The unique fit of a scleral lens raises concern that the landing zone may cause compression of the conjunctival tissue, which can potentially lead to resistance of aqueous humor outflow and increased intraocular pressure (IOP).1 However, researchers from the University of Houston College of Optometry recently found that scleral lenses have a minimal effect on IOP homeostasis in normal eyes during lens wear; they also have an insignificant impact on optic nerve head morphology in healthy adult eyes.
The big take-away from the study isn’t necessarily the actual data, which shows minimal changes with scleral lens wear in normal eyes, but rather, the evaluation of the methodologies themselves, says researcher Maria K. Walker, OD, MS.
“As we showed, not all instruments can be considered reliable to evaluate IOP during scleral lens wear, and really none of the instruments currently being used have been properly calibrated for this purpose,” she says. “By using the OCT as an indirect assessment of IOP in this study, we have opened a new area of possible research to assess the potential impact of an IOP increase during lens wear, and have introduced practitioners to a tool that may be useful when evaluating the impact of scleral lenses on ocular health in their practice,” she said.
The investigation enrolled 26 healthy adults who wore scleral lenses on one randomly selected eye for six hours, while the fellow eye served as the control. The researchers measured global minimum rim width with OCT and IOP using a tonometer at baseline, two and six hours after scleral lens application, and again after lens removal. The study considered changes in central corneal thickness and anterior chamber and fluid reservoir depths.
The investigators observed minimum rim width thinning in both the test (-8μm) and control (-6μm) eyes after six hours of scleral lens wear, although the magnitude of thinning was not significantly greater in the lens-wearing eyes. Additionally, mean IOP, when measured with the Icare tonometer, significantly increased +2mm Hg in the test eyes, with no change in the control eyes.
However, when the researchers used the Diaton tonometer, they reported mean IOP changes of +0.3mm Hg in the test eyes and +0.4mm Hg in the control eyes. Diaton tonometry showed poor within-subject variation and poor correlation with Icare, the researchers noted. No clinically significant changes were observed in central corneal thickness or anterior chamber depth, the study noted.
Walker M, Pardon LP, Redfern R, Patel N. IOP and optic nerve head morphology during scleral lens wear. Optom Vis Sci. 2020;97(9):661-68.