Assessing scleral toricity induced lens flexure and contact disparity using anterior segment optical coherence tomography

Purpose

To determine the influence of scleral toricity on the extent of lens contact and in-vivo flexure using anterior segment optical coherence tomography (AS-OCT), and to identify variables related to lens decentration.

Methods

Scleral toricity at a chord of 15 mm was measured using Pentacam corneoscleral profilometry (CSP) from 10 healthy young participants (22 ± 2 years) with normal corneas. Participants were fitted with the same 16.0 mm rotationally symmetric scleral lens design (hexafocon A material). AS-OCT was used in conjunction with ImageJ analysis to document the disparity of lens contact at the 15 mm chord primary toric meridians and to assess lens flexure. Additionally, central fluid reservoir (FR) depth and lens decentration were measured.

Results

A significant correlation was found between scleral toricity (mean 155 ± 95 μm) and both the magnitude of lens flexure, and the disparity in lens contact between the scleral primary toric meridians at the 15 mm chord diameter (r = 0.83, p = 0.003 and r_s = 0.83, p = 0.005 respectively). Mean lens decentration values were 0.30 ± 0.18 mm inferior-temporal net decentration, 0.26 ± 0.16 mm inferior decentration and 0.13 ± 0.1 mm temporal decentration. This was significantly associated with central FR depth (r_s = 0.91, p = 0.0005 and r_s = 0.73, p = 0.02 and r_s = 0.71, p = 0.03 respectively). No significant correlation was found between lens decentration and scleral toricity (p > 0.05).

Conclusion

Scleral toricity was significantly associated with AS-OCT measured lens flexure and contact disparity at primary toric landing locations defined by profilometry. Reducing central FR depth appears to be a good strategy for improved lens centration. Whilst equalising lens contact along toric meridians is beneficial for addressing lens flexure, the influence of this on centration is less clear.