Colour Vision Flashcards
For the D-15 Dichotomous test, what is it used to assess? What does it involve?
-red green and blue yellow colour vision defects
-patient has to arrange coloured caps in a sequence which determines type and severity of colour vision defect
What are the conditions of the d-15 dichotomous test?
-px is sat so they’re viewing the caps from 50cm
-standard illuminant C instead of room lighting for illumination
-there’s no time limit
-caps are initially randomised
What and how on the recording sheet shows severity of the defect in d15 dichotomous test?
The number of crossings:
-2 or less indicate moderate colour vision deficiency
-more than 2 indicate a severe colour vision defect
What and how on the recording sheet shows severity of the defect in d15 dichotomous test?
The number of crossings:
-2 or less indicate moderate colour vision deficiency
-more than 2 indicate a severe colour vision defect
How does the recording sheet for d15 dichotomous test tell you the type of defect?
Orientation of the crossings indicate wether it’s a protan, deutan or tritan colour defect
What are the conditions of the city test?
- px should view book at 35-50cm
-use standard illuminant - allow up to 3 secs per page
In the city test what are part 1 and part 2 each for and what happens in them?
Part 1 is for screening and part 2 is for classification
-in part 1, Px has to work out if one of the three dots is a different colour and then identify which one is different
-in part 2, Px has to tell the examiner which of the 4 dots around the central dot is the same colour as the central dot
How do you know if a patient has a colour deficiency and what type in the city test
-In part 1 if the px gets less than 8 correct then they have a colour deficiency
-In part 2 if they have any entries for protan, deutran and tritan then they may have a colour deficiency
What pathologies behind colour defects is Ishihara good for detecting?
-maculopathies
-subtle optic neuropathies
What is a disadvantage of the ishihara test?
Not good at determining the severity of the defect
What is the ishihara test?
The most common test for detecting red-green colour deficiencies
What are the conditions for the ishihara test?
-patient should view the book at 66-75cm
-use standard illuminant
-allow up to 4secs per page
-use 17 plates for screening: 1 demonstration, 1 transformation and 8 vanishing (only trichomats see)
How will anomalous trichromats see ishihara vanishing plates?
See an alternate digit (trichromats see nothing)
what are the three types of cones?
M cone = green cone = middle cone
L cone = red cone = long wavelength cone (most numerous)
S cone = blue cone = short wavelength cone (least numerous)
how many cones do we have?
7 million
what percent of each cone make up total cones in the retina
- blue (S) = 5%
- green (M) = 35%
- red (L) = 60%
what does univariance mean and what does this therefor suggest?
when all wavelength of info is lost when light hits one cone and reacts with the visual pigment hence a single cone cannot distinguish a specific colour as cones response is determined by number of photons absorbed instead of the specific wavelength of those photons
what are the two colour vision theories?
-young/helmholtz trichromatic theory
-Herring opponency
what does young/helmholtz trichromatic theory show
most colours in the visual spectrum could be matched with 2 other colours but 3 were needed in order to match every colour we can receive hence the conclusion that there are three primary colours
how does herring opponency theory contradict young/helmholtz trichromatic theory
as it concludes that there are three opponent mechanisms within our visual system where he proposed we have a blue vs yellow visual channel, a red vs green visual channel and a black vs white visual channel (bipolar channels)
what is max wavelength absorption for each cone?
Blue = 440nm
green = 535nm
red = 565nm
what connects the LGN to the higher cortical areas?
optic radiations
what are the 2 pathways from the retina to the LGN in the visual cortex? what are they each for?
-parvocellular pathway: R_G chromatic channel and achromatic luminance channel
-koniocellular pathway: B-Y Chromatic channel
in the visual cortex, where do neurones from koniocellular layers synapse and what are they called here?
in layer 3 called blobs
in the visual cortex, where dol cells in the parvocellular layers synapse?
in layer 4C(beta) and then post synaptic projections to layer 3 to separate chromatic and achromatic info
what happens in the red-green channel in herring’s opponency theory?
