prescribing for presbyopia
Managing GP Corneal Warpage
BY MARY JO STIEGEMEIER, OD, FAAO

Contact lens wear can result in distortion and warpage of the corneal surface. Corneal molding can occur with soft, GP and multifocal lens wear. Contact lens-associated corneal warpage may result from corneal hypoxia, poorly centered GP lenses, mechanical insult from lens binding and epithelial wrinkling from poorly fit soft lenses.

Patients who have corneal warpage are often asymptomatic. Many do not own spectacles and depend solely on their contact lenses to correct their refractive error.

Use corneal topography and manifest refraction to diagnose and to follow to resolution the transient or permanent changes from corneal warpage.

At least four topographical changes can result from corneal warpage. These include:

1. Reversal of the normal topographical pattern of progressive flattening from center to periphery.

2. Central irregular astigmatism.

3. Inferior steepening in a smile-like pattern (keratoconus-like images), superior flattening.

4. Loss of radial symmetry.

Refractive changes also occur with corneal molding.

For patients who experience corneal warpage, I discontinue all soft lens wearers for at least one week and rigid lens wearers for at least two to three weeks, then have patients return to the office for repeat topographies and refractions. If you see irregularities, don't have a consistent refraction or cannot get a clean 20/20 refraction endpoint, wait another two to three weeks and then repeat these measurements. When the difference in refraction is less than 0.50D, the spherical equivalent and astigmatism values have not changed and the cylinder axis is within 15 degrees, I deem the refraction stable. Resolution of the topographical changes will occur along with the refractive stability.

Patients who've experienced corneal warpage are at increased risk for its recurrence. Such patients should purchase glasses in their final prescription, and you should encourage them to wear their glasses correction for at least an hour in the morning and for an hour in the evening while awake. This will help them control their wearing time and become aware of any spectacle blur.

A Presbyopic Case

I recently saw a patient who had been very happy with her GP bifocal lenses until the last few months. She is 59 years old and has worn GPs for at least 32 years. She has successfully worn posterior aspheric simultaneous vision multifocal GPs for about 15 hours each day until a few months ago.

She had several minor complaints all centered around vision, with no reports of discomfort, redness or reduced wearing time.

Visual acuity was 20/60 in each eye for distance and 20/20 binocularly for near. Over-refraction yielded no improvement in distance acuity. Manifest refraction yielded a prescription of less myopic correction and increased oblique astigmatism with an endpoint that was unclear and less than 20/20. Topography revealed flattening of the superior cornea and an inferior steepening in a smile pattern.

Vision with current spectacles was blurred slightly and her vision did not rebound as it used to after switching to spectacle wear.

We temporarily discontinued this patient's GP multifocal lenses, then performed sequential refractions until they were stable and her visual acuity reverted to her baseline visual acuity (20/20 OU in this case) and sequential topographies until her maps became more regular with less superior flattening and inferior steepening. I then refit her into an anterior aspheric multifocal GP design in a high Dk/t material. This design helped the centering and movement of her multifocal lenses and allowed an alignment fitting approach. The higher oxygen transmissibility also helped decrease any hypoxic changes.

Dr. Stiegemeier is in private practice in Beachwood, Ohio. She lectures throughout the country on the subject of contact lenses and performs clinical research.

Contact Lens Spectrum, Issue: November 2006