Poster Presentation

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

Professor Cai Yu
The First Hospital of Peking University

Abstract

Purpose

To evaluate the association between corneal biomechanical parameters and visual field (VF) progression in normal tension glaucoma (NTG) using a 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 device 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 visit (per 3-6 months). Corneal biomechanical parameters were compared between progressive and nonprogressive eyes using the independent-sample t test and Mann-Whiteny U test. Spearman correlation analysis was used to explore the relationship between the corneal biomechanical parameters and the VF progression. Receiver operating characteristic curves (ROC) 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 on schedule. Eleven of them were excluded by one or more uncontrolled intraocular pressure (IOP) during follow-up (IOP reduction less than baseline 30%). 37 eyes of 37 diagnosed NTG patients were enrolled. Ten eyes reached a progression endpoint. There were no significant difference in age, CCT, axial length, baseline IOP and baseline VF between the two groups. There were significant lower Time A1 (7.10±0.17 msvs. 7.37±0.28 ms, P=0.002), Length A1 (1.74[1.61-1.77] mm vs. 1.78 [1.77-1.79] mm, P=0.002) and significant higher Velocity A1(0.16 [0.141-0.161] m/s vs. 0.15 [0.142-0.150] m/s, P=0.009), DefAmpl HC(1.22±0.13 mm vs. 1.12±0.11 mm, P=0.013) in progressive eyes compared with nonprogressive eyes. There was no significant difference in other parameters between the two groups. Correlation analysis showed that Time A1, Length A1, Velocity A1 and DefAmpl HC were correlated with VF progression.Time A1 demonstrated the highest AUC which was at 0.817(P=0.001) among Time A1, Length A1, Velocity A1 and DefAmpl HC. The cut-off set of Time A1 was 7.2ms and the sensitivity was 80%, specificity was 82.8%, respectively. The AUC of Length A1 (0.78, P=0.003), Velocity A1 (0.734, P=0.012) and DefAmpl HC (0.713, P=0.022) respectively.

Conclusions

There were differences in corneal biomechanical parameters between progressive eyes and nonprogressive eyes of VF in patients with NTG. There were lower Time A1, Length A1 and higher Velocity A1, DefAmpl HC in progressive eyes. This indicates that quicker response to reach first-degree applanation and larger degree of corneal deformability in progressive eyes. It's predicted that the more easily deforming of cornea, the smaller tolerance of sclera and lamina cribros on IOP, which lead to the optic disc more vulnerably, either. 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 which were obtained by Corvis-ST.