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Description: | ILFORD COLOUR FILTER B (tooled into the leather pouch). SPE[CTRU]M GREEN 604 (printed on a paper label inside the pouch) 604 GREEN (written in white ink, now almost illegible, on the leather pouch). MANU Ilford circa 1940 Ilford, Essex, England. This green filter was used in a Pickford-Nicholson anomaloscope. It is made from a suspension of a green dye in a water soluble gel, such as gelatine. The dye filters out all other colours of the spectrum leaving 0nly the green light.
An anomaloscope is used to detect two kinds of colour blindness caused by inherited and acquired defects. One is a protanomaly: a mutated form of the long-wavelength pigment, whose peak sensitivity is at a shorter wavelength than in the normal retina. Protanomalous individuals are less sensitive to red light than normal. This means that they are less well able to discriminate colors, and they do not see mixed lights as having the same colors as normal observers. They also suffer from a darkening of the red end of the spectrum. This causes reds to reduce in intensity to the point where they can be mistaken for black. Protoanomaly is a fairly rare form of colorblindness making up about 1% of the male population.
Another is deuteranomaly: a mutated form of the medium-wavelength pigment. The medium-wavelength pigment is shifted towards the red end of the spectrum resulting in a reduction in sensitivity to the green area of the spectrum. Unlike protanomaly the intensity of colors is unchanged. This is the most common form of colorblindness making up about 8% of the male population.
Anomaloscopes have been developed to specifically diagnose different types of colour deficiencies. They are able to determine whether a person has normal or deficient colour vision, whether a deficiency is protan or deutan and whether the person is a dichromat or anomalous trichromat.
This instrument has a light source in the form of a standard 1930,s gas-filled general service incandescent lamp with a coiled wreath filament. the light from the lamp passes through a beam splitter formed by an aluminium diaphragm with a selection of ten pairs of different sized apertures. The beams are then focused by a pair of plano-convex lens. The beams of light are focussed onto a selection of broad band; red, yellow,grey,blue, violet, blue-green and blue plus green filters held in vertical slides controlled by microscope rack and pinions. The light from each filtered beam then passes through a slot whose horizontal dimensions are adjusted by microscope stage screws. The two beams are then refocussed by another pair of plano-convex lenses on to an opalised glass screen. The subject views the screen. By altering; the size of apertures in the diagphragm, the height and colour of the filters, and the width of the slot, the operator can ajust the overalll illumination and the degree of colour mixing on the screen.
This type of instrument has been used to detect coulour blindness caused by glaucoma and *Diabetes mellitus* and hypoxia, it is sufficiently sensitive to be able to detect colour blindness in subjects who show no obvious abnormalities in the retina and therefore can be used as diagnostic of the conditions. | License: | http://www.hmag.gla.ac.uk/spirit/rights/ | Publisher: | Hunterian Museum and Art Gallery, University of Glasgow | Rights holder: | Hunterian Museum and Art Gallery, University of Glasgow | Subjects: | SCIENTIFIC COLLECTION : | Source: | Hunterian Museum | Creator: | Hunterian Museum and Art Gallery, University of Glasgow | Identifier: | http://www.huntsearch.gla.ac.uk/cgi-bin/... | Language: | en-GB | Go to resource |
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