Anomalies of Color Vision

Question 1

What is the prealence of color vision defect in males and females in the population?v

Answer 1

• Large random population surveys show prevalence of deficiency of:
  
  • European Caucasians is about 8% in men, 0.4% in women
  • Between 4% and 6.5% in men of Chinese and Japanese ethnicity
• The male: female prevalence ratio is markedly different in Europeans and Asians
  
  • Inherited – majority
    
    • Usually non-progressive
  • Acquired – less prevalent
    
    • Secondary to ocular disease

Question 2

Name the 3 basis on which color vision defect can be classified.

Answer 2

• Classification based on:
  
  • Origin
  • Type of color defects – clinical testing
  • Classification based on Color Matching Test

Question 3

How is color vision defect classified based on origin?

Answer 3

• 2 Principal Types of Color Defect:
• Inherited – congenital
• Acquired

Question 4

How is color vision defect classified based in Clinical testing?

Answer 4

• Classification of color vision status based on the minimum number of primary colors used to match perceived colors
  
  • Trichromatism – require 3 primaries to make a match
  • Dichromatism – require 2 primaries to make a match
  • Monochromatism – require 1 primary to make a match

Question 5

What is protan dichromacy known as?

Answer 5

• Protanomalous (defective pigment) / Protanopia (missing completely) trichromacy
• Aka protanomaly
• Red/green color defective

Question 6

What is Deutan anomalous trichromatic known as?

Answer 6

• Aka. Deuteranomaly
• Deuteranopia (missing pigment) / deuteranomalous (defective pigment) trichromacy

Question 7

If the S cone is missing in an individual, what is the condition known as?

Answer 7

• Tritanopia – completely defective S cone
• Tritanomalous trichromacy – tritanomaly
  
  • Defective but present

Question 8

How is color vision defect classified based on Color Matching Test?

Answer 8

• Classification of color vision status is based on the minimum number of primary colors used to match perceived colors
  
  • Trichromatism –
    
    • Normal trichromacy
    • Anomalous trichromacy – 3 photopigments are present but the absorption spectrum of ONE of these photopigments is displayed
      
      • Protanomaly
      • Deuteranomaly
      • Tritanomaly
  • Dichromatism
    
    • Protanopia
    • Deuteranopia
    • Tritanopia
  • Monochromatism
    
    • Rod monochromacy
    • Cone monochromacy

Question 9

In Deutranomaly, the M cone pigment are shifted toward which wavelength?

Answer 9

• Deuteranomaly – displacement right towards longer wavelengths
• Prontanomaly – displaces left towards shorter wavelengths
• The displacement of cone photopigments result in deficient color discrimination

Question 10

If L cone pigments are missing completely, what is it called? What replaces the L cone pigment?

Answer 10

• Protanopia – the L cone is completely missing
• The missing photopigment is presumably replaced by a remaining photopigment

Question 11

What are the characteristics that distinguish anomalous color vision defectives from an individual with normal color vision?

Answer 11

• In Anomalous trichromacy 3 photopigments are present
  
  • But the absorption spectrum of ONE of these photopigments is displayed to an abnormal position
• Among the characteristics that distinguish Anomalous color vision from COLOR NORMALS are:
  
  • Spectral sensitivity – chromatic & Luminance
  • Wavelength discrimination
  • Color confusion lines
  • The perception of saturation
• The Chromatic System can be identified in human subjects by:
  
  • Determining spectral sensitivity for large stimuli
  • Flashed for long duration
  • On a photopic white background

Question 12

What is the peak spectral sensitivity of anomalous trichromatic? How is it different than normal? Why are the peaks displaced?

Answer 12

• Anomalous trichromacy: spectral sensitivity function has 3 peaks – 440, 520, 620
• Normal Trichromacy: 426, 530, and 557
• Anomalous trichromacy peaks are displaced due to interaction between the L and M cones
• Dichromacy – only 2 peaks

Question 13

Why is there a greater displacement of peak luminosity function in Protanopia than deutranopia?

Answer 13

• Greater displacement in protanopia (than deuteranopia) suggests that L-cones play more of a role in generating normal V(l) function than do M-cones

Question 14

How is the luminosity function dislocation manifest in Anaomalous trichromacy when compared to Dichromacy?

Answer 14

• Anomalous trichromacy – the luminosity functions in anomalous trichromacy manifest the same general dislocation as dichromatic functions, but less pronounced

Question 15

Describe the wavelength discrimination ability of Protanopes, Deuteranopes & Tritanopes (compared to normals).

Answer 15

• For both protanopia and deuteranopia, there is relatively well-developed wavelength discrimination in the region of 490 nm (shorter wavelength)
  
  • BUT at longer wavelengths – beyond approximately 545 nm – there is no ability do discriminate between stimuli on the basis of wavelength differences alone
• In tritanopia there is well-developed wavelength discrimination at longer wavelengths, but poor wavelength discrimination in the region of 495 nm
• WAVELENGTH DISCRIMINATION =
  
  • Color normal (normal trichromats) – have down to 1 nm discrimination capability near 490 and 590 nm
  • Protanopes and deuteranopes only discriminate well between 450 and 540
  • Tritanopes have a gap with no discrimination between 460 & 480
  • A normal observer can distinguish approximately 150-200 variations in color
  • The dichromatic (protanopic and deuteranopic) observers are able to distinguish perhaps 20-30 colors

Question 16

What is color confusion lines? What is copunctal points?

Answer 16

• Color confusion lines – the limited ability of people with dichromacy to distinguish among colors can be illustrated by plotting their COLOR CONFUSION LINES on the CIE diagram
• Confusion lines originate from copunctal points
• All colors falling along a confusion line are indistinguishable

Question 17

Describe the color confusion lines for Protanopes, Deuteranopes & Tritanopes.

Answer 17

• Deuteranopia and protanopia share a color confusion line that is tangential to the spectral locus from approximately 545 to 700 nm.
  
  • the colors associated with these wavelengths (green, yellow, orange, and red) are confused with each other, hence the term red-green color anomaly
• in tritanopia, blue-violet and yellow are confused with each other, thus the term blue-yellow anomaly

Question 18

Name the colors where Protanopes and Deuteranopes share color confusion.

Answer 18

• Green, yellow, orange, and red

Question 19

Where does saturation of colors (white.neutral point) occur for normals, Protanopes, Deuteranopes, and Tritanopes?

Answer 19

• The perception of saturation –
  
  • In normal trichromacy, 570 nm appears less saturated (more WHITISH) than do other wavelengths
    
    • So for NORMALS it is hard to distinguish yellow from white
  • For deuteranopia & protanopia –
    
    • Its 498 nm (deuteranopia) and 492 nm (deuteranopia)
      
      • These particular wavelengths appear WHITE – they are totally desaturated and are referred to as neutral points
        
        • Wavelength discrimination is best in the region of the neutral point
  • For tritanopia – the neutral point is approximately 569 nm
• Individuals with normal color vision and anomalous trichromacy DO NOT manifest neutral points
• Upon questioning, a person with dichromacy may report that certain green traffic lights appear WHITE (or whitish)

Question 20

How are individuals with color vision defects able to assign accurate color labels?

