“Does LASIK Correct Astigmatism Better than Glasses or Contact Lenses?”

- By SCOTT W. TUNIS, M.D., F.A.C.S.

The second article in our series “Considering your Laser Vision Correction Options” addresses the frequently asked question,

“Does LASIK correct astigmatism better than glasses or contact lenses?”

In order to understand how laser vision correction corrects astigmatism, it is important to understand the nature of astigmatism, how it causes blurred vision, and how it can be corrected by different methods.

Astigmatism is not a disease, but rather a refractive error of the eye which simply causes blurred vision. If the cornea (the front window of the eye) has a surface curvature which is spherical, such as the shape of a basketball, the eye has no astigmatism. If the cornea has a toric shape, like the surface of a football, it has two different curvatures on the surface, and has astigmatism. These two curvatures are usually at right angles to each other with one curvature steeper and one flatter. A greater difference in curvatures creates a larger amount, or magnitude, of astigmatism.

In addition, astigmatism also has an axis (direction) which is determined by the orientation of the steeper curvature of the cornea. Put another way, the football shape of the cornea can be pointed in any direction like the needle of a compass. Thus, astigmatism has a magnitude and a direction which are equally important.

Glasses and contacts correct blurred vision from astigmatism by using the opposite shape of the correcting lens to “cancel out” the abnormal shape of the eye. For this reason, the frame of the glasses or the fit of the contacts must match exactly the correct magnitude and direction of the astigmatism of the eye. Any deviation in the compensating lens will cause blurred or fluctuating vision. This is why patients with astigmatism and glasses can tolerate very little twisting or maladjustment of the frame as it sits on their face. Similarly, patients with toric (astigmatism correcting) contact lenses frequently notice large fluctuations in vision as the contact lens spins on the eye. These problems arise because glasses and contacts simply compensate for the abnormal shape of the underlying cornea by adding the opposite shape in the correcting lens in front of the eye.

Laser vision correction and LASIK, on the other hand, actually correct the astigmatism by reshaping the cornea, eliminating the two different curvatures, thereby creating the correct spherical shape of the cornea. Laser vision correction actually corrects astigmatism, it does not compensate for the refractive error in a similar manner to glasses and contacts.

As a result, patients with astigmatism frequently notice better vision with LASIK than with contacts or glasses. In fact, with the newest laser software, LASIK can frequently correct larger magnitudes of astigmatism than can even be placed in glasses or is available in contacts. In addition, patients with small amounts of astigmatism who do not wear toric contacts notice better vision after LASIK than with spherical contacts.

Next in our series of articles:
“Recurrent Contact Lens Infections and the LASIK Alternative”

Scott W. Tunis MD FACS Named to the PS250 - Premier Surgeon Top 250 List of Innovators

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Considering Your Laser Vision Correction Options

- BY SCOTT W. TUNIS, M.D., F.A.C.S.

LASIK and other types of Laser Vision Correction procedures have been performed in the United States since 1994 with over 15 million procedures performed. These remarkable procedures have evolved as the technology has improved over the years, indications have expanded allowing more patients to enjoy clearer vision without glasses or contacts, and far superior results are obtained when compared to those of the early procedures.

Despite the widespread acceptance of LASIK and a vast amount of public information which is readily available, there remain certain areas of particular interest, as well as sources of potential confusion, to patients who are considering the procedure. In this report, the first of a series, we will examine and clarify some of the most common issues and choices patients face when considering Laser Vision Correction.

Bladeless All Laser LASIK vs. Microkeratome Blade LASIK

In LASIK, a microscopic corneal flap is created under which an excimer laser applies the patient’s prescription. Healing of the corneal flap is quite rapid, allowing highly functional vision within 12 hours. The corneal flap can be made with a femtosecond laser (bladeless) or with an automated instrument called a microkeratome (using a microscopic blade).

Currently about two thirds of the procedures in the United States are done with a microkeratome. Both are excellent methods of performing LASIK, but most importantly, there are no statistical differences in visual outcomes between the two procedures. The prescription that is applied to the eye is the same with both methods and the success rate in achieving 20/20 vision is the same.

There are, however, important differences between the two methods. Microkeratome technology requires more training and experience, yet it is significantly less expensive, takes less time in surgery, and nearly always causes less discomfort than bladeless. Bladeless technology may be a better choice in patients with certain corneal parameters, and is generally easier to learn and to use by surgeons who are less experienced in corneal surgery. It is important to choose a surgeon who offers both technologies, allowing the selection of the best procedure for you.

I Have Good Distance Vision but I Hate My Reading Glasses! Is Laser Vision Correction for Me?

Over the past decade several procedures such as LTK, CK, and multifocal IOLs have been promoted as being able to eliminate reading glasses in patients over 40 while not reducing their distance vision. Despite the desirability of such a procedure, there is no technology that will create normal vision both at near and at distance simultaneously in an eye of a patient over the age of 40. As all patients who wear only reading glasses can attest to, distance vision is blurred when looking through a reading prescription. Unfortunately, research testing of bifocal laser prescriptions has been uniformly unsuccessful… and, not surprisingly, the laser “time machine” which reverses the normal aging process has yet to be invented!

Nonetheless, LASIK may eliminate distance and reading glasses simultaneously in patients over 40 given the correct scenario. If a patient can function well with one eye corrected for distance and one corrected eye for near, which is called monovision, and which many patients already achieve by wearing a distance contact in one eye and a reading contact in the other eye, then LASIK monovision is a highly successful option. LASIK monovision corrects one eye for distance and one eye for near, allowing a patient over age 40 to see both without glasses or contacts.

In patients who wear reading glasses only who are not regular contact lens wearers, a short trial of a reading contact lens in the non dominant eye with their current Eye Doctor can usually determine if they can have LASIK monovision.

Next in our series of “Considering your Laser Vision Correction Options"
• Recurrent Contact Lens Infections: Can I Still Have LASIK?
• Does LASIK Correct Astigmatism Better than Glasses & Contacts?