What's Astigmatism
And name two major defects of the eye
Astigmatism is a vision condition that causes blurred vision due either to the irregular shape of the cornea, the clear front cover of the eye, or sometimes the curvature of the lens inside the eye.
The two major defects of vision are myopia and hypermetropia.
Myopia: It is the defect of the eye because of which distant objects cannot be seen clearly. Image is formed in front of the retina. It is also called Nearsightedness.
Cause: This defect of vision occurs when the eyeball slightly elongates from front to back. This causes light rays to focus at a point in front of the retina, rather than directly on its surface.
Remedy: It can be corrected by an appropriate concave lens.
Hypermetropia: It is the defect of the eye because of which nearby objects cannot be seen clearly. Image is formed in behind the retina. It is also called Farsightedness.
Cause: This defect of vision occurs when the eyeball slightly shortens from its original size. This causes light rays to focus at a point beyond retina.
Remedy: It can be corrected by an appropriate convex lens.