Question

What are the defects of the eyes? How is rectified?

Answer 1

Hint: In this question we have been asked to determine the defects of eyes and how are they rectified. Therefore, to solve this question, we shall discuss the defects in the eyes. We shall also discuss a few factors causing these eye defects. This shall help us in understanding how to rectify these effects or correct them. Therefore, we will discuss the ways to correct them as well.

Complete step-by-step solution:
The defects in the eyes can occur due to macular degeneration, cataracts, or glaucoma. The major defects in eyes are 1) Myopia 2) Hyperopia 3) Astigmatism 4) Presbyopia
In Myopia the objects at the distance appear to blur and the object near can be seen clearly. Now, this happens because the eyeball is relatively longer which focuses the image in front of the retina rather than on it. The prescribed lens for correcting Myopia is of negative value. Therefore, Myopia can be corrected by using a concave lens to focus the image in the retina as shown in the figure below.

Similarly, in Hyperopia the objects at the distance can be seen clearly and the objects near are a blur. Now, this happens because the eyeball is relatively shorter or the refractive power of the lens of the eye is too weak, which focuses the image behind the retina rather than on it. The prescribed lens for correcting Myopia is of positive value. Therefore, Hyperopia can be corrected by using a convex lens to focus images in the retina as shown in the figure below.

Astigmatism occurs when the light rays do not fall on a single focal point on the retina. This defect occurs due to non-uniformity in the curvature of the cornea. It can be corrected by using a special spherical cylindrical lens that is placed out of the focus of the axis.
Presbyopia is the natural degradation or thickening of the lens of the eye. It is a defect that usually occurs with old age. It can be cleared using suitable lenses.

Note: The eye produces a clear fluid that fills space between cornea and iris. This fluid filters through a special drainage system. The intraocular pressure (IOP) is the balance between the production and drainage of this fluid. Glaucoma is a disease that results from increased IOP. This causes irreversible damage to the optic nerve and retinal fibers.