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9 Color Vision
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with CVD. The error score for each cap is the
absolute sum of differences between adjacent
caps. The error score of each color cap can be
plotted on a radial line; the subsequent polar plots
can reveal the type and severity of the defect. The
total score can be calculated by summing up the
errors of all caps and subtracting 170 (2 × 85
caps). Quantifying and plotting the score can be
expedited by entering the scores in template
Excel sheet.
Advantages:
• Quanties the severity ofCVD unlike other
screening tools.
• Useful to quantify colour vision deciency
even inacquired retinal diseases
Disadvantages:
• Time-consuming
• Performance is associated with IQ [17]
9.5.2.2 D15 Test
This test is similar to the FM 100 hue test,
except that the D15 test is a screening tool.
This test involves a color arrangement task in
which the patient arranges 15 caps in a natural
sequential manner. The step sizes in chromaticity are much larger in the D15 test than in
the FM 100 hue test. The number on the back
of the color caps can be mapped on a special
charting map to identify the type of CVD.In
the D15 test, the samples are shown in the
color space (Fig. 9.4a). Colors become more
desaturated as one moves toward the neutral
point. The lines are joined based on the numbers on the color caps, and the resultant lines
parallel to the confusion axis yield the type of
defect (Fig.9.4b).
There are other types of color arrangement
tasks, such as:
(a) ColorDx D15 test
Fig. 9.4 CIE coordinates ofD15 caps in the CIE 1931
color space (panel a) and interpretation of the results. R
refers to the reference cap(panel a). A normal trichromat
is expected to make no errors (panelb- upper left). The
lines that emerge parallel to 4 and 13 will likely be deutan
defects(panel b- upper right). Similarly, patterns of a line
parallel to 3 and 12 represent the protan defect(panel b -
lower left). The lines emerging parallel to 7 and 15 caps
represent the tritan defect(panel b- lower right). Note that
D15 does not distinguish between anomalous trichromats
vs. dichromats
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A. R. Hathibelagal
(b) Desaturated D15 test
(c) Lanthony D15 test
9.5.3 Color Matching
9.5.3.1 Anomaloscope
The anomaloscope works on the principle of
color matching. It allows differentiation between
anomalous trichromats and dichromats. The test
can also be used to subclassify the type of
CVD.In this test, the subject views a 2° circular
eld. The upper half comprises of a green
(549 nm) and red (664 nm) mixture, which the
operator controls. The observer controls the
lower half eld which is ayelloweld (589nm).
There is an adapting screen (9 cm) called the
Trendelenburg screen below the eyepiece used
for preadapting before a color match to obtain
stable color-matching results. The outcomes are
categorized by the size of the matching range and
the midpoint position. The red/green mixture
range can vary from 0 (pure green) to 73 (pure
red). The R-G setting and wavelength specications can vary slightly across different instrument
manufacturers. The normal midpoint position for
trichromats is around 40 units and a matching
range of 3–4units. Matches made by individuals
with CVD are not acceptable to normal trichromats. Deuteranomalous individuals require more
green, and protanomalous individuals require
more red in color matching. One way to differentiate a protanope from a deuteranope is based on
the luminance of the yellow (too dark in protanopes vs. normal luminance in deuteranopes).
The anomaly quotient is derived using the R/G
ratio of the tested individual divided by the R/G
ratio of a normal trichromat.
An anomaly quotient >1.33 indicates a prot-
anomaly, and <0.75 indicates a deuteranomaly.
One of the disadvantages of an anomaloscope is
that it requires the examiner administering the
test to be trained. The Pickford-Nicolson anomaloscope is more customizable in terms of eld
size and the type of defect that can be investigated. One of the general instructions for any
anomaloscope testing would be to avoid naming
the color and ask the observer what they perceive.
Additionally, the establishment of a devicespecic, population-specic normative database
is recommended.
The other tests based on the color-matching
principle are as follows:
(a) The Medmont-C test, which allows one to
differentiate protans from deutans.
(b) The Sloan achromatopsia test is used for
detecting rod monochromats.
(c) The City University Test is also based on
color matching.
