Pseudoisochromatic plates Flashcards
What colour defect does Ishihara screen for?
R-G
On Ishihara, how many seconds should you show the px each page?
4 seconds
On Ishihara, which plates are transforming and what does this mean?
Plates 2-9
Numbers will appear different to an anomalous trichromat, and a dichromat will see no number
On Ishihara, which plates are vanishing and what does this mean?
Plates 10-17
Both anomalous trichromats and dichromats will see no number
On Ishihara, which plates are hidden digit and what does this mean?
Plates 18-21
CV deficiencies will see a number, ‘normals’ won’t see a number
On Ishihara, which plates are classification and what does this mean?
Plates 22-25
Determines the severity of the defect - depending on severity, px will see one or both numbers
On the classification plates of Ishihara, when the number on the right is more obvious, what does this mean?
Protan deficiency
On the classification plates of Ishihara, when the number on the left is more obvious, what does this mean?
Deutan deficiency
On Ishihara, which plates are pathways and what does this mean?
Plates 26-38
Images of pathways instead of numbers, for use with small children or non-verbal pxs
What is a disadvantage of the pathway plates on Ishihara?
Reduced efficiency due to needing longer presentation time
What is sensitivity?
The proportion of true positives picked up by a test - e.g. how many people who actually have a deficiency are picked up.
What is specificity?
The proportion of true negatives picked up by the test - e.g. how many people are not picked up on test who are not deficient.
When doing rapid screening on Ishihara, how many of each plate should you use?
Demonstration
4 transformation
2 vanishing
Classification (if relevant)
On Ishihara, should you show everyone the classification plates? Why?
No
If they pass the rest of the test with no errors, they are not CV deficient, so no classification is needed.
What are MacAdam ellipses?
On the CIE diagram, ovals of varying sizes and orientations within which all the colours look the same
How are the colours on Ishihara chosen?
Chosen along colour confusion line for the defect they are testing
Outside of MacAdam ellipses so ‘normals’ can tell the difference
Background greys are chosen from further along colour confusion lines
Numbers are chosen from more central location on colour confusion line
What deficiencies does the HRR test for? Does it assess severity?
R-G and tritan
Yes, assesses severity
How many demonstration plates does the HRR test have?
4
How many screening plates does the HRR test have?
How many plates screen for R-G defects and how many for B-Y?
6
4 R-G
2 B-Y
How many diagnostic (assessing severity) plates does the HRR test have?
How many plates are for R-G defects and how many for B-Y?
14
10 R-G
4 B-Y
Should you continue the HRR test if the px passes the screening plates?
No
The HRR test has a reduced specificity, what does this mean?
It will pick up ‘defects’ on px’s who do not truly have a defect (false positive), so is not as reliable
