Astigmatism is a refractive error of the eye (as are nearsightedness and farsightedness). Refractive errors result in the focal point in the eye being in front or behind the retina (instead of on top of the retina), causing varying levels of impaired vision if left uncorrected.
Where in myopia light focuses in front of the eye, and in hyperopia it focuses behind the eye, astigmatism is the result of multiple focal points existing in front or behind the eye (or a combination of both). This is usually the result of an abnormally-shaped cornea.
Corneas are round (like an orange); astigmatism occurs when the cornea is ovoid (like an egg). Due to the out-of-round shape, the principal meridians are out of alignment.
There are three main types of astigmatism:
The general signs of astigmatism are fairly generic and are often confused with other refractive errors (and even presbyopia). Signs include eye strain, especially when reading or working at a computer, headaches, and eye fatigue.
Like other refractive errors, the simplest and most common correction are corrective lenses in the form of eyeglasses or contact lenses. This type of correction is non-invasive and affordable.
Toric contact lenses are lenses that are specifically designed to correct astigmatism. They are soft lenses made of common hydrogel or silicone hydrogel, though rigid gas permeable options are available.
Toric lenses can have different powers at different meridians of the lens, correcting the principal meridian misalignment. They can also cause the lens to rotate, changing the orientation of the cornea to better accommodate the prime meridians.
Gas permeable contact lenses are rigid lenses that force the eye to adapt to the shape of the contact lens. This corrects the astigmatism.
GPC lenses require an adjustment period, and some people find that they simply cannot adopt to GPC lenses. These lenses are also more expensive than regular lenses and require a more detailed exam before using them.
Laser refractive surgery can correct most forms of astigmatism. The surgery itself is relatively painless, with a couple of weeks of postoperative discomfort. It is also fairly affordable, though less so than corrective lenses.