Influence of Corneal Biomechanical Properties on Intraocular Pressure Differences Between an Air-Puff Tonometer and the Goldmann Applanation Tonometer

Purpose: To estimate the influence of corneal properties on intraocular pressure (IOP) differences between an air-puff tonometer (NT530P; Nidek) and the Goldmann applanation tonometer (Haag-Streit).Patients and Methods: The influence of central corneal thickness (CCT), keratometry, and Ocular Response Analyzer (Reichert) measurements of corneal viscoelasticity [corneal hysteresis (CH) and corneal resistance factor (CRF)] on IOP differences between tonometers was evaluated.Results: The CRF was calculated to be the best predictor of the differences in IOP readings between tonometers (r(2)=0.23; P<0.001), followed by CCT (r(2)=0.15; P=0.003) and CH (r(2)=0.14; P=0.003). Keratometry performed very poorly as lone predictor of IOP differences. In a multiple regression model, CRF, CH, and CCT together accounted for 25% (r(2)=0.25; P<0.01) of the variance in IOP reading differences between tonometers.Conclusions: Corneal resistance to applanation induced by either contact or noncontact tonometers was calculated to be the most determinant factor in influencing IOP differences between applanation tonometers.