Dark adaptation with limited light and color vision.

Abstract

Dark adaptation is a prerequisite for many activities which must be carried out in subdued light. In the field of roentgenology, it has long been recognized as a necessity for satisfactory fluoroscopic examination. For this reason, radiologists customarily cover their eyes with various types of light-restricting shades for periods varying from ten to thirty minutes prior to undertaking the procedure. The most common form of dark-adaptation glasses in use at the present time is a shielded face-fitting goggle with a red plastic filter. This permits light of the longer wave lengths to pass, but effectively restricts the wave lengths below 600 millimicrons, which would desensitize the receptors for low illumination if transmitted to the retina. Moreover, it serves to decrease the total intensity of light of all wave lengths entering the eyes. During the period of dark adaptation or accommodation, the radiologist is strictly limited in the use of his time; he cannot examine films and properly does not give any opinion concerning them; neither can he see color. The loss of acuity of vision and the inability to recognize differences in wave lengths (color) are extremely disadvantageous, as they prevent recognition of cyanosis, blood in vomitus, stools, urine, etc., and skin lesions, particularly those of an erythematous nature, which may be important in overall diagnosis. Generally, the radiologist uses accommodation time for handling of correspondence or other administrative activities but even here he is handicapped by the lack of color vision. Marginal notations in a red pencil, for example, are completely invisible while red adapting glasses of the usual variety are worn. In November 1955, Doctor William A. Faraghan described a modification of glasses for dark adaptation in a Letter to the Editor of RADIOLOGY (1). Doctor Faraghan noted an initial inequality of dark adaptation of the right and left eyes when fluoroscopy was preceded by covering one eye with a head mirror for performance of bronchography. The eye covered by the reflecting mirror was consistently better adapted than the other. This was interpreted to mean that the tubular vision provided by the central aperture of the head mirror resulted in some degree of dark adaptation even though the procedure had been carried out in a brightly lighted room. To test this possibility, Dr. Faraghan removed the red filter from a pair of standard goggles and replaced it with opaque cardboard having a black inner surface; two holes, 8 mm. in diameter (approximately equal to half that of a head mirror), were cut in the cardboard to center over the pupil of each eye. The frames held the clear apertures approximately 2.5 cm. in front of the eye, producing a partial collimating effect. With this modification, adequate adaptation was achieved under conditions of normal illumination and even during inspection of banks of viewing boxes.