Abstract
Abstract: :
Purpose: To assess the electrofunctional responses of the retina and visual cortex in patients with ocular hypertension (OHT). Methods: 148 subjects (68 OHT patients, mean age 51.6±7.13 years, and 80 age–matched normal subjects) were enrolled. Normal subjects had IOP < 22 mmHg, normal 24/II HFA visual field (VF), no history of eye or optic nerve disease, no previous ocular surgery, no family history of POAG and a refraction between ± 2 diopters. OHT subjects had an IOP ≥ 22 mmHg without medical treatment on repeated measurements, no history of eye or optic nerve disease, no previous ocular surgery, refraction between ± 2 diopters and normal VF. In all enrolled subjects, we simultaneously recorded Pattern Electroretinograms (PERGs) and Visual Evoked Potentials (VEPs) using high contrast (80%) checkerboard stimuli subtending 60’of visual arc, and reversed at the rate of 2 reversals/s. In OHT patients, PERGs and VEPs were recorded after obtaining an IOP < 22 mmHg by means of topical medical treatment. Our recordings were considered abnormal when exceeding + 3 SD (for implicit times) or – 2 SD (for amplitudes) with respect to mean values observed in the normal population. Results: OHT patients showed PERG and VEP implicit times significantly (ANOVA, P<0.01) delayed and PERG and VEP amplitudes significantly (P<0.01) reduced when compared to normal subjects. PERG P50 implicit time was abnormal in 76% of OHT patients; PERG P50–N95 amplitude was abnormal in 82% of OHT patients; VEP P100 implicit time was abnormal in 85% of OHT patients; VEP N75–P100 implicit time was abnormal in 54% of OHT patients. Retinocortical–time (RCT, difference between PERG P50 and VEP P100 implicit times, an index of neural conduction along postretinal visual pathways) was delayed in 1% of OHT patients. No significant (P>0.01) correlations were found between electrophysiological parameters and age, IOP with or without medical treatment, VF values in OHT patients. Conclusions: These electrofunctional (PERG and VEP) results suggest that OHT patients may show an early dysfunction of the innermost retinal layers, as detected by PERG recordings. On the other hand, neural conduction along postretinal visual pathways is not altered in OHT patients, as suggested by the presence of abnormal VEP implicit times with concomitant normal RCT.
Keywords: electroretinography: clinical • ganglion cells • visual fields