Aspheric and Reverse Geometry Lenses: Successful Alternatives to Surgery

BY GARREN T. CRANER, O.D., & DANA J. MORSCHAUSER, O.D.
JUNE 1996

Surgery isn't always the best option. A simple contact lens fit managed this patient's resolved interstitial keratitis.

A 33-year-old male, originally from Afghanistan, was referred to our clinic for a photorefractive keratectomy consult. He wanted to improve his visual acuity, especially when driving. The patient had a long-standing history of decrease in vision greater in the left eye at both distance and near since an episode of "serious eye infection" bilaterally approximately 20 years ago. At the time, he was unable to obtain treatment for the condition due to the lack of appropriate health care in his country. All other general and family ocular history was negative except for current treatment for a stomach ulcer.

DIAGNOSTIC DATA

A subjective refraction revealed the following correction and acuities:

O.D.: +6.50 -3.00 x 005, 20/30 DV and 20/30- NV

O.S.: +8.50 -3.25 x 007, 20/70 DV and 20/80- NV

Retinal acuities measured by a Potential Acuity Meter (PAM) indicated:

O.D.: 20/25

O.S.: 20/30

FIG. 1: CORNEAL TOPOGRAPHY REVEALED IRREGULAR CORNEAL SURFACES IN BOTH EYES DUE TO INTERSTITIAL KERATITIS OF AN IDIOPATHIC ORIGIN. THE PATIENT PRESENTED WITH REDUCED VISUAL ACUITIES.

Keratometry readings revealed distorted mires OU with the following readings:

OD: 39.75 @ 175, 43.87 @ 085

OS: 38.62 @ 188, 44.00 @ 098

Corneal topography indicated irregular corneal
surfaces in both eyes (Fig. 1).

Slit lamp findings showed areas of central corneal scarring within the stromal layers, OS greater than OD, that encroached upon fixation, OS greater than OD. Associated with this were areas of corneal thinning in both eyes and a hemosiderin line OD (Fig. 2). We observed ghost vessels in the stromal layers entering from the limbus toward the areas of scarring. There was no corneal staining with NaFl, however, we observed slight areas of pooling OU. We noted corneal arcus in the periphery of both eyes.

Intraocular pressures by applanation tonometry were 16mm Hg OD and 14mm Hg OS. Dilated fundus exam was unremarkable.

DIAGNOSIS

Based on these findings, we diagnosed interstitial keratitis. We sent the patient for a blood workup, which revealed negative results on both VDRL and FTA-ABS tests and showed an elevated cholesterol level.

Further testing and questioning demonstrated no signs of decreased auditory function nor symptoms of vertigo or tinnitus. Thus, it was our opinion that the interstitial keratitis was not related to syphilis nor to Cogan's syndrome, but of an idiopathic origin with reduced visual acuities secondary to stromal scarring and irregular corneal surfaces.

DISCUSSION

While the patient was initially referred for PRK consideration, this treatment option was contraindicated for two reasons. First, for refractive use, the excimer laser is currently not approved to correct hyperopia. Second, while the excimer laser has therapeutic uses for removal of corneal opacities, the depth of the ablation necessary for this patient's stromal scarring would be contraindicated as the resultant postoperative corneal thickness would be less than 250µm. This would also induce a further hyperopic shift in the patient's prescription.

A PAM showed good retinal acuities, thus the decrease in vision was due in part to a poor refracting surface at the anterior cornea and also media opacification secondary to the stromal scarring. These factors could be treated with penetrating keratoplasty, but surgery brings its own side effects including graft rejection. This was of increased concern due to the presence of ghost vessels within the stroma and the knowledge of an increased incidence of graft rejection in vascularized host corneas. For this reason, we opted to fit contact lenses to provide best corrected visual acuity. If this approach failed due to media opacification, we'd reconsider penetrating keratoplasty.

Believing an aspheric back surface lens would compensate for the irregular corneal surface and provide good alignment, we began trial fitting with a Boston Envision aspheric rigid gas permeable lens. The lens fit well in the right eye and showed a normal with-the-rule fluorescein pattern. The corneal topography helped demonstrate the irregular surface with steepening along the vertical meridian and a sharp inferior drop-off (Fig 2). This initial trial lens continued to shift between a lid and an aperture fit so we ordered a minus carrier lenticular lens that provided a stable lid fit. Final parameters OD of the Boston Envision lens were: 10.3mm diameter; 8.1mm base curve; +4.25 power; minus carrier lenticular.

In the left eye, an aspheric lens proved to be unstable with central fluorescein pooling with peripheral alignment. A second trial lens of a reverse geometry design with a secondary curve steeper than the base curve, provided better centration and corneal alignment. In this case the central cornea was flatter than the periphery as in post-RK, PRK and PK for which these lenses were designed. The corneal topography of the left eye demonstrated both the irregular surface and the flat central cornea relative to the periphery (Fig 2). However, a secondary curve two diopters steeper than the base curve showed edge lift, which we eliminated with a secondary curve four diopters steeper to contour the periphery. Again, a minus carrier lenticular lens stabilized the shift between lid and aperture fit. We chose the following final parameters OS: Menicon Plateau lens; 10.0mm diameter; 8.0mm O.Z.; 8.65mm base curve; 7.85mm S.C.; +10.25 power.

We dispensed both lenses with a plano overrefraction in both eyes, with the following best resultant visual acuities:

OD: 20/30+2

OS: 20/50+

At subsequent visits the patient reported increased acuities compared to spectacle wear and good comfort with no signs of deleterious effects upon ocular health.

Reverse geometry contact lenses have previously been reported as successful for irregular and postsurgical corneas. Similar designs are available from Conforma Labs (RK-Bridge) and from Contex Lenses (OK Lens Series). CLS

Dr. Morschauser is currently doing a research fellowship in contact lenses, cornea and refractive surgery at SUNY College of Optometry where she is an assistant clinical instructor. She recently completed a residency in cornea and contact lenses.

Dr. Craner is a recent graduate of SUNY College of Optometry. He practices in Long Island, N.Y., specializing in contact lenses.

The authors have no proprietary interest in Conforma, Contex, Menicon or Polymer Technology.

References are available upon written request to the editors at Contact Lens Spectrum. To receive references via fax, call 1-800-239-4684 and request Document #14. Be sure to have a fax number ready.