Relationship between central and mid-peripheral corneal refractive power changes after orthokeratology

Pauline Kang

Abstract

Purpose: To describe changes in corneal refractive power (CRP) across the horizontal and vertical corneal meridians after overnight orthokeratology (OK).

Methods: Nineteen myopic subjects (-1.54 ± 0.77D; 28 ± 7 years) were fitted with BE OK lenses (Capricornia Contact Lens, Australia). Corneal topography (E300; Medmont Pty Ltd, Australia) and central refraction (Shin-Nippon NVision-K 5001 autorefractor) were measured at baseline and after 14 nights of OK. Raw corneal topographic data were imported into a customized MATLAB program to determine CRP along the horizontal and vertical corneal meridians in 0.5mm steps from videokeratoscope (VK) center. Ratios of CRP change after OK at 3.5mm from the VK center relative to CRP change in the central cornea (+0.50 to -0.50mm from VK) were calculated.

Results: There was a significant reduction in CRP from baseline between 2.5mm temporal and 2mm in the nasal cornea (all p < 0.05) and an increase in CRP between 2.5 to 3.5mm in the nasal cornea and 3.5 to 4mm in the temporal cornea (all p < 0.05). Similarly along the vertical meridian, there was a significant reduction in CRP between 2.5mm inferior and 1.5mm in the superior cornea (all p < 0.05) and an increase in CRP at 2.5 to 3.5mm in the superior cornea (all p < 0.05). Increases in CRP from baseline in the inferior cornea failed to reach statistical significance (all p > 0.05). Relative increase in CRP at 3.5mm in the temporal and nasal cornea was 1.8 and 2.2 times the central CRP change. Along the vertical meridian, relative increase in CRP at 3.5mm in the superior cornea was 1.9 times the central CRP change.

Conclusions: OK lenses caused significant change in CRP along the horizontal and vertical meridians. Confirming previous reports, there was significant central corneal flattening and mid-peripheral corneal steepening. The mid-peripheral increase in CRP was approximately 1.8 to 2.2 times the amount of reduction in central CRP.

Details

Year: 2016

Program Number: 160116

Author Affiliation: University of New South Wales

Co-Authors: Vinod Maseedupally, Helen Swarbrick

Co-Author Affiliation: School of Optometry and Vision Science, UNSW, School of Optometry and Vision Science, UNSW

Room: 211AB