Intraocular Pressure Measurement Variability in the Ocular Hypertension Treatment Study

To characterize intravisit variability of Goldmann applanation tonometry (GAT) and identify factors associated with intraocular pressure (IOP) measurement variability using longitudinal data from the Ocular Hypertension Treatment Study (OHTS).

A post hoc analysis of a multicenter, randomized clinical trial.

The OHTS trial participants.

Intravisit IOP measurements obtained using a standardized GAT protocol in OHTS were analyzed over 15 years of follow-up. Two measurements (IOP₁ and IOP₂) were obtained per eye at each visit, with a third measurement (IOP₃) performed if IOP₁ and IOP₂ differed by >2 mmHg. The intravisit differences in IOP measurements were assessed. Multivariable mixed-effects logistic regression models were used to identify factors associated with the need for IOP₃ measurement during follow-up.

Intravisit IOP variability and measurement variability.

The analysis included 1636 OHTS participants who had 35 636 patient visits (71 249 eye-visits, defined as a visit when at least 1 IOP measurement was performed for a given eye) and 145 236 IOP measurements. The first 2 measurements were within 2 mmHg in 96.2% of eye-visits. Although 44.8% of paired measurements were identical, IOP₁ was more often higher than IOP₂ (54.4%, P < 0.001). In 3.8% of eye-visits, IOP₃ was performed and lowered the final recorded IOP in 63.4%. Baseline need for IOP₃ (odds ratio (OR) 1.52; 95% confidence interval (CI), 1.14-2.03; P = 0.004), higher current visit IOP (OR 1.06 per 1 mmHg higher IOP; 95% CI, 1.04-1.09; P < 0.001), and baseline higher pattern standard deviation (OR 1.26 per 1 dB higher; 95% CI, 1.04-1.52; P = 0.02) were independently predictive of need for IOP₃ during follow-up, while randomized treatment assignment was not (OR 1.02; 95% CI, 0.88-1.19; P = 0.78).

Goldmann applanation tonometry remains the most common procedure in ophthalmology. In the OHTS, GAT demonstrated modest measurement variability. Intraocular pressure measurement variability was associated with characteristics known to be risk factors for the development of primary open-angle glaucoma. These findings have implications for clinical decision-making, trial design, and the application of the OHTS risk calculator. Clinicians should maintain a low threshold for repeating measurements when intravisit measurements are inconsistent or when making a clinical decision based on a single IOP measurement.

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