9.5.4 Threshold-Based Digital Color
Vision Tests
Digital color vision tests are usually thresholdbased tests. The most common threshold-based
tests are as follows:
(a) CAD (Color Assessment and Diagnosis) test
(b) Cone contrast test
(c) Cambridge color Test
9.5.4.1 CAD Test
The Color Assessment and Diagnosis (CAD) test
was developed by Barbur etal. at City, Universityof
London(U.K.) [18, 19]. It consists of a specialized
color-calibrated display connected to another
computer with a pre-installed CAD program. The
saturation threshold is measured in each of the 16
different hues and separate chromatic thresholds,
namely R-G and B-Y thresholds are computed.
The normative valuesfor the CAD test have been
established [19]. Based on comparisons with the
age-matched normative values, the severity of
color vision is classied as mild, moderate, or
severe color vision loss [20].
9.5.4.2 Procedure
The procedure involves identifying the least
amount of saturation required fora given hue to
detect the direction of the target. In this task, a
colored target moves in one of the four diagonal
directions (Fig.9.5a), and the participant’s task is
a
b
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Fig. 9.5 A screengrab of the CAD test stimuli and the
summary of the CAD test report. Panel (a) shows four
different colored targets in a dynamic noise background
(note that the noise [black and white squares] appears
static in this gure; however, the noise is dynamic during the test). At any point during the test, only one colored stimulus would be presented. Panel (b) shows the
CAD summary results of an individual with deutan de-
to identify the location where the targets’ end
position will be. The difculty (saturation) of the
target is adjusted based on an adaptive staircase
procedure. A resultant single outcome variable is
ciency and normal Y-B color vision. Chromatic thresholds computed for each hue direction are plotted in the
color space of the 1931 CIE (Commission Internationale
de l'éclairage) on panel (b). The small central ellipse
indicates the normative values from a large cohort of
normal trichromats. The thresholds outside the ellipse
are abnormal and aligned with the deutan confusion
lines (green)
ing levels of chromatic contrast, the higher the
score (indicating normal trichromatic vision).
Conversely, lower scores indicate CVDand they
can be graded.
obtained separately for R-G and B-Y color vision
(Fig.9.5b). The lower the CAD score, the better
the color vision.
The same group that developed the CAD test
developed the CAD screener program. This test
is aimed at only screening the CVDs. The CAD
screener has high sensitivity and specicity and
is a 2-alternate forced-choice test. The target
moves either in the upper left or upper right
direction. Only those who fail the CAD screener
test are recommended for complete CAD testing.
Currently, the CAD test is used for occupational
color vision purposes in aviation and transport
industries in the UK.
9.5.4.4 Cambridge Color Test
The Cambridge Color Test [22] is now part of a
suite of tests developed by Cambridge Research
Systems (Kent, U.K.). The test works on the principle of pseudoisochromatic plates. There are
two different test modes: the Ellipse test and the
Trivector test. The participant’s task is to identify
the opening’s direction (1 of 4 options) in the letter C. This procedure is repeated for different
hues, and the results are presented as ellipses.
The bigger the ellipse, the poorer the color vision.
The orientation provides the chromatic axis classifying protans/deutans/tritans.
Besides the above four categories of colour
9.5.4.3 Rabin Cone Contrast Test
Cone contrast is a letter-based digital color vision
test [21]. The cone-isolating axis is L, M, or S
cone. There are a total of 20 letters. The larger the
number of letters read by the person across vary-
vision tests described, there color-naming tests
are typically used for occupational purposes. The
important colors for transport and navigation are
red, green, orange, and white [20]. In many countries, including India, the lantern test is used to
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Table 9.3 Comparison across different color vision tests
Pseudoisochromatic
Parameters
Advantages Easy to use
Disadvantages Wear and tear of the
Examples Ishihara, HRR
Indications Screening purpose Screening and
plates
Relatively cheaper
High sensitivity
plates over time
Lack of uniform
cut-off criteria can
result in poor
specicity
The number of
plates read does not
indicate the severity
of the color vision
loss
plates, Dalton
Isochromatic plates,
Dvorine plates
Color
arrangement tests
Both versions
(screening and
quantication)
are available
Makes the task
interesting
Monocular cues
can affect test
results
Understanding
the task is
challenging for
some subjects
D15, FM 100
Hue test,
Lanthony
desaturated test
quantifying the
type of defect
and severity
Color-matching
tests
Anomaloscope
can distinguish
anomalous
trichromats from
dichromats
Extensive
training of the
operator is
required
Expensive
Medmont C and
Anomaloscope
testing
To differentiate
the types of
CVD
(anomalous vs
dichromats).
