Symmetric scleral lenses reduce postlens tear layer asymmetries
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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.
Perspective
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Pam Satjawatcharaphong, OD, FAAO, FSLS
It is well understood that a properly fit scleral lens fully vaults the cornea. However, the recommended vault amount has evolved along with our understanding of scleral design and impact on ocular physiology. Questions of whether the thickness of the PLTL impacts oxygen transmission, optical quality, debris accumulation and comfort have been posed, so better understanding of PLTL behavior may help provide answers.
Many patients wearing sclerals have irregular corneal topography, with highest elevation at a noncentral point, so the wide 5-mm zone examined in this study may be useful for evaluating this population. The study showed the PLTL decreased exponentially before quickly plateauing 90 to 120 minutes after lens application, and it was determined that lens settling is best evaluated as a percent reduction of the initial vault.
This information may assist in diagnostic fitting and predicting how a lens may behave over time based off initial PLTL thickness and allowed settling time. If unable to allow a lens to settle for at least 90 minutes, this study suggests estimating approximately 30% reduction in PLTL. Additionally, because PLTL is asymmetric in most eyes, to achieve more uniform PLTL practitioners may choose diagnostic lenses with customized asymmetric haptics.
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