Keywords
visual field - glaucoma - virtual reality perimetry - Melbourne Rapid Field - tablet
perimetry
Introduction
Visual field examinations quantify functional glaucoma damage and therefore play a
vital role in glaucoma diagnostics and management. The classical visual field examination
involves static automated hemisphere perimetry using a hemispherical bowl in a darkened
room. Many patients find this subjective examination challenging, as it requires time,
concentration, and a learning curve. One study examining glaucoma patient preferences
for follow-up examination showed the visual field examination to the least popular
of all the examinations, including intraocular pressure measurement and instrumental
diagnostics [1]. Other studies have also shown visual field examination to cause more anxiety in
patients compared to other glaucoma examinations, which also diminishes reliability
in the results [2], [3].
The necessity of hemisphere perimetry has been questioned, especially during the pandemic.
Novel innovative perimetry methods such as a virtual reality perimeter headset (VR
headset) or head-mounted display (HMD) and tablet-based perimetry offer many benefits
over the conventional method and may play an important role in glaucoma management
in the future [4].
The aim of this study was to determine the acceptance of new portable systems amongst
glaucoma patients.
Methods
Sampling
The study sample consisted of 204 glaucoma patients aged between 19 and 93 (mean age:
67.5 ± 12.6). Each patient was examined using conventional hemisphere perimetry (HP)
first, followed by either one of the two new perimetry methods (virtual reality headset
or tablet-based perimetry) at the Department of Ophthalmology, University Hospital
Cologne, Germany. Two different examiners consecutively and independently performed
data collection and patient examination in the two groups. The devices used were:
1. Octopus 900 (Haag-Streit Germany) for hemisphere perimetry, 2. PalmScan VF 2000
(MicroMedicalDevice, USA) for virtual reality perimetry (VRP) using a VR headset in
Groups 1 and 3; and Melbourne Rapid Fields (MRF) Glaucoma app (version 5.0, Glance
Optical Pty.Ltd., Melbourne, Australia) in Group 2, running on an iPad Pro (Apple
Inc., USA) for tablet-based perimetry (TBP). The PalmScan VF200 system and MRF app
were both CE-certified Europe and FDA-approved in the USA.
We used a modified Hodapp glaucoma classification system based on the reference values
of hemisphere perimetry on each group, results as follows: Mean deviation more than
− 6 dB: mild, − 6 to − 12 dB: moderate, and less than − 12 dB: severe.
The Cologne University Ethics Committee approved the study (reference: 21 – 1502_2);
all patients signed their informed consent.
Examination procedure
We briefed the patients on the examination procedure and obtained their written consent
at the beginning of each examination. All patients were familiar with hemisphere perimetry
(HP) and had already taken an HP examination more than once in the past. We then explained
the specifics of each examination using the two novel methods to the patients. Each
patient was examined using classical hemisphere perimetry ([Fig. 1]). We used the standard system at our hospital, TOP 30 – 2 (Tendency-oriented Perimetry)
for the purpose. Trend-oriented perimetry optimises rapid threshold testing, reducing
examination times by almost 80% to only 2 – 4 minutes compared to 6 – 8 minutes using
a dynamic strategy or 10 – 12 min with the normal strategy [5], [6]. The TOP algorithm methodically correlates thresholds at neighbouring locations.
The first test points are presented at levels above the threshold, easily
guiding inexperienced patients into the test method.
Fig. 1 Examination situation using a classic hemispherical perimeter (Octopus, Haag-Streit):
The patient sits slightly leaning forward in front of the hemisphere perimeter. The
examiner adjusts the seat height to align the patientʼs head. The patient holds a
wired clicker in the right hand. The right eye is covered for the left eye to be examined.
After that, we used one of the two new perimetry methods using either a VR headset
or a tablet to examine the patients. Finally, each patient completed a questionnaire
after taking the two visual field examinations ([Fig. 2] and [3]).
Fig. 2 Patient questionnaire on the examination using a virtual reality headset compared
to classical hemisphere perimetry.
Fig. 3 Patient questionnaire on the tablet-based examination compared to classical hemisphere
perimetry.
Virtual reality perimetry
The VR headset consists of three components: A head-mounted display (MHD), a clicker,
and a tablet. The examination procedure is similar to classical hemisphere perimetry.
