A Comparison of Structural versus Functional Changes in Eyes with Open-angle Glaucoma

Abstract

Abstract: : Purpose: To compare structural changes in the neural rim of the optic nerve head to multifocal visual evoked potential (mfVEP) responses and to achromatic automated perimetry. Methods: Twenty patients with open-angle glaucoma were enrolled in the study. Humphrey 24-2 visual fields (HVF) were obtained from each eye and optic discs were assessed with a confocal scanning laser ophthalmoscope (HRT-II). Monocular mfVEPs were obtained from each eye using a pattern-reversal dartboard array with 60 sectors and a diameter of 44.5 degrees. Recording electrodes were placed at the inion (I) and I+4 cm, and at two lateral locations up 1 cm and over 4 cm. Monocular and interocular analyses were performed to identify locations with abnormal mfVEP responses [1,2]. 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 [3]. If the percentage of the rim area was lower than the 99.9% limit the respective sector was classified as abnormal. The measurements for the six sectors were related to the HVF locations and the 60 sectors of the mfVEP display based on a map defined by Garway-Heath et al [4]. Results: Of 240 sectors tested (40 eyes x 6 sectors), 19% on HVF, 23% on mfVEP and 11% on HRT testing were significantly different from control subjects. There were no significant deficits in 164 sectors. There was agreement for 86% of the sectors when the HVF and mfVEP results were compared, and for 80% of the sectors when either HRT and HVF, or HRT and mfVEP results were compared. Conclusions: Although there was general agreement among measures of structure and function, abnormalities were found on twice as many sectors for mfVEP and HVF testing than on scanning laser ophthalmoscopy. The results suggest that the two measures of visual function may be more sensitive than the measure of optic nerve head structure. 1. Hood et al. (2002) Arch Ophthal 2. Hood and Greenstein (2003), Prog Ret Eye Res. 3. Wollstein et al. (1998) Ophthal. 4. Garway-Heath et al. (2000) Ophthal.

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