ND - Colour Vision Disorders II - Week 6 Flashcards
What was an early proposition on the cause of CVD?
The vitreous was blue tinted, absorbing all red light
What is the fundamental concept behind dichromacy regarding colour matching?
Only need two colours in a mixture to match all colours compared to three in normals
What is the peak spectral sensitivity in protanopes, deuteranopes, and normals (what wavelength)? Is the change from normals trivial?
P - 540nm
D - 563nm
Normal - 555nm
Reduction of sensitivity is not trivial
When doing dichromatic colour matching, do deuteranopes and protanopes perform similarly or very differently?
Very similar
Consider a long wavelength presented to a deuteranope and a normal. How do they see it in terms of luminosity?
They see it dimmer than the other two
Are protanopes or deuteranopes more able to discriminate colour?
Deuteranopes generally perform better than protanopes
What nanometre length is required to detect a difference over most of the spectrum? How many discriminally different spectral hues does this result in?
<2nm
Estimated number of hues is 150
Consider a CIE diagram. Movement in what direction relative to C (the centre white) will cause a change in hue and saturation?
Hue - Movement orthogonal to C, towards one of three ends of the diagram
Saturation - movement towards C decreases saturation
Consider the amount of colour needed to add to white before a change is noticed. How do normals compare to portanopes?
Generally elevated thresholds across the entire spectrum
What is the neutral point of dichromacy? What is it for protans and deuterans?
A region in the spectrum where it is impossible to saturate in dichromats
P - 495.5nm
D - 500.4nm
How are confusion loci constructed using the spectral neutral point?
The sectral neutral point is marked on the CIE diagram (edge)
The R+B mix that matches the neutral point (from colour matching) is plotted on the bottom straight line of the diagram between red and blue
The two points are connected, giving one confusion line
Wavelength steps (in the smallest increment they are able to discriminate) are plotted in either direction of the spectral neutral point, giving confusion lines for the rest of the spectrum
Using the spectral neutral point to construct confusion loci, how many colours are protans and deuterans estimated to be able to discriminate?
P - 17
D - 27
Consider protan and deuteran confusion loci. Which appear to show convergence on cone fundamental and which do not? Which have parallel loci and which do not?
P - appears to converge on cone fundamental (in the red area)
D - parallel confusion loci and no convergence
Consider a protanopic CIE diagram. What colours appear on this diagram for protans and how does saturation change as confusion loci move towards to spectral neutral point?
The top-right section (which is originally green and red) is saturated yellow, and becomes more saturated as the loci move to the neutral point
The blue bottom left corner is still saturated blue, but becomes only a less saturated blue as the loci move towards the neutral point
At the neutral point itself, it is white across that entire locus
Is there any viable theory of a pre-retinal filter for CVD?
No