We use __________ lens to correct Hypermetropia
Hypermetropia can be corrected by using a convex lens. A convex lens converges the incoming light such that the image is formed on the retina.
For the myopic eye, the defect is cured by
In myopia, u = infinity , v = d = distance of far point
By 1/F = 1/v - 1/u
We get f = -d
Since the f is negative, the lens used is concave.
The near point of a human eye is at a distance of
The near point of the eye is the minimum distance of the object from the eye, which can be seen distinctly without strain. For a normal human eye, this distance is 25 cm. The far point of the eye is the maximum distance to which the eye can see the objects clearly. The far point of the normal human eye is infinity.
A person suffering from myopia can see upto 3m.The power of lens required to rectify is
Given ,v = -3m or -300cm
u = -infinity
f = ?
according to lens formula ,
1/f = 1/v - 1/u
1/f = -1/300 - (-1/infinity)
1/f = -1/300 + 1/infinity
focal length = -300 cm or -3metre
power = 1/focal length(metre)
power = -1/3
power = -0.33 dioptre
One of the reasons for myopia is
Tightening the smart eye band causes the eyeball to elongate, just as squeezing the middle of a peeled hard-boiled egg causes the egg to lengthen. In long-sighted people this pushes the retina backwards, bringing close-up objects back into focus.
A person suffering from myopia cannot see clearly beyond 1 m. What should be the focal length of the concave lens that will correct his vision?
The focal length of the concave lens should be -1 m as object at infinity forms image at focus.
Cataract can be cured by
Surgery to treat cataracts involves removing the clouded lens and replacing it with a synthetic new one. This procedure is safe and very effective.They're researching eye drops that may dissolve cataracts so patients don't have to go to surgery.
A person is suffering from both defects of vision, myopia and hypermetropia. He should use:
Bifocal lenses are the lenses which are used for the people who suffer from both defects of vision that are hypermetropia and myopia, for those people who suffer from presbyopia or astigmatism. These lenses have two distinct powers and hence they serve two functions :- one is for distant vision and the other is for near vision. The lenses are divided into two parts. The upper part consists of concave lens which serves for distant vision at the lower part consists of convex lens which serves for near vision.
Image is formed for the shortsighted person:
Short-sightedness (myopia) usually occurs when the eyes grow slightly too long, which means they're unable to produce a clear image of objects in the distance.
A defective eye cannot see close objects clearly. This is because their images are formed
A defective eye cannot see close objects clearly because there image is formed beyond retina. This defect as known as farsightedness. Here rays from near object could not be converged at retina due to focal length of the eye lens could not be decreased. So, image is formed beyond retina.
If the image was formed in front of the retina rather than behind the retina, then the person would need to correct the vision problem by using a:
Nearsighted individuals have image formed in front of the retina. They must correct the problem by wearing a lens which provides for some diverging of light prior to reaching the lens of the eye. This will move the image further from the lens of the eye and back towards the retina.
An optician used concave lens to correct the defect of eye so that the customer can see clearly. Which defect of vision could it be?
The most common are nearsightedness, farsightedness, astigmatism and presbyopia. Concave and convex lenses compensate for defects in the eye, bending light rays to place them precisely on the retin and correcting vison. A concave lens is thinner in the center and thicker on the edges.
A person with defective eyesight is unable to see objects clearly nearer than 1.5 m. He wants to read a book placed at a distance of 30 cm from his eyes. The type of a required lens and its focal length is
This person suffers from the defect of hypermetropia.
For him u = -30cm, v = -1.5 m = -150cm
Therefore, focal length of corrective lens to be used by him is
1/f = 1/v- 1/u = 1/-150 - 1/-30 = 4/150 = 37.5cm
The positive sign shows that the lens needed is a convex lens of focal length 37.5 cm.
Hence, power of lens needed
P =1/f = 100/37.5 = 2.67D
A person has near point of his vision shifted to 50 cm. What lens must be used to see an object placed at 25 cm from the eye? What is the power of the lens?
When object is placed at 25 cm, then a virtual image should form at 50 cm.
So, u = -25 cm, v= -50 cm.
So, 1/f = 1/-50 - 1/-25
f = 50 cm = 0.5 m
Power, P = 1/f = 1/0.5 = +2D
Therefore , a convex lens is needed.
Isha’s eye balls are too short due to which she cannot see
She is suffering from hypermetropia in this case focal length of her eyeball is decreased and hence the image is formed behind the retina so she cannot see nearby objects as they r already close to her eyes and the image is formed behind the retina but she can see objects that r far as their image is formed on the retina
Among the following statements, the statement that does not hold true for shortsightedness is
Option ( c) does not hold true for Shortsighteness because
The image is formed in front of the retina.
A boy is wearing glasses and says that he cannot see the object kept at a distance without glasses. He is suffering from
As Myopia is a defect of vision in which a person cannot see the distant object clearly. This can be corrected by using the concave lens of appropriate focal length
The cause of Presbyopia is
Presbyopia occurs in old age when the eye lens hardens and loses its flexibility due to the weak ciliary muscle. In this situation the human eye becomes unable to focus on distant as well as near by objects. Hence option(d) is the correct answer.
The far point of a myopic person is 80 cm in front of the eye. What is the nature and power of the lens required to correct the problem?
For person affected with myopic condition, the image instead of forming on retina, it forms in front of it. In order to cure such type of defect, concave lens of power - 1.25D is used.
Presbyopia for human eye can be removed by using:
By far the most common and simplest treatment for presbyopia is bifocal or progressive lens eyeglasses. A bifocal lens is split into two sections. The larger, primary section corrects for distance vision, while the smaller, secondary section allows you to see up close.