Color-naming
tests
Easy to use
Practical
Often, the
manufacturer
does not
support repair
and spare parts,
especially for
lantern tests
City University
Test, Lantern
tests
To test the
naming of
colors for usage
in an
occupational
environment
A. R. Hathibelagal
Digital color vision
tests
Can be used in
screening as well
as for
quantication of
the severity of
CVD
Expensive and
regular
calibration
Cannot
distinguish
between
anomalous
trichromats and
dichromats
CAD test,
Cambridge Color
Test, Rabin Cone
Contrast Test
Can be used to
quantify the
severity of
congenital and
acquired
conditions
Also suitable for
setting
upoccupational
safety color
vision standards
grade and assess the severity of color vision loss.
There are many versions of lantern tests, such as
the Holmes Wright, CN Lantern, Edridge-Green
lantern, and Farnsworth lantern tests. The
Dvorine test also has a color-naming component
present in it. The summary of the different types
of color vision tests is provided in Table9.3.
Several commercially available lenses use different wavelength-ltering mechanisms across
the visible spectrum to claim that CVD can be
‘cured’. The “true improvements” with these lters are typically noticed in individuals with
anomalous trichromacy and not with dichromats.
The variable results of these lters could be
attributed to the lack of a classication of anoma-
lous trichromats from dichromatsin many of the
studies and the type of task performedbythe participants. Therefore, the outcomes of aids for
CVD is not straightforward to judge and should
be dealt on a case-to-case basis.
9.6 Acquired Color Vision
Deciency
Acquired color vision deciency is distinct from
congenital color vision deciency in several
aspects, such as type of defect, magnitude, and
stability (see Table 9.4 for more details).
Therefore, it is critical that monocular testing is
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Table 9.4
color vision deciency
Congenital color vision
deciency
Mostly R-G defect Can be either R-G or
Stable throughout the life Can improve or worsen
Other visual functions,
such as acuity and
contrast sensitivity are
normal
Type of defect can be
identied
Males are more affected No gender predilection
Table 9.5
show acquired color vision deciencies
R-G defect B-Y defect
Optic neuritis Age-related macular
Papillitis Chorioretinitis
Leber’s optic atrophy Central serous retinopathy
Stargardt disease
Fundus avimaculatusaMyopic retinal
Dominant cystoid
macular dystrophy
Best disease
B-Y Blue-yellow, R-G Red-green
a
Indicate exceptions to Koellner’s rule
Difference between congenital and acquired
Acquired color vision
deciency
B-Y defect
depending on the
magnitude of the disease
Other visual functions
are also affected
Can be non-specic
Common retinal and optic nerve diseases that
degeneration
a
a
Glaucoma
degeneration
Diabetic retinopathy
a
Retinitis pigmentosa
Papilledema
Hereditary autosomal
dominant optic atrophy
a
a
a
done in individuals with acquired color vision
testing. Retinal or optic nerve diseases are the
two most common reasons for acquired color
vision deciency (see Table9.5 for more details).
Koellner’s rule states that the inner retina and
optic nerve defects cause R-G defects, and the
outer retinal and media defects cause B-Y defects.
However, there are several exceptions to this rule.
Color vision can also be considered a functional
biomarker to monitor the efcacy of treatment
outcomes in retinal diseases [23, 24]. Color
vision can be adversely affected even in systemic
conditions, such as prediabetes [25], before ocular involvement. Color vision outcomes can
alsohelpin arriving at the correct diagnosis. For
example, autosomal dominant tritan (B-Y) defect
is specic to autosomal dominant optic atrophy.
In addition, the Verriest classication, named
after the ophthalmologist Guy Verriest, is the
most commonly used classication to categorize
acquired R-G and B-Y defects to predict the
potential diagnosis [26].
9.7 Conclusions
It is important to test color vision regularly in
clinical practice. It is also crucial to decide on the
choice of color vision test based on one’s understanding of the strengths and limitations of the
test and its requirements on an individual basis.
Depending on the severity and type of color
vision defect, one can be counseled regarding
viable career choices and suggest potentialaids
for helping in everyday life.
Funding Hyderabad Eye Research Foundation.
Disclosure None.
References
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SS, Hussaindeen JR, Ramani KK. Dalton’s
pseudo- isochromatic plates and congenital color
vision deciency. Clin Exp Optom. 2020;103:853–7.
