Efficacy of TonoLab in detecting physiological and pharmacological changes in rat intraocular pressure: Comparison of TonoPen and microneedle manometry

Abstract

To assess the efficacy of two noninvasive tonometers, TonoLab and TonoPen-XL, in detecting physiological or pharmacological changes of intraocular pressure (IOP) in rat eyes, by comparing them with the microneedle method. Sprague Dawley rats, bred under a 12-h light-and-dark cycle, were used. Under systemic anesthesia, eyes were cannulated by a microneedle connected to a transducer and a water reservoir. Variable intracameral pressure was attained by changing the reservoir height, and the resulting tonometer readings were compared. Then, the daytime and nighttime IOP, and the effect at 2 h after latanoprost instillation, were measured with the three devices. TonoLab and TonoPen-XL readings (y) were strongly correlated with microneedle tonometer readings (x) (y=0.96x-4.3, r2=0.985, and y=0.48x+3.9, r2=0.985, respectively), but TonoPen-XL readings were only half those of the microneedle tonometer. Nocturnal elevation of IOP was significant both with TonoLab and with the microneedle tonometer (P<0.001), but not with TonoPen-XL. Latanoprost significantly elevated IOP by 3.0+/-2.1 with TonoLab and by 1.1+/-1.1 mmHg with the microneedle tonometer (P<0.05), but not with TonoPen-XL. TonoLab provides readings similar to those of a microneedle tonometer, and diurnal variations and drug effects were detectable. TonoLab promises to be a noninvasive and useful method for physiological and pharmacological studies in rat eyes.