colour vision Flashcards
Why is colour vision assessment important for certain careers?
It is important for careers like police, armed forces, pilots, and electrical engineers.
What are some educational fields where colour vision is relevant?
Chemistry, geography, and history.
Why is colour vision important for safety?
It helps in recognizing traffic lights, electrical wiring, and electronic PCBs.
How is colour information coded at the level of ganglion cells?
Through 2 opponent colour channels (Red vs. Green, Yellow vs. Blue) and 1 opponent luminance channel (White vs. Black).
What is the visible spectrum range for the human eye?
380-780 nm.
What are the three types of photoreceptors responsible for trichromatic vision?
S, M, and L cones.
To what wavelength is the red cone photoreceptor most sensitive?
620-700 nm (long wavelength).
To what wavelength is the green cone photoreceptor most sensitive?
500-575 nm (medium wavelength).
To what wavelength is the blue cone photoreceptor most sensitive?
450-490 nm (short wavelength).
How do cones and rods differ in function?
Cones function at high illuminance levels, while rods function at low levels of illumination.
What percentage of cones are sensitive to short wavelength (blue light)?
Only 2%.
Where are genes coding for red and green cone photopigments located?
On the long arm of the X chromosome.
Where is the gene coding for blue cone photopigments located?
On chromosome 7.
Why is congenital colour vision deficiency more common in men than women?
It is a recessive X-linked trait, affecting 1 in 12 males and 1 in 250 females.
What is a protan deficiency?
Confusion between reds and greens, both appearing as desaturated yellow.
What is a deutan deficiency?
Confusion between reds and greens, both appearing as desaturated yellow.
What is a tritan deficiency?
Confusion between blues, yellows, and greens, appearing as pink or turquoise.
What do monochromats perceive?
Only brightness variations.
What is dichromacy?
A condition where two cones are active, but one is missing (e.g., protanope, deuteranope, tritanope).
What is anomalous trichromacy?
All three cones are active, but one or more has an abnormal sensitivity.
What is a common cause of acquired colour vision defects?
Secondary to pathology, ocular/systemic disease, or drug-linked causes.
What type of acquired colour vision defect is usually monocular?
Blue-yellow defects.
What does Type 1 colour defect resemble and what condition is it associated with?
Resembles protan (red-green) defects and is found in macular dystrophy and hydroxychloroquine toxicity.
What does Type 2 colour defect resemble and what condition is it associated with?
Resembles deutan (red-green) defects and is found in retrobulbar optic neuritis.
What condition is associated with Type 3 blue-yellow defects?
Central and peripheral retinal lesions, POAG, AMD, DR.
When should colour vision be tested?
During a child’s first eye test, family history of colour deficiency, occupational reasons, or disease diagnosis.
What is the recommended illumination for colour vision tests?
The test must be administered under recommended illumination, such as daylight.
How should refractive correction be managed during colour vision tests?
Perform with the appropriate refraction in place.
What are the screening plates in the Ishihara test designed to do?
To identify colour vision defects by showing numbers seen differently by people with normal and defective vision.
What is a major disadvantage of the Ishihara test?
It does not detect blue-yellow (tritan) defects.
How does the City University test classify colour vision defects?
It classifies defects as protan, deutan, or tritan based on the patient’s response to chroma plates.
What does the Farnsworth D-15 test involve?
Sorting 15 coloured caps in natural hue order to determine the type and severity of colour vision defects.
What is a disadvantage of the Farnsworth D-15 test?
It cannot differentiate between anomalous trichromats and dichromats.
What vision standards exist for the army regarding colour vision?
Individuals who can distinguish red and green may still qualify for certain roles.
What is the standard for colour vision in pilots?
Failing 9 or more plates on the Ishihara test disqualifies a candidate.
What are some disadvantages of the City University test?
It is more complex and requires more effort to administer than other tests.
