3.1.4- colour defect

Question 1

What light source should you use and not use in colour vision testing?

Answer 1

• Don’t use tungsten or natural daylight

- Fluorescent light or something

Question 2

How do you know a colour vision defect is congenital?

Answer 2

Found in both eyes equally and does not change overtime

Question 3

What difficulties might protans face?

Answer 3

• Matching coloured objects such as clothes, paints and materials used in crafts and hobbies
• Differentiating differently coloured objects such as ripe and unripe fruit, school workbooks, features on maps
• Judging when meat is cooked
• Recognising skin rashes and sunburn
• low intensity red lights are difficult to see like car and bicycle retroreflectors

Question 4

What problems may someone with colour vision deficienct generally face?

Answer 4

• Road traffic signlas
• Less chance of being accepted for certain jobs within the armed forces, police force, fire brigade, aviation and railway industry
• Difficulty at pursuing a career that needs the ability to discriminate colour e.g. histology, photography, paint and textiles industries, interior decorating and electronics. Medical practitioners might find it diffcult to identify and know the extent of coloured clinical signs

Question 5

How to conduct an Ishihara test?

Answer 5

• Good quality and quantity of illumination
• Held at 75 cm and each plate viewed <=3 seconds (although deviation does not significantly change results
• Binoc for congenital screening, monoc for aquired screening
• For non colour deficient mistakes allow a second attempt, if 3 or more errors then try and classify (not seen or one number less visible than the other)
• Use table to see results
• Record as Ishihara 15/16 correct, normal colour vision or if not then 8/16 correct deutan-px advises re effect and future career restrictions

Question 6

How to conduct a The City University (TCU) Test?

Answer 6

• Correct quantity and quality of light
• If grading the severity of congenital defect detected using Ishihara, measure binoc, if aquired monoc
• hold test 35cm away, at right angles to px line of sight, 3 seconds per page
• make sure px does not touch the pages, just point or say which one
• advise px on jobs, hobbies and future career choices
• record like this for binoc: ishihara failed:see attached TCU sheet 8/10 tritan px advised e.t.c

Question 7

What colours do different types of colour deficient px get mixed up between?

Answer 7

Dichromats (2 out of 3 cone photopigments):
-Deuteranopes lack green catching and protanopes lack red catching- both confuse red through orange and yellow to green

Anomolous trichromats (all 3 cone photopigments, but either red or green photopigment provide less discriminative colour vision than normal), colour vision anomaly can range from near normal to near dichromat levels:

• Protanomalous trichromats and deuteranomalous trichromats confuse red and brown, green and brown, yellow and orange, pink and grey, purple-red and grey. More likely to be confused if pale/dull/dim lighting
• all protans insensitivie to red light