Color vision has been reported to be affected
in simulated hypoxic conditions (Wilmer
and Berens, 1918; Velhagen, 1936; Schmidt,
1937; Kobrick, 1970; Smith et al., 1976; Vingrys
and Garner, 1987; Richalet et al., 1999) as well
as during exposure to altitude hypoxia (Mod-
ugno, 1982; Richalet, 1983; Richalet et al., 1988;
Richalet et al., 1989; Karakucuk et al., 2004). The
tests used to detect color vision changes in
these studies were anomaloscopes (Richalet,
1983; Vingrys and Garnes, 1987; Richalet et al.,
1988; Richalet et al., 1989; Richalet et al., 1999),
American Optical HRR plates (Vingrys and
Garner, 1987), desaturated D15 panel (Leid and
Campagne, 2001), or the Farnsworth–Munsell
100-hue (FM-100 hue) test (Smith et al., 1976;
Karakucuk et al., 2004). Most previous studies
tested only a part of the color vision spectrum
HIGH ALTITUDE MEDICINE & BIOLOGY
Volume 9, Number 1, 2008
© Mary Ann Liebert, Inc.
Color Vision in the Tritan Axis Is Predominantly
Affected at High Altitude
and IGOR TEKAVC
Tekavcˇicˇ-Pompe, Manca, and Igor Tekavcˇicˇ. Color vision in the tritan axis is predominately af-
fected at high altitude. High Alt. Med. Biol. 9:38–42, 2008.—The purpose of this study was to eval-
uate color vision during high altitude mountain climbing by applying the Mollon–Reffin Mini-
malist test to 14 climbers, all of whom were participating in the expedition to Ama Dablam (6812
m) in Nepal. Before leaving for Nepal (at 300 m), all 28 eyes showed normal color vision in all
3 axes. At 1300 m, 100% of eyes showed normal color vision in the protan and deutan axes, while
25% showed minimally reduced color discrimination in the tritan axis. At 4000 m, 100% showed
normal deutan axis, 4% minimally reduced protan axis, and 72% minimally reduced tritan axis
discrimination. At 5400 m 100% of eyes tested showed normal protan and deutan axis discrim-
ination, while 75% showed minimally and 25% moderately reduced tritan axis discrimination.
Back home at 300 m 3 days after return, 100% showed normal deutan, 4% minimally reduced
protan, and 38% minimally reduced tritan axis discrimination. One year later, all eyes showed
normal color vision in all three axes. Changes in tritan axis discrimination correlated well with
increased heart rate (r0.69; p0.0001) and decreased oxygen saturation (r0.71; p0.001)
at high altitude. This study shows that the tritan color vision axis is predominantly affected at
high altitude, but that this reduced color discrimination is transient.
Key Words: color vision; tritan/protan/deutan color vision axis; natural hypoxic conditions;
Mollon–Reffin “Minimalist” test
Eye Clinic, University Medical Centre, Ljubljana, Slovenia.
Department of Neurosurgery, University Medical Centre, Ljubljana, Slovenia.
and were therefore able to demonstrate only
changes in the red–green chromatic axis. For
this reason, predominantly a decrease in green
versus red sensitivity was shown (Richalet et
al., 1988; Richalet et al., 1989; Richalet et al.,
1999) at high altitude. However, the study by
Smith et al. (1976) demonstrated the specific ef-
fect of simulated hypoxia on color vision per-
formance, which consisted of a greater pro-
portion of errors in the tritan axis. A similar
effect was demonstrated at moderate altitude
(3000 m) (Karakucuk et al., 2004).
The aim of this study was to monitor color
vision changes during the ascent to 5400 m
without supplemental oxygen by using the
Mollon–Reffin Minimalist test, which enables
testing color vision in the deutan, protan, and
tritan color vision axes.
Fourteen mountain climbers (28 eyes) were
included in the study (1 female and 13 male,
mean age 52.4 12.2 yr). They were all partic-
ipants in an October 2005 Slovenian expedition
to Ama Dablam (6812 m), a summit located in
Nepal in the Himalayan range. All mountain
climbers were seasoned amateurs and were ac-
customed to living at an altitude of around 300
m. None of the participants had any color vi-
sion deficiencies (which was documented
through Ishihara plates and the FM-100 hue
test). Their visual acuity was excellent without
any, or with very mild, spectacle correction.
