Correction of corneal astigmatism

10 August 2016

Like being near-sighted or far-sighted, having astigmatism is not a disease or an eye health problem. 

What is astigmatism?

Astigmatism is what causes your vision to be blurry, no matter what you’re looking at—meaning it affects your vision at all distances. Medically speaking, astigmatism occurs when the cornea is shaped more like an AFL ball than a soccer ball (i.e., the surface is more curved in one axis than another). There are different types of astigmatism (you may have been told you have regular or irregular astigmatism, or that you have myopic astigmatism, hyperopic astigmatism, or mixed astigmatism). This is a very common occurrence—a study of more than 11,000 people in the U.K. who wear glasses found almost half had significant astigmatism If you include lower amounts of non-significant astigmatism, it is even more common—in fact almost everyone has astigmatism to some degree! The good news for most patients is that this can be corrected at the time of cataract surgery. What is the best way to treat low astigmatism at the time of cataract surgery? Most people need to rely on glasses when they have astigmatism, and that may not be desirable. When you have cataract surgery, your natural lens is being replaced with an artificial lens. Because of technology advances in the past decade or so, we now have the capability of treating astigmatism at the time of your cataract surgery. There are two ways we can correct your astigmatism when you have cataract surgery—we can create little cuts on your cornea (called limbal relaxing incisions or peripheral corneal relaxing incisions) or we can implant a special kind of artificial lens that will correct the astigmatism internally (called a toric lens). For patients with corneal astigmatism above 0.60D, we usually recommend a toric lens since they have been shown to be more accurate at correcting astigmatism and have the most reproducible results. It is important to note, however, that most people with astigmatism will still need spectacles after cataract surgery. What the toric lens provides, however, is a much-reduced need for those spectacles. For some patients who had very low levels of astigmatism before surgery, the toric lens may reduce the astigmatism to a point where it’s not noticeable. To give you an example of how a toric lens can help improve your astigmatism, here are my results for approximately 400 patients who were treated with a toric lens when they had cataract surgery:

 

The Y Axis looks at astigmatism before and after surgery for different groups of patients; the bigger the green bar, the more astigmatism was present before surgery. The red bar is a measure of astigmatism after surgery. The T values along the X axis indicate the different groups. The lower the “T” number, the lower the level of astigmatism (so, people who received a T2 lens had much less astigmatism than those who received a T9 lens). What patients might find interesting is that people with higher amounts of astigmatism (who received anywhere from a T4 to a T9 lens) had about 70% of their astigmatism eliminated, but patients with much less astigmatism had a smaller percentage of astigmatism eliminated—around 33%. A 2014 study from Moorfields Eye Hospital compared the postoperative vision in people who had peripheral corneal relaxing incisions in one eye and a toric lens in the other eye when they had cataract surgery. The Moorfields study showed patients preferred the toric lens, as the eye receiving the toric lens had the better vision without glasses than the eye that had the extra incisions. If you have astigmatism and need cataract surgery, your surgeon to determine will need to spend more time determining which replacement lens you’ll need than if you did not have astigmatism. You probably will still need to wear glasses after the surgery (but likely not nearly as often as before surgery).