Measurement of Intraocular Pressure in Awake Mice

To determine whether the Goldmann applanation tonometer can be modified to measure intraocular pressure (IOP) in the awake mouse. Tonometers with reduction of the biprism angles in the applanating tips and in the weight applied by the instrument were tested in anesthetized mice in calibration experiments. Then a tonometer with the appropriate configuration of tip and weight was used in conscious, unsedated mice. Tonometry in mice required a biprism angle of 36 degrees and weight applied of 25 mg per scale division (2 g full scale). This tonometer was calibrated in mice against manometrically measured IOP and showed good agreement across the range of IOP tested (0-50 mm Hg). In conscious mice the measured mean Goldmann value was 13.7 +/- 3.2 mm Hg (mean +/- SD; 95% confidence interval, 13.1, 14.2 mm Hg). The Goldmann tonometer, the standard for measuring the IOP in the human eye, was modified to measure this fundamental physiologic parameter in the awake mouse. This measurement is required to confirm success in genetically engineering a model in the powerful mouse system, which mimics elevated IOP in humans. The model will open new avenues for studying the causes of the optic neuropathy of glaucoma, the regulation of IOP, and new therapeutic approaches to prevent the irreversible loss of vision from this disease.