Repeatability and accuracy of applanation resonance tonometry in healthy subjects and patients with glaucoma

Abstract

Purpose: To evaluate the repeatability and accuracy of the applanation resonance tonometer (ART) used in the automatic servo-controlled version, and to evaluate the influence of central corneal thickness (CCT) on the ART intraocular pressure (IOP) measurements.

Methods: This prospective, randomized, single-centre study included one eye of 153 subjects (35 healthy volunteers and 118 patients with glaucoma). All participants underwent ultrasonic CCT measurement, followed by IOP evaluation with Goldmann applanation tonometer (GAT) and ART in random order. A single operator measured the IOP with each tonometer three times. Intra-examiner variability was evaluated using the coefficient of variation (CoV), intraclass correlation coefficient (ICC) and test-retest differences. Intermethod agreement was assessed using the Bland-Altman method. Linear regression analysis was used to evaluate the relationship between IOP measurements and CCT.

Results: The mean IOP was 17.7 ± 4.4 mmHg with GAT and 20.6 ± 5.3 mmHg with ART (p < 0.001). CoV and ICC were, respectively, 5 ± 3% and 0.99 for GAT, and 8 ± 4% and 0.96 for ART (intermethods differences, p = 0.001). The ART test-retest differences significantly increased with increasing mean IOP (p = 0.003). The mean IOP difference (ART minus GAT) was 3.0 ± 4.0 mmHg, which increased with increasing mean IOP (p < 0.001). Both GAT IOP and ART IOP readings were significantly directly related to the CCT values (p = 0.03 and p = 0.004, respectively; intermethods difference, p = 0.32).

Conclusions: The ART intra-examiner repeatability was excellent, although significantly lower than that of GAT, and decreased at higher IOP levels. ART significantly overestimated GAT IOP measurements, especially at higher IOP range. Both GAT and ART appeared similarly influenced by CCT value.

Keywords: Goldmann applanation tonometry; accuracy; applanation resonance tonometry; central corneal thickness; intraocular pressure; repeatability.