An ultra-high-speed Scheimpflug camera for evaluation of corneal deformation response and its impact on IOP measurement.

PURPOSE: To investigate the test-retest variability of and factors associated with the corneal deformation response, and evaluate its impact on IOP measurement.
METHODS: Forty normal and 140 glaucoma suspect/glaucomatous eyes of 104 individuals were prospectively included for repeated measurements of corneal deformation response by an ultra-high-speed Scheimpflug camera, followed by corneal hysteresis and corneal resistance factor measurements by the ocular response analyzer, and dynamic contour tonometry (DCT) (the reference standard) and Goldmann applanation tonometry (GAT) during the same visit. The test-retest variability of corneal deformation response was evaluated. Univariate and multivariate linear mixed models were used to identify factors (age, manifest spherical refractive error, axial length, IOP, central corneal thickness [CCT], corneal curvature, corneal hysteresis, and corneal resistance factor) associated with corneal deformation response and the difference between DCT and GAT measurements.
RESULTS: Corneal deformation amplitude (CDA) had an intraclass correlation coefficient of 0.86. There was no difference in CDA between the glaucoma and nonglaucoma groups. A higher IOP, a younger age, and a greater CCT were associated with a smaller CDA (P ≤ 0.002) (n = 180). In the univariate analysis (n = 180), the difference between DCT and GAT measurements was associated with spherical refractive error (P = 0.037), CCT (P = 0.004), and CDA (P < 0.001) after adjusting the effect of IOP (DCT). In the multivariate analysis, the only factor associated with the IOP difference was CDA (P = 0.003).
CONCLUSIONS: CDA was a reliable indicator to quantify corneal deformation response. CDA, rather than CCT, was the key source of measurement error of GAT.