Vitamin A deficiency modifies the mfERG: a case study of rod influence on the mfERG.

We report an observational case study which showed that the rod pathway may have a significant effect on the multifocal electroretinogram (mfERG). A 68-year-old lady diagnosed with Vitamin A deficiency underwent standard ERG and mfERG. ERG rod and cone function were analysed and the first order mfERG responses were determined. At presentation, there was no demonstrable rod function on ERG testing and normal cone function. mfERG P1 amplitude responses were normal but mfERG P1 latency responses were significantly delayed. Four weeks after initiating treatment with intramuscular Vitamin A, ERG rod function significantly improved. However, cone amplitude was reduced and the 30 Hz flicker latencies decreased. Furthermore, mfERG P1 latency returned to normal and interestingly mfERG P1 amplitude responses showed a significant reduction. These results alter our understanding of the mfERG response by indicating that there is a possible inhibitory influence on mfERG responses from rod pathway systems.