Electrophysiological and Anatomical Changes in the Outer Retina After Iodoacetic Acid Injection in the Rabbit

Abstract

Abstract: : Purpose: To study the rabbit model of retinal damage following iodoacetic acid (IAA) injection using electrophysiology and histology. Methods: 19 Dutch–belted rabbits were injected intravenously with IAA (20mg/kg body weight). Electroretinogram (ERG) measurements were recorded pre– and post– IAA injection up to 6 months. Visual evoked potentials (VEP) were recorded 14 days, 28 days, 3 and 6 months after IAA injection. After the VEP measurement, the animals were euthanized and the eyes were enucleated and processed histologically. Specimens were stained with azure II and calbindin to analyze the histological changes occurring in the whole retina and the inner retina (horizontal cells), respectively. Results: The mean ERG amplitude before treatment was 150±32mV (22 eyes). After IAA injection, the mean ERG amplitude decreased significantly to 46±72mV (22 eyes) at 1 hour, 64±40mV (22 eyes) at 1 day, 52±37mV (22 eyes) at 3 days, 63±41mV (22 eyes) at 7 days, 94±49mV (22 eyes) at 14 days, 116±47mV (20 eyes) at 28 days, 120±57mV (14 eyes) at 3 months and 99±44mV (8 eyes) at 6 months. Compared to 1 hour after injection (the lowest amplitude), the ERG amplitude showed statistically significant recovery after 14 days (p<0.01: Bonferroni/Dunn). The mean VEP amplitude was 50±49mV (6 eyes) 14 days, 204±221mV (10 eyes) 28 days, 180±175mV (10 eyes) 3 months, and 137±78mV (8 eyes) 6 months after IAA injection. This is lower than the mean VEP amplitude of 14 healthy control eyes not injected with IAA (261±131mV, previous data). Compared to 14 days after injection (the lowest amplitude), the VEP amplitude showed a significant increase after 1 and 3 months (p<0.01: Bonferroni/Dunn). Histology of the eyes with abnormal electrophysiology revealed destruction of the photoreceptor layer. However, the damage was restricted to the outer retina with the inner retina remaining intact (horizontal cell layer). Conclusions: Damage to the outer retina is observed on both electrophysiologic and histologic study after IAA injection in the rabbit. This model may provide a useful tool for the experimental study of the artificial retinal prosthesis

Keywords: retina • electrophysiology: non-clinical • anatomy