Telemetric monitoring of 24 h intraocular pressure in conscious and freely moving C57BL/6J and CBA/CaJ mice

Abstract

Purpose: To study change patterns of 24 h intraocular pressure (IOP) in conscious and freely moving mice using telemetry.

Methods: Adult C57BL/6J and CBA/CaJ mice were entrained to a standard 12 h light and 12 h dark cycle. A telemetric pressure transmitter was implanted subcutaneously on the upper back of each light-dark entrained mouse, and the pressure catheter tip was inserted into the vitreous chamber. Broadcasted IOP data were received at 120 Hz. Means of 2 min IOP were recorded every 5 min for 4-13 days to generate the 24 h IOP pattern in each mouse strain. The pattern of IOP in the C57BL/6J strain was also determined under an acute constant dark condition for 24 h.

Results: There were distinct patterns of 24 h IOP in the C57BL/6J and CBA/CaJ mouse strains. Under the standard light-dark condition, IOP was higher during the dark period than the light period in both strains. Elevation in IOP from the light period to the dark period was significantly smaller in the CBA/CaJ strain (1.6+/-1.7 mmHg, mean+/- standard deviation (SD), n=21) than in the C57BL/6J strain (3.4+/-2.5 mmHg, n=20). The 24 h IOP pattern in the C57BL/6J strain persisted under an acute constant dark condition (n=8).

Conclusions: Distinct change patterns of 24 h IOP appeared in these two mouse strains. Although mean IOP during the dark period was significantly higher than the light period in both strains, the magnitudes of light-dark IOP elevation differed. The 24 h IOP change pattern can be driven endogenously in the absence of light.

Figure 1

Continuous 13 day record of intraocular pressure (IOP) in one conscious and freely moving C57BL/6J mouse. Recording started at noon under the 12 h light (6 AM to 6 PM) and 12 h dark cycle. Each dot represents a 2 min IOP mean for a 5 min interval. The trend-line was determined using the moving average of 72 data points. The recording system failed near the end of 13 days. A spontaneous IOP fluctuation seen on day 4 in this mouse could appear anytime during the data collection periods in other mice.

Figure 2

Change pattern of 24 h intraocular pressure (IOP) in C57BL/6J mice. Error bars represent SEM. Repeated measures ANOVA indicated a statistical difference in the hourly IOP averages under the standard light-dark and the acute constant dark conditions but not in the control experiment.

Figure 3

Variations of intraocular pressure (IOP) from the 24 h means in CBA/CaJ and C57BL/6J mice. Error bars represent SEM. Dashed line represents the zero variation from the 24 h IOP mean. A time-dependent IOP rise during the period of 4–7 PM only appeared in the C57BL/6J strain.