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 (r2=0.23; P<0.001), followed by CCT (r2=0.15; P=0.003) and CH (r2=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% (r2=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.