Abstract
Purpose :
In mouse eyes perfused ex-vivo, measured values for aqueous outflow facility (C) are variable depending upon whether perfusate is introduced into the anterior chamber (AC) or the posterior chamber (PC) via the cannulating needle. AC perfusion causes posterior iridial bowing, pupillary block, and traction on the scleral spur, leading to an increase in C. PC perfusion by contrast does not cause this effect, resulting in significantly lower calculated values for C. However the equivalent situation in living mice has not been reported. Here we investigated if AC versus PC perfusion in the living mouse eye leads to different calculated values for C.
Methods :
C57BL/6J mice (all ♀, 20-24 weeks of age) were divided into 4 groups (4 animals/group). All animals were anesthetized (ketamine 100 mg/kg; xylazine 10 mg/kg, intraperitoneal injection) and C was measured in both eyes simultaneously of each animal via a technique of constant flow infusion. Perfusate to each eye was delivered from a 50 μL glass microsyringe. In groups 1 and 2 the AC or PC was cannulated with a 30G needle, respecively. To investigate the effect of ciliary muscle (CM) and iridial tone on C, groups 3 and 4 were perfused (AC or PC, respectively) in the same manner, but tropicamide (muscarinic receptor antagonist) was added to the perfusate at a concentration of 100 μM.
Results :
C in groups 1 (AC perfusion) and 2 (PC perfusion) was 22.6 ± 2.4 nL/min/mmHg versus 23.1 ± 2.4 nL/min/mmHg, respectively (mean ± SEM, P = 0.869). In groups 3 (AC perfusion) and 4 (PC perfusion),tropicamide induced cycloplegia (confirmed by histology) and mydriasis (pupil diameters: group 1 (1.12 ± 0.07 mm), group 2 (1.25 ± 0.07 mm), group 3 (3.41 ± 0.12 mm), group 4 (3.62 ± 0.05 mm); mean ± SEM). Differences in pupil diameters between groups 1 and 3, and 2 and 4, were highly significant (P < 0.0001). C in group 3 was greater than C in group 4 (22.4 ± 4.0 nL/min/mmHg versus 13.6 ± 1.6 nL/min/mmHg, respectively (mean ± SEM, P = 0.0341)).
Conclusions :
C in living mice is not different when measured by constant flow infusion with the cannulating needle placed in the AC or the PC. However in cycloplegic/mydriatic mouse eyes C is greater when eyes are perfused via the AC. CM and/or iridial tone plays a role in the establishment of C.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.