Doctor's Notes on Astigmatism
Astigmatism is an eye problem that causes blurred vision. To see clearly, the eye must focus light into a single plane onto the back of the eye at the retina. In astigmatism, a point (or spot) of light is focused at two different planes, resulting in blurred vision. In an eye without astigmatism, the surface of the cornea is shaped like a Ping-Pong ball, where all the curves are the same (a spherical surface). In an eye with astigmatism, the surface of the cornea is shaped more like a football, where there are two different surface curves located 90 degrees apart (a toric surface).
Symptoms of astigmatism include blurred vision, difficulty seeing fine details both close-up or at a distance, eye strain, eye fatigue, squinting, or headaches in addition to blurring and distortion of vision at all distances.
In an eye with astigmatism, vision is blurred due to the inability of the optical elements of the eye to focus a point object into a sharply focused image on the retina. Astigmatism makes it difficult to see fine details, both close-up or at a distance. Small amounts of astigmatism may not be noticed at all. Other astigmatism symptoms and signs are
- Most astigmatism does not have a recognized cause other than merely an anatomical imperfection in the shape of the cornea, where the front curvature of the cornea is toric, rather than spherical.
- A small amount of astigmatism is considered normal and does not represent a disease of the eye. This type of astigmatism is extremely common and frequently is present at birth or has its onset during childhood or young adulthood.
- There is some hereditary basis to most cases of astigmatism, and most people with astigmatism have it in both eyes.
- Astigmatism is often associated with myopia (nearsightedness) or hyperopia (farsightedness).
- Astigmatism can increase in amount during the growing years.
- In regular astigmatism, the meridians in which the two different curves lie are located 90 degrees apart. Most astigmatism is regular. In irregular astigmatism, the two meridians may be located at something other than 90 degrees apart or there are more than two meridians.
- A scar in the cornea, resulting from an injury or infection, or a disease called keratoconus may also cause astigmatism. This type of astigmatism is usually irregular.
When it comes to signs of eye disease, Americans are blind to the facts. A recent survey showed that while nearly half (47%) of Americans worry more about going blind than losing their memory or their ability to walk or hear, almost 30% of those surveyed admitted to not getting their eyes checked.
The following slides take a look at some of the signs and symptoms of some of the most common eye diseases.
Kasper, D.L., et al., eds. Harrison's Principles of Internal Medicine, 19th Ed. United States: McGraw-Hill Education, 2015.