title: Variability of Tear Osmolarity in Patients With Dry Eye.
abstract: OBJECTIVE
  Knowledge about the variability of measurements using the TearLab Osmolarity System is necessary when evaluating the clinical utility of readings.
  
  
  OBJECTIVE
  To examine the variability of tear osmolarity measured by the TearLab Osmolarity System in patients with Sjögren syndrome (SS), patients with blepharitis, and control participants.
  
  
  METHODS
  Cross-sectional study at a tertiary care academic center from June 13, 2012, to March 21, 2013. Participants included 74 eyes of 37 patients from a volunteer sample (18 patients with SS, 11 patients with blepharitis, and 8 control participants) who were evaluated using the TearLab Osmolarity System, with 3 consecutive osmolarity measurements taken at 1-minute intervals in a session; 15 of these patients had the same measurements taken by the same examiner in 2 additional sessions on the same day (9 AM-10 AM, 12 PM-1 PM, or 3 PM-4 PM). Most patients with SS and patients with blepharitis were taking systemic or topical dry eye medications at the time of enrollment.
  
  
  METHODS
  Mean osmolarity and its variability calculated from a linear mixed model for each disease group that accounts for the variations attributable to different patients, eyes, and sessions and measurement error specific to each disease group.
  
  
  RESULTS
  Mean tear osmolarity was 307 mOsm/L, 304 mOsm/L, and 301 mOsm/L in the SS, blepharitis, and control groups, respectively (P = .46). The error associated with repeated measurements within a session in the patients without dry eye (10.5 mOsm/L [95% CI, 9.0-12.4]) was significantly lower than in the patients with blepharitis (14.6 mOsm/L [95% CI, 12.5-17.5]; P = .006) and patients with SS (15.8 mOsm/L [95% CI, 14.2-17.8]; P < .001) but a difference in the error of repeated measurements between patients with blepharitis and patients with SS was not identified (P = .46).
  
  
  CONCLUSIONS
  There was increased variability attributable to error in repeated measurements in patients with SS and patients with blepharitis compared with control participants. The high variability of TearLab osmolarity readings in all groups makes the clinical interpretation of measurements unclear.
authors: Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia.
authors: Vatinee Y
authors: VY
authors: Bunya
authors: Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia.
authors: Nicole M
authors: NM
authors: Fuerst
authors: Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia.
authors: Maxwell
authors: M
authors: Pistilli
authors: Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia.
authors: Bridgette E
authors: BE
authors: McCabe
authors: Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia.
authors: Rebecca
authors: R
authors: Salvo
authors: Campus Biomedico University, Rome, Italy.
authors: Ilaria
authors: I
authors: Macchi
authors: Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia.
authors: Gui-Shuang
authors: GS
authors: Ying
authors: Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia.
authors: Mina
authors: M
authors: Massaro-Giordano
mesh_terms: D000328:Adult; D000368:Aged; D001762:Blepharitis / Q000175:diagnosis*; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009994:Osmolar Concentration; D012859:Sjogren's Syndrome / Q000175:diagnosis*; D013666:Tears / Q000737:chemistry*