Answer 20

• Color Labeling –
  
  • Although individuals with red-green dichromacy are essentially monochromatic for wavelengths beyond approximately 545 nm, they can do surprisingly well at labelling colors, especially when other cues are present
  • A person with protanopia or deuteranopia may, for instance, have no difficulty labeling an apple as red and a banana as yellow (color memory)
    
    • This is an easy task because he has learned that others label apples as red and bananas as yellow
    • This individual is likely to have more difficulty assigning labels to the colors forming a pattern on a shirt because he may not have witnessed other people naming the colors
    • Although a person with dichromacy does not have a wavelength-based discrimination for long-wavelength stimuli, we should be careful when drawing conclusions regarding his perceptions of these stimuli (whether he uses brightness etc.) as we cannot be certain of what a person with dichromacy perceives
  • In deuteranopia & protanopia, the spectrum is divided into blue and yellow regions separated by the neutral point wavelength, which is perceived as WHITE
    
    • Wavelength discrimination is best in the region of the neutral point
    • Yellow – the region of the spectrum where individuals with red-green anomalies have no wavelength-based discrimination
      
      • For instance, a person with deuteranopia might say the entire region is yellow, while a person with protanopia could interpret the dimming at longer wavelengths as a reddening
      • Note: the decrease in brightness at longer wavelengths that is experienced in protanopia
  • In tritanopia – the neutral point separates green and red regions
    
    • In this case, the shorter and longer wavelength regions of the spectrum are separated by the neutral point at approximately 569 nm

Question 21

What is the prevalence of Protans, Deutans, and Tritans in a population?

Answer 21

• Inherited color defects are congenital, genetically inherited, and without other associated abnormality
• The majority of red-green anomalies are inherited, transmitted in an X-linked recessive fashion
  
  • Consequentially, they are considerably more common in men than women, with prevalences of approximately 8.0% and 0.4% respectively
• Inherited tritan anomalies are extremely rare and transmitted in an autosomal dominant fashion
• Prevalence in males:
  
  • Protanopia:5%
  • Protanomaly 1%
  • Deuteranopia: 1%
  • Deuteranomaly: 1%
  • Tritan defects 0.005%

Question 22

What is the most and least prevalent type of color vision defect?

Answer 22

• Most: protanopia
• Least: tritan defects (tritanopia and tritanomaly)

Question 23

What are the societal implication of color vision defects?

Answer 23

• These defects are not physically debilitating, but they can have a major impact on one’s life
• Some may not even be aware of their deficiency until a peer makes fun of their choice of color in art class, which they must learn to cope
• Many who have a color vision deficiency learn of it only after they FAIL a color vision test
  
  • Some who are informed that they are so afflicted deny it
• Some color-defective individuals are defensive and understandably insolent when forced to deal with the consequences of their deficiency, which can deny them employment in certain occupations
• Certain occupations related to public safety may have color vision standards that exclude individuals with anomalous color vision
  
  • Airline pilot, firefighter, US custom & border protection, USDA meat inspector (ishihara)
• For other professions, NORMAL COLOR DISCRIMINATION can be an advantage:
  
  • Chemical or electrical engineering, pharmacy, optometry, ophthalmology, dentistry, surgery, videographer
• Individuals with red-green color anomalies may have difficulty distinguishing among colors that are dark (e.g., socks) or desaturated (pastels) if these colors fall along the red-green confusion lines
  
  • Their ability to discriminate and name colors is improved by increasing the level of illumination
• Unfortunate that many individuals learn of their color deficiency when they take a color vision test as part of a physical examination for employment and then are disqualified for the position after years of planning
  
  • Eye care practitioners should ensure that color testing is done at a yong age for the purpose of providing good baseline data
  • Parents and teachers should be informed
  • Parents counselled about child’s career choices

Question 24

Do sunglasses interfere with the ability of patients with inherited anomalies to quickly and correctly identify colored traffic signals?

Answer 24

• YES – certain non-neutral tints (i.e., colors other than GRAY) make it more difficult for these individuals to detect and recognize TRAFFIC LIGHTS
• This result suggests that colored sunglasses should NOT be recommended for patients who have anomalous color vision (especially protans who may have difficulty seeing Red traffic lights even under normal conditions)

Question 25

Explain why Protans perceive REDS as dim or dark.

Answer 25

• The photopic luminosity curve peaks at approximately 555 nm – it has this shape because there is a disproportionately large input (approximately 2 or 3 to 1) from LWS cones compared to MWS cones & little/no input from SWS cones
  
  • Consequently, compared to color normal, one would predict that protanopes (who lack LWS photopigment) and protanomalous trichromats, (who have an LWS photopigment that is more like the normal MWS photopigment), would experience a severe reduction in the relative brightness of RED LIGHTS
  • Examples proving:
    
    • Protans have difficulty seeing automobile REAR TAIL & BRAKE LIGHTS under conditions in which it is easy for color normal to see them
      
      • This can lead to delayed reaction times, which has been linked to a higher incidence of rear-end automobile accidents in protans
  • Protans may also have difficulty seeing RED traffic lights even under normal conditions
  • Deep-Red (long-wavelength) surface colors may look quite black to protanopes
  • The red light- emitting dioees on consumer electronic devices can be difficult for protans to see
  • Deep-red laser pointers can be invisible to protans
  • Deutans have NO significant relative LOSS of luminosity compared to normal – this is also the case for deuteranomalous trichromats

Question 26

Describe the inheritance pattern of Red-Green Color Vision Defect if father is normal, mother is anomalous

Answer 26

• Daughters: 100% carriers but color normal
• Sons: 100% color deficient (anomalous)

Question 27

Describe the inheritance pattern of Red-Green Color Vision Defect if father is normal, mother is carrier

Answer 27

• Daughters: 50% carriers, 50% color normal
• Sons: 50% color deficient (anomalous), 50% normal

Question 28

Describe the inheritance pattern of Red-Green Color Vision Defect if father is anomalous, mother is normal

Answer 28

• Daughters: 100% carriers but color normal
• Sons: 100% color normal

Question 29

Describe the inheritance pattern of Red-Green Color Vision Defect if father is normal, mother is normal

Answer 29

• Daughters: 100% color normal
• Sons: 100% color normal

Question 30

Describe the inheritance pattern of Red-Green Color Vision Defect if father is anomalous, mother is carrier

Answer 30

• Daughters: 50% color deficient (anomalous); 50% carriers but color normal
• Sons: 50% color deficient (anomalous); 50% color normal

Question 31

Describe the molecular genetics of Red-Green Color Vision Anomalies

Answer 31

• The X-chromosome typically has one copy of the L-cone opsin gene an one or more copies of the M-cone opsin gene
• Intergenetic –
  
  • Normal
  • Dichromacy
• Intragenetic –
  
  • Normal
  • Dichromacy
  • Anomalous trichromacy
• Hybrid gene – the basis for anomalous trichromacy

Question 32

Describe the difference between acquired and inherited (congenital) color vision defect.

