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Original Article
Performance of real-world functional vision tasks by
blind subjects improves after implantation with the
Argus® II retinal prosthesis system
Gislin Dagnelie PhD,
1
Punita Christopher PhD,
2
Aries Arditi PhD,
3
Lyndon da Cruz MD,
4
Jacque L Duncan MD,
5
Allen C Ho MD,
6
Lisa C Olmos de Koo MD,
7
José-Alain Sahel MD,
8
Paulo E Stanga MD,
9
Gabriele Thumann MD,
10
Yizhong Wang MD,
11
Maura Arsiero PhD,
2
Jessy D Dorn PhD,
2
Robert J Greenberg MD
2
and the Argus® II Study Group
1
Lions Vision Research and Rehab Center, Johns Hopkins University, Baltimore, Maryland,
2
Second Sight Medical Products Inc, Sylmar,
5
University of California, San Francisco,
7
Department of Ophthalmology, University of Southern California, Los Angeles, California,
3
Lighthouse Guild, New York, New York,
6
Wills Eye Hospital, Philadelphia, Pennsylvania,
11
Retina Foundation of the Southwest, Dallas,
Texas, USA;
4
Moorfields Eye Hospital, London;
9
Manchester Royal Eye Hospital, Manchester, UK;
8
Quinze-Vingts National Ophthalmology
Hospital, Paris, France; and
10
Geneva University Hospital, Geneva, Switzerland
ABSTRACT
Background: The main objective of this study was to
test Argus II subjects on three real-world functional
vision tasks.
Design: The study was designed to be randomized
and prospective. Testing was conducted in a
hospital/research laboratory setting at the various
participating centres.
Participants: Twenty eight Argus II subjects, all pro-
foundly blind, participated in this study.
Methods: Subjects were tested on the three real-world
functional vision tasks: Sock Sorting, Sidewalk Track-
ing and Walking Direction Discrimination task
Main Outcome Measures: For the Sock Sorting task,
percentage correct was computed based on how ac-
curately subjects sorted the piles on a cloth-covered
table and on a bare table. In the Sidewalk Tracking
task, an ‘out of bounds’count was recorded,
signifying how often the subject veered away from
the test course. During the Walking Direction Dis-
crimination task, subjects were tested on the number
of times they correctly identified the direction of tes-
ters walking across their field of view.
Results: The mean percentage correct OFF versus ON
for the Sock Sorting task was found to be significantly
different for both testing conditions (t-test, P<0.01).
On the Sidewalk Tracking task, subjects performed
significantly better with the system ON than they
did with the system OFF (t-test, P<0.05). Eighteen
(18) of 27 subjects (67%) performed above chance
with the system ON, and 6 (22%) did so with system
OFF on the Walking Direction Discrimination task.
Conclusions: Argus II subjects performed better on all
three tasks with their systems ON than they did with
their systems OFF.
Key words: activities of daily living, clinical trial, out-
come measures, retinal prosthesis, visual performance.
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and
distribution in any medium, provided the original work is properly cited, the useis non-commercial and no modifications or adaptations are made.
jCorrespondence: Dr Gislin Dagnelie, JHU Lions Vision Center, Wilmer Woods 358, 1800 Orleans St, Baltimore, MD 212877-0023, USA. E-mail
gdagnelie@jhmi.edu
Received 5 April 2016; accepted 31 July 2016.
Competing/conflicts of interest: All authors, through their participating institutions, were supported by research funds from Second Sight Medical
Products Inc (SSMP). Punita Christopher, Maura Arsiero, Robert J. Greenberg, and Jessy Dorn are employees of and have stock options in SSMP.
Robert J. Greenberg has an equity interest in SSMP and intellectual propertyrightstotheArgus®IIretinalprosthesis system and related technology.
Funding sources: Funded by National Institutes of Health grant no. 5R01EY012893 (R.J.G., principal investigator) through the National Eye
Institute, and by Research/?Development of Artificial Retinas for the Blind and National Institutes of Health grant no. 1RC3EY020778-01
(R.J.G., principal investigator). The clinical trial was sponsored by Second Sight Medical Products, Inc.
