Coloured glasses
have been with us for at least two centuries, but it is only in the last three
decades with the advent of plastic (resin) lenses that it has been possible to
obtain almost any desired spectral transmission quickly and simply. The tint
required for therapeutic purposes has to be selected with precision. The Intuitive
Colorimeter permits the choice of colour to be made simply and quickly.
The Intuitive
Colorimeter is a simple optical device that shines coloured light on a page
of text and allows the user to vary the light with three controls, one for
colour (hue), one for strength of colour (saturation) and one for brightness
(luminance). The variation of hue and saturation is continuous. Luminance may
be selected from one of four levels.
The text used as
stimulus material consists of random letters arranged in strings to resemble
words in a paragraph. The clarity can therefore be assessed independently of
the linguistic and semantic content of the text.
An examination
with the colorimeter typically consists of a preliminary assessment, followed
immediately by a detailed assessment. The preliminary assessment is undertaken
by comparing perception under white light with that under light of various
hues, systematically selected and briefly presented. At each of 12 hues, evenly
spaced around a hue circle, the saturation is increased and then decreased. The
purpose is to identify any hues that have beneficial perceptual effects and,
equally importantly, to identify any that are aversive. Following this initial
assessment, detailed assessment is performed. The choice of beneficial hue is
refined with the eyes colour-adapted. Saturation and hue are alternately
optimised, saturation by method of adjustment, and hue by two-alternative
forced choice from similar hues of the appropriate saturation.
The optimal
colour, once selected, is replicated by a combination of tinted
trial lenses, and these are worn for a period sufficient to assess their
effects on the perception of surface colour, as well as on reading.
The assessment
procedure described above minimises exposure to aversive hues, and it allows
the tint to be selected quickly and efficiently under conditions of colour
adaptation. The tint is provided by glasses with a smooth spectral transmission
that minimises any change in tint under lighting having various uneven spectral
power distributions.
The system for
precision tinting described above is available under Medical Research
Council license from Cerium Visual
Technologies
You can obtain
the name of a Colorimeter specialist near you if you are in the UK or elsewhere.