Changes in the juxtapapillary retinal pigment epithelium following intravenous injection of sodium iodate. A light and electron microscopic study using horseradish peroxidase as a tracer.

The effect of an intravenous injection of sodium iodate on the retinal pigment epithelium immediately surrounding the optic nerve head has been investigated using horseradish peroxidase as a morphological tracer. A sodium iodate injection leads to a necrotic reaction of practically the complete retinal pigment epithelium. The juxtapapillary pigment epithelium, however, showed only attenuation and depigmentation without any necrotic reaction 4 and 12 days after the injection. Twenty-six days following the injection the epithelium had almost normalized. The result of this study thus demonstrates a noteworthy resistance of the juxtapapillary retinal pigment epithelium against the sodium iodate effect. At no stage was there a clear indication of a breakdown of the permeability barrier constituted by the juxtapapillary retinal pigment epithelium. Horseradish peroxidase moved into the peripapillary sensory retina by lateral diffusion from the surrounding retina and diffused into the optic nerve head proper, confirming the presence of a diffusional pathway through the Kuhnt intermediary tissue.