Ocular and Non–Ocular Influences on Optic Disc, Cup and Neuroretinal Rim Areas – The Australian Twin Eye Study

Abstract

Purpose: : To identify ocular and non–ocular correlations and influences on the normal variance of the optic disc, cup and rim area in twins recruited as part of the Australian Twin Eye Study.

Methods: : A total of 964 twins were recruited as part of the Australian Twin Eye Study. Biometric data and data from ophthalmic evaluation, including stereo optic disc photographs (Nidek 3DX stereo–camera) were analysed. Statistical testing and linear regression analyses determined the significance and strength of the independent variables on the variance of the optic disc, cup and rim area.

Results: : Data from 964 twins (1928 eyes) was used. The optic disc area was most strongly correlated to the cup and rim area. Age correlated with cup and rim area, accounting for 11% of the variance in cup and 17% of the variance in rim area (increasing age linked to larger cups and smaller rims). Birthweight accounted for 5% of the variance of the disc area and 6% of the rim area (heavier babies having on average larger discs and rims). Body weight was responsible for 16% of the variance of rim area (heavier subjects having larger rim areas). Intraocular pressure accounted for 11% of the variance in rim area (with higher intraocular pressures linked to smaller rim areas – independent of age). Central corneal thickness measurement accounted for 5% of the variance of the cup (thicker corneas on average having smaller cups). Corneal curvature was strongly correlated to disc and cup area. Corneal curvature explained 10% of the variance of the disc area and 14% of the cup area (with flatter corneas being linked to larger disc and cup areas).

Conclusions: : Many ocular and non–ocular parameters are associated with the variance of the normal optic disc, cup and rim size. Knowledge of these associations adds to our understanding of the genetic and environmental influences which exist in determining the optic disc, cup and rim traits. These same influences may play a role as independent risk factors or modifiers in diseases of the optic disc, such as glaucoma.

Keywords: optic disc • imaging/image analysis: non-clinical