Correlation between corneal hysteresis, corneal resistance factor, and ocular pulse amplitude in healthy subjects

Purpose: The Ocular Response Analyzer (ORA) measures corneal biomechanical properties: corneal hysteresis (CH) and the corneal resistance factor (CRF). The Pascal Dynamic Contour Tonometer (PDCT) measures the ocular pulse amplitude (OPA), which represents the systolic-diastolic variation in intraocular pressure (IOP). Both ORA(R) and OPA values are lower in glaucoma patients than in normal patients. Our purpose was to assess whether there is a correlation between CH, CRF, and OPA values in healthy subjects. Design and participants: Prospective observational study including 81 eyes of 41 healthy adult volunteers. Patients with ocular eye disease, previous refractive or intraocular surgery, contact lenses, or topical or general medications were excluded. Methods: Patients underwent four ORA, three OPA, and two Goldmann Applanation Tonometry (GAT) measurements. For each device, the mean of all measurements were considered for this study. The statistical analysis by Spearman rank correlations was performed for right (RE), left (LE), and both eyes. The correlation between the two eyes of each subject was taken into account and canonical correlations were calculated using the SAS statistical software to improve the power of the analysis. Results: The mean age was 43.6 +/- 14.6 years. The mean central corneal thickness was 545 +/- 32 mu m for RE, 553 +/- 34 mu m for LE, and 550 +/- 32 mu m for both eyes. The mean IOP(GAT) values for RE, LE, and both eyes were, respectively 14.3 +/- 2.9 mmHg, 14.0 +/- 2.9 mmHg, and 14.2 +/- 2.9 mmHg. Spearman correlations were not statistically significant for separated RE and LE analysis. For both eyes, these correlations were r(S) = 0.210, p = 0.193 for OPA/CH and r(S) = 0.388, p = 0.013 for CPA/CRF. The Spearman correlation was statistically significant for OPA/CRF. This result was confirmed by canonical correlations (p = 0.002) and in addition, CH was statistically correlated to OPA in the latter analysis (p = 0.010). Conclusion: A statistically significant correlation was found between corneal biomechanical property values as measured by ORA(R) and ocular pulse amplitude values as measured by PDCT in healthy subjects.