title: Diurnal variation of ocular hysteresis in normal subjects: relevance in clinical context.
abstract: BACKGROUND
  This study was conducted to assess the diurnal variation in ocular hysteresis, as measured by the Ocular Response Analyser to establish a relationship between diurnal hysteresis variation and diurnal intraocular pressure (IOP) variation.
  
  
  METHODS
  Forty-two normal eyes of 21 colleagues and staff in a teaching hospital in Birmingham, UK, were recruited. The IOP and hysteresis were measured by the Ocular Response Analyser. The central corneal thickness (CCT) was measured using a hand-held ultrasonic pachymeter in the mid-pupillary axis.
  
  
  RESULTS
  The mean ocular hysteresis at 8 am was 12.7 +/- 2.3 mmHg, at 11 am was 12.2 +/- 2.0 mmHg, at 2 PM was 12.7 +/- 2.1 mmHg and at 5 PM was 12.7 +/- 1.7 mmHg; the difference between the values at any time of measurement was not statistically significant (P > 0.9, repeated measures). IOP as measured by non-contact tonometry was 18.4 +/- 2.8 mmHg, 17.9 +/- 3.3 mmHg, 16.9 +/- 3.1 mmHg and 16.8 +/- 3.2 mmHg, respectively, for the same time period; the difference between the values in the morning and afternoon was statistically significant (P < 0.0001, repeated measures). The CCT was 548.8 +/- 29.5 microm, 547.0 +/- 31.4 microm, 548.2 +/- 29.6 microm and 548.6 +/- 29.4 microm, respectively; the difference between the values was not statistically significant at any time points. Multiple regression analysis showed the relationship between IOP and hysteresis was not statistically significant (P = 0.9).
  
  
  CONCLUSIONS
  The ocular hysteresis reading was almost constant throughout the day, whereas the IOP readings showed highest values in the morning with a reducing trend being lowest in the afternoon. The CCT values were almost stable throughout the day. IOP appears to vary independently of a variation in hysteresis or CCT.
authors.affiliation: Birmingham Heartlands and Solihull NHS Trust, Solihull, UK.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Laiquzzaman
authors.forename: Rajan
authors.initials: R
authors.lastname: Bhojwani
authors.forename: Ian
authors.initials: I
authors.lastname: Cunliffe
authors.forename: Sunil
authors.initials: S
authors.lastname: Shah
mesh_terms: D000328:Adult; D000368:Aged; D002940:Circadian Rhythm / Q000502:physiology*; D003187:Compliance; D003315:Cornea / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D014065:Tonometry, Ocular; D014463:Ultrasonography