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Robert Honkanen, Patrick Sibony, Crystal Kania, Yuchen Liu, Pranav Patel, Kevin Kaplowitz, F. James Rohlf; Geometric Morphometric Analysis of the Peripapillary RPE / Bruchs Membrane complex in Glaucomatous and Normal Eyes. Invest. Ophthalmol. Vis. Sci. 2013;54(15):82.
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© ARVO (1962-2015); The Authors (2016-present)
Geometric Morphometrics (GM) was used to evaluate shape variation (SV) of the peripapillary RPE and Bruch’s membrane (ppRPE/BM) complex in a well defined glaucoma (Glc) group and normals (Nl).
We compared SD-OCT images of 96 glaucoma (Glc) Glc and 29 normal (Nl) eyes. Glc diagnosis required both a glaucomatous visual field (VF) defect and a corresponding optic nerve abnormality. (IOP not used as a criteria) Data was analyzed using standard GM techniques including a generalized least squares Procrustes superimposition, thin-plate spline, permutation statistical analysis, principal component analysis (PCA), and partial least squares analysis (PLS). Glc status, age, central corneal thickness (CCT), refractive error (RE), peak IOP (IOPmax), IOP at time of OCT scan (IOPscan), visual field mean defect (MD) and pattern standard deviation (PSD) were analyzed as covariables.
Nl and Glc eyes have a slight V shape that steepens as the neural canal opening (NCO) is approached. Glc status and RE (increasing myopia) show a statistically significant posterior displacement of the ppRPE/BM complex and a widening of the NCO (p=0.1%, 1000 permutations). Glc and RE account for 6.3%, and 5.9% of the observed SV. PCA showed 2 main effects. PC 1 (anterior/posterior movement of the ppRPE/BM) and PC 2 (variation in NCO width) account for 44.1% and 36.1% of the SV respectively. There is large overlap in SV between Nl and Glc eyes. Regression and PLS analysis showed no statistically significant dependence of SV on age, CCT, IOPmax, or IOPscan. In the Glc eyes, SV was not correlated with type of Glc, MD or PSD.
Evalution of ppRPE/BM SV using GM can detect abnormal eyes in papilledema and optic nerve sheath meningioma. Glc and Nl eyes also show a small, statistically significant difference in ppRPE/BM complex shape. However, this technique is of limited value for determining Glc status because of large overlap in SV between Nl and Glc eyes. The lack of correlation between SV and cofactors associated with Glc (IOP/CCT/MD/PSD) also suggests this technique is of limited value for this condition. Optimization of the the technique, perhaps with use of a vertical scan line through the ON may improve the ability to differentiate normal from glaucomatous eyes.
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