Abstract
Purpose::
To introduce a 3D histomorphometric strategy for measuring laminar and peripapillary scleral (ppscleral) position and thickness and use it to describe laminar and ppscleral deformation following moderate IOP elevation in the young adult monkey eye.
Methods::
ONH and ppsclera from both eyes of three Early Glaucoma (EG) monkeys (one eye normal, one eye given laser-induced EG) were 3D reconstructed (2.5 x 2.5 x 3.0 µm voxel) as previously described (IOVS, 2004; 45:4378). Within 40 serial, radial, digital, sagittal section images (every 4.5°) of each reconstruction, Bruch’s membrane opening (BMO) and the anterior and posterior laminar and ppscleral surfaces were delineated by 5 delineators 2 of whom repeated both eyes of 1 monkey 2 additional times. A least-squares ellipse was fit to the 80 BMO points to establish a BMO-centroid and BMO zero reference plane (BMO-ZRP) and laminar and ppscleral position (relative to BMO-ZRP) and thickness were calculated and continuously mapped for each eye. For each monkey, a clinically-aligned, between-eye difference map for each parameter was generated by converting OS data to OD configuration, overlaying BMO-centroids and subtracting (EG - N) data at each point. Data was pooled by quadrant (8) and region (3) to test for statistically significant differences by ANOVA.
Results::
The PP sclera was anteriorly displaced (suggesting BMO was bowed posteriorly relative to it) but not substantially thickened or thinned and the lamina cribrosa was profoundly bowed posteriorly (greatest centrally, then mid-peripherally and least peripherally) and thickened in all 3 EG eyes and within the delineations of either 4 of 5 or 5 of 5 delineators. Where treatment effects were significant, delineator variability and reproducibility effects were either not significant or significant but small by ANOVA.
Conclusions::
A new method of clinically-oriented, 3D histomorphometry demonstrates posterior bowing of the ppsclera accompanied by central bowing and diffuse thickening (not thinning) of the lamina cribrosa at the onset of CSLT-detected ONH surface change in young adult monkeys exposed to moderate IOP elevations.
Keywords: optic disc • lamina cribrosa • astrocytes: optic nerve head