Page 369 - Handbook of Biomechatronics

Current Advances in the Design of Retinal and Cortical Visual Prostheses 363

was the Argus I (Second Sight Medical Products) (Humayun et al., 2003,
2012). The intraocular array included 16 platinum (Pt) electrodes in a 4
by 4 arrangement, with an 800μm pitch which corresponds to a field of view
(FOV) of 10degrees (diagonally) (Caspi et al., 2009; Humayun et al., 2003).
The electrodes were fixed in a silicone rubber platform and wired via a trans-
scleral cable to the extraocular part of the device. Following implantation
with the Argus I, all of the six subjects reported the appearance of phos-
phenes upon stimulation of the retina (de Balthasar et al., 2008; Yanai
et al., 2007; Mahadevappa et al., 2005). The brightness of the phosphenes
was directly correlated to the stimulation amplitude and frequency (Caspi
et al., 2009; Humayun et al., 2003). A 10-year follow-up study in one sub-
ject reported that the tissue-implant interface remained stable (Yue et al.,
2015). The second-generation device, Argus II, consists of a higher elec-
trode density with 6 by 10 channels, with a distance of 525μm between elec-
trodes (FOV 22degrees diagonally), thus covering a larger area of the FOV
than the Argus I. The device was so far implanted in over 100 patients. In a
study published in 2013, patients reported an improvement in the ability to
localize high contrast objects and to detect motion, with at least two of the
recipients able to read letters (da Cruz et al., 2013; Dorn et al., 2013). The
best VA achieved with this implant was 20/1262, as tested with the visual
grating acuity (VGA) test, which is still considered as legal blindness
(<20/200) (Ho et al., 2015; Humayun et al., 2012). Some of the patients
experienced ocular damage such as conjunctival erosion (2 out of 30),
endophthalmitis (3 out of 30), and hypotony (3 out of 30), which was treated
without permanent complications (Humayun et al., 2012). In a 5-year
postimplantation study published in 2016, it was reported that the majority
of the recipients did not experience severe adverse effects that are related to
the device or to the surgical procedure, and that the improvement in visual
function was maintained (da Cruz et al., 2016).
The IRIS I and IRIS II epiretinal systems originate from the IMI device.
The IMI array with 49 iridium oxide (IrOx) included a polyimide (PI) thin
film encapsulation for both the electrodes and the extraocular stimulator
(wired to the electrodes). The IMI system employs a radio frequency
(RF) wireless transmission route for power and an infrared (IR) link for data
(Hornig et al., 2007). Switching on and off of the device by opening and
closing of the eyelid is possible through the optical link (Keser€u et al.,
2009). As evaluated in a chronic implantation trial conducted in three
patients for 9 months, the recipients were able to recognize simple light pat-
terns. Later, an acute implantation (up to 45min) was tested in 20 subjects,