Ishihara pseudoisochromatic plates.
This test is the most widely used test for red-green colour deficiency, and clinical trials have shown that it is the most efficient. The full version contains 38 plates - 25 plates contain numerals, and thirteen plates containing pathways. An abridged version containing 24 plates is available as well, and a concise version containing 14 plates was also introduced in 19891.
Of the 25 plates containing numerals, one is for demonstration of the visual task, 20 are for red-green screening, and four are for classification of red and green cone deficiencies. There are also three plates intended for use with nonverbal subjects1.
All the screening plates containing numerals except the hidden digit designs are extremely effective. Dichromats and anomalous trichromats fail most of the plates and cannot be distinguished by the number of errors made. Only people with slight protan and deutan defects read some plates correctly1.
American Optical plates. (HRR test)
This test is designed to identify protan, deutan and tritan defects, and to grade their severity. The test consists of 24 plates containing symbols and employs neutral colours which increase in saturation in successive plates of the test. There are four introductory plates, six plates for colour vision screening, and fourteen plates for grading the severity of protan, deutan and tritan defects1.
The HRR test is valuable for its grading function and for the detection of tritan defects. Only moderate or severe tritan defects are identified. Although the grading plates are effective, it is not possible to distinguish dichromats and severe anomalous trichromats from the test results1.
The Ishihara and HRR plates are often used together in a clinical examination. The Ishihara plates are used for red-green screening and the HRR plates for estimating the severity of colour deficiency and for tritan screening1.
The City University test.
The City University test is derived from the D-15 panel. It contains ten plates. Each plate displays a central colour and four peripheral colours. The observer must select the peripheral colour which looks most similar to the central colour. Three colours are typical isochromatic confusions for protan, deutan and tritan deficiency. The fourth colour is an adjacent colour in the D-15 sequence and is the normal preference1.
The classification of congenital protan and deutan defects is imprecise due to the limited choice of confusion colours. Therefore, this test is a grading test, and not a screening test. The City University test can be used in a test battery to provide information about the severity of the colour defect if a test format other than the FM D-15 test is necessary1.
The City University tritan test.
The City University test consists of five plates. Three plates are for tritan screening and two plates are to distinguish severe tritan defects. The test is intended to supplement the Ishihara test to provide comprehensive colour vision screening. There is no introductory design, and all five plates contain circle, cross, and triangle symbols. The plates successfully identify congenital tritan defects and have been used extensively in the study of acquired colour deficiency in diabetic patients1.
The Farnsworth Munsell D15 test.
The FM D-15 test consists of 15 loose caps and one fixed cap (the reference cap) in one box. The hue of each cap has been chosen so that adjacent caps have approximately equal hue differences. When the caps are arranged in order out of their box they form a hue circle. As a result, errors can be made across the hue circle1.
The standard D15 test divides people into two groups. The first group consists of people with normal colour vision and slight colour deficiency; the second group consists of people with moderate and severe colour vision deficiency. Typical results are obtained in congenital protan, deutan, and tritan colour deficiency1.
This test was not designed for screening. It is also not a test to separate the colour anomalous from the dichromat. It separates sufficiently affected deutans from sufficiently affected protans. It also separates sufficiently affected deutans and protans from those not seriously affected once the presence of the defect has been established by some other means2.
The Farnsworth-Munsell 100 hue test (F-M 100 hue)
The F-M 100 hue has been designed to detect all types of colour vision abnormality from the mildest red-green defect to total achromatopsia. It separates persons with normal colour vision into classes of superior, average and low colour discrimination and measures the axes or zones of colour confusion in those with defective colour vision2.
The F-M 10 hue test consists of 85 caps which form a perfect hue circle of the visual spectrum. The hue circle is divided into four parts for the testing. Each has an additional fixed or pilot cap at either end of the box and 22 or 21 loose caps. The four boxes render it impossible to confuse reds with greens, or blues with yellows2.
The F-M 100 hue test is the most comprehensive of the Farnsworth Munsell type tests, giving both differential diagnosis and progression of the disease. The test can be used to screen for any type of colour vision loss. However, the test takes a long time to complete, especially when a patient has an acquired loss and therefore must be tested monocularly2.
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