title: The Berkeley Contact Lens Extended Wear Study. Part I : Study design and conduct.
abstract: OBJECTIVE
  The primary aim of the Berkeley Contact Lens Extended Wear Study (CLEWS) was to test the hypotheses that extended wear of rigid gas-permeable (RGP) contact lenses with greater oxygen permeability (Dk) reduces the incidence of contact lens-associated keratopathy (CLAK) and increases the survival rate in RGP extended wear (EW). In this article we describe the clinical trial design in detail, present the results of subject recruitment and retention, and provide the baseline demographic and ocular characteristics of the CLEWS subjects, whose data will be analyzed to address the study aims in a companion article.
  
  
  METHODS
  A randomized, concurrently controlled clinical trial.
  
  
  METHODS
  Subjects were fitted with day wear (DW) high-Dk RGP lenses and then adapted to EW. Subjects who adapted to EW were then randomly assigned to either high- or medium-Dk RGP lenses for 12 months of 6-nights/week EW.
  
  
  METHODS
  Slit-lamp assessment and grading of 17 possible keratopathies, measurement of refractive error and corneal curvature, and symptoms. Follow-up data were collected every 3 months.
  
  
  RESULTS
  From 545 subjects entering the DW adaptation phase, 201 adapted to EW and were randomly assigned to medium- or high-Dk lenses for 12 months of EW. The baseline characteristics of the two study groups were similar and did not differ from the 344 DW subjects who failed to adapt to EW. The distributions of oxygen transmissibility for the two study groups were disjoint, indicating that each group received distinctly different levels of hypoxia.
  
  
  CONCLUSIONS
  We show that CLEWS was appropriately designed to address the study hypotheses, was conducted with regard for the safety of the subjects, and adhered to rigorous protocols designed to control for bias and ensure the integrity of study data. We establish the internal validity of between-group statistical comparisons and characterize our study population to permit informed evaluation of the applicability of our results to the contact lens-wearing population in general.
authors.affiliation: Division of Public Health Biology and Epidemiology, School of Public Health, University of California, Berkeley, California 94720-2020, USA.
authors.forename: R E
authors.initials: RE
authors.lastname: Fusaro
authors.forename: K A
authors.initials: KA
authors.lastname: Polse
authors.forename: A D
authors.initials: AD
authors.lastname: Graham
authors.forename: C M
authors.initials: CM
authors.lastname: Gan
authors.forename: R K
authors.initials: RK
authors.lastname: Rivera
authors.forename: M C
authors.initials: MC
authors.lastname: Lin
authors.forename: T L
authors.initials: TL
authors.lastname: Sanders
authors.forename: N A
authors.initials: NA
authors.lastname: McNamara
authors.forename: J S
authors.initials: JS
authors.lastname: Chan
mesh_terms: D000328:Adult; D002986:Clinical Trials as Topic / Q000379:methods*; D003262:Contact Lenses, Extended-Wear / Q000009:adverse effects / Q000706:statistics & numerical data*; D003316:Corneal Diseases / Q000209:etiology / Q000378:metabolism / Q000517:prevention & control*; D005260:Female; D006801:Humans; D000860:Hypoxia / Q000378:metabolism / Q000517:prevention & control; D008297:Male; D010100:Oxygen / Q000378:metabolism; D010539:Permeability; D017755:Prosthesis Fitting; D011785:Quality Assurance, Health Care; D012107:Research Design; D012495:San Francisco
chemical_list: D010100:Oxygen