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Soumya Mukherjee, Phillip Andrew Bedggood, Bao N Nguyen, Andrew Turpin, Allison M McKendrick; Population variability of temporal raphe in myopia. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2140.
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© ARVO (1962-2015); The Authors (2016-present)
Recent advances in OCT imaging technology now permit ready visualization of the temporal nerve fiber raphe. Such imaging has revealed that the orientation of the raphe can vary markedly between individuals, challenging the utility of commonly used glaucoma indices which assume a horizontal orientation. Retinal stretch in myopic eyes could further affect raphe orientation, and this is important since myopic eyes are at greater risk of developing glaucoma. Here we sought to characterize the variability in temporal raphe position in eyes of varying axial length.
80 participants were recruited, with mean age 25 years and spherical equivalent ranging from 0D to -13D. Two partially overlapping high density scans were acquired with the Heidelberg Spectralis OCT (vertical B-scans, 11 µm separation, 10x15° area). Following automatic segmentation, en face intensity images were generated at the nerve fiber layer and montaged to cover an area from the fovea to ≈15° temporal. The axis of symmetry was manually graded at 4 locations across the image to determine raphe orientation. The angle between fovea and disc was automatically determined by the Spectralis assessment of Bruch’s membrane opening, with manual adjustment and confirmation by the operator. Axial length and vitreous chamber depth were measured by A-scan ultrasonography. The relationship between measured parameters was assessed using Spearman rank correlations with statistical significance defined as p<0.05.
Vitreous chamber depth was not correlated with the angle between the raphe/fovea/horizontal (rho=0.006, P=0.96) nor the raphe/fovea/disc (rho=0.15, p=0.18); it was weakly correlated with the angle between the disc/fovea/horizontal (rho=0.22, p=0.04), such that the disc tended to insert less superiorly to the fovea in longer eyes. There was a medium correlation between the raphe/fovea/horizontal angle and the disc/fovea/horizontal angle (rho=0.43, p<0.001), such that more superior insertion of the disc tended to be partially compensated by less superior orientation of the raphe.
The results do not support the hypothesis that myopic eye stretch causes any systematic deviation in the temporal nerve fiber raphe. This simplifies the need to consider the refractive status of the eye when determining the correct axis of symmetry for calculation of glaucoma indices in OCT or visual field testing.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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