Colour Vision All Flashcards
What is the most common type of colour vision problem?
Deutranomolous (anomolous deutranopia) which accounts to around 5% of the 8% of colour blind men.
What are the three categories for colour blind / colour vision problems?
Anomolous Trichromacy - meaning that there is a reduction in the type of cone. They are faulty, but have the cones available. i.e. Deutranomoloy.
Dichromacy - so only two of the cones are present. This would be things like protanopia (red).
Monochromacy - no colour at all.
What are the colour vision problem types (i.e. colours etc…)
Protanopia - no ability for red. Protanomoly - reduced red. Deutranopia - no ability for green. Deutranomoly - reduced geen. (most common) Tritanopia - no ability for blue. Protanomoly - reduced ability for blue.
What is red/green colour deficiency?
Red/green colour deficiency is the term used for anyone who has deutranomoly or protanomoly.
What is red/green colour blind?
Deutranopia and protanopia.
What is the rarest type of colour deficiency?
Monochromacy - extremely unlikely. No colour perception at all, and often have to wear sunglasses in normal lighting conditions.
How does a child inherit colour vision problems, and is it the case for all types?
It is passed via the X chromasome, and is X linked RECESSIVE. So if a child is born with a mother who is a carrier (but not colour blind) then there will be a 50/50 chance that the boy will be colour blind. There is also a 50/50 chance that a daughter will be a carrier - but would require both parents to be colour blind for her to become colour blind herself. That’s why it’s far more common in males, as only one X is needed for the defect - females require BOTH X chromasomes. If they have one, they are just a carrier - it’s RECCESSIVE!
What colours do people with red/green colour deficiency have a hard time telling the difference between?
Reds, greens, browns and oranges.
What do people with tritanopia / trianomolous defects have difficulty with colour wise?
Seeing the difference between blue and yellow, violet and red, blue and green.
What tests are available for colour vision in practice?
Ishihara and the city colour vision test (city university test).
What does the Ishihara test for?
Red/Green colour deficiency only.
What does the City test for?
All colour vision problems.
Explain how the City test is conducted?
There is a central dot with colour and then 4 outside (above,below,left,right). The patient selects which corresponds with the central colour. This is then plotted on a score card to see if there is a deu,pro or tri.
Talk through the Ishihara plates…
The test starts with a demonstration plate - which can be seen by all.
2nd is the transformation plates - a different number will be seen by patients with red/green deficiency compared to normals.
We then progress onto a vanishing plate set - meaning that only normal colour vision patients will see a number.
Hidden plates are then seen - no number for normal colour vision but red/green deficiency will see a number.
Diagnostic plates follow - these are to differentiate between red / green deficiency (deu and pro).
Finally we have the tracing plates which can only be seen by those with colour deficiency (red/green) and can be done by tracing the lines… OR there may ONLY be a line for those with normal colours, and none / the wrong line for colour deficiency.
Occupations that require trichromacy
Police
Electrician
Pilot
Train driver