15. Honson VJ, Dain SJ.Analysis of the mark II edition
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16. Cotter SA, Lee DY, French AL.Evaluation of a new
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AC. Performance on the Farnsworth-Munsell 100hue test is signicantly related to nonverbal IQ.Invest
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JL.Color vision tests for aviation: comparison of the
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Smartphone-Based Ophthalmic
https://t.me/med1917
Imaging
AnandSivaraman , DivyaParthasarathyRao ,
andShanmuganathanNagarajan
10
10.1 Introduction
Smartphones are ubiquitous assets in medical
diagnostics [1]. The VISION 2020 “Right to
Sight” Global Initiative, introduced by the World
Health Organization (WHO) and the International
Association for the Prevention of Blindness
(IAPB), aims to eliminate needless visual impairment and maximize the functional potential of
those with unavoidable blindness [2, 3].
Conditions needing immediate attention include
refractive errors, cataracts, diabetic retinopathy
(DR), glaucoma, corneal blindness, and childhood blindness [2, 4].
Smartphones have been the agbearers of
technology and innovation for over two decades.
They are the personal digital assistants of healthcare professionals, with more than 87% using
either a smartphone or a tablet in their practice
[5]. Their ease of use, portability, connectivity,
and documentation ability through capturing
high-resolution photos and videos at considerable speed with improved camera sensors, fast
processors, high storage capacities, and applications have made them excellent choices for point-
A. Sivaraman (*) · S. Nagarajan
Remidio Innovative Solutions Pvt,
Bengaluru, India
e-mail: anand@remidio.com; shan@remidio.com
D. P. Rao
Remidio Innovative Solutions Inc., Glen Allen, VA, USA
e-mail: drdivya@remidio.com
of- care testing. Ophthalmology relies heavily on
investigations, and in this regard, smartphonebased ophthalmic imaging has gained widespread
adoption in eye care. It is a versatile tool for
patient education, telemedicine-based screening,
and diagnosis using AI-based triaging, academic
research, and clinical documentation.
Additionally, they serve as affordable solutions
for resource-constrained settings.
10.2 A Brief History
ofSmartphone-Based
Ophthalmic Devices:
Evolution ofTechnology
Retinal vasculature is the only part of the human
circulatory system that can be viewed noninvasively. Hence, fundus photography using
smartphone-based devices showed potential in
detecting retinal and, subsequently, systemic diseases [6]. Lord etal. were the rst to demonstrate
the possibility of using a slit lamp and +78D lens
in combination to perform indirect ophthalmoscopy with a +20D lens and phone camera, along
with a penlight, and showed intra-operative captures on a smartphone using a microscope [7, 8].
Bastawrous etal. modied the design for capturing images from videos wherein one could use
the ashlight of the phone itself without a separate penlight [9]. In this design, one could simply
hold a +20D/+28D lens in one hand and the
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024
T. Das, P. Satgunam (eds.), Ophthalmic Diagnostics, https://doi.org/10.1007/978-981-97-0138-4_10
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A. Sivaraman et al.
Fig. 10.1 Adapter-based fundus imaging: (from left to right; rst row) the iExaminer, D-Eye, and Paxos Scope; (second row) PEEK Retina, Volk iNview, and the oDocs Nun
smartphone in the other. Haddock etal. further
improvised on this method by using an application to modify the focus, intensity, and exposure
of the camera while capturing the video. In the
same device, a Koeppe lens was used in addition
to the 20D lens to keep the eyelids open, keep the
cornea wet, and get a better eld of view under
anesthesia [10]. Ryan etal. compared the use of a
20D lens in one hand and an iPhone 5in the other
to capture videos of each eye and compared the
screenshots taken from those videos to standard
3-eld non-mydriatic and 7-eld mydriatic retinal photography on 300 pharmacologically
dilated people with diabetes with good sensitivity
and specicity [11]. This led to further developments in smartphone-based image acquisition for
ophthalmology with improved sensors, image
processing, and light sources; these techniques
also leveraged the use of 3D printed adapters and
eventually developed stand-alone devices integrated with smartphones to capture ophthalmic
images [12, 13]. The iExaminer was the rst
smartphone-based fundus imaging adapter
approved by the US FDA in 2013 [12]. Following
this, multiple adapter-based fundus imaging
modalities like D-Eye, PaxoScope, PEEK Retina,
Volk iNView, and ODocsNun (Fig. 10.1) have
been validated in various settings primarily for
monitoring diabetic retinopathy. These systems
relied on applications to adjust light settings or
modify the light coming from the camera ash
[6, 8]. The systems also used optical designs such
as coaxial illumination or cross-polarizer-based
designs, often requiring pupillary dilation, and
had a eld of view (FOV) between 20° and 55° in
a single shot [12–14]. Such adapters were major
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115
breakthroughs as they could, to some extent,
reduce the operational skills needed (due to their
ergonomic design) to image the central and
peripheral retina through montages [14].
