ESCRS - PP01.07 - To Determine The Optimal Region From Which To Derive Corneal Topographic Astigmatism (Cort) In Keratoconic Eyes.

To Determine The Optimal Region From Which To Derive Corneal Topographic Astigmatism (Cort) In Keratoconic Eyes.

Published 2022 - 40th Congress of the ESCRS

Reference: PP01.07 | Type: Free paper | DOI: 10.82333/ty5t-ry71

Authors: Noel Alpins* 1 , James Ong 2 , J Bradley Randleman 3 , George Stamatelatos 4

1Centre of Eye Research (CERA),The University of Melbourne,Melbourne,Australia, 2ASSORT,NewVision Clinics,Melbourne,Australia, 3Cleveland Clinic Foundation,Cole Eye Institute,Ohio,United States, 4Optometry,NewVision Clinics,Melbourne,Australia

Purpose

To evaluate whether it is possible to customize corneal astigmatism measurement for keratoconic eyes to better match the perceived visual image, which would enhance outcomes of toric implants or laser vision correction of associated astigmatism.

Setting

NewVision Clinics, Cheltenham, Australia; and Centre of Eye Research Australia (CERA), Melbourne University, Australia.

Methods

Potential measures of corneal astigmatism are derived from raw total corneal power data (179 eyes from 124 patients) derived from a corneal tomographer. The measures are derived from varying regions on the cornea, both in extent and center position. The measures of corneal astigmatism are evaluated according to their vectorial difference from the manifest refractive cylinder, which is the ocular residual astigmatism (ORA). The lower the variability of the ORA, the better the corneal astigmatism measure corresponds to the manifest refractive cylinder. The variability of the ORA is quantified in this paper by the root-mean-squared distance of the ORA from the summated vector mean in double angle space (ORArms).

Results

ORArms are calculated for all possible corneal astigmatism measures, which are derived from varying inner and outer annular extents, and centered on corneal vertex, thinnest point, front apex, and back apex, and pupil center, as well as various points between the corneal vertex and the corneal thinnest point. For each different annulus center, the annular extent that minimizes the ORArms is reported. Results are stratified by keratoconus severity.

Conclusions

For eyes with mild keratoconus, corneal astigmatism measures centered on corneal vertex tend to correspond more closely with manifest refractive cylinder than other measures centered on corneal vertex, corneal apex (front or back), or pupil center. For eyes with moderate keratoconus midpoint between the corneal vertex and thinnest point corresponds more closely with manifest refractive cylinder. All these custom measures outperform simulated keratometry. None of the corneal astigmatism measures correspond closely with manifest refractive cylinder for severe keratoconus.