Precision and reliability in tonometry: Comparison of Corvis ST and iCare in glaucoma patients on the Ecuadorian coast

Background This study aimed to compare IOP or tonometric measurements obtained with the Corvis ST and the iCare rebound tonometer in glaucoma patients seen at an ophthalmology center on the Pacific coast of Ecuador. Methods This study retrospectively reviewed clinical records obtained between June 2023 and January 20 across six institutional sites. A total of 434 patients with bilateral glaucoma met the inclusion criteria. Each participating site had a single trained examiner responsible for all measurements during the study period, ensuring consistency within each location. Mean differences between instruments were evaluated using repeated measures analysis, and inter-method agreement was assessed using Bland–Altman plots. Results The biomechanically corrected IOP (bIOP) from the Corvis ST was lower than the iCare IOP measurements in 79% of eyes; the overall mean difference was 1.7 millimeters of mercury (standard deviation 2.8; P < 0.001). The limits of agreement for the corrected mode ranged from –6.1 to +2.7 millimeters, compared with –9.8 to +3.8 for the uncorrected setting. Variability, assessed by the coefficient of repeatability, was 32% lower with bIOP than with the rebound tonometer. Central corneal thickness correlated with uIOP readings (uncorrected intraocular pressure from the Corvis ST) (r = 0.32, P < 0.01), but not with the corrected values or with the iCare measurements. Right and left eyes showed consistent patterns. Conclusion The biomechanically corrected bIOP yielded the most consistent, corneal-thickness-independent estimates of IOP. Although iCare remains convenient for screening, bIOP measurements appear superior for precise monitoring and therapeutic decision-making in glaucoma care.