A defect of vision due to non-sphericity of the cornea. The defect is corrected by using cylindrical surfaced lenses.

A genetic defect found usually in males. A colour blind mother will always produce colour blind sons. Colour blind people are unable to differentiate between red and green. It can easily be detected through a special chart with various colour dots.

Also known as Hypermetropia, it is a defect of vision due to which near objects are not seen clearly. The defect can be corrected by using convex lenses of suitable focal length.

A defect in which accommodative power is gradually lost with increasing age as the lens' converging power decreases.

Also known as Myopia, it is a defect in which one cannot see distant objects properly. It is corrected by using concave lenses of suitable focal length. Patients may possibly become normal with progress in age.

Certain precautions are always helpful in retaining good eyesight:

* Never read books while lying down. Read while sitting.

* Avoid reading late in the night.

* While reading, make sure that the light falls on the book.

* Watch TV from a distance.

* Use computer filters on your PC screens to avoid direct rays.

* Boiled carrots are the best thing for gaining sharp eyesight.