ND - Colour Vision Disorders III - Week 7 Flashcards
What do photoreceptors truly do? What does this mean about how they interpret colour?
It can only count the number of photons it absorbs, it cannot tell wavelength
Single cones are colour blind
Multiple cones with different sensitivities are needed
When colour matching, how many wavelengths do monochromats need?
Only one wavelength, and adjusting intensity
What are the three kinds of monochromacy?
Typical (rod) monochromacy
Blue cone monochromacy
Atypical monochromacy
Is typical monochromacy easy to diagnose? List 6 things to look out for.
Easy to diagnose
Lowered VA with no obvious explanation
Painless photophobia
Nystagmus
Reduced sensitivity to red light
Total colour blindness
Other affected family members
What is VA like in typical monochromacy?
Equivalent to rod VA
Consider a typical monochromat. Would their VA increase with increasing illiminances?
Up to a point, but will start decreasing again due to saturation
List 5 characteristics of typical monochromcy photophobia.
Painless
Aversion to light
See better in dim light
Blink/squint/sunglasses
Photophobia is common but not invariable
Is nystagmus universal in typical monochromacy? Explain.
No, it is common but not universal
Younger subjects seem to show it, but not older
Are there any retinal changes with typical monochromacy?
None apparent
What is the association between typical monochromacy and myopia?
Early reports of squinting and decreased viewing distance (to increase angular size of near work) erroneously lead to the notion of association wth myopia (there is no association)
How do typical monochromats perform on pseudo-isochromatic plates?
Fail but irregular responses
How do typical monochromats perform on Farnsworth D15?
On average, arrange in order of scotopic reflectance
How do typical monochromats perform on Nagel anomaloscopes??
Full range but setting with increasing red because of scotopic spectral sensitivity
What is the mode of inheritance for typical monochromacy?
Autosomal recessive
List 5 findings for the mechanisms of typical monochromacy and list 2 implications of these findings.
Scotopic spectral sensitivity
Lowered VA
Preference for dim light
Nystagmus
-due to scotoma at rod free foveal area
-not a motor anomaly
These findings suggest:
-absence of cones
-cones not functioning