What is CVI?


Contrast Sensitivity

Contrast sensitivity is a measure of the ability to differentiate shades of grey.

Colour contrast sensitivity is not a scientific term, it is a descriptor for the ability to differentiate that amount of grey scale in colour, for example:

A shade is a colour with a bit of black added (eg navy blue).

A tint is a colour with a bit of white added (eg light blue).

This section is only dealing with contrast sensitivity.

Contrast is measured as a percentage of luminosity.

Contrast sensitivity is a measure of our ability to see difference between different shades of grey. It can be measured against a white background, therefore:

This diagram (below) shows the shades of grey, each 10% different level of luminosity, decreasing from 100% white to 0% black.

Note - all these shadings are approximate and are illustrative to help explain the numbers used. Note - all these shadings are approximate and are illustrative to help explain the numbers used.

If we look at the lightest shade of grey next to white and compare it to the white, we get the contrast sensitivity for the difference between the two shades.

With a contrast sensitivity of 5% the person can see the shades of grey against a white background to this level:

So, the smaller the percentage difference you can tell the difference between, the better your contrast sensitivity. It is important to realise that contrast sensitivity is not luminosity, even though they can both be measured as percentages.

Contrast sensitivity is the lowest percentage of luminosity visible between shades of grey.

Connor's contrast sensitivity has been measured at 46%. This means that anything with a contrast between shades of grey less than 46% is not visible to Connor. This would equate to the following:

Contrast sensitivity is often missed, particularly because of this:

Acuity is measured using black on white - 100% contrast sensitivity, or the lowest level of contrast sensitivity recordable. Whilst high contrast is needed to test visual acuity, further tests need to be undertaken to also assess contrast sensitivity.

Low contrast sensitivity can have similar effects to low visual acuity, as briefly discussed in the previous section.

The pictures below have been simulated by a beta version of SightSim to show approximately how the image would look to someone with reduced levels of contrast sensitivity

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Further examples of images that have been edited to show different reduced levels of contrast sensitivity can be found in Simulated Images section.


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At CVI Scotland we are devoted to helping people understand cerebral visual impairments, and together working towards developing the understanding of this complex condition.