Comparison of intraocular pressure measurements obtained by Goldmann applanation tonometer, corvis ST and a conventional non-contact airpuff tonometer in eyes with previous myopic refractive surgery and correlation with corneal biomechanical parameters.

PURPOSE

To assess the agreement among four types of intraocular pressure (IOP) measurements: IOP obtained by Goldmann applanation tonometer (IOP-GAT),IOP obtained by an air-puff tonometer (Nidek NT-510) (IOP-NCT), the non-corrected IOP obtained by the Corneal Visualization Scheimpflug Technology (IOP-Corvis) and the biomechanically corrected IOP obtained by the Corvis ST (bIOP-Corvis) in eyes having undergone myopic refractive surgery and correlate their differences with corneal biomechanical parameters.

METHODS

This prospective, observational study recruited 104 non-glaucomatous, post-myopic refractive surgery eyes. Each patient underwent IOP evaluation via GAT, Nidek NT-510 and Corvis ST. Difference in IOP readings was assessed by ANOVA analysis. Tonometer intermethod agreement was assessed by the Bland-Altman method. The difference between the IOP measurements was correlated against corneal thickness(CCT), age, gender, type of refractive surgery and corneal biomechanics with mixed effects linear regression analysis.

RESULTS

bIOP-Corvis showed the highest values (14.77 ± 2.3 mmHg), followed by IOP-NCT (13.95 ± 2.6 mmHg), IOP-GAT (13.46 ± 2.9 mmHg) and IOP-Corvis (12.56 ± 3.1 mmHg). There were statistically significant differences in IOP measurements among all the ANOVA pairwise comparisons. Bland Altman analysis revealed a notable bias (all P < 0.01) among bIOP-Corvis and IOP-NCT, bIOP-Corvis and IOP-Corvis, bIOP-Corvis and IOP-GAT, IOP-NCT and IOP-Corvis, IOP-NCT and IOP-GAT and IOP-Corvis and IOP-GAT. We observed a strong correlation of the difference between bIOP-Corvis and IOP-NCT with patient age (P < 0.001), CCT (P < 0.001), of the difference between bIOP-Corvis and IOP-Corvis, with type of refractive surgery (P = 0.012), age (P = 0.050), CCT (P < 0.001), the stiffness parameter at first applanation(SP-A1) (P = 0.008), Ambrozio Relational Thickness horizontal (ARTh) (P < 0.001), of the difference between bIOP-Corvis and IOP-GAT, with CCT (P < 0.001), ARTh (P < 0.001), Deformation Amplitude Ratio (DA Ratio) (P = 0.035), of the difference between IOP-NCT and IOP-Corvis, with type of refractive surgery (P = 0.002), CCT (P = 0.031), SP-A1 (P = 0.014), ARTh (P < 0.001), of the difference between IOP-NCT and IOP-GAT with ARTh (P < 0.001) and of the difference between IOP-Corvis and IOP-GAT with SP-A1 (P = 0.027).

CONCLUSION

The different IOP values obtained by Corvis ST, NCT and GAT tonometers do not have a steady relationship in their measurements between them and cannot be considered interchangeable in post-myopic refractive surgery eyes. These differences from each pair of IOP measurements are correlated with corneal biomechanics,CCT and age. Our results suggest that the smaller degree of myopic correction may lead to a lower difference between the tonometers' readings.