Drischel and Schaubitzer described experiments which lead them to conclude that procaine hydrochloride (Novocaine), instilled into the conjunctival sac of normal human subjects, or injected intravenously, had parasympathomimetic effects upon the pupil, similar to pilocarpine.1
The authors recorded pupillary reactions to standardized short light flashes, using an infrared-sensitive photoelectric device which registered light reflected by the iris. In this type of instrument, a beam of dark red-infrared light is directed upon the eye. When the iris expands during pupillary contraction, more of this light is reflected, and thus a photocell, exposed to the reflected light, emits more current. Conversely, when the iris surface shrinks during pupillary dilation, the photoelectric current is reduced.
The absolute amount of light reflected by the iris varies from subject to subject because of different degrees of pigmentation of the eyes and other factors. The photocurrents obtained were therefore amplified arbitrarily until the responses to
IRENE E. LOEWENFELD. The Iris as Pharmacologic IndicatorII. A Supposed Parasympathomimetic Effect of Novocaine Upon the Pupil. Arch Ophthalmol. 1963;70(4):535–539. doi:10.1001/archopht.1963.00960050537018