Answer 32

• Inherited Color vision anomalies –
  
  • Heterozygous female (xX) is a carrier (x to take place of X with the bar over it)
  • A male with the defect gene has anomalous color vision (xY)
  • Because the gene is recessive, a female must be homozygous (xx) to express the color vision anomaly
    
    • Note: a son (male) always receives the defective gene from the mother
      
      • Patients sometimes incorrectly assume that color anomalies are transmitted from father to son
• Acquired color vision anomalies –
  
  • Secondary to disease or toxicity
  • May be either red-green or blue-yellow in nature
    
    • Because blue-yellow anomalies are so rarely inherited, it must be assumed that such an anomaly is acquired until proven otherwise
    • Acquired anomalies may be unilateral or asymmetric

Question 33

Describe Laterality in Acquired Anomalies.

Answer 33

• Must be assumed any difference in the color vision of the two eyes, as demonstrated on a color vision test, is due to an acquired anomaly
• Because acquired anomalies may be asymmetric, important to perform color vision tests monocularly when screening for these conditions
• If a patient with a unilateral anomaly is tested binocularly, the results may be normal, reflecting the performance of the unaffected eye
• The test should be first administered monocularly to the eye most likely to harbor disease

Question 34

Describe the features of Autosomal Recessive (AR) achromatopsia. What lenses would help such patients?

Answer 34

• Rare condition where the patient manifests monochromatic vision; fully expressed at birth
• Autosomal Recessive Achromatopsias – common
  
  • Two types:
    
    • Complete AR Achromatopsia – only rods are present
    • Incomplete AR Achromatopsia – residual L/M cone function
  • Signs & Symptoms:
    
    • No or very poor color discrimination, nystagmus, photophobia and VA ~20/200
  • Differential diagnosis is not always straight forward
• Dark red lenses
  
  • Minimize rhodopsin bleaching
  • Recommended for bright light conditions

Question 35

Describe the features of X-linked (XL) achromatopsia. What lenses would help such patients?

Answer 35

• X-Linked (XL) Achromatopsia – recessive inheritance
  
  • Referred to as Blue or S cone monochromacy
  • Contain only rods & S cone (though sometimes other cone types can be present)
  • Clinical signs & Symptoms:
    
    • Similar to rod monochromacy
• Magenta colored lenses
  
  • Minimizes rod saturation
  • Provide light to enable S cones may provide relief to patients

Question 36

What is the difference between Achromatopsia and cerebral achromatopsia?

Answer 36

• Cone Monochromacy –
  
  • A rare disorder where VA is normal but patients exhibit monochromatic color matching
  • Appears to involve a defect in postreceptoral processing of color information
• Achromatopsias – retina
• Cerebral Achromatopsia – Extrastriate cortex

Question 37

What is chromatopsia? Give 2 examples two conditions where it can be present.

Answer 37

• Chromatopsias –
  
  • Not true color vision anomalies
    
    • They do not typically produce a decreased ability to discriminate colors
  • Represent distortion of color vision
• 2 conditions where it can be present:
  
  • (1) Cataract Extraction
    
    • Perception of blueness (cyanopsia)
  • (2) Can be secondary to drugs/medications
    
    • Digitalis may produce – Xanthopsia (yellow vision)
    • Fluorescein in fluorescein angiography – xanthopsia

Question 38

Define Synesthesia. Why does it occur?

Answer 38

• A neurological phenomenon in which stimulation of ONE sensory or cognitive pathway leads to automatic, involuntary experiences in a SECOND sensory or cognitive pathway
• Cortical modules appear to be abnormally linked to each other such that stimulation of one sense results in the activation of another
• Increased cross-talk between regions specialized for different functions may account for the many types of synesthesia
• In one form of synesthesia, the presentation of a LETTER or a NUMBER results in the perception of a COLOR
  
  • For instance, the patient may report the perception of:
    
    • Green whenever he/she is presented with the number 5
    • Red when presented with the number 9
  • Not only can the effect be elicited by physical presentation of a stimulus, there is evidence that the same perception can result without external presentation of the trigger stimulus
  • The patient may, for example, experience GREEN when asked to perform a mental calculation whose answer is the trigger stimulus (e.g., 4 + 1)

Question 39

What is chromesthesia?

Answer 39

• Another common form of synesthesia is the association of SOUNDS with colors
• For some, everyday sounds such as doors opening, cars honking, or people talking can trigger seeing colors
  
  • For others, colors are triggered when musical notes and/or keys are being played
• People with synesthesia related to music may also have perfect pitch because their ability to see/hear colors aids them in identifying notes or keys

Question 40

Define Kollner’s Rule with few examples.

Answer 40

• According to Kollner’s rule, outer retinal disease and media changes result in blue-yellow color vision anomalies, whereas disease of the inner retina, optic nerve, visual pathawys, and visual cortex results in red-green anomalies
• This general guideline is not correct in every instance, and important exceptions have been reported
• Post receptoral lesions are more likely to affect both the types of cones opponent neuron channels
• It is not uncommon for a blue-yellow anomaly to be presen tin the early stages of an eye disease, and change into a red-green anomaly as the disease progresses (the reverse also may happen)
• A pt may manifest a nonselective loss

Question 41

What type of color vision defect may occur in AMD, Diabetic Retinopathy, and Nuclear Sclerosis, Cataract?

Answer 41

Question 42

What are the Aims of Color Vision Testing?

Answer 42

• Based on the knowledge of confusion lines
• Color vision testing is the existence of highly predictable confusion lines that allows for clever diagnostic distinction between color defective types
• Goals:
  
  • Screening – i.e., congenital vs. acquired
  • Diagnosis – i.e., type and severity
  • Vocation or occupational testing
• Determining protan vs. deutan congenital deficiencies: inability to detect red (protan) can have greater occupational consequences
• Focus also on differentiating red-green vs. blue-yellow acquired defects
  
  • Red-green – cone and optic nerve disease
  • Blue-yellow – retinal and choroidal disease

Question 43

Provide few examples of pseudoiochromatic (PIC) plate tests

Answer 43

• Ishihara
  
  • Sensitive
  • Protan and deutan defects
• HRR
  
  • Sensitive
  • Protan, deutan, tritan, and severity
• CVTME – color vision testing made easy

*patterns of objects, letters, or numbers placed on isoluminant backgrounds

Question 44

State few examples of Arrangement color vision tests

Answer 44

• Color cap tests
  
  • Farnsworth-Munsell 100
  • Panel D-15
  • Lanthony Desaturated D15

Question 45

State few examples of color matching tests

Answer 45

• Anomaloscopes
• C100
• CUT

Question 46

State an example of naming & occupational color vision tests

Answer 46

• NAMING
  
  • E.g., often PIC, but sometimes tests specifically designed for vocation/occupations (Lantern tests)
• OCCUPATIONAL COLOR TESTS
  
  • Rabin Cone Contrast Test

Question 47

What is the role of disappearing (vanishing) plates in Pseudoisochromatic plate tests?

