title: Variability of intraocular pressure measurements in observation participants in the ocular hypertension treatment study.
abstract: OBJECTIVE
  To describe variability of intraocular pressure (IOP) measurements within the same eye and between right and left eyes over a 60-month period in participants in the Ocular Hypertension Treatment Study.
  
  
  METHODS
  Analysis of data from a prospective, randomized clinical trial.
  
  
  METHODS
  Eight hundred ten participants randomized to the observation group.
  
  
  METHODS
  Intraocular pressure measurements were obtained at the baseline visit and every 6 months thereafter. Pearson correlation coefficients were calculated for IOP measurements in the same eye between visits and for IOP measurements between right and left eyes of participants at each visit. Differences in IOP measurements between visits are reported in percent change (>15%, >20%, and >30%) and in millimeters of mercury (<3 mmHg, 3-5 mmHg, and >5 mmHg). The effects of regression to the mean, consistency in time of day, and sequence of IOP measurement of right and left eyes were examined.
  
  
  METHODS
  Correlation of IOP measurements between consecutive 6-month visits.
  
  
  RESULTS
  The correlation of IOP measurements within the same eye between consecutive visits was r = 0.62, whereas the correlation of IOP measurements between right and left eyes at the same visit was r = 0.72. Thirteen percent of eyes had >20% change in IOP between consecutive visits. Sixty-six percent of eyes had a change in IOP within 3 mmHg, and 10% of eyes had a change in IOP >5 mmHg between visits. Eyes with a higher baseline IOP had a lower IOP at 6 months. There was a stronger correlation of IOP measured within 2 hours of the time of day between visits (r = 0.56) than >2 hours apart (r = 0.39). IOP of the right eye, which was measured first, was 0.3+/-2.8 mmHg higher than the left eye.
  
  
  CONCLUSIONS
  The variability of IOP measurements in the same eye between consecutive visits is moderate and is greater than the variability of IOP measurements between right and left eyes at the same visit. Factors affecting the variability of IOP measurement include regression to the mean, time of day, and measurement order. Knowledge of variability in IOP and its measurements may help clinicians establish a more accurate baseline IOP, target IOP, and assessment of medication effect.
authors.affiliation: Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Anjali M
authors.initials: AM
authors.lastname: Bhorade
authors.forename: Mae O
authors.initials: MO
authors.lastname: Gordon
authors.forename: Brad
authors.initials: B
authors.lastname: Wilson
authors.forename: Robert N
authors.initials: RN
authors.lastname: Weinreb
authors.forename: Robert N
authors.initials: RN
authors.lastname: Weinrab
authors.forename: Michael A
authors.initials: MA
authors.lastname: Kass
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000959:Antihypertensive Agents / Q000627:therapeutic use; D002940:Circadian Rhythm / Q000502:physiology; D005260:Female; D005500:Follow-Up Studies; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D019370:Observation; D009798:Ocular Hypertension / Q000188:drug therapy / Q000503:physiopathology*; D009819:Office Visits; D011446:Prospective Studies; D014065:Tonometry, Ocular
chemical_list: D000959:Antihypertensive Agents