Full-field ERG and visual fields in patients 5 years after discontinuing vigabatrin therapy

Autosomal recessive Stickler syndrome associated with homozygous mutations in the COL9A2 gene

Background: Stickler syndrome is a hereditary disorder of collagen tissues causing ocular, auditory, orofacial, and joint manifestations. Ocular findings typically include vitreous degeneration, high myopia, retinal detachment, and cataract. Many subjects demonstrate sensorineural or conductive hearing loss. The inheritance is autosomal dominant with mutations in COL2A1, COL11A1, or COL11A2 or autosomal recessive due to mutations in COL9A1, COL9A2, or COL9A3. We describe a family with Stickler syndrome caused by homozygous loss-of-function mutations in COL9A2.Methods: Two brothers from a consanguineous family were examined with genetic testing, visual acuity, Goldmann perimetry, full-field and multifocal electroretinography (ffERG, mERG), optical coherence tomography (OCT), fundus autofluorescence (FAF), fundus photography, and pure-tone audiograms.Results: Both subjects were homozygous for the mutation c.1332del in COL9A2. Their parents were heterozygous for the same mutation. The boys demonstrated reduced visual acuity, vitreous changes and myopia. The proband was operated for retinal detachment and cataract in one eye. FfERG revealed reduced function of both rods and cones and mERG showed reduced macular function. No morphological macular changes were found by OCT or FAF. Both brothers have severe sensorineural hearing loss with down-sloping audiograms but only subtle midface hypoplasia and no, or mild joint problems.Conclusion: Only a few families with Stickler syndrome caused by COL9A2 mutations have been reported. We confirm previous descriptions with a severe ocular and auditory phenotype but mild orofacial and joint manifestations. Moreover, we demonstrate reduced macular and overall retinal function explaining the reduced visual acuity in patients with Stickler syndrome also without retinal complications.

Vigabatrin-Induced Retinal Functional Alterations and Second-Order Neuron Plasticity in C57BL/6J Mice

Purpose

Vigabatrin (VGB) is an effective antiepileptic that increases concentrations of inhibitory γ-aminobutyric acid (GABA) by inhibiting GABA transaminase. Reports of VGB-associated visual field loss limit its clinical usefulness, and retinal toxicity studies in laboratory animals have yielded conflicting results.

Methods

We examined the functional and morphologic effects of VGB in C57BL/6J mice that received either VGB or saline IP from 10 to 18 weeks of age. Retinal structure and function were assessed in vivo by optical coherence tomography (OCT), ERG, and optomotor response. After euthanasia, retinas were processed for immunohistochemistry, and retinal GABA, and VGB quantified by mass spectrometry.

Results

No significant differences in visual acuity or total retinal thickness were identified between groups by optomotor response or optical coherence tomography, respectively. After 4 weeks of VGB treatment, ERG b-wave amplitude was enhanced, and amplitudes of oscillatory potentials were reduced. Dramatic rod and cone bipolar and horizontal cell remodeling, with extension of dendrites into the outer nuclear layer, was observed in retinas of VGB-treated mice. VGB treatment resulted in a mean 3.3-fold increase in retinal GABA concentration relative to controls and retinal VGB concentrations that were 20-fold greater than brain.

Conclusions

No evidence of significant retinal thinning or ERG a- or b-wave deficits were apparent, although we describe significant alterations in ERG b-wave and oscillatory potentials and in retinal cell morphology in VGB-treated C57BL/6J mice. The dramatic concentration of VGB in retina relative to the target tissue (brain), with a corresponding increase in retinal GABA, offers insight into the pathophysiology of VGB-associated visual field loss.

VIGABATRIN TOXICITY IN INFANCY IS ASSOCIATED WITH RETINAL DEFECT IN ADOLESCENCE: A Prospective Observational Study

PURPOSE

The purpose was to determine whether vigabatrin (VGB) (Sabril)-attributed retinal toxicity defined by electroretinogram in early childhood is associated with visual system defect in adolescents after discontinuation of VGB.

METHODS

This prospective cross-sectional study included 24 children previously treated with VGB and monitored in early childhood by electroretinogram for VGB-attributed retinal defects. Ten had been diagnosed with VGB-attributed retinal defect (Group I) and 14 had no VGB-attributed retinal defect (Group II). Outcome measures were extent of monocular visual fields using Goldmann kinetic perimetry and RNFL thickness at the optic nerve head, using optical coherence tomography.

