Effect of corneal astigmatism on intraocular pressure measurement using ocular response analyzer and Goldmann applanation tonometer.

Purpose: To assess the effect of corneal astigmatism on intraocular pressure (IOP) measurements using an Ocular Response Analyzer (ORA) and a Goldmann applanation tonometer (GAT).

Methods: We prospectively examined 59 normal eyes of 59 healthy volunteers (18 men, 41 women; age, mean +/- standard deviation, 40.5 +/- 14.2 years; age range, 19-68 years). We quantitatively assessed the values of corneal-compensated intraocular pressure (IOPcc) and Goldmann-correlated intraocular pressure (IOP(G)) using an ORA (Reichert Ophthalmic Instruments). We also measured the IOP using a GAT (GAT-IOP). The amount of corneal astigmatism was assessed with an autokeratometer. We carried out these measurements three times, and the mean value obtained was used for statistical analysis.

Results: The mean IOPcc, IOP(G), and GAT-IOP were 14.7 +/- 2.6, 14.0 +/- 2.8, and 14.2 +/- 1.7 mmHg respectively. The mean corneal astigmatism was 0.94 +/- 0.55 D. We found no significant correlation between IOPcc and corneal astigmatism (Pearson's correlation coefficient r = -0.04, p = 0.79), or between IOP(G) and corneal astigmatism (r = 0.09, p = 0.52). However, we found a weak, but significant, correlation between GAT-IOP and corneal astigmatism (Pearson's correlation coefficient r = 0.34, p = 0.009).

Conclusions: Both IOPcc and IOP(G) measured with ORA were less affected by the amount of corneal astigmatism, and the GAT-IOP readings were significantly higher in eyes with greater corneal astigmatism, suggesting that IOPcc as well as IOP(G) may be helpful for accurate IOP measurements in eyes with some corneal astigmatism.