Testing was performed in Ljubljana (300 m,
28 eyes tested) before leaving for Nepal and
then in Katmandu (1300 m, 28 eyes tested), at
base camp (4000 m, 28 eyes tested), and at the
first camp (5400 m, 8 eyes tested). Three days
after returning to Ljubljana, 12 climbers (24
eyes) were retested. Between each test at dif-
ferent altitudes, 3 to 5 days had passed. At each
altitude, besides color vision, three other pa-
rameters (blood pressure, heart rate, and oxy-
gen saturation) were also measured. Twelve
climbers (24 eyes) repeated color vision testing
1 yr after returning from the expedition.
Color vision was tested with the Mollon–Ref-
fin Minimalist test (Mollon et al., 1991). This test
has shown its value because it is quick to ad-
minister and presents the easiest possible task
to the patient, who is required simply to iden-
tify a colored probe chip among five achromatic
distracter chips of varying lightness. The probe
chips vary in chroma, and their chromaticities
lie along dichromatic confusion lines (protan,
deutan, and tritan) that pass through the chro-
maticity of the achromatic chips. As in the first
Ishihara plate, the first chip used is a saturated
orange, which does not lie on any confusion
line, to demonstrate the task and identify pre-
tense or gross pathology. A simple staircase
procedure is then used to establish, for each
confusion line, the number of the chip that can
be reliably distinguished from the distracters.
Altogether there are 15 chips, 5 from each con-
fusion line (deutan, protan, and tritan). The in-
vestigator marks down a number for the last
chip distinguished from distracters (1, normal;
2, minimally reduced; 3, moderately reduced; 4,
markedly reduced; 5, extremely reduced color
vision in a particular axis). The test has proved
its value in testing children (Shute et al., 1998)
and could also be very useful in testing color
vision in extreme environmental conditions
such as high altitude. The value of this test is in
monitoring acquired color deficiencies, and it
can therefore represent an alternative to the FM-
100 hue test or desaturated D-15 test, both of
which demand more time to be completed
(Mollon et al., 1991). Testing conditions were
uniform for all: a bright sunny day was chosen,
the climbers were facing the northern sky, and
sunglasses were not worn before or during the
test. Each eye was tested separately.
Oxygen saturation (S
) and heart rate were
measured with a pulse oximeter (SIMS-BCI,
Inc; 3301, Waukesha, Wisconsin, USA), and
blood pressure was measured with a sphygmo-
manometer (Accoson LTD, London, England).
Statistical significance was set at p0.05,
whereas for correlation Spearman rwas used.
RESULTS AND DISCUSSION
Color vision changed with altitude. Changes
in the deutan axis (green) and the protan (red)
axis were minimal, whereas changes in the tri-
tan (blue) axis were moderate (r0.48; p
COLOR VISION AT HIGH ALTITUDE
Normal color vision was observed in all eyes
tested (28/28) at the initial altitude (300 m) in
all three color vision axes. At 1300 m, no
changes were observed in the deutan or protan
axis, but 7/28 eyes tested showed minimal
changes in the tritan axis. At 4000 m there were
no changes in the deutan axis, whereas 1 of 28
eyes tested showed minimal changes in the
protan and 20 in the tritan axis. At 5400 m, no
changes in the deutan and the protan axis were
observed in 8/8 eyes tested, while all eyes
tested showed abnormal color discrimination
in the tritan axis (6/8 minimal and 2/8 mod-
erate). Back at 300 m, no changes in the deutan
axis were observed in 24/24 eyes tested,
whereas 1 eye showed minimal changes in the
protan axis. Nine eyes, among them all 8 with
changes in the tritan axis at 5400 m, showed
minimal changes in the tritan axis. Details are
shown in Fig. 1.
Twelve climbers were retested 1 yr later, and
no color vision changes were shown in any
Blood pressure, oxygen saturation, and heart
rate changed with altitude. The ranges for
blood pressures (systolic and diastolic), oxygen
saturation, and heart rates at different altitudes
are shown in Table 1.
A correlation between color vision and other
parameters was found. Reduced color vision in
the tritan axis correlated well with increased
heart rate (r0.69; p0.0001) and decreased
oxygen saturation (r0.71; p0.001) at high
altitude. Details are shown in Fig. 2.
