Anomalous

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Anomalous Color Vision
Biology of CVD Detection of CVD Treatment of CVD
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Biology of CVD 1. Does normal color vision
(trichromatic) provide perfect color vision?
Spectral resolution. 2. What is meant by color
blind? 3. Dichromats 4. Anomalous Trichromats
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Normal color vision
Although we are certain that our color vision is
perfect we must recall trichromatic color
theory and metamers. That is, stimuli that are
spectrally very different can appear identical.
This indicates that we have poor spectral
resolution, and thus we are all partially
spectrally blind.
Anomalous Color Vision 1. Genetic
(photoreceptor anomaly) Dichromats Monochromats
Anomalous Trichromats 2. Acquired (retinal
disease)
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Cone spectral absorption curves
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S
R
M
L
Prevalence ()
Normal Trichromat
M/F
Protanope
1/0.02
X-linked recessive
Deuteranope
1.1/0.01
X-linked recessive
Tritanope
Autosomal Dominant
0.002/0.001
Protanomalous
1/0.02
X-linked recessive
5/0.38
Deuteranomalous
X-linked recessive
Autosomal Recessive
.003/.002
Rod Monochromat
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Scematic diagram of cone opsin protein strand
which is imbedded in and traverses the disc
membrane within the cone outer segment. Each
circle indicates an amino acid.
The red amino acids (helix 6) are the two that
determine if the photopigment will be L or M.
Changing these two produces a 16 - 24 nm shift in
peak absorption.
Yellow amino acids dimorphism produces small
changes in spectral tuning of L or M pigments of
color normals and anomalous trichromats. These
are the spectral tuning sites.
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Distribution of Rayleigh match midpoints
(relative amount of R in RG mix that matches
monochromatic yellow of 580nm) made with
Anomaloscope
Bimodal male distribution
Color indicates the appearance of anomalous match
to a person who matches with 0.5 Red.
R G
580
Explanation there are two L-cone pigments with
equally common genes, men have either one other
other and this influences their Rayleigh matches.
Women, who have two x-chromosomes, have both
pigments in separate cones, thus manifesting
intermediate matches to men.
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Photopigment Gene on X-chromosome
There is a single gene for L cone pigment and
either 1, 2, or 3 (2 most common) duplicate (but
not identical) genes for the M cone pigment.
Leters show amino acids coded for on gene
exons
introns
Dl28nm
There are 7 substitution sites in sections 2-5 of
the gene that affect peak absorption in normals
Due to large homology between L and M cone genes,
there is considerable mixing of genetic code, and
thus diversity in LM cone pigments, which can be
seen by examining the peak absorption lmax.
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Variability in absorption spectra of L and M cone
photopigments pigments thought to occur in humans
due to genetic heterogeneity.
Dl28nm in normal trichromats, lt28nm in
anomalous trichromats
Notice that there is a range of L and M functions
each shifted slightly along the wavelength scale.
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The Spectral Proximity hypothesis for anomalous
trichromats.
Genetic documentation of anomalous trichromats
shows that those with severe anomalies have
smaller spectral separation between LM
absorptions, those with mild anomalies have
separations approaching those of normals.
Note the single Lcone pigment gene and 1-3 Mcone
pigment genes. The Mcone pigment gene closest to
the Lcone gene on the X chromosome determines the
Mcone opsin.
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Five examples showing the sex-linked inheretance
pattern for Protanopia and Deuteranopia (from
Schwartz).
normal
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Spectral Sensitivity curves for protanopia and
deuteranopia.
Note that protanopes, and to a lesser extent
protanomalous trichromats are less sensitive to
long wavelengths.
Should protanopes be allowed to drive trucks?
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Cone sensitivities plotted on linear scale (Smith
and Pokorny)
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Conse sensitivities plotted on log scale (Smith
and Pokorny)
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Protanope
M and S cones
M-cone S-cone
Neutral Point l confused with white492 nm
monochromat
indistinguishable
Will a mixture of 400 600 nm (non-spectral
purple) appear white?
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Deuteranope
L and S cones
L-cone S-cone
Neutral Point l confused with white498 nm
monochromat
indistinguishable
Will a mixture of 400 600 nm (non-spectral
purple) appear white?
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Tritanope
L and M cones
l (569 nm) confused with white
Very poor discrimination
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Color discrimination How good are we?
Protanomalous deuteranomalous trichromats
Normal trichromats
1. Wavelength Discrimination
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Coding color by the relative response amplitudes
of the different cone types
Cone spectral sensitivity curves
1.20
Because the proximity of L and M cone pigment is
increased (pigments are more similar) in
anomalous trichromats, the difference signal (L-M
or M-L) is reduced. If L M cones have
identical pigment, there is not L-M signal, and
thus the L-M opponent system cannot signal
redness or greeness, and thus color vision is
restricted to blues and yellows.
