Color Vision Anomalies Flashcards
____% of the population manifests anomalous color vision
4.5
Most prevalent color vision anomalies
Inherited
- noprogressive and pose no threat to vision
- may have profound effect on the performance of cortina activities, including those encountered at school and on the job
Acquired color vision anomalies
- Less prevalent than hereditary anomalies
- secondary to disease or drug toxicity
- can be important diagnostic tool
Missing one of the three cone photopigment
Dichromacy
When does deuteranopia occur
When chlorolabe is missing
Protanopia
Absence of erythrolabe
Tritanopia
Absence of cyanolabe
The commonly accepted replacement model of deuteranopia and protanopia
The missing photopigment is replaced by a remaining photopigment
- deuteranopia: chlorolabe replaced by eryhthrolabe
- protanopia: erythrolabe replaced by chlorolabe
Three photopigment present, but the absorption spectrum of on of these photopigment is displaced to an abnormal position
Anomalous trichromacy
Deuteranomalous trichromacy (deuteranomaly)
Chlorolabe spectrum is displaced toward longer wavelgnth
Prtanomalous trichromacy (protanomly)
Erythrolabe spectrum is displaced towards shorter wavelgnth
Anamolous trichromacy: these diplacesmnt of the cone photopigment from their optimal positions results in
Deficiency color discrimination
-the greater the displacement of the photopigments, the more severe the color vision anomaly
Deutranomly
M cone spectrum displaced toward longer wavelgnth
Protanomly
The L cone spectrum is displaced toward shorter wavelgnth
Erythrolabe affected
Protan
Erythrolabe missing
Protanopia
Erythrolabe absorption spectrum is displaced
Protanomalous (anomalous) trichromacy
Chlorolabe is affected
Deutan
Chlorolabe is missing
Deuteranopia
Chlorolabe absorption spectrum is displaced
Deuteranomalous trichromacy
Cyanolabe affected
Tritan
People with ____ and ____ vision tend to confuse reds and greens
Protan and deutan
- RGcolor vision anomaly
- inherited usually
Individuals with ____ vision confuse blue and yellow
Tritan
- BY color vision anomaly
- rarely inherited and almost always acquired
Do people with color vision proces chromatic information differently than individuals with normal color vision?
Yes
Characteristics that distinguish anomalous color vision are
Spectral sensitivity, wavelgnth discrimination, color confusion lines, and the perception of saturation
What is the rarest color vision anomaly
Inherited tritan anomalies
The protanopia Vlambda curve is displaced how
Substantially displaced toward shorter wavelengths
The deuteranopia Vlambda curve is different how
Shoes a very slight displacement toward longer wavelengths
The displacement of the deuteranopia luminosity function is _____
Minimal
-for clinical purposes it may be considered normal
Which color vision anomaly has a relatively normal luminance curve
Deuteranopia
What does the normal Vlambda function result from
The addition of M and L cone inputs
The absence of erythrolabe and the luminance curve
Protanopia, causes the luminance curve to be displaced toward shorter wavelengths
The absence of chlorolabe (deuteranopia) and the luminance curve
Causes the Vlambda function to be displaced toward longer wavelengths
The greater dislocation of the protanopia luminance function suggests what
That L cones play a greater role in generating the normal Vlambda function than do M cones
Why do people with protanopia find it difficult to see certain red objects
The Vlambda function is displaced toward shorter wavelgnth
Projecting a beam of light of 680nm light (red laser) onto a screen: normal vs protanopia
This is easily seen as a bright red spot in normal color vision, but it is invisible to a person with protanopia
-since erythrolabe is absent, the 680,nm quanta of light are simply not absorbed
The luminosity functions in anomalous trichromacy vs dichromatic functions
Manifests the same general dislocation as dichromatic functions, but less pronounced
Protanomalous trichromacy and the luminosity function
The luminosity function is displaced toward shorter wavelgnth but less so then in protanopia
-as with protanopia, it may be difficult to see certain red objects
Deuteranomalous trichromacy and the luminosity function
Manifests minimal displacement of the luminosity toward longer wavelengths
-this displacement is even less than that found in deuteranopia, resulting in a function that is clinically normal
Which types of color vision anomalies have well-developed wavelengths discrimination in the region of 490nm
Protanopia and deuteranopia
-at longer wavelengths (>545) there is no ability to discriminate between stimuli on the basis of wavelgnth differences alone
What what wavelength is there no ability to discriminate between stimuli on the basis of wavelgnth differences alone in protanopia nad deuteranopia
Above 545
How many cone pigments do patients with deuteranopia and protanopia have that’s can absorb beyond 545nm
One
-this manifests monochromatic color matching in this region of the spectrum
How are protanopia and deuteranopia patients able to discriminate stimuli longer than 545nm?
