Influence of ocular monochromatic aberrations in the development and/or progression of myopia

Abstract

Aim: To determine an association if any, between ‘on’ and ‘off-axis’ ocular aberrations and a myopic change in refractive error using the data obtained longitudinally.

Methods: On and off-axis aberrations of cyclopleged eyes (5 mm pupil diameter) of 646 children were measured during 2004-2005 (age, 12.7 ± 0.4 years) and 5 years later in 2009-2010 (age, 17.1 ± 0.5 years). Change in spherical equivalent (M) from baseline to follow-up visit was determined and eyes characterised as ‘myopic change’ (≥ 0.50D), ‘no change’ (from 0.49D to +0.49D) and ‘hyperopic change’ (≥ +0.50D). Baseline data of eyes with ‘myopic change’ and ‘no change’ were compared to determine if any baseline characteristics predicted a future myopic change. Also, the change in ‘on’ and ‘off-axis’ aberrations with time were correlated with change in M, using general linear model. Significance level was set at p<0.05. Additionally, data from 675 adolescents (16.0 ± 0.7 yrs) were analysed to determine the contribution of corneal and internal aberrations to total aberrations.

Results: At baseline 15% of eyes were myopic, 27% emmetropic and 58% hyperopic. 26%, 70% and 4% of all eyes showed myopic change, no change and hyperopic change respectively. None of the baseline ‘on’ and ‘off-axis’ aberrations and retinal image quality measures was associated with a ‘myopic change’ in M. With time, eyes with ‘myopic change’ showed a decrease in on-axis spherical aberration [C(4,0)] and a hyperopic shift in relative peripheral refractive error (RPRE), whereas eyes with ‘no change’ had an increase in on-axis C(4,0) and no difference in RPRE. Eyes with Type III and Type IV skiagram at baseline showed the most (61%) and the least (17%) myopic change respectively. Across refractive error (RE) groups, corneal aberrations were not different and were compensated for with internal aberrations resulting in less net total aberrations. However, internal aberrations differed between RE groups with less negative internal C(4,0) observed in hyperopes (-0.038 ± 0.05 μm) compared to emmetropes (-0.081 ± 0.04 μm) and myopes (-0.090 ± 0.04 μm).

Conclusion: None of the baseline ‘on and ‘off-axis’ aberrations predicted a future myopic change in refractive error. However, the eyes with Type III skiagram (asymmetry in astigmatism in nasal and temporal quadrants) showed the most myopic change in refraction. It may be possible this asymmetry in astigmatism (characteristic feature of Type III skiagram) observed at temporal retina could play a role in myopic change and needs to be explored further. The hyperopic shift in RPRE with time for eyes with ‘myopic change’ is possibly a consequence of ocular growth. The variation in internal C(4,0) between refractive error groups and differences in C(4,0) with time in eyes with ‘myopic change’ versus ‘no change’ directs focus to the crystalline lens. There may be variations in crystalline lens characteristics such as asphericity, curvature, refractive index between refractive error groups and with ocular growth and needs further investigation.