The wide field multifocal ERG reveals a retinal defect caused by vigabatrin toxicity

Retinal nerve fibre layer attenuation: clinical indicator for vigabatrin toxicity

PURPOSE

To investigate whether persistent visual field defects among patients exposed once to the antiepileptic drug vigabatrin (VGB) were associated with peripapillary retinal nerve fibre layer thickness (RNFLT) attenuation.

METHODS

Nine individuals with partial epilepsy and VGB-attributed visual field loss (group 1; 18 eyes) and seven age- and gender-matched individuals with epilepsy and no previous VGB exposure (group 2; 14 eyes) were included in the study. Full-field 120 point screening perimetry out to 60 degrees from central fixation using the Humphrey Field Analyzer was performed. RNFLT was quantified by optical coherence tomography (OCT) using Fast RNFLT protocol, Stratus OCT (3.0) after pupillary dilation. The results from the right eye are presented in this article.

RESULTS

Among the patients with VGB-attributed visual field loss, five patients had only peripheral field defect (group 1a) and the remaining four had advanced field defects both in the periphery and within 30° from central fixation (group 1b). None of the patients in the control group had manifest visual field loss. The mean RNFLT among the patients with VGB-attributed visual field loss was significantly attenuated compared to the controls [mean total RNFLT: group 1: 75.6 ± 12.7 μm, group 2: 103.5 ± 9.7 μm, mean difference 27.9 μm, (CI 15.9-39.9; p < 0.001)]. RNFLT values classified as borderline according to normative database (Stratus OCT) occurred more frequently among individuals with VGB-attributed visual field loss than in controls (frequency in group 1: 6/9; group 2: 0/7, p = 0.011). The nasal, superior and inferior quadrants of RNFLT in individuals with VGB-attributed visual field loss were significantly attenuated, while no difference was detected in temporal quadrants compared to controls. Both individuals with peripheral and those with advanced visual field losses in the VGB group had attenuated mean total RNFLT compared to controls (p = 0.006, p = 0.002, respectively). Occurrence of borderline classification of total RNFLT ≤5th percentile was more frequent among individuals with advanced visual field loss than among controls (p = 0.048).

CONCLUSION

Persistent visual field loss attributed to VGB is associated with reduced peripapillary RNFLT and was detected both among patients with advanced and among patients with only peripheral visual field defects. Measurements of RNFLT with OCT might be considered as a diagnostic supplement in the follow-up of patients exposed to vigabatrin.

Binasal visual field defects are not specific to vigabatrin

This study investigated the visual defects associated with the antiepileptic drug vigabatrin (VGB). Two hundred four people with epilepsy were grouped on the basis of antiepileptic drug therapy (current, previous, or no exposure to VGB). Groups were matched with respect to age, gender, and seizure frequency. All patients underwent objective assessment of electrophysiological function (wide-field multifocal electroretinography) and conventional visual field testing (static perimetry). Bilateral visual field constriction was observed in 59% of patients currently taking VGB, 43% of patients who previously took VGB, and 24% of patients with no exposure to VGB. Assessment of retinal function revealed abnormal responses in 48% of current VGB users and 22% of prior VGB users, but in none of the patients without previous exposure to VGB. Bilateral visual field abnormalities are common in the treated epilepsy population, irrespective of drug history. Assessment by conventional static perimetry may neither be sufficiently sensitive nor specific to reliably identify retinal toxicity associated with VGB.

The clinical applications of multifocal electroretinography: a systematic review

Multifocal electroretinography (mfERG) is an investigation that can simultaneously measure multiple electroretinographic responses at different retinal locations by cross-correlation techniques. mfERG therefore allows topographic mapping of retinal function in the central 40-50 degrees of the retina. The strength of mfERG lies in its ability to provide objective assessment of the central retinal function at different retinal areas within a short duration of time. Since the introduction of mfERG in 1992, mfERG has been applied in a large variety of clinical settings. This article reviews the clinical applications of mfERG based on the currently available evidence. mfERG has been found to be useful in the assessment of localized retinal dysfunction caused by various acquired or hereditary retinal disorders. The use of mfERG also enabled clinicians to objectively monitor the treatment outcomes as the changes in visual functions might not be reflected by subjective methods of assessment. By changing the stimulus, recording, and analysis parameters, investigation of specific retinal electrophysiological components can be performed topographically. Further developments and consolidations of these parameters will likely broaden the use of mfERG in the clinical setting.

Surveillance électrophysiologique des patients épileptiques traités par Vigabatrin

Vigabatrin is a GABA mimetic antiepileptic agent that has been used for 10 years in cases of epilepsy that resist other treatments. Since 1997, concentric visual field defects have been reported. Before any visual symptom complaint, they quickly become irreversible and highly disabling. To prevent this visual impairment, the monitoring protocol must be defined with reliable and well-supported tests, so that patients treated with Vigabatrin can be regularly monitored. Our purpose was to know if EOG impairments were frequent, if their severity was proportional to visual impairment, and if the Arden ratio could be a predictive criterion of Vigabatrin toxicity. Seventy-two patients treated with Vigabatrin for 2-10 years were examined, and EOG results were compared with a normal population EOG and then the patient's visual field. The monitoring protocol proposed includes EOG, which seems to be the most sensitive and specific diagnostic tool for screening Vigabatrin-treated patients.