Some Basic Statistics of Clinical Tonography

¹ Department of Ophthalmology, The University of Illinois, College of Medicine Chicago, Ill. 60612

Measures of the test-retest consistency of tonographic outflow facility measurements are derived from replicate tests on outpatients with ocular hypertension or chronic open-angle glaucoma. Standard deviations of about ±0.02 apply to such repeat tonographies performed at specific test-times. Recognizable components of this variation are (1) uncertainties inherent in the tonographic tracing and (2) parallel, genuine fluctuations of C in both eyes, steered, apparently, by an extraocular common mechanism. Evidence suggestive of a decrease in facility at higher pressures is reported. A five-minute interval between the tonographies on the two eyes reduces consensual or sequence effects to the level of clinical insignificance. A substantial calibration discrepancy exists between the 5.5 and the 7.5 Gm. scales.