CHANGES IN ULTRASTRUCTURE AND FUNCTION OF THE SHEEP PIGMENT EPITHELIUM AND RETINA INDUCED BY SODIUM IODATE1

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Abstract
The delayed effects on the sheep pigment epithelium and retina of sodium iodate, as studied three days after the injection, included electrophysiological as well as morphological changes. The c‐wave of the ERG was abolished, and the a‐ and b‐waves were substantially reduced in amplitude, which was also the case as early as about 100–150 min after the injection. The cornea‐negative potential earlier having replaced the c‐wave was no longer present, however. In addition to changes in the pigment epithelium seen already at an earlier stage, marked ultrastructural damage was observed also in the neuroretina, particularly in the photoreceptor cells and the Müller cells, but involving all layers except the ganglion cell axons. The receptor outer segments were greatly vesiculated and disorganized and the inner segments vacuolized. The more vitread cells of the retina showed various degrees of oedema with distended mitochondria and a reduced amount of cytoplasmic structures. It appears that the effects on the neuroretina of sodium iodate are to a great extent caused by the insufficient membrane and metabolic properties of the pigment epithelium. From this series of three papers it can be concluded that sodium iodate primarily damaged the pigment epithelium, thereby destroying the structural organization of the latter and abolishing the c‐wave. Later the neuro‐retina was affected, first in the form of a‐ and b‐wave reductions and then also as ultrastructural changes. It thus seems that the early stage after injection of sodium iodate may provide a valuable possibility of studying the electrophysiological effects on the neuroretina of various drugs without interference of the potentials from the pigment epithelium.