© 2016 The Authors Clinical & Experimental Ophthalmology published by John Wiley & Sons Australia, Ltd on behalf of Royal Australian
and New Zealand College of Ophthalmologists
Clinical and Experimental Ophthalmology 2017; 45: 152–159 doi: 10.1111/ceo.12812
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INTRODUCTION
The Argus® II, the first commercially available
retinal prosthesis, is intended to partially restore
useful vision in blind patients with severe to pro-
found retinitis pigmentosa. Several tests have been
developed to test subjects’improvement in vision
with the Argus II system in a clinical trial.
1,2
Most
of these tests involve computer-based tasks that are
conducted in a highly controlled, laboratory setting.
Additionally, we also use self-reported and observer
rated instruments such as the Massof Activity
Inventory,
3
VisQOL
4
and FLORA
5
to quantify the
improvements in the ability of subjects to perform
real world activities of daily living (ADL) while
using the Argus II system. However, most of these
instruments that are currently in use for low vision
testing consist of tasks that are often beyond the
scope of what subjects can do with the Argus II
system. This research study was thus developed to
test subjects on real-world functional vision tasks
that can be scored in an objective manner. These
tasks were designed to approximate everyday
activities that a totally blind individual may not be
able to do, and to measure –in a less-controlled, more
real-world environment –whether the Argus II
system helped the subjects successfully perform them.
These functional vision tasks encompassed several
aspects of everyday life: housekeeping chores, social
engagement, and orientation and mobility. Each of
these aspects was represented by one task developed
for this research study: sock sorting, sidewalk track-
ing, and perceived direction of walking. The sock
sorting task was designed to mimic the real-world
scenario of sorting light and dark laundry. It
represents a task that is difficult or impossible to do
without vision (i.e. through tactile cues alone). The
Sidewalk Tracking task was developed to assess
subjects’ability to visually track an edge such as the
border between a sidewalk and grass in a real-world
outdoor setting, as the visual analogue of the
‘shorelining’technique commonly employed by
white cane users to follow the wall of a building or
corridor, a curb, or other tactile guidance.
6
The ability
to follow along such an edge and detect the transition
between two surfaces of different brightness levels
may be useful to blind subjects for mobility and
orientation purposes in their daily life. The Walking
Direction Discrimination (WDD) task was developed
to assess subjects’ability to identify the direction of
motion of a person passing in front of them. The
ability to detect people moving nearby and identify
their direction may be useful to blind subjects in
unfamiliar environments or in social situations.
METHODS
The Argus II system consists of an implant that is
surgically placed on and in the eye and external
equipment that is worn by the subject. The implant
consists of a receiving antenna and an electronics case
that are secured to the outside of the eye using a stan-
dard scleral band and sutures, and an intraocular
electrode array that is secured to the retina over the
macula using a retinal tack (Fig. 1a). The electrode
array contains 60 electrodes arranged in a 6 × 10 grid.
The external equipment consists of the Argus II
glasses and the Argus II Video Processing Unit
(VPU) (Fig. 1b). A small video camera and transmit-
ting antenna are mounted on the glasses. The VPU
is worn by the subject on a shoulder strap or belt,
and is used to process the images from the video cam-
era and convert the images into electrical stimulation
commands that are wirelessly transmitted to the
implant. The electrodes in the array emit stimulation
pulses whose amplitude corresponds to the bright-
ness of the scene in that location. Stimulation of the
remaining retinal cells results in visual percepts that
subjects learn to interpret.
The Argus II clinical trial enrolled 30 subjects, 14
from the United States and 16 from Europe, with an
average age of 58 years (standard deviation: 10 years)
at time of implantation. All subjects had Retinitis
Pigmentosa with the exception of one subject who
had Choroideremia. Subjects were implanted with
the Argus II Retinal Prosthesis System in one eye,
typically the worse-seeing eye. All subjects were
profoundly blind and had bare light perception or
no light perception at implantation.
