Precise tests of acuity, spatial and temporal contrast, colour and stereo vision
Metropsis is a complete test suite suitable for clinical, pre-clinical research, applied vision research, drug trials, screening, sports science and human factors research. The tests have been developed to investigate diseases of the eye and the brain, as well as changes in visual functions as a secondary effect of systemic disorders, such as cardiovascular diseases or neurological dysfunctions.
Guide Price: £13250
Investigate the limits of colour discrimination
The Cambridge Colour Test provides a rapid means of screening subjects for colour vision deficiencies; but it also can be used to examine in more detail the changes in colour discrimination that occur as a result of congenital or acquired conditions. It allows the investigator to monitor quantitatively over time the progression or remission of disease. Many drugs affect colour vision and the pharmacologist will find the test well suited to monitoring the short-term or long-term course of such side-effects.
The test determines discrimination ellipses in colour deficient subjects by probing chromatic sensitivity along the colour confusion lines. Ellipses measured in individuals with even slightly anomalous colour vision are characteristically orientated and enlarged.
Easy to use
The procedure is easy to use for both the investigator and the subject. It uses the familiar Landolt C stimulus, defined by the two test colours that are to be discriminated, on an achromatic background.
The Cambridge Colour test uses the proven concept of introducing spatial and luminance noise into the stimulus, which is composed of grouped circles randomly varying in diameter and having no spatial structure. The Landolt C is therefore defined by chromaticity alone, ensuring that the subject's responses are not due to luminance or spatial cues in the stimulus, and thus avoiding the necessity for a preliminary procedure to find isoluminance for the test colours.
The test is conceptually very simple to explain to the subject, who responds to the orientation of the Landolt C using the 4-button infra-red response box. The chromaticity of the components of the C is varied along the protan, deutan and tritan lines (or other chromatic axes if desired) using a standard descending psychophysical staircase procedure.
The Cambridge Colour Test is an established method and has been widely used for both clinical and basic research including an extensive normative data set.
Aims of the Test
The low-vision version of the Cambridge Colour Test (lvvCCT) aims to measure chromatic discrimination in patients affected by low vision.
The test was developed by Simunovic et al. and published in the journal Vision Research (1998, 38, 3413-3419).
The test has been implemented by Cambridge Research Systems and made available as a protocol of the Metropsis system.
The stimuli used in the lvvCCT consist of four discs presented on a neutral background in a diamond-shaped array; each disc subtends 4° at 1.5 m and is separated by 2.5° from adjacent discs.
On each presentation, one of the discs differs in chromaticity from the remaining three (which remain of neutral hue).
Using a 4-key response box, the observer indicates which disc differs from the others in colour.
The luminance of each disc is randomly generated on each trial, thus the observer can distinguish the coloured target from the grey distractors only on the basis of its colour.
If the observer answers correctly, the saturation of the target decreases approaching gray; if the observer answers incorrectly, the saturation increases.
The test uses a staircase procedure to measure the minimum saturation required to discriminate the target from the distractors.
Example of a Saturation Change Across Trials
The test can be run in its shorter version, which aims to measures chromatic discrimination along the Protan (P), Deutan (D), and Tritan (T) confusion axes, or in its long version, which probes chromatic discrimination along 20 different axes.
An observer with a P defect will have a high P threshold; an observer with a D defect will have a high D threshold; an observer with a T defect will have a high T threshold.
Discrimination thresholds of normal trichromats usually do not exceed 100 units; whereas discrimination thresholds of affected observers are expected to be much higher.
In total, it will take approximately 5-6 minutes to measure the monocular P, D, and T discrimination thresholds in a naïve observer.
The test is run in free view, thus the observer does not need to fixate. This makes the test easier for observers with central scotomas.
The test is accurate and very sensitive to small changes in chromatic discrimination.