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John P Kelly, Avery H Weiss, Francine Baran; Horizontal optic nerve diameter correlates with RNFL and visual function in optic nerve hypoplasia.. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5071.
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© ARVO (1962-2015); The Authors (2016-present)
Previous work has shown that the optic nerve fiber count is correlated with the optic nerve cross-sectional area in controls. We investigated the relationship of horizontal optic nerve diameter with nerve fiber layer thickness (RNFL) and visual function in children with bilateral optic nerve hypoplasia.
Retrospective chart review of 28 children (age range 2.4 – 20 years; mean 9.4; s.d. 4.9). Optical coherence tomography (Heidelberg Spectralis SLO/OCT) was used to image the maximal horizontal optic nerve diameter, average RNFL thickness (global), and the fovea. The edges of Bruch’s membrane defined the optic nerve diameter. Nystagmus precluded analysis of optic nerve area and RNFL sectors. Visual acuity was measured by Allen optotypes or by Teller Acuity Cards. All visual acuities were converted into age-corrected log MAR values. Visual evoked potentials (VEPs) signal-to-noise ratios were averaged across reversing checks (163 and 84 arc minutes) and onset of horizontal gratings (0.5 and 2 c/deg).
Average RNFL ranged from 13 to 110 microns (14 right eyes, 11 left eyes) while the corresponding horizontal optic nerve diameter ranged from 390 to 1377 microns (mean 958; s.d. 306). Average RNFL thickness was correlated with horizontal optic nerve diameter (r2 = 0.60; p < 0.0001; n=25). The equation defining the relationship was: Average RNFL = 0.074 * disk diam - 18.8. RNFL findings were similar if only one eye was examined. Visual acuity from the better eye was also correlated with horizontal optic nerve diameter of the better eye (r2 = 0.49; p < 0.0001; n=27). The equation defining the relationship was: logMAR = -0.001 * disk diam + 1.6. VEP signal-to-noise ratios from the better eye were also correlated with horizontal optic nerve diameter of the better eye (r2 = 0.68; p < 0.001; n=9).
A strong relationship exists between horizontal optic nerve diameter with average RNFL and with visual function. Meta-analysis of published normative RNFL measurements at the lower range of normal was also consistent with a strong relationship between horizontal optic nerve diameters with average RNFL. The data suggest the nerve canal in optic nerve hypoplasia parallels the neurogenesis of the retinal ganglion cells. The data are not consistent with late stage apoptosis in which we would predict a normal size optic canal.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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