Based on luminance
- a stimulus at 575nm would appear brighter than an equal energy stimulus of 600nm
- when equated for luminance, these stimuli are indistinguishable
Origin of color confusion lines for each color vision anomaly is referred to as
Copunctal point
All colors falling along _______ are indistinguishable
Color confusion lines
Patients with deuteranopia and protanopia tend to confuse which two colors
Reds and greens, hence the term RG color anomaly
In tritanopia, which two colors are confused
Blues and yellow,s thus the term blue-yellow anomaly
In normal trichromacy, ___nm appears less saturated (more whiteish) than other wavelengths
570
Deuteranopia function for saturation shows the least amount of saturation at
498
-appears white and are called neutral points
The protanopic function for saturation shows the least amount of saturation at
492
-appears white and are referred to as neutral points
Neutral point in deuteranopia
498
Neutral point in protanopia
492
Neutral point in tritanopia
569
Neutral point in those with normal color vision and anomalous trichromacy
Do not manifest neutral points
How can you determine a neutral point based on color confusion lines in deuteranopia and protanopia
Where the confusion line passes through the white
-all stimuli falling along one of these lines are confused with white
A person with dichromacy may report that a certain free traffic light appears
White
-these traffic signals are approximate metamers of the dichromatic neutral points
Anomalous trichromacy and neutral points
They do not experience neutral points
-the do display abnormal saturation perception
Deuteranomalous trichromacy and the least saturation
498
What wavelength shows the least amount of saturation in protanomalous trichromacy
492
Individuals with RG dichromacy are essential monochromatic for wavelengths beyond
Approximately 545
-still label colors surprisingly well especially when other cues are available
What can people with RG dichromacy not label correctly
They can label apples and bands properly because they know that other people call these objects certain colors
They cannot label patterns on a shirt that are plaid green and red
-may assign color labels on the basis of brightness cues and the context within the garment is worn
How does the spectrum appear to deuteranopia and protanopia patients /
Divided into blue and yellow regions separated by the neutral point wavelength, which is perceived as white
Where is wavelgnth discrimination best in deuteranopia and protanopia
In the region of the neutral point
How does the spectrum look for tritanopia
Red and green with a neutral point separating the two colors at 569
Between deuteranopia and protanopia, which one has a decrease in brightness in longer wavelengths
Protanopia
The majority of RG anomalies are ________
Inherited
-X-linked recessive
RG anomalies are more common men or women
Men
Prevalence of RG anomalies is ____ dependent
Race
-highest in whites
The most commonly inherited anomaly is
Anomalous trichromacy (protanomaly; dueteranomaly)
How are inherited tritan anomalies inherited
Autosomal dominant
Extremely rare
A females must be _____ in order to express the color vision anomaly
Homozygous
-the gene is recessive and she is usually just a carrier
Boys always receive the defective color vision gene from their
Mothers
If the father is affected with color deficiency and the mother us unaffected and not a carrier, how will that affect their offspring?
Sons will be unaffected
All daughters will be carriers
If unaffected father and a carrier mother for color anomalies has offspring, how \will they affected?
