The association between corneal biomechanical parameters and visual field progression in patients with normal tension glaucoma

Abstract

Objective: To evaluate the association between corneal biomechanical parameters and visual field (VF) progression in normal tension glaucoma (NTG) using the Corvis-ST device, and to evaluate the ability of corneal biomechanical parameters to predict the VF progression. Methods: Corneal biomechanical parameters of newly diagnosed NTG patients were obtained using Corvis-ST in the baseline follow-up visit. The VF progression was defined as a 4-point increase in the Advanced Glaucoma Intervention Study (AGIS) score compared to the baseline in three consecutive follow-up visits (per 3-6 months). Corneal biomechanical parameters were compared between progressive and nonprogressive VF loss eyes using the independent-sample t test and Mann-Whitney U test. Spearman correlation analysis was used to explore the relationship between the corneal biomechanical parameters and the VF progression. Receiver operating characteristic curves were studied for the parameters and the sensitivity and specificity for distinguishing between progressive and nonprogressive glaucomatous eyes. The areas under the receiver operating characteristic curves (AUC) were also evaluated. Results: Sixty patients with NTG were enrolled in this study. Among them, 12 were lost to follow-up. A total of 48 patients completed all follow-up visits on schedule. Eleven of them were excluded due to one or more uncontrolled intraocular pressure (IOP) during the follow-up (less than 30% IOP reduction from the baseline). Thirty-seven eyes of 37 diagnosed NTG patients were enrolled. Ten eyes reached a progression endpoint. There was no significant difference in age, central corneal thickness, axial length, baseline IOP or baseline VF between the two groups. There was significant difference in Time A1 [(7.10±0.17) ms vs. (7.37±0.28) ms, t=-3.357, P=0.002], Length A1 [1.74(1.61, 1.77) mm vs. 1.78(1.77, 1.79) mm, Z=-3.036, P=0.002], Velocity A1 [0.16(0.14, 0.16) m/s vs. 0.15(0.14, 0.15) m/s, Z=-2.627, P=0.009] and DefAmpl HC [(1.22±0.13) mm vs. (1.12±0.11) mm, t=2.601, P=0.013] between progressive and nonprogressive glaucomatous eyes. Correlation analysis showed that Time A1, Length A1, Velocity A1 and DefAmpl HC were correlated with VF progression (r=-0.521, -0.463, 0.401, 0.349, P<0.05) . Time A1 demonstrated the highest AUC (0.817, P=0.001), followed by Length A1 (0.780, P=0.003), Velocity A1 (0.734, P=0.012) and DefAmpl HC (0.713, P=0.022). The cut-off set of Time A1 was 7.2 ms, the sensitivity was 80.0%, and the specificity was 82.8%. Conclusions: There were differences in corneal biomechanical parameters between eyes with progressive and nonprogressive VF loss in patients with NTG. There were lower Time A1 and Length A1 values and higher Velocity A1 and DefAmpl HC values in progressive glaucomatous eyes. This indicates a quicker response to reach first degree applanation and a larger degree of corneal deformability in progressive eyes. It is predicted that the easier deforming of the cornea, the smaller tolerance of the sclera and lamina cribros on IOP, making the optic disc more vulnerably. This may be one of the causes of glaucomatous optic nerve damage. Time A1 was the best parameter to predict the progression of VF among the corneal biomechanical parameters obtained by Corvis-ST. (Chin J Ophthalmol, 2018, 54: 171-176).