Visual field examination method using virtual reality glasses compared with the Humphrey perimeter

Abstract

Purpose
To present a visual field examination method using virtual reality glasses and evaluate the reliability of the method by comparing the results with those of the Humphrey perimeter.

Materials and methods
Virtual reality glasses, a smartphone with a 6 inch display, and software that implements a fast-threshold 3 dB step staircase algorithm for the central 24° of visual field (52 points) were used to test 20 eyes of 10 patients, who were tested in a random and consecutive order as they appeared in our glaucoma department. The results were compared with those obtained from the same patients using the Humphrey perimeter.

Results
High correlation coefficient (r=0.808, P<0.0001) was found between the virtual reality visual field test and the Humphrey perimeter visual field.

Conclusion
Visual field examination results using virtual reality glasses have a high correlation with the Humphrey perimeter allowing the method to be suitable for probable clinical use.

Full text

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Clinical Ophthalmology 2017:11 1431–1443
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METHODOLOGY
open access to scientific and medical research
Open Access Full Text Article
http://dx.doi.org/10.2147/OPTH.S131160
Visual eld examination method using virtual
reality glasses compared with the Humphrey
perimeter
Stylianos Tsapakis
Dimitrios Papaconstantinou
Andreas Diagourtas
Konstantinos Droutsas
Konstantinos Andreanos
Marilita M Moschos
Dimitrios Brouzas
1st Department of Ophthalmology,
Nat ion al and Kapodistrian University
of Athens, Athens, Greece
Purpose: To present a visual field examination method using virtual reality glasses and evaluate
the reliability of the method by comparing the results with those of the Humphrey perimeter.
Materials and methods: Virtual reality glasses, a smartphone with a 6 inch display, and
software that implements a fast-threshold 3 dB step staircase algorithm for the central 24° of
visual field (52 points) were used to test 20 eyes of 10 patients, who were tested in a random
and consecutive order as they appeared in our glaucoma department. The results were compared
with those obtained from the same patients using the Humphrey perimeter.
Results: High correlation coefficient (r=0.808, P,0.0001) was found between the virtual reality
visual field test and the Humphrey perimeter visual field.
Conclusion: Visual field examination results using virtual reality glasses have a high correlation
with the Humphrey perimeter allowing the method to be suitable for probable clinical use.
Keywords: visual fields, virtual reality glasses, perimetry, visual fields software, smartphone
Introduction
Automated perimetry is a useful method to assess visual fields in many ophthalmic
and neurological diseases. Current perimeters are accurate, but they have a number
of disadvantages. Visual field testing is a time-consuming process. It is inconvenient
and stressful for debilitated, claustrophobic, ill, or elderly patients to keep their heads
still in the perimeter bowl throughout the test. To overcome these problems, visual
field testing using a video projector has been proposed.1 The majority of computerized
perimeters are specialized pieces of hardware/software. They typically consist of a
projection area, an embedded microcontroller, an input device for the operator, and
a button for the patient. These devices, built for physicians’ offices or hospitals, are
bulky, heavy, and expensive. They are not portable, and they cannot be used at bedside.
However, smartphones are found everywhere, and they are inexpensive. Virtual real-
ity (VR) glasses have some advantages in visual field testing. They are lightweight,
portable, comfortable, and affordable, and there is no need for an eye patch.
The possibility of using VR glasses for visual field testing has been described since
1998, patent no: US5737060A. However, at that time, hardware and software was an
issue. Smartphones and similar portable devices were not as improved as they are today.
VR glasses for smartphones did not exist. Win98 was actually just a shell over DOS.
The first iPhone was released on January 9, 2007, whereas the Android version 1.0
was released on September 23, 2008. For these reasons, specialized hardware was
used with built-in liquid crystal display (LCD).2–4
Correspondence: Dimitrios Brouzas
10 G Papandreou Street, Byron,
Athens 16231, Greece
Tel/fax +30 21 0765 2909
Email brouzas@yahoo.com
Journal name: Clinical Ophthalmology
Article Designation: Methodology
Year: 2017
Volume: 11
Running head verso: Tsapakis et al
Running head recto: Evaluation of visual field examination method using virtual reality glasses
DOI: http://dx.doi.org/10.2147/OPTH.S131160
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This article was published in the following Dove Press journal:
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Commercially available visual reality glasses with
built-in displays do not perform well. These VR glasses are
usually built for gaming, and the display is usually small
with low resolution. This requires moving the fixation point,
which confuses older patients, whereas custom-built VR
glasses with bigger displays are more expensive and lack
standardization. For these reasons, widespread testing of
visual field using VR glasses has been limited.
Today’s smartphones are much more powerful, afford-
able, have bigger displays, and standardization can be
achieved by selecting proper hardware/software.
Materials and methods
To test the reliability of visual fields using visual reality
glasses, 20 eyes of 10 patients, who were chosen randomly
and consecutively at our glaucoma department, were tested
successively using a Humphrey perimeter and the VR
glasses method within hours for comparison. Approval was
obtained from the Ethical Committee of the General Hospital
of Athens “G Gennimatas”. Written informed consent was
obtained from all patients in the study.
Trust EXOS 3D VR glasses and Alcatel One Touch Pixi
4 (6) 8050D smartphone with 6 inch display were used. The
patients were allowed to wear his/her glasses during testing
if they felt it was necessary (Figure 1A–C).
Virtual display focus distance is adjusted with the 2
rotating knobs on the sides. Trial glasses were not used as
the patient could wear his/her glasses during testing if neces-
sary (Figure 1C).
Proprietary software implementing a fast-threshold 3 dB
step staircase algorithm at central 24°/52 points of visual field
was used for the purpose of testing (Figure 2). The projected
stimuli intensity was distributed on a logarithmic scale.
The typical luminosity of a LCD screen is 250 cd/m2.
The results of a visual field test depend on the luminosity of
the examination display. As different smartphone models
may be used for visual field testing, the luminosity of a
display must be adjusted in order to make sure that the data
are consistent from one visit to another and between suc-
cessive tests. This allows for the data to be analyzed over
time and between different installations.
Contrast ratio is the ratio of luminance between the
brightest white and the darkest black that can be produced.
Brightness sets the black point and determines the low light
output level (black level) of the display.
Gamma describes the relationship between the pixel level
and the luminance of the monitor (the light energy it emits).
LCDs are considered linear devices; therefore, technically
they do not need gamma correction. Gamma correction,
however, corrects for the deficiencies (non-linearity) of
cathode ray tube (CRT) monitors.
The software uses gamma 1.0 because LCDs are linear
but gamma is adjustable to match the viewing system’s
gamma for optimum performance (Figure 3).
The VR glasses gamma is set separately (Figure 4).
The display’s gamma/brightness/contrast can be visually
calibrated.5,6 Visual calibration is sufficiently reliable to be
used as an alternative to calibration using an expensive pho-
tometer.5 The software uses a gray scale step wedge for display
adjustment. The settings should be set to a point that makes the
shades of gray distinct and clearly visible (Figure 5A–D).
In our case, for better accuracy and comparability, a pho-
tometer was used and the luminosity of white color was set
Figure 1 Virtual reality glasses. (A) front view, (B) rear view, and (C) prescription
glasses used with virtual reality glasses.

