Contact Lens Case Reports
Etiology of Scleral Lens-Induced Conjunctival Prolapse
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
In assessing corneal topography, two primary maps are used—the axial display map and the elevation display map. The axial display shows the dioptric power of the corneal surface at any given point. The elevation map shows the height and therefore the shape of the eye at any given point.
Figure 1 shows an eye that has advanced keratoconus, successfully wearing a scleral lens for two years, with apparent fluorescein “thinning” from 12 o’clock to 3 o’clock. The axial map clearly shows dioptric flattening in this area and dioptric steepening exactly 180 degrees away (Figure 2). The elevation display map more closely corresponds with the actual fluorescein pattern, with the lens being in closest apposition to the cornea where it is highest (the red) from 12 o’clock to 3 o’clock.
Figure 1. The fluorescein pattern of the scleral lens on the eye described in Figure 2.
Figure 2. The axial and elevation display maps of a patient who has advanced keratoconus with a subsequent scleral lens-induced, conjunctival prolapse at 8 o’clock.
Corneal Elevation and Conjunctival Prolapse
This relates to conjunctival prolapse. If the lens is closest to the cornea at the point of greatest elevation (red), clearly the lens will be furthest away from the corneal surface where it is lowest (blue).
All scleral lenses resting solely on the sclera/bulbar conjunctiva position slightly inferior on the eye due to two factors: the shape of the superior cornea, which is often more elevated in pathologic eyes, and more importantly, the gravitational forces acting on the thicker, cornea/limbus clearance lens. The inferior lens position and the inferior corneal depression create a significant void that can run from 3 o’clock to 9 o’clock. Negative pressure forces the conjunctiva into the area of greatest clearance. In this patient, prolapse is noted at 8 o’clock.
Figure 3 shows advanced pellucid marginal degeneration where conjunctival prolapse has occurred at both 4 o’clock and 8 o’clock. The axial display map shows the greatest dioptric curvature at 4 o’clock and 8 o’clock, but the elevation display map shows that the corneal surface is highest from 10 o’clock to 2 o’clock and lowest at 4 o’clock and 8 o’clock. The conjunctival prolapse occurred exactly where the lens clearance was greatest, i.e. 4 o’clock and 8 o’clock.
Figure 3. The axial and elevation display maps of a patient who has advanced pellucid marginal degeneration with a subsequent scleral lens-induced, conjunctival prolapse at 4 o’clock and 8 o’clock.
In certain patients, the conjunctiva will be drawn into any areas with significant lens clearance. This environment is most often present inferiorly due to either the slightly low positioning of scleral lenses or the lower corneal height (inferior depression) common in pathologic eyes. CLS
Patrick Caroline is an associate professor of optometry at Pacific University. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.