Overview
Astigmatism is a type of refractive error where light rays focus at different points in the eye. It is a common condition where light entering the eye gets bent or focused unequally in one meridian versus another. A common analogy is a spoon (or football) with its curvatures varying, being less curved, or flatter, along the length of the spoon and more curved along the width of the spoon. A person with astigmatism sees a smear or shadow image coming off the object viewed.
It can coexist with nearsightedness or farsightedness, and will cause things to appear blurry at distance and near. Uncorrected astigmatism may also cause eyestrain and headaches.
Fortunately, glasses or contact lenses usually easily correct the condition. Contact lenses that correct astigmatism fall into two main types: rigid gas permeable and soft.
Two types of astigmatism – Regular and Irregular
Regular Astigmatism, applies to the majority of those with the condition, and occurs when part of the eye that needs the most amount of power exists 90 degrees away from the area in the eye needing the least amount of power. It is symmetrical, and because of this regularity, it is easily corrected with glasses or contacts.
Irregular Astigmatism is when the cornea, the front curve of the eye, is not smooth or asymmetric. This causes light to be scattered throughout the eye with many different focus points. Neither glasses nor soft contacts can correct this condition; therefore rigid gas permeable lenses are often a medical necessity to provide the bearer with crisp vision.
Causes
Astigmatism is not a disease. It often occurs naturally with some likelihood of a familial inheritance. It can change naturally over a person's lifetime. Sometimes, astigmatism can be a symptom of eye diseases such as keratoconus or cataracts. It also can be a result of various ocular surgeries or injuries.
How is Astigmatism Detected?
Astigmatism is easily quantified by two common tests during an eye exam, Keratometry and Refraction:
Keratometry is a quick test measuring the two main corneal curvatures of the cornea. Your eye doctor may do this as part of a routine eye exam. It is especially important if you are being fit with contact lenses.
Refraction is the part of the exam in which you choose between a variety of views or lenses to determine your prescription for glasses and eventually contact lenses.
Not as commonly used is topography, which is a mapping of the cornea to show astigmatism with even greater detail. Topography may be done if you are considering surgery or if there is suspicion of irregular astigmatism.
