Purpose
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.
Methods
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.
Results
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.
Conclusion
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.