Novel method of chronically blocking retinal activity

The ethylene-vinyl acetate copolymer Elvax has been used as a vehicle to de liver bioactive substances to discrete areas of the nervous system. Here we report a novel use of Elvax to chronically block retinal activity. Small p ieces of Elvax containing the sodium channel blocker tetrodotoxin (TTX) wer e surgically implanted into the vitreous humor of ferret eyes. Observations of the light-induced pupillary reflex combined with electrophysiological a ssays of vitreous humor confirmed that these implants completely blocked re tinal activity for up to 25 days without apparent retinal damage. The advan tages of this procedure over previous methods requiring multiple daily inje ctions of TTX, and alternative experimental applications are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.