Abstract
Purpose :
Knowledge of corneal material properties is essential in the assessment of corneal ectasia and other related pathologies. The aim of this study was to examine the agreement of corneal biomechanics assessment using two dynamic Scheimpflug analyzers.
Methods :
33 subjects (10M/23F) aged 19 to 35 years with healthy corneas were enrolled in the study. A random eye of each subject was measured 3 times using two Corvis ST instruments, placed on the same ophthalmic table and running the same firmware. 3-minute breaks were taken between the measurements. IOP and biomechanical-compensated IOP (bIOP) was assessed as well as the Corvis biomechanical index (CBI), ranging from 0 to 1, that encompasses several important corneal structural parameters. For each subject, median values of considered parameters were taken for further analysis.
Results :
Central corneal thickness ranged between 510 and 610 μm. For IOP, the mean difference between the instruments was −1.2 mmHg with limits of agreement (LoA) between −4.6 and 2.2 mmHg. Similar results were obtained for bIOP with mean difference of −1.3 mmHg (LoA: −4.6 and 1.9 mmHg). Those differences were statistically correlated with their corresponding mean values (R = 0.592, p < 0.001 and R = 0.505, p = 0.003 for IOP and bIOP, respectively), indicating a proportional bias. For CBI, the mean difference was 0.06 with LoA between −0.30 and 0.43. Despite being healthy subjects, one had mean CBI value of 0.78 indicating high risk of ectasia and 5 other subjects had mean CBI values greater than 0.25, indicating moderate risk of ectasia. For CBI, the differences were also statistically significantly correlated with mean values (R = 0.460, p = 0.007) and that correlation was stronger for CBI < 0.5 (R = 0.871, p < 0.001). Statistically significant differences between the two instruments were noted for all considered parameters (Wilcoxon signed-rank test: p < 0.001, p < 0.001 and p = 0.018 for IOP, bIOP and CBI, respectively).
Conclusions :
Measurement of corneal material properties with two dynamic Scheimpflug analyzers showed moderate agreement between the instruments when measuring IOP and poor agreement in the assessment of CBI. The study was limited to subjects with healthy corneas and normal levels of IOP. Further research is needed to evaluate such an agreement between the instruments for other groups of subjects, particularly those at risk of corneal ectasia.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.