Passive radiotelemetry of intraocular pressure in vivo: calibration and validation of continual scleral guard-ring applanation transensors in the dog and rabbit.

Continual monitoring of intraocular pressure (IOP) by passive radiotelemetry, with a miniature scleral applanating device, mounted in a haptic contact lens (applanating transensor) is reported in the rabbit and dog. Several prototype transensors were calibrated in vivo in the rabbit and dog; a consistent linear output was obtained for each eye, although reproducibility of the slope between eyes over a period of time was less than ideal. Accuracy of determination of IOP was found to be better for the rabbit and will have to be improved before the instrument can be applied to the human. Multiple regression analysis of calibration studies in six rabbits established that the transensor output was not significantly affected by the small changes in body temperature and atmospheric pressure encountered during the study. Continual scleral tonometry with a standard Mackay-Marg tonometer showed that ocular rigidity has a significant effect on calibration curves, in contradistinction to standard Mackay-Marg corneal tonometry. A time-dependent decay in tonometer readings was more evident in canine eyes with low ocular rigidity. Since the transensor is also a guard-ring applanating device, calibration may be necessary for individual eyes and species.