316 Colour Vision Flashcards
3 theories of colour vision
Young
Helmholtz
Hering
CV theory by young
Thought 3 primary colours in colour mixing = RGB
CV theory by helmholtz
Introduced overlapping spectral sensitivities that explains what happens at PR level of retina
CV theory by Hering
There’s 4 primary colours RGBY arranged in opponent pairs where third pair is luminance mechanism
Helps explain after images and proven as no reddish green colour
Current understanding of what happens from Ganglion cell level onwards
Characteristics of inherited colour vision defects
Present from birth where type and severity is same throughout life
Type can be diagnosed precisely
CVD affects BE equally but VA and VF normal
Mainly Red-Green and males
How are the confusion loci different from anomalous trichromats
Lines are shorter for an anomalous trichromatic and don’t include the full range of colours
What are monochromats
Can only see B&W cuz they only have rods or 1cone+rod (atypical)
SO VA is bad, they have photophobia and nystagmus
What are dichromats (Opias)
Have only 2 types of photo pigment (1 missing) so they have confusion Loci where colours that look the same
Note if luminance is controlled then they see a limited number of colours
What are trichromats
Have all 3 colour pigments and so can be colour normals or anomalous trichromats
What’s an anomalous trichromats
One photpigment has a different sensitivity
MOST COMMON CVD but can be mild or severe as dichromat
What’s an extreme anomalous trichromat
Px with possible abnormal medium AND long photopigments causing matching range of an anomalous cope extending to both sides of normal range instead of just one side in protanomal/deuteranomal
Prevalence of CVD
Anomalous trichromat
Deutan-> protan -> Tritan
Characteristics of acquired CVD
Onset after birth where type and severity changes with time
Hard to diagnose/classify
Monocular differences in severity CVD and decrease in VA/VF defects
Greater chance of B-Y defects and affects both Males and Females equally
What are the 2 common types of acquired CVD classification systems and what’s impt about it
Verriests Classification
Kollners rule
Impt as classifications can change v quickly if different optoms grade a CVD since acquired CVD changes as pathology worsens and different systems are used
Describe Verriests Classification (acquired CVD) Type 1
Protan like mild to severe confusion of RG hues
Little/no loss of BY
Moderate/severe reduction in VA
Describe Verriests Classification type 2
Deutan like, mild to severe confusion of RG hues
Mild loss of BY
Moderate to severe reduction in VA
Describe Verriests Classification type 3
Tritan like mild to moderate confusion of BY hues
Lesser impairment of RG
VA normal or moderately reduced
What does Kollners rule state and how is it innacurate
Blue-Yellow CVD are from disorders of retina while Red-Green CVD is from disorders of optic nerve
Many exception where many pathologies start with BY CVD and then become RG
Example of type 1 Verriest acquired CVD - protan like
Progressive cone dystrophies
RPE dystrophies
Example of type 2 Verriest classified acquired CVD (deutan like)
Optic neuritis
Example of type 3 acquired CVD Verriest - Tritan like
CSR/AMD
Rod and Rod-Cone dystrophies
Retinal vascular disorders
Peripheral retinal lesions
Glaucoma
AD optic atrophy
What’s acquired achromatopsia
Total colour blindness from injury to central occipital lobe
What’s Colour agnosia
Inability to recognise a colour while being able to perceive or distinguish it e.g thinking a blue banana is normal
Injury to V4
What’s colour anoma
Can point to colour of object but can’t say name
Injury to V4
What’s chromatopsia
Vision appears to have a coloured tint like looking through tinted lenses BUT colour discrimination is normal
What’s Cyanopsia and it’s cause
Blue vision
Cataract removal as it was supposed to absorb blue light
Viagra
What’s xanthopsia and it’s cause
Yellow vision
From medication e.g digoxin
What’s erythropsia and it’s cause
Red vision
Snow blindness or atropine use
What’s chloropsia and it’s cause
Green vision
Epinephrine or lead poisoning
What’s Ianthinopsia or violet vision
Violet vision
Cannabis use
Why illumination important in Cv
Diff illumination changes appearance of colours so could be easier so px with CVD pass or harder so ppl with good discrimination make mistakes
What are the types of CV tests
Pseudoisochromatic plates - identify letter from background
Hue discrimination/sorting tests - arrange hues in sequence
Colour matching
Colour naming
Example of hue discrimination/sorting test
D15
Desat D15
100hue
Example of colour matching
Anomaloscope
MedmontC100
Example of colour naming
Falant Lantern
CAD
Tests good for detecting THERE IS a CVD
Ishihara pseudoisochromatic plates
Red desat test
Farnsworth D15
Lanthonys Desat D15/Tritan album
Etc
What’s good at DIAGNOSING the type of CVD
Medmont c100
Anomaloscope
Lantern and CAD
Rabin come contrast test
Why’s medmont c100 good for diagnosing CVD
Because it can differentiate programs and deutan
CANT between dichromat and trichromats tho
How does anomaloscope diagnose CVD
Looks at length of matching range and it’s orientation to give diagnosis of severity and type
Uses R+G = Yellow And looks at limit of matching so which colours look the same
How does lantern and CAD diagnose CVD type
Identify px with certain occupations
How does Rabin come contrast test diagnose by defect type
Sees if only one cone is affected or more than one cone affected
What does the anomaloscope determine
If normal or CVD
if protan or deutan
If dichromat or anomalous trichromat
MOST reliable if matching wavelength widely separated
On an anomaloscope what do dichromat results look like
Dichromat - can match every red greed mix with a yellow luminance so line touches both ends matching 0 and 73
On an anomaloscope what do anomalous trichromat results look like
