PURPOSE. To determine differences in scleral permeability, as measured by diffusion of macromolecules, by using fluorescence recovery after photobleaching (FRAP), with reference to differences by mouse strain, scleral region, and the effect of experimental glaucoma.METHODS. In three mouse strains (B6, CD1, and B6 mice with mutation in collagen 8a2[Aca23]), we used FRAP to measure the diffusion of fluorescein isothiocyanate-dextran, molecular weight 40 kDa, into a photobleached zone of sclera. Scleral regions near the optic nerve head (peripapillary) and two successively more anterior regions were compared. Sclera from mouse eyes subjected to chronically elevated intraocular pressure after bead injection into the anterior chamber were compared to fellow eye controls. FRAP data were compared against estimated retinal ganglion cell axon loss in glaucomatous eyes.RESULTS. Diffusion rates of dextran molecules in the sclera were significantly greater in Aca23 and B6 mice than in CD1 mice in a multivariate model adjusted for region and axial length (P < 0.0001). Dextran diffusion significantly decreased in glaucomatous eyes, and the decline increased with greater axon loss (P ¼ 0.0003, multivariable model). Peripapillary scleral permeability was higher in CD1 than B6 and Aca23 mice (P < 0.05, multivariable model, adjusted by Bonferroni).
CONCLUSIONS.Measurement of the diffusion rates of dextran molecules in the sclera showed that glaucoma leads to decreased scleral permeability in all three mouse strains tested. Among mouse strains tested, those that were more susceptible to glaucomatous loss of retinal ganglion cells had a lower scleral permeability at baseline.Keywords: glaucoma, mouse, experimental model, sclera, diffusion, permeability, photobleaching, dextran G laucoma is the second leading cause of world blindness and its principal risk factors include the effect of intraocular pressure (IOP) acting to decrease the number of retinal ganglion cells (RGCs). Intraocular pressure is a mechanical load that generates stress and strain in the sclera, which are magnified at the optic nerve head (ONH). The largest mechanical strains have been measured in in vitro inflation experiments in the peripapillary region, immediately adjacent to the ONH.1 The sclera acts on the ONH, where axons of RGCs pass out of the eye, and suffers damage related to the effects of IOP.2,3 Thus, the behavior of the sclera is highly relevant to glaucoma injury and its study may be useful in improved diagnosis as well as new therapeutic avenues.The sclera comprises three-quarters of the human ocular circumference and is 75% to 90% collagen, with additional elastin fibrils and proteoglycans. 4,5 The scleral proteoglycans include heparin sulfate, chondroitin sulfate, dermatan sulfate, keratan sulfate, hyaluronan, aggrecan, and several small leucinerich proteoglycans.6,7 These may have important functional significance for the mechanical responses of the sclera. 8 Scleral thickness is greatest at the peripapillary zone, followed by the limbus, and is...