Naloxone eye drops reverse the miosis in runners--implications for an endogenous opiate test

Naloxone 0.16% ophthalmic drops or placebo drops were self-administered to one eye by 13 runners 250 times in a double-blind fashion over three weeks of various intensities and durations of running. An increasing incidence of miosis after running and ipsilateral mydriasis after the naloxone eye drops were administered was noted to correlate with increased run durations. During 34 runs of over 30 minutes duration, 20 subject runs (59%) developed miosis in both eyes and mydriasis in the eye treated with naloxone, but none of 10 subject runs over 30 minutes (9 of which showed miosis) developed mydriasis after placebo drop administration. Calculations (means, SEM) of pupil sizes in various run durations revealed an increased occurrence of miosis which was reversed with naloxone in over 30 minute runs at a significance level greater than 0.005 (single tailed "t" test). It is suggested that exercise generated endogenous opiates cause pupillary miosis, and that ophthalmic naloxone to one eye can block this exercise pupillary effect resulting in ipsilateral mydriasis. Suggestions are given for a simple "Naloxone Anisocoria Test" for the presence or absence of elevated endogenous opiates.