Colour Vision

 
|

CB 2

 
|
 

CB 3

 
|
 

CB 4

 
|
 

CB 6

 

How severe is my colour deficiency?


Diagnosis. - go see an eye specialist.



Colour vision testing is the study of error.

All colours can be formed by combining points from within a colour space in CVD with reduced visible spectrums different mixes of light are indistinguishable.

Hence all the follow tests use combinations of colour which to normal vision are easily identifiable but which fall along the known and predictive lines of colour confusion for reduced spectrum vision.

The CIE Colour space, reduced in saturation towards the centre of the colour space. And saturation is one of the features of colour vision tested here. Another is brightness. The CIE takes no account of how luminous the light falling on the coloured object is, however CVD routinely use brightness as a means of telling similar colours apart. Two tests here examine the role brightness has in detecting Colour Vision Deficiencies.

These are only estimates however, as good a result as they can manage it is advisiable to repeat tests and combine results but to always seek to advice of trained eye specialists to administer properly calibrated exams. These tests serve merely as indicators.


Ishihara Pseudo-isochromatic tests plates. (does not discriminate for luminosity)

The classic test, and one with which many will be familiar. Shinobu Ishihara painted hs original plates in 1917. The test comes in 24 and 38 plate varieties, the larger discriminates for differences in anomalous dichromacy and full dichromacy


Vanishing plates, contrast plates, trace plates






Farnsworth D-15 Colour arrangement Test (weak saturation) (visual results shown on CIE 1931 colour space, sverity of defincieny in arrnagment can be plotted along protan, duteran and train axises.


Alternative D-15 Test: Colblindor. MEasures the moment of inertia, according to Vingrys and Ewan King Smith, whcih asess for type of CVD, severity of CVD and degree of selection and consistency over randomness.



A full Farnsworth test consist of up to 100 discs of varying hues.



Anomaloscope - tests colour matching by altering brightness. In CVD reduced spectrum don't have as many actual distinct hues available to vision This is an online simulation of a real anomaloscope which uses very expensive equipment to mix brightness levels of Yellow light under one lamp and Red and Green light under.


Computer monitors use the colour space Red. Green and Blue to make up the colours on display, hence this is not and cannot be an adequate reproduction of an anomaloscope (and why all vision tests should be conducted by an eye specialist - these serve merely as indicators.)
Red-Green colourblindness doesn't mean 'likely to confuse red and green' , the iso-chromatic lines on the CIE space confirm this: there are many regions of colour which can be confused or are indistinguishable due to the reduction in spectrum. People with CVD often rely on intuition and context to recognise a specific colour, important in this intuition is the level of saturation (hue) and brightness. The Simulated Anomaloscope establishes that varying the level of brightness can for someone with CVD, create matching pairs of apparent colour when the actual hue is different.



CIE Iso-chromatic test (eliminates brightness as a variable)


The CIE calculates what colour is seen by the human eye. Because people with CVD have a reduced spectrum they cannot discriminate colours from a restricted set of visible wavelengths, as a result on the CIE it is possible to draw lines where colours of mixed hues are generated but along the iso-chomatic lines CVD suffers will confuse the colours.
The CIE only accoutns for what colours are visible and does not accoutn for brightness, the white-light setting or environmental factors.

Colblindor
The Simulated Anomaloscope forced you to alter brightness to select colour matches (even for the CVD vision where none exist) The next test eliminates brightness as a variable and concentrates only on hue.
The CIE Isochomatic test generates three possible colours which fall along the same iso-chromatic line but each are the same brightness. For normal vision this isn't a problem: oranges, yellows and greens don't look alike. They can sufficiently discriminate the various similar wavelengths but this isolates the CVD suffer specific difficulty which is next to impossible with a reduced visible spectrum therefore it is a better study of error than the Ishihara plates.


Best results take the isochromatic test 3 times, 50 screens. Take an average of your result.
There's no standard measurement, but below 50% indicates a CVD the close to 33% (i.e guesswork) the greater the severity of the restriction in colour discrimination along the isochromatic lines.