Sense organ “The Eye” | Additional Study Material for NEET PDF Download

Q -1 Eye has how many extraocular muscles.

Answer – Eye has six extraocular muscles namely superior oblique, inferior oblique, superior rectus, inferior rectus, medial rectus, lateral rectus,

Q -2 Describe the roles of each eye muscles.

Answer –

• Superior oblique regulated by trochlear IV cranial nerve, move eyeball down & in,
• Inferior oblique regulated by oculomotor III cranial nerve, move eyeball up & out
• Superior rectus regulated by oculomotor III cranial nerve, move eyeball up
• Inferior rectus regulated by oculomotor III cranial nerve, move eyeball down
• Medial rectus regulated by oculomotor III cranial nerve, move eyeball toward nose
• Lateral rectus regulated by oculomotor III cranial nerve, move eyeball away from nose

Q -3 Wall of eyeball formed of how many layer.

Answer – The wall of eyeball formed of three layers or coats, outer layer fibrous coat middle layer vascular coat and inner layer is nervous coat

Q -4 What you know about fibrous coat of eyeball.

Answer – It is thick & tough layer made-up of dense avascular connective tissue formed the outer most layer of eyeball, giving shape to eyeball, this layer is consist of two part – sclera and cornea.

Sclera- It is white part of eye, most of it part concealed in orbit, maintain shape of eye and give protection to eye. It is about 5/6 fibrous coat

Cornea- It forms about 1/6 part of fibrous coat, it is actually a highly organized group of cells and proteins, due to presence of collagen fibers it is transparent and do not reflect light. Cornea receives nutrients from tears and aqueous humour, filled in chamber behind it. Cornea contributes to formation of clear image. If cornea is not in proper shape its transparency is lost, the image will not be focused on the retina and blurred vision will result. It protect eye from UV radiation. Cornea is covered by thin and transparent membrane called conjuctiva composed of stratified epithelium and continued over the inner surface of the lids, does not cover the part of the cornea over the iris.

Q -5 Describe the middle layer or vascular coat of eyeball.

Answer – Vascular coat of the eyeball is distinguished into three region namely choroid, ciliary body and iris 

Choroid – Choroid lies in contact with the sclera is delicate, highly vascular and pigmented part. Provide dark colour due to presence of black pigment (melanin) , prevent reflection of light to absorbing it. Have blood vessels for nourishing the retina.

Ciliary body – It is thicker and less vascular than choroid, inner surface is folded to form ciliary process. Have ciliary muscles which are circular sheet of smooth muscles fibres that form bundles of circular and radial muscles which alter the shape of the lens during accommodation.

Iris – It is circular, muscular diaphragm containing the pigments, which give rise colour to eye, present in anterior part of vascular coat lies behind cornea. Its central perforation is pupil, the size of pupil regulated by irridial muscles these muscles are under control of central nervous system.

A biconvex and transparent lens present behind the iris, it is formed of laminated fibrous tissue and is capable of undergoing change in its curvature. The lens is covered by lense capsule and suspended to the body by suspensory ligament.

Q -6 Describe the nervous coat of eyeball.

Answer – Inner most layer is non-vascular light sensitive coat, called retina. It is formed of three portions, the optic part which lies along choroid, the ciliary part in contact with ciliary body and irridial part which is in contact with posterior part of iris.

The optic part of retina differentiated into two parts – pigmented and nervous. Pigmented parts have cuboidal cells with dark granules and fringe like protoplasmic processes, continue beyond ora serrata. The nervous part is transparent and is made of three lalyers from out to inside include the layer of receptor cells, layer of bipolar ganglion cells and layer of ganglion cells. Receptor cells include rods & cones.

The portion of retina exactly opposite to pupil is called as yellow spot or macula lutea or area centralis. Yellow spot has shallow depression in centre called as fovea centralis. It is place of most distinct vision due to predominance of cones cells. Near yellow spot an another spot present which lacks receptor cells because optic nerve exit from here, called as blind spot. 

Q -7 What you about chambers of eyeball.

Answer – Eyeball has two chambers –

• Aqueous chamber (anterior, small in size)
• Vitreous chamber (posterior, larger)

Aqueous chamber – Present between the cornea and the lens, filled with clear watery fluid “aqueous humour”. Maintain the shape of cornea and supply nutrient to both lens and cornea.

Vitreous chamber – Present between lens and retina, filled clear transparent jelly like substance called “vitreous humour”. Maintain the shape of eyeball and contribute to intraocular pressure and also to focusing of light on retina.

Q -8 How eye work during vision.

Answer – Eye work as photographic camera, light rays are focused by conjunctiva, cornea, aqueous humour, lens, vitreous humour, and retina.

Change in retina when light rays fall on it –

• Light      →     Receptor cells rods & cones in retina     →    Breaking of light sensitive pigments present in rods and cones by specific wavelength of light   →    Stimulation of rods and cones and generation of nerve impulse   →  Impulse transmitted to bipolar nerve cells     →    Impulse transmitted to ganglion cells     →       Nerve impulse in the axon of ganglion cells converge and form the optic nerve        →       Impulse transmitted to brain       →      Perception of light by brain cells (in visual area of cerebral cortex)

Q -8 What is role of cones in vision.

Answer – Cones is responsible for colour vision have pigment iodopsin are adapted to vision in bright light

Q -9 What is role of rods in vision. 

Answer – Rods are responsible for clear vision have pigment rhodopsin. Function of pigment is as follows

In light:       Rhodopsin   →     Retinene + Scotopsin + Energy + Generation of nerve impulse

In darkness:  Retinene + Scotopsin + Energy from ATP       →         Rhodopsin

Q -10 What is night-blindness.

Answer – When we go from bright light to darkness takes few minutes for vision, this time is taken to re-synthesize rhodopsin from retinene and scotopsin. Retinene is derivative of vitamin A (retinol), we all know that rhodopsin is necessary for vision in deam light so deficiency of vitamin A lead to deficiency of rhodopsin which lead to “night-blindness”

Q -11 What is myopia or near-sightedness.

Answer – In this person see closer object properly, but can’t see image of distant objects. Because image of distant objects is formed in front of retina, this defect is removed by use of concave lens.

Q –12 What is hypermetropia or far-sightedness 

Answer – In this person can see distant image properly, but can’t see closer image. Because image of closer formed behind retina, this defect can be over-come by use of convex lens.

Q –13 Describe presbyopia 

Answer – It is common defect in old age people due to loss of elasticity of lens and reduced power of accommodation. It can be corrected by use of reading glasses, bifocal, trifocals or contact lenses.

Q -14 What is accomodation 

Answer – Accomodation is an adjustment for distant and close vision during which contraction of ciliary muscles release tension in the suspensory ligaments and allows the lens to elastically recoil and bulge out n both of its side.