title: Retinal vessel tortuosity in response to hypobaric hypoxia.
abstract: OBJECTIVE
  Retinal vascular tortuosity is associated with retinopathy of differing etiologies, including hypertension, diabetes, and hypoxia. However, detailed understanding of the underlying pathophysiology is lacking. The aim of this study was to map changes in tortuosity associated with hypoxia at high altitude, and to determine the influence of sildenafil and an antioxidant preparation on altitude-induced tortuosity.
  
  
  METHODS
  We measured the tortuosity of retinal vessels using a semi-automated method in 35 young, healthy subjects exposed to hypobaric hypoxia for 7 days at 5200 m, and compared the measurements to those from the same vessels at sea level. These subjects simultaneously took part in a randomized double-blind placebo-controlled trial of sildenafil and antioxidant. Comparison of tortuosity between these subgroups was performed.
  
  
  RESULTS
  High altitude was associated with the development of retinal tortuosity in individual vessels. A nonsignificant trend suggests this is limited by prophylaxis with sildenafil or antioxidant.
  
  
  CONCLUSIONS
  Retinal vessel tortuosity increases rapidly at high altitude. We suggest that retinal vessel tortuosity at altitude may result from increased sheer stress causing elongation of vessel segments and that this might be limited by agents that act to preserve nitric oxide dependent vasodilation.
  
  
  BACKGROUND
  NCT00664001, NCT00627965.
authors.affiliation: Malawi-Liverpool-Wellcome Trust Clinical Research Programme, College of Medicine, Blantyre, Malawi. Ian.maccormick@gmail.com
authors.forename: Ian J C
authors.initials: IJ
authors.lastname: MacCormick
authors.forename: John
authors.initials: J
authors.lastname: Somner
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Morris
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: MacGillivray
authors.forename: Rupert R A
authors.initials: RR
authors.lastname: Bourne
authors.forename: Suber S
authors.initials: SS
authors.lastname: Huang
authors.forename: Alasdair
authors.initials: A
authors.lastname: MacCormick
authors.forename: Peter A
authors.initials: PA
authors.lastname: Aspinall
authors.forename: J Kenneth
authors.initials: JK
authors.lastname: Baillie
authors.forename: A A Roger
authors.initials: AA
authors.lastname: Thompson
authors.forename: Bal
authors.initials: B
authors.lastname: Dhillon
mesh_terms: D000293:Adolescent; D000328:Adult; D000531:Altitude; D000975:Antioxidants / Q000627:therapeutic use*; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000150:complications*; D008297:Male; D009051:Mountaineering; D010781:Photography; D010879:Piperazines / Q000627:therapeutic use*; D011687:Purines / Q000627:therapeutic use; D012164:Retinal Diseases / Q000209:etiology* / Q000473:pathology / Q000517:prevention & control; D012171:Retinal Vessels / Q000473:pathology*; D000068677:Sildenafil Citrate; D013450:Sulfones / Q000627:therapeutic use*; D014665:Vasodilator Agents / Q000627:therapeutic use*; D055815:Young Adult
chemical_list: D000975:Antioxidants; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D014665:Vasodilator Agents; D000068677:Sildenafil Citrate