Colour vision

Question 1

What is colour vision?

Answer 1

The ability to discriminate between different colour excited by light of different wavelengths

Question 2

Which photoreceptor has the function of colour vision?

Answer 2

Cones

Question 3

When are cones activated?

Answer 3

In photopic vision= bright light

Question 4

When are rods activated?

Answer 4

In scotopic vision =low light, all colours are seen as grey in low light

Question 5

What is the purpose of colour vision?

Answer 5

Identifying objects Survival value eg. ripe vs unripe fruit Enriches perceptual experiences

Question 6

Which area in the brain is damaged causing colour blindness?

Answer 6

Lingual Gyrus (area V4)

Question 7

What is the clinical name for colour blindness?

Answer 7

Achromotopsia

Question 8

What are the 3 types of cones? (each containing a photopigment)

Answer 8

S cones contain S pigment (short wavelength M cones contain M pigment (medium wavelength L cones contain L pigment (long wavelength

Question 9

What do these pigments do?

Answer 9

Each cones contains a different photopigment which are photosensitive meaning they respond to particular wavelengths of light:

Question 10

What light does S pigment absorb?

Answer 10

Blue

Question 11

What light does M pigment absorb?

Answer 11

Green

Question 12

What light does L pigment absorb?

Answer 12

Orange/Red

Question 13

What is colour blindness caused by?

Answer 13

The absence of one of the pigments (S/M/L)

Question 14

If one of the pigments is absent, what is this referred as? What is a person with normal colour vision called

Answer 14

Dichromacy or the patient is a dichromat Normal= trichromat

Question 15

Where is the word dichromacy derived from?

Answer 15

The term is from di meaning “two” and chroma meaning “colour”. (as only 2 out of the 3 pigments are present)

Question 16

What is the loss of S cones called (loss of BLUE vision)?

Answer 16

Tritanopia (very rare)

Question 17

What is the loss of M cones called (loss of GREEN vision)?

Answer 17

Deuteranopia

Question 18

What is the loss of L cones called (loss of RED vision)?

Answer 18

Protanopia

Question 19

Which types of colour deficiency are congenital (x-linked)

Answer 19

Red-green deficiency (protanopia and deutronopia)

Question 20

Which gender is congenital colour defect more common in and why?

Answer 20

Males as X linked disorder (Males have X,Y chromosomes whereas females have X,X so for male to have colour vision defext only one X chromosome needs to be defective but for female both have to be defective)

Question 21

What do protanopes see?

Answer 21

They can’t see red, orange and green-it appears brown and faded

Purple is indistiguishable from blue as there is no red component

They see blue and yellow as normal

Question 22

What do deautranopes see?

Answer 22

Same as protanopes

They can’t see red, orange and green-it appears brown and faded

Purple is indistiguishable from blue as there is no red component

They see blue and yellow as normal

Question 23

What colour appear very clear to people with red-green defects?

Answer 23

Blues and yellows

Question 24

What is Protanomalia and Deuteranomalia colour defects?

Answer 24

Protanopia is complete & Protanomaly is partial Deuteranopia is complete & Deuteranomaly is partial

Protanomaly and Deautronoamly happens when the cones are present but don’t function properly whereas in ProtANOPIA and DeautrANOPIA the cones are missing completely.

Question 25

What is total colour blindness?

Answer 25

Tritanopia A failure in the appreciation of blue and yellow may be termed tyritanomalia if partial, and tritanopia if complete

Question 26

What every day tasks are affected in patients with a colour vision defect?

Answer 26

Matching colours clothes, paints Ripe vs unripe fruit, judging if meat is cooked Recognising sunburn and skin rashes Road traffic signs

Question 27

What difficulty to protans have on the road and why?

Answer 27

Due to their red light insensitivity, they will have trouble seeing low intensity red lights such as car and bicycle retroreflectors

Question 28

What jobs can a person with a colour vision defect who fails the Ishihara not do in the UK?

Answer 28

-Pilot -Air traffic controller -Flight engineer or flight navigator in the armed forces or civil aviation authority -Firefighter -Train driver or railway signaller

Question 29

What other careers will be difficult to pursue?

Answer 29

-Photography -Paint and textiles -Interior decorating -Electronics -Medical professionals report difficulty seeing body colour changes, blood in urine etc Optometrists report difficulty seeing disc pallor or red eyes or retinal haems You can still drive a car, motorbike, bus or lorry.

Question 30

What do you do if you find a child has colour vision defect?

Answer 30

Inform px and parent and write letter fo school about the conditions and how they can help

Question 31

How do you tell the parent?

Answer 31

Explain the problem, effect on education, career choice, reassure that it is not a disease and does not get worse.

Question 32

Why do you need to write to the school?

Answer 32

Widespread use of colour in teaching materials can lead to unsupported children falling behind in class Write letter to school so they can make adjustments for the child

Question 33

What adjustments can you suggest to the school?

Answer 33

Labelled crayons/felt tips To seat CVD pupils in good natural light

Question 34

Give example how you would word the letter to the school

Answer 34

John has protanopia, a congenital colour deficiency. He sees colours but sees them differently to other children and will confuse some colours particularly reds, green and browns but also purples, oranges and yellows. These colours are more likely to be confused if they are pale or dull or viewed in dim lighting. Here are some suggestions that may help John: write suggestions

Question 35

What are the types of tests to test colour vision?

Answer 35

Ishihara City D15 100 hue

Question 36

What is the Ishihara test for?

Answer 36

Quick screening for red-green colour deficiency Most commonly used and also a required entrance test for many professions

Question 37

What are the disadvantages of the Ishihara test?

Answer 37

Does not assess tritan problems Less useful for grading the severity of the defect or monitoring acquired defects After several years the colours fade so it loses its validity

Question 38

How do you use Ishihara test?

Answer 38

Room light on, 75cm away at right angle to line of vision, answer should be given without more than 3 second delay 38 total plates: 25 with number and 26-38 are for non verbal patients

Question 39

How can you use 26-38 for non verbal patients/can't read numbers?

Answer 39

They trace the line between the to X's Should be done within 10 seconds

Question 40

How do you interpret the Ishihara results?

Answer 40

Normal colour vision reads all or makes 1 or 2 mistakes Colour defect: 6 or more errors Severe trichromats can't see any numbers after 12

Question 41

What is the first plate for?

Answer 41

everyone should see it even if they have a CVD, can catch out malingers if they say they can't see

Question 42

What do transformation Nos. 2-9 plates show?

Answer 42

The number is seen by those with normal colour vision A different number is seen by people with red-green colour deficiency. Those with total colour blindness and weakness are not able to read any numeral.

Question 43

What do vanishing Nos. 10-17 plates show?

Answer 43

The number is seen by those with normal colour vision but cannot be seen by people with red-green colour deficiency.

Question 44

What do hidden digit Nos. 18-21 plates show?

Answer 44

The number cannot be seen by those with normal colour vision AND those with total colour blindness but can be seen by people with red-green colour deficiency

Question 45

What are plates 22-25 for?

Answer 45

Protan/deutan classification In protanopia and strong protanomalia, only see the number on the right In deuteranopia and strong deuteranomalia, only see the number on the left. If neither number is seen, protan/deutan classification must be made using another test