title: Effects of apraclonidine on aqueous humor dynamics in human eyes.
abstract: OBJECTIVE
  The mechanism by which apraclonidine, an alpha 2-adrenergic agonist, lowers intraocular pressure (IOP) was evaluated in humans.
  
  
  METHODS
  In a randomized, double-masked, placebo-controlled study, 0.5% apraclonidine was given topically twice daily for 1 week to one eye in each of 21 ocular hypertensive volunteers. The other eye was treated similarly with vehicle. Before and after 1 week of treatment, aqueous flow, uveoscleral outflow, fluorophotometric outflow facility, intraocular pressure, tonographic outflow facility, episcleral venous pressure, and outflow pressure were either directly measured or mathematically calculated. Values were compared in treated versus contralateral control eyes and on baseline versus day 8 of treatment.
  
  
  RESULTS
  When compared with both contralateral control eyes and baseline day, fluorophotometric outflow facility in the apraclonidine-treated eyes increased by 0.09 to 0.10 microliter/minute/mmHg (P < 0.04), IOP decreased by 3.1 to 5.2 mmHg (P < 0.0001), and outflow pressure decreased by 3.3 to 4.2 mmHg (P < 0.0001). When compared with baseline day only, aqueous flow in the apraclonidine-treated eyes decreased by 0.3 microliter/minute (P < 0.04), and episcleral venous pressure decreased by 1.0 mmHg (P < 0.001). Episcleral venous pressure also decreased in the control eyes compared with baseline day by 1.3 mmHg (P < 0.001). When compared with contralateral control eyes only, uveoscleral outflow in the apraclonidine-treated eyes decreased by 0.47 microliter/minute (P < 0.03). Tonographic outflow facility showed no change when compared with either contralateral control eyes or baseline values.
  
  
  CONCLUSIONS
  The apraclonidine-induced reduction in intraocular pressure was associated with an increase in fluorophotometric outflow facility, decrease in aqueous flow and decrease in episcleral venous pressure compared to baseline. The lack of a significant difference in aqueous flow and episcleral venous pressure between treated and contralateral control eyes may represent a contralateral drug effect.
authors.affiliation: Department of Ophthalmology, University of Nebraska Medical Center, Omaha 68198-5540.
authors.forename: C B
authors.initials: CB
authors.lastname: Toris
authors.forename: M E
authors.initials: ME
authors.lastname: Tafoya
authors.forename: C B
authors.initials: CB
authors.lastname: Camras
authors.forename: M E
authors.initials: ME
authors.lastname: Yablonski
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000328:Adult; D000368:Aged; D000869:Anterior Eye Segment / Q000378:metabolism; D001082:Aqueous Humor / Q000378:metabolism*; D003000:Clonidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004311:Double-Blind Method; D005260:Female; D015590:Fluorophotometry; D006801:Humans; D007429:Intraocular Pressure / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D009798:Ocular Hypertension / Q000188:drug therapy*; D009883:Ophthalmic Solutions; D014065:Tonometry, Ocular
chemical_list: D000316:Adrenergic alpha-Agonists; D009883:Ophthalmic Solutions; C016986:apraclonidine; D003000:Clonidine