Duration of anesthesia affects intraocular pressure, but not outflow facility in mice

The study of aqueous humor dynamics (AHD) in mice is becoming more prevalent as more strains with elevated intraocular pressure (IOP) are developed. High IOP is usually associated with reduced outflow facility making this one of the more important AHD parameters to evaluate. Ocular measurements in mice require anesthesia that has profound effects on IOP but unknown effects on outflow facility. This study evaluates the effects of anesthesia duration and latanoprost treatment on outflow facility and IOP in BALB/c mice.

IOPs were measured in conscious and anesthetized mice by tonometry. Outflow facility was evaluated in 15-min intervals at three pressure levels over two 45-min periods. Comparisons were made between latanoprost-treated eyes and untreated contralateral eyes. To determine the effect of anesthesia duration on IOP, a microneedle method was used to follow IOP for 120 min in separate mice.

IOP was 9.7 +/- 0.3 mmHg (mean +/- SEM) in conscious mice and 7.1 +/- 0.02 within 10 min of anesthesia initiation (p < 0.01). IOP changed significantly between but not within assessment periods. IOP at 75 min was significantly (p = 0.004) reduced compared to IOP at 15 min after initial anesthesia. In control eyes, outflow facility did not change between the two 45-min assessment periods during the 120 min test (p = 0.80). In latanoprost-treated eyes, outflow facility increased compared with control eyes during both assessment periods (p = 0.03). A test of filters in series with known resistance found that the method was sensitive enough to detect a change in outflow facility of 0.001 microl/min/mmHg.

Administration of ketamine/xylazine anesthesia for 120 min did not alter outflow facility or lessen the effect of latanoprost on outflow facility in mice as determined by a new analysis system. Accurate IOP measurements must be made within minutes of anesthesia administration but outflow facility measurements can be made with less haste.