Topographical Changes after Everted Silicone Hydrogel Wear
Reports have recently emerged in the ophthalmic literature related to topographical and refractive changes associated with silicone hydrogel lens wear. In a Pacific University study, we found everted (inside-out) lenses could induce significant corneal changes and that subjects consistently rated everted lens comfort as equal to that of non-everted lenses.
To further test this, one of us (PC), wore an everted –10.00D Night & Day lens (CIBA Vision) on his amblyopic left eye for a continuous wearing period of 30 days. We took baseline corneal topography measurements after the fitting and then follow-up measurements after 10 hours, one week and four weeks of lens wear.
|Figure 1. Difference display map after 10 hours of overnight lens wear.|
|Figure 2. Topography following one week of continuous lens wear.|
|Figure 3. Topography following one month of continuous lens wear.|
After 10 Hours Overnight Wear
The difference display map showed little or no change at the center of the cornea. The area adjacent to the central cornea showed approximately –1.50D of concentric flattening surrounded by a zone of midperipheral steepening (Figure 1).
At one week, the central apical power had flattened –1.37D. A distinct "central island" (zone of less topographical change) was evident. Surrounding it was a concentric zone of greater flattening (–4.50D at its flattest point). In the midperiphery, note a concentric zone of corneal steepening similar to that in GP corneal reshaping (Figure 2).
At four weeks, the central apical power demonstrated –3.12D of corneal flattening. The central island remained evident; however, the midperipheral cornea had flattened –6.75D at its flattest point (Figure 3).
Despite the limitations of this pilot study, we made two intriguing observations. First, wearing everted silicone hydrogel lenses can result in significant topographical changes. Second, patients can comfortably wear everted lenses for 30 days.
Patrick Caroline is an associate professor of optometry at Pacific University and is an assistant professor of ophthalmology at the Oregon Health Sciences University. He is also a consultant to Paragon Vision Sciences and SynergEyes, Inc. Mark André is director of contact lens services at the Oregon Health Sciences University and serves as an assistant professor of optometry at Pacific University. He is also a consultant for Alcon Labs, CooperVision and SynergEyes, Inc.