Comparison of intraocular pressure measurement between rebound, non‐contact and Goldmann applanation tonometry in treated glaucoma patients

BACKGROUND: To compare the intraocular pressure readings obtained with the iCare rebound tonometer and the 7CR non-contact tonometer with those measured by Goldmann applanation tonometry in treated glaucoma patients. DESIGN: A prospective, cross-sectional study was conducted in a private tertiary glaucoma clinic. PARTICIPANTS OR SAMPLES: One hundred nine (54 males : 55 females) patients including only eyes under medical treatment for glaucoma. METHODS: Measurement by Goldmann applanation tonometry, iCare rebound tonometry and 7CR non-contact tonometry. MAIN OUTCOME MEASURES: Intraocular pressure. RESULTS: There were strong correlations between the intraocular pressure measurements obtained with Goldmann and both the rebound and non-contact tonometers (Spearman r-values ≥ 0.79, P < 0.001). However, there were small, statistically significant differences between the average readings for each tonometer. For the rebound tonometer, the mean intraocular pressure was slightly higher compared with the Goldmann applanation tonometer in the right eyes (P = 0.02), and similar in the left eyes (P = 0.93); however, these differences did not reach statistical significance. The Goldmann correlated measurements from the non-contact tonometer were lower than the average Goldmann reading for both right (P < 0.001) and left (P > 0.01) eyes. The corneal compensated measurements from the non-contact tonometer were significantly higher compared with the other tonometers (P ≤ 0.001). CONCLUSIONS: The iCare rebound tonometer and the 7CR non-contact tonometer measure intraocular pressure in fundamentally different ways to the Goldmann applanation tonometer. The resulting intraocular pressure values vary between the instruments and will need to be considered when comparing clinical versus home acquired measurements.