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Collagen Crosslinking, Keratoconus, Scleral Shape
Collagen crosslinking (CXL) for keratoconus is known to decrease, halt or even partially reverse progression of keratoconus. We report on a case where a substantial effect on scleral shape was also demonstrated. This keratoconus patient, who was successfully wearing a scleral lens, underwent collagen crosslinking OS. Three months post crosslinking, the patient was unable to wear his previous scleral lens due to lens discomfort. Elevation mapping pre and post crosslinking, with a new corneal-scleral topography system, showed a decrease in size and change in shape of the cone, as well as a substantial change in the scleral elevation pattern at a 16mm chord diameter. The change in the scleral elevation pattern was best observed on scleral shape plots which graph the sagittal height (SAG) value on the Y-axis vs. meridian on the X-axis. The pre-crosslinking plot resembled a standard toric curve although the depression inferiorly at 330° was deeper than that superiorly by 250µ. The post-crosslinking plot changed substantially with the steep axis superiorly being markedly attenuated: the SAG superiorly (102°) decreased post-crosslinking by >300µ. Attempts to virtually fit the eye surface post-crosslinking with a standard posterior toric haptic demonstrated a good fit superiorly and a poor fit inferiorly. The post-crosslinking scleral toricity plot was used to obtain quantitative information to manufacture a custom design conforming to this specific eye. The resulting lens was comfortable, well centered and resulted in a BCVA of 20/30.
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