contact lens Q&A

Managing LASIK-Induced Irregular Astigmatism

DAVID I. GEFFEN, OD
JANUARY 1998

A patient who underwent LASIK about three months prior complains of blur OS especially at night and ghosting. Visual acuity is OD 20/20- and OS 20/30-. Refraction is OD plano -0.50 x 175, 20/20; OS -0.50 -0.50 x 006, 20/20-. Spectacles do not relieve the symptoms. Corneal topography shows an inferior displaced ablation. Keratometry readings are: OD 39.00 / 39.50@90 mires clear; OS 38.75 / 39.25@70 mires, Grade 1+ distortion. You know the decentered ablation has caused irregular astigmatism in the optical zone of this patient's eye. The question is:

How do you manage irregular astigmatism associated with LASIK?

Irregular astigmatism, one of the most common complications of LASIK, may be caused by a decentered ablation and irregularity in the corneal cap. Usually, the decrease in acuity is one to three lines, and while many patients won't be symptomatic, some patients are bothered by decreased visual acuity, distortion, ghosting or glare. You have two options for managing irregular astigmatism: surgery and contact lenses.

OPTION 1: Surgery

Surgery may help smooth the surface, depending on the nature of the irregularity. If the cap is the problem, lifting and reseating it may help. If topography reveals a decentered ablation, a new LASIK or PRK procedure may be necessary. The goal is to create a new ablation that is centered. The problem with this is that the patient may become hyperopic unless there was an undercorrection prior to the second surgery. Some surgeons have used astigmatic keratectomy (AK) to help decrease the irregularity, which may help flatten the steeper meridian and smooth out the optic zone area.

OPTION 2: Contact Lenses

Rigid contact lenses have been used for many years to correct corneal irregularities, and postsurgical corneas usually fare very well with RGPs. I'd suggest that the patient in the opening example start with contact lenses. Understanding the corneal topography is important for proper fitting. The ablation zone is approximately 6.0mm wide and the cap diameter is about 9.0mm, so I'd trial fit using large diameter gas permeable lenses.

Trial fitting is imperative with postsurgical corneas. It's extremely difficult to predict the lens fit from topography and keratometry readings alone. Lens diameter will greatly affect how stable the fitting will be. If you don't have large diameter trial lenses, ask your lab to borrow a set.

The central 6.0mm of the cornea will be much flatter than the periphery, which remains close to the original. By fitting on the peripheral cornea and vaulting the central apex, I often use 10.0mm to 11.0mm diameter lenses. Base curves typically are close to the original keratometry readings. I've been using a new design from Infinity Optical called the Post-Surgical Cornea Design (PSC design). This lens has a spherical central zone and an aspheric periphery that helps to stabilize the fit while providing excellent optics. The lens can be made in any material, and I suggest moderate to high Dk materials with good wettability.

Allow five to 10 minutes for the lens to stabilize before assessing the fluorescein pattern. Lenses may adhere or tighten after being on the eye for a few minutes. The fluorescein pattern should show central pooling with light intermediate bearing and peripheral clearance. The lens should move one to two millimeters with the blink. Centration is ideal, but sometimes you must accept some decentration due to the flat central topography. The large diameter helps prevent flare and glare problems.

Dr. Geffen is in a joint refractive surgery practice in San Diego. He is also a consultant for Infinity Optical.20