4. Pseudoisochromatic Plates Flashcards
Why is colour vision test important?
For people to select an occupation that will require colour vision
Most CV tests work along what 2 features?
- Isochromatic colour confusion
- Abnormal wavelength discrimination
Is it true that colour naming is avoided in CV tests?
YES
Expectation: when used for occupational uses.
What are the 4 main types of colour vision tests?
- Pseudoisochromatic Plates
- Hue discrimination/ arrangement tests
- Lantern tests
- Anomaloscopes
What is the most common CV test? and why?
Ishihara test.
Straightforward, easy and quick to use.
Describe the Ishihara test plates?
It is a book with colour plates that have numbers on them.
Many version available- most common version is 38.
What defects does Ishihara test identify?
Red- green defects only (protan and deutan).
What kind of light is used in ishihara test and what light is not used?
Use standard illuminant C.
No tungsten light used.
How long do you present 1 plate in the ishihara test?
Not more then 4 seconds. If patient does not respond in 4 seconds: record as: patient can not see.
Describe Ishihara plate testing results in terms of plates and what is seen by normal patients and what is seen by colour vision defective patients.
- Test is held 66-75cm away and each plate is presented for 4 seconds.
- Plate 1: Is seen by both patients.
- Plate 2-9 are known as transforming digits: a normal person and a red- green deficient person will see different numbers on the plate. Known as transforming digits.
- Plate 10-17: known as vanishing digits- in this plates only trichromats will be able to see colour and CV defective patients will not see any number.
- Plate 18-21: known as hidden digits. Normal patients will see nothing, CV deficient patients will see digits.
- Plates 22-25: known as classification- *Only used if defect was identified in previous plates. It is used to identify the difference between protan and deutan and indicate the severity.
(TVHC- Transformation, vanishing, hidden digits and classification).
In practice how many plates from the ishihara test are used?
1- 17
Are misreading’s on the vanishing plates recorded as a fail?
No
What causes misreading on the ishihara plates by normal people?
The numbers are written in serif design
How many mistakes on minimum is considered as a fail in the ishihara test?
3 errors
What 4 items are found in the recording sheet?
- Px name
- D.O.B
- Illumination used
- Which eye is tested
Why are BE used when performing ishihara test?
Because it is used to detect congenital defects
How are results recorded for ishihara test- which numbers are circled?
Circle the number seen by patient- it can be the number seen by a normal person or the number seen by a person with red-green defect. It can be any number from the 2 columns but it must be circled.
AND if patient gives a number that is not present in any column: record the incorrect answer in the sheet.
After 17 plates are tested: grade the patient: ERRORS/ 17- (PASS/FAIL).
How is the ishihara test adaptatively used in clinics?
RAPID SCREENING: 4 transforming plates, 2 vanishing plates, demonstrating and classification plates.
What does the CIE diagram represent?
A diagram that represents all colours numerically and graphically.
What is MacAdam Ellipses represent?
It represents colour reproduction tolerance- if you look at the colour at the ellipses (centre of the cross). You have to move along that cross by that distance of the ellipse before you notice a difference in that colour preserved by your visual system from that at the centre.
Out of the 4 colour vision tests which test is used for occupational use?
Lantern test
Out of the 4 colour vision tests which test is considered to be the gold standard test?
Anomaloscope
What is the 1st plate in ishihara test called?
Demonstration plate
Is misreading on vanish plates recorded as a fail?
No- its a pass because it suggests they have Colour Vision to identify the number in the 1st place.
Is Ishihara test used for screening or classification and assessment of severity?
Used for screening but not useful for classification and assessment of severity.
In the CIE graph, what does the non- spectral purples represent?
These are colour not related to a specific wavelength
What does the HRR plate test assess?
Red- green and tritan defects.
It also assesses the severity of the defect.
How are pseudoiscochromatic plates designed?
Background and number colours chosen based on easily confused colours for protanopes and deuteranopes. The dots on the plate are made of random sizes and colour intensities.
Colour confusion is also known as?
Isochromatic
Isochromatic colour confusion is specific to?
Specific to the direction the colours that confuse to each type of colour vision deficiency.
How are HRR plates used?
- 4 demonstrating plates are used- they are not scored, just used to help the patient understand how the test is done.
- 6 plates used for screening test: 4 for red- green defect and 2 for tritan.
- Present the plates in 4 quarters- ask patient 3 questions: How many symbols do you see? Where are the symbols? What are the symbols?
Patient is given 3 seconds to answer correctly. - If correct: tick to show correctly answered. If wrong: draw in the boxes what the patient saw.
TO PASS THE TEST: All symbols need to be seen correctly.
What is the next step if patients do not pass the HRR test?
Diagnostic plates are used.
Ishihara vs HRR plates?
Ishihara is better at identifying red- green defects. It has much higher sensitivity and specificity.