- Red and green cell receives excitatory input from the L cone receptor and inhibitory input from the M receptor
- Opponent cells have opponent receptive fields e.g. green on cells and red on cells
- When green on cell is excited, you perceive green and when it is inhibited, there is no perception
what is the pathway for how colour is perceived starting from retinal ganglion cells
- Red green chromatic channel goes through parvocellular pathway in the lateral geniculate nucleus
- Blue yellow chromatic channel goes through koniocellular pathway in the lateral geniculate nucleus
- Optic radiations
Visual cortex
In visual cortex, the cells are organised into hypercolumns and each correspond to a point on the retina - Neurons in koniocellular layers synapse in layer 3 (blobs)
- Neurons in parvocellular layers synapse in layer 4Cbeta
Post synaptic projections go to layer 3 - Reaches the colour analysis destination
- Colour analysis destination contains info from blobs and interblobs
- This info is combined with form, texture and edge info which then contributes to overall perception
what are the two types of colour vision defects?
congenital and acquired
what are the 5 key functions of the visual cortex?
-feature detection
-colour processing
-depth perception
-motion detection
-object recognition
what does it mean in terms of the visual cortex if a patient reports being able to see colour without form?
there is no input from interblobs
compare and contrast congenital vs acquired colour defects
-congenital defects mainly affect males while acquired has equal prevalence in males and females
-both have onset after birth
-in congenital, the type and severity of the colour deficiency is constant whereas in acquired, the type and severity of the deficiency varies
-congenital is easy to classify while acquired is not
-congenital affects both eyes equally whereas acquired has monocular differences
-in congenital va and vfs are normal (apart from in monochromats) whereas in acquired, va and vfs may be affected
why are congenital colour defects more common in males?
as they are X linked recessive inheritance
what are the two types of congenital defects?
-where the cone is absent/ non functioning = dichromat
-cone has impaired sensitivity = anomalous trichromat
what are the three types of dichromat?
-protanopia (L cone)
-deutreranopia (M cone)
-tritanopia (S cone)
whats the most common congenital defects seen in practise?
red green defects
-protanopia and deuteranopia in males
what are the three types of anomalous trichromats?
-protanomalous trichromat (L)
-deuteranomalous trichromat(M)
-tritanomalous trichromat (S)
what kind of vision do protanopes have and how is that of deuteranopes different?
-protanopes have reduced sensitivity at long wavelengths so there’s dimming effects causing confusion with reds and blacks
-deuteranopes don’t experience dimming because they still have L cones where they can see longer wavelengths of light
what colours may protanopes confuse?
red and black
why is monochromacy rare? what is atypical monochromacy?
-as the gene which causes it is on chromosome 3 and it has a recessive inheritance pattern
-In atypical cone monochromacy, they only have s cones, VA is better than rod monochromacy
what colours are protanopes not able to distinguish? what colours might they not be able to distinguish?
-red-yellow-green
-black or dark gray
what colours are deuteranopes unable to distinguish?
red-yellow-green
(same as protanopes just without the dimming)
what colours are patients with tritanopia unable to distinguish?
blue-green-yellow
what do anomalous trichromats confuse?
pale desaturated colours but not bright and saturated ones
what are the two types of monochromats?
-rod monochromats (achromatopsia) - no functioning cone cells
-cone monochromats - onlu one type of functioning cone cell
symptoms of rod monochromacy?
-complete colour blindness
-photophobia
-poor visual acuity
what monochromacy type is worse?
rod monochromacy
what type of congenital colour deficiencies cause colour vision defects?
-protanope
-deuteranope
-protanomalous trichromat
-deuteranomalous trichromat
what type of congenital colour defiencies caise blue-yellow defects?
-tritanope
-tritanomalous trichromat
what cause acquired colour vision defects?
disease processes, stroke, injury, trauma, toxicity which cause damage to any part of the visual pathway responsible for the processing of colour
how are acquired colour defects classified?
using Kollner’s classification, it classifies the type of acquired colour vision defects putting them into three broad groups trying to match them from the known groups in congenital colour defects
what are the 3 types of colour deficiencies in Kollner classification system?
-type 1: red-green
-type 2: red-green
-type 3: blue-yellow
What is type 1 acquired deficiency associated with?
-progressive cone dystrophies
-chloroquine toxicity
What is type 3 acquired deficiency associated with?
