Quantitative measures of alteration in the astrocytic lamina of mouse optic nerve head with experimental glaucoma

Abstract

Purpose : To characterize the structure of the astrocytic lamina in the mouse optic nerve head and analyze its detailed changes after chronic intraocular pressure (IOP) elevation.

Methods : Mouse eyes were studied as ex vivo explants from 4-6 months old GFP-glutamate transporter-GLT1 mice whose astrocytes are spontaneously fluorescent; 3 eyes had 6 weeks of IOP elevation after microsphere injection into the anterior chamber, and 3 were controls. Explants were mounted in an inflation chamber and the astrocytic lamina of the optic nerve head was imaged by a Zeiss 710 laser scanning microscope using two-photon fluorescence at a standard IOP of 10mmHg, fixed by cannulation (Figure). A modified Filter algorithm (Campbell et al. 2015) was used to enhance the image contrast of the astrocytic cell processes. The filtered images were processed with morphological algorithms (D’Amore et al. 2010) to extract structural features of the lamina including: average width of astrocytic processes, areal density of the cell processes and cell bodies, and orientation of the processes. Outcomes for glaucoma eyes and controls were compared with t-tests.

Results : Both the areal density of processes and of cell bodies were statistically smaller in glaucoma eyes (Table). The average width of astrocyte cell processes for glaucoma eyes was smaller than those of normal eyes (2.72 ± 0.23 μm, 2.53 ±0.04 μm, p=0.33, Table), though it was not significant. Analysis of the orientation distribution of the astrocytic processes over the entire lamina showed an isotropic distribution, with no preferential alignment for both glaucoma and control eyes.

Conclusions : Changes in the astrocytic structure within the optic nerve head in experimental glaucoma indicate structural alterations that may be contributory in injury to retinal ganglion cell axons. The methods developed can provide detailed analysis of biomechanical alterations during inflation testing in the ex vivo model.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.