Author: Andre Messias
Co-authors: Germano Dalfito, Renata Moretto, Jayter Paula
Abstract
PurposeThere is no definitive indication for what best sensitive ERG protocol should be used to investigate retinal function abnormalities in glaucoma, but it has been shown that eyes with optic nerve disorders show abnormalities on luminance-response amplitude interrelation, therefore in this study we aim to report the light-adapted full-field ERG luminance-response in glaucoma patients at early phase.
Methods
Nine patients (n=9 eyes) with primary open-angle glaucoma but preserved visual acuity and no other ocular disease were evaluated. Patients yielded visual field test (Humphrey – Zeiss; SITA-Fast 24-2) and spectral-domain optical coherence tomography (Heidelberg) measuring peripapillary retinal nerve fiber layer thickness (RNFL). Full-field ERG (RETeval, LKC) was recorded using skin electrodes and fully dilated pupils with a short “photopic-Hill” protocol using a series of 8 flash stimuli logarithmically spaced from 0.1 to 22 cd·s/m2. b-wave amplitude was fit as function of flash strength using a Gaussian model, to determine maximal b-wave amplitude (Vmax), flash strength at Vmax (x0), and width of the Gaussian component (w). Data were compared with 9 healthy subjects (control) in the same age range.
Results
All subjects showed visual acuity of 20/20, visual field mean deviation was -5.5 ±1.7 dB and RNFL thickness 93.5 ± 16.5 µm. Comparing glaucoma subjects to controls (mean ± SEM), the following measurements did not show a statistically significant difference: dilated pupil diameter 6.6 ± 0.35 mm vs. 6.8 ± 0.3 mm (p=0.3), and x0 6.4 ± 0.9 cd·s/m2 vs. 4.4 ± 0.8 cd·s/m2 (p=0.1). In contrast, these measures did show differences: Vmax 22.5 ± 3.8 µV vs. 36.2 ± 3.7 (p=0.02), and w 8.2 ± 0.5 cd·s/m2 vs. 5.0 ± 0.5 for CTRL (p=0.0006). No significant correlation was found between photopic hill parameters and pupil size, visual field MD, age or RNFL thickness.
Conclusions
These data indicates that parameters derived from luminance-response series, which measure cone-driven function, is changed in subjects with early glaucoma. While our sample size is small, the width of the ERG photopic hill shows promise in the early detection of glaucoma.