Stiles-Crawford chromatic effect in congenital colour defective observers.
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Air traffic controllers perform a number of tasks which involve color identification, color discrimination, and color naming. Normal color vision is required for air traffic controllers, although the requirement is currently under review. The most critical task involving color is the distinction of red and black on flight strips; the distinction must be made reliably, quickly, and routinely for flight safety. In this study of four protanopes and three normals, all the protanopes were unable to make this distinction reliably under the lighting levels encountered at air traffic control (ATC) centers, whereas none of the normals had any difficulty. Protanopes also made numerous errors with other ATC tasks involving color. The use of a red filter, often recommended to aid color defectives, actually made performance worse and additionally compounded the usual protanopic loss of brightness for red light. When Snellen visual acuity was tested using the red filters, protanopes needed up to four times larger letters than the color normals. It is concluded that protanopes have inadequate vision for safe performance of some current ATC tasks.
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All 954 boys and 1064 girls attending two schools in north-western Ethiopia were tested in February 1988 for colour blindness using the Ishihara plates. A total of 40 colour blinds (4.2%) were found among males and 2 (0.2%) among females. There were 31 (3.2%) deutans and 9 (0.9%) protans among males. Both female colour blinds were deutans. This study confirms a previous observation on the gene frequency of colour blindness in this population. For the first time it also provides information on the frequency of this polymorphism in female Ethiopians, as well as types of red-green defects.
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Disturbances in colour vision are a well-reported adverse ocular effect to toxic levels of digoxin. We present a case history of a patient with both colour vision changes and transient visual field defects to therapeutic serum levels of digoxin.
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Screening of red-green colour vision defects was done for 52 school children (22 boys and 30 girls) and 231 trade school students (226 boys and 5 girls) with three different kinds of pseudo-isochromatic plates: Ishihara (1983), Boström-Kugelberg (1972), and Standard Pseudoisochromatic Plates part 1 (SPP 1) 1978, and with three different kinds of vision screeners: Keystone View Model DVS 2, Bausch and Lomb Vision Tester, and Rodenstock Farbentestscheibe 3040.173. After these tests, each subject was examined with the Nagel Anomaloscope; this revealed 26 red-green defectives in the study group. Ishihara found 20/26 (76.9%), Boström-Kugelberg 24/26 (92.3%), and SPP 1 17/26 (65.4%) of the defectives. None of the normals were diagnosed as defectives with Ishihara or SPP 1. With Boström-Kugelberg four normals were diagnosed as defectives. Keystone found 24/26 (92.3%), Bausch and Lomb 26/26 (100%), and Rodenstock 25/26 (96.2%) of the defectives. But 9, 21, and 112 normals, respectively, were diagnosed as defective. In the present study, the Boström-Kugelberg and Ishihara plates as well as Keystone Vision Screener and Bausch and Lomb Vision tester came close to an effective screening test and could be recommended for screening red-green colour vision defects in occupational health care.