Figure 1. The Argus II System. (a) Implanted
components of the system. (b) External compo-
nents of the system.
© 2016 The Authors Clinical & Experimental Ophthalmology published by John Wiley & Sons Australia, Ltd on behalf of Royal Australian
and New Zealand College of Ophthalmologists
Functional vision tasks using Argus® II 153
Twenty seven subjects performed all three tests
between 1 January and 30 November 2010. Subject
S2 was not available for testing during this study
period, and S13’s device was explanted before this
study commenced. Subject 25 discontinued participa-
tion after the first test, because of intermittent prob-
lems with the implant (the external antenna could
not consistently establish a radio-frequency link with
the implanted antenna, so we could not guarantee a
continuous data and power stream to the electrode
array). Subjects performed these tests during or close
to a clinical follow-up visit. The follow-up time
varied for each subject depending on the time of
implantation (Argus II subjects were implanted over
the course of about two years), between a minimum
of 6 months and a maximum of 36 months post-
implant. The tests were conducted during subjects’
regular psychophysics testing sessions (all three
tasks were not necessarily assessed during the same
session). Testing was performed by clinical site staff
and/or Second Sight Medical Products staff under
direction of the site principal investigator.
The Argus II clinical trial is a multi-centre trial and
is being conducted in accordance with the Declara-
tion of Helsinki and the national regulations for
medical device clinical trials in the countries where
the study is being conducted. The National Ministries
of Health in each of these countries have approved
this study. This study has also been approved by
the ethics committees or institutional review boards
of participating centres. All subjects consented to
participate. The clinical trial is posted on www.
clinicaltrials.gov, trial registration number
NCT00407602.
Task 1: sock sorting
Twenty-eight (28) subjects were included in this
assessment. Subjects were presented with 30 socks
jumbled together in a pile: 10 pure white socks, 10
pure black socks and 10 of an intermediate gray
colour. To avoid the presence of non-visual cues, all
socks were made of the same material, size and
shape; all socks were bought from the same manufac-
turer and were intended to be indistinguishable by
touch. The subjects’task was to sort the socks into
three piles representing the three different colours.
Some subjects counted piles and ensured that they
had 10 socks in each pile; others simply sorted
according to what colour they believed each sock to
be, resulting in some piles with more or fewer than
10 socks.
The task was performed in the clinic, in lighting
conditions that varied from site to site, but that can
all be qualified as medium to bright indoor lighting.
Subjects sorted the socks four times: once each with
the Argus II system ON and OFF and the surface of
the table covered in a known-colour of cloth (either
black or white, as preferred by the subject), and once
each with the system ON and OFF on a bare table.
Only one subject chose to use a white-coloured cloth;
all other subjects used a black-coloured cloth. Bare
tables were as-found in the clinical site testing
rooms; they were various types of desks and tables
of various colours of wood or laminate. This condi-
tion was intended to produce a more ‘real-world’test,
as blind Argus II users will not always have control
over the level of contrast available in the environ-
ment where they use the system. Subjects performed
all tests binocularly. All test conditions comprising
the task were assessed in the same session with the
exception of subject S4, who completed some condi-
tions in a second session less than a month after the
first session.
After the subjects had finished sorting the socks
and identified which pile was which (i.e. ‘white
pile,’‘gray pile,’‘black pile’), the number of each
colour in each pile of socks was counted. Results
were thereafter recorded as the number of
correctly-sorted white, gray and black socks. For
some analyses, results were further compiled to
yield a total percent correct across all colours.
T-tests (assuming unequal variance) were used to
test for significant differences between the means
for various conditions. Figure 2 shows a subject
performing the sock-sorting test.
Figure 2. Photograph of an Argus II subject performing the
Sock Sorting task.
