Gordon N. Dutton

Peripheral retinal dysfunction in patients taking vigabatrin

Objective: To assess the wide-field multifocal electroretinogram (WF-mfERG) for assessment of retinal function in vigabatrin-treated patients. Methods: Thirty-two adults who had taken vigabatrin for at least 3 years for localization-related epilepsy underwent WF-mfERG, ERG, logMar visual acuity and color vision evaluation, Humphrey visual field analysis (static perimetry), and funduscopy. The group was matched with a cohort of patients who had never received vigabatrin. Results were compared with a normative data set (120 drug-free controls) with respect to potential bilateral abnormalities in response timing. Results: There were no significant differences between groups in visual acuity or color vision testing. Of the vigabatrin patients, 19 (59%) had bilateral visual field defects compared to none of the controls. Using WF-mfERG, all patients on vigabatrin with visual field defects showed abnormalities (100% sensitivity) and only 2 of the 13 patients without a field defect showed retinal abnormalities (86% specificity). Conclusions: WF-mfERG may be useful for detecting retinal pathology in patients taking vigabatrin. The majority of previous reports based on subjective testing may have underestimated the prevalence of peripheral retinal toxicity related to the drug.

Evidence that children with special needs all require visual assessment

Design A protocol-based ophthalmological assessment was performed on-site by a skilled investigator. Patients Children attending schools for special needs in Glasgow were offered eye care within their school. Outcomes for the first 240 participants are reported. Outcome measures Number of children for whom visual acuity could be measured and the results of refraction. Results 228/240 (95%) children were able to co-operate in a complete or nearly complete assessment of visual function. Visual acuity could be reliably assessed in 190 children using a range of tests from preferential looking to logMAR charts. 23/190 (12.1%) were found to be visually impaired according to WHO criteria. 105/228 (46.1%) subjects were found to have a refractive error which required correction. 50/105 subjects were wearing an adequate correction (ie, difference of less than 0.75 D sphere or cylinder compared with the retinoscopy result obtained on screening) and 55 (24.1%) children were prescribed a new correction. The prevalence of all types of refractive error was found to be significantly higher in the population with special needs, in particular the learning disabilities subgroup, compared with normal children. High hyperopia and astigmatism were common. Conclusion With patience, suitably adapted methods, a familiar environment and skill, visual assessment is feasible in the majority of children with special needs. The prevalence of reduced visual acuity is high and unaddressed correctable refractive error is a major cause.

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.

Wide field multifocal and standard full field electroretinographic features of hemi retinal vein occlusion.

The purpose of this study was to document the standard full field electroretinographic (ERG) and wide field multifocal electroretinographic (WF-mfERG) findings in eyes with recent onset hemi-retinal vein occlusion (HRVO) and to compare the electro-diagnostic findings in the affected and fellow eyes with reference to normative data. Eight patients with HRVO were assessed using ERG and WF-mfERG. WF-mfERG first order responses from the affected hemi-retinae and the unaffected hemi-retinae in each affected eye were compared. WF-mfERG responses from each affected hemi-retina and from the symmetrical hemi-retina of each fellow eye were compared. ERG responses between affected and unaffected eyes were also compared. All electrodiagnostic tests were compared to normative data (5–95% confidence limits derived from age-related controls). WF-mfERG P1 and N1 implicit times were greater for the affected hemi-retinae than for the unaffected hemi-retinae (p <0.05). WF-mfERG N1 and P1 implicit times were prolonged (p < 0.05) and WF-mfERG P1/N1 amplitude ratios were significantly reduced (p < 0.05) for the affected eyes when compared with the fellow eyes. Maximal b-wave, cone b-wave and flicker implicit times were prolonged (p < 0.05) when comparing affected and fellow eyes. These results indicate that retinal injury due to HRVO culminates in significant delay of both ERG and WF-mfERG implicit times. These results suggest that WF-mfERG in combination with ERG may have a role in the management of HRVO.

Blindsight in children: does it exist and can it be used to help the child? Observations on a case series

Damage to the occipital lobe of the brain results in hemianopia when unilateral, and cerebral blindness when bilateral. However, in some cases a degree of visual function persists in the blind visual field. This aim of this study was to describe this phenomenon of‘blindsight’in a cohort of children with brain‐damage and to relate the clinical features to their visual evoked potentials. We performed a retrospective analysis of 541 case records of children referred to a tertiary vision‐assessment clinic in the Royal Hospital for Sick Children, Glasgow, UK from 1992 to 2002. A total of 541 patients were analyzed (243 females, 298 males; age range 2mo to 19y 6mo, mean 6y 2mo). In 19 children with profound visual impairment and four children with hemianopia (12 females, 11 males; age range 1 to 18y, mean age 8y 3mo), evidence of perception of movement in the blind visual field was found and is described. Flash visual evoked potentials varied from no response to normal and was not correlated with visual behaviour. Recognition, detection, and use of this phenomenon in children is vital to their rehabilitation and interaction with their surroundings.

Argon laser photocoagulation of fluorescein stained retina--an unrecognised hazard?

Sodium fluorescein staining of the retina following fluorescein angiography may affect the absorption characteristics of argon ion laser photocoagulation. This hypothesis was investigated by performing laser photocoagulation on control and fluorescein stained porcine retinas. The resultant damage was viewed by scanning electron microscopy. In both specimens, argon irradiation produced damage to the pigment epithelium and overlying photoreceptor layer. The control sample showed a deep cylindrical burn, indicative of internal heating, in both retina and choroid. The fluorescein stained sample showed damage consistent with thermal interaction from the surface downwards leaving the choroid relatively spared. This preliminary study demonstrates that fluorescein staining of the retina changes the absorption site of argon laser light and this subject clearly merits further investigation.