This study showed reduction in the tritan
color vision axis with increased altitude. Color
vision changes were detected with the mini-
malist test, which proved to be very useful for
this purpose. Tritan color vision changes cor-
related well with increased heart rate and de-
ˇ-POMPE & TEKAVC
Normal Minimal reduction Moderate reduction
FIG. 1. Color vision changes in the deutan, protan, and tritan axes during the mountain ascent at four different al-
titudes. Results are shown in percentage of eyes tested at each altitude.
creased oxygen saturation at high altitude.
Changes in color vision were, however, not
permanent, since 1 yr after the expedition all
the climbers showed normal color vision.
High altitude hypoxia can trigger color vi-
sion reduction, which has been previously de-
scribed in experimental hypoxic conditions
where the tritan axis was predominately af-
fected (Smith et al., 1976) and in natural hy-
poxic conditions at moderate altitude (3000 m)
(Karakucuk et al., 2004). This study has shown
that color vision in the tritan axis is even more
affected at higher altitude. On the other hand,
this study showed only minimal changes in the
red (protan) and no changes in the green (deu-
tan) axis. Previous studies reported either no
changes (Leid and Campagne, 2001) or a rela-
tive decrease in green versus red (Richalet et
al., 1988) in natural hypoxic conditions. The tri-
tan axis was not tested in these studies.
It is known from other studies of retinal dis-
eases that color vision is predominantly re-
duced in the tritan color vision axis because of
the greater vulnerability of S cones in compar-
ison to L and M cones (Sample et al., 1986;
Greenstein et al., 1989).
The relatively high mean age of climbers par-
ticipating in the study (52.4 yr) could also have
partly contributed to the higher scores on the
tritan axis, as has been reported by the authors
of the test (Mollon et al., 1991). The study by
Karakucuk et al. (2004) showed an increased
number of errors using the FM-100 hue test at
3000 m in a high school student population.
The results of this study are comparable to our
results despite the age difference. In addition,
most of the changes to color vision in our study
were reversible after returning to 300 m: al-
ready 3 days upon arrival and 1 yr later, all the
eyes showed normal color vision. We are aware
COLOR VISION AT HIGH ALTITUDE
Altitude (m) BP syst (mmHg) BP diast (mmHg) S
(%) Hr (beats/min)
300 100–140 70–90 98–100 54–69
(n14) (125.7 11.5) (81.4 6.2) (99.3 0.6) (63.6 5.2)
1300 105–145 70–90 97–100 56–76
(n14) (127.9 13)0. (81.8 6.8) (98.8 1.1) (67.1 5.7)
4000 110–150 70–95 94–99068–84
(n14) (131.1 11.4) (86.8 6.3) (97.5 1.4) (74.4 5.5)
5400 140–150 80–90 84–92078–86
(n4) (142.5 4.6)0(85.0 3.7) (87.5 3.2) (83.0 3.2)
300 105–140 70–90 97–100 54–72
(n12) (126.3 10.8) (79.6 5.3) (99.0 0.7) (65.4 5.4)
The range of values, mean value, and standard deviation for all climbers tested are shown.
BP syst, systolic blood pressure; BP diast, diastolic blood pressure; S
, oxygen saturation; Hr, heart rate.
FIG. 2. A. Correlation between heart rate (Hr) and changes in the tritan color vision axis (Spearman r0.69; p0.0001).
B. Correlation between oxygen saturation (S
) and changes in the tritan color vision axis. (Spearman r0.71; p0.0001).
that illuminant changes minimally with alti-
tude; however, this does not change the fact
that 38% of eyes showed changes in tritan axis
upon arrival back home (at 300 m).
We conclude that high altitude can adversely
affect color vision, predominantly hue dis-
crimination on the tritan color vision axis.
The authors would like to thank Professor
John Mollon, who provided the color vision test
and gave us useful instructions, and all the par-
ticipants in the study. The authors would also
like to thank Mr. Ignac Zidar for his help in sta-
tistical evaluation of the data.
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Address reprint requests to:
University Medical Centre
1000 Ljubljana, Slovenia
Received April 25, 2007; accepted in final
form July 19, 2007.
ˇ-POMPE & TEKAVC