a metre, each small square represents an angle of 1°.

Uses of Tests for Macular Disease and Optic Nerve Lesions

• Screening for macular disease.
• Diagnosing subtle optic nerve lesions.

Ophthalmoscopy for Optic Disc Evaluation

• Conducting ophthalmoscopy with red-free light (green light) is particularly useful for evaluating the optic disc.

Photostress Test: Procedure and Purpose

• The Photorstress test is a basic form of the dark adaptation test, where visual pigments are bleached by exposure to light.

Procedure for the Photostress Test

• Assess the best corrected visual acuity of the patient.
• Instruct the patient to focus on a pen torch held 3 cm away for 10 seconds.
• Record the time taken to read any three letters from the pre-test acuity line, known as the Photostress Recovery Time (PSRT).
• Compare the results with the other eye.
• PSRT (Pupil-Size-Related Time) is elevated in macular conditions such as Cystoid Macular Edema (CME) and Central Serous Retinopathy (CSR).
• However, it is not raised in optic nerve lesions.

Methods for Evaluating Macular Disease in Opaque Media

When assessing macular disease in patients with opaque media, various methods can be employed to evaluate the macula's functionality.

• Two-point Discrimination Test: This test offers a fundamental understanding of the macula's performance.
• Pin Hole Test: Utilizing a pinhole aperture enhances focus and minimizes scattering caused by corneal scars and cloudy lenses.
• Maddox Rod Test: This test examines the continuity of the rod placed in front of the eye across all quadrants. Any break or distortion indicates a potential retinal issue.
• Amsler Grid: The Amsler Grid is employed to rule out visual distortions (metamorphopsia) or blind spots (scotoma).
• Purkinje Vessel Shadows: This method relies on the entoptic phenomenon, where visual effects originating from within the eyes are perceived. In the absence of retinal problems, the shadows of retinal blood vessels should be visible.
• Blue-field Entoptoscope: In the absence of retinal issues, moving dots representing white blood cells should be visible, moving smoothly in all four quadrants. This technique also utilizes the entoptic phenomenon.
• Interferometers: Particularly useful for individuals with immature cataracts, this test assesses the macula's resolving power by employing two light beams to create a pattern on the retina. The patient indicates the direction of the patterns, starting with larger patterns and gradually progressing to smaller ones.
• PAM (Potential Acuity Meter): The PAM displays a standard Snellen chart through a small clear area of an immature cataract, proving most reliable for individuals with visual acuities of 6/60 or better.
• Electrophysiological Tests: These tests include the Electroretinogram (ERG) and Visual Evoked Potential (VEP) to assess the macula's function.

Electroretinogram (ERG)

• The Electroretinogram (ERG) is a diagnostic test that measures the electrical activity of the retina in response to bright light. This activity is recorded under both light-adapted and dark-adapted conditions.
• During the test, two main waves are observed:
• a wave. This wave is generated by the photoreceptors in the retina.
• b wave. This wave is produced by the activity of bipolar cells in the retina. The b1 wave reflects activity from both rod and cone cells, while the b2 wave indicates activity from cone cells only.
• To specifically isolate rod responses, a fully dark-adapted eye can be stimulated with a dim light flash. Cone responses can be elicited by using a fully light-adapted eye exposed to a bright light flash or by employing a flicker light stimulus of 30-40 Hz.

In individuals with retinitis pigmentosa (RP), the ERG amplitudes are significantly reduced. Typically, the scotopic ERG is affected, while the photopic response remains within normal limits.

2. Visual Evoked Potential (VEP)

• When light reaches the retina, it triggers a sequence of nerve impulses.
• These impulses are then transmitted to the visual cortex.
• The electroencephalogram (EEG) is recorded in the visual cortex during this process.
• This procedure illustrates the activity from the ganglion cell layer of the retina all the way to the visual cortex in the brain.

3. Electrooculogram (EOG)

• The electrooculogram measures the resting electrical potential difference between the electrically negative cornea and the electrically positive back of the eye.
• This measurement reflects the activity of the retinal pigment epithelium (RPE) and the photoreceptors in the eye.
• Various diseases, particularly those affecting the RPE, can influence this measurement.

Fluorescein Angiography (FA)

FA is a diagnostic procedure used to examine the blood flow in the retina and choroid, as well as to detect abnormalities in blood vessels caused by various eye conditions.

Technique. During FA, a 10% solution of sterile sodium fluorescein dye is injected into the antecubital vein. Serial photographs of the fundus are taken at specific intervals:

• First photograph:. seconds after injection
• Subsequent photographs: every second for the next 20 seconds, and then every 3-5 seconds for one minute
• Final photographs: taken after 10 minutes

Structures Examined. FA allows visualization of the following structures:

• Uveal tissue: including the iris, ciliary body, and choroid
• Retina

Avascular structures, such as the lens and cornea, cannot be visualized using this technique.

Results. The findings from FA can be classified as normal, hypofluorescence, or hyperfluorescence.

• Hypofluorescence. This indicates blocked fluorescence and can be caused by factors such as haemorrhage, exudates, or capillary nonperfusion (CNP).
• Hyperfluorescence. This suggests leakage or defects in the retinal pigment epithelium (RPE). Leakage typically increases in size, while RPE defects remain unchanged in size.

Differential Diagnosis (D/D): Sudden Painless Loss of Vision

• Central Retinal Artery Occlusion
• Vitreous Haemorrhage
• Retinal Detachment
• Central Retinal Vein Occlusion
• Central Serous Retinopathy
• Optic Neuritis
• Methyl Alcohol Amblyopia

Differential Diagnosis (D/D): Sudden Painful Loss of Vision

• Acute Congestive Glaucoma
• Acute Iridocyclitis
• Chemical Injuries to the Eyeball
• Mechanical Injuries to the Eyeball

Diabetic Retinopathy

Overview

• Diabetic retinopathy (DR) is a complication of diabetes that affects the eyes. It involves damage to the tiny blood vessels in the retina, the part of the eye responsible for capturing images and sending them to the brain. This condition is a result of long-term high blood sugar levels, which can lead to various changes in the retinal blood vessels.

Pathogenesis of Diabetic Retinopathy

The development of diabetic retinopathy is linked to several key factors:

• Hypoxia: This refers to a lack of oxygen in the retinal tissues, which can occur due to several reasons:
• Reduced levels of 2,3-diphosphoglycerate (2,3-DPG) can impair the release of oxygen from hemoglobin to the tissues.
• High levels of glycosylated hemoglobin indicate poor blood sugar control and can reduce the oxygen-carrying capacity of blood.
• Excess glucose in the cells can lead to the accumulation of sorbitol and fructose through the polyol pathway, increasing osmotic pressure and causing cellular swelling.
• Impaired glucose metabolism can lead to an increased release of growth factors, such as growth hormone. This, in turn, raises the levels of fibrinogen and alpha-2 globulin in the blood, promoting the hyperaggregation of red blood cells (RBCs) and platelets. This hyperaggregation can further impair blood flow and contribute to the damage of retinal blood vessels.

Pathophysiology of Diabetic Retinopathy

• Diabetic retinopathy involves the loss of pericytes, which are contractile cells that help to stabilize the blood-retinal barrier.
• The loss of these cells leads to mechanical weakening of the capillary wall, making it more susceptible to damage.
• As a result, there is focal dilatation and disruption of the blood-retinal barrier, allowing for abnormal fluid and protein leakage.
• This process contributes to the formation of microaneurysms, which are small outpouchings of the capillary wall.
• Microaneurysms are typically located around areas of capillary dropout and are indicative of early diabetic retinopathy.
• During ophthalmoscopy, they appear as red dots, while on fluorescein angiography, they are seen as hyperfluorescent dots due to the leakage of dye from the damaged vessels.