-Cataract
-Glaucoma
-AMD
-Diabetic retinopathy
What is type 2 acquired deficiency associated with?
-Optic neuropathy
-Ethambutol toxicity
what are the most common acquired colour vision defects?
blue yellow (type3)
why does cataract cause type 3 defect?
When the lens yellows with age, it causes absorption of shorter wavelengths of light
how can acquired colour vision defects be used to diagnose disease?
-Diabetic retinopathy also is associated with type 3 defect which can occur before retinopathy actually occurs - can be used as a warning
-2009 study detected colour vision changes before visual defects in open angle glaucoma - typically expect type 3 but any CV changes can occur
-AMD is associated with type 3 defect in early stages of disease
how can you use colour vision to test for optic neuritis?
typically causes red-green colour deficiency:
-Can test this in desaturated red test: Get a red target and tell the patient to occlude one eye and then switch between the eyes. Affected eye will see the red colour as more washed out/ dull which indicates optic neuritis
what is cerebral achromatopsia?
an acquired colour vision defect due to damage of V4 where you can only see in black and white
what is agnosias?
object recognition defect
what us anomia?
inability to name colours properly
when can drugs affect colour vision
if the dose is exceeded or treatment is prolonged
what are the 3 ways of specifying colour?
-the munsell system
-Newton’s colour circle
-CIE
what are the 3 different properties of colour according to the munsell tree?
-hugh (wavelength) 5 principle hues, 5 intermediate hues
-value (brightness) 0-10
-chroma (saturation) 1-8
why is it useful to split up colour into its three different properties as in the munsell colour tree?
so you can
-replicate colours
-split colours into categories
what are the drawbacks of the munsell colour tree?
-not mathematical
-takes time
what are the 5 principle and 5 intermediate hues of the munsell tree?
-(B,G,Y,R,P)
-(PB, BG, GY,YR, RP)
what are the drawbacks of newtons colour circle as a way of specifying colour?
Due to interaction of R-G / B-Y not possible to represent all colours using positive values for RGB pigment so you end up having to use negative of a colour which we cant see
how is CIE the best way of specifying colour?
-Allows you to use coordinates to look at colour interactions
-Allows you to manipulate properties of colours - colour vision test development
-Graphical/ algebraic representation of all colours - understanding of colour deficiency
-Better than newton’s circle as no negative colours
how does macadam elipse work?
by displaying colour graphically, in each elipse, colours within the ellipse are perceived the same and a colour in the ellipse and a colour outside the ellipse would be perceived different for someone with normal trichromatic vision
what do colour confusion lines do?
In a dichromat - if you pick any colour along the confusion line, the colours will be perceived as the same
what is anomaloscope?
a gold standard device and this is the only test that can definitely identify between a dichromat and an anomalous trichromat
how does an anomaloscope work?
-Top field will change from fully green to fully red by moving the top dial.
-In part 1, bottom field is always yellow and dial can be moved to change the brightness and the goal is for the patient to get the top and bottom field the same
-In part 2, examiner pre-sets red-green field and patient has to then match it with the yellow
If you were to design a clinical test for colour vision,
what would you want it to do?
- Screen, grade and classify colour vision defects
- Identify and differentiate congenital and acquired
colour vision defects - Select personnel for occupations with colour
vision requirements
how can an anomaloscope distinguish between normal colour vision and protanopia and deutranopia?
as Protanopes & Deuteranopes
can match ANY mixture of red &
green by adjusting the yellow while normals match between 37-44 for ‘red-green’ value
& 13-16 for yellow as all three anomaloscope primaries fall on a common confusion line
what anomaloscope results show a more severe colour vision defect?
the closer the points match, the more severe the defect
how can anomaloscope results help distinguish between protanopes and deutranopes?
as for duetranopes, any red green mixture matches one constant yellow luminance whereas for protanopes, green matches with high yellow luminance and red matches with low yellow luminance
what’s the most frequently used colour vision test in clinical practise?
