Paradoxical enhancement of the ERG c‐wave by a small dose of sodium iodate

Abstract

The early effects of sodium iodate (NaIO3) on the ERG c- and b-waves were studied in rabbits. When 30 mg NaIO3/kg body weight was administered intravenously, the c-wave amplitude decreased and was replaced by a potential of opposite polarity. However, the administration of 20 mg/kg of NaIO3 enhanced the c-wave remarkably. Twenty min after administration, the mean c-wave amplitude significantly increased (P less than 0.001) to 211 +/- 6.2% of the pre-administration amplitude, whereas that of the control was 108 +/- 13.0%. The b-wave amplitude showed no significant changes. When 10 mg/kg of NaIO3 was administered, the enhancement of the c-wave was not remarkable. These effects were similar in both pigmented and albino rabbits. A lower blood concentration of NaIO3 applied to the basal side of the retinal pigment epithelium (RPE) may initially affect only the basal membrane of the RPE resulting in the decrease in the basal membrane resistance (Rba). This would explain the transient increase in the c-wave amplitude with 20 mg NaIO3/kg.

The Relationship of Central Foveal Thickness to Urinary Iodine Concentration in Retinitis Pigmentosa With or Without Cystoid Macular Edema

“…But at a low concentration injected intravenously in albino and pigmented rabbits sodium iodate acutely and reversibly enhanced the c-wave, which is a physiological measure of RPE integrity. 42 So, perhaps higher physiological levels of iodine could promote RPE integrity in RP patients with intraretinal cysts. Iodine might serve a similar role also in patients with CME secondary to uveitis, who are thought to have lost integrity of the outer blood-retina barrier and RPE pump, 43 or in patients with CME secondary to diabetic retinopathy, given that dysfunction of the outer blood-retina barrier has been observed in diabetic patients.…”

Potassium iodate retinopathy

“…Later it was determined that the iodate ions in the drug produced a disturbance ofretinal pigment epithelium resembling retinitis pigmentosa. Many investigators induced toxic effects on the retinal pigment epithelium in animals by intravenously administering sodium iodate in a dose of 10-40 mg/kg body weight for the purpose of studying the structure and function of pigment epithelium and visual cells (Nilsson et al 1977;Textorius & Wilander 1981;Nao-i et al 1986;Nishimura et al 1990). It has been shown that potassium iodate and sodium iodate have nearly identical oral toxicities.…”