Biological Considerations for an Intraocular Retinal Prosthesis - Artificial Sight: Basic Research, Biomedical Engineering, and Clinical Advances - page 22

Figure 1.19. Schematic diagram of an all-intraocular retinal prosthesis; although the coil
is shown inside the capsular bag, it can alternatively be placed in the sulcus, in front of
the anterior capsule (the area between the iris and the ciliary body).
frame, and both the receiver coil and the chip inside the eye. Perhaps the best
place for the receiver coil is inside the capsular bag, after removal of the natural
lens (a place at which, following cataract surgery, the artificial intraocular lens
is inserted). The chip can be placed either along the cable or adjacent to the coil.
Surgery involves both anterior and posterior segments of the eye. In a typical
surgery, a standard vitrectomy is followed by a corneal incision along the limbus.
A circular window from the anterior portion of the lens capsule is then removed
and the lens is subsequently expressed out of the eye; finally, the central portion
of the posterior capsule is also removed. At this stage, the anterior and posterior
segments of the eye are connected to each other, and the array and cable can
be inserted into the eye through the corneal incision, and then passed through
the remnants of the lens capsule. The coil (which usually has a large diameter)
can be placed either between the anterior and the posterior part of the capsule
(inside the capsular bag) or in front of the capsule, and sutured to the sclera if
necessary. Finally, the array is tacked onto the retina, and both the corneal and
the scleral incisions are then closed with sutures. The feasibility of this surgery
has been demonstrated on cats [57].
The advantage of the all-intraocular method is that there would be no
connection between the inside and the outside of the eye at the conclusion of
the surgery. However, there are some other concerns. The heat produced by the
receiver coil may be damaging to the eye; the stability of the coil in the capsule
is also a concern.
Unlike the current epiretinal prosthesis in which the excess cable can either
be folded inside the eye or pulled outside of it, with the all-intraocular design
the excess cable may touch and damage the retina. Considering the variability