RESULTS

Of those able to complete testing (6 eyes Group I and 16 eyes Group II), Goldmann results revealed results of visual field loss in Group I and not in Group II. The optical coherence tomography results demonstrated attenuation of the RNFL in all 6 eyes of Group I participants and in only 1 eye of 10 Group II participants. Optical coherence tomography data were nonoverlapping between Group 1 and Group II eyes.

CONCLUSION

The VGB-attributed retinal toxicity identified by means of electroretinogram in infancy was associated with visual field loss and RNFL attenuation of the retinal nerve when tested in adolescence.

Attenuation of the retinal nerve fibre layer and reduced retinal function assessed by optical coherence tomography and full-field electroretinography in patients exposed to vigabatrin medication

PURPOSE

To investigate the clinical value of assessment of peripapillary retinal nerve fibre layer (RNFL) thickness with OCT in addition to the evaluation of retinal function measured by full-field electroretinography (ff-ERG) in patients with suspected vigabatrin (VGB)-attributed visual field defects.

METHODS

Visual fields from adult patients in our clinical follow-up program for VGB medication were analysed. Twelve patients with suspected VGB-attributed visual field defects were selected for the study. They were re-examined with computerized kinetic perimetry, ff-ERG and OCT (2D circle scan).

RESULTS

Constricted visual fields were found in all patients. Comparative analysis of ff-ERG parameters showed reduced b-wave amplitudes for the isolated and the combined rod and cone responses (p < 0.0001). The a-wave, reflecting photoreceptor activity, was reduced (p = 0.001), as well as the summed amplitude of oscillatory potentials (p = 0.029), corresponding to inner retinal function. OCT measurements demonstrated attenuation of the RNFL in nine of 12 patients, most frequently superiorly and/or inferiorly. No temporal attenuation was found. Significant positive correlations were found between the total averaged RNFL thickness, superior and inferior RNFL thickness and reduced ff-ERG parameters. Positive correlations were also found between RNFL thickness and isopter areas.

CONCLUSION

OCT measurements can detect attenuation of the RNFL in patients exposed to VGB medication. RNFL thickness correlates with reduced ff-ERG parameters and isopter areas of constricted visual fields, indicating that VGB is retino-toxic on several levels, from photoreceptors to ganglion cells. The study also supports previous studies, suggesting that OCT measurement of the RNFL thickness may be of clinical value in monitoring patients on vigabatrin therapy.

Electrophysiological evaluation of retinal function in children receiving vigabatrin medication

PURPOSE

To evaluate retinal function in children taking vigabatrin and to explore the influence of age and dose parameters on the results of full-field electroretinography (ff-ERG).

METHODS

The ff-ERGs from 14 children receiving vigabatrin were compared with ff-ERGs from healthy controls. Treated children were further grouped according to age (pre-school = 12-71 months; older = 72-228 months). Parameters of drug dosage were compared.

RESULTS

Treated children showed rod and cone dysfunction reflected by reduced b-wave amplitudes for the isolated rod response, the combined rod-cone response, and the 30-Hz flicker response. The a-wave amplitude and implicit time for the combined rod-cone response, reflecting photoreceptor function, were also altered. Further evaluation of age groups revealed similar findings in the pre-school group but not in the older group. Alterations in ff-ERG were seen in 57% of the treated children. Pre-school children had received significantly higher daily drug doses with start of medication at younger age. No differences were found concerning cumulative doses or duration of medication.

CONCLUSION

Alterations in ff-ERG are as frequent in children as in adults and the results indicate that exposure to high daily doses of vigabatrin may be associated with increased risk of retinal dysfunction, including photoreceptor damage, not previously shown in children. Thus, recommendations of careful follow-up for children receiving vigabatrin are supported.

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.

The safety and tolerability of newer antiepileptic drugs in children and adolescents

The newer antiepileptic drugs (AEDs) provide more therapeutic options and overall improved safety and tolerability for patients. To provide the best care, physicians must be familiar with the latest tolerability and safety data. This is particularly true in children, given there are relatively fewer studies examining the effects of AEDs in children compared with adults. Since we now have significant paediatric literature on each of these agents, we provide a comprehensive and current literature review of the newer AEDs, focusing on safety and tolerability data in children and adolescents. Because the safety profiles in children differ from those in adults, familiarity with this literature is important for child neurologists and other paediatric caregivers. We have organized the data by organ system for each AED for easier reference.