What is astigmatism?

Here there is more than one point for the focus of light.

The reason is often a slightly bent cornea (as an analogy—if you press the side of transparent flexible plastic saucer between your hands, the direction in which the sides are being pressed makes the outside curvature of the saucer steeper than the other direction). The difference in curvature between the steeper and the flatter curve which splays out and flattens expressed as a power is a measure of the astigmatism.

To correct astigmatism, we need a lens which will bend the light in only one plane and not in the other. These types of lenses are called cylindrical or toric lenses and are always specified by an axis direction.

What are the types of astigmatism?

There are two types of astigmatism, regular and irregular.

Regular astigmatism is the type which can be completely controlled with spectacle lenses.

This is the most common type of astigmatism and is quite harmless. It hardly ever progresses beyond 2-3 dioptres.

Irregular astigmatism occurs usually from a disease of the cornea or injury. In this type of astigmatism there are multiple points of focus because of corneal irregularity and here a cylindrical spectacle lens cannot help. This is one of the few conditions which can only be controlled by contact lenses which alone can give good vision.

How is astigmatism controlled?

Regular astigmatism is controlled by using spectacles with lenses termed cylindrical or toric which are always specified by an axis. It can also be controlled by contact lenses.

Irregular astigmatism can be controlled only by contact lenses which replace the irregular corneal surface by the regular front surface of the contact lens and thus give good vision.

Dustin Flores

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