PC - Clinical Assessment of Colour Vision - Week 9 Flashcards
Name 6 indications for testing colour vision.
- First visit of the patient
- When advice is needed for the learning needs of children
- When advice is needed for day to day activities
- When vocational advice is needed
- When a certificate of visual fitness is needed
- When an ocular disease is suspected
Describe examples of why colour vision is important.
As an optometrist, its needed to look for signs of disease Electrician, for wires Pilot Whether food is cooked Identifying fruit/vegetables Identifying danger Identifying trauma to self, like blood
What is the prevalence of CVD in women vs men?
8% in women, 0.5% in women
Define protanopia/protanomaly.
Missing (-ope) or anomalous (-nomal) red cone photopigment
Define deuteranopia/deuteranomaly.
Missing (-ope) or anomalous (-nomal) green cone photopigment
Define tritanopia/tritanomaly.
Missing (-ope) or anomalous (-nomal) blue cone photopigment
What are the three components of testing for CVD?
Detection
Assessing severity
Congenital vs acquired
what do most tests for CVD rely on?
Colour confusions
Describe colour confusion for protan, deutan, and tritan using a chromaticity chart. Define the orientation for each.
Protan - lines fan outward from the top right corner
Deutan - horizontal, slightly oblique (top left to bottom right)
Protan - fan outward from the bottom corner
Each line represents a colour confusion, where any two colours selected along a single line would be seen as the same colour by the individual with the given conditions.
What are pseudoisochromatic plates, and how do they work? Why does it use its specific patterning?
They are spots of colour that are coloured such that they fall on the same line of confusion.
Individuals with CVD will not be able to see the numbers.
circles are used so that the distinct outline of the number is hidden.
What is the most commonly used edition of pseudoisochromatic plates?
Ishihara’s Test
Describe the introduction plates of the ishihara test.
What 4 things are these plates used for?
- Checks VA is sufficient (6/18)
- Seen by all observers (normal and those with CVD)
- Demonstrates the test
- Detects malingerers
Describe the transformation plates of the ishihara test.
Combines hidden and vanishing parts.
Normal trichromats see one number, CVD afflicted see another.
Describe the vanishing plates of the ishihara test.
Trichromats see a number
CVD afflicted see nothing
Describe the hidden plates of the ishihara test.
Trichromats see random lines
CVD afflicted see a number
Describe the classification plates of the ishihara test, and what its used for.
2 plates with 2 numbers.
Each number uses a different confusion line to identify the defective cone system.
Consider the classification plate for the ishihara test. What would protans and deutans confuse?
Protans confuse red and grey
Deutans confuse purple and grey
Describe the tracing plates of the ishihara test. Which population is it suitable for?
A squiggly line of random direction is seen by trichromats.
Patient is asked to trace it out with a cottonbud.
Suitable for children.
Name 5 advantages of the ishihara test.
- High sensitivity and specificity
- Robust (not sensitive to illumination changes)
- Inexpensive
- Readily available
- Easy to administer
Which of the three protan, deutan, and tritan, can the ishihara test not account for?
Tritan (no tritan plates)
Consider the number of errors an given individual has on an ishihara test. Can it be used as an indication of severity?
Explain in terms of the number of errors.
No, 15 or fewer errors indicates a mild defect.
More than 15 is not an indication of higher severity.
What are the limitations of the ishihara test in terms of diagnosis?
Diagnosis by type is not very good, sometimes its wrong.
Describe the Richmond HHR, and the populatin its suitable for.
Uses pseudoisochromatic plates with shapes on them. Suitable for children.
Can the Richmond HHR detect protan, deutan, and tritan?
Yes, even tritan