Risk Factors for Diabetic Retinopathy

• Duration of Diabetes: The length of time a person has been diagnosed with diabetes is the most significant risk factor for developing diabetic retinopathy. The longer the duration, the higher the risk.
• Metabolic Control: Maintaining good control of blood glucose levels can substantially delay the onset of diabetic retinopathy. Improved metabolic control reduces the risk of developing complications associated with diabetes.
• Pregnancy: Pregnant women with diabetes are at an increased risk of developing diabetic retinopathy, as pregnancy can affect blood sugar levels and vascular health.
• Anemia: The presence of anemia may exacerbate the risk of diabetic retinopathy, potentially due to impaired oxygen delivery to retinal tissues.
• Hypertension: High blood pressure is a known risk factor for various diabetic complications, including retinopathy. It can contribute to vascular damage and exacerbate existing retinal issues.
• Renal Disease: The presence of renal disease in individuals with diabetes can increase the risk of developing diabetic retinopathy. Kidney dysfunction may impact overall metabolic control and vascular health.

Classification of Diabetic Retinopathy

• Simple Background Diabetic Retinopathy
• Pre-Proliferative Diabetic Retinopathy
• Proliferative Diabetic Retinopathy

A. Simple Background DR (BDR)
Clinical Features:

• Microaneurysms. These are the earliest visible indicators of diabetic retinopathy (DR). In DR, there is a loss of pericytes, leading to a mechanical weakening of the capillary wall. Microaneurysms often occur in areas where capillaries have dropped out. They appear as red dots during an eye examination and as hyper-fluorescent dots on fluorescein angiography.
• Haemorrhages. These can be dot and blot or flame-shaped.
• Hard exudates and a few soft exudates are present; hard exudates are caused by leaked lipids, while soft exudates come from axonal debris. Retinal edema is also a feature.
• Macular oedema. This involves retinal thickness or hard exudates within 1 disc diameter (DD) of the fovea centre (1500 µm). If the fovea is affected by edema or hard exudates, it is a common cause of visual impairment in diabetic patients, especially those with type 2 diabetes.
• CSMO (Clinically Significant Macular Edema) is identified by one or more of the following:
• Retinal edema within 500 µm of the fovea centre.
• Hard exudates within 500 µm of the fovea if linked to nearby retinal thickening (which may be outside the 500 µm limit).
• Retinal edema that is one disc area (1500 µm) or larger, with any part within one disc diameter of the fovea centre (1 DD is 1.5 mm).

Treatment of Diabetic Retinopathy

A. Non-Proliferative Diabetic Retinopathy (NPDR)

Medical treatment:

• Maintain strict glycemic control to manage blood sugar levels effectively.
• Provide anti-hypertensives if the patient has high blood pressure to control blood pressure levels.
• Use anti-oxidants to help reduce oxidative stress.
• If Clinically Significant Macular Edema (CSMO) is present, perform laser photocoagulation-either focal or grid-after conducting fluorescein angiography to assess the extent of edema.

B. Pre-Proliferative Diabetic Retinopathy

Vascular changes:

• Venous looping, beading, and sausage-like segmentation are observed in retinal veins.
• Arterioles become narrow and may be obliterated, indicating severe vascular changes.
• Dark blot hemorrhages are indicative of hemorrhagic retinal infarcts, signifying serious damage.
• Presence of multiple cotton-wool spots, which are areas of localized retinal edema.
• IRMA (Intraretinal Microvascular Abnormalities) refers to arteriovenous shunts resulting from capillary closure, indicating severe retinal ischemia.
• Ensure strict follow-up to monitor for progression to Proliferative Diabetic Retinopathy (PDR).
• If CSMO is present, manage it according to established protocols.
• The usual medical treatment includes maintaining strict control of blood sugar levels to prevent further progression.

C. Proliferative Diabetic Retinopathy (PDR)

• Neovascularization: This involves the growth of new blood vessels, which can occur at the optic disc (NVD) or elsewhere in the retina (NVE).
• Vitreous Detachment: In PDR, vitreous detachment is usually incomplete.
• Hemorrhage: There can be intravitreal and pre-retinal hemorrhages. Pre-retinal hemorrhages, also known as prehyaloid hemorrhages, are typically boat-shaped and located between the internal limiting membrane and the posterior hyaloid face.

Complications of PDR:

• Persistent intra-gel vitreous hemorrhage: This refers to ongoing bleeding within the vitreous gel.
• Retinal detachment: This can occur as both tractional and rhegmatogenous types.
• Opaque membranes: These membranes are found on the posterior surface of the detached hyaloid face of the vitreous.
• Rubeosis iridis: This condition can lead to neovascular glaucoma (NVG).
• Burnt-out stage: This stage is characterized by an increase in the fibrous component.

Management and Treatment of PDR

• Anti-hypertensive medications: These are often essential for managing patients with PDR to control systemic blood pressure.
• Antioxidants: Antioxidants also play an important role in the management of PDR.
• Panretinal photocoagulation (PRP): This is the preferred treatment for PDR and can be done using Argon laser, double frequency NdYAG (Yellow laser), or Diode laser. The aim of PRP is to convert hypoxic areas into anoxic ones, which leads to the shrinkage of new blood vessels and prevents further neovascularization.
• Pre-retinal hemorrhages: When pre-retinal hemorrhages obstruct the view of the retina for PRP, laser treatment may increase the risk of additional retinal and vitreous hemorrhages. Therefore, PRP should be avoided in cases of pre-retinal hemorrhage.

Method of PRP:

• In PRP, either the Goldmann or Panretinal photocoagulation lens is typically used.
• Initial burns are made in a double arc formation.
• These burns are positioned 2 disc diameters (approximately 3 mm) temporal to the macula.
• This placement acts as a visual barrier, preventing accidental burns to the fovea.
• Around 2000-3000 burns are applied in a scatter pattern.

Surgical Management:

• In cases of proliferative diabetic retinopathy that are complicated, surgical options include:
• Pars plana vitrectomy:. surgical procedure to remove the vitreous gel from the eye.
• Retinal detachment surgery:. procedure to repair a detached retina.
• Surgical extraction of cataracts: Removal of cataracts that have developed due to diabetes.

Management of Neovascularization in Diabetic Retinopathy

• Argon Laser PRP: This technique is used to address gaps in the treatment of neovascularization.
• Xenon-Arc Photocoagulation: This method involves applying photocoagulation over previous laser scars to manage neovascularization.
• Cryotherapy: Cryotherapy can be applied to the anterior retina as a treatment option for neovascularization.
• Anti-VEGF Injections: The latest approach for resistant cases of Diabetic Retinopathy (DR) involves administering Anti-VEGF (Vascular Endothelial Growth Factor) injections in the vitreous cavity.

Vision Loss in Diabetic Patients

• Cataract:. gradual, progressive, and painless loss of vision in a diabetic patient is most commonly due to cataracts.
• Cystoid Macular Edema (CME): The most common cause of moderate vision loss in a diabetic patient is CME.
• Vitreous Hemorrhage: Floaters in a diabetic patient can indicate vitreous hemorrhage. However, they may also be associated with other conditions such as retinal tears or detachment.

Differential Diagnosis of Soft Exudates/Cotton-Wool Spots

• Diabetic retinopathy
• Hypertensive retinopathy
• Toxaemia of pregnancy
• HIV infection
• Collagen disorders such as discoid lupus erythematosus (DLE), polyarteritis nodosa (PAN), and scleroderma
• Purtscher's retinopathy

Conditions Leading to Rubeosis Iridis

• Central Retinal Vein Occlusion (CRVO)
• Eales disease
• Sickle cell retinopathy
• Carotid occlusive disease
• Ocular ischemic syndrome
• Fuchs's heterochromic cyclitis
• Exfoliation syndrome

Studies Conducted in Diabetic Retinopathy (DR)

• DRS: Diabetic Retinopathy Study
• ETDRS: Early Treatment Diabetic Retinopathy Study
• DRVS: Diabetic Retinopathy Vitrectomy Study
• Wisconsin's Epidemiological Study of Diabetic Retinopathy

Examination Schedule

• Age at Onset
• Follow-up
• Time of First Examination
• 0-30 years
• 31 years and older
• 5 years after onset
• At time of diagnosis of DM
• Every year
• During
• In first trimester
• Every 3 months

Central Retinal Vein Occlusion

Central Retinal Vein Occlusion (CRVO) is the second most prevalent retinal condition after diabetic retinopathy.

