Question

The disease of astigmatism in human eye is because of:
(A) Unequal and uneven curvature of eye lens
(B) Eye lens being of organic matter
(C) Eye membranes being thick
(D) Opacity development in eye lens

Answer 1

Hint: We know that the lens is flexible and its curvature is controlled by ciliary muscles through the zonules. By changing the curvature of the lens, one can focus the eye on objects at different distances from it. This process is called accommodation. The suspensory ligaments connected to the ciliary muscles help in changing the curvature of the lens. Higher angles of curvature lead to shorter focal lengths due to the fact that light waves are refracted at a greater angle with respect to the optical axis of the lens. The symmetric nature of bi-convex lenses minimizes spherical aberration in applications where the image and object are located symmetrically. Based on this concept we have to answer this question.

Complete step-by step answer:
Astigmatism is an optical defect in which vision is blurred due to inability of the optics of the eye to focus a point object into a sharp focused image on the retina. This may be due to an irregular or tonic curvature of the cornea or lens.
It should be known that Astigmatism is a common vision problem caused by an error in the shape of the cornea. With astigmatism, the lens of the eye or the cornea, which is the front surface of the eye, has an irregular curve. This can change the way light passes, or refracts, to your retina. This causes blurry, fuzzy, or distorted vision.
Thus, we can say that Astigmatism may be present from birth, or it may develop after an eye injury, disease or surgery. Astigmatism isn't caused or made worse by reading in poor light, sitting too close to the television or squinting.

Hence, the correct answer is Option A.

Note: When the curvature of the eye lens is excessive, then the focal length of the eye decreases. This results in the formation of an image in front of the retina. This whole situation makes the image blur and causes myopia. On the other hand, blind spot, small portion of the visual field of each eye that corresponds to the position of the optic disk (also known as the optic nerve head) within the retina. There are no photoreceptors (which are rods or cones) in the optic disk, and, therefore, there is no image detection in this area. When light hits the retina (a light-sensitive layer of tissue at the back of the eye), special cells called photoreceptors turn the light into electrical signals. These electrical signals travel from the retina through the optic nerve to the brain. Then the brain turns the signals into the images we see.