Astigmatism

What is Astigmatism?

Astigmatism is an optical error correctable with glasses, contact lenses, or surgery. The cornea (the window to the eyeball) accounts for most of the astigmatism of the eye. The radius in one meridian is different than the meridian 90 degrees away. Another words instead of being round like basket ball, the cornea is shaped like a egg. You can create an astigmatic surface by lightly squeezing a rubber ball on the two opposite sides. This is just another optical error. Astigmatism may be low, moderate or high in amount. Astigmatic corrections are incorporated into your eye glass prescription. Patients with astigmatism may be near-sighted, farsighted, or presbyopic.

Is It True That Contact Lenses Do Not Correct for Astigmatism?

No. Special soft lenses, designed to correct for astigmatism, are called Toric lenses. These lenses have an astigmatic correction fabricated into the lens. For them to work properly, the lens must move up and down without twisting upon the blink. Rotation of the lens with blinking results in unstable vision. Another way of correcting for astigmatism with contact lenses is to use a firm or gas permeable lens which neutralizes the toric surface of the cornea.

Can LASIK Correct Astigmatism?

Yes. It does an excellent job. Some lasers do a better job with different types of astigmatism.

Can Cataract Surgery Correct Astigmatism?

Yes Traditional cataract surgery corrects only the non-astigmatic component of the refractive error. However, for milder to more moderate astigmatism a procedure called Astigmatic keratotomy (AK) can either eliminate or significantly reduce corneal astigmatism. Small incisions are made in the periphery of the cornea to relax the cornea and decrease the astigmatic errors. If the astigmatism is significant, premium intra-ocular implants designed to correct the astigmatism can be used. Lastly, glasses can be used it significant astigmatism is present.

What is Irregular Astigmatism or Keratoconus?

The shape of the cornea is distorted, thus, the astigmatism is unpredictable. Glasses can not be fabricated to correct for this optical error. Firm or rigid contact lenses must be used to neutralize the surface of the irregular astigmatism. As a matter of fact, contact lenses were initially prescribed in the 1920’s to correct for this condition. If a patient has Keratoconus and contact lenses provide adequate vision, then no other treatment should be contemplated. However, if the patient can not tolerate a contact lens or can not see well out of his/her contact lenses, either intra-stromal rings or a corneal transplant to replace the old cornea should be performed. The procedure is usually successful (90%). Keratoconus because of its irregular astigmatism and associated corneal thinness is a contra-indication for LASIK (refractive surgery).