Factors that Increase the Risk of CRVO:

• Age: The risk of CRVO increases with age, particularly in the 6th and 7th decades of life.
• Systemic Hypertension: High blood pressure is the most significant risk factor for CRVO.
• Blood Dyscrasias: Conditions that lead to high blood viscosity, such as chronic leukemias and polycythemia, increase the risk of CRVO.
• Intraocular Pressure: An increase in intraocular pressure is also a risk factor for CRVO.
• Hypermetropia: While hypermetropia (farsightedness) can be a factor, it is not always considered a primary risk for vein occlusion.
• Congenital Anomaly:. congenital anomaly of the central retinal vein can predispose individuals to CRVO.
• Periphlebitis: Inflammation of the retinal veins associated with conditions like Sarcoidosis and Behcet's disease can increase the risk of CRVO.

Types of Central Retinal Vein Occlusion (CRVO)

• Non-ischemic CRVO
• Ischemic CRVO
• CRVO in young adults (also known as papillophlebitis)
• Ischemic CRVO is associated with more severe decreased visual acuity compared to non-ischemic CRVO.
• Relative afferent pupillary defect (RAPD) is indicative of ischemic CRVO.
• Tortuosity and dilation of retinal veins are common findings in CRVO.
• Hemorrhages such as dot-and-blot and flame-shaped types, especially around the optic disc, are observed.
• Cotton-wool spots are more prevalent in ischemic CRVO.
• Optic disc edema and hyperemia are present in CRVO cases.
• Macular edema with possible cystoid changes may occur.
• Neovascular glaucoma can develop 90 to 100 days after ischemic CRVO.
• A typical feature of CRVO includes multiple flame-shaped hemorrhages around the optic disc.
• Fluorescein angiography is used to determine the type of occlusion in CRVO.
• In cases of ischemic CRVO, prompt panretinal photocoagulation is necessary to prevent neovascular glaucoma.
• In non-ischemic CRVO, hemorrhages may resolve on their own, and treatments such as peribulbar or intravitreal steroid injections (IVTA) may be administered to aid absorption.

Central Retinal Artery Occlusion (CRAO)

Causes:

• Emboli: Small clots or debris from the heart or carotid artery can block the central retinal artery.
• Vessel Blockage: Plaques or inflammation can obstruct the blood vessels.
• High Intraocular Pressure: Often a significant factor in severe cases.
• Amaurosis Fugax:. brief loss of vision that may precede a sudden and severe painless loss of vision.
• Cilioretinal Artery: Patients with dual blood supply to the macula from both the central retinal artery and the cilioretinal artery may retain some central vision after CRAO.

Signs and Symptoms:

• Marcus-Gunn Pupil: Also known as relative afferent pupillary defect, indicates a problem with the optic nerve or retina.
• Retina Edema: Cloudy appearance of the retina due to swelling.
• Cherry-Red Spot:. distinctive sign at the centre of the fovea.
• Retinal Artery Narrowing: Significant narrowing of retinal arteries, making them appear thread-like.
• Cattle-Track Appearance: Segmentation of blood flow in venules and arterioles.
• Optic Atrophy: Possible in later stages of the condition.

Management:

• Ocular Emergency: CRAO is an ocular emergency; the patient should be advised to lie flat.
• Ocular Massage: Firm ocular massage can help reduce intraocular pressure.
• Intravenous Acetazolamide: Administering 500 mg intravenously for rapid pressure reduction.
• Inhalation Therapy: Inhalation of a mixture of 5% CO and 95% O ₂  to help relax the patient.
• Anterior Chamber Paracentesis: This procedure aids in quickly lowering intraocular pressure.

Differential Diagnosis of Cherry-Red Spot

• Tay-Sachs disease is a form of gangliosidosis.
• Niemann-Pick disease falls under the category of sphingolipidosis.
• Other types of gangliosidosis include:
  • Type I-Generalised gangliosidosis
  • Type II-Sandhoff's disease
  • Sialidosis, also referred to as Cherry-red spot myoclonus syndrome
• Gaucher's disease
• Metachromatic leucodystrophy
• Blunt trauma to the eye can also lead to the appearance of a cherry-red spot.
• This occurs due to a phenomenon known as Berlin's edema, where a milky white cloudiness affects a large area of the foveal region.
• The cherry-red spot may fade or undergo changes in pigmentation.
• If the spot persists, it can lead to the development of a lamellar hole, which may progress to a full-thickness macular hole over time.

Hypertensive Retinopathy

When examining the fundus in cases of hypertensive retinopathy, the following characteristics are typically observed:

• Vasoconstriction: This refers to the narrowing of blood vessels in the retina.
• Leakage: There is evidence of fluid leakage from the blood vessels.
• Arteriosclerosis: This indicates hardening and thickening of the retinal blood vessels.
• Hollenhorst plaques: These are cholesterol-based retinal emboli associated with an increased risk of Branch Retinal Artery Occlusion (BRAO) and Central Retinal Artery Occlusion (CRAO). In hypertensive retinopathy, Hollenhorst plaques often coexist with atherosclerotic changes.
• Other types of retinal emboli: These include platelet-fibrin and calcific emboli.
• Arteriolar attenuation: This refers to the narrowing of arterioles in the retina.

A-V Crossing Findings

A-V crossing findings in hypertensive retinopathy indicate changes in the arteries and veins due to atherosclerosis. Hemorrhages are commonly observed as flame-shaped, and in some cases, vitreous hemorrhages may also be present. Exudates, both hard and soft, can be seen in the retina. Hard exudates in the macular area are arranged radially, forming what is known as the macular star, while soft exudates are more prevalent in cases of malignant hypertension. Retinal edema may involve the macula, and in severe cases, swelling of the optic nerve head, known as papilloedema, can occur.

Hypertensive Retinopathy: Causes of Significant Vision Loss

• Retinal hemorrhages affecting the macula.
• Macular edema.
• Vision loss does not occur due to papilloedema, as this condition does not impact visual acuity.

Grading of Hypertensive Retinopathy

• Grade I: Mild generalized attenuation of the arterioles.
• Grade II:
  • Severe generalized and focal arteriolar attenuation.
  • Salus sign: An S-shaped deflection of veins at the arteriovenous junction.
• Grade III:
  • Hemorrhages.
  • Exudates.
  • Copper-wiring of arterioles.
  • Bonnet sign/Gunn's sign.
• Grade IV:Papilloedema with features of Grade III and silver wiring of arterioles.

Additional Ocular Effects of Hypertension

• Central vein occlusion and branched vein occlusion are conditions that can occur due to hypertension.
• Retinal artery occlusion is another ocular complication associated with high blood pressure.
• Elschnig's spots are ischemic choroidal infarcts observed in patients with malignant hypertension.
• Macroaneurysms can also be a result of elevated blood pressure in the eyes.
• Non-arteritic anterior ischemic optic neuropathy is an optic nerve condition linked to hypertension.
• Ocular motor nerve palsies may occur in hypertensive patients, affecting eye movement.
• Subconjunctival haemorrhages are bleeding under the conjunctiva that can be seen in hypertension cases.
• Occipital infarct refers to a stroke in the occipital lobe, which can be associated with high blood pressure.

Toxaemia of Pregnancy

• Eclamptic retinopathy, also known as toxaemia of pregnancy, presents similar features to hypertensive retinopathy.
• In severe cases, widespread oedema can lead to retinal detachment.
• Persistent retinal vessel spasm results in severe retinal hypoxia, causing cotton-wool spots and superficial haemorrhages.
• Macular star and flat macular detachment can occur due to oedema.
• The presence of retinopathy related to serious pregnancy complications should be taken seriously as it may indicate a need for termination of pregnancy. otherwise, there is a risk of permanent visual loss.

Retinitis Pigmentosa

Retinitis pigmentosa refers to a group of inherited conditions characterized by the gradual degeneration of photoreceptors in the retina, specifically affecting the rod cells. This condition falls under the category of photoreceptor dystrophy and is usually sporadic in nature.

Inheritance Patterns:

• Autosomal Dominant (AD): This type has the best prognosis and is the most common form after sporadic cases.
• X-linked Recessive: Generally has a poorer outlook compared to other types, although individual cases may vary.
• Autosomal Recessive (AR): This type also contributes to the inheritance of retinitis pigmentosa.