Answer 47

1. The target/stimulus is defined by a color difference from the background
2. Color differences of the target/symbol straddle confusion lines
3. If the color differences are aligned on or close to the dichromatic confusion lines, the object is invisible to those with certain color deficiencies
   
   1. It serves to detect both types but not to distinguish them
4. CHROMATICITIES OF A “DISAPPEARING PLATE” FROM ISHIHARA’S TEST:
   
   1. The colors of the figure and the background are in the portion of color space, where there is little difference between protans and deutans
   2. The colors straddle both confusion lines and the figure will not be seen by either type of CVD
5. Shortcomings:
   
   1. Slower administration for CVD

Question 48

What is the role of transformation plates in Pseudoisochromatic plate tests.

Answer 48

1. Design intentions: to provide an alternate response for the color vision defectives
2. Contain colors that can be confused with the background and others that are not
3. Those with –
   
   1. Normal color vision – see one thing
   2. Color deficiency – see another thing, generally just slightly altered
4. Confirms that the test is understood
5. Prevents the frustration found with blank plates

aka ambiguous or alteration plates**

Question 49

What is the role of combination plates in Pseudoisochromatic plate tests?

Answer 49

• Incorporates both disappearing and demonstration figures
• Color normal: might report 2 figures
• Color deficiency: report 1 figure
• These plates are useful because there is always something to which the CVD can respond

Question 50

What is the role of diagnostic plates in Pseudoisochromatic plate tests?

Answer 50

1. Design: multiple disappearing plates for different color vision deficiencies
2. These disappearing plates have two figures
3. Example: Ishihara one plate that would disappear (be diagnostic) for protans and one for deutans
   
   1. Normal: should see both the 2 and the 6
   2. Deutan: type CVD should see 2 more easily, whereas a protan see the 6

Question 51

Which color vision test would you use as a screening test to determine a color vision defect?

Answer 51

• Ishihara
• HRR (Hardy-Rand-Rittler) (????)

Question 52

Describe the Ishihara PIC Test.

Answer 52

• Ishihara – sensitive for screening red-green CVD
• Published in 1906 – first PIC test in commercial product
• Available as 38- and 24- plate editions
• Has HIGH SENSITVITY and SPECIFICITY
• Useful in children above 5 years
• Can perform acceptably even when it is given under the wrong illumination
• The figures on each plate are embedded in a random pattern of variably-sized dots
• The test comprises a demonstration plate, disappearing, alteration, hidden, and diagnostic plates
  
  • The colors of the figure and background are carefully chosen to lie close to confusion lines
• Interpretation of 24-plate edition:
  
  • As assessment of the readings of plates 1 to 15 determines the normality or defectiveness of color vision
  • If 13 or more plates are read normally, the color vision is regarded as NORMAL (up to 6 errors)
  • If only 9 or less than 9 plates are read normally, the color vision is regarded as deficient
    
    • However, in reference to plates 14 to 15, only those who read the numerals 5 and 45 and read them easier than those on plates 10 and 9 are recorded as abnormal readings
  • It is rare to find a person whose recording of normal answers is 14-16 plates
    
    • An assessment of such a case requires the use of other color vision tests, including the anomaloscope

Question 53

Describe the Performance & Sensitivity of the Ishihara PIC Test.

Answer 53

• Ishihara – Performance/sensitivity:
  
  • The individual plates of Ishihara’s test have sensitivities (in identifying color defectives) and specificities (identifying color-normal) typically between 0.85 and 0.95
  • The test as a whole performs “very close to 1” in both sensitivity and specificity implying its excellent in failing color defectives (sensitivity) and passing color-normals (specificity)
  • There is a tendency for it to
    
    • PASS: very mild deutans
    • FAIL: some normal with poor discrimination (But without being identifiably protan or deutan)
  • Ishihara PIC test does not distinguish between dichromats and anomalous trichromates (i.e., protanope from protanamalous, deuteranope from deuteranomalous)
    
    • But useful in differentiating protan and deutan

Question 54

What are shortcomings of the Ishihara PIC test?

Answer 54

• 2 Major Shortcomings (compared to HRR):
  
  • (1) Isharaha has no TRITAN plates
  • (2) Does NOT provide a severity diagnosis
• Other shortcomings:
  
  • Relatively mildly affected CVDs (protanamalous, deuteranomalous) may make as many errors like dichromats (protanopes, deuteranopes)
  • Can be memorized as its always presented the same way
  • Difficult to administer in children younger than 5 years
  • Does not distinguish between dichromats and anomalous trichromats (i.e., protanope from protanomalous, deuteranope form deuteranomalous)

Question 55

What are Common Mistakes in the Interpretation of the Ishihara PIC Test?

Answer 55

1. Using the wrong failure criterion leading to misdiagnosis
2. Assuming that patients who make many errors have a “Severe” color vision deficiency
   
   1. Number of errors on the Ishahara test is NOT a measure of severity, except that a very small number of errors may indicate a mild CVD
3. Diagnosing plates to different protan and deutan CVD that are well designed but DO NOT ALWAYS YIELD A DIAGNOSIS
4. Sometimes the diagnosis is WRONG and in 30-40% of cases – NO diagnosis is possible because both numerals are seen or neither is seen

Question 56

What is the role of demonstration plate in Pseudoisochromatic plate tests.

Answer 56

Demonstration plate

1. Plate has luminous reflectance cues and/or color differences that do not lie on confusion line
2. Ex) Ishihara & HRR demo plates
3. Color vision is not necessary for a correct response
4. Useful for demonstration on how the test symbols look
5. Also useful for picking up on malingerers
   
   1. Malingerer – pretends to exaggerates incapacity

Question 57

What is the expected perception of Quantitative & Hidden-digit plates in Pseudoisochromatic plate tests.

Answer 57

• Quantitative plates
  
  • A set of plates with increasing color difference
  • Confusion with small color difference – mild
  • Confusion with large color difference – moderate/severe
  • Example: Hardy-Rand-Rittler (HRR)
• Hidden-digit plates
  
  • Opposite of a disappearance test
  • Visible only to those with color deficiency
  • Normals should not see anything, whereas a CVD should see 5

Question 58

Describe the HRR Pseudoisochromatic (PIC) Plate Test.

Answer 58

• Contains demonstration, screening, and diagnostic plates
  
  • Demonstration plates = 4 plates
  • Screening plates = 6 plates (2 blue-yellow, 4 red-green)
  • Diagnostic plates = 14 plates (10 red-green, 4 blue-yellow)
    
    • There are 20 test plates, 4 for screening red-green (protan/deutan) CVD, 2 for blue-yellow (tritan/tetartan) CVD
    • 10 for classifying and assessing the severity of red-green CVD
    • 4 for classifying and assessing the severity of blue-yellow CVD
• N a few cases where the color defective is very mild, a patient may fail to see correctly some of the symbols in the SCREENING PLATES (5-10), but see correctly all symbols in the DIAGNOSTIC PLATES (11-24)
  
  • The screening plates must be given a second time with the test book

Question 59

Describe the HRR Color Test Procedure.

