title: Effect of head tilt on repeatability of optic nerve head parameters using cirrus spectral-domain optical coherence tomography.
abstract: OBJECTIVE
  To assess the repeatability of measuring optic nerve head (ONH) parameters using the Cirrus optical coherence tomography (OCT), as well as to assess the effect of head tilt on these measurements.
  
  
  METHODS
  Thirty healthy participants with no evidence of glaucoma were recruited for the study. Visual acuity, intraocular pressure, standard automated perimetry and ocular examination were performed for each participant. One eye was then randomly selected and scanned undilated with the Cirrus OCT in 3 positions (neutral, 30° right tilt and 30° left tilt).
  
  
  RESULTS
  Data collected from 29 eyes were used for analysis. One patient was omitted due to poor scan quality. The repeatability of the ONH parameters was analyzed using analysis of variance, coefficient of variation (COV) and intraclass correlation coefficient (ICC). Analysis of variance showed no statistically significant difference between 3 scans in a single position. There was good agreement between measurements (ICC 0.919-0.996, COV 1.94%-5.48%). Even with the presence of head tilt, repeated scans in the 3 positions showed good agreement as well (ICC 0.888-0.996, COV 2.04%-5.39%).
  
  
  CONCLUSIONS
  Serial measurements of ONH parameters using the Cirrus OCT are found to have good repeatability. The ONH parameters with Cirrus OCT also maintain good repeatability despite head tilt.
authors: Department of Ophthalmology, Tan Tock Seng Hospital, National Healthcare Group Eye Institute, 308433, Singapore.
authors: Lilian Hui Li
authors: LH
authors: Koh
authors: Department of Ophthalmology, Tan Tock Seng Hospital, National Healthcare Group Eye Institute, 308433, Singapore.
authors: Muhammad Amir
authors: MA
authors: Ismail
authors: Department of Ophthalmology, Tan Tock Seng Hospital, National Healthcare Group Eye Institute, 308433, Singapore.
authors: Sae Cheong
authors: SC
authors: Yap
authors: Department of Ophthalmology, Tan Tock Seng Hospital, National Healthcare Group Eye Institute, 308433, Singapore.
authors: Elizabeth Poh Ying
authors: EP
authors: Wong
authors: Department of Ophthalmology, Tan Tock Seng Hospital, National Healthcare Group Eye Institute, 308433, Singapore.
authors: Leonard Wei Leon
authors: LW
authors: Yip
keywords: artifacts; glaucoma; head movements; imaging; optical coherence tomography