Common Symptoms:

• Nyctalopia: Difficulty seeing in low light conditions.
• Impaired Dark Adaptation: Trouble adjusting to darkness after being in a brightly lit environment.

Decreased visual acuity may occur due to associated conditions such as cystoid macular edema.

Fundus Features:

The characteristic features of retinitis pigmentosa are primarily observed in the mid-periphery of the retina and include a classic triad of findings:

• Retinal Bone-Spicule Pigmentation: The presence of pigmentary changes in the form of bone-spicule-like deposits in the retina.
• Pale, Waxy Disc: This finding indicates progressive optic atrophy and is associated with the degeneration of optic nerve fibers.

Other Ocular Features: Common Conditions and Their Implications

• CME: Cystoid macular edema.
• OAG: Open-angle glaucoma.
• PSC: Posterior subcapsular cataract.
• PVD: Posterior vitreous detachment.
• Keratoconus:. condition characterized by the thinning and cone-like shape of the cornea.
• Myopia: Also known as nearsightedness, where distant objects appear blurry.
• Disc Drusen: Accumulation of abnormal material on the optic disc, which can be a benign finding but may have clinical implications.

Investigations:

• ERG (Electroretinography): Shows subnormal amplitude, particularly in the scotopic (dark-adapted) phase, indicating retinal dysfunction.
• Perimetry: Reveals a ring scotoma due to mid-peripheral retinal involvement. This finding is also associated with open-angle glaucoma, where it is referred to as a double arcuate scotoma.

Atypical Retinitis Pigmentosa

• Retinitis Punctata Albescens: Characterized by the presence of white dots in the retina instead of the typical bony spicule pigmentation.
• Sector RP: Involvement is limited to a sector of the retina rather than the entire midperiphery, differentiating it from classic RP.
• Pericentric RP: The disease originates in the central retina, contrasting with the usual mid-peripheral onset.
• RP with Exudative Vasculopathy: This variant involves retinal damage accompanied by exudative changes, which can lead to significant vision loss.
• Retinitis Pigmentosa Sine Pigmento: Bony spicules are absent in this variant; instead, there is a dispersion of pigment that resembles a salt-and-pepper fundus appearance.

Systemic Associations

• Bassen-Kornzweig syndrome: This syndrome involves a trio of conditions: Retinitis pigmentosa, abetalipoproteinemia, and acanthocytosis.
• Refsum's syndrome: This condition arises from issues in phytanic acid metabolism, impacting various tissues, including the eyes.
• Usher syndrome: Usher syndrome is characterized by Retinitis pigmentosa accompanied by hearing loss. It is the most prevalent condition associated with Retinitis pigmentosa.
• Cockayne syndrome: This syndrome often manifests as dwarfism during childhood.
• Kearns-Sayre syndrome: This syndrome is marked by a combination of Retinitis pigmentosa, weakness of the eye muscles, and cardiac problems.
• Mucopolysaccharidosis: This group of disorders is caused by the buildup of complex carbohydrates in the body.
• Bardet-Biedl syndrome: This syndrome includes features such as intellectual disability, extra fingers or toes, and Retinitis pigmentosa.
• Laurence-Moon syndrome: Laurence-Moon syndrome presents symptoms similar to Bardet-Biedl syndrome, along with spastic paraplegia.
• Friedreich's ataxia: This condition is characterized by lack of coordination and involuntary eye movements.

Differential Diagnosis of Night Blindness

• Xerophthalmia: This condition involves dry eyes and is caused by a deficiency of vitamin A.
• Retinitis Pigmentosa:. genetic disorder that leads to the progressive degeneration of the retina, affecting night vision and peripheral vision.
• High Myopia: Also known as pathological myopia, this condition involves severe nearsightedness that can lead to retinal changes and night vision problems.
• Congenital Stationary Night Blindness:. hereditary condition present from birth that causes difficulty seeing in low light conditions, but with stable vision over time.
• Fundus Albipunctatus:. retinal disorder characterized by the presence of white dots in the retinal fundus, affecting night vision.
• Oguchi's Disease:. rare genetic condition that affects the retina and leads to night blindness and changes in retinal appearance.
• Choroideremia:. genetic disorder that leads to progressive loss of vision due to degeneration of the choroid, retinal pigment epithelium, and retina, affecting night vision.

Treatment

Currently, there is no effective treatment available to alter the progression of these diseases.

Retinal Degenerations

A. Benign Peripheral Retinal Degenerations

• Microcystoid Degenerations: These involve the formation of small cystoid spaces within the retinal layers, typically considered a benign condition.
• Snowflake Degenerations: Characterized by the presence of white, snowflake-like opacities in the retina, these degenerations are usually benign and not sight-threatening.
• Paving-Stone Degenerations: This type involves the appearance of paving-stone like patterns in the retinal pigment epithelium, indicative of benign changes.
• Honey-Comb Retinal Degenerations: These are marked by a honeycomb-like pattern in the retina, representing a benign degenerative process.
• Drusen: The presence of drusen, which are small yellowish-white accumulations of waste material in the retina, can signify early retinal changes and are often associated with age-related macular degeneration.
• Oral Pigmentary Degenerations: These involve the degeneration of retinal pigment epithelium with pigmentary changes and are generally considered benign.

B. Factors Increasing Risk of Vitreo-Retinal Degenerations Leading to Rhegmatogenous RD

1. Lattice Degenerations:

• Typically found in individuals with high myopia.
• Characterized by circumferential, spindle-shaped areas of retinal thinning.
• These areas may be associated with the formation of holes or tears in the retina, which can trigger retinal detachment.

2. Snail-track Degenerations:

• Comprise bands of densely packed snowflake-like structures.
• These degenerations feature large round holes, making retinal detachment a common occurrence.

3. Other Degenerative Conditions:

• Acquired retinoschisis involves the splitting of the sensory retina into two layers: the choroidal layer and the vitreous layer.
• White with pressure describes the appearance of the retina under varying pressure conditions.
• White without pressure similarly refers to the retina's appearance under different pressure conditions.

What is Retinal Detachment?

• Retinal detachment occurs when the sensory retina separates from the retinal pigment epithelium (RPE) due to fluid buildup beneath the retina.

Types of Retinal Detachment

• Rhegmatogenous Detachment: This type happens when there is a tear or hole in the retina. It is often triggered by posterior vitreous detachment (PVD) in older individuals, conditions like high myopia, aphakia, or trauma.
• Tractional Detachment: Tractional retinal detachment occurs when bands of traction develop due to the growth of new blood vessels. This type is commonly associated with conditions that cause neovascularization.
• Exudative Detachment: Exudative retinal detachment is caused by problems in the choroid, leading to fluid leakage into the space beneath the retina. This can occur due to inflammation or issues with blood vessels. Conditions such as posterior uveitis, Central Serous Retinopathy (CSR), Coats' disease, tumors like choroidal melanoma and retinoblastoma, or sudden low eye pressure from surgery or globe perforation can lead to exudative detachment.

Symptoms of Retinal Detachment

• Floaters: Floaters are small opacities in the vitreous caused by the dispersion of pigment from retinal pigment epithelial cells. They are commonly associated with rhegmatogenous retinal detachment and, in some cases, exudative retinal detachment (due to vitreous cells). However, floaters are not typically seen in tractional retinal detachment.
• Photopsia: Photopsia refers to the perception of flashes of light, usually resulting from the irritation of photoreceptor cells. This symptom is most commonly linked to rhegmatogenous retinal detachment and, to a lesser extent, tractional retinal detachment. It is not a feature of exudative retinal detachment.
• Visual Field Defects: Visual field defects correspond to the area of the retina that is detached. Patients may experience loss of vision in specific areas of their visual field depending on the location of the detachment.
• Diminished Visual Acuity: Diminished visual acuity occurs when the central part of the retina is affected by the detachment. This can lead to a significant decrease in overall visual clarity and sharpness.