The patient puts on the headset, which is secured using head straps. Well-adjusted
headbands compensate for the weight of the VR headset, which also contains a smartphone;
the examination uses this smartphoneʼs screen. The VR headset is padded. The surface
contacting the patientʼs face can be cleaned using disinfectant, or a pre-cut disposable
hygiene cover can be used instead. The patient holds the clicker in one hand and pushes
the button or switch after seeing a light stimulus that appears during the examination.
The patient can be kept in a comfortable position during the examination ([Fig. 4]). The clicker connects to the tablet using Bluetooth. The examiner guides the examination
on the tablet. We used the manufacturerʼs recommended standard system, Central 24-2
Threshold, with our glaucoma patients. According to the manufacturer, this examination
strategy is one of the most commonly used and is recommended for examinations on glaucoma
patients. Also note that this test strategy uses several test points for localising
the blind spot and as fixation control in contrast to the TOP strategy used in hemisphere
perimetry, explaining the high number of test points applied and longer test duration.
The tablet requires a Wi-Fi connection. The examination ends with the result shown
on the tablet; this result can also be exported to PDF format and printed out if required.
Fig. 4 a Visual field testing using a VR headset. The patient sits in a comfortable position,
puts on the VR headset, and holds the wireless clicker in one hand. b Sample printout of an examination result using a VR headset.
Tablet-based perimetry
Tablet-based perimetry (TBP) requires a tablet and an installed app. The MRF glaucoma
app was designed for iOS and runs on iOS version 8 or newer. The lightness level on
the display is automatic. The patient holds the tablet at around a foot away. The
room needs to be darkened without any reflections from external light sources reaching
the surface of the tablet, and the eye not being examined needs to be covered. The
patient keeps focused on a red cross (fixation cross) appearing in the middle of the
display at the beginning of the examination. This serves to localise the blind spot
and test the central visual field. The fixation cross then moves to the four corners
of the tablet, one after the other. Fixation is controlled by following the location
of the blind spot. The patient taps anywhere on the tablet surface or in touch circle
at the lower right area of the screen with the thumb or index finger on seeing a light
stimulus ([Fig. 5]), so
the patient registers a response to light stimuli directly on the tablet screen. The
app has an optional multilingual acoustic assistance feature that sounds at regular
intervals to keep the patient focused; this feature can also be switched off. Our
examinations took place under normal lighting conditions during daytime hours in examination
rooms at our hospital.
Fig. 5 a Visual field testing using a tablet. The patient holds the tablet in the hand supported
on a table. The eye being examined remains open with an eye patch covering the other
eye. The patient sees the fixation cross in the middle of the tablet screen (thick
arrow). The touch zone is in the bottom right corner. The light stimulus (thin arrow)
appears to the left of the fixation cross and is presented to the patient. The patient
taps the surface of the tablet to register seeing the light stimulus. b Sample printout of an examination result using the Melbourne Rapid Fields tablet
app.
We used Central 24 – 2 Full Grid Threshold Test system, a modified version of the
24 – 2 system that tests 24° × 21° of the visual field, in the present contribution.
a modified 24 – 2 software package that tests 24° × 21° of the visual field. The test
uses fifty-six fixed points and takes around four minutes for each eye. The manufacturer
recommends this test strategy for examinations on glaucoma patients.
Results
We examined 204 patients in total. Group 1 (VRP) encompassed n = 101 patients and
202 eyes, compared to 103 patients and 206 eyes in Group 2.
The average age of patients in Group 1 (n = 101) was 69.1 ± 11.9 and 66.0 ± 13.2 in
Group 2 (n = 103) (age given as the mean ± standard deviation).
Gender distribution was 52% (male) in Group 1 and 40.4% (male) in Group 2.
Glaucoma stages in Group 1 and Group 2, respectively, according to the modified Hodapp
classification were as follows: 37.9% and 44.5%: mild; 27.6% and 26%: moderate; and
34.5% and 29.5% severe.
[Tables 1] and [2] summarise the results of the questionnaire from the patients in the two groups.