50% of sons will be affected
50% of daughters will be carriers
The highly homologous genes for the M and L photopigment opsins are positioned on the _____ chromosome in a ______ array
X
Head-to-tail array
Head-to-tail array of M and L cones on the X chromosome suggests what
Erroneous crossover of genetic information could occur when the pair of X chromosomes aligns and exchanges genetic information during meiosis
The gene encoding for the M cone opsin could erroneously align with the gene encoding for the L cone opsin, leading to an unequal exchange of genetic information
- one of the X chromosomes does not have the gene coding for the M cone opsin
- offspring could have deuteranopia with this gene
- other chromosomes has multiple copies and will not be affected
The resultant hybrid gene from intragenetic crossover leads to
- normal photopigment, or
- the nonexpression of the photopigment (dichromacy), or
- an aberrant photopigment (anomalous trichromacy)
Molecular bassi of anomalous trichromacy
An aberrant photopigment from the hybrid genes resulting from intragenetic crossover of genetic material
A hybrid gene that differs substantially from the normal gene may result in
Severe anomalous trichromacy
-the deviant photopigment absorption spectrum almost completely overlaps that of the other long wavelgnth photopigment
When the hybrid gene is more similar to the normal gene, the result may be
A milder form of anomalous trichromacy
-the location of the deviant absorption spectrum is almost normal
Acquired anomalies of color vision
Secondary to disease or toxicity and may be B-Y or R0G
-because B-Y are so rare, it must be assumed that such an anomaly is acquired until proven otherwise
Inherited anomalies are secondary to
Stable physiological variations
-remain unchanged throughout life and result in clear-cut results on color vision tests
The pathological processes that produce acquired anomalies are often
Variable in their course
-result in color vision anomalies that may not be stable and may not produce clean test results
Inherited anomalies are unilateral or bilateral?
Bilateral and symmetric
Acquired anomalies are bilateral or unilateral?
May be unilateral or asymmetric
It must be assumed that any difference in the color vision of the two eyes is due to
An acquired anomaly
-important to perform these monocularly when screening for conditions
Why is it important to test color vision monocularly
Because if someone has acquired anomaly in one eye and not the other, it could be missed and results could seem notrmal
Kollners rule
- Changes in the transmission properties of the crystalline lens secondary to aging result in blue-yellow color vision anomalies
- outer retinal disease also result in blue-yellow color vision anomalies
- disease of the inner retina, optic nerve, visual pathways, and visual cortex results in RG anomalies
Aging changes in the lens leads to ______ color visions anomalies
Blue-yellow
Outer retinal diseases result in_________ color anomalies
Blue-yellow
Disease of the inner retina, optic nerve, visual pathways, and visual cortex results in _______ color anomalies
R-G
The nature of a______ defect can change over time
Acquired
Can change from RG to BY
Can a patient manifest both a BY and RG anomaly simultaneously
Yes
- sometimes referred to as non selective loss
- optic neuritis
Rare conditions where the patient manifests monochromatic (or nearly monochromatic) vision
Achromatopsia
The most common achromatopsia
Autosomal recessive
-can be complete and incomplete (residual M/L cone function)
Signs and symptoms of achromatopsia
No or very poor color discrimination, nystagmus, photophobia, and VA of 20/200
What kind of lenses minimize the bleaching of rhodopsin
Dark red
- permit rod function under brighter lighting conditions
- may be recommended
X linked achromatopsia
Very rare
Recessive manner
Magenta lenses
Contains S cones and rods
Cone monochromacy
Rare
VA normal, but monochromatic color matching
-defect in postreceptoral processing of color information
Retinal and cerebral achromatopsia
Retinal is inherited and cerebral is due to a lesion in extrastriate cortex
-prior to developing the lesion, the patient has normal color perception, but subsequently perceives a black and white world
These are not true color vision anomalies because they do not typically p[roduce a decreased ability to discriminate colors, they represent a distortion of color visions, like looking through a colored filter
Chromatopsia
-patients report that objects have a colored or tinged halo
When do chtromatopsias occur
Secondary to various medications
- digitalis (xanthopsia)
- fluorescein (xanthopsia)
Chromatopsia may follow
Cataract extraction
- removal of nuclear sclerotic cataract exposed the retina to more blue light than it has experience in some time
- results in cyanopsia
- eventually diminishes
Most commonly used color vision tests
