What is Astigmatism caused by?
Your cornea should be round, like a ball. However, if the cornea isn’t round, then the lens cannot focus the image onto the retina properly. You’re probably familiar with being nearsighted or farsighted — that happens when the cornea is rounded, but either bulges out a bit or not enough. In those cases the lens focuses the image, but either in front of or behind the retina.
However, if the cornea isn’t actually round, but rather slightly oval looking from the front, then the image doesn’t focus at all. What happens is that the long part of the oval focuses at one point, and the narrow part focuses at a different point. There are three types of astigmatism.
- Hyperopic Astigmatism: Both of the points the eye focuses on are behind the retina (instead of on the retina, as with normal vision)
- Myopic Astigmatism: Both of the points the eye focuses on are in front of the retina.
- Mixed Astigmatism: One of the focal points for the eye is in front of the retina, and the other is behind the retina.
The three types of astigmatism can be the result of an oddly shaped cornea (corneal astigmatism), or an oddly shaped lens (lenticular astigmatism). Corneal astigmatism can be corrected with lenses or laser surgery. But, Lenticular astigmatism is less common, and may be addressed with contact lenses or laser surgery to the cornea to compensate.