Clinic Prep: Colour Vision Revision

Question 1

List 5 indications for a colour vision assessment

Answer 1

When advice is required to tailor the learning needs of kids
When advice is required for day-to-day visual tasks
When vocational advice is required (e.g. can I be a pilot)
When a certificate of visual fitness has been requested (e.g. for an occupation or licence)
When an ocular disease is suspected that can affect colour vision (Some conditions will have deficiencies like B-Y or R-G. So do an ishihara etc.)

Question 2

What colour vision defect may AION/GCA result in? (2)

Answer 2

Achromatopsia [partial or total absence of CV]

Dyschromatopisa [deficiency in perception of colours]

Question 3

What colour vision defect may NAION (Non-arteritic ischaemic optic neuropathy) result in?

Answer 3

R-G deficiency and red desaturation

Question 4

What colour vision defect may a toxic/nutritional or an ischaemic optic neuropathy result in?

Answer 4

Dyschromatopsia. This can often be the first sign of this condition

Question 5

What colour vision defect may a patient with any optic neuritis result in?

Answer 5

Dyschromatopsia and red desaturation. They can also have contrast/brightness problems (i.e. things appear less bright/sharp)

Question 6

What colour vision defect may Leber’s syndrome involve?

Answer 6

Early B-Y then later R-G defect

Question 7

What colour vision defect may Kjer’s disease involve?

Answer 7

B-Y defect

Question 8

What type of colour vision deficiency can optic nerve diseases traditionally cause?

Answer 8

R-G deficiency

Question 9

What colour vision deficiency (if present) is glaucoma primarily associated with?

Answer 9

B-Y deficiency

Question 10

List the 3 broad categories of CVD

Answer 10

Protans (red cone problem)
Deutans (green cone problem)
Tritan (blue cone problem)

Question 11

What is the most common type of CVD?

Answer 11

Deutanomaly (5% in males)

Question 12

What percentage of men have a congenital CVD of some kind?

Answer 12

8%

Question 13

What are the 3 steps in testing for CVD?

Answer 13

Detect (screening tests)
Assess severity (grading tests)
Determine if congenital vs acquired

Question 14

List 4 types of screening tests for CVD. By what principle do these tests work?

Answer 14

Pseudochromatic (PIC) Plates
Hue discrimination (arrangement) tests
Lanterns
Anamolascopes

These tests rely on colour confusions across “confusion lines” on the CIE diagram

Question 15

Provide an example of a CVD test that doesn’t rely on confusion lines

Answer 15

Medmont C-100

Question 16

Describe what the 24 plates on Ishihara represent, using a mnemonic to guide you

Answer 16

"I Think Vinay Has Carpal Tunnel"
Introduction (plate 1)
Transformation (plates 2-7)
Vanishing (8-13)
Hidden (14-15)
Classification (16-17)
Tracing (18-24)

Question 17

What are 2 purposes of the introduction plate?

Answer 17

Checks VA is sufficient (6/18)

Detects malingerers

Question 18

How do transformation plates work?

Answer 18

Normal trichromats see one figure, CVD sees a different figure/number

Question 19

How do vanishing plates work?

Answer 19

CVD sees nothing

Question 20

How do hidden plates work?

Answer 20

CVD sees a figure whereas normals dont’

Question 21

How do classification plates work?

Answer 21

Use different confusion loci to identify which cone system is defective.
Protans confuse red/grey (say “6”), Duetans confuse purple and grey (say “2”)
If both numbers seen –> milder defect/less indication of CVD
If no numbers seen –> severe RG with high density macula pigment

Question 22

When are tracing plates used?

