PTK and Contact Lenses
Manage Corneal Disease

BY ROBERT CAMPBELL, M.D. & PATRICK CAROLINE, C.O.T., F.A.A.O.
JULY 1996

The indications for PTK are limited to patients with decreased visual acuity, symptoms of pain or discomfort, or contact lens intolerance severe enough to cause disability. The conditions include: epithelial basement membrane dystrophy; subepithelial dystrophies, i.e., granular, lattice, Reis-Bucklers; irregular scars and opacities after trauma, surgery or infection; and pathologic surface irregularities, i.e., nodules, band keratopathy.

PREOPERATIVE ASSESSMENT

When assessing patients for PTK, the practitioner must consider the type and depth of the pathology, its proximity to the center of the pupil and the refractive error.

Type and Depth of Pathology -- The various types of pathologies respond differently to the 193nm excimer laser. A high frequency (hard) condition such as band keratopathy has different ablation characteristics than low frequency (soft) defects such as nebulae.

The excimer laser removes pathology within the anterior one-fifth of the cornea. Pathology treatment should be confined to the anterior 100µm of the cornea to maintain corneal integrity.

Location -- Superficial central or paracentral surface opacities are generally a good indication for PTK. Surface ablation of these defects can dramatically improve corneal clarity and reduce irregular astigmatism.

Preoperative Refractive Error -- There is the potential to induce significant changes in refractive error as the anterior corneal pathology is removed. Failure to consider this could turn an anatomically successful PTK into a refractive failure. If the preoperative refractive error is myopic, this may be desirable. If the eye is hyperopic preoperatively, the central PTK will invariably result in increased hyperopia.

FIG. 1: PREOPERATIVE PHOTOGRAPH OF THE
PATIENT'S LEFT EYE WITH LATTICE DYSTROPHY

LATTICE DYSTROPHY

Our case involves a 52-year-old male with a history of recurrent corneal erosion secondary to lattice dystrophy. For 12 years, the patient had been adequately managed with bandage soft contact lenses. Eventually his best corrected visual acuity decreased to 20/40 OD and 20/80 OS with frequent erosions OS.

Manifest refraction was -1.50 -1.50 x 165 degrees OS and -2.00 -2.25 x 15 degrees OD.

The patient underwent PTK to his left eye to a depth of 100 microns (Fig. 2). Postoperatively, the clarity of the central cornea improved significantly. Manifest refraction was +5.00 -1.25 x 175 degrees with a visual acuity of 20/40.

FIG. 2: CORNEAL PROFILE FOLLOWING THE PTK PROCEDURE.

[FIG. 3: POSTOPERATIVE RGP.]

Due to some residual surface irregularity, we prescribed a standard RGP lens (Fig. 3). The patient tolerated the lens well with no recurrence of the corneal erosions and a final visual acuity of 20/25.

In selected cases, PTK and contact lenses may be a viable alternative to the more invasive surgical techniques. CLS

Dr. Campbell is medical director of the Park Nicollet Contact Lens Clinic & Research Center, Minnetonka, Minn. Patrick Caroline is an assistant professor of optometry at Pacific University, Forest Grove, Ore., and director of contact lens research at Oregon Health Sciences University, Portland, Ore.