Symmetric scleral lenses reduce postlens tear layer asymmetries
The use of symmetric scleral lenses led to decreased postlens tear layer asymmetries instantaneously following insertion in healthy eyes, according to findings published in Eye & Contact Lens.
Stephen J. Vincent, PhD, and colleagues sought to quantify regional variations in postlens tear layer thickness (PLTL) during scleral lens wear.
“A fundamental aspect of any scleral lens fitting is the assessment of the postlens tear layer thickness since insufficient clearance may lead to adverse physiological outcomes such as corneal bearing and staining or lens adhesion, while excessive clearance may result in lens decentration and reduced visual performance or impede the transmission of atmospheric oxygen to the cornea,” Vincent, of the contact lens and visual optic laboratory at the Queensland University of Technology in Australia, and colleagues wrote.
The researchers analyzed data of 15 healthy adults (mean age, 22 years) with normal corneas who were fitted with a 16.5 mm diameter rotationally symmetric scleral lens in one eye. They measured PLTL across the central 5 mm ranging from 0 to 480 minutes after lens insertion using a 12 radial line scan OCT imaging protocol.
Vincent and colleagues identified tilted optic zones immediately after insertion, with the greatest PLTL asymmetry between nasal and temporal regions (156±22 µm more clearance temporally) and superior nasal and inferotemporal regions (124±12 µm more clearance inferotemporally). Lens settling magnitude located in each region was associated with the initial PLTL (r = 0.59-0.77; P .02).
The superior nasal PLTL furthest from the pupil center stabilized after 90 minutes compared with other regions that stabilized in 4 hours, the researchers wrote. PLTL decreased by 29%, while PLTL asymmetries between opposing regions decreased by 30% after 8 hours of lens wear on average.
“To achieve a uniform PLTL during scleral lens wear, a customized haptic is probably required for the majority of eyes (eg, toric multimerdian-specific, or impression-based design) to ensure scleral alignment and to minimize lens decoration,” the researchers wrote. – by Earl Holland Jr.