Effect of Recording Duration on Diagnostic Performance of Multifocal Visual Evoked Potentials in High-Risk Ocular Hypertension and Early Glaucoma

Abstract

Purpose:: Evaluate the effect on performance of reducing multifocal visual evoked potential (mfVEP) recording duration from 16 to 8 minutes per eye.

Methods:: Both eyes of 185 subjects with high-risk ocular hypertension or early glaucoma were studied. Pattern-reversal mfVEPs were obtained using VERIS^TM and a 4-electrode array. Two 8-minute recordings were obtained for each eye in an ABBA order. The 1st recording for each eye was compared against 1-Run (1R) mfVEP normative data. The average of both recordings for each eye was compared against 2-Run (2R) normative data. mfVEP abnormalities were defined using 10 clustering criteria. Visual fields were obtained by standard automated perimetry (SAP) within an average of 22.3 days of mfVEP. Stereo disc photographs and Heidelberg Retina Tomograph (HRT) images were obtained at 1 visit, which was within 24.8 days (average) of the mfVEP and 33.1 days (average) of SAP. Two masked experts graded the disk photos as glaucomatous optic neuropathy or normal. The overall Moorfields Regression Analysis from the HRT was used as a separate diagnostic classifier. Thus, 4 diagnostic standards were applied, 2 based on optic disc structure alone and 2 based on disc structure and SAP. Sensitivity (% of abnormal eyes per diagnostic standard that had an abnormal mfVEP) and specificity (% of normal eyes that had a normal mfVEP) were compared for 1R and 2R mfVEPs.

Results:: Approximately 33% fewer eyes were classified as abnormal by the 1R mfVEP, but agreement between 1R and 2R mfVEP classification was near 90% for all cluster types. Diagnostic performance of the 1R mfVEP was similar to that of the 2R mfVEP for all diagnostic standards. Sensitivity was higher for the 2R mfVEP, while specificity was higher for the 1R mfVEP. The lower number of eyes classified as abnormal, as well as the lower sensitivity for the 1R mfVEP, are due to a decrease in the lower limit of normal signal-to-noise ratio (SNR) that results from decreased signal averaging.

Conclusions:: If high sensitivity is sought, 2R mfVEP provides better discrimination for eyes with higher SNR. If specificity is more important, then 1R mfVEP provides adequate sensitivity and requires 50% less test time. Thus 1R mfVEP is an efficient way to confirm (or refute) the extent of visual field loss in patients with moderate or advanced glaucoma, those with unreliable visual fields, malingering or functional visual field loss.

Keywords: electrophysiology: clinical • perimetry • optic disc