Defects of the eye

Short sightedness (Myopia):

 The people suffering from this defect can see the near thing clearly but the distant object are seen blurred. In this disorder, the image is formed in front of retina rather than on retina. One of the reason for short sightedness is abnormally elongated eyeball. This defect can be corrected by fitting spectacles with appropriate concave lenses.

Longsightedness (Heteromyopia):

 This defect make people hard to see the near objects clearly whereas they can see distant objects without any problem. In this defect, the image is formed behind the the retina. It can be corrected by wearing spectacles fitted with appropriate convex lenses.

Cataract:

In this disorder transparency of the lens of the eye lost and it becomes hard and opaque. It commonly occurs in old age. The main symptom is blurring of the vision. This lens is removed surgically and a new man made lens is implanted.

Glaucoma:

 It is a disorder in which the pressure of the fluid in the eye becomes abnormally produce partial or complete loss of vision. Sever pain in eyes, dull vision, perception of rainbow rings around the light at night are its main symptoms. Also treated with eye drops.

Contact lenses:

 These are very thin, shell like discs stuck on the cornea. They are used simply for the cosmetic purpose or to correct defective vision. Powered contact lenses alter the power of cornea. These lenses not only correct most of the defects in vision for which glasses are prescribed but can also correct some conditions that glasses cannot. 

Astigmatism:

 It is a disorder of eye in which the front surface of the eye is not evenly spherical. Although the eye is perfectly healthy but the corneal surface has discrepencies in its curvature, so that magnification in one  direction is greater than in others. A person with astigmatism might see horizontal lines clearly but vertical lines look blurred. Special kind of lenses or  contact lenses provide a solution to astigmatism.