© 2016 The Authors Clinical & Experimental Ophthalmology published by John Wiley & Sons Australia, Ltd on behalf of Royal Australian
and New Zealand College of Ophthalmologists
154 Dagnelie et al.
Task 2: sidewalk tracking
Twenty-seven (27) subjects were tested on the
Sidewalk Tracking task. For this task, the tester
identified three different 20-foot (6-m) stretches of
grass or low shrubbery bordered by concrete or
asphalt such as a sidewalk, driveway, parking lot,
etc. Some edges were straight; others were curved
or angled. The subject was asked to walk along
each of the three paths on the pavement within
1 m of the edge without stepping off the pavement,
as shown schematically in Figure 3. The subject did
not use any mobility aid such as a cane or a guide
dog during the test. The test consisted of three trials
with the system ON and three trials with the
system OFF. The order of trials was varied by the
tester. All six trials were completed on the same day
with the exception of subject S22, who completed
the trials with the System ON a week after the trials
with the System OFF, in the same location.
Performance was measured by the number of times
the subject moved out of bounds, that is, when they
stepped off the pavement or when they moved farther
than 1 m away from the edge. If subjects moved out of
bounds during the trial, the tester corrected their posi-
tion accordingly, and subjects continued to complete
the trial. A video of a subject performing this task is
included as supplemental material online (Video S1).
Task 3 –Walking Direction Discrimination
(WDD)
Twenty-seven (27) subjects were included in this
activity. For this task, the subject was seated, and
markers were placed 10 feet away. The test began
with two testers positioned on the markers, on either
side of the subject, as shown in Figure 4. Every 15 s,
prompted by an audible beep, one of the testers
crossed the subject’sfield of view by walking from
one side to the other. A few seconds after the audio
prompt, the subject identified in what direction the
tester was moving.
This was a two-alternative forced-choice test; if the
subject did not see movement he/she was required to
guess. The test consisted of 40 trials. Some care was
taken to reduce the possibility of auditory cues –for
example, testers may have removed their shoes if
the floor material was hard. As the task was intended
to represent real-world conditions, however, no
masking noise or noise-cancelling headphones were
used. The task was performed with the system ON
and OFF. Performance was measured by the number
of correct answers, that is, the trials in which the
subject correctly identified the direction of the person
passing in front of him/her.
RESULTS
Task 1: sock sorting
Figure 5 shows the mean percent correct and stan-
dard deviation for all four testing conditions (system
ON and system OFF, felt-covered table and bare
table). As indicated by the stars in Figure 5, the mean
percentages correct OFF versus ON conditions are
significantly different for both the felt-covered table
Figure 3. Schematic of the Sidewalk Tracking task.
Figure 4. Schematic of the Walking Direction
Discrimination task.
© 2016 The Authors Clinical & Experimental Ophthalmology published by John Wiley & Sons Australia, Ltd on behalf of Royal Australian
and New Zealand College of Ophthalmologists
Functional vision tasks using Argus® II 155
and the bare table (t-test assuming unequal
variances, P<0.01). We also found that the mean
percentage correct was significantly greater for the
felt-covered table versus the bare table with the system
ON (t-test assuming unequal variances, P<0.01); this
suggests that subjects can more reliably identify the
colour of the socks against the felt-covered table.
A large majority of subjects perform better on this
task with the system ON than with it OFF (27 of 28
with the felt-covered table, and 21 out of 28 with the
bare table). Subject S8 is an exception; this subject
performed noticeably better with the system OFF in
both conditions. The subject noted during testing that
it was possible for him to feel the difference between
the white socks and the other colours with no visual
information, which likely explains the outlier results.
To investigate whether there was a difference in
performance for different colours of socks, the aver-
age percent correct was calculated for each colour
over all subjects when using the felt-covered table
and bare table (system ON). In other words, for
white, the number correct for white socks divided
by the total number of white socks was calculated.