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Evaluation of visual eld examination method using virtual reality glasses
at 130 Lux (approximately 410 asb). This was about 50% of
the maximum available brightness for the smartphone used
(Alcatel Pixi 4(6) 8050D).
Software features
1. Fast-threshold, 3 dB step staircase strategy, 52 points,
central 24° of visual field.
2. The software uses the Heijl–Krakau blind spot method
to monitor fixation. The software detects the blind spot
by projecting stimuli at maximum luminosity at expected
blind spot locations until finding the correct response.
3. The software pauses the test in case of fixation loss.
4. Supra threshold stimuli are used to check for false
negative results. The software also checks for false posi-
tive responses.
5. Variable stimuli presentation rate, adjusted to patient’s
response time.
6. Stimuli presentation time 250 ms.
7. Initial patient’s response waiting time 500 ms, adjusted
to patient’s response time.
The software includes eye tracking capability using AForge.
NET computer vision and artificial intelligence language. The
source code and binaries of the project are available under the
terms of the Lesser GPL and the GPL (GNU General Public
License). Pupil diameter and eye movements were not recorded
during examination because they were not supported by the VR
glasses used. The points are projected using proper trigonom-
etry adjustment to compensate for the classical perimeter bowl
of VR glasses so that stimuli appear on the retina as if they were
projected from a classical bowl perimeter (Figure 6).
Examination procedure
During testing, the patient should sit comfortably, put on the VR
glasses, and adjust the head straps. The VR glasses should not be
tilted, off-center, too high, or too low. Pupil distance should be
adjusted with the rotating knob on top. To optimize image qual-
ity, focus distance should be adjusted with the 2 rotating knobs
on both sides of the VR headset until the picture is sharp.
The VR glasses should be positioned appropriately to
avoid lens rim artifact (LRA), which can sometimes be
confused as nasal step scotomas. According to a study in cen-
tral static threshold visual fields (Humphrey 30-2 Program)
performed with a corrective lens, LRA was present in 10.4%
of 704 fields examined retrospectively and 6.2% of 276 fields
evaluated prospectively.7
LRA occurred in one of our patients. If it occurs, then
the test should be repeated with better placement of the VR
glasses (Figure 7).
Figure 2 Computer – Virtual reality glasses – computer setup.
Figure 3 Gamma correction adjustment for PC.

