The effects of indocyanine green and endoillumination on rabbit retina: an electroretinographic and histological study

Abstract

Aim: To evaluate the functional and morphological retinal toxicity associated with intravitreal injection of indocyanine green (ICG) dye in rabbit eyes during vitrectomy with endoillumination.

Methods: 20 eyes of 10 New Zealand pigmented rabbits were used in the study. All eyes underwent pars plana vitrectomy and removal of posterior vitreous cortex under endoillumination. In one eye of each rabbit, intravitreal injection of 0.1 ml of 2.5 mg/ml ICG was applied for 30 seconds followed by 10 minutes of endoillumination. The control eye had endoillumination only without ICG injection. Dark adapted and light adapted electroretinograms (ERGs) were performed before the surgery and 1 week after surgery for serial comparisons. Rabbits were killed 1 week after surgery and eyes were enucleated for histological examination.

Results: Serial ERG comparisons showed significant reduction in the light adapted a-wave amplitude (p = 0.037) and significant delays in the dark adapted and light adapted b-wave latencies (p = 0.020 and p = 0.038, respectively) in the ICG treated eyes. Histological examinations demonstrated loss of photoreceptor outer segments with focal absence of photoreceptors in some areas in the ICG injected eyes.

Conclusions: Vitrectomy followed by intravitreal injection of 2.5 mg/ml ICG for 30 seconds with endoillumination may result in retinal toxicity causing functional and morphological retinal damages in rabbit eyes. The lowest concentration of ICG should be used if necessary for intraocular use to prevent potential retinal toxicity.

Figure 1

(A) The dark adapted ERG waveforms and (B) light adapted ERG waveforms of 2.5 mg/ml ICG treated and control rabbit eyes.

Figure 2

(A) Light microscopy of eyes without ICG injection showing preservation of retinal morphology in all layers. (B) Light microscopy of eyes treated with 2.5 mg/ml ICG showing loss of the outer segments of the photoreceptors, focal absence of photoreceptors, and localised areas of RPE irregularities. Focal areas of cellular oedema were also seen in the outer nuclear and inner nuclear layers. (RPE, retinal pigment epithelium; OS, outer segment; IS, inner segment; ONL, outer nuclear layer; OPL, outer plexiform layer; INL, inner nuclear layer; IPL, inner plexiform layer; GCL, ganglion cell layer; NFL, nerve fibre layer. Haematoxylin and eosin stain, original magnification ×400.)