Association between optic disc parameters and refractive error

Abstract

Purpose : Myopia has previously been associated with changes in optic disc morphology and size, which itself interacts with ocular elongation. Here, we study the relationship of spherical equivalent (SE) of refractive error and optic disc area (corrected for ocular magnification vs. uncorrected), disc ovality, and disc rotation angle.

Methods : From the population-based LIFE Adult study, a subgroup with extended eye examination was selected with reliable autorefractive SE (iProfiler Plus, Carl Zeiss Vision, Aalen, Germany) and peripapillary SLO fundus images (Spectralis SD-OCT, Heidelberg Engineering, Heidelberg, Germany). On fundus images, optic disc borders were marked on 16 equidistant radial locations (see Fig.1). Disc area, i.e. the area enclosed by the tracing, was additionally corrected for magnification by a method based on defocusing (Garway-Heath et al., Br. J. Ophthalmol. 82(6), 643-649, 1998). An optimal ellipse was fitted to each disc with the center, long and short axis, and rotation angle as parameters. Disc ovality was calculated as the ratio between the long and short axis. To study the relationship between angle, ovality, SE, and disc area, full Bayesian model comparisons of all parameter combinations were calculated with Bayes factor compared to the null model as the selection criterion.

Results : 557 eyes of 285 subjects were selected (sex and age-stratified; age range: 25 to 85 years). Uncorrected disc area was positively correlated with SE (r=0.24, p<0.001). No significant correlation remained after correction for magnification (r=-0.04, p=0.32). The Bayesian model comparison revealed no relationships between rotation angle and any other parameters (Fig.2A). Larger ovality was associated with more negative SE (r=-0.14, p=0.001) and smaller corrected disc area (r=-0.20, p<0.001). The Bayesian model comparison revealed a combination between SE and disc area to be the best model for ovality (Fig.2B).

Conclusions : The positive association between disc area and SE disappears after correction for ocular magnification, which indicates that myopic optic discs only seem to be smaller due to an increased distance between the lens and optic disc. Disc ovality, which can be used as a two-dimensional estimate of disc tilt and has previously been discussed as a risk factor for optic neuropathies, is related to myopia, smaller corrected disc area, and strongest to their combination.

This abstract was presented at the 2019 ARVO Imaging in the Eye Conference, held in Vancouver, Canada, April 26-27, 2019.

 

Fig.1

 

Fig.2