Noninvasive intraocular pressure measurements in mice by pneumotonometry

PURPOSE. To develop a reliable, noninvasive, continuous, and easily implemented system for measuring intraocular pressure (IOP) in mice. METHODS. Pneumotonometry was adapted for measurement of mouse IOP. Measurements were compared with those obtained with the servo-null micropipette system (SNMS) and with direct anterior chamber cannulation. Heart rate was monitored by the precordial pulse, EKG, or tail pulse in anesthetized mice. The characteristic ocular hypotensive response to mannitol was assessed as an additional validation of the method. RESULTS. Measurements of IOP obtained using pneumotonometry agreed closely with values measured by SNMS or by direct cannulation. IOP oscillations were synchronous with the heart rate, with a coherence peak between them of ∼2 Hz, equal to the pulse frequency. Hypertonic mannitol reduced IOP from 13.7 ± 0.9 mm Hg by 7.7 ± 0.7 mm Hg after 15 minutes. CONCLUSIONS. Pneumotonometry is a reliable and noninvasive method for the measurement of IOP in mice and may permit comparisons of IOP to hemodynamic factors. This system is simpler and more adaptable for glaucoma research than previously reported methodologies for measuring IOP in mice.