title: Instability of 24-hour intraocular pressure fluctuation in healthy young subjects: a prospective, cross-sectional study.
abstract: BACKGROUND
  Elevated intraocular pressure (IOP) is a major risk factor for the development and/or progression of glaucoma, and a large diurnal IOP fluctuation has been identified as an independent risk factor of glaucoma progression. However, most previous studies have not considered the repeatability of 24-hour IOP measurements. The aim of this study was to evaluate the instability of 24-hour IOP fluctuations in healthy young subjects.
  
  
  METHODS
  Ten healthy young volunteers participated in this prospective, cross-sectional study. Each subject underwent 24-hour IOP and systolic/diastolic blood pressure (SBP/DBP) assessments both in sitting and supine positions every 3 hours, once a week for 5 consecutive weeks. Mean ocular perfusion pressure (MOPP) was then calculated for both positions. The intraclass correlation coefficients (ICCs) of maximum, minimum, and fluctuation parameters were computed for IOP, SBP/DBP, and MOPP. Fluctuation was defined as the difference between maximum and minimum values during a day.
  
  
  RESULTS
  Among the serial measurements taken over a 24-hour rhythm, the maximum/minimum values of IOP, as well as BP, showed excellent agreement: regardless of position, all ICC values were over 0.800. Most of the BP fluctuation values also showed excellent agreement. IOP fluctuation, however, did not show excellent agreement; the ICC of sitting IOP fluctuation was just 0.212. MOPP fluctuation also showed poor agreement, especially in the sitting position (ICC, 0.003).
  
  
  CONCLUSIONS
  On a day to day basis, 24-hour IOP fluctuations were not highly reproducible in healthy young volunteers. Our results imply that a single 24-hour IOP assessment may not be a sufficient or suitable way to characterize circadian IOP fluctuations for individual subjects.
authors.forename: Yoo Kyung
authors.initials: YK
authors.lastname: Song
authors.forename: Chang-Kyu
authors.initials: CK
authors.lastname: Lee
authors.forename: Jiwon
authors.initials: J
authors.lastname: Kim
authors.affiliation: Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Republic of Korea. samini@yuhs.ac.
authors.forename: Samin
authors.initials: S
authors.lastname: Hong
authors.forename: Chan Yun
authors.initials: CY
authors.lastname: Kim
authors.forename: Gong Je
authors.initials: GJ
authors.lastname: Seong
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D003430:Cross-Sectional Studies; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D011187:Posture; D011446:Prospective Studies; D015203:Reproducibility of Results; D014065:Tonometry, Ocular