Astigmatism

'Normal' Vision

The front surface of the eye, known as the Cornea, acts as a lens through which light is collected. With good eyesight, the image that you are viewing is normally brought into focus on the back of the eye which is called the retina.

Eyesight difficulties tend to occur when that image is not able to be correctly focused on the retina and your vision becomes blurred.

When you look at something, light from that object passes into the eye through your cornea then through the lens towards the retina at the back of the eye. In 'normal' or healthy eyes the lens and cornea focus these light rays onto a small area of your retina and this enables you to view objects clearly

However, your vision can sometimes lose clarity which can be due to a variation in these 'normal' parameters.

These variations are split into two main categories: short and long sightedness.

Astigmatism

Astigmatism is classed as a refractive disorder of the eye whereby there is a disparity in the focussing power of the lens in different meridians.

Typical astigmatism is characterised by an irregular profile of the cornea whereby the curvature in one meridian is more then that of the perpendicular meridian.

In simple terms the curvature of the cornea is similar to that of an American football or rugby ball which is varies over the surface instead of having a constant radius like the curve of a football (which is a sphere).

In regular stigmatism, the meridians in which the two different curves lie are located 180 degrees apart.

In irregular astigmatism, the two meridians may be located at something other than 180 degrees apart. Usually astigmatism is hereditary.

A number of people that suffer from eyesight problems have been born with an  oblong shaped cornea. These vision problems tend to get worse as they age.

Eye injuries can be the cause of astigmatism if they occasion scarring of the cornea. Astigmatism may also arise from certain types of eye surgery or from keratoconus, a disease that causes a gradual thinning of the cornea.

If you suffer from astigmatism you probably find that objects can appear distorted or blurry at a distance or even near up. The severity can range from mild to severe and cause blurry vision, headaches, squinting or strain on the eyes.

Example of astigmatic prescription