What is hypermetropia, myopia, astigmatism? How do these common eye defects occur? Info about eye defects.
Differences in the shape of the eye ball cause images to focus behind or in front of the retina, resulting in vision problems.
A farsighted person sees distant objects very clearly but not near objects. The eyeball is too short from front to back or the lens is less curved. The image falls behind the retina. Convex lenses are used to correct this eye defect. Old people become farsighted because their lenses become less flexible.
A nearsighted person sees near objects clearly but not distant objects. The eye ball is too long or the lens is too curved. The image falls in front of the retina. Concave lenses are used to correct this eye defect.
Astigmatism is caused by an uneven lens or cornea. So the images do not focus clearly on the retina. This causes blurred vision at all distances. It is corrected by cylindrical lenses.