High Myopia Increases IOP-dependent Lamina Cribrosa Beam and Peripapillary Scleral Strains in Tree Shrews

Abstract

Purpose : To investigate the effect of high myopia on IOP-dependent 3D micro-scale strains in the juvenile tree shrew optic nerve head (ONH) using two-photon fluorescence microscopy.

Methods : Juvenile tree shrews were randomly assigned to 2 groups: normal visual experience (n=4) and -10D lens-induced monocular high myopia (n=4). Eyes were enucleated, stained for 1 hour with CNA35-tdTomato, mounted at the equator using a custom pressurization chamber, preconditioned with 8 cycles from 5 to 45 mmHg, and imaged at 5, 15, 30, and 45 mmHg IOP using a two-photon microscope (Nikon A1 MP). The microscope was equipped with a fast resonant scanner to minimize artifacts due to creep and a specialized objective with 8.2mm working distance to allow imaging from inside the eye. 3D displacement fields were obtained using digital volume correlation. Maximum principal strains of the peripapillary sclera (PPS) and lamina cribrosa beams (LCB) were calculated and compared between groups using generalized estimating equation (GEE).

Results : All lens treated eyes developed high myopia (-11.06 ± 0.63 D). Across all sectors, LCB and PPS strains increased significantly with IOP (p < 0.001) and were significantly higher in the high myopic eyes compared to control and normal eyes (p < 0.001). No obvious asymmetric increase in sectorial strain was identified (p > 0.05).

Conclusions : High myopia leads to an overall increase in LCB and PPS strains in the tree shrew ONH. The high micro-scale strains may increase the risk for pathologic ONH remodeling and glaucoma in the high myopic eye.

This is a 2020 ARVO Annual Meeting abstract.

 

(a) Boxplot of maximum principal strain distributions across animal treatment groups generated using the GEE model. Strains in normal animal tissue were not significantly different from those in control tissue (p = 0.067), while strains in treated tissue were significantly different (p < 0.001). (b) Boxplot of maximum principal strain distributions across the measured regions of the tree shrew ONH from the GEE model. Laminar beams displayed a higher average and larger spread of strain when compared to peripapillary scleral strains, though not significantly different (p > 0.05). *** significant difference (p < 0.001)

 

Maximum intensity projection images of normal (a), control (b), and treated (c) tree shrew lamina cribrosas with median intensity in Z maximum normal strain maps measured at 30 mmHg overlayed.