Examination Findings in Retinal Detachment

• Grey Reflex: The presence of a grey reflex indicates retinal detachment due to the loss of the normal choroidal glow. In exudative and rhegmatogenous types, retinal detachments typically appear convex, while they are concave in tractional types.
• Fluid Shift: Fluid shift is a finding primarily associated with exudative retinal detachment.
• Pigmented Line:. pigmented line may be visible at the border of attached and detached retina in older cases of retinal detachment. This finding is more common in older detachments.
• Hole:. hole may be present in cases of rhegmatogenous retinal detachment but is not necessarily observed in tractional or exudative types.

Methods for Examining the Retina

• +90D Lens/Hruby Lens: These lenses are primarily used for examining the central retina in detail.
• 3-Mirror Contact Lens: The 3-mirror contact lens allows for a comprehensive examination of the entire retina, including the peripheral areas.
• Direct Ophthalmoscopy: Direct ophthalmoscopy is useful for viewing only the central fundus of the eye and is not suitable for peripheral examination.
• Indirect Ophthalmoscopy: Indirect ophthalmoscopy, with or without scleral indentation, is particularly effective for examining the peripheral retina. This method allows for a wide-field view of the retina and is essential for detecting peripheral retinal detachments.

Additional Investigations

• ERG (Electroretinography): Subnormal results may indicate retinal issues.
• Ultrasonography: Particularly useful in unclear situations for diagnosing retinal conditions.
• B scan: Helps determine if the retina is detached by showing evidence of detachment.
• Retinal detachment (RD): Causes a noticeable shortening of the axial length of the eye.
• Rhegmatogenous retinal detachment: Treatment focuses on closing the break in the retina to prevent further detachment.

DACE Procedure

• Drainage: Involves the drainage of subretinal fluid (SRF) to relieve pressure and facilitate repair.
• Air Injection: Air or other substances such as saline, expanding gases, silicone oil, and perfluorocarbons are injected into the vitreous cavity. Perfluorocarbons, being heavy yet low in viscosity, are easily injected.
• Cryotherapy: Generally preferred over laser photocoagulation, especially for retinal breaks in difficult locations.
• Explant: Used to buckle or encircle the area around retinal holes, creating an indentation to prevent reopening of the breaks.
• Exudative Retinal Detachment: Requires treatment of the underlying cause, such as choroidal tumours or age-related macular degeneration.
• Tractional Retinal Detachment: Involves pan-retinal photocoagulation (PRP) to address hypoxia, removal of traction bands, and repositioning of the retina to its normal location.

Bull's Eye Maculopathy

Bull's Eye Maculopathy is a condition characterized by a distinctive pattern in the eye, where the central area shows increased pigmentation surrounded by a lighter zone and a darker ring. This condition leads to a moderate decrease in vision, typically ranging from 6/18 to 6/24.

Differential Diagnosis of Bull's Eye Maculopathy

• Chloroquine toxicity
• Batten's disease. A genetic disorder causing the accumulation of lipopigments in the body, often resulting in vision impairment and other neurological issues.
• Benign concentric annular macular dystrophy
• Bardet-Biedl syndrome
• Cone dystrophy
• Leber's Amaurosis (occasionally)

Chloroquine Toxicity

Chloroquine toxicity can lead to several eye-related side effects, including:

• Retinotoxicity
• Corneal deposits. Also known as Cornea Verticillata or Vortex Keratopathy, these are bilateral golden deposits in the cornea. They appear in a swirling pattern, starting from below the pupil and spreading outward while avoiding the limbus.

Optic Neuritis

• The risk of retinotoxicity increases when the total dose exceeds 300 g or if the treatment duration is longer than 1 year.

Chloroquine Maculopathy can be categorized into the following stages:

1. Premaculopathy:

• Normal visual acuity (e.g., 20/20 vision ).
• Scotoma to red target located between 4° and 9° from fixation.
• Defect in the Amsler grid test.

2. Established Maculopathy:

• Visual acuity between 6/9 and 6/12.
• Loss of the foveolar reflex.
• Subtle parafoveal halo of RPE pallor.
• Mild central scotoma to a white target may be present.
• Changes up to stage 2 are reversible upon stopping the drug.

3. Bull's Eye Maculopathy:

• Visual acuity: Ranges from 6/18 to 6/24.
• Foveolar changes: Central foveolar hyperpigmentation is observed, surrounded by a depigmented zone. This is encircled by a hyperpigmented ring.

4. Severe Maculopathy:

• Visual acuity: Ranges from 6/36 to 6/60.
• Foveal appearance:. pseudohole is present at the fovea, accompanied by widespread surrounding retinal pigment epithelium (RPE) atrophy.
• Note:. pseudohole refers to an appearance where the fovea seems to have a hole, indicating foveal retraction, which is a significant feature in maculopathy.

5. End Stage Maculopathy:

• Visual acuity: Severely reduced.
• RPE and choroidal changes: Marked atrophy of the retinal pigment epithelium (RPE) is observed, with larger choroidal blood vessels becoming visible.
• Retinal vessel changes: Attenuation of retinal arterioles is noted, along with pigment clumping in the peripheral retina.

Cystoid Macular Edema (CME)

Cystoid Macular Edema (CME) is a condition characterized by the accumulation of fluid in the outer and inner layers of the retina, specifically around the foveola. While this condition can sound serious, it is often harmless.

Causes of Retinal Vascular Leakage

• Diabetic Retinopathy (DR):. complication of diabetes that affects the blood vessels in the retina.
• Branch Retinal Vein Occlusion (BRVO): Occurs when a branch of the retinal vein becomes blocked, leading to fluid leakage.
• Intermediate Uveitis: Inflammation of the intermediate part of the uvea, which can cause fluid accumulation.
• Aphakic or Pseudophakic Cystoid Macular Edema: CME that occurs after cataract surgery when the natural lens is removed (aphakia) or replaced with an artificial lens (pseudophakia).

Retinitis Pigmentosa (RP): In the absence of retinal vascular leakage or degenerative causes, RP can be a cause of CME. RP is a genetic disorder that leads to the gradual degeneration of the retina, affecting the photoreceptor cells.

Postoperative CME: This type of CME can occur after cataract surgery and is referred to as "Irvine Gass syndrome." It is believed to result from either vitreous traction (pulling of the vitreous gel on the retina) or the release of prostaglandins (inflammatory substances) during the postoperative inflammatory response.

Inflammatory CME: This type of CME may develop due to various causes of posterior uveitis, which is inflammation of the posterior part of the uvea.

Sequelae of Long-Lasting Cases:

In cases of CME that persist for a long time, there is a possibility of developing large cystic spaces in the macula. These cystic spaces can lead to more severe complications, including:

• Lamellar Holes: Partial thickness holes in the macula, which can result in a decrease in vision.
• Full-Thickness Macular Holes: Complete thickness holes in the macula, leading to significant vision loss.

Types of Macular Edema:

• Cystoid Macular Edema: This type occurs due to the disruption of the blood-retinal barrier, leading to fluid accumulation in cystic spaces. Importantly, there are no structural changes in the foveal tissue itself.
• Non-Cystoid or Amorphous Macular Edema: In this type, there is distortion of the capillary structure at the macula. This can be observed in conditions such as neovascularization (the formation of new blood vessels) or due to traction forces acting on the retina.

Characteristic Indication on Fluorescein Angiography: The hallmark indication of CME on fluorescein angiography is the "Flower-Petal Pattern." This pattern helps in the diagnosis and differentiation of CME from other retinal conditions.

Treatment Options for Macular Edema:

• Systemic Carbonic Anhydrase Inhibitors: These medications are used to reduce fluid buildup in certain types of macular edema by inhibiting the carbonic anhydrase enzyme, which plays a role in fluid secretion.
• Laser Photocoagulation: This treatment involves the use of laser to create small burns in the retina, helping to seal leaking blood vessels and reduce fluid accumulation in some vascular-related cases of macular edema.
• Systemic Steroids: Corticosteroids administered systemically can help reduce inflammation and fluid accumulation in various types of macular edema.
• Central Serous Retinopathy (CSR) is a condition that primarily affects young to middle-aged adult males. It is characterized by a problem with the retinal pigment epithelium (RPE), leading to the accumulation of fluid in the subretinal space. This fluid buildup causes local detachment of the sensory retina at the macula, resulting in sudden blurred vision in one eye.
• Patients may also experience a relative scotoma, and visual acuity can range from 6/9 to 6/12, which can be improved with a plus lens. A notable feature of CSR is the elevation of the sensory retina at the posterior pole, often accompanied by a glistening or ring reflex.

