Effect on mydriasis of modifying the volume of phenylephrine drops

The cardiovascular effects of topically administered phenylephrine 10% are well known and can be minimised by reducing the concentration of drops administered. By modifying the dimensions of the dropper tip we reduced the volume of the drops administered, and therefore the total dose of phenylephrine, without altering the concentration. No difference in the mydriasis produced by drops of small and normal volume could be detected. Since a smaller dose of phenylephrine is administered with smaller drops, the risk of systemic side effects could be reduced by modifying the tips of eyedroppers.