Refractive state after instillation of paredrine and neosynephrine.

IN ophthalmic practice, drugs such as hydroxyamphetamine hydrobromide (Paredrine) and phenylephrine hydrochloride (Neosynephrine) are commonly used to produce mydriasis without alteration of refractive state. There is, however, no definite evidence that the refractive state is completely unaffected by these drugs, and experimental information on this subject is limited. Of some interest in this regard is the report of Campbell and Robson (1959) that after instillation of Paredrine (1 per cent.) into the conjunctival sac: "the drug takes about 20 to 40 minutes to produce mydriasis and thereafter there is a period of about one hour when a fixed dilated pupil is obtained without a detectable effect on the ciliary muscle. After this period, some subjects show a slight diminution in the amplitude of accommodation". Thus, the effect of Paredrine on accommodation is small or absent, but still unanswered is the question of a possible effect of this drug on the resting refractive state. One way by which a mydriatic might affect the resting refractive state is through a significant direct action on the ciliary muscle such as occurred after conjunctival instillation of 10 per cent. phenylephrine hydrochloride in rabbits by Roth (1965). A less obvious possibility is that decreased depth of focus, increased image degradation, and raised retinal illuminance resulting from pupil dilatation may be responsible for a shift in the resting refractive state. The purpose of this investigation was to learn if the results of customary (clinical) refractive examination can be affected by instillation of a mydriatic that presumably does not exert a direct influence on the ciliary muscle. In the following section, some aspects of the test procedure, because of their fundamental importance to the experimental design, are described in considerable detail. For example, a study like this must give careful attention to instillation of the test drug, measurement of the resting refractive state, and stabilization of head and eye position to reduce the possibility of artefacts.