The influence of cornea properties on rebound tonometry

Purpose: To determine the influence of corneal thickness, corneal hysteresis (CH), and corneal resistance factor (CRF) on intraocular pressure (IOP) measurements obtained using the iCARE rebound tonometer. Design: Cross-sectional study. Participants: One hundred twenty-five eyes of 125 normal healthy subjects. Methods: Intraocular pressure was determined in all subjects using the iCARE at both central and temporal corneal regions. Corneal thickness at these 2 regions was determined by ultrasonic pachymetry. Corneal hysteresis and corneal resistance factor were measured using an ocular response analyzer. Goldmann applanation tonometry (GAT) was also performed on all eyes. Main Outcome Measures: Intraocular pressure, corneal thickness, corneal hysteresis, and corneal resistance factor. Results: Although the peripheral cornea was significantly thicker than the central cornea, IOPs obtained by the iCARE at the 2 regions were similar and significantly higher than GAT measurements. There were an overestimation at higher IOPs and an underestimation at lower IOPs relative to GAT measurements. Multiple regression analysis showed a significant correlation between the iCARE and CH (partial correlation r = -0.67, P<0.01) and CRF (partial correlation r = 0.82, P<0.01). The correlation between the iCARE and central corneal thickness was not significant. Conclusions: Rebound tonometry is affected by corneal properties including CH and CRF but not corneal thickness. Ophthalmology 2008; 115:80-84 (c) 2008 by the American Academy of Ophthalmology.