IntroductionAstigmatism occurs in about 1 in 3 adults. It is a very common refractive disorder of the eye. A refractive disorder occurs when the eye cannot clearly focus images. The three most common types of refractive disorders are:
CausesAstigmatism can occur for two reasons. It can occur because the cornea, the clear front layer of the eyeball, has an irregular shape or curvature. This is called corneal astigmatism. Astigmatism can also occur because of irregularities in the natural lens inside the eye, otherwise known as lenticular astigmatism.
TypesAstigmatism can be regular or irregular. Regular astigmatism means that the steeper side is perpendicular to (90 degrees away from) the flatter side. Again, this is similar to the shape of a football. If you were to grip a football with your fingers, the steeper side of the football runs parallel to your fingers. The flatter side, running from one tip to the other tip, is 90 degrees away. Irregular astigmatism occurs when the steeper side is not perpendicular to the flatter side. Irregular astigmatism can also occur if the degree of steepness changes along the length of the curve. Conditions affecting the cornea, or the clear covering of the eye, can lead to irregular astigmatism. Keratoconus and pellucid marginal degeneration are two corneal diseases which may lead to irregular astigmatism. It is especially important that these patients never undergo refractive surgery such as LASIK because they have a higher risk of corneal instability.
SymptomsIf you have mild astigmatism, you may not have any symptoms (doctors use the term "asymptomatic" to describe when the condition is not causing any symptoms or complaints to the patient). With higher amounts of astigmatism, you may have blurry vision, eye strain, eye fatigue, or headaches. You may also see halos around lights, ghosting, and double vision. Keep in mind that other conditions such as near-sightedness, far-sightedness, dry eyes, and cataracts can cause similar symptoms.
DiagnosisMost people will complain of blurred vision, headaches, or eye strain before they are diagnosed with astigmatism. Children may fail vision screening exams at school because of astigmatism.
If you have normal vision, your vision will be recorded as 20/20. If you have abnormal vision, the second number (or the denominator) will increase. For instance, if your vision is 20/60, you can only see at 20 feet what a normal eye should be able to see from 60 feet away.If your vision is not 20/20, your doctor may perform a refraction. A machine holding lens (called a phoropter) is held in front of your face. Your doctor will offer you choices between two different lens to determine whether you have a refractive disorder such as astigmatism. If you hear the doctor asking you "if one or two is better or sharper?", you are undergoing a refraction. A refraction is not only used to determine a need for glasses, but it is also crucial to determine the best corrected vision. This is helpful to determine whether a cataract may be ready for surgical removal.
Prescription BasicsOne way to tell if you have astigmatism is to look at your glasses prescription. Your glasses prescription should be written in this format:
Prescription: Sphere Cylinder Axis
Prescription #1: -1.00 +2.00 x 180 or
Prescription #2: -1.00 -2.00 x 180
TreatmentYou should see an eye care professional if you have blurred vision, headaches, or eye strain in order to determine whether you have astigmatism (or another eye condition).
The word Toric may apply to a contact lens or an intraocular lens - both are used to correct astigmatism.If you have irregular astigmatism, eyeglasses and soft contact lens may not provide clear vision. You may need to wear hard contact lens, also called rigid gas permeable (RGP) lens, to fully correct the irregular astigmatism. Irregular astigmatism can also be corrected with refractive surgery (LASIK is one type of refractive surgery).