Table 1 Results from asking patients for their general impression of the new perimetry methods;
Group 1 (VRP: VR perimetry with a headset) and group 2 (tablet). This table summarises
the results of the two subgroups using the VR headset (VRP) and the tablet; this necessarily
includes blank cells in the table.
|
Questions
|
Group 1 (VRP)
|
Group 2 (tablet)
|
|
Yes
|
No
|
Donʼt know
|
Yes
|
No
|
Donʼt know
|
|
Are you familiar with using virtual reality headsets or tablets?
|
6%
|
94%
|
0%
|
58.4%
|
41.6%
|
0%
|
|
Did you experience any difficulties using the clicker with the VR headset?
|
3%
|
96%
|
1%
|
|
|
|
|
Did you feel you were more distracted using the tablet compared to hemisphere perimetry
during the examination?
|
|
|
|
26.3%
|
68.7%
|
5.1%
|
|
Did you experience any difficulties tapping the tablet interface when you saw a light
stimulus?
|
|
|
|
11.1%
|
85.9%
|
3%
|
|
Did you feel that you could see the light marks less clearly using the VR headset
or on the tablet compared to hemispherical perimetry?
|
19%
|
77%
|
4%
|
0%
|
99%
|
1%
|
|
Did you experience more difficulties keeping focused on the fixation point on the
tablet compared to hemisphere perimetry?
|
|
|
|
9.1%
|
90.9%
|
0%
|
|
Did you find the examination more tiring using the VR headset or tablet compared to
hemisphere perimetry?
|
8%
|
91%
|
1%
|
5.1%
|
84.8%
|
10.1%
|
Table 2 Results from the patient survey on direct comparison between the two devices they
used – conventional method vs. new method.
|
Group 1 (VRP)
|
Group 2 (tablet)
|
|
VRP
|
HP
|
Both the same
|
Tablet
|
HP
|
Both the same
|
|
VRP: Virtual reality headset perimetry; HP: hemisphere perimetry
|
|
Which examination method could you see yourself using regularly to monitor your condition?
|
80%
|
7%
|
13%
|
81.8%
|
3%
|
15.2%
|
|
Which examination method did you prefer for duration?
|
35%
|
14%
|
51%
|
54%
|
11.1%
|
34.8%
|
|
Which procedure did you prefer for keeping focused?
|
54%
|
6%
|
40%
|
62.1%
|
10.1%
|
27.8%
|
|
Which procedure did you prefer for comfort (head and body posture)?
|
86%
|
7%
|
7%
|
90.9%
|
6.1%
|
3%
|
In Group 1, 58% of patients found the VR headset easier to use compared to the conventional
method, 19% much easier, and 19% the same; 4% found it more difficult.
In Group 2, 53.5% of patients found the tablet easier to use compared to the conventional
method, 35.4% much easier, and 8.1% the same; 2% found it more difficult.
In Group 1, 51% of the patients expressed no preference for either method regarding
duration compared to 40% regarding need to keep focused, followed by a preference
for the VR headset at 35% for duration and 54% for the need to keep focused. In contrast,
54% of patients in Group 2 preferred the tablet regarding duration and 62.1% regarding
focus whereas 34.8% expressed no preference for duration and 27.8% for focus, rating
both methods the same. The only statistically significant difference between the two
groups (VRP and TBP) applied to duration and need to keep focused at p < 0.001 and
p = 0.022, respectively (chi-square test). There were no significant differences in
choice and comfort regarding the new methods.
The visual field examination using the VR headset took 6.26 ± 1.88 min (mean ± standard
deviation; min. 2.11, max. 15.15 min) compared to 4 ± 0.71 min (mean ± standard deviation;
min. 2, max. 6.03 min) using the tablet. In contrast, the hemisphere perimetry examination
took 2.67 ± 0.98 min (mean ± standard deviation; min. 1.66, max. 9.88 min).
Discussion
The results of the present contribution revealed that most “experienced” glaucoma
patients found the perimetry examination to be less strenuous using either of the
novel perimetry methods (VRP and TBP) compared to hemisphere perimetry (HP). The portability
of the two devices provides an explanation for the high level of satisfaction regarding
comfort and ergonomics in the examination. Hemisphere perimetry requires the patientʼs
head position to be secured, whereas the two new perimetry devices are flexible in
this regard. This allows for a high degree of versatility in examination conditions
– a visual field examination using one of the new methods may be performed at the
patientʼs bedside, on children, or on patients with physical disabilities with difficulties
positioning themselves in front of a hemisphere perimeter, such as patients confined
to a wheelchair.
Portable systems are also less expensive than conventional hemisphere perimeter systems;
apart from that, they are suitable for home use in self-monitoring or in areas with
limited ophthalmological care, such as in rural areas [7], [8]. In addition, the novel methods are also suitable for visual field examinations
on children. Groth et al. examined fifty healthy children and adolescents aged 8 to
17 using a VR headset – albeit a different model from the one used in the present
contribution – and showed a high level of patient satisfaction qualifying the method
as a novel option for visual field examinations in this age group [9]. Tablets are also now widely used in the classroom, so children are becoming increasingly
familiar with this kind of device.
