Astigmatism is a difficult concept to grasp.
Like Myopia (shortsighted) or Hyperopia (long sighted) it results in a blurred image without correction.
Astigmatism is very common and most people, even the ones who don’t wear glasses have some degree of it.
It is commonly found in long and shortsighted people in addition to their long or shortsightedness.
WHAT IS ASTIGMATISM
Normally, the image of whatever we are looking is focused by our eye onto the retina at the back of the eye.
If we are looking at a cross. then both the vertical and horizontal components of the cross will both be on the retina and therefore in focus.
In astigmatism, each stroke of the cross will be focused in a different location. As an example. the vertical stroke may be on the retina but the horizontal might be in front or behind the retina.
Thus a lens is required which focuses only the part that isn’t on the retina but rather in front or behind it. Such a lens is called a toric lens. Other variations include one of the arms of the cross in front of the retina and the other arm even further in front, this is called myopic astigmatism, both arms behind the retina which is hyperopic astigmatism or one in front and the other behind called mixed astigmatism.
A point of light will not appear as a point but rather a blur circle.
WHAT CAUSES ASTIGMATISM
There are two main reasons why astigmatism may occur. The most likely is that the cornea which is the front surface of the eye, may not be spherical in its shape (like a soccer ball) but rather more ovoid. That is to say, shaped more like an egg or an Australian rules football. The other reason is that the lens within the eye may be unusually shaped.
CORRECTION OF ASTIGMATISM
Correction of astigmatism is usually done with glasses or contact lenses, but this can also be done with laser vision correction or by lens implant
Since the laser effectively ‘resurfaces’ the cornea, any deviation from sphericity can be eliminated and thus astigmatism corrected.
In the case of lens implant surgery, wether purely for vision correction or for cataract, a special lens called a toric lens is implanted. A toric lens has essentially two focal points.