The measurement of the dark adaptation of the eye has usually been confined to laboratory observers because of the time such an examination requires and because of the complexity of the instruments used. Consequently, valuable clinical information has frequently been over-looked. To simplify this examination, I devised an instrument for clinical use and adopted an empiric standard of dark adaptation units.
The instrument consists of a standard, on which is mounted a light-proof box, exactly 1 meter long and 12 cm. high and wide (Fig. 1). At one end is an open eye piece, so shaped as closely to approximate the orbital rim (Fig. 2 A). At the other end of the box is an iris diaphragm, E, whose diameter can be varied from 1 to 15 millimeters. Two and five-tenths cm. beyond this is another iris diaphragm, F, with an opening ranging from 10 to 25 mm. in diameter.
GRADLE HS. A NEW INSTRUMENT FOR THE CLINICAL MEASUREMENT OF DARK ADAPTATION. JAMA. 1916;LXVII(17):1208-1210. doi:10.1001/jama.1916.02590170016005