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Jui-Kai Wang, Patrick A Sibony, Randy H Kardon, Mark J Kupersmith, Mona K Garvin, IIHTT OCT Sub-Study Committee, NORDIC Idiopathic Intracranial Hypertension Study Group; Change in the Deflection of the Neural Canal Opening Over Time with Acetazolamide Treatment in Idiopathic Intracranial Hypertension. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2233.
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© ARVO (1962-2015); The Authors (2016-present)
In papilledema, Bruch’s membrane (BM) bordering the neural canal opening is often deflected inward toward the vitreous in contrast to normal eyes (Sibony et al., IOVS, 2011, 2014). We prospectively compared OCT-derived changes in the BM shape with acetazolamide (ACZ) plus diet compared to placebo plus diet in the Idiopathic Intracranial Hypertension Treatment Trial (IIHTT). A novel semi-automated method for quantifying the BM shape was developed for this purpose.
For each of the 126 subjects enrolled in the OCT substudy of the IIHTT (OCT Sub-Study Committee, IOVS, 2014), the central slice from the Cirrus OCT high-definition (HD) 5-line raster scan at baseline, 3 months, and 6 months (as available) was used to perform the statistical shape analysis. After manually marking the two Bruch’s membrane opening points in each slice, 9 landmark points were automatically placed along Bruch’s membrane on each side of the neural canal border, extending out radially for 2500 microns (Fig. 1). Principal component analysis was used to create a shape model using the landmark points at baseline. The second principal component coefficient, reflecting the angle and direction of the neural canal border, was then computed at each time point for study eyes in the two treatment groups.
In this analysis, 73 out of 126 subjects in IIHTT OCT substudy had 5-line raster data available at all time points for the study eye. In the ACZ plus diet group (n=39), the neural canal shape measure became more positive (deflecting away from the vitreous cavity, Fig. 2 left) over time and was significantly greater (p < 0.01) than in the placebo plus diet group (n=34), as shown in Fig. 2. The mean neural canal shape measure changes from baseline to 3 months were 0.64 ± 1.10 in the ACZ group vs. -0.04 ± 0.93 in the placebo group; from baseline to 6 months, the changes were 0.87 ± 1.26 in the ACZ group vs. 0.03 ± 0.83 in the placebo group.
Displacement of the neural canal border at the optic nerve head reflects the translaminar pressure differential between the retrolaminar and intraocular fluid compartments and appears to be a biomarker of successful treatment of raised intracranial pressure.
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