Pathogenesis

• Central Serous Retinopathy (CSR) involves a problem with the retinal pigment epithelium (RPE), which leads to the buildup of fluid in the subretinal space. This fluid accumulation causes local detachment of the sensory retina at the macula, resulting in sudden blurred vision in one eye. Patients may also experience a relative scotoma, and visual acuity can range from 6/9 to 6/12, with potential improvement using a plus lens. A characteristic feature of CSR is the elevation of the sensory retina at the posterior pole, marked by a glistening or ring reflex.

Fluorescein Angiography

• Fluorescein angiography in Central Serous Retinopathy (CSR) reveals two distinct patterns: the "smoke-stack" appearance and the "ink-blot" appearance. These patterns help in diagnosing and understanding the extent of the condition.

Classification of Central Serous Retinopathy (CSR)

Central Serous Retinopathy (CSR) can be classified based on histological and clinical criteria.

Histological Classification (Sitzmann Classification)

• Type I: Characterized by the detachment of the sensory retina.
• Type II: Involves the detachment of the retinal pigment epithelium (RPE).
• Type III: An intermediate type where both the sensory retina and RPE are elevated.

Clinical Classification

I. Typical CSR

• Best Corrected Visual Acuity (BCVA) of 6/6 or better.
• Macular detachment of less than 3 disc diameters (DD).
• Presence of pinpoint inkblot or smoke-stack leakage on Fundus Fluorescein Angiography (FFA).
• Spontaneous resolution of the condition.

II. Atypical CSR

• Profound loss of vision with BCVA less than 6/60.
• Large area of macular detachment exceeding 3 disc diameters.
• Irregular, double, or multiple leakage patterns on FFA with a large collection of serous fluid.
• Lack of spontaneous resolution.
• Note: Spontaneous resolution of Atypical CSR is common within 6 to 12 months.

Treatment

• Laser Photocoagulation: This treatment option can expedite symptomatic relief by promoting faster resolution of serous detachment in Atypical CSR cases.

Myopic Maculopathy

Fundus Changes in Pathological Myopia

• Annular Crescent:. crescent-shaped area of atrophy surrounding the optic disc.
• Islands of Chorioretinal Atrophy: Areas of atrophy in the choroid and retina located at the posterior pole of the eye.
• Lacquer Cracks: Disruptions in Bruch's membrane that can lead to the formation of new blood vessels in the choroid (choroidal neovascularization).
• Posterior Staphyloma:. localized posterior bulging of the eye wall.
• Foster-Fuchs Spot: Hemorrhages at the macula with secondary pigmentary changes, also referred to as Fuchs flecks.
• Macular Holes: Full-thickness defects in the macula.
• Lattice Degenerations and Peripheral Retinal Holes: Degenerative changes in the peripheral retina associated with the formation of holes.
• Tigroid Fundus:. characteristic appearance of the fundus due to choroidal tessellation.
• Degeneration of the vitreous gel leading to a more fluid-like consistency.
• Retinal Detachment: Rhegmatogenous retinal detachment occurring due to holes in the peripheral degenerative areas.
• Subretinal Neovascularization: The formation of new blood vessels beneath the retina.

Fundus Findings in Hypermetropia

• Watered Silk Retina: Characterized by a sharp foveal reflex at the macula, giving a "watered silk" appearance.
• Pseudopapillitis: Indicated by a reduced cup-to-disc (C:D) ratio and blurred margins of the optic disc.
• Vascular Abnormalities: Unusual tortuosity and abnormal branching of retinal vessels.
• Macular Position: The macula is situated further from the optic disc compared to an emmetropic eye.

Additional Observations

• Pseudodivergent squint: This condition, also known as pseudo-exotropia, occurs due to a large angle kappa or angle alpha.
• Small eye with shallow anterior chamber: The patient presents with a small eye and a shallow anterior chamber.

Eales' Disease (Periphlebitis Retinae)

• Eales' disease primarily affects young males and leads to a sudden and painless loss of vision without any apparent injury.

Etiology

• The exact cause of Eales' disease is idiopathic.
• In some cases, there is a link between hypersensitivity to tubercular protein and peripheral retinal vasculitis.

Presentation

• Patients may experience sudden blurring of vision due to vitreous hemorrhage.
• Eales' disease is often recurrent in nature.

On Examination

• Examination may reveal sheathing of small peripheral retinal veins.
• Severe proliferative retinopathy can lead to extensive vitreous or retinal hemorrhage, potentially resulting in tractional retinal detachment (TRD).

Complications

• Rubeosis iridis, which can progress to neovascular glaucoma (NVG).
• Development of cataracts.
• Need for pan-retinal photocoagulation (PRP).

Age Related Macular Degeneration

Definition: Age-related macular degeneration (ARMD) refers to the visual impairment seen in individuals over 50 years old, associated with the presence of drusen, geographic atrophy of the retinal pigment epithelium (RPE), or changes due to sub-retinal neovascularization.

Types of ARMD: There are two main types of ARMD:

• Non-exudative ARMD
• Exudative ARMD

A. Non-Exudative ARMD (Geographical Atrophy)

• Prevalence: This is the most common type of ARMD, accounting for approximately 90% of cases.
• Clinical Features: Characterized by gradual and mild to moderate vision impairment that develops over several months or years.
• Examination Findings:
  • Initial presence of drusen (small yellowish deposits under the retina).
  • Development of sharply defined circular areas of RPE atrophy, associated with varying degrees of loss of the choriocapillaries, known as geographic atrophy.
• Pathological Features: Involves slowly progressive atrophy of the retinal pigment epithelium (RPE) and photoreceptors.
• Management: While there is no cure for non-exudative ARMD, management strategies and supportive treatments are available. The use of low vision aids may also be beneficial for affected individuals.

B. Exudative ARMD

• Incidence: Exudative ARMD is less common than non-exudative ARMD but has a more severe impact on vision.
• Clinical Features: Visual impairment in exudative ARMD can occur within days and may lead to complete loss of central vision.
• Examination Findings:
  • Choroidal Neovascularization: The formation of new blood vessels in the choroid layer of the eye.
  • RPE Detachment: Characterized by a sharply defined dome-shaped elevation at the back of the eye, which can vary in size and may lead to complications such as tear of the RPE.

Choroidal Neovascularization: Overview and Treatment

Choroidal neovascularization (CNV) involves the growth of fibrovascular tissue from the choriocapillaris through defects in Bruch's membrane into the sub-retinal pigment epithelium (RPE) space and eventually into the subretinal space. This process is characterized by the proliferation of abnormal blood vessels and fibrous tissue, leading to various ocular conditions.

Differential Diagnosis of Sub-Retinal Neovascular Membrane

• Wet Age-Related Macular Degeneration (ARMD)
• Presumed Ocular Histoplasmosis Syndrome (POHS)
• Severe Myopia
• Angioid Streaks
• Choroidal Naevus
• Choroidal Rupture
• Inappropriate Laser Photocoagulation
• Optic Disc Drusen

Treatment Options for Wet ARMD

The treatment approach for wet ARMD varies based on the location of the neovascular membrane in relation to the foveal avascular zone (FAZ).

• Extrafoveal Membranes. Located more than 200 microns from the center of the FAZ. Treatment typically involves laser photocoagulation using a blue-green laser to destroy the membrane.
• Subfoveal Membranes. These membranes involve the center of the FAZ. Treatment options may include photodynamic therapy (PDT), transpupillary thermotherapy (TTT), and intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) drugs such as ranibizumab or aflibercept.
• Juxtafoveal Membranes. These membranes are located close to, but not involving, the center of the FAZ (within 200 microns). Treatment may involve laser photocoagulation or other therapies depending on the specific case.

