Agreement among Goldmann Applanation Tonometer, Easyton Transpalpebral Tonometer, Tonopen, and Icare in Patients with Keratoconus

OBJECTIVES: The objective of the study is to evaluate the agreement between Goldmann applanation tonometer (GAT) and Easyton transpalpebral tonometer, Tonopen, and Icare in patients with Keratoconus. METHODS: This cross-sectional study included 46 eyes of 26 patients with keratoconus. Intraocular pressure (IOP) is measured using easyton, icare, tonopen, and GAT. Measurements were compared and the influences of corneal topographic variables on IOP measurement were evaluated. Bland–Altman plots were used for assessing agreement between different tonometers. RESULTS: The mean age of the participants was 24.08±6.76 (range, 18–47) years (15 males and 11 females). The highest of the mean IOP values measured with different tonometers was obtained with Easyton (12.33±1.65), followed by Tonopen (11.59±2.17), GAT (10.67±1.52), and Icare (10.04±2.33). The mean IOP value measured with Easyton was significantly higher than that measured with GAT (p<0.001). There was no significant difference between GAT and either Tonopen (p=0.154) or Icare measurements (p=0.732). There was no significant difference between Tonopen and Easyton measurements (p=0.421). Icare measurements were correlated with central corneal thickness and keratometric values. GAT measurements were correlated with only Kmax. Thirty-eight (82.6%) of the differences were within the agreement limits (assumed clinically important deviation of up to ±2 mmHg) of GAT and Tonopen, 73.9% (n=34) were within the agreement limits of GAT and Icare, and 78.3% (n=36) were within the agreement limits of GAT and Easyton. CONCLUSION: Compared with GAT, the gold standard method, Easyton IOP readings were higher, while both Tonopen and Icare readings were similar to GAT. All three tonometers showed acceptable agreement with the GAT, however, Tonopen showed the greatest agreement.