Means and standard deviations are shown in Figures
6 and 7 for the felt-covered table and bare table
conditions, respectively. There is no significant
difference in mean percentage correct between white
and gray socks when using the felt-covered table
(t-test, P>0.05); however, mean percentages correct
for black and gray socks are significantly different
(P<0.01), as are those for white and black socks
(P<0.01), when using the felt-covered table, as
indicated by stars on the figure. This suggests that
subjects can more reliably identify black socks than
white or gray socks. There is no significant difference
in mean percentages correct between white and gray
socks, white and black socks, and black and gray
socks, when using the bare table. This suggests that
subjects have equal difficulty identifying the black,
white or gray socks on the bare table.
Task 2: sidewalk task
Figure 8 shows a comparison between the system
ON and OFF performance for all tested subjects.
Eighteen (18) of 27 subjects (67%) performed better
(i.e. fewer ‘out of bounds’) with the system ON
when compared to system OFF, and seven (27%)
performed better with the system OFF (two sub-
jects had equal performance ON and OFF). Mean
Figure 5. Mean percent correct, sock sorting,
all conditions. Stars indicate significant differ-
ence, t-test assuming unequal variances,
P<0.01.
Figure 6. Mean percent correct, sock sorting,
by colour (felt-covered table). Stars indicate sig-
nificant difference, t-test assuming unequal vari-
ances, P<0.01.
© 2016 The Authors Clinical & Experimental Ophthalmology published by John Wiley & Sons Australia, Ltd on behalf of Royal Australian
and New Zealand College of Ophthalmologists
156 Dagnelie et al.
and standard deviation for ON and OFF are shown
in Table 1. A paired t-test was used to compare the
number of out of bounds errors with system ON
and system OFF for all subjects. Results indicate
that subjects performed significantly better with
the system ON than they did with the System
OFF (two-tailed t-test, P<0.05).
Task 3: Walking Direction Discrimination
Figure 9 shows a comparison between system ON
and OFF performance for all tested subjects. Accord-
ing to the binomial distribution (one-tailed), scoring
26 or more correct answers out of 40 is significantly
above chance. Eighteen (18) subjects performed
above chance with the system ON, and six subjects
performed above chance with the system OFF. (One
of these performed significantly above chance only
with the system OFF, and the other three performed
significantly above chance in both conditions.)
DISCUSSION
Task 1 –sock sorting
The task of sorting laundry by colour was suggested
by Argus II subjects as a task they would like to be
able to do without help but cannot perform without
sight. Based on that suggestion, an objectively scored
sock sorting task was developed to be performed in
real-world conditions (i.e. with varying lighting and
table surface colour across the different clinical sites).
This study demonstrated that Argus II subjects were
able to sort white, gray and black socks by colour
significantly better with their systems ON than they
were with their systems OFF. This held true whether
the background colour was controlled (either white
or black, according to the subject’s preference) or
uncontrolled (a bare table). However, performance
Figure 7. Mean percent correct, sock sorting,
by colour (bare table). Stars indicate significant
difference, t-test assuming unequal variances,
P<0.01.
Figure 8. Number of out-of-bounds, sidewalk
tracking task. Stars indicate significant differ-
ence, paired t-test, P<0.05.
Table 1. Sidewalk task summary results
Out of bound counts –
system ON
(Mean ± SD)
Out of bound counts –
system OFF
(Mean ± SD)
P-value
(paired
t-test)
4.93 ± 2.62 6.85 ± 3.03 P<0.05
© 2016 The Authors Clinical & Experimental Ophthalmology published by John Wiley & Sons Australia, Ltd on behalf of Royal Australian
and New Zealand College of Ophthalmologists
Functional vision tasks using Argus® II 157
was better with the felt-covered table; this is not
surprising, as the felt cover held two important
advantages: it likely increased the contrast between
the socks and the table (compared to intermediate
shades of the bare tabletops), and it was a known
colour –subjects knew whether the felt was black
or white, so perhaps had an easier comparison for
the sock colour. Subjects were generally aware of
the colour of the bare table, but may not have had a
precise mental image of the table colour.
