By David F. Chang, MD
Correcting or reducing astigmatism is a common and popular option for many patients undergoing cataract surgery. This will benefit those individuals with astigmatism who do not expect or intend to wear eyeglasses at all times after surgery.
What is astigmatism?
Like nearsightedness, astigmatism describes a common type of natural blur or misfocus in healthy eyes that is corrected by wearing eyeglasses. It results from an inherited, imperfect optical shape of the cornea, the clear front window of the eye. The shape of your cornea should be perfectly round, but if is more oblong (like the back of a spoon) instead of spherical, then it will misfocus details causing your natural vision to be blurrier compared to patients without astigmatism. The more astigmatism one has, the blurrier the vision is without eyeglasses. There is no benefit to having astigmatism because it increases natural blur at every viewing distance – far, near, and in between. Corrective eyeglasses compensate for this corneal shape to optically correct this blur and to optimally focus eyes with astigmatism.
Although it has nothing to do with cataracts, astigmatism can be significantly reduced or eliminated at the time that cataract surgery is done. By mapping your corneal shape in the office preoperatively with diagnostic testing called corneal topography, we can calculate the amount of astigmatism correction that your eye should require in eyeglasses for the clearest vision following cataract surgery. One option is to build this astigmatism correction into the artificial lens that is selected for your cataract surgery. This is called a TORICcorrection and this feature will result in a more customized lens implant for your eye.
An alternative to a toric lens
An alternative to correcting astigmatism with a toric artificial lens implant is to improve and correct the cornea shape at the time of cataract surgery. This is done by making microscopic slits in the outer edge of the cornea, where they cannot be seen or felt. This technique is called astigmatic keratotomy and is perfectly safe and effective. Guided by the preoperative topography measurements, these microscopic slits are placed in a precise location to reduce the undesirable oblong shape of the cornea. There is no pain involved and you will not be able to feel these slits. They do not require the cataract surgery to be performed any differently and do not effectively lengthen the surgical time. `
Astigmatic keratotomy is optional and does not at all affect the eye’s health. The goal is to reduce one’s dependence upon eyeglasses. Astigmatism may not be eliminated completely. Nevertheless, if it is significantly reduced, the vision without glasses will be improved and the eyeglass prescription will be less “strong”. Like LASIK and other refractive procedures, astigmatic keratotomy addresses the inconvenience of eyeglasses and is not covered by health insurance, such as Medicare. For those patients hoping to enhance their ability to see without glasses, this is an excellent option to combine with their cataract operation.