Pseudoisochromatic plate tests
- straightforward and easy
- number plates arranged in a book
Typical design of pseudoisochromatic plates
Vanishing plates
- consist of a figure embedded in a spectral different background
- the colors that constitute the figure and the background all fall on a common color confusion one
What do pseudoisochromatic plates not distinguish between
Dichromatic and anomalous trichromatic vision
What do pseudoisochromatic plates distinguish between
Protan and deutan anomalies
Do all color tests have plates to distinguish BY anomalies
No
Limitations of computer based vision tests that use pseudoisochromatic plates
The chromaticities of the plates may vary from computer to computer due to variations in hardware and software settings
Waggoner computerized color visio test
Monitor color calibrated is performed to overcome variations
Consists of 15 colored caps that form a hue circle within the CIE diagram
Farnsworth dichomatous test
The D-15 test is referred to as an
Arrangement test
How is the farnsworth D-15 test scored
By connecting the cap numbers in the sequence arranged by the patient
-anomalies may show crossovers on the hue circle that corresponds to color confusion lines
What does the farnsworth D-15 tesl allow
The differentiation of protan, duetan, and tritan anamolies
What does the farnsworth D-15 not allow
The differentiation of dichromacy from anomalous trichromacy
Because the farnsworth D-15 has low sensitivity, what can happen
Certain individuals with anomalous trichromacy may pass the test
Advantage of the farnsworth D-15
Capacity to detect tritan losses (unlike ishihara)
What color test can detect tritans
Farnsworth D-15
HRR plates can differentiate
Protan
Deutan
Tritan
What can HRR not differentiate
If they shave anaomlous trichroamcy or if they are dichromat
Rabin cone contrast test (CCT)
- Allows assessment of the functionality of each of the three types of cones
- uses computer
- each column contains optotypes that are detectable based on contrast as defined for only one of the three cones
- as the patient reads down a column, the cone contrast decreases until a threshold is reached
- this test allows a cone threshold to be obtained for each of the three differnt cones
- staircase procedure
Used for military
Rabin cone contrast
What is the only color vision test that can determine between a dichromat or a trichromat
Nagel anomaloscope
For nagel anaomaloscope, in protanopia, the luminance function is displaced
Toward shorter wavelgnth
The 546nm stimulus in nagel anomaloscope: protanopia
Appears bright
Nagel anomaloscope: protanopia, a the 670nm appears
Dim
A apatient with _______ adjusts the 590mn test field to a high radiance when matching 546nm and to a low radiance when matching 670nm
Nagel anomaloscope
Protanopia
_____ color anomalous remain stable throughout life and pose no threat to vision
Inherited
- can interfere with performance of cortina visual related activities
- let teachers know
Acquired color loss in child
Could indicate a central nervous system lesion and must be thoroughly investigated
Color vision standards and occupations
Some occupations have color visions requirements
People with RG color anomalies may have difficulty distinguishing among colors that are ________ or ________ if these colors fall along the red green confusion lines
Dark or desaturated
Do colored sunglasses interfere with the ability of patients with inherited anomalies to quickly and correctly identify color traffic signals?
Certain non-neutral tints may make it more difficult for these individuals to detect and recognize traffic lights
-this suggests that color sunglasses should not be recommended for patients who have anomalous color vision
Protan anomalies have been associated with an increased frequency of what kind of accedes
Rear end becasuse they cant tell the tail lights are red
Acquired anomalies are most commonly
BY
How should acquired color testing be
Monocularly
Lighting conditions for color vision testing
Standard illumination C lighting condition
Macbeth lamp
Incandescent lightning and color vision testing
The patient may perform better than if the proper illumination were usd
Red contact lens used best in
Monchromat I
-lets them act as a dichromat if worn in one eye
Are glasses a cure for someone with color deficiency
No
Gene therapy for color deficiency
The replacement of defective genes in people with color deficiencies offers the promise to cure color blindness
The ___ cone system is apparently more vulnerable to certain pathological processes than the other two cones
S cone
SWAP
Short wavelgnth automated perimetty
-low number of S cones
Assess S system function in certain eye diseases
SWAP
Background for SAWP
Yellow to suppress M and L cones
Red desaturation test
Comparison between two eyes looking at a red cap if you suspect one eye is has a deificneicy
-good for central and peripheral vision as well
