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While I am not an advocate of electrically illuminated test objects in preference to the ordinary methods now used in mapping out the visual field and the blind spot, I believe such devices have their field of usefulness and can often be employed to advantage, for example, in office or dispensary work on dark days or in the evenings, and bedside examinations in poorly illuminated rooms or wards. To meet such requirements I have devised, and used for nearly two years, an illuminated color finder patterned after the very excellent and well-known instrument of Dr. Clifford Walker of Boston.
The instrument is about 10 inches long, and the head contains four perfect colors (white, blue, red and green) made in thin paper and protected by layers of glass, arranged on a slide which is controlled by a thumb guide placed out of the way near the handle. The thumb guide
Calhoun FP. AN ELECTRIC COLOR FINDER: TO BE USED IN MAPPING OUT THE VISUAL FIELD AND THE BLIND SPOT. JAMA. 1916;LXVI(21):1622. doi:10.1001/jama.1916.25810470004018c
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