Decreases in cone sensitivity are associated with vigabatrin treatment

Abstract

Vigabatrin (VGB) is an anti-epileptic drug used to treat Infantile Spasms (IS). 30% of adult patients treated with VGB develop a constricted visual field¹. Treatment with VGB is associated also with a reduction in the 30 Hz flicker response amplitude of the electroretinogram (ERG) in 20-30% of infants treated. It is believed that this reduction may be an electrophysiological surrogate for a visual field defect^2,3. A retrospective cohort study of 118 ERGs recorded from 65 children, diagnosed with IS and treated with VGB at The Hospital for Sick Children, was conducted. Photopic responses to a series of flash intensities were collected and data were fit to the Hood and Birch⁴ model for isolating the maximum response and sensitivity of the cone photoreceptor response. 30 Hz Flicker amplitude (uV) was also scored. All data were corrected for age and presence of seizures. Cone maximum response was not significantly affected by VGB use. Cone sensitivity decreased over the course of VGB therapy (ANOVA ; P < 0.05). This decrease persists after discontinuation of the drug (P < 0.001). Although there was no strong correlation between age-adjusted flicker amplitude and age-adjusted cone sensitivity (r2 = 0.0439), it is worth noting that of 16 ERGs recorded from 11 patients with significantly reduced flicker amplitude, 14 showed cone sensitivity loss (mean flicker = -0.309, mean cone S = -39.32). These results suggest that cone sensitivity may be a biomarker of changes due to VGB use.

Acknowledgments

Supported by Vision Science Research Program and Canadian Institute of Health Research Master's Award.