Applications of Isolated-Check Visual Evoked Potential in Early Stage of Open-Angle Glaucoma Patients

Abstract

Background: Standard automated perimetry does not sufficiently detect early open-angle glaucoma (OAG) in the clinic. New visual function tests for early glaucoma damage are therefore needed. The present study evaluated whether an isolated-check visual evoked potential (icVEP) could be used to detect visual function abnormalities in early-stage OAG and to explore potential related factors.

Methods: This was a cross-sectional study. Thirty-seven OAG patients with early-stage visual field loss (mean deviation ≥ -6.00 dB) detected by the Humphrey Field Analyzer (30-2 SITA program) and 26 controls were included in this study. Optical coherence tomography (OCT) was used to detect retinal nerve fiber layer (RNFL) defects. The icVEP preferentially evaluates the magnocellular-ON pathway. VEPs were recorded and signal-to-noise ratios (SNRs) were derived based on multivariate analysis. Eyes that yielded an SNR ≤1 were considered abnormal. Receiver operating characteristic (ROC) curve analysis was used to estimate the accuracy of group classification. Correlations between SNRs and related factors were analyzed.

Results: Based on an SNR criterion of 1, the icVEP had a sensitivity of 62.2% and a specificity of 92.3% for diagnosing early-stage OAG with 74.6% classification accuracy. The ROC curve analysis, however, suggested that an SNR criterion of 0.93 would produce the highest classification accuracy (77.3%). Both RNFL thinning in the temporal superior quadrant on OCT and number of abnormal test points in the central 11° visual field (pattern deviation, P < 0.5%) significantly correlated with the SNR (P < 0.05).

Conclusions: The icVEP detected visual function abnormalities in approximately 3/5 of eyes with early-stage OAG with greater than 90% specificity. SNR correlated with both a decrease in RNFL thickness and severity of central visual field loss.

Keywords: Cross-Sectional Study; Isolated-Check; Open-Angle Glaucoma; Signal-To-Noise Ratios; Visual Evoked Potential.

Figure 1

The results of a typical case of early-stage OAG: (a) Abnormal icVEP results; (b) outcomes of peripapillary RNFLT classification on the report of OCT. Thickness change in RNFL = RNFLT value (black number) − the standard value from a database of normal people (green number in brackets); (c) Central 16 test points of the pattern deviation on the Humphrey Field Analyzer 30-2 SITA program corresponding to central 11° visual field. RNFL: Retinal nerve fiber layer; RNFLT: Retinal nerve fiber layer thickness; OCT: Optical coherence tomography; G: Global; N: Nasal; T: Temporal; NS: Nasal superior; TS: Temporal superior; NI: Nasal inferior; TI: Temporal inferior; icVEP: Isolated-check visual evoked potential; OAG: Open-angle glaucoma.

Figure 2

Example of a bright-check condition (positive contrast) on a screen of the icVEP. icVEP: Isolated-check visual evoked potential.

Figure 3

The diagrammatic sketch of the icVEP examination. icVEP: Isolated-check visual evoked potential; GND: Grounding electrode; Cz: Central midline; Pz: Parietal midline; Oz: Occipital midline.

Figure 4

ROC curve for the data collected from the SNR of icVEP of OAG patients and controls. ROC: Receiver operating characteristic; SNR: Signal-to-noise ratios; icVEP: Isolated-check visual evoked potential; OAG: Open-angle glaucoma.