There are two primary types of astigmatism: regular or corneal, resulting from the irregular surface of the cornea which should be smooth; and irregular or lenticular, resulting from the irregularly shaped lens behind the cornea. Regular astigmatism is composed of five different types, however. The difference occurs due to how each eye is classified. The level of nearsightedness, or myopia, and farsightedness, or hyperopia, determine the type of regular astigmatism in each eye. The degree of condition is determined by the severity of the distortion of the cornea or lens.
Regular astigmatism results from an oblong, or football-shaped, cornea. The misshapen cornea can distort an image into two points instead of just a single image. It is the determination of which eye is affected, or to which level, that will establish the type of regular astigmatism the patient has. If one eye is normal and the other is nearsighted, simple myopic astigmatism is the diagnosis. Simple hyperopic astigmatism results from normal vision in one eye, coupled with farsightedness in the other.
Compound myopic or compound hyperopic astigmatism occurs when both eyes are either nearsighted or farsighted, respectfully. When one eye is nearsighted and the other is farsighted, mixed astigmatism is diagnosed. Irregular astigmatism causes light to be distorted from the uneven surface of the cornea, which typically manifests as multiple images from a single object.
Both regular and irregular astigmatism can be hereditary. Therefore, parents with the condition should have children checked periodically. Many experts believe that everyone is born with some level of astigmatism; however, it is just a matter of whether it increases over time causing a moderate to severe condition, or remains the same as in the case of mild astigmatism. Studies have shown that this condition tends to be more or less prevalent in certain races.
Treatment for regular astigmatism can be achieved through the use of contact lenses or prescription eyeglasses. Although traditional hard lenses were used in the past, there are now soft lenses, called toric lenses, and rigid gas permeable lenses available. Laser-assisted in-situ keratomileusis, or LASIK surgery, is also available for treatment.
Irregular astigmatism can generally only be corrected through the use of contact lenses or with refractive surgery. Refractive surgery is tailored to the individual, as the procedure must address the specific irregularities within the eye. No two patients will have identical abnormalities.