Congenital CV defects Flashcards
What are the features of congenital colour vision defects?
Onset at birth
Type and severity are constant
Both eyes affected equally
Easy to classify
VA and VFs normal (except monochromat)
Higher prevalence in males (8%) (females 0.4%)
What causes dichromacy?
Missing cone or cone not functioning
What causes anomalous trichromacy?
Reduced sensitivity in cone
What is protanopia? Which colours are hard to differentiate between?
L cone missing (red)
green, yellow, red
What is deuteranopia? Which colours are hard to differentiate between?
M cone missing (yellow)
yellow, red, green
What is tritanopia? Which colours are hard to differentiate between?
S cone missing (blue)
blue, green, yellow
What is small field tritanopia?
no S cones in fovea so foveal vision has defect
Are dichromats or anomalous trichromats more common in practice?
Anomalous trichromats
What is a protanomalous trichromat?
Reduced sensitivity of L cones
What is a deuteranomalous trichromat?
Reduced sensitivity of M cones
What is a tritanomalous trichromat?
Reduced sensitivity of S cones
What is the difference between sensitivity curves for dichromats and anomalous trichromats?
Dichromats - one curve missing entirely
Anomalous trichromats - curves closer together so find it hard to distinguish between colours
What kind of colours might an anomalous trichromat confuse if the defect is mild?
Pale/desaturated
What is a rod monochromat and what are some signs?
No cones at all - only rods
Reduced VA (6/60)
Photophobic
Nystagmus
No colour vision at all
What is a cone monochromat and what are some signs?
Only have one type of cone
Reduced VA (6/9-6/24)
