Diagnosis and Management of Corneal Surface Irregularity

Corneal topography and a bit of sleuthing revealed the nature of this recent onset diplopia.

BY GREGORY J. NIXON, OD
JANUARY 1999

Since the cornea is the principal refractive surface of the eye, diseases and disorders affecting the integrity of corneal tissue can often degrade the optical quality of ocular images. One striking example is keratoconus, where a thinned, protruding cornea often results in irregular astigmatism that can decrease visual acuity and create optical distortion. However, there are more subtle forms of corneal irregularity that can compromise vision. The following case report highlights one such example.

Patient History and Symptomatology

A 58-year-old woman, J.W., presented to our clinic for routine examination. Significant ocular history included a diagnosis of primary open angle glaucoma in November of 1993. Due to hypersensitivity to multiple topical glaucoma medications, she underwent argon laser trabeculoplasty in April of 1995. Her optic nerve health, visual fields and IOP have remained stable in the postoperative period without the use of any medications. J.W. had worn quarterly replacement spherical contact lenses successfully for two years, but at this visit, she complained of doubling and ghosting of images while wearing contact lenses or spectacles. Examination revealed intact binocular function and pinpointed the ghosting as a monocular phenomenon. J.W. exhibited monocular diplopia in the right eye and monocular triplopia in the left eye. The polyplopia in each eye persisted while she viewed through full spherocylindrical correction (OD -1.25 -0.50 x 103; OS -2.00 -0.50 x 091), but was eliminated while she viewed through a pinhole OU.

Keratometry readings were: 41.37/41.75@090 OD and 41.75/42.12@090 OS with clear, smooth, complete mires OU. Corneal topographic analysis, however, revealed irregular topography OU, with flat islands occurring within the pupillary zone OU (Fig. 1). Slit lamp examination revealed map-like basement membrane irregularities OU characteristic of epithelial basement membrane dystrophy (EBMD) (Fig. 2) in the locations corresponding to the flat islands shown by the corneal topography. This irregular thickened basement membrane and subsequently elevated epithelium resulted in a negative fluorescein staining pattern in the affected areas (Fig. 3). Examining the remaining ocular structures revealed clear media, clear lens and intact retina OU.

FIG. 2: Map-like basement membrane irregularities common in EBMD.

FIG. 3: Negative fluorescein staining in EBMD.

RGP Fitting for Irregular Corneas

Rigid gas permeable lenses are a commonly accepted management tool for irregular corneas. Severely irregular corneal surfaces, such as those found in advanced keratoconus or in postsurgical eyes, commonly require advanced fitting procedures and special contact lens designs. However, a cornea with mild surface irregularity can be successfully fit with standard RGP designs and fitting techniques. The benefit of using an RGP design is that the tear lens created between the RGP lens and the irregular corneal surface prevents the formation a distorted optical image. A soft lens has no true tear lens, and its draping effect conforms to the irregularity that exists on the corneal surface.

In J.W.'s case, an in-office RGP trial fitting revealed an excellent lid-attached fit with an alignment fluorescein pattern and adequate edge lift OU. More importantly, the RGPs completely eliminated the polyplopia OU. We educated J.W. on the optical benefits an RGP lens would provide to her cornea, which a soft lens could not. We also discussed the expectations and time frame of RGP adaptation. Based on the success of the trial fitting, I ordered RGP lenses manufactured in FluoroPerm 30 with the following specifications: 8.26mm BCR, 8.3mm OZD, 9.7 OAD, -0.75D OD and 8.26mm BCR, 8.3mm OZD, 9.7 OAD, -1.25D OS. J.W. quickly adapted to the lenses and has since maintained crisp, clear, comfortable, single vision with 20/20 acuity OU.

The Differential Diagnosis

It is of utmost importance to determine the nature of recent onset diplopia in an adult. Specifically, you must rule out a binocular misalignment that may be secondary to an orbital mass, a neurological lesion or muscular degeneration or decompensation. If binocularity is intact and the diplopia persists under monocular viewing conditions, there are a number of conditions you must consider in the differential diagnosis of monocular diplopia. Typical causes include an uncorrected refractive error, corneal irregularity, cataract or retinal problem.

J.W. exhibited monocular diplopia OU that persisted with full spherocylindrical correction. Ocular health evaluation revealed a clear lens and flat and intact retina OU. In this case, a corneal topographer was of great benefit in discovering the subtle corneal irregularity and pinpointing the cornea as the cause of the visual disturbance. For practitioners without a corneal topographer in the office, elimination of monocular diplopia with the application of a trial RGP lens can confirm the presence of an irregular corneal surface. As this case illustrates, trial RGP contact lens application is valuable because a corneal defect may be too subtle to detect with a keratometer.

Dr. Nixon is a clinical assistant professor at The Ohio State University College of Optometry and is a fellow of the AAO.