title: The use of HRT with and without the aid of disc photographs.
abstract: OBJECTIVE
  To evaluate the measurement of optic disc morphology using Heidelberg Retinal Tomography (HRT) with and without the aid of optic disc photos.
  
  
  METHODS
  One hundred three children (aged 11 and 12 y, 52 boys) were selected randomly from the Singapore Cohort study of Risk Factors for Myopia. Optic nerve head topography and retinal nerve fiber layer thickness measurements were assessed using the HRT-