Colour Vision

Question 1

Indications

Answer 1

First consult
Career/vocational advice
Advice required for day-to-day tasks: safe cooking & eating, personal safety & appearance, communication
Advice to tailor learning needs of kids
Certificate of visual fitness requested
Suspected ocular disease
All children

Question 2

CVD prevalence

Answer 2

8% of men, 0.5% woman in European societies
Common, prevalence varies with ethnicity (highest in Europe & certain parts of Asia)

P/PA, D: 1%
DA: 5%

Question 3

What is the design for PIC plates?

Answer 3

Pseudoisochromatic plates are examples of colour camouflage. Colours within each confusion zone are substituted without notice. CVD Px will not be able to differentiate these colours, however normal CV Px will.

Individual elements are spots of colour, arranged so that a figure emerges from the background in different ways for normals and CVDs.

Dot matrix breaks up distinct figure outline, concealing shape.

14, 24, 38 plate editions

Question 4

Ishihara plates

Answer 4

1. Introduction: checks VA is sufficient (6/18), detects malingerers

2-7. Transformation: combines hidden and vanishing concepts
Normal see one figure, CVD see other figure
i.e. 8 looks like 3, 3 looks like 5

8-13. Vanishing: figure and ground made is isochromatic dots
CVD sees nothing

14-15. Hidden: camouflaged figure for N, CVD sees figure
*plate 14: CVD sees 5
plate 15: CVD sees 15

16-17. Classification: 26 & 42, makes use of confusion loci
Protans confuse red & grey: 6 of 26
Deutans confuse purple & grey: 2 of 26
If no numbers are seen, severe RG defect with high density macula pigment

18-24. Tracing: within 10s

Question 5

Why is the Ishihara the test of choice?

Answer 5

High sn (1.0) and sp (0.98)
Not too sensitive to illuminant changes
Cheap
Readily available
Easy to use

Question 6

Ishihara limitations

Answer 6

No T plates
Number of errors not indicative of severity
≤ 15 errors = mild defect
Diagnosis by type not very good

Question 7

Richmond HRR

Answer 7

Symbols (no letters)
Sn and sp almost as good as Ishihara (Confirmation of Ishihara)
1-4 demonstration (4 = no figure for malingerers, memorisation)
Next 6 = screening plates
Next 14 = diagnostic (type & extent)

*how many colour symbols, what are they, where are they?

Question 8

City University

Answer 8

Detection of moderate to severe RG & BY defects
Each plate: 5 coloured circles
Central test colour surrounded by 4 comparison colours (3/4 selected as typical confusion colours for P, D & T)
1 demonstration plate, 10 test plates for scoring

@35cm
Px identifies which is most identical to central test colour within 3s
Record form categorises type and score out of 10 is totalled. Number of mistakes in normal column indicates severity.

Question 9

Farnsworth D2

Answer 9

Tritan defects
Single plate with 2 different coloured squares (B & G) formed by coloured circles
Background = purple coloured circles

N: Sees G and B squares, with G brighter
If only B/B is clearer = tritan error
If only sees G = not a tritan error

Question 10

Lanthony album

Answer 10

Detection and grading of T defects as well as acquired CVD

6 plates, from 0 to 5.
0 = demonstration plate (orange)
1 big square, with little square in a corner (needs to identify)
Blue dots decrease in saturation from plate 1 to 5
Score last correct plate
Slight and moderate CVD Px still pass

Question 11

Farnsworth D15

Answer 11

Principle: colours lying on confusion loci are placed next to each other, colours encircle illuminant C

15 loose colour caps

Pass (1-2 transpositional errors): normal, mild
Fail (2 or more diametrical crossings): moderate to severe CVD
*Number of crossings unreliable as severity indicator
Good test-retest reliability

Orientations of crossings classifies type of CVD
P = \
D = /
T = / (but almost horizontal)

Single colour (esp. at 7) non sig.
53-75% of CVD fail D15 (dichromats), 33%-50% anomalous trichromats

Question 12

Farnsworth Munsell M 100 hue

Answer 12

85 loose cap colours, encircle illuminant C at approximately the same chroma and value

Record numerical order chosen by Px
Score = numerical sum of differences between preceding and following caps
Plot + radial distribution indicates type of defect

Intended for use in vocational guidance, congenital and acquired CVD

Question 13

Medmont C-100

Answer 13

Differentiates P and D
Very good sn and sp
Cheap
1-2 minutes testing time

Question 14

Lantern tests

Answer 14

Assesses CV of those seeking to enter aviation industry, etc. req. recognition of signal lights under controlled viewing conditions.

R, G, W lights (Y in some)
Test statistic = accuracy of colour naming

Question 15

Anomaloscopes

Answer 15

Definitive diagnosis of P vs. D
Large and expensive
2 phases: 
- R-G ratio, constant luminance
- Examiner sets R-G ratio, Px adjusts luminance of yellow to match

Repeat 3x, allow 10s for match
Observer looks away into dim room between matches to avoid adaptation

Normal RG=40-44
Normal Y = 15-17

Question 16

Which tests are for detection, which for assessment?

Answer 16

DETECTION

• Ishihara
• Richmond HRR
• City University
• Farnsworth D2
• Lanthony album

ASSESSMENT

• Farnsworth D15
• Lanthony desaturated D15
• H16
• Farnsworth Munsell M 100 hue
• Oscar/Medmont C 100

Question 17

Lanthony desaturated D15

Answer 17

use of desaturated colours to set a higher level of difficulty, only those with very mild defect will pass

poor sp - normals often make errors

Question 18

H16 test hue discrimination

Answer 18

more saturated than Lanthony desaturated, sets lower level of difficulty to identify those with SEVERE CVD

≥ 3 diametrical crossings = fail
orientation indicates type of CVD