Repeatibility and reproducibility of applanation resonance tonometry

Purpose:To assess repeatability (intra-observer variability) and reproducibility (inter-observer variability) of intraocular pressure (IOP) measurements with Applanation Resonance Tonometry (ART) and to evaluate possible influential factors. Methods:The study included 178 patients (101 glaucoma, 63 healthy and 14 with OHT; one eye per subject) from two Italian centers (Eye Clinic of San Paolo Hospital of Milan and University of Siena). IOP was measured once with a Goldmann applanation tonometer (GAT) and twice by ART (ART1, ART2) in a randomized sequence, by a single operator to assess intra-operator variability. To assess inter-operator variability 2 operators, chosen randomly (A and B, B and C, A and C), performed 2 measurements each (in random order; i.e. A B A B; B A B A) on the same patient. Repeatability and reproducibility were assessed by the coefficient of variation (CoV) and intraclass correlation coefficient (ICC). Results:ART1 was 0.4±2.8 mmHg higher than ART2 (p<0.001). Results were not influenced by randomization test order. Intra-operator CoV was 7.6%±7.6%, and ICC was 0.88 (95%CI: 0.85-0.91). Inter-operator CoV ranged between 6.0%±10.8% and 8.0%±6.8%, and ICC between 0.906 and 0.917. ART1 and 2 were respectively 1.8±3.8 and 1.4±4.3 mmHg higher than GAT (p<0.001). Results were unaffected by diagnosis, age, central corneal thickness, keratometry, operator, randomization sequence. Conclusions:ART repeatability and reproducibility were almost perfect. Tonometry measurements with ART tended to be overestimated compared with GAT.