Effect of locally applied prazosin on the kinetics of the pupillary light reflex

The effect of locally applied prazosin on pupillometric measures was studied in healthy volunteers, in an attempt to identify the role of α₁-adrenoceptors in the recovery time of the light reflex. Prazosin antagonized the mydriatic effect of phenylephrine, but did not alter that of tropicamide. Miotic responses to a range of light stimuli were measured under ambient temperature conditions of 22°  C and 40°  C. The 40°  C condition was associated with shorter recovery times of the light reflex; prazosin increased the recovery time under both temperature conditions. Response amplitude was not affected by the temperature condition or prazosin. The results are consistent with the hypothesis that sympathetic neuromuscular transmission is involved in the redilatation of the pupil following a miotic response to light stimulation.