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Daniel Lemor, Paul J DeMarco, Jonathan D Nussdorf; Defining the structure-function horizontal meridian of the human macula in glaucoma. Invest. Ophthalmol. Vis. Sci. 2014;55(13):972.
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The conventional practice during Spectralis® SD-OCT posterior pole asymmetry analysis is to arbitrarily orient the horizontal meridian through the center of the optic nerve head. We tested the validity of this practice in glaucoma patients with split-fixation visual field loss. We hypothesized that the asymmetric visual field loss will be reflected in an SD-OCT macular hemifield difference and thus define an anatomic horizontal meridian.
We identified 17 stable glaucoma patients who manifest split fixation on HVF 24-S/S testing and performed Heidelberg Spectralis® SD-OCT posterior pole asymmetry analysis. The posterior pole asymmetry analysis image was oriented in a systematic manner with the macular thickness grid centered on the fovea, and its horizontal meridian intersecting the optic nerve head at five pre-selected equidistant locations along its longitudinal axis. The posterior pole asymmetry analysis for each optic nerve head intercept generated average superior and inferior retinal hemifield, and temporal quadrant, thickness ratios.
The subjects had a HVF 24-2 S/S average Mean Defect=8.58 (SD= 4.76) and an average Pattern Standard Deviation=10.12 (SD=2.68). A one-way repeated measures ANOVA demonstrates a significant difference between the horizontal intercept locations for the hemifield ratios [F(4, 16)=4.12, p<.005], as well as for the temporal quadrant ratios [F(4,16)=13.3, p <.0001]. Tukey post-hoc pairwise comparisons of the hemifield and quadrant thickness ratios demonstrate a significant difference between the superior and inferior poles (p<.01). The thickness ratios for both the hemifield and temporal quadrants increase as the horizontal meridian migrates towards the inferior pole of the optic nerve head and reaches a maximum at the inferior pole.
We demonstrate that in order to maximize the congruency of the macular structure-function relationship in patients with glaucoma, the horizontal meridian of the posterior pole asymmetry grid should intersect near the inferior pole of the optic nerve head. This is in contradistinction to the arbitrary practice of placing the horizontal median through the center of the optic nerve head.
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