Astigmatism – What Does It Mean?
Astigmatism, aside from being a difficult word for children to say, is a very common refractive error causing the light that enters the eye to be focused at two different points. Unlike nearsightedness or farsightedness, people who have astigmatism often experience blurry or distorted vision at all distances.
What Causes Astigmatism?
Your eyes work by refracting or bending light through your cornea and focusing it upon your retina. Your retina then converts it into electrical impulses and sends them to your brain. In a normal eye, the cornea is round, focusing light to a central point within your eye. When a person has astigmatism, the cornea is shaped more oval, like a football. This results in multiple focal points . Astigmatism causes your vision to appear blurry, fuzzy, or distorted at all distances.
Types of Astigmatism
The normal eye has two meridians. It might be helpful to think of it like the equator or prime meridian of the earth. One meridian is vertical and the other is horizontal.
A regular corneal astigmatism is when your meridians are perpendicular to each other, or 90 degrees apart. Regular astigmatism is the most common type of astigmatism.
An irregular astigmatism is when your eye’s meridians aren’t perpendicular with each other. This can be the result of Keratoconus, a degenerative eye disease in which the cornea gradually thins. Irregular astigmatisms can also be the result of an eye injury in which the scarring or damage from the injury misshapes the cornea. Irregular astigmatisms can’t be corrected with the use of corrective lenses.
Typically, symptoms from astigmatism become apparent in a person’s earlier years. A comprehensive eye exam at your eye doctor will be able to reveal whether you have an astigmatism. Eye exams are extremely important for children and young adults as they may not realize their vision isn’t clear. Your eye doctor will use the same tests for astigmatism as they would to see if you’re nearsighted or farsighted.
Visual Acuity Test
An eye chart is used to determine your level of visual acuity, or how clearly you are able to see. We have computerized eye charts which provide us with many options for checking your acuity.
Your eye doctor can use a retinoscope or autorefrator to examine your eyes and measure your level of refractive error. Your optometrist also uses a phoroptor, or the large machine on a swinging arm you typically imagine when you envision a trip to the eye doctor. Placing the phoroptor in front of your face, the eye doctor will flip through different lenses while having you read an eye chart. By switching between lenses until you’re able to see the chart most clearly, your optometrist will now be able to determine your prescription.
To specifically measure the curvature of the cornea, your eye doctor can use an autokeratometer or corneal topographer.
There are several different ways to treat astigmatism and restore your vision. Prescription glasses and contact lenses are the most commonly used methods for restoring vision from astigmatism.
Prescription glasses designed to treat astigmatism use specialized corrective lenses. These contain specific focal points which compensate for the variations in the shape of the cornea.
Due to the fact that astigmatism results from an irregularly shaped cornea, traditional contact lenses will not work in all scenarios. Toric soft lenses or special gas-permeable contact lenses can be used to correct the astigmatism.
Refractive eye surgery, the most common of which is LASIK, can be performed to permanently correct some cases of astigmatism. If you are curious about LASIK, talk to one of our eye doctors to set up a comprehensive eye exam today. Our optometrists can help determine if you would be a good candidate and would see benefit from undergoing corrective eye surgery.