Answer 59

• Demonstration:
  
  • The demonstration plates (1-4) are not scored
  • Show these demonstration plates in a sequence saying: “I am going to show you some colored symbols. Without touching them, how many do you see? Where are they?”
  • Unless the patient is malingering or totally color deficient, two colored symbols should be seen on each of the plate 1-2: first demonstration (0X and X∆), one colored symbol (O) on the 3^rd, and no colored symbol on the 4^th demonstration plate
  • Tell the patient that these symbols may appear in any of the 4 corners of the page
  • Ask the patient to trace the symbols they see with a small brush
  • Then say: “The test itself is made up of just three symbols with 2, 1, or 0 on a page. Some of them will be harder for you to see as they may be less strong in color.”

Question 60

How do you Interpret HRR Color Test?

Answer 60

• Interpretation of responses:
  
  • A correct response to a plate includes the number, name, and location of all colored symbols on the plate
  • An error is failure to see all symbols, or an incorrect name of any symbols, or an incorrect location
• Normal Color Vision:
  
  • A patient who gives correct responses to all 6 screening plates has normal color vision
    
    • Testing may be stopped at this point
  • A patient who makes ONE or MORE errors in the screening plates but NONE in the subsequent diagnostic plates, and upon retesting gives correct responses to all of the screening plates (5-10), has normal color vision in the eye being tested

Question 61

Describe Defective Color Vision Determined by HRR Testing.

Answer 61

• Type of Defect:
  
  • Red-green deficiency
    
    • Protan if the total number of checks in the protan column is greater than in the deutan column
    • Deutan if the total number of checks in the deutan column is greater than in the protan column
    • Unclassified as to type of red-green deficiency if the number of checks is the same in the protan an ddeutan columns, or if errors have been made in only the screening plates
  • Blue-Yellow Deficiency
    
    • Tritan if the number of checks in the tritan column is greater than in the tetartan column
    • Tetartan if the total number of checks in the tetartan column is greater than in the tritan column
    • Unclassified as to type of blue-yellow deficiency if the number of checks is the same in the tritan and tetartan columns, or if the errors have been made only in the screening series
  • Extensive scattered errors throughout the various groups of plates may indicate:
    
    • Malingnering
    • Monochromatism – total color blindness
    • Low color discrimination approaching monochromatism
• Extent of Defect:
  
  • The HRR test recognizes 3 degrees of extent of defect:
    
    • Mild
    • Medium
    • Strong
  • The last group of plates in which error occurs gives the extent of the patient’s color deficiency
  • For example, in a case of red-green deficiency:
    
    • If the last error occurs in either group of plates 7-10 or 11-15 and there are no errors in plates 16-20, the defect is MILD in extent
    • If the last error occurs in plates 16-18 and there are no errors in plates 19-20, the defect is MEDIUM in extent
    • If errors occur in plates 19-20, the defect is STRONG
  • Similarly, in a case of Blue-Yellow Deficiency
    
    • If the last error occurs in plates 5-6 and there are no errors in plates 21-24, the defect is MILD
    • If the last error occurs in plates 21-22 and there are no errors in plates 23-34, the defect is MEDIUM
    • If errors occur in plates 23-24, the defect is STRONG

Question 62

How do you Classify Sensitivity & Specificity on HRR Performance?

Answer 62

• HRR – Screening Plates
  
  • When the manufacturer criterion for FAILING, 2 or more errors with the screening plates (i.e., 1 error is allowed) is used:
    
    • The Richmond HRR test has a
      
      • Sensitivity of 1.00
        
        • In correctly identifying color defectives
      • Specificity of 0.975
        
        • In correctly identifying color-normal
  • When the criterion for falling is 3 or more errors with the screening plates
    
    • Sensitivity of 0.98
    • Specificity becomes 1.0
• HRR – Diagnostic Plate Performance:
  
  • Red-Green CVD were
    
    • Correctly classified as protan or deutan on 86% of occasions
    • Unclassified on 11%
    • Incorrectly classified on 3%
  • All those graded as having a “mild” defect by the Richmond HRR test – PASSED the Farnsworth D15 test and had an anomaloscope range of 30 or less
  • Not all dichromats (protanope/deuteranope) were correctly classified as “STRONG”
    
    • Those graded as “MEDIUM” and “STRONG” defects – included Dichromats and those who have a mild color vision deficiency based on the results of the Farnsworth 15 test and the anomaloscope range

Question 63

What are the Advantages of HRR Testing?

Answer 63

• Has tritan screening & diagnostic plates
• Classifies protan, deutan, tritan and severity
• Can be used with very young children because it uses symbols, a circle, a triangle, and a cross
  
  • Can often be named or traced by young children before they can read numbers

Question 64

Describe the HRR Diagnostic Plates: (**exam bonus question)

Answer 64

• Reproduction of plate 20 of the HRR pseudoisochromatic plates (4^th edition)
  
  • The circle may not be visible in deuteranopia or deuteranomaly, while the triangle may not be visible in protanopia or protanomaly
• Example of a diagnostic plate from the HRR test
  
  • The colors of the symbols lie on the Protan and Deutan confusion loci
    
    • This means that depending on the saturation fo the color of the symbols and the severity of the color vision deficiency, they MAY NOT BE DISTINGUISHED from the grey dots of the background
    • They are “Vaninishing” plates (similar to the plates in the Ishihara)
• There are also plates where symbols have colors that lie on the TRITAN confusion loci
  
  • The tritan plates in the HRR test also have symbols with colors that lie on the so-called Tetartonpia confusion locus but as tetertanopia does not exist, these are not of any value
  • Does not discriminate dichromacy from anomalous trichromacy

Question 65

What is one of the Earliest Arrangement Tests?

Answer 65

• Holmgren Wool Test – subject is asked to sort colors (e.g., woll yarn, caps) into sequences or groups
  
  • Colors have same Munsell values and Chroma and differ by Munsell Hue
  • 5 Munsell hues: Red, Yellow, Green, Blue and Purple
  • 5 Hue Subcategories (partitions) – RY, YG, GB, PB, RP, each subdivided into 10 steps (e.g., 1-10 RP), for 100 hues

Question 66

Describe the Axes of Confusions in the Polar Diagram of FM 100 Results.

Answer 66

• The further out from the center, the worse the severity of the CVD

Question 67

Which color vision test would you use to detect acquired color vision defect?

Answer 67

• FM 100 Hue Test in Acquired Color Vision Deficiency
  
  • Means of monitoring treatment
    
    • Diabetic retinopathy – tritan defect
    • Retrobulbar neuritis associated with MS
      
      • Recovery of red-green defect
    • Vitamin A deficiency
      
      • Recovery of nonspecific hue discrimination loss following oral dose of Vitamin A
• The Farnsworth D-15 / Dichotomous D-15 / Panel D-15 / Regular D-15 has been used widely in evaluation of acquired color vision defects
• The Lanthony desaturated D15 test is useful for detecting mild acquired color vision deficiencies (where subtle acquired losses occur)
  
  • Ex: cataract, glaucoma

Question 68

Describe X-Chrome Contact Lenses in the FM 100 Test.

Answer 68

• Deuteranomalous error reduction
• Recovery of nonspecific hue discrimination loss following oral dose of vitamin A

Question 69

Which arrangement color vision test would you use to distinguish acquired color vision defect from inherited color vision test?

