Dr. Arvind Varma is a practicing ophthalmologist who runs a clinic in Nerul, Navi Mumbai. Besides writing on common eye problems, Dr. Varma will also answer specific queries.

Here is a list of some terms commonly used to describe certain eye disorders and the various types of lens used to set them right.

• Myopia: Myopia is a type of Refractive Error in which the image of the object is formed in front of the retina. This is set right with concave (-) spherical lenses.

• Hypermetropia: Hypermetropia is a type of Refractive Error in which the image of the object is formed behind the retina. This is set right with convex (+) spherical lenses.

• Astigmatism is another type of optical system defect in which the power of the system in one meridian (say 0 to180 degrees axis) is different from that in the other meridian (say 90-270 degrees axis).
Because of the two different powers in the same eye, two or more images of the object are formed. This is like seeing ghost images on TV when the signal is poor. Such a person gets confused and is not able to see clearly. Astigmatism is corrected with a special type of lens called cylindrical lens. These lenses act upon a meridian to decrease or increase its power. This way both meridians become equal in power and form a sharp image.

• Presbyopia is a condition in which the distance vision is still clear but near vision becomes blurred. It usually sets in around after forty. This can be corrected by wearing Convex (+) lenses.

We need different powers for distance and near vision. Our lens changes its shape to provide us with the extra power needed for near vision. With age we loose this facility and reading or near work becomes difficult.

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