title: Influence of corneal astigmatism, corneal curvature and meridional differences on corneal hysteresis and corneal resistance factor.
abstract: BACKGROUND
  This study investigated the influence of corneal astigmatism, corneal curvature and meridional differences on corneal hysteresis (CH) and the corneal resistance factor (CRF) in a group of normal Chinese persons.
  
  
  METHODS
  Ninety-five participants were recruited and data from the eye with higher corneal astigmatism were analysed. The anterior corneal curvature was measured by corneal topography. The Goldmann-correlated intraocular pressure (IOPg), corneal-compensated intraocular pressure (IOPcc), CH and CRF at different meridians (default horizontal position, 10°, 20° and 30° along the superotemporal and inferonasal meridians) were obtained from an ocular response analyser. The corneal powers at these specific meridians also were calculated.
  
  
  RESULTS
  At the default position, the IOPg and CRF had weak correlations with corneal astigmatism, while the IOPcc and CH were not significantly correlated with corneal astigmatism. Both the IOPg and IOPcc were measured significantly higher at the default position. The CH and CRF were lower at the default position but the difference in the CRF from obliquity could not reach statistical significance. The CH was not significantly correlated with the corneal power at all meridians. The CRF correlated with the corneal power only at 30° superotemporal.
  
  
  CONCLUSIONS
  Corneal astigmatism and head tilt did not have much effect on the measurement of CH and the CRF, both of which were lowest along the horizontal meridian. Clinically, the difference was small. The influence of corneal power on CH and the CRF was minimal.
authors: School of Optometry, The Hong Kong Polytechnic University, Hong Kong SAR, China.
authors: Yin-zhi
authors: YZ
authors: Wong
authors: Andrew K C
authors: AK
authors: Lam
mesh_terms: D000328:Adult; D044466:Asian People; D001251:Astigmatism / Q000473:pathology* / Q000503:physiopathology*; D001696:Biomechanical Phenomena / Q000502:physiology; D003315:Cornea / Q000473:pathology* / Q000503:physiopathology*; D004548:Elasticity / Q000502:physiology; D005260:Female; D006257:Head; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D011187:Posture; D014065:Tonometry, Ocular; D055815:Young Adult