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Patrick A. Sibony, Robert Honkanen, Mark Kupersmith, Matthew Strachovsky; Geometric Morphometric Analysis of the Peripapillary RPE- layer in Optic Nerve Sheath Meningiomas. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3930.
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© ARVO (1962-2015); The Authors (2016-present)
Geometric Morphometrics (GM) was used to compare the shape of the peripapillary retinal-pigment-epithelium Bruch's-membrane layer (ppRPE/BM) imaged on the SD-OCT raster of patients with presumed optic nerve sheath meningiomas (pONSM) to normal subjects.
We compared two groups: 30 normals to 8 patients (9 eyes) with pONSM. We digitized 20 equidistant semi-landmarks on OCT images of the RPE/BM layer , 2500 microns on each side of the neural canal opening (NCO). Data was analyzed using standard GM techniques including a Generalized Least Squares Procrustes Superimposition, Principal Component Analysis (PCA), thin-plate spline and permutation statistical analysis to evaluate differences in shape. We also analyzed other variables with respect to shape including tumor size-proximity to the globe, age, RNFL, disc height .
All pONSM patients were female (ages37-66); 7 had unilateral and 1 had bilateral optic nerve enlargement. Eight of the eyes had disc edema, 4 with shunt vessels, one had optic atrophy. The ppRPE/BM layer in normals is V-shape pointing away from the vitreous as has been previously shown; the ppRPE/BM layer in pONSM is indented causing an inverted-U shapeddeformation skewed nasally toward the vitreous. PCA, showed a significant difference between normals and pONSM (permutation, n=10,000, p=.0002). The size and proximity of the tumor to the globe correlates with the shape of peripapillary RPE (r=.88, p=.01). Correlation between shape variables and RNFL (r=.51), disc height (r=.67) and age (r=.67) were not statistically significant.
The shape of the ppRPE layer in pONSM is charactized by an inverted U shape or indentation that differs significantly from normals. It is indistinguishable from the shape we previously reported in papilledema and is not caused by disc edema. We proposed that the shape difference in papilledema is a consequence of the translaminar pressure gradient and the material properties of the peripapillary sclera (IOVS 2011.52:7987). The mechanism in pONSM is unknown. We suggest that it probably involves a change in the compliance and / or localized CSF hydrops of the distal optic nerve sheath.
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