1.00
Protanomalous L-cones
0.80
L
S
0.60
M
0.40
0.20
0.00
400
450
500
550
600
650
700
Wavelength (nm)
Opponent Mechanisms
2.50
2.00
L- M
1.50
1.00
0.50
0.00
400
450
500
550
600
650
700
-0.50
Wavelength (nm)
-1.00
L-M
LM-S
-1.50
-2.00
-2.50
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What colors do dichromats see?
500
500
500
500
Red-green color vision defectives (CVDs) do not
see reds or greens, but only blues and yellows.
This is a simulation to show how the spectrum
will appear
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IU campus seen through the eyes of a protanope or
deuteranope
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Protanopia CIE representation of confused colors
Two sample deutanopic confusion lines
Neutral point 492 nm
Notice that Protan and Deutan confusion lines are
virtually identical between Red and Green (700 nm
to 530 nm)
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Deuteranopia CIE representation of confused
colors
Neutral point 498 nm
Two sample protanopic confusion lines
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Tritanopia CIE representation of confused colors
Neutral point 569 nm
No confision lines shared with Protans or Deutans
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CIE 1931 Color Spce appearance to
dichromats (approximate simulation)
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Detection of CVD
Perform Test that requires either (1) correct
color naming or (2) normal color
discrimination (a) pseudoisochromatic
plates (b) color ordering tests (e.g.
D15) By far the most common in Optometric
practice.
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Pseudoisochromatic Plates e.g. Ishihara plates
Screen for either Protan or Deutan
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Another example employing oranges and greens to
screen for either Protan or Deutan defects.
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Plate diagnostic for Protan and Deutan
What will a Protan see and what will a deutan see?
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D-15 Color Ordering Test
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CIE 1931 xy color space showing the color
locations of the 15 colors used in the D15 tes.
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Protan and Deutan color confusion lines for D-15
Protan confusion point
Deutan confusion point
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Appearance of Protan or Deutan order to normal
trichromat
Appearance of Protan or Deutan order to dichromat
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Nagel anomaloscope Useful to diagnose
protanomalous and deuteranomalous trichromats
Subjects must adjust the relative intensity of
the R and G stimuli to match the monochromatic
yellow.
Ratio R/RG
546 670
R/(RG)
580
Note that protanomalous trichromats need much
more red (670 nm) in the red/green mixture to
match the monochromatic yellow, whereas
deuteranomlous trichromats need much more green.
This is because of the shift to shorter
wavelengths in the Lcone photopigment
(protanomaly) or the shift to longer wavelengths
of the Mcone photopigment (deuteranomaly).
Dichromatic Protanopes and Deuteranopes will
accept any mixture of RG as a color match for
the monochromatic yellow.
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Farnsworth, who invented the D15 test, also
invented a much more sensitive test called the
100 hue test. It is also a color ordering test,
but instead of one set of 15 colors there are 4
sets of 21/22 colors (oranges, greens, blues, and
purples). Note although it is called the 100
hue, there are only 85 colored samples! This test
is used in research, but not as a standard
clinical test.
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Lantern Tests These are not routinely used in
Optometry, but they are an integral part of color
vision testing in certain professions, such as
airplane pilots, certain military personnel, etc.
They are color identification tests (not color
discrimination tests), because pilots and other
professional must be able to correctly identify a
red as a red and a green as a green
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Problems associated with CVD
What vision problems are encountered by those
with color vision defects (dichromats or
anomalous trichromats)? Barry Cole (Australia)
Journal of Clinical and Experimental Optometry,
2004 (http//www.optometrists.asn.au/ceo/backissue
s/vol87/no4/3274) 102 patients diagnosed as
having color vision problems in the Optometry
clinic.
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Problems experienced by physicians with CVD
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Acquired Color Anomalies
Retinal Disease, Choroidal disease, Optic Nerve
disease and yellowing of the lens can all produce
color vision anomalies.
Drugs Antidiabetics R-G Erythromycin B-Y Viagra
B-Y (looks blue) Toxins Ethenol R-G or B-Y
Pathology Lens yellowing B-Y Optic
Neuritis R-G Papillitis R-G Glaucoma B-Y Diabet
es B-Y
Unlike the genetic disorders, most of these color
anomalies are progressive (they change over time)
and many are associated with other vision
problems (e.g. VA loss).
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Change in lenticular transmission with age
Yellowing of the lens
Vision through an old lens can be simulated in a
young eye with a yellow filter.
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Yellowing of lens generates a Blue/Yellow, or
Tritanopic-like color vision deficit. Recall
that Tritanopes confuse whites yellows.
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Normal Color Deficiencies 1.
Scotopic Achromatopsia (only one receptor type
functioning at low light levels) 2.
Foveolar Tritanopia (no S-cones in foveola) 3.
Transient Tritanopia (S-cones repond poorly to
tansients) 4. Small Field Tritanopia (image of
small target misses any S-cones)