Have you ever wondered how we perceive colors and if everyone sees them the same way? Let’s learn one of the easy and commonly used colour vision tests, which is the “Ishihara Test”.
The Ishihara colour vision test is a fascinating tool to screen the presence of red-green colour vision defects, it is based on the Pseudoisochromatic (PIC) plates. It Comes in three different forms: 16 plates, 24 plates, and the latest one with 38 plates.
The 38-plate version consists of 6 different types of plates as follows:
- The first type of plate is called Demonstration plate. This plate is used for demonstration purposes and malingering patients. The numbers on the plates are read the same by all normal or red-green deficient or total colour blind
- 2nd type are transformation plates which are from page no 2 to 9. A number seen by a normal person appears different to a red-green colour deficient. For plate no 2, A normal person would see 8 but a red-green deficient would read 3. Similarly, in plate no 3 a normal person would see 6 but a red-green deficient would read 5. Likewise, you can check the response on the interpretation chart below.
- Next are vanishing plates from page 10 to 17. In these plates, a normal person can see numbers but a red-green deficient cannot see any number. So, if you are not able to read any number here you may have colour vision deficiency.
- Next from page 18 to 21 are the hidden digit plates. These are opposite to vanishing plates, where a normal person will not see any number but a colour vision deficit will see numbers. So, if you cannot see any numbers here don’t worry that’s a normal response.
- 5th type are the diagnostic plates from page 22 to 25. These are used to differentiate protans from deutans. Protans are the ones who have a problem with red colour and the deutans are the ones who have a problem with green colour. In these plates, protans can see digits on the right side but deutans can see digits on the left side.
- Following these are the tracing plates from page 26 to 38, for someone who cannot read the numbers. The person is asked to trace the coloured line from one X mark to another.
Procedures:
The test is performed at a distance of 50 cm uniocularly under good illumination. The Numeral plates should be answered within 3 seconds and the pathway tracing should be completed within 10 seconds
Interpretation:
- Out of the initial 21 plates, If a person can read 17 or more plates correctly then his/her colour vision is regarded normal. But if the person can read only 13 or fewer plates correctly then it is interpreted as the person having a red-green colour deficiency.
- The person identified as red-green deficit will be shown diagnostic plates (22-25) to differentiate between protans or deutans.
