Mydriatic response to different concentrations of intracameral phenylephrine in humans.
OBJECTIVE
To assess the mydriatic response to concentrations of intracamerally injected phenylephrine from 0.15 mg/mL to 30.00 mg/mL (0.015% to 3.000%) in human eyes.


METHODS
Department of Clinical Science/Ophthalmology, Umeå University Hospital, Umeå, Sweden.


METHODS
Comparative case series.


METHODS
This prospective randomized double-masked study comprised patients scheduled for phacoemulsification cataract surgery. At the beginning of the procedure, patients received an intracameral injection of 0.15 mL of phenylephrine 0.15, 0.5, 1.5, 5.0, 15.0, or 30.0 mg/mL. To assess the mydriatic response, the pupil size was registered over 60 seconds using digital video recording. Then, the surgery was performed in the standard manner.


RESULTS
The study evaluated 42 patients. The mydriatic response was almost identical at the 4 lower phenylephrine concentrations (0.15 to 5.00 mg/mL; 0.015% to 0.500%), with final pupil sizes of approximately 4.3 mm. The 2 higher concentrations gave significantly larger pupils as follows: mean 5.80 mm ± 0.79 (SD) for 15.0 mg/mL (1.5%) and 6.65 mm ± 0.57 for 30.0 mg/mL (3.0%).


CONCLUSIONS
Results show that phenylephrine injected intracamerally does not have a linear mydriatic dose-response relationship in humans. At very high concentrations, phenylephrine may bind to and stimulate receptors other than the α(1)-receptor, explaining this phenomenon.
Behndig
Anders
A
Department of Clinical Science/Ophthalmology, Umeå University Hospital, Umeå, Sweden. anders.behndig@ophthal.umu.se
Lundberg
Björn
B
D000368:Aged; D000867:Anterior Chamber / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007267:Injections; D008297:Male; D009184:Mydriatics / Q000008:administration & dosage*; D018918:Phacoemulsification; D010656:Phenylephrine / Q000008:administration & dosage*; D011446:Prospective Studies; D011680:Pupil / Q000187:drug effects*
D009184:Mydriatics; D010656:Phenylephrine