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Ananthavalli Kumarappah, Carol A Westall, Arun Reginald, Ray Buncic; Evaluation of Optical Coherence Tomography in Patients with Vigabatrin Toxicity Identified by ERG. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3395.
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Vigabatrin,an antiepileptic drug, is associated with visual field reductions in 30-50% of adults (vigabatrin attributed field loss, VAFL). The 30-Hz flicker electroretinogram (ERG) is recommended for screening young children taking the drug. Vigabatrin ERG reduction (VAER) is reported if there has been significant reduction in age-corrected 30-Hz flicker amplitude from the baseline measurement on two consecutive visits. VAFL has also been associated with peripapillary retinal nerve fibre layer (RNFL) thickness attenuation. The purpose of this study is to evaluate the relationship between VAER in a pediatric population and peripapillary RNFL parameters by optical coherence tomography (OCT). This study also aims to understand changes in the combined ganglion cell layer (GCL) and inner plexiform layer (IPL) in patients with VAER. To date, no other study has reported on GCL/IPL thickness at the macula in vigabatrin patients.
This cross-sectional study includes individuals who were previously on VGB and monitored for toxicity using ERG. Thirteen of 22 individuals were able to undergo OCT testing and four of the 13 individuals developed VAER during treatment. The 13 participants underwent the optic disc (200x200) and macular cube (512x128) scans on the OCT (Cirrus; Carl Zeiss Meditec). Optic disc scan was used to generate RNFL parameters. Based on the macular scan, a ganglion cell analysis (GCA) algorithm generated GCL/IPL thickness parameters.
Individuals with VAER exhibited attenuated global RNFL at the optic disc compared to individuals without vigabatrin toxicity (p<0.0001). Three of four individuals with VAER manifested thinning of the nasal, superior and inferior quadrants in the presence of a normal temporal nerve fiber layer. Spatial mapping by clock hour segments shows that all superior segments are significantly attenuated and that the temporal segments are the least attenuated. GCA did not reveal any differences in the thickness of the GCL/IPL between participant with and without VAER. However, upon spatial analysis, we note a slight reduction in the thickness of the inferior segment of the GCL/IPL.
Visual field testing is difficult in this population due to developmental and cognitive delays. RNFL attenuation correlates strongly with VAER suggesting that OCT imaging may be a potential alternative to ERG testing for monitoring vigabatrin toxicity.
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