Treatment for Subfoveal and Extremely Juxtafoveal Lesions

• Photodynamic Therapy (PDT). This treatment uses a photosensitizer, such as verteporfin, which accumulates in the neovascular tissue. A specific laser light (690 nm, diode laser) is then applied to damage the vessel wall selectively, sparing normal tissue.
• Transpupillary Thermotherapy (TTT). TTT involves closing choroidal neovascular lesions through hyperthermia. It uses a low irradiance, long-pulse diode laser (810 nm) to deliver heat to the choroid and RPE, helping to close the abnormal blood vessels. This technique is particularly useful for subfoveal lesions.
• Anti-VEGF Drugs. Intravitreal injections of anti-VEGF drugs, such as ranibizumab or aflibercept, are administered to inhibit neovascularization and reduce fluid leakage associated with CNV.

Other Treatment Modalities for Age-Related Macular Degeneration (ARMD)

• Submacular Surgery. This surgical intervention involves the removal of the submacular neovascular membrane and is considered in specific cases of ARMD.
• Macular Translocation Surgery. This advanced surgical technique involves relocating the macula to a healthier area of the retina, away from the damaged blood vessels.
• Research on Trace Metals and Antioxidants. Ongoing studies are exploring the potential role of trace metals and antioxidants in managing ARMD, aiming to identify their therapeutic benefits.
• Anti-Angiogenic Factors. Experimental treatments involving interferon alpha, interleukin 12, fumagillin derivatives, and thalidomide are being investigated for their anti-angiogenic properties in ARMD management.

Understanding Retinopathy of Prematurity (ROP)

Retinopathy of Prematurity (ROP) is a condition that affects premature infants, particularly those who have been exposed to high levels of oxygen. To understand why ROP occurs, it's important to know how the retina develops. The retina is unique because it doesn't have any blood vessels until the fourth month of pregnancy. At that point, blood vessels start to grow from the hyaloid vessels located at the optic disc, and these vessels extend towards the edges of the retina. By eight months of pregnancy, these blood vessels reach the inner nasal edge of the retina, but the outer temporal edge is not reached until at least a month after the baby is born.

Because the retina is not fully developed at birth, it is very fragile and vulnerable to damage from oxygen. This is why being born too early is the biggest risk factor for developing ROP.

Types of ROP

• Active ROP: This type refers to the active stage of retinopathy of prematurity, where there are signs of ongoing damage and abnormalities in the retina.
• Cicatricial ROP: This type refers to the later stage of retinopathy of prematurity, characterized by scarring and abnormal tissue growth in the retina.

Stages of ROP

• Stage I (Demarcation line): In this initial stage, a thin, twisted, grey-white line appears. This line runs parallel to the ora serrata and separates the immature peripheral retina from the vascularised posterior retina.
• Stage II (Ridge): The demarcation line observed in Stage I develops into a ridge of tissue that extends outward from the retina.
• Stage III (Ridge with extra-retinal fibrovascular proliferation): This stage often occurs around 35 weeks after conception. The ridge in this stage turns pink due to the growth of fibrovascular tissue on the surface of the retina and into the vitreous. This growth can lead to bleeding in the retina and vitreous.

Stage IV (Sub-total Retinal Detachment):

• Tractional RD starts at the edges and moves toward the centre.

Stage V:

• Total Retinal Detachment.

Treatment of ROP:

• Cryotherapy or laser photocoagulation is used to ablate the avascular immature retina.

The Role of Vitamin E Therapy:

• The effectiveness of Vitamin E therapy is debated and is linked to the following process:
• Excessive free radicals decrease, leading to:
• Vitamin E acting as an antioxidant.
• Preventing spindle cell migration.
• Producing angiogenic factors which decrease.
• If retinal detachment occurs, scleral buckling is performed.

Screening of ROP:

• All infants under 36 weeks gestational age or weighing less than 1500 grams who received supplemental oxygen should be screened for ROP.
• Ideal screening time: Add 4 weeks to postnatal age or between 31 and 33 weeks.
• Before 32 weeks, screening has limited value as pupils are hard to dilate and the fundus is hard to see due to vitreous haze from Tunica vasculosa lentis.
• After 36 weeks. ROP rarely occurs.

Toxic Maculopathy

• Can be caused by the following drugs:
• Chloroquine
• Quinine
• Phenothiazines
• Chlorpromazine (Largactil)
• Thioridazine (Melleril)
• Tamoxifen
• Canthaxanthin

Purtscher's Retinopathy

• Causes:
  • Trauma: Head and chest trauma can trigger Purtscher's retinopathy.
  • Systemic Conditions:
  • Acute Pancreatitis: This severe pancreatic condition can lead to Purtscher's retinopathy.
  • Systemic Lupus Erythematosus: An autoimmune disorder that can cause various complications, including retinal issues.
  • Chronic Renal Failure: Kidney failure can contribute to the development of this condition.
  • Thrombotic Thrombocytopenic Purpura:. blood disorder that can lead to Purtscher's retinopathy.
• Emboli: Blockage of retinal capillaries by emboli such as fat or air can lead to retinal and optic atrophy.
• Clinical Features: The condition is characterized by multiple cotton-wool exudates and haemorrhages around the optic disc.
• Treatment: There is currently no known treatment for Purtscher's retinopathy. While significant vision recovery is rare, some patients may experience partial improvement depending on the severity of the condition and timely intervention. Implementing medical or surgical therapy for the underlying condition can help prevent further damage.

Coats' Disease

• Coats' disease is the most severe form of retinal telangiectasia and always affects one eye.
• This condition is more prevalent in boys than in girls and can lead to leukocoria (white pupillary reflex),strabismus (misalignment of the eyes), and vision loss.
• It is characterized by the accumulation of large areas of yellowish fluid both inside and beneath the retina.
• Coats' disease is often associated with the presence of dilated and twisted retinal blood vessels at the back and sides of the eye.
• The condition can result in severe complications, including:
  • massive sub-retinal exudation (fluid leakage beneath the retina),
  • exudative retinal detachment (detachment of the retina due to fluid accumulation),
  • the formation of a retrolental mass (a mass behind the lens).
• Other potential complications of Coats' disease include:
  • secondary cataract (clouding of the lens),
  • rubeosis iridis (abnormal blood vessel growth in the iris),
  • uveitis (inflammation of the uvea),
  • secondary glaucoma (increased intraocular pressure),
  • phthisis bulbi (shrinkage of the eyeball).

Persistent Hyperplastic Primary Vitreous (PHPV)

• PHPV occurs when the primary vitreous does not regress as it should.
• There are two types of PHPV: anterior and posterior.
• Anterior PHPV is the more common type, usually affecting one eye, and is seen in a small eye.
• It presents as a retrolental mass with elongated ciliary processes.
• If the ciliary processes retract, they can pull forward, leading to:
  • tearing of the posterior capsule of the lens,
  • lens swelling,
  • secondary angle-closure glaucoma.
• Posterior PHPV is less common, typically affecting one eye, and is associated with small eyes.
• It is characterized by a white, dense membrane extending from the optic disc to the peripheral retina or retrolental area.
• This may be accompanied by:
  • a pale optic disc,
  • retinal detachment.

Epidemic Dropsy

Epidemic dropsy occurs when mustard oil is contaminated with argemone oil. The toxic alkaloid sanguinarine present in argemone oil is responsible for this condition. Sanguinarine disrupts the oxidation of pyruvic acid, leading to its accumulation in the blood, which can have harmful effects on the body.

A. Systemic Features

• Sudden swelling in both legs without inflammation.
• Diarrhoea.
• Difficulty in breathing (dyspnoea).
• Heart failure and potential death.

B. Ocular Features

• Hypersecretory glaucoma:. condition characterized by increased fluid production in the eye, leading to elevated intraocular pressure.
• Fundus Findings:Increased capillary permeability and vessel tortuosity in the retina can result in:
  • Disc edema: Swelling of the optic disc.
  • Retinal edema: Swelling of the retina.
  • Accumulation of hard exudates: Deposits in the retina due to leakage of fluid and proteins.

Photoreceptor Dystrophies

A. Retinitis Pigmentosa

Primarily affects the rod photoreceptors in the retina.

B. Cone Dystrophy: Clinical Features

• Day Blindness: Difficulty seeing in bright light conditions.
• Progressive Loss of Visual Acuity: Gradual decline in sharpness of vision.
• Defective Colour Vision: Impaired ability to perceive colors accurately.
• Ophthalmoscopy Findings:
  • Bulls-eye Maculopathy: Characteristic pattern of damage in the macula.
  • Attenuated arterioles, pale waxy disc, and bony spicules may also be present.
• Photopic ERG: Subnormal or unrecordable results indicating poor cone function.

