Visual concomitants of retinal spreading depression

The visual concomitants of spreading depression in the chick retina consist of a number of expanding concentric rings of different width and darkness around a stimulated area. The most peripheral ring consists of a narrow dark line. More central follow a light ring, then a wide dark band and most central, a light area. These rings correspond with changes in light reflected from the retina, measured with a microphotometric method (Martins-Ferreira and de Oliveira Castro, 1966). The dark outline and the dark ring correspond with minima of reflected light. It was suggested that the dark rings are caused by swelling of the Müller fibers due to a K+ release from the retinal tissue during SD. The swollen fibers would transport light to the layer of receptors where it is absorved by the choroidea, leaving less light to be reflected to the vitreal surface. The light rings would be due to an increase in reflectivity of neural tissue when invaded by SD. The dark and light bands would be caused by the local dominance of the effects of the swelling of Müller fibers, or of the increase in reflectivity of the neural tissue during SD.