Task 2 –sidewalk task
This task was developed to test blind subjects’ability
to detect and track edges in a real-world outdoor
situation where lighting and contrast conditions are
uncontrolled, a task that subjects had previously
reported as difficult. It is thus encouraging that these
results demonstrated that Argus II subjects, as a
group, performed significantly better on this
uncontrolled task with their system ON versus OFF.
Moreover, a quarter of the subjects performed at least
50% better with system ON versus OFF, that is, the
number of errors with the system ON was less than
67% of that with the system OFF.
Time to complete this task was not measured, as
the test was stopped each time a subject strayed out
of bounds. It has been shown, however, that System
ON tasks tend to take longer than performing the
same task System OFF.
7
We would expect the case
to be the same here –sidewalk tracking with the
System ON is slower, but more accurate.
One may object to the notion that the Sidewalk
Tracking task is representative of daily activities:
Blind people travelling alone will use either a guide
dog or a white cane, and an unaccompanied Argus
II wearer should still use a white cane for reasons of
safety, both to avoid obstacles and changes in ground
level, such as steps, and to signal their blindness to
other pedestrians and to motorists. One should real-
ize, however, that certain visible markings, such as
paint lines on pavement, may not lend themselves
to tactile detection. As an example, an Argus II
wearer can use the crosswalk lines to safely cross
the street, but the cane she is using will not protect
her from veering out of the crosswalk before reaching
the other side of the street.
Task 3 –Walking Direction Discrimination
This task was developed to mimic a real-world situa-
tion in which a blind subject, sitting in a stationary
position, identifies the walking direction of people
passing in front of him or her (as might be useful
while sitting on an outdoor bench or in a social situ-
ation). Argus II subjects, as a group, have signifi-
cantly better performance on this task with their
systems ON than OFF (two-tailed t-test, P<0.05).
Although 15 subjects were able to perform signifi-
cantly above chance with their systems ON, only four
were able to reach this performance with the system
OFF. Those four were likely using auditory cues to
perform the task without the system. Although this
task could be controlled to eliminate auditory cues,
it is believed to be more valuable to present a real-
world environment (while still controlling enough
factors to allow for objective measurement of perfor-
mance). In this way, the results shown here represent
actual benefit of the system and other sensory infor-
mation, compared with use of only residual vision
and other sensory information.
The tasks are representative of ADL tasks and
were developed as a complementary assessment for
Argus II subjects; they mimicked activities that sub-
jects perform in their daily lives, but were objectively
scored. They provided information about how
subjects can use their systems for complex tasks in
different uncontrolled environments.
Figure 9. Walking Direction Discrimination re-
sults for each subject. Dotted line indicates per-
formance significantly above chance according
to the binomial distribution, P<0.05.
© 2016 The Authors Clinical & Experimental Ophthalmology published by John Wiley & Sons Australia, Ltd on behalf of Royal Australian
and New Zealand College of Ophthalmologists
158 Dagnelie et al.
The results indicated that performance on these
tasks varied across subjects, but that as a group,
Argus II subjects performed better on all three tasks
(Sock Sorting, Sidewalk Tracing and WDD) with
their systems ON than they did with their systems
OFF.
Interestingly, high performance on these tasks did
not always correspond to high performance on other
tasks such as character recognition
8
or grating visual
acuity (data not shown). However, more importantly,
some subjects performed very well on these func-
tional vision tasks but not as well on other assess-
ments. This suggests that when assessing the benefit
that subjects have received from use of the Argus II
system, certain daily activities may show benefits
that cannot easily be demonstrated in standardized
laboratory tests.
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SUPPORTING INFORMATION
Additional Supporting Information may be found in
the online version of this article at the publisher's
web-site:
Video S1. Sidewalk tracking task.
© 2016 The Authors Clinical & Experimental Ophthalmology published by John Wiley & Sons Australia, Ltd on behalf of Royal Australian
and New Zealand College of Ophthalmologists
Functional vision tasks using Argus® II 159
