The influence of centre thickness on miniscleral lens flexure

Abstract

Decreasing the centre thickness from 350 μm to 150 μm resulted in <0.25 D increase in lens flexure for a high Dk and low modulus material. Scleral toricity >200 μm was associated with more in-vivo lens flexure. When intentionally reducing scleral lens centre thickness to enhance oxygen transmissibility, customised back surface designs may be required to minimise in-vivo flexure in eyes with >200 μm scleral toricity at a 15 mm chord.

Scleral asymmetry as a potential predictor for scleral lens compression

“…For consistency with existing literature, scleral toricity was also calculated only using two perpendicular meridians . Vincent et al .…”

“…To assess the repeatability of this methodology the Coefficient of Variation (CoV) was calculated. Moreover, scleral toricity was calculated as the greatest difference in scleral sagittal height between two perpendicular meridians …”

“…Such an unequal weight bearing of the lens could lead to sectorial impingement and compression of the conjunctiva, especially in highly irregular scleras . Similarly, it was recently shown that scleral asymmetry is associated with scleral lens flexure …”

Optical coherence tomography and scleral contact lenses: clinical and research applications

“…Scleral toricity has been defined as the greatest difference in scleral sagittal height between two perpendicular meridians (for a specified chord) and increases with increasing distance from the limbus (about 100 μm at 15 mm chord to 400 μm at a 20 mm chord) . This further emphasises that for smaller diameter scleral lenses (with a proximal landing zone edge of 15 mm or less) a rotationally symmetric lens design may be acceptable; however, larger scleral lenses may require customised haptic designs to ensure lens stability with minimal decentration and lens flexure (particularly for thinner lenses and scleral toricity ≥ 200 μm) …”

“…Scleral sagittal depth data is particularly useful for initial scleral lens selection (after factoring in additional depth to allow for adequate corneal clearance and lens settling), since measures of corneal radius of curvature only partially correlate with the back optic zone radius of the optimal scleral lens . Similarly, corneal astigmatism is of little use in initial lens selection because there is a weak relationship between corneal and scleral astigmatism for both magnitude and orientation …”