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Tsapakis et al
Figure 4 Gamma correction adjustment for mobile device.
Abbrevations: VR, visual reality; APK, Android package kit.
Figure 5 Mobile device display adjustments and points to be tested. (A) gamma correction, (B) brightness adjustment, (C) left eye points, and (D) right eye points.
To avoid LRA, the software allows the doctor to project
all stimuli (at maximum intensity so that all points are
clearly visible, provided there is no absolute scotoma)
and make appropriate adjustments. In most cases, this is
enough (Figure 8).
The software locates the blind spot automatically and
adjusts the location and size of the test points. Furthermore,
the location and size of test points can be set manually.
Each eye was tested separately, and no eye patch was
used. During testing, the patient should stare at the central
fixation point and click a mouse whenever he/she sees a
visual stimulus on the display (Figure 9).
The patient is free to change position or move his/her head
while testing. VR glasses are lightweight; they weigh ~385 g
while the smartphone weighs ~179 g. The patient may use
his/her hand to hold the VR glasses, making testing more
comfortable.
Twenty eyes of 10 patients appearing randomly and con-
secutively at the visual fields lab were tested successively
using a Humphrey perimeter and the VR glasses method
within hours for comparison.
The results were statistically analyzed and compared.
The patients tolerated the VR test very well. All the
patients reported that it was much more comfortable com-
pared to the standard bowl perimeter (Humphrey).

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Evaluation of visual eld examination method using virtual reality glasses
Figure 6 Trigonometrical projection to compensate bowl perimetry.
Figure 7 Rim lens artifact.
Statistical analysis
Point-to-point correlation coefficient (r) between the VR
glasses and the Humphrey perimeter was computed for each
eye and for all eyes together using the InStat version 3.05 of
GraphPad Software, Inc. When the distribution of values was
not normal, nonparametric Spearman correlation coefficient
(r) was used.
VR glasses tests are 24° (52 points), whereas Humphrey tests
are 30° (76 points). Only the corresponding (common 52 points)
between these are taken into consideration (Figures 10–16).
Results
Table 1 Point to point Spearman coefcient (r) between the two
methods for each eye
Eye Spearman correlation
coefcient (r)
Standard
deviation
P-value
(one-tailed)
1 0.736955 6.594795 ,0.0001
2 0.765154 4.90298 ,0.0001
3 0.875855 5.1637 ,0.0001
4 0.792082 2.449182 ,0.0001
5 0.773847 3.754133 ,0.0001
6 0.75502 5.163674 ,0.0001
7 0.865649 2.717742 ,0.0001
8 0.833976 6.698726 ,0.0001
9 0.838132 2.870508 ,0.0001
10 0.766863 5.146533 ,0.0001
11 0.870688 2.422245 ,0.0001
12 0.848471 2.828427 ,0.0001
13 0.850762 2.313561 ,0.0001
14 0.889794 2.154654 ,0.0001
15 0.745111 9.614359 ,0.0001
16 0.829142 3.223862 ,0.0001
17 0.725046 5.796804 ,0.0001
18 0.806027 3.376511 ,0.0001
19 0.879466 3.225733 ,0.0001
20 0.722703 4.385763 ,0.0001
Total results
Mean Spearman
correlation coefcient (r)
Mean standard
deviation
P-value
(one-tailed)
0.808537 4.19494 ,0.0001

