Axial length and visual function in high myopia

Abstract

Purpose : To study the relationship between axial length and visual impairment in (high) myopia.

Methods : A total of 6,271 participants were included (RS-I: N = 662 (55+ years of age); RS-II: N = 1074 (55+ years); RS-III: N = 1148 (45+ years); ERF: N = 2353 (25+ years); and MYST: N = 671 high myopia (spherical equivalent (SE) ≤ -6 D) cases and 363 controls (SE ≥-1.5 & ≤ 1.5 D), 25+ years)). Participants received an extensive ophthalmic examination, including best-corrected visual acuity (VA), auto-refraction (SE), and measurements of axial length (AL) and corneal curvature (CC). Analyses were based on data from right eyes. Severe visual loss was defined according to the WHO criteria; visual impairment (VI) as VA <0.3 and VA ≥0.05; blindness as VA <0.05. The frequency of visual loss was calculated as a function of AL (in mm), stratified by age. Cumulative risk of severe visual loss per AL category (reference AL: 23-24 mm) was assessed using Kaplan-Meier product-limit analysis.

Results : Mean AL in RS-I, RS-II, RS-III and ERF combined was 23.38 mm (SD: 1.15); in MYST, mean AL was 27.36 mm (SD: 1.62) in cases and 23.49 mm (SD: 0.76) in controls. The correlation of AL between right and left eyes was high (population-based R² = 0.906; case control R² = 0.932) . The frequency of severe visual loss in high myopes increased with age (P trend <0.0001). The risk of severe visual loss was 1.8% in high myopes aged 40, irrespective of AL; by age 80, however, the cumulative risk was 7% for AL 23-24 mm, 30.5% for AL 26-28 mm, 44.7% for AL 28-30 mm, and 90.5% for AL ≥30 mm. Mean age at onset was strongly related with AL, and varied from 45 years in AL >28 mm to 58 years in AL 26-28 mm.

Conclusions : The risk of severe visual loss in high myopes highly correlates with AL, and reaches extremely high figures in AL ≥30 mm. In high myopes, each incremental increase in AL worsens the long-term visual prognosis.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.