Of the many vision problems that exist, astigmatism may be the most misunderstood. Even the name, astigmatism is confusing since a person doesn’t suffer from a stigmatism, but instead has astigmatism. The condition results from a refractive error just like farsightedness or nearsightedness. It is not an eye disease nor is some type of eye health issue. Instead, it is simply an issue involving how the eye focuses light.
When a person has astigmatism, light doesn’t focus correctly on the retina. It does not narrow to properly focus on the retina which is required to see clearly. Instead, light focuses on multiple points, either behind or in front of the retina or both.
Symptoms Of Astigmatism
Individuals with astigmatism will usually experience distorted or blurred vision at all distances. They may have headaches or eye strain, especially after completing prolonged visual tasks such as reading. Another common symptom is squinting.
The Causes Of Astigmatism
Astigmatism typically results because of an irregularly shaped cornea. In a healthy eye, the cornea is symmetrically round. In an eye with astigmatism, the cornea is shaped like a football, and one meridian is much more curved than the other. The meridians are the vertical and horizontal lines across the cornea. With astigmatism, the vision problems are caused by issues with the meridians. The meridians which are the flattest and steepest are called the principal meridians. Astigmatism may also be caused when the lens of the eye is not shaped correctly. When this occurs, a patient has lenticular astigmatism.
Different Categories Of Astigmatism
Astigmatism is categorized into three different types:
- Myopic astigmatism happens when both of the eye’s principal meridians are nearsighted.
- Hyperopic astigmatism happens when one or both of the eye’s principal meridians are farsighted.
- Mixed astigmatism happens when one of the principal meridians is nearsighted and the other principal meridian is nearsighted.
Astigmatism is also categorized as regular astigmatism or irregular astigmatism. When the eye’s principal meridians are perpendicular to each other, a person has regular astigmatism. When the meridians are not perpendicular to each other, a person has irregular astigmatism. Irregular astigmatism may be caused by several things including keratoconus which is a condition that causes the cornea to gradually get thinner, an eye injury or eye surgery.
Astigmatism Is A Common Condition
Most people get astigmatism early in life. This is why it is important to schedule regular eye exams for children. If left untreated, astigmatism can cause problems with learning. According to a recent study which looked at more than 2,000 children who were between 5 and 17 years old, childhood astigmatism is a significant issue. This study found that more than 28 percent of those examined had astigmatism of 1.0 diopter or greater.
Testing For Astigmatism
During a regular eye exam, the doctor will test for astigmatism just like they do for farsightedness or nearsightedness. There are two primary ways to test for astigmatism. In the manual test called a retinoscopy, the doctor will shine a light into the eye and using a series of lenses, will test how the light focuses in the eye.
Many eye doctors are either replacing or supplementing the retinoscopy with a test that uses automated instruments. These tests are faster and provide quicker preliminary results for astigmatism and other types of refractive errors. Following these tests, the eye doctor will also perform a manual refraction. This test further refines the tests for astigmatism.
During the manual refraction which is also known as a subjective or manifest refraction, the doctor uses a phoropter to test for the level of astigmatism. The phoropter consists of several lenses which the doctor will introduce in front of the patient’s eyes. The patient then compares how well they see with each lens.
The patient will look at an eye chart while the eye doctor demonstrates different lenses. The doctor will ask the patient different questions designed to determine the patient’s eyeglasses prescription.
When a patient is diagnosed with astigmatism, the eye doctor can correct their vision using several methods including refractive surgery, contact lenses or eyeglasses. Correcting astigmatism requires an eye doctor to use “cylinder” lens power in addition to the spherical lens power which corrects farsightedness or nearsightedness. Cylinder lens power corrects the differences between the powers of the eye’s principal meridians. For example, a eyeglasses prescription correcting myopic astigmatism would read -2.75 -1.00 x 90. Similarly, a contacts prescription correcting astigmatism would contain the same information.
Another option for those with astigmatism is gas permeable contact lenses. These are rigid lenses and may be used to optically replace the eye’s refracting surface. This means an axis and cylinder power may not be necessary, however, this will depend on the severity and the type of astigmatism that is being corrected. This is also true for hybrid contact lenses.
LASIK surgery is another possibility for correcting astigmatism. This is a quick and painless surgery that takes seconds, but which produces great results. LASIK has been used for years, but recent advancements have made this one of the safest surgeries available. Improvements in equipment and technology have also resulted in price reductions making LASIK an option for more people.
It is important to discuss all options with a patient’s eye doctor. What will work for one person may not be a good choice for another. Every individual is unique, and the choice of glasses, contacts or LASIK should be carefully considered.