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608 LIN ET AL.

acuity. At year three, with the facilitation of the Argus the visual experience of the patients, enabling faster
II system, 25 of 28 patients (89.3%) performed better and more accurate object identification and visual
in square localization, 15 of 27 patients performed scene segmentation. Therefore, it is of tremendous
better in the detection of the direction of motion, and interest to further understand the electrically-elicited
one-third of the patients had the grating visual acuity color perception in Argus II patients in pursuit of the
measured at 2.9 LogMAR or better, averaging at 2.5 goal to restore color vision in the blind.
LogMAR (21). LogMAR, as a measure of the subject’s In 2015, surgery of Argus II implantation was
ability to resolve details as small as one minute of performed for the first time in a dry AMD patient
visual angle, can be calculated by taking the base-10 in Manchester, UK. This phase I clinical trial aimed
logarithm of the reversal of Snellen acuity; for exam- to evaluate the safety and efficacy of Argus II in
ple, a 20/20 vision corresponds to 0 LogMAR and a late-stage AMD. The implant partially restored the
20/200 vision to 1 LogMAR. To put these visual acuity patient’s central vision, enabling him to “see the
measurements into perspective, it’s worth noting that outline of people and objects” and “walk around
a person able to count fingers at two feet is considered and see things.” This study, despite being at an early
to have 20/2000 vision or 2.0 LogMAR. One patient phase, suggests that the central vision restored by
achieved a grating acuity of 20/1,262 (1.8 LogMAR), the Argus II and similar prostheses may integrate
roughly matching the acuity theoretically achievable with the patient’s remnant peripheral vision and act
at the Argus II electrode density (19). Additionally, synergistically to enhance the visual experience of
the implant provides functional vision and long-term the advanced AMD patients (7).
benefits to the orientation and mobility of the patients Overall, as the first retinal implant with regulatory
in more real-life-like settings, such as finding a door approval, Argus II offers exciting opportunities to
and following a line on the floor (7). study prosthetic vision in a relatively large cohort of
In addition to standard clinical tests, laborato- patients. Results from clinical studies provide strong
ry-based exploration of Argus II-produced prosthetic evidence that this epiretinal electronic implant is
vision was carried out in subsets of the subjects. In effective in restoring meaningful vision to patients
a study, eleven subjects demonstrated the ability to blinded by photoreceptor degeneration. To date,
identify high contrast shapes (22). In another study, nearly 300 patients have been implanted with Argus
letter recognition was evaluated. The results showed II worldwide.
that 70% of the patients were able to recognize letters Despite the encouraging results summarized
with horizontal and/or vertical components only. Half above, the Argus II implant, containing only 60
of the subjects could recognize letters that had oblique electrodes (i.e., 60 pixels), is not able to restore high
or curved components (23). Luo et al. conducted acuity vision. Further improvement in the spatial
studies to evaluate the ability to identify common resolution demands advanced microelectronic and
objects from 2D to 3D under high contrast settings hermetic packaging technologies that would allow for
in seven subjects (24,25). Overall, subjects with the a higher electrode density on the chip. Furthermore,
implant activated exhibited improved performance, improvement in the power and data management is
and the improvement is largely dependent on the con- needed to permit sufficient power supply and rapid
trast at the edge. Recently, it has been reported that data transmission to the implant while keeping heat
up to nine different colors can be elicited depending generation under check. Finally, novel design and
on the stimulation parameters. The most prominent implantation techniques that can hold the electrode
colors are white, yellow, and blue (26). Perception of array in closer proximity to the retina are desirable
different colors could be elicited from the same retinal for increased stimulation efficiency (3).
area with different parameters, and the subjects could The past decade has witnessed the rapid growth in
simultaneously perceive two distinct colors at two retinal prostheses. It should be noted that, in addition
retinal locations (27). Color information, if success- to Argus II and other epiretinal implants, subret-
fully integrated into the prosthetic vision by being inal and suprachoroidal implants have also made
encoded in electrical pulses, will significantly enhance tremendous progress. Among others, Alpha-IMS,