Answer 22

Suitable for children or patients who can’t read numbers

Question 23

List 5 benefits of ishihara

Answer 23

High sensitivity and specificity
Robust
Inexpensive
Readily available
Easy to administer

Question 24

List 3 limitations of ishihara

Answer 24

No tritan plates
Number of errors not really an index of severity
Diagnosis by type not very good, sometimes can be wrong

Question 25

Name 4 other PIC plate tests and what they test for

Answer 25

Richmond HRR: Screens for P/D/T.
City Uni: May detect moderate to severe RG and BY defects. Differentiates P, D and T.
Farnsworth F2: Tests if tritan or not tritan
Lanthony album: only assess BY defects. Not commonly used since slight and moderate CVD may still pass

Question 26

How does Richmond HRR work? What questions should you ask the patient? (3)

Answer 26

Uses shapes
24 plates: 4 demonstration, 6 screening, 14 diagnostic
Ask the patient:
How many coloured symbols?
What are they?
Where are they?

Question 27

How does City Uni work?

Answer 27

4 dots surround a centre dot. Looking at the middle dot, which dot looks the most similar to the middle dot

Question 28

How does Farnsworth F2 work?

Answer 28

2 squares (green and blue) on purple background.
Normal CV: sees 2 squares in correct location, with green square clearer
Tritan: Only blue or blue clearer
R-G/Not tritan: only sees green square

(NB: not commercially available)

Question 29

How does the lanthony album work?

Answer 29

Diamond shape or square with a smaller square in one of its corners.

“Can you tell me if the top corner, bottom corner, left corner, or right corner looks different?”

Question 30

List 5 types of tests for assessment (not detection) of CVD

Answer 30

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

NB: the first 4 are arrangement tests (will tell severity and type of CVD)

Question 31

Describe the Farnsworth D15

Answer 31

“out of all these caps, pick one that is closest to the 1st colour, then keep going and pick another cap that’s closest in colour to the one you just put down”

1st colour is fixed and there’s 15 colours surrounding it

Question 32

How are the results of the Farnsworth D15 interpreted?

Answer 32

The orientation of crossings calssifies the type of CVD (e.g. tritan has horizontal diametrical errors, protan has left slanted diagonal errors, duetan has right slanted diagonal errors)

Question 33

What is considered a fail for Farnsworth D15?

Answer 33

2 or more diametrical crossings

NB: number of crossing give some indication of severity, but may be unreliable

Question 34

If someone passes Farnsworth D15, but you still think something is wrong, what test can you try next?

Answer 34

Lanthony desaturated D15 (provides higher level of difficulty)

Question 35

What is the main limitation of Lanthony desaturated D15?

Answer 35

Poor specificity - normal CV often make errors

Question 36

If someone fails Farnsworth D15, how can you make the test a little easier for them for further clarification?

Answer 36

Lanthony H16 test (is more saturated therefore lower level of difficulty)

Question 37

What is considered a fail in the Lanthony H16 test?

Answer 37

3 or more diametrical crossings

Question 38

How does the Farnsworth Munsell M100 hue test work?

Answer 38

It’s a hue circle of 85 closely spaced colours to be arranged in order of colour.

The results are plotted onto a radial graph, and the lower the error score, the less severe the CVD is. The pattern of spokes will also tell you about the type of defect

Question 39

How does the pattern of spokes on the Munsell M100 hue test differ for different CVDs?

Answer 39

Protan - horizontal spokes
Duetan - oblique spokes
Tritan - vertical spokes

Question 40

What is the purpose of the Medmont C100?

Answer 40

Differentiates between protans and deutans

Question 41

Can the Medmont C100 pick up carriers for protan/deutan deficiencies?

Answer 41

yes

Question 42

How does the Medmont C-100 work?

Answer 42

Patient looks at flickering light and they adjust the knob at the top until it stops flickering, then you turn it around and the numbers will tell you whether they are:
Protan (if -5 to -2)
Duetan (+2 to +5)
Normal (-2 to +2)

Question 43

What are lantern tests deisned for?

Answer 43

Occupations that require recognition of signal lights

Question 44

Which test is the only definitive test to differentiate between protans and deutans?

Answer 44

Anomaloscopes

Question 45

How do anomaloscopes work?

Answer 45

A circle with 2 hemifields: a test field (yellow 590nm) and a mixture field (red 670nm and green 546nm).

Patient adjusts the intensity of red and green until the mixture field matches the test field.