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The Relationship between Progression in Axial Length/Corneal Radius of Curvature Ratio and Spherical Equivalent Refractive Error in Myopia

Jong, Monica, PhD1,2*; Sankaridurg, Padmaja, PhD1,2; Naduvilath, Thomas John, PhD1; Li, Wayne, BAppl(Math)3; He, Mingguang, MD4,5

doi: 10.1097/OPX.0000000000001281

SIGNIFICANCE This study demonstrates that mean axial length/corneal radius of curvature ratio (AL/CR) can be used to detect low and high myopia but cannot clinically monitor myopia progression because the relationship between AL/CR and progression in myopia is different between low and high myopia.

PURPOSE The purpose of this study was to investigate the relationship of AL/CR with magnitude and progression of myopia.

METHODS Retrospective analysis was conducted comparing the right eyes of those with high myopia (n = 308; age, 7 to 16 years; myopia sphere, −6.00 diopters or worse) with those with low myopia (n = 732; age, 7 to 16 years; myopia sphere, between −0.50 and −3.50 diopters; cylinder, ≤1.00 diopters). Baseline axial length, corneal radii of curvature, and cycloplegic objective refraction were analyzed. Myopia progression in the low-myopia group at 6- and 12-month follow-up was measured, and the differences in slopes of AL/CR were compared for slow (<0.75 diopters) and fast progressing (≥0.75 diopters).

RESULTS Mean AL/CR values were significantly different (P < .001) between high myopia (3.46 ± 0.10) and low myopia (3.16 ± 0.07). In high and low myopia, slopes of axial length versus corneal curvature radius were not significantly different (P > .05), and slopes of AL/CR versus spherical equivalent were significantly different after adjusting for spherical equivalent and age (P < .05). Slopes of AL/CR progression and spherical equivalent progression were significantly different in low myopia between fast and slow progressing (P < .001), but the relationship between progression in AL/CR and progression in spherical equivalent was not strong.

CONCLUSIONS The AL/CR can be used to classify different grades of myopia, but it is not useful in determining the magnitude of myopia or monitoring progression because AL/CR is not linearly related to spherical equivalent and because progression in AL/CR is not strongly related to spherical equivalent progression.

1Brien Holden Vision Institute, Sydney, New South Wales, Australia

2School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia

3Brien Holden Vision Institute, Guangzhou, China

4Zhongshan Ophthalmic Centre, Sun Yat Sen University, Guangzhou, China

5Centre for Eye Research Australia, University of Melbourne, Melbourne, Victoria, Australia *

Submitted: November 13, 2017

Accepted: June 3, 2018

Funding/Support: Brien Holden Vision Institute (to MJ).

Conflict of Interest Disclosure: The authors have no proprietary interests or conflicts of interest.

Study Registration Information: ChiCTR-TRC-00000029 - Myovision1 and ChiCTR-TRC-13003396 - concentric; GZ, China.

Author Contributions: Conceptualization: MJ, PS; Data Curation: MJ, TJN, WL, MH; Formal Analysis: MJ, TJN, WL; Funding Acquisition: MH; Investigation: MJ, PS, MH; Methodology: MJ, PS, TJN; Project Administration: MJ, MH; Software: TJN; Supervision: PS; Validation: MJ, WL; Writing – Original Draft: MJ; Writing – Review & Editing: MJ, PS, TJN, MH.

© 2018 American Academy of Optometry