Advantages [15]
• The implementation of point-of-care diagnostics for patients at risk
• Their optical designs come with pre-dened
illumination and imaging paths that eliminate
the need for manual alignment of the illuminating beam with the optical axis for capturing
images
Disadvantages [6, 15, 16]
• The use of coaxial illumination in adapters
causes corneal glare and reex artifacts
• The need for mydriasis for a wider view of the
retina
• The cross-polarizers used to eliminate reection artifacts might lead to non-uniform illumination of the retina causing overexposure of
the optic disc and a lack of illumination of the
tertiary vessels around the macula
• The distribution of colors is a function of the
LED used in smartphones and is not under the
control of the photographer
• The ability of the illumination to meet the
ISO15004 ophthalmic safety standard needs
to be established for every phone used
This chapter will describe some of the
smartphone- based imaging modalities currently
used and practiced in eye care. In the process, we
will also introduce some commercially available
and regulatory body-approved devices that the
authors are familiar with. This should not be construed as a promotion of these products as
describing all devices is out of the scope of this
chapter.
10.3 Fundus Imaging
Present-day smartphone-based devices are moving toward high-quality, reex-free fundus
images. Two of these devices are described
below.
10.3.1 Fundus onPhone (FOP)
andNon-mydriatic Fundus
onPhone (FOP NM)
Non-mydriatic fundus on phone (FOP NM-10)
(Remidio Bangalore, India) captures ~45° FOV
retinal image without dilation (Fig. 10.2) [17].
The device can be used in a desktop or hand-held
mode as per the user's needs [18–20].
Technology: The FOP utilizes a patented
annular illumination-based optical design, infrared (IR) light, and the voice coil motor of the
Fig. 10.2 The fundus on phone (FOP) device, Hand-held (left) and desktop (right) modes of use
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Fig. 10.3 The optical
design of the fundus on
phone devices (detailed
optical design available at
reference patent: retinal
imaging device:
US20140146288A1).
Notations: 60—retinal
imaging device, 62—
illumination module,
64—light source, 66—
illumination axis, 68—
condenser
lens, 70—diffuser, 72—
beam splitter, 74—
transparent plate, 76—light
absorber, 78—projection
lens system, 80—planoconvex lens, 82—doublet
lens, 84—shield, 86—
cornea illumination
doughnut, 88—perforated
mirror, 90—hollow
cylinder 92—projected
portion of the hollow
cylinder, 94—an elliptical
stopper, 96—pupil
illumination doughnut
A. Sivaraman et al.
smartphone camera to remove chromatic aberrations, improve image quality, and obtain highquality images without reection artifacts. The
optical design of the FOP includes an illumination module and an imaging module set perpendicular to each other, with the help of multiple
beam splitters, condensing lenses, mirrors,
absorbers, and diffusers, devoid of crosspolarizers [16, 21]. An annular illuminationbased design provides the camera with a clear
central imaging. A porosity mirror, placed
between the condensing (Objective) and imaging
lens, ensures that all reections are absorbed,
leaving no glare or corneal reection artifacts
(Fig.10.3) [22].
The FOP and the FOP NM-10 have been validated in multiple settings for detecting different
grades and severities of diabetic retinopathy
(DR) and in the tele-screening of DR in realworld settings [18–20].
10.3.2 Vistaro
The Vistaro™, a wide-eld fundus imaging system,
(single shot ~60°) can image an ~90° FOV with
two elds, covering more than a standard 7-eld
ETDRS could visualize [16]. The device, albeit
mydriatic, works on a minimum pupil size of
5 mm. It has a unique auto-capture algorithm
(Fig.10.4) to automatically capture images upon
reaching the correct working distance. The device
captures images of people with refractive errors
from −20D to +20D. The Vistaro™ is equipped
with a unique patient-management software to capture and store images at all times. When there is
internet connection available, the device also backs
up the images to a Health Insurance Portability and
Accountability Act (HIPAA)-compliant cloud
server. The stored images can be sent to specialists
over third- party applications, in real time, or on a
feed- forward basis using telemedicine [16].
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