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

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.