C. Leber's Amaurosis: Clinical Features

• Blindness: Present at birth or within the first few years of life.
• Pupillary light reactions are either absent or severely diminished.
• Oculodigital Syndrome: Characteristic condition where constant eye rubbing by the child leads to enophthalmos due to fat resorption.
• ERG: Unrecordable results indicating severe retinal dysfunction.
• Fundus Findings:
  • Salt and Pepper Fundus: Characteristic mottled appearance of the retina.
  • Bull's Eye Maculopathy: Specific pattern of macular damage.
  • Optic Disc Pallor: Waxy appearance of the optic disc and attenuation of arteries.

D. Congenital Stationary Night Blindness

• Normal fundus appearance.
• Non-progressive condition characterized by night blindness.
• Absence of dark adaptation abilities.

E. Congenital Stationary Night Blindness with Fundus Changes

• Fundus Albipunctatus.
  • Presence of tiny yellow-white spots extending from the posterior pole to the periphery of the retina.
  • Macula is spared, resulting in unaffected visual acuity.
  • Unlike retinitis punctata albescens, retinal blood vessels, optic disc, and peripheral visual field remain normal.
• Oguchi's Disease.
  • Autosomal recessive form of congenital stationary night blindness associated with fundus discoloration and abnormally slow dark adaptation.
  • Characterized by Mizou's phenomena. Temporary reversal of night blindness and normalization of fundus appearance after one hour in the dark.
  • Condition arises from overstimulation of rod photoreceptors.

Dystrophies of the Retinal Pigment Epithelium (RPE)

Dystrophies of the retinal pigment epithelium (RPE) refer to a group of inherited eye disorders that primarily affect the RPE, a layer of cells located at the back of the eye, crucial for the health and function of the retina. The RPE plays a vital role in maintaining the photoreceptor cells responsible for vision by recycling visual pigments, providing nutrients, and removing waste products. When these cells are disrupted due to genetic mutations, it can lead to progressive vision loss.

A. Best's Vitelliform Macular Dystrophy

Best's vitelliform macular dystrophy is a genetic eye disorder that affects the retinal pigment epithelium (RPE) and is characterized by the accumulation of lipofuscin, a waste material, in the RPE cells. This condition leads to progressive vision loss, particularly in central vision, due to the degeneration of photoreceptor cells in the macula.

Clinical Features: Best's vitelliform macular dystrophy is divided into five stages:

• Stage I (Pre-vitelliform): In this initial stage, the electro-oculogram (EOG) test shows abnormal results, indicating dysfunction in the RPE. However, individuals are asymptomatic, and the fundus appears normal upon examination.
• Stage II (Vitelliform): During this stage, yellow spots caused by the accumulation of lipofuscin granules appear at the level of the RPE. This stage is characterized by the presence of the "egg-yolk lesion" or "sunny side up" appearance, where yellow material accumulates in the subretinal space at the macula.
• Stage III (Pseudohypopyon): In this stage, part of the "egg-yolk" lesion is absorbed, leading to a change in its appearance.
• Stage IV (Vitelliruptive): This is a more advanced stage where the egg-yolk lesion breaks down, resembling a "scrambled egg" appearance. Visual impairment becomes evident, and the macula develops a hypertrophic scar. There may also be the formation of a vascularized scar with choroidal neovascularization, a condition where new blood vessels grow beneath the retina, leading to further complications.

B. Adult Foveomacular Vitelliform Dystrophy

• Adult foveomacular vitelliform dystrophy is a mild and benign condition that typically does not cause significant visual symptoms.
• In contrast to Best's disease, the foveal lesions observed in this condition are smaller, appear later in the disease course, and do not undergo the same evolutionary changes.
• The electro-oculography (EOG) test results in adult foveomacular vitelliform dystrophy are usually normal or only slightly abnormal, indicating the function of the retinal pigment epithelium is relatively preserved.

C. Stargardt's Macular Dystrophy- Fundus Flavimaculatus

• Stargardt's macular dystrophy is a genetic eye disorder that primarily affects the retinal pigment epithelium (RPE) and is characterized by the degeneration of photoreceptor cells in the macula, leading to progressive vision loss.
• Fundus flavimaculatus is considered a variant of Stargardt's macular dystrophy, and both conditions are believed to be caused by similar genetic mutations.
• The disorder is inherited in an autosomal recessive manner, meaning that both parents must carry the mutated gene for the condition to manifest in their offspring.
• Stargardt's macular dystrophy and Fundus flavimaculatus affect both sexes equally, with no significant difference in the prevalence between males and females.

Stargardt's Disease

• Stargardt's diseaseusually manifests in the 1st or 2nd decade of life.
• It results in impaired visual acuityand is characterized by nonspecific mottling at the fovea.
• The disease features oval lesions at the macula, approximately 1.5 DD in size, with a "snail-like" or "beaten-bronze" reflex.
• Atrophic changes occur in the retinal pigment epithelium (RPE) and choriocapillaris, with secondary effects on the photoreceptors.
• This condition leads to marked visual impairment, and the prognosis is generally poor.

Fundus Flavimaculatus Clinical Features:

• Typically presents in the 4th and 5th decades of life.
• Patients may be asymptomatic for many years unless the foveola is affected.
• Ill-defined yellow-white spots or flecks appear at the level of the RPE, which can be round, oval, linear, or fish-tail shaped, scattered throughout the posterior pole and mid-periphery of both eyes.
• New lesions develop peripherally while older ones may reabsorb.
• In 50% of cases, the fundus shows a vermillion colour.
• Electroretinography (ERG) and electrooculography (EOG) are only abnormal in advanced cases.
• Peripheral visual field and night vision usually remain normal.

Angioid Streaks

• Angioid streaks occur due to dehiscence in the collagenous and elastic components of Bruch's membrane, resulting in secondary changes in the retinal pigment epithelium (RPE) and choriocapillaris.
• Systemic associations include:
  • Pseudoxanthoma elasticum.
  • Paget's disease.
  • Ehlers-Danlos syndrome.

Choroidal Dystrophies

A. Choroideremia

• Choroideremia primarily affects males, with females acting as carriers.
• The condition is characterized by a widespread, mottled loss of pigment in the retinal pigment epithelium (RPE). Over time, this progresses to large areas of RPE and choroidal atrophy in the mid-retina.
• Unlike primary retinal dystrophies, the retinal blood vessels in Choroideremia remain normal.
• In individuals with Choroideremia, the Scotopic ERG is undetectable, and the Photopic ERG demonstrates a severe reduction.

B. Gyrate Atrophy

• Gyrate Atrophy is an extremely rare condition caused by a deficiency in the mitochondrial matrix enzyme Ornithine Aminotransferase. This deficiency results in elevated levels of ornithine in various bodily fluids, including plasma, urine, cerebrospinal fluid, and aqueous humor.
• Individuals with Gyrate Atrophy often develop axial myopia and exhibit scalloped circular patches of chorio-retinal atrophy in the peripheral retina. This is accompanied by vitreous degeneration, and in advanced stages, retinal vessel attenuation may occur.
• Other ocular features associated with Gyrate Atrophy include:
  • Blunting of the ciliary processes
  • Iris atrophy
  • Development of posterior cataracts
• Electroretinography (ERG) and Electro-oculography (EOG) results in Gyrate Atrophy are typically non-recordable. Treatment options for this condition include:
  • Pyridoxine (Vitamin B6) supplementation
  • Following a diet low in proteins and arginine

C. Central Areolar Choroidal Dystrophy

• This condition mainly impacts the macula, resulting in decreased visual acuity due to the presence of an atrophic lesion.
• When the disease is localized, both Electroretinography (ERG) and Electrooculography (EOG) tests show normal results.

D. Generalized Choroidal Atrophy

• This condition involves extensive atrophy of the Retinal Pigment Epithelium (RPE) and the choriocapillaris.
• Patients may experience night blindness and reduced visual acuity, which can significantly affect their daily activities.