Page 370 - Handbook of Biomechatronics

364 Lilach Bareket et al.

confirming the ability to identify and describe phosphenes following stim-
ulation of the retina (Keser€u et al., 2012). In a 3-month follow-up test, the
majority of the patients showed no sign of damage due to the surgery or to
the electrical stimulation, except for one patient with peripheral retinal
detachment (which was successfully treated) (Keser€u et al., 2012). The com-
pany has obtained CE mark for the IRIS II in July 2016 (Hornig et al., 2017).
The EPIRET3 prosthesis was so far evaluated through two clinical trials:
a short-term trial (4 weeks) and a long-term trial (7–18 months) conducted
in six and three volunteers with blindness due to RP, respectively (Roessler
et al., 2009; Schimitzek et al., 2016; Menzel-Severing et al., 2012). The
extraocular component of the EPIRET3 includes a computer system, a
transmitter unit, and a transmitter coil attached to a holder placed in front
of the eye. The intraocular part consists of a receiver coil, all necessary elec-
tronics, and an array with 25 electrodes (Roessler et al., 2009). Similar to the
IMI device, the EPIRET3 chip is also encapsulated with polymer [poly-
dimethylsiloxane (PDMS)]. The 4-week long trial was designed to evaluate
the efficacy and safety of the device and of the surgical procedure (Roessler
et al., 2009). The implant remained stable for the duration of the study, and
removal was performed successfully in all patients. It was concluded that the
tissue reaction was within an acceptable range, with temporary inflammation
developed in all of the patients. Two cases of more adverse effects were
detected: a sterile hypopyon in one case and a retinal tear that occurred dur-
ing explantation, in the second case (Roessler et al., 2009). Both of these
conditions were successfully treated. All patients reported visual responses
triggered by electrical stimulation through the implant (Klauke et al.,
2011). Some of the patients were able to discriminate signals applied at dif-
ferent locations of the array as well as pattern orientations. In the second
study, some of the patients developed gliosis near the tacks used to attach
the implant to the tissue (Menzel-Severing et al., 2012). Although gliosis
does not appear to pose a major health risk, it may contribute to deteriora-
tion in the functionality of the implant. Strong glial proliferation of glia cells
is part of the immune response of the retinal tissue to the presence of the
implant (Dyer and Cepko, 2000). Formation of such glial encapsulation
can potentially widen the gap between electrodes and their target neurons,
thus increasing the amount of charge required for stimulation.
Currently, at preclinical experimental stage is the high-resolution
epiretinal system with 600 pixels (Bioretina) that is being developed by
Nanoretina. Employing three-dimensional (3D) microelectrodes the
high-density array is designed to penetrate from its location at the outer