Fluorescein Angiographic Findings in Blind Patients Treated by an Active Subretinal Implant

Abstract

Purpose:: To assess the integrity of the retinal vasculature on top of and in the proximity of a subretinal implant by fluorescein angiography (FA).

Methods:: Six patients (6 eyes) with retinitis pigmentosa (RP) were implanted with an active subretinal implant via a transchoroidal surgical approach (Zrenner et al., ARVO 2006; Sachs et al., ARVO 2006)). The cable-bound implant consisted of two separate entities on the subretinal tip of a polyimide foil: a 4*4 electrode array for direct (light-independent) stimulation (DS) and a microphotodiode-array (MPDA) with ca. 1500 light-sensitive elements. Study duration was 4-5 weeks. FA was performed in standard manner before and several weeks after implantation; severity of the fluorescein angiographic findings were graded from - to +++. Function tests with electrical and light stimulation were performed.

Results:: In 5 patients drop-out of the retinal capillaries was observed. Some degree of retinal microaneurysm formation (+ to ++) and various degrees of vessel rarefactions at the region overlying the MPDA and DS (+ to +++) were seen. One patient decided to keep the implant for a period of one year; FA findings remained stable, only microaneurysm formation increased in the last 3 months. One eye developed mild macular edema. Slight venous dilation and small retinal neovascularization was seen over the implant in 1 eye. No retinal vascular changes were seen outside a 1 mm-margin around the implant. In 1 eye FA was not consistently interpretable due to nystagmus. Four subjects had pattern recognition via direct electrical stimulation and two patients reported visual perceptions through the MPDA. The retina of 1 patient after >30 yrs of blindness did not respond to electrical stimulation within the safety limit.

Conclusions:: Although some amount of localized retinal ischemia overlying the subretinal implant was seen after implantation, the changes of retinal perfusion during the observation period were not correlated to functional outcome. Even eyes with marked retinal ischemia reacted to electrical pattern stimulation, except in 1 eye with late stage of degeneration. Further investigations will have to elucidate the role of the surgical trauma to induce these changes, the influence of a foreign body as a diffusion barrier between RPE and retina, or the influence of electrical stimulation on these effects.

Keywords: retinitis