title: Vascular response to extended wear of hydrogel lenses with high and low oxygen permeability.
abstract: OBJECTIVE
  The purpose of this study was to determine the impact of extended wear of high and low oxygen permeability (Dk) lenses on the development or resolution of limbal hyperemia and corneal neovascularization in a randomized prospective clinical trial.
  
  
  METHODS
  Adapted daily-wear contact lens wearers were randomly assigned to one of two groups. The low-Dk group (N = 23) wore etafilcon A lenses (Dk/t = 40) for up to 7 days and 6 nights, and the high-Dk group (N = 39) wore lotrafilcon A lenses (Dk/t = 175) for up to 30 days and nights. Limbal hyperemia and neovascularization were assessed and graded during 9 months of extended wear. A stratified analysis to determine how change in ocular redness depended on initial presentation was also conducted.
  
  
  RESULTS
  On a 0 to 100 scale, extended wear of low-Dk lenses resulted in a 16-point increase in limbal hyperemia (p < 0.0001); no significant change occurred with the high-Dk lenses. The difference was greatest for low-Dk participants who initially presented with lower levels of hyperemia (N = 18). There was a slight resolution of redness in participants who initially presented with higher levels of hyperemia (N = 10) after wearing the high-Dk lenses. Neovascularization increased by an average of 0.5 on a scale of 0 to 4 in low-Dk lens wearers (p < 0.0001) but remained unchanged in the high-Dk lens wearers. The increase was most marked for the low-Dk group with lower levels of neovascularization at baseline.
  
  
  CONCLUSIONS
  Subjects who wore lenses with higher oxygen permeability for 9 months of extended wear exhibited a lower vascular response of the ocular surface compared with subjects who wore lenses of lower oxygen permeability for the same period. This result was found both for the surface limbal vessels and in the deeper neovascular stromal vessels. Moderate neovascularization also developed after 3 months of extended wear of low-Dk hydrogels, whereas high-Dk lenses caused no neovascularization.
authors.affiliation: Centre for Contact Lens Research, School of Optometry, University of Waterloo, Ontario, Canada. kdumble@sciborg.uwaterloo.ca
authors.forename: K A
authors.initials: KA
authors.lastname: Dumbleton
authors.forename: R L
authors.initials: RL
authors.lastname: Chalmers
authors.forename: D B
authors.initials: DB
authors.lastname: Richter
authors.forename: D
authors.initials: D
authors.lastname: Fonn
mesh_terms: D000328:Adult; D003262:Contact Lenses, Extended-Wear / Q000009:adverse effects*; D016510:Corneal Neovascularization / Q000209:etiology* / Q000378:metabolism; D005260:Female; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D006940:Hyperemia / Q000209:etiology* / Q000378:metabolism; D016850:Limbus Corneae / Q000098:blood supply*; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D010539:Permeability; D011446:Prospective Studies
chemical_list: D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D010100:Oxygen