Comparison Of The Icare Rebound Tonometer And The Applanation Tonometry In Cohort Of 546 Eyes Of Healthy Eyes And Eyes Following Prk, Lasik, Cxl, And Pciol Surgery

To evaluate agreement, correlation, and proportional bias between applanation tonometry (AT) and rebound tonometry (iCare) across healthy eyes and eyes following PRK, LASIK, CXL, and PCIOL surgery, with adjustment for age.

Private tertiary refractive clinic

Methods
In this cross-sectional study, 546 eyes were analyzed (Healthy n=160, PRK n=134, LASIK n=80, CXL n=40, PCIOL n=132). Intraocular pressure (IOP) was measured using AT and iCare. Descriptive statistics and paired comparisons were calculated per group. Agreement was assessed using intraclass correlation coefficients (ICC, two-way random, absolute agreement) and Bland–Altman analysis. Age-adjusted differences between groups were evaluated using ANCOVA. Pairwise comparisons were Holm-corrected. Proportional bias was tested using linear regression of measurement difference (AT − iCare) on mean IOP.

Across all groups, iCare measured significantly higher IOP than AT (all p<0.001). Mean differences (AT − iCare) ranged from −1.51 mmHg (LASIK) to −2.65 mmHg (PRK). Correlation was moderate to strong (r=0.47–0.74), and ICC ranged from 0.46 (Healthy) to 0.71 (PRK). Bland–Altman analysis demonstrated wide limits of agreement in all groups. Age-adjusted ANCOVA confirmed significant group effects for AT (p=1.7×10⁻⁸), iCare (p=9.1×10⁻¹⁰), and measurement difference (p=7.1×10⁻⁵). Proportional bias was significant overall (slope −0.17 mmHg/mmHg, p=7.2×10⁻⁶) and was most pronounced in CXL and PRK groups. Interaction testing demonstrated that proportional bias differed significantly between groups (p=0.004).

iCare tonometry systematically overestimates IOP compared with AT across healthy and post-surgical eyes. Agreement varies by surgical status, and proportional bias—particularly after PRK and CXL—suggests increasing divergence at higher IOP levels. These devices should not be considered interchangeable, especially in post-refractive populations.