Abstract
Purpose::
To determine how Y27632 (Y27; a selective Rho-kinase inhibitor) effects outflow facility (C), outflow patterns, and the morphology of inner wall (IW) and juxtacanalicular tissue (JCT) in monkey vs human eyes.
Methods::
Eight monkey and 8 human eyes were perfused at 15 mmHg with Dulbecco's PBS containing 5.5 mM glucose (GPBS) to establish a baseline C. Anterior chambers were exchanged for GPBS with or without 50 µM Y27 (N = 4 in each group) and perfused with additional 0.3ml . All eyes were exchanged for GPBS with fluorescent microspheres (0.5µm; 0.002%) and perfused with 0.3 ml to label the hydrodyamic patterns of outflow before perfusion-fixation with Karnovsky's fluid. Confocal images were taken along Schlemm's canal (SC) in radial and tangential sections. The total length (TL) and the tracer-decorated length (L) of the IW were measured. The average percent effective filtration length (PEFL=L/TL) was calculated. Sections with SC were processed and examined by light microscopy. The TL of IW and the length exhibiting separation in JCT (SL) were measured. The average percent separation length (PSL= SL/TL) was calculated.
Results::
In Y27 treated monkey eyes, the increase in C was 0.59±0.11 µl/min/mmHg (Mean±SE) vs 0.18±0.05 in controls (p=0.03). The percent changes between Y27 (114.9±14.9%) vs control eyes (44.3±9.7%) were significant (p=0.01). Y27 eyes showed a more uniform tracer pattern than controls, with extensive labeling along the IW of SC. The PEFL in Y27 eyes (82.5±1.2%) was 3.4X larger than controls (24.2±4.2%, p<0.001). Unlike control eyes, by light microscopy, the JCT region of Y27 eyes appeared distended. The PSL was 2.2X larger in Y27 eyes (75.2±4.0%) than controls (33.5±5.3%; p=0.001). In human eyes, the change of C with Y27 was 0.02±0.01 µl/min/mmHg vs 0.02±0.03 (p=0.98) in controls. The percent change between Y27 eyes (8.1±3.0%) and controls (11.3±13.4%) was not significant (p=0.83). Segmental distribution of tracer in the TM was seen in both control and Y27 eyes, with clustering of tracers near collector channel ostia. The PEFL in Y27 eyes (47.4±6.5%) vs in controls (39.0±12.5%) was not significant (p=0.41). No discernable separations between the IW and JCT and in the JCT were found in Y27 or control human eyes.
Conclusions::
Y27 significantly increases C by redistributing aqueous outflow through a larger and looser area of the JCT in monkey but not in human eyes. This correlates with the hydrodynamic and morphological differences seen in the IW and JCT region, supporting the hypothesis that IW/JCT connectivity influences outflow hydrodynamics to control C.
Keywords: outflow: trabecular meshwork • drug toxicity/drug effects • imaging/image analysis: non-clinical