Have small matching range away from normal but if severe then have large matching range but not touching both ends
Protanomals ~ 40-73
Deuteranomals ~ 0-40
What do results if deutan and protan look like on anomaloscope
Deutan - luminance level is contact so best fit line is horizontal
Protan luminance level is less when more reds is added so best for line is downward slope
The munsell system defines colour by hue value and chroma what are these three
Hue is colour as commonly defined There’s 10 hues and Each hue has 10 steps
Value is amount of light reflected where 0 is black and 10 is white
Chroma is amount of colour present
How does farnsworth munsell 100 hue work
Sorting test or hue discrimination
4 boxes of colour caps each box has 21 caps except first of 22 so has total of 85 and these caps vary only by hue so NOT value or chroma
Finds error score and compares to pop normals where performance is age related and there can be learning effects
How is error score calculated on F M 100 hue
Compares each cap with one beside it and if in order there’s a difference of 1 each side giving total of 2
Subtract 2 from each result so if in order it’s a result of 0
Add score for each box and if <20 hrs superior CV, 20-100 average, >100 below average
What is 100 hue used for
Not a screening test so no pass or fail BUT used to monitor or ass acquired CVD - beware learning effect
ALSO used to identify colour normals with very good colour discrimination like printing industry
What’s computer analysis if sorting tests for
Reduced noise so helpful when error score is large when trying to find the axis of confusion
Uses vector analysis where S index is measure of randomness and C index is severity
What’s Rabin come contrast test
Computer based test testing each cone function
Monocular test using similar letter to Bailey Logie but larger sizes for blue cone
Letter appear for 1-1.6 sec and if px doesnt select an answer within the time it’s markedlas incorrect
Describe lantern test
Colour naming
Where one or 2 lights are shown and their colour has to be named
Usually can only use 3 or 4 names so have to decide if a yellowish light is closer to white or green or red
Why is lantern important for occupation
Pilots have to be able to tel green from red lights to navigate and at night no other clues are available so have to be strict
Describe Farnsworth Lantern “Falant”
2 vertically separated lights where px names lights using only red green and white
Normal room illumination with 8 feet test distance
One light of each pair is dimmer than the other so luminance cannot be used to distinguish colours
Describe Holmes-Wright Lantern
Uses signal colour so 2 red 2 green + white
9 combinations used at test distance of 6m
Type A is aviation and 2 lights separated vertically
Type B is marine and 2 lights separated horizontally
Describe CAD Colour Assessment and Diagnosis
CV test to establish colour discrimination limits that’s safe for pilots in civil aviation
Deuteranomalous px with CAD threshold <6SN and protanomlous px with <12SN have to do the PAPI test as well as normal trichromats
Why do we need History and VA in full colour vision assessment
History - prev known/fam Hx, diff between eyes or time and wearing colour CL
VA - needs to be good for tests
most lanterns require clear distance vision
Other test are closer so needs reading glasses
In a full CV assessment what are things to watch out for in Ishihara D15 Medmont C100 Optec900 Anomaloscope CAD Farnsworth munsell 100 hue
Ishihara monocular random order
D15 monocular and repeat if failed but I’d pass then go desat d15
Medmont C109 need average of 7 readings
Optec900 binocular distance glasses with lights
Anomaloscope if know inherited then either eye but if suspect acquired DO each eye separately
CAD and 100 hue blah blah
General CV assessment order for occupations
Pass ishihara but if fail other test usually lantern needs to be passed
Often exclude protan but accept mild deter animals
Reasons for CV standards
Safety as many lives stake and quick reaction time needed
Accuracy to identify correctly
Repeatability
Name CV tasks in aviation WITH AND WITHOUT redundancy
Without - PAPI precision Approach Path Indicator, parking lights
WITH - navigation lights, rotating beacons on ground vehicles, Runway threshold
Police CV standard
Ishihara 24 plate edition where if 3 or more errors made on plate 2-17 then need further check
With 100 hue, D15 or Falant confirmed with medmont c100
Criteria not met if any of further checks failed or protan defect found
Armed forces CV standard
CPA is pass with ishihara or equivalent plates
CPB is fail with ishihara but pass with approved lantern
CPC is fail with both ishihara and lantern
Civil aviation authority CV standard
For class 1 2 or 3 medical certificate
Ishihara 24 plate edition
If ishihara failed then (Holmes Wright lantern OR Falant) AND anomaloscope
If either lantern is passed and anomaloscope shoes CVD isn’t protan/anomalous then can get any of 3 certificates
If either lantern fails OR Falant pass with anomaloscope saying protan/anomalous then ONLY class 1 or 2 issued WITH restrictions
Can a person with CVD fly
They need to be able to distinguish colours used in air navigation and correctly identify aviation coloured lights
So if they can’t do this then they can’t have a class 1 licence but can have class 2 with condition of flying only in daytime
Marine CV standard
Must pass Holmes Wright Lantern B
Railways (Tram Driver) CV standard
Pass with ishihara but if failed then practical test used to assess suitability
Tram drivers have no CV requirement
Firemen CV standard
No CV requirement
Electrical engineering CV standard
Pass on D15 means less mistakes when selecting electrical wiring
Live/active =brown or red
Neutral = light blue or black
Earth = green-yellow stripe or green
