Comparison Of Anterior Segment Structures In Two Rat Glaucoma Models: An Ultrasound Biomicroscopic Study

PURPOSE. Optic nerve disease in chronic IOP elevation rat glaucoma models develops at different rates. This study was undertaken to investigate whether anterior chamber (AC) changes develop in two popular models in vivo and whether the changes are related to IOP.METHODS. Ten female Wistar rats and 12 male Brown-Norway rats were subjected to episcleral vein cauterization (EVC) and hypertonic saline episcleral vein sclerosis (HSEVS), respectively. Contralateral untreated eyes served as controls. IOP was recorded for a period of 5 to 6 weeks, and with the rats under anesthesia, the eyes were imaged with an ultrasound biomicroscope. Measurements of the AC depth (ACD), trabecular-iris angle (TIA), iris thickness at the thickest point near the pupillary margin (IT), angle opening distance (AOD; at 200 mu m from the scleral spur), and ciliary body area (CBA) were compared between control eyes of the two strains and between experimental and control eyes within each strain. The differences were correlated with IOP history.RESULTS. Eyes subjected to EVC demonstrated greater increases in IOP than eyes subjected to HSEVS. Between rat strains, control eyes differed significantly in all the parameters studied, except for ACD. No difference was detected between experimental and control eyes in the EVC group. In contrast, experimental eyes in the HSEVS group had similar to 71% larger ACDs and similar to 32% smaller CBAs than did the contralateral control eyes (P < 0.001). ACD and CBA correlated well (R-2 = 0.80 and 0.51, respectively) with IOP in the HSEVS group. Two of the experimental eyes in this group showed the presence of ultrasound-scattering material in the AC.CONCLUSIONS. Despite apparently higher IOP exposure, eyes in the EVC rat model of glaucoma do not undergo changes in the AC. In contrast, eyes subjected to HSEVS display deepening of the AC and reduction in size of the ciliary body within 5 to 6 weeks. These changes correlate to IOP exposure and may be the result of specific changes induced by the experimental intervention. These models are likely to rely on different mechanisms of pressure elevation and cannot be used interchangeably.