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Figure 8 Software visual eld test user interface.
Figure 9 Patient taking the test.
Figure 10 (Continued)
In each eye and in all eyes together, the mean difference
value between the two methods was statistically significant
at P,0.0001.
The correlation coefficient (r) in all tests between the two
methods was statistically extremely significant at P,0.0001.
Discussion
VR glasses perimetry has many similarities to classical bowl
perimetry. There are some differences due to the hardware
used. In all bowl perimeters, the results are comparable to
a significant degree, but they are not identical because each
perimeter is different from others.
For example, in the Octopus perimeter, a 5 dB attenua-
tion is equal to 316 asb, whereas in the Humphrey perimeter,

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Evaluation of visual eld examination method using virtual reality glasses
Figure 10 Results, eye 1–3.
Figure 11 (Continued)

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Tsapakis et al
Figure 11 Results, eye 4–6.
Figure 12 (Continued)
the VR glasses perimetry method and the Humphrey perimeter,
yet the correlation coefficient (r) between the two methods
was statistically extremely significant (r=0.808, P,0.0001;
Table 1). For this reason, if we want the results to be comparable,
then the same device should be used for consecutive tests.
a 5 dB attenuation is equal to 3160 asb. In Humphrey, 0
dB correspond to 10,000 asb, whereas in Octopus, 0 dB
correspond to 1,000 asb stimulus. Such differences make
comparisons more difficult between different devices. This
justifies the statistical difference between the mean values of

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Evaluation of visual eld examination method using virtual reality glasses
Figure 12 Results, eye 7–9.
Figure 13 (Continued)
Visual field testing is a subjective examination. The
variability is significant, and the more visual field damage
there is, the greater is the variability of the results.8,9 Test-
ing the same eye/patient twice in the same day using the
same machine does not produce identical results. It should
be noted that the differences between devices are mainly
due to the differences in the hardware used and the lumi-
nosity of the devices. As the available luminosity and
luminosity steps of one device approaches the other, the
results become more comparable, if both perimeters are

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Tsapakis et al
Figure 13 Results, eye 10–12.
Figure 14 (Continued)
their heads freely. Furthermore, VR glasses method has
low cost, and this makes it suitable for use when cost is an
important factor.
High correlation coefficient between VR glasses and the
Humphrey perimeter shows that the method is reliable at least
when compared to the Humphrey perimeter and probably
suitable for clinical use.
running the same algorithm. The results between different
perimeters are similar but not identical. Other studies have
found corresponding results.10–15
The most important advantages of VR glasses method
are the ease of use and the comfortable patient position; in
fact, it has been found that the patients tolerated the test well
and fixation losses occurred rarely.16 The patients moved

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Evaluation of visual eld examination method using virtual reality glasses
Figure 14 Results, eye 13–15.
Figure 15 (Continued)
An additional application for smartphones is Visual
Fields Easy designed to use the iPod screen to perform a fast
screening test of the visual fields developed at the University
of Iowa (Iowa City, IA, USA).
Virtual Eye perimeter is another device operated through
a portable Windows computer (laptop or desktop). A simple,
single-screen graphical user interface was designed to
emulate the performance of standard instruments such as the

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Tsapakis et al
Figure 16 Results, eye 19, 20.
Figure 15 Results, eye 16–18.
Humphrey field analyzer (HFA II), from Carl Zeiss Meditec
(Dublin, CA, USA), or Easyfield from Oculus (Wetzlar,
Germany). This device requires VR goggles with proprietary
interface electronics and a trial lens holder; when the stimulus
is detected, the fixation point moves to the position of the
detected stimulus.14–16
The Kasha visual field is a system that uses two full color
0.7 inch ×0.7 inch LCD systems. Early trials comparing this

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Evaluation of visual eld examination method using virtual reality glasses
head-mounted perimetry device with the Humphrey field
analyzer have found comparable results in terms of field
classification. The authors stated that further trials were
necessary in order to fully evaluate this device relative to the
standard perimetry tools such as the Humphrey or Goldmann
field analyzers.4
The advantages of our system are that it does not require
proprietary hardware; the screen is large enough, which
eliminates the requirement of moving the fixation point, and
the patient uses his/her own glasses.
The software is freely available to non-profit institutions
by contacting the corresponding author or by sending an
email at info@visual-field.com.
Disclosure
The authors report no conflicts of interest in this work.
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