4. Pseudoisochromatic Plates

Question 1

Why is colour vision test important?

Answer 1

For people to select an occupation that will require colour vision

Question 2

Most CV tests work along what 2 features?

Answer 2

1. Isochromatic colour confusion
2. Abnormal wavelength discrimination

Question 3

Is it true that colour naming is avoided in CV tests?

Answer 3

YES
Expectation: when used for occupational uses.

Question 4

What are the 4 main types of colour vision tests?

Answer 4

1. Pseudoisochromatic Plates
2. Hue discrimination/ arrangement tests
3. Lantern tests
4. Anomaloscopes

Question 5

What is the most common CV test? and why?

Answer 5

Ishihara test.
Straightforward, easy and quick to use.

Question 6

Describe the Ishihara test plates?

Answer 6

It is a book with colour plates that have numbers on them.
Many version available- most common version is 38.

Question 7

What defects does Ishihara test identify?

Answer 7

Red- green defects only (protan and deutan).

Question 8

What kind of light is used in ishihara test and what light is not used?

Answer 8

Use standard illuminant C.
No tungsten light used.

Question 9

How long do you present 1 plate in the ishihara test?

Answer 9

Not more then 4 seconds. If patient does not respond in 4 seconds: record as: patient can not see.

Question 10

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.

Answer 10

1. Test is held 66-75cm away and each plate is presented for 4 seconds.
2. Plate 1: Is seen by both patients.
3. 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.
4. 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.
5. Plate 18-21: known as hidden digits. Normal patients will see nothing, CV deficient patients will see digits.
6. 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).

Question 11

In practice how many plates from the ishihara test are used?

Answer 11

1- 17

Question 12

Are misreading’s on the vanishing plates recorded as a fail?

Answer 12

No

Question 13

What causes misreading on the ishihara plates by normal people?

Answer 13

The numbers are written in serif design

Question 14

How many mistakes on minimum is considered as a fail in the ishihara test?

Answer 14

3 errors

Question 15

What 4 items are found in the recording sheet?

Answer 15

1. Px name
2. D.O.B
3. Illumination used
4. Which eye is tested

Question 16

Why are BE used when performing ishihara test?

Answer 16

Because it is used to detect congenital defects

Question 17

How are results recorded for ishihara test- which numbers are circled?

Answer 17

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).

Question 18

How is the ishihara test adaptatively used in clinics?

Answer 18

RAPID SCREENING: 4 transforming plates, 2 vanishing plates, demonstrating and classification plates.

Question 19

What does the CIE diagram represent?

Answer 19

A diagram that represents all colours numerically and graphically.

Question 20

What is MacAdam Ellipses represent?

Answer 20

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.

Question 21

Out of the 4 colour vision tests which test is used for occupational use?

Answer 21

Lantern test

Question 22

Out of the 4 colour vision tests which test is considered to be the gold standard test?

Answer 22

Anomaloscope

Question 23

What is the 1st plate in ishihara test called?

Answer 23

Demonstration plate

Question 24

Is misreading on vanish plates recorded as a fail?

Answer 24

No- its a pass because it suggests they have Colour Vision to identify the number in the 1st place.

Question 25

Is Ishihara test used for screening or classification and assessment of severity?

Answer 25

Used for screening but not useful for classification and assessment of severity.

Question 26

In the CIE graph, what does the non- spectral purples represent?

Answer 26

These are colour not related to a specific wavelength

Question 27

What does the HRR plate test assess?

Answer 27

Red- green and tritan defects.
It also assesses the severity of the defect.

Question 28

How are pseudoiscochromatic plates designed?

Answer 28

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.

Question 29

Colour confusion is also known as?

Answer 29

Isochromatic

Question 30

Isochromatic colour confusion is specific to?

Answer 30

Specific to the direction the colours that confuse to each type of colour vision deficiency.

Question 31

How are HRR plates used?

Answer 31

1. 4 demonstrating plates are used- they are not scored, just used to help the patient understand how the test is done.
2. 6 plates used for screening test: 4 for red- green defect and 2 for tritan.
3. 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.
4. 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.

Question 32

What is the next step if patients do not pass the HRR test?

Answer 32

Diagnostic plates are used.

Question 33

Ishihara vs HRR plates?

Answer 33

Ishihara is better at identifying red- green defects. It has much higher sensitivity and specificity.