Regarding examination duration and need to keep focused, patients did not show a clear
preference for any method with mixed preferences for the new perimetry examination
method compared to the conventional method. Even so, the VRP and the TBP duration
averaged around two to three times that of hemisphere perimetry. For VRP, this was
due to the increased number of test points used by the system compared to HP. We used
the standard system recommended by the manufacturer for glaucoma patients. One possible
explanation for the longer study duration could be the large number of patients with
severe glaucoma – the more defects there were, the longer the examination took. Other
authors also came to a similar conclusion on duration [10], [11].
Another benefit from the portable systems would be the potential increase in patient
compliance and adherence due to the obvious opportunity for telemedical application.
The tablet-based method would seem especially promising in this regard due to the
widespread use of these devices in the population. More than half the patients we
examined (58.4%) reported that they were already familiar with using a tablet. Prea
et al. demonstrated very high patient compliance with weekly self-testing at home
both over a short and a long period – six weeks and twelve months – in a medium-sized
to large cohort of glaucoma patients in two telemedicine studies [12], [13]. This clearly indicates the high level of suitability for TBP in telemedical care
with patients bringing their visual field test results taken at home for follow-up
assessment at the ophthalmologistʼs appointment.
The diagnostic accuracy of these portable systems has been tested on small patient
cohorts for validation in the literature. Shetty et al. demonstrated very good glaucoma
detection using VRP (PalmScan 2000; the same device as the one we used) in a study
on 166 eyes [14]. Harris et al. demonstrated good comparability between the MRF app and hemisphere
perimetry in forty healthy patients [15]. Kong et al. also showed a strong correlation in their results from TBP using the
MRF app compared to hemisphere perimetry as well as a comparable test-retest reliability
[16]. Further validation studies are still required to establish equivalence in the new
methods compared to HP. However, there are currently several VR headset and tablet-based
perimetry app manufacturers on the market, so the technology is highly heterogeneous.
Another important factor is patient selection for examination using the new methods,
especially TBP. At total of 68.7% of patients in Group 2 (tablet) reported that they
were no longer distracted during the examination using the tablet compared to hemisphere
perimetry. This means that more than one in four patients at 26.3% reported feeling
more distracted using TBP. This needs to be considered in selecting patients. Apart
from that, 99% of the patients in Group 2 reported not experiencing any problems in
seeing the light stimuli on the tablet. This is a surprisingly unambiguous response
running contrary to potential expectations that the reflective tablet surface might
pose a potential visibility problem. Some studies on TBP have even proposed specific
strategies for optimal tablet positioning away from windows, or partition wall installations
to shield the tablet display from reflections [17]. We took no such measures in the present contribution,
and yet none of our patients reported any issues seeing the stimuli, which was most
likely because they intuitively took a proper posture while holding the tablet.
Another important point is that comparability is lower in TBP compared to hemisphere
perimetry in severe glaucoma. Prince et al. showed significant deviations in diagnostic
accuracy using TBP in moderate to severe glaucoma in a West African cohort of 103
patients, but potential for screening in a resource-poor setting [18].
A similar study by Freeman et al. examined eighty-one patients with TBP using the
MRF app with the aim of determining acceptance, using a questionnaire for the purpose.
Just over nine in ten patients at 90.1% reported very good experiences with the tablet,
with 75% responding that they would be willing to use this perimetry method with a
tablet on a weekly basis [19].
The aim of our study was to evaluate how our patients experienced the examination
using the new methods towards determining their potential acceptance amongst glaucoma
patients in Germany. We found a clearly favourable positive response on acceptance
for the new methods. This is a promising trend, representing a potential door opener
for portable perimetry methods and telemedicine, especially regarding patient adherence.
Conclusion
Portable perimetry devices are a promising development with the potential for a paradigm
shift in glaucoma care in Germany. This is the first study in Germany to gauge subjective
perceptions of visual field examinations using either VR headsets or tablet-based
apps amongst glaucoma patients. These survey results unambiguously demonstrate that
glaucoma patients are generally open to using these new and innovative visual field
examination options. High levels of patient acceptance could lead to good patient
adherence. These innovative perimetry methods are also suitable for visual field examinations
at home and in telemedical care scenarios. Our results warrant further studies on
validating the two devices against conventional hemisphere perimetry towards implementing
these new methods in Germany in the long term.
