The eye is spherical in shape and has a diameter of 2.3 cm on an average. The internal structure of the eye includes- cornea, iris, pupil, lens, ciliary muscles, retina, nerve cells, optic nerve, and yellow spot, aqueous and vitreous humor, and suspensory ligament.
Defects of a Human Eye
There are few common eye disorders seen in all individuals and are caused by several factors. These conditions can be improved by the corrections. The defects include:
Myopia:– This is also called as the short-sightedness. A person with this eye defect can only see the nearby objects clearly compared to distant objects. This condition can be corrected using a concave lens.
Hypermetropia:– This is also called as the farsightedness. A person with this eye defect can only see the distant objects clearly compared to near objects. This condition can be corrected using a convex lens.
Presbyopia:– This is an age-related condition caused due to the weakening of ciliary muscles, hardening of the lens, and reduced lens flexibility. A person with this defect usually finds difficulties to focus on nearby objects unable to read or write.
Cataract:– This is an age-related condition caused due to the loss of transparency of the lens by erosion of lens proteins. It usually results in blurry vision, cloudy lenses and can be corrected by replacing the old lens with an artificial lens.