TABLE I.

Comparison Between Sub- and Epiretinal Visual Prosthesis Characteristics

Sub-Retinal Visual Prosthesis Characteristics	Epi-Retinal Visual Prosthesis Characteristics
Ab externo surgical approach is minimally invasive	Requires chronic purs plana micro-cable entry into eye and/or intra-ocular electronic components
Heat-dissipating implanted electronic components can be mounted outside the sclera	Heat dissipation by intra-ocular prosthesis components may cause elevated temperature of the retina
Electrical stimulation is introduced closer to former photoreceptor sites and pre-synaptic cells	Electrical stimulation is introduced very close to remaining retinal ganglion cells
Uses specialized surgical tools and techniques that can be mastered by retinal surgeons with practice	Uses common vitreo-retinal surgical techniques, e.g. retinal tacks
Bulk of prosthesis is located against fatty tissue of eye orbit; device moves together with the eye	Has intra-ocular and/or intra-cranial components
Natural fixation of electrode array due to suction that holds the retina in place; retinal detachment due to surgical procedure resolves quickly, and array’s presence does not cause subsequent detachment.	Fixation of electrode array requires some form of retinal tack which can dislodge, e.g. due to trauma