Ishihara test
In Ishihara test, how do the transforming plates work?
part of the number is from colours confused by protanopes and deuteranopes, the rest is from location, not confused with background
in the Ishihara test, how do vanishing plates work?
check slide 21 cv 2
how do classification plates work in Ishihara test?
a duetan only sees the first number and a protan only sees the second number as the background is gray, and each of the two digits colour is taken from a different colour line on the graph *check slide 22 cv 2`
compare and contrast HRR test with Ishihara test
HRR test uses plates similar to ishihara however, it’s different to Ishihara because it also assess tritan defects, can tell you about severity and only used vanishing plates whereas ishihara only does protan and deutan defects without telling of severity and uses both vanishing and classification plates
what shapes does HRR test consist of?
24 vanishing designs, circle, cross and triangle
what plates does HRR test contain?
-4 demonstration plates
-6 screening plates
-14 diagnostic plates
-4 red green screening plates
name 2 colour arrangement tests?
-Farnsworth D-15
-Farnsworth -Munsell 100 hue
compare and contrast D-15 and 100 hue colour vision tests
-D15 and 100 hue are similar as they both need a desk space and the patient to have manuel dexterity
- d15 is quicker than 100 hue
what defects do D15 and 100 hue allow identification for?
protan, deutan and tritan defects
how do you interpret results of 100-hue test?
-direction of the spikes indicates the type of defect
-numerical score indicates severity of the defect
how are cap colours in colour arrangement CV tests chosen?
based on the confusion lines on the CIE diagrams and most errors occur where a given confusion line touches the hue circle so you can tell what the defect is depending on what confusion line the hue circle touches
in the 100 -hue test, how do the direction of the spikes tell you the type of CV deficiency?
depending on the direction (check screen shots)
what does the initial demonstration in the Mollon Reffin test do?
where an orange cap is placed among 5 gray caps (check CV 2 slide 44) to identify gross pathology
How does the Mollon Reffin test work?
uses a staircase method to find the cap the patient can see that is closest to the middle on the CIE graph. Normal pxs will see all the caps
What is the lantern CV test for?
for occupational testing where the failure standard is set for each occupation - to diagnose if there is a colour vision deficiency and has a pass or fail criteria, does not check type or severity
what are the 3 types of lantern tests?
-Bayern lantern
-Holmes-Wright
-Giles- Archer lanterns
why can you not tell a px their results from the lantern test?
because the test done in practice may not directly relate to how they will perform in the test done at the specialised testing center.
is the giles archer lantern test used today?
no as each test has different interpretation
for the holmes-wright lantern test, who is it for?
-Type A for aviation (UK armed services and Civil Aviation Authority, CAA)
-Type B for marine (British Marine Coastguard and Safety Agency)
for the Holmes-wright lantern test, what colours are used and how are they presented? what do you have to tell the Px taking the test?
-5 colours (2 red, 2 green and 1 white)
-presented in pairs 9 combinations) with each pair presented 3 times = 27 presentation and 5 seconds presentation for each pair with no errors allowed
- You have to tell the Px if the pairs are being presented horizontally or vertically
why are lantern tests becoming less common
due to the inconsistent results between the different type of lantern tests
what is the beyne lantern test for?
Type 1 for marine & rail transport
Type 2 for aviation
how does the colour assessment and diagnosis test work?
-If you can detect colour, then you will be able to detect the direction the target moves, if you cant see the direction of movement then it’s likely you cant see the target
-this means you can determine threshold for perception of pure colour signal
-allows you to determine colour deficiency presence and severity
how do you interpret CAD test results?
-If threshold is established in the grey area on the graph then colour vision is considered normal
-the further the points away from the grey, the more severe the defect
-results are compared to normal values
check cv 3 slide 11
what occupations need colour vision test?
-police no monochromats
-fire officer, no monochromats or dichromats
-train driver, normal colour vision
-engineer, CV standards only for certain roles
-electricians, specific to employer
what two situations is colour vision use for?
-denotive situations
-connotative situations
how can coloured lenses be used to correct CV defect?
by using lenses that modify;
-hue
-saturation
-object brightness
look at cv 3 powerpoint slide 17 onwards for inheritance and punnet squares
ok
how is the ishihara test adapted for people who are not numerate?
on the other side of the plates there are crosses for PX to read instead
what result would you expect from a normal participant in mollon reffin test?
P1, D1 and T1
