Contact Lens Case Reports
Scleral Lenses Do Not Center
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
Modern scleral lenses have been a “game changer” for many of our patients, dramatically improving the quality of their lives. However, in our October 2013 Case Reports column, we described 14 “unknowns” related to these lenses and stressed the need for greater research into all of these areas. In this Case Reports column, we add Number 15 to our growing list of unknowns.
Problem: Scleral Lens Position
How is it that when we place a 16mm to 18mm scleral lens onto an eye, it inevitably decenters, inferior and temporal? We observe this finding with both the white light and cobalt blue light of the slit lamp (Figure 1). To understand this phenomenon, let’s look at each position independently.
Figure 1. Slit lamp observation of the inferior/temporal position of scleral lenses. Note the classic fluorescein thinning pattern in the superior/nasal quadrant.
Why do scleral lenses decenter inferiorly? While the exact mechanisms are unclear, we believe it is multifactorial, involving: 1) gravitational force secondary to the weight of the lens and the fact that it is a modality designed specifically to completely clear the cornea and the limbus; 2) the “watermelon seed” effect of the upper lid as it passes across the surface of the lens; and, perhaps most importantly, 3) optical coherence tomography (OCT) observations at Pacific University that have shown that the superior sclera is indeed higher than the inferior sclera. Therefore, when the lens is placed onto the eye it lands first at the point of greatest elevation and forces the lens in the opposite direction.
Why do scleral lenses decenter temporally? We have a slightly greater understanding as to why scleral lenses decenter temporally. We have observed that the nasal sclera is significantly higher than the temporal sclera and that this finding is greater in right eyes than in left eyes (Figure 2). This height differential is related to the presence of a “notch” on the nasal side of the sclera at a chord of approximately 13mm (Figure 3). The “notch” appears to be related to the fact that as the nasal sclera approaches the peripheral cornea, it does so with a relatively flat angle. The flat angle transitions (at a chord of 13mm) to that of the (steeper) angle. We believe that it is this nasal (higher) and temporal (lower) asymmetry that accounts for the temporal decentration of scleral lenses.
Figure 2. Composite OCT images of the height differential between the nasal and temporal quadrants, right eye and left eye.
Figure 3. As the sclera approaches the nasal limbus, it forms an acute angle or “notch.” It is at this spot that the scleral lens lands first, forcing the lens to decenter temporally.
When the inferior and temporal decentration forces are present, we see the “classic” dark fluorescein thinning pattern always in the superior nasal portion of the peripheral cornea. We currently have studies underway to see whether scleral lens decentration can be improved with toric haptic designs and asymmetric, quadrant-specific designs. CLS
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Contamac. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.