Are multifocal VEP findings in glaucoma suspects consistent with structural findings?

Abstract

Abstract: : Purpose: There is recent evidence that the multifocal VEP (mfVEP) can detect field defects in glaucoma suspect (GLS) eyes that are not detected by achromatic automated perimetry. [1] Here we compare mfVEP results to structural measures of the neural rim of the optic nerve head in GLS patients with normal achromatic perimetry results. Methods: Twenty–three GLS patients (46 eyes) with glaucomatous optic discs were included in this study. The criteria for GLS included vertical cup–disc ratio ≥0.6, and/or a disc asymmetry ≥0.2, and/or peripapillary nerve fiber layer defect, and/or focal disc notching, and/or disc hemorrhage. All patients had normal achromatic perimetry, as defined by a PSD within 95% and a glaucoma hemifield test within normal limits on the Humphrey visual field (HVF) 24–2 program. Monocular mfVEPs were obtained from each eye using a pattern–reversal dartboard array, 44.5 deg in diameter, and containing 60 sectors. Recording electrodes were placed at the inion (I) and I+4 cm, and at two lateral locations up 1 cm and over 4 cm from I. Monocular and interocular analyses were performed. [2,3] For the mfVEP a hemifield was defined as abnormal based on the following cluster test: 3 or more contiguous points had p<0.05 and at least one of these points had p<0.01. [3,4] Optic discs were assessed with a confocal scanning laser ophthalmoscope (HRT–II). The image of the optic nerve head was divided into six sectors. The rim and disc area measurements for each sector were compared to a normal database using Moorfields regression analysis. [5] For the HRT a hemifield was classified as abnormal if the percentage of the rim area was lower than the 99.9% limit for the respective sector(s). Results: Of the 46 eyes, 18 had mfVEP field defects and 19 had defects on HRT testing. Of the 92 hemifields (46 eyes x 2 hemifields), 55 were normal and 14 were abnormal on both tests. There was agreement for both tests for 75 % of the hemifields. The disagreements were approximately equally divided between abnormal hemifields on HRT which were normal on mfVEP (n=11) and normal hemifields on HRT which were abnormal on mfVEP (n=12). Conclusions: There was modest agreement between the measures of structure and function; however some abnormalities found on mfVEP testing were not found on HRT and vice versa. Refs: 1. Thienprasiddhi (2003) ARVO . 2. Hood et al (2002) AO. 3.Hood and Greenstein (2003) Prog Ret Eye Res. 4. Goldberg et al (2002) AJO.5. Wollstein et al. (1998) Ophthal.

Keywords: electrophysiology: clinical • imaging/image analysis: clinical • ganglion cells