Answer 69

• The D-15 has been widely used in the evaluation of acquired color vision defect

Question 70

What is the strength and weakness of Farnsworth D15 test?

Answer 70

• The D-15 Test:
  
  • Designed to “distinguish the functionally color blind from the moderately color defective and the normal” (hence called dichotomous)
• The D-15 has been widely used in the evaluation of acquired color vision defect
• Strengths:
  
  • Spacing of the colors along confusion lines makes it relatively
    
    • Easy test to pass for normal trichromats
    • Many anomalous trichromats
    • BUT almost all dichromats fail
  • The test has good test-retest reliability for pass/fail with a coefficient of reliability of between 0.96 and 1.0
  • MOST CLINICALLY USEFUL TEST
    
    • Allows to discriminate protan, deutan, and tritan defects
• Weakness:
  
  • Although it allows to discriminate protan, deutan, and tritan defects, it does NOT allow to discriminate between dichromacy and anomalous trichromacy
  • Has low sensitivity – hence some subjects with Mild defects (anomalous trichromacy) may pass the test

Question 71

Describe the Design of the Farnsowrth D-15 Test.

Answer 71

• Dichotomous pass/fail results, where those with failure may have problems with some day-to-day tasks and occupations
  
  • The Farnsoworth D15 test was designed to classify patients into those who are likely to experience difficulties with their color vision and those who are not
• A patient arranges 15 colored caps in a tray with a fixed reference cap at one end
  
  • Each successive cap is the closest (similar) match to the one that preceded it
• Farnsworth D15 categorizes patients with abnormal color vision into one of two categories… Those who:
  
  • PASS and have mild color deficiency
  • FAIL and have a moderate-to-severe deficiency
• The primary use of the D15 is categorization into Mild and Moderate/Severe
  
  • Failure is based on number of crossings: 2 or more crossings is deemed as FAILURE
  • The orientation of the diametrical CROSSINGS gives information on the type of CVD
  • It can be relied on for classification by type when there are diametrical crossings
• Was originally designed to set a level of difficulty such that those who passed it would be able to identify the colors of wires used in transformers
• Some clinicians presume that hose who pass the Farnsworth D15 test have a mild deficiency that is unlikely to cause significant handicap in everyday color tasks
  
  • This is not entirely true!
    
    • While many of those who pass the D15 test can recognize the colors of signal lights and recognize complex surface color codes, a good number cannot

Question 72

A young male fails the Ishihara Color Plate Test but PASSES the Farnsworth D-15 arrangement test. What does this indicate?

Answer 72

• Failing Ishihara = red-green color deficiency
  
  • Can be anomalous trichromat or dichromats
• But if there are no errors on the Farnsworth D15 test, there is no indication of whether the protan or deutan variety is present
  
  • So in this case it indicates anomalous trichromacy (protanamlous/deuteranamalous)
• Protanopes and deuteranopes, as well as extreme anomalous trichromats (who are nearly dichromatic or severe), fail both the Ishihara and Farnsworth D15 tests, and their error axes are diagnostic of these conditions

Question 73

What is the Munsell value and chroma of standard D15 and Lanthony desaturated D15 test?

Answer 73

• Standard D15:
  
  • Munsell Value: 5
  • Munsell Chroma: 4
  • VARIES IN HUE
• Lanthony Desaturated D15:
  
  • Munsell Value: 8
  • Munsell Chroma: 2
  • VARIES IN HUE
  • So the color differences are substantially smaller than D15

Question 74

Describe the design of the F 100 Hue test.

Answer 74

• 100 caps with colored papers, 1.5˚ from eye to desktop
• 85 caps – 15 removed to create relatively equal just noticeable differences between caps
  
  • 4 trays
    
    • Tray 1: 22 caps
    • Tray 2-4: 21 caps
  • Form Hue Circle in CIE
• Typically used under standard Illuminant C (daylight)
• Total Error Score (TEST) plotted in score sheet
• Error Score (TES): indicates severity of the defect
• Midpoint indicates the type of color vision defect
• Cap score (for each cap) – sum oof differences between neighboring caps

Question 75

What is the downfall of FM 100 Hue test?

Answer 75

• Length of test – time consuming (used rarely)
• Doesn’t distinguish dichromacy from anomalous trichromacy (i.e., protanope vs. protanomalous)

Question 76

What is the benefit of FM 100 Hue test?

Answer 76

• Provides a means of monitoring color vision changes & treatments

Question 77

Describe the Lanthony Desaturated D15 Test.

Answer 77

• Identical to Farnsworth D15, except the color caps are much less saturated than D15
• Detects anomalous trichromacy (sensitive test)
• A higher level of illuminance than any other test (600 to 800 lux) is specified
• CVD subjects passing the D15 may, as expected from the smaller color differences, FAIL the lanthony D15
• Small color differences of Lanthony D15 lead to normal making minor transpositional errors
  
  • This tends to blue the distinction between normal and abnormal

Question 78

Which color vision test distinguish between dichromats and anomalous trichromats?

Answer 78

• ONLY CLINICAL INSTRUMENT that can provide a complete diagnosis of Red-Green color vision anomaly including differential diagnosis of DICHROMACY from ANOMALOUS TRICHROMACY: Nagel Anomaloscope

Question 79

Which is the gold standard of Color vision? What is the basis for this test?

Answer 79

• Gold Standard: Nagel Anomaloscope
  
  • Bipartite field viewed through an eye-piece
• Diagnoses the 4 major X-linked color defects

Question 80

What is the basis for the nagel anomaloscope?

Answer 80

• Mixture field – the upper half: consists of red and green wavelengths
  
  • Mixture scale setting 0 to 73 represent various combinations of 546 (green) to 670 (red)
• Test field – lower half: consists of a fixed yellow test field
  
  • Test field knob setting 0-35 varies test field yellow Brightness/Luminance
• Observer: the task of the observer is to adjust the wavelengths of red and green primaries on the Mixture field, to match the brightness and color of the yellow test field so that they both appear identical (Metameric match)
  
  • The observer’s red-green balance can be used to distinguish a red-green dichromacy from anomalous trichromacy
• Nagel primaries: fall along protan and deutan lines of confusion and it constitutes Rayleigh Equation
• New Nagel anomaloscope can detect TRITAN!
  
  • Unlike the old Nagel anomaloscope’s, where none of the 3 primaries were absorbed by the S-cones **primary one tested on

Question 81

Explain the nagel anomaloscope in in terms Rayleigh and Moreland equation.

Answer 81

• Based on the Rayleigh equation for Protan/Deutan:
  
  • Red + Green = yellow
    
    • E.g., 670.8 + 546 = 589.3 nm (Nagel) **don’t worry about this equation
• Based on Moreland equation for Tritan:
  
  • Blue + Green = blue-green

Question 82

How does the MIXTURE FIELD & TEST FIELD (in Nagel Anomaloscope) appear to Color-Normals in Deuteranomaly?

Answer 82

• Mixture Field:
  
  • Setting: 0-45
  • Appearance in Normal Trichromacy: Green (0) to yellow (45)
• Test Field:
  
  • Setting: 17
  • Appearance in Normal Trichromacy: yellow

Question 83

How does the MIXTURE FIELD & TEST FIELD (in Nagel Anomaloscope) appear to Color-Normals in Protananomaly?

Answer 83

• Mixture Field:
  
  • Setting: 45-73
  • Appearance in Normal Trichromacy: yellow (45) to red (73)
• Test Field:
  
  • Setting: 10
  • Appearance in Normal Trichromacy: dim yellow

Question 84

How does the MIXTURE FIELD & TEST FIELD (in Nagel Anomaloscope) appear to Color-Normals in Deuteranopes?

Answer 84

• Mixture Field:
  
  • Setting: any setting from 0 to 73 will be matched
  • Appearance in Normal Trichromacy: Green (0) to yellow (45) to red (73)
• Test Field:
  
  • Setting: 17
  • Appearance in Normal Trichromacy: yellow

Question 85

How does the MIXTURE FIELD & TEST FIELD (in Nagel Anomaloscope) appear to Color-Normals in Protanopes?

Answer 85

• Mixture Field:
  
  • Setting: any setting from 0 to 73 will be matched
  • Appearance in Normal Trichromacy: Green (0) to yellow (45) to red (73)
• Test Field:
  
  • Setting: 35-5
  • Appearance in Normal Trichromacy: bright to dim yellow

Question 86

What is the appearance of the color mixture (Top field) when color-normals view a protanomalous match?

Answer 86

• When a color-normal views a protanomalous match, the color mixture will look red

Question 87

What is the appearance of the mixture field when color-normals view a deuteranomalous match?

Answer 87

• When a color-normal views a deuteranomalous match, the color mixture will look green

Question 88

What is the appearance of the Mixture field, when a deuteranomalous trichromat views a Normal color match (of mixture & test field)?

Answer 88

• The color will look more red because deuteranomalous trichromats are green deficient

Question 89

What is the appearance of the top Mixture field, when a protanomalous trichromat views a normal color match (of mixture & test field)?

Answer 89

• the initial appearance will look more green because protanomalous trichromats are red deficient

Question 90

What are the mixture field settings at for deuteranomalous and protanomalous individuals on Nagel Anomaloscope?

Answer 90

• 0 to 45 = deuteranomalous
• 45 to 73 = protanomalous
• *note protanomalous and protanope individuals will also want to adjust the brightness setting of the test field – often lower brightness

Question 91

What Color Vision Test is capable of a full classification of congenital CVD?

Answer 91

• Nagel anomaloscope is capable of determining:
  
  • Anomalous trichromats from normal trichromats
  • Dichromats from anomalous trichromats

Question 92

What are some causes of Blue-Yellow defects?

Answer 92

• Macular pigment and crystalline lens variability

Question 93

Describe the Medmont C-100 Test.

Answer 93

• Flicker matching (rapid alternation) of Red (659) and Green (560) using dual light emitting diode
• Subject controls luminance ratio of red and green
• Reliably distinguishes: protans from normal
  
  • Does not distinguish deutans from normal

Question 94

Describe the CITY University Test.

Answer 94

• Book format (appearance of pseudoisochromatic plate test – but not classified as so)
  
  • Because of this design – not strictly/purely a color matching test, but it incorporates D15 hues mimicking an arrangement test (but not classified so)
• Task: match the central hue with one of the peripheral hue (which appears similar)
  
  • Of the 5 hues, one choice is the adjacent D15 hue, one each lies on each of the protan, deutan, and tritan confusion loci
• Forced Choice Procedure test – subject is forced to match a color/response for each plate (as opposed to having nothing visible)
  
  • Psychophysical procedure
• Similar difficulty to the D15 and can be an alternative

Question 95

Describe the Farnsowrth Lantern (FaLant) Test and the Stereo Optical OPTEC 900 Test.

Answer 95

• Neither are commercially available
• Farnsworth Lantern – 2 light lantern for US navy, with Red, Green and White
• Stereo Optical OPTEC 900 – used in US military, FAA

Question 96

What are the 3 Occupational Tests?

Answer 96

• D15
• Lantern Tests
• The Rabin Cone Contrast Test (CCT)

Question 97

What are the 3 Occupational Tests?

Answer 97

• D15
• Lantern Tests
• The Rabin Cone Contrast Test (CCT)

Question 98

Describe the Rabin Cone Contrast Test (CCT).

Answer 98

• Gold standard/sole CV test for US air force and US military
• Detects severity of cone deficiency and congenital color deficiencies
• Unlike other CV tests: Rabin Cone test measures the severity of cone function loss, and tracks cone function over time, aiding in the detection of disease and monitoring disease progression and efficacy of treatment

Question 99

What types of acquired color deficiencies can be detected and monitored by the Rabin Cone Contrast Test?

Answer 99

• ARMD, Glaucoma, Diabetic Retinopathy, MS, Parkinson’s disease, TBI, Retinal Toxicity due to high-risk meds such as Plaquenil

Question 100

What Color Vision Testing can be used for Reimbursement purposes?

Answer 100

• Rabin CCT Stimulus
• FM-100 Hue Test
• Nagel Anomaloscope
• Insurance – separate CPT code (92283) $47 technical + 9 professional ~$56 reimbursement
• Other CV tests (HRR/Ishihara) – charged with the eye exam

Question 101

What are the frequently confused colors by red-green dichromacy (protanopia/deuteranopia)?

Answer 101

• Light grayish purple (mauve) -> gray
• Pink -> gray
• Green -> white
• Green -> gray
• Light yellowish brown (beige) – green
• Dark purplish red (maroon) – brown
• Olive – brown
• Light green – light yellow
• Light green – light orange
• Light yellow – light orange
• Light yellowish green (chartreuse) – pink
• Light purple – light blue
• Light orange – light red

Question 102

What are the recommended lighting conditions for color vision tests?

Answer 102

• Illuminant C or MacBeth Lamp – not readily available
  
  • FM 100, Regular D-15, Lanthony D-15 – strictly Illuminant C
• Indirect sunlight
  
  • Screening: Ishihara – performs well in room lighting and sometimes even in incorrect illumination
  • HRR – okay to perform in room lighting – away of variable results that may pass mild color defectives
• Non-standard fluorescent tube – Varilux F15T8/BLX – advisable
• Not advisable lighting:
  
  • Standard fluorescent
  • Unfiltered incandescent source – patient may perform better due to varying luminance profile
    
    • Incandescent source should be used with appropriate (blue) filters

Question 103

What are some Recommendations for CV testing?

Answer 103

• Practitioners should never rely on a single color vision test regardless of the color vision standard
• Lighting/illumination for testing
  
  • Lighting should be color temperature (Tcp) 6500 K and color-rendering indices (Ra) should be greater than 90 (Ra > 90)
  • Illuminance levels should be between 200 and 30 lux if detection of color vision deficiency is a priority or between 300 and 1000 lux if the need is to tes tat the level where illuminance has minimal influence on performance
• Illuminance should be reported when testing color vision
• Time limits should be set between 1 and 2 minutes
• Repeat testing (beyond the specified test and one retest) should be carried out only with authorization
• Initial and repeated results should be reported

Question 104

Describe Inherited CV anomalies.

Answer 104

• Stable, no threat to vision
• Children should be screened at pre-school level
• Parents and teachers informed
• Parents counseled about career choices (airline pilot, firefighter)
• May have difficulties distinguishing colors in dull illumination

Question 105

What tests are best to screen acquired anomalies?

Answer 105

• HRR (Richmond 4^th edition)
• Standard Pseudoisochromatic Plate Test (SPP-2)
  
  • SPP-1
    
    • Tests for red-green defects
  • SPP-2
    
    • Tests for blue-yellow defects
• D-15 Tests
• SWAP or Moreland Anomaloscope
• These tests are to establish baseline data during first visit and are to be performed monocularly with the worst eye first

Question 106

List the Ocular Diseases associated with Acquired Color Defects: Red-green & Blue-yellow defects

Answer 106

• **conditions that are exceptions to Kollner’s Rule
• Blue-Yellow acquired anomalies:
  
  • Glaucoma **
  • Diabetes
  • Retinal detachment
  • Age-related maculopathy
  • Chorioretinitis
  • Central serous retinopathy
  • Papilledema
  • Hereditary autosomal dominant optic atrophy
• Red-Green Defects:
  
  • Optic neuritis
  • Papillitis
  • Leber’s optic atrophy
  • Toxic amblyopia
  • Lesions of the optic nerve and pathway
  • Dominant cystoid macular dystrophy **
  • Hereditary juvenile macular degeneration **
  • Fundus Flavimaculatus **

Question 107

List the commonly used drugs associated with Acquired color vision defects.

Answer 107

• Red-Green Defects:
  
  • Antidiabetics (oral)
  • Tuberculostatics
• Blue-Yellow Defects:
  
  • Erythromycin
  • Indomethacin
  • Trimethadione
  • Chloroquine derivatives
  • Phenothiazine derivatives
• Red-Green and/or Blue-Yellow Defects:
  
  • Ethanol
  • Cardiac glycosides (digitalis, digitoxin)
  • Oral contraceptives

Question 108

Do sunglasses interfere with the ability of inherited anomalies to quickly and correctly identify colored traffic signals?

Answer 108

• Yes
• Certain non-neutral tints (other than grey) may make it difficult
• Tinted lenses should not be recommended to CVD
• Protan anomalies have been associated with increased rear-ended automobile accidents

Question 109

Describe Patient Management Strategies for Adult Patients.

Answer 109

• Determine the type of color vision defect and occupational needs of the patient
• Explain the nature of the defect (inherited/acquired)
• Seek family history if inherited
• Inform probability of their child/grandchild being color vision defective
• Depending on defect type, explain the consequences of day-to-day living (like driving)
• Explain that CVD cannot be treated, but can be HELPED with filters while performing specific tasks
  
  • But the Enchroma Glasses don’t work for everyone
• Caution on career choices
• Recommend avoidance of driving with sunglasses
• Caution them about driving at night in new towns/cities where streetlights may blend into traffic lights

Question 110

Describe Patient Management Strategies for Children.

Answer 110

• Inform the teacher
• Counsel parents about the career choices

Question 111

Explain the use of colored filters for color vision defectives.

Answer 111

• Filters cannot fully correct CVDs – but some pt’s may benefit from colored filters
• If the color defective has well defined and predictable problems with specific colors, it is relatively straightforward to introduce a colored filter that can exaggerate the brightness differences of two colors
  
  • Example: red-green confusions can be viewed with a red filter to make the red object become relatively brighter, thereby distinguishable
  • Selective filtering of the most desaturated colors for color defectives may enhance the appearance of an otherwise dull scene
• Colors that fall on the confusion lines of dichromats can be moved off them
  
  • However, it should always be assume that the discrimination of some other colors has been reduced by adding this filter
  • Nonetheless, in an environment or workplace in which a limited number of important colors must be distinguished from each other, there is a good application of filters for color defectives

Question 112

What happens when one eye receives a different color filter than the other eye?

Answer 112

• There is a theoretical possibility that the brain of the color defective could learn to interpret this differential information in a way that leads to an increase in color discrimination abilities overall
  
  • However, this does not occur (or vary rare) in practice

Question 113

Should colored filters (including tinted spectacles or CLs) be used for color tests?

Answer 113

• NO
• Use of colored filters to help an individual pass an Ishihara test / HRR cannot be construed as overall improvement in color vision – it is like allowing an individual to stand closer to the acuity chart so that he can read the 20/20 line
  
  • The result is misleading

Question 114

Should monocularly worn X chrom lenses be worn for driving?

Answer 114

• NO – it could impair depth perception and possible confusion/interference with perceiving traffic lights

Question 115

Explain the role of X-chrom contact lens for color vision defectives

Answer 115

• X-chrom lens is a red contact lens worn on one eye
• Designed to improve color discrimination in dichromats and anomalous trichromats
• It is a long-pass filter, blocks shorter wavelengths and transmits longer wavelengths
• There is a deuteranomalous error reduction and recovery of nonspecific hue discrimination loss following oral dose of Vitamin A on F100 Test

Question 116

What are limitations of X-chrom contact lenses?

Answer 116

• Some patients suppress the eye that has the contact lens, others tend to fuse the image
• Based on improved performance on the pseudoisochromatic plate tests, it has been claimed that the x-chrome lens improves color vision
• Same claim has been made when viewing binocularly through large colored filter
• This does not indicate improved color discrimination
• Red contact lens use is questionable
• A handheld red filter may be helpful to some patients
• Counseling: parents, adults – restrictions in certain occupations, about alternate careers

Question 117

Describe the role of gene therapy in restoring color vision in Monkeys.

Answer 117

• Replacement of defective gene in color blindness offers promise to cure color blindness
• Animal studies (mice, monkeys) have shown that it is possible to confer color vision by injection a gene of the missing photopigment using gene therapy
  
  • Improved color vision in dichromatic monkeys by injecting the virus carrying the opsin gene
  • Further work needed to demonstrate the efficacy and safety of such an approach in humans

Question 118

What is the Technique of Gene Therapy for CVD?

Answer 118

• Recombinant adeno-associated virus (rAAV) = vector
• cDNA of opsin gene found in the L or M cones can be delivered to a fraction of cones via subretinal injection
• effects lasts until the cones die or the inserted DNA is lost within the cones
• not attempted in humans yet – but should be feasible for humans eventually

Question 119

Describe the SWAP test and what cone function can be assessed using SWAP test?

Answer 119

• SWAP = short wavelength automated perimetry
• The S cone (blue-yellow pathway) is more vulnerable to certain pathological conditions like Glaucoma
• SWAP has been developed to detect early glaucoma by isolating S-system function
• Humphrey visual field apparatus can be adapted by replacing standard white stimulus with a short wavelength stimulus to maximize S cone sensitivity & yellow background to suppress (adapting) L & M cone systems
• SWAP – sensitive measure of glaucomatous nerve damage