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These authors suggest that new strategies should be developed for measuring IOP and corneal biomechanics during lens wear. Photo: Christine Sindt, OD. Click image to enlarge. |
It’s been shown that scleral tissue compression and changes in fluid reservoir occur during scleral lens wear. To understand these changes, Spanish researchers sought to evaluate the short-term influence of scleral lenses of different diameters on intraocular pressure (IOP) and corneal biomechanics. A secondary objective was to investigate the relationship between fluid reservoir thickness and these parameters. They found only small changes in corneal biomechanical parameters, and IOP values induced by short-term wearing of scleral lenses did not have a significant clinical impact. The findings were reported in Eye & Contact Lens.
A total of 30 participants were randomly fitted with lenses of diameter 15.80mm (called the L1group) or 16.80mm (L2) on the right eye and worn for two hours. IOP and corneal biomechanical parameters were measured with the Corvis ST before and after lens removal. Fluid reservoir thickness at zero and two hours of wear was measured using anterior segment OCT.
Biomechanical parameters decreased after removal of each lens type. The biomechanical parameters first applanation time, stiffness at first applanation decreased after L1 removal, whereas a decrease in highest concavity time and an increase in highest concavity radius were observed after L2 removal. A significant negative (though moderate) correlation was found between highest concavity deformation amplitude and fluid reservoir thickness with L1 lenses.
These results suggest that the cornea becomes weaker with the wear of this smaller lens of the two studied. “The use of scleral lenses induces mild corneal edema, which could alter the structure and organization of the cornea and affect its biomechanics,” the researchers explained in their paper. “This edema mainly originates from the corneal epithelium, which is easily deformable and is the main reference surface for measuring corneal biomechanical parameters. Therefore, small changes in this layer are likely to increase corneal weakness.”
After wearing the larger lenses (L2), the corneal biomechanical parameters affected were different but similar to those found in the L1 group. “This lack of agreement,” the researchers wrote, “might suggest that their effect on corneal biomechanics is minimal.”
The Corvis ST provides two IOP values, one that does not take corneal biomechanics into account (IOPnct) and one that corrects the IOP value based on corneal biomechanical parameters (bIOP). The latter value provides a more true assessment of the effect of scleral lenses diameter on IOP, the paper explains.
“Beyond the effect on corneal biomechanics, supporting a smaller diameter scleral lens near the limbus may contribute to increased IOP by compressing structures involved in aqueous humor outflow,” the authors explained. “However, in the current study, a decrease in IOPnct was observed (-0.74mm Hg with L1 and -0.19mm Hg with L2), although it was only significant after L1 wear.” They go on to explain that this is related to the fact that IOPnct is derived from first applanation length, which was found to be more affected after L1 wear.
The decrease in biomechanically corrected IOP was significant after wearing both scleral lenses (-1.04mm Hg with L1 and -0.80mm Hg with L2), although the scleral lenses diameter was not a determining factor for the observed changes, the authors explained. These results showed that scleral lenses did not cause an increase in IOP after wear and that compression in the different scleral zones according to diameter did not affect IOP.
A possible limitation of the study is that IOP measurements were not performed during scleral lens wear, the authors acknowledged. “Removing the scleral lenses may reduce some of the lens compression on the sclera, which is observable even several hours after wearing,” they wrote. “This would alleviate the possible obstruction of aqueous humor outflow while reducing IOP to levels similar to those before scleral lenses wear.”
The authors concluded that there is a need to develop new strategies for measuring IOP and corneal biomechanics during lens wear that can confirm whether the changes observed after removal are real and not partially derived from this process.
Click here for the journal source.
Queiruga-Pineiro J, Martinez-Alberquilla I, Rodriguez-Una I, et al. Assessment of corneal biomechanics and intraocular pressure with scleral lenses of different diameters. Eye Cont Lens. February 4, 2025. [Epub ahead of print].
