What is Astigmatism?
Astigmatism in simple terms means that the shape of the cornea (clear portion of the eye in front of the pupil) is shaped like a football versus a basketball. Therefore, light or objects are not focused to a clear point on the retina but as a line. People with this condition will have ghost images or see streaks of light at night from lights as the light is focused to a line not a clear point. The condition can be regular or irregular. Regular astigmatism is by far the most common type. In this type the football shape is symmetrical. In the irregular type the football is warped. Irregular astigmatism is usually caused by a disease or injury to the cornea which results in an irregular surface to the cornea.
Diagnosing Astigmatism or Astigmatism Test
Astigmatism is usually found during the refraction when a person has an eye exam. A refraction is done with you answering which lenses you see better with while positioned behind a machine called a phoropter. A keratometer is a device that measures the curvature of the cornea and this can be used to objectively measure the condition.
Correction of Astigmatism with Contact Lenses
There are three basic types of contact lenses that can correct the condition:
- Toric contact lenses
- Gas permeable contact lenses
- Hybrid contact lenses
Gas Permeable Contact Lenses
Gas permeable contacts are semi-rigid lenses that float on the tear film. The rigid contact lenses vault over the cornea and the tears fill in under the contact lens. This corrects the football shape as the rigid lens is round like a basketball. Gas permeable lenses are initially not as comfortable as soft contacts and you need to follow a wearing schedule as you gradually increase the wearing time. They do prove excellent vision.
Toric Soft Contact Lenses
Toric soft contact lenses are designed similar to glasses in that the prescription is designed by the shape of the lens to correct the condition. The lenses are curved just the opposite of the shape of the cornea to correct the astigmatism. The contact lens need to stay oriented in the correct axis as to align with the astigmatism. This is done by three possible methods. One is accomplished by thin and thick zones on the contact to keep it oriented correctly. The bottom of the lens is truncated to align with the lower lid to keep it oriented. The contact lens is thicker and heavier in one area of the lens to keep it oriented correctly. Examples of this type of contacts are:
- Air Optix for astigmatism
- Acuvue Oasys for astigmatism
Hybrid Contact Lenses
Hybrid contact lenses consist of a central gas permeable lens which is surrounded by a soft lens material. This provides the clear vision of a gas permeable lens with the additional comfort of the peripheral soft lens material.
Contact lenses can be used to correct the blurred vision associated with astigmatism. There are a variety of contact lenses that can be used to correct the vision. You eye doctor can discuss which might be best for you.