title: Regulation of intraocular pressure after water drinking.
abstract: OBJECTIVE
  Acute oral water loading transiently elevates intraocular pressure (IOP) via mechanisms that remain unexplained. We tested the possibilities that water drinking might elevate IOP by creating a blood-aqueous osmotic gradient, or that it might instead alter active ion pumping and the formation of aqueous humor.
  
  
  METHODS
  In the first series, 16 young, healthy individuals were studied during dehydration and for 1 hour after rehydration (14 mL H2O/kg body weight). Hematocrit, total plasma osmolality, and plasma colloid osmotic pressure were determined simultaneously with measurements of IOP. In a second series (N = 16), rehydration occurred after pretreatment with either placebo or a topical carbonic anhydrase inhibitor (1 drop 2% dorzolamide in each eye, 12 and 2 hours before oral water loading).
  
  
  RESULTS
  In both series, mean IOP increased significantly 15 minutes after water ingestion and remained elevated above baseline for 45 minutes. In contrast, colloid osmotic pressure and hematocrit were unaltered by water drinking, and neither these variables nor total plasma osmolality correlated with IOP. In the second series, pretreatment with dorzolamide reduced baseline IOP, but failed to alter the magnitude or time course of IOP elevations induced by water drinking.
  
  
  CONCLUSIONS
  Because water drinking failed to create a blood-ocular osmotic pressure gradient, neither vitreous hydration nor increased aqueous ultrafiltration can explain increases in IOP after acute hydration. Because the increase in ocular tension apparently also is independent of active bicarbonate pumping, factors affecting aqueous drainage must explain the water drinking effect.
authors: Medical Sciences Program, Indiana University, Bloomington 47405, USA.
authors: M
authors: M
authors: Brucculeri
authors: T
authors: T
authors: Hammel
authors: A
authors: A
authors: Harris
authors: V
authors: V
authors: Malinovsky
authors: B
authors: B
authors: Martin
mesh_terms: D001082:Aqueous Humor / Q000378:metabolism; D018916:Blood-Aqueous Barrier / Q000502:physiology*; D002257:Carbonic Anhydrase Inhibitors / Q000008:administration & dosage; D004326:Drinking / Q000502:physiology*; D005500:Follow-Up Studies; D006801:Humans; D007429:Intraocular Pressure / Q000187:drug effects / Q000502:physiology*; D009883:Ophthalmic Solutions; D009995:Osmosis / Q000187:drug effects; D012016:Reference Values; D013449:Sulfonamides / Q000008:administration & dosage; D013876:Thiophenes / Q000008:administration & dosage
chemical_list: D002257:Carbonic Anhydrase Inhibitors; D009883:Ophthalmic Solutions; D013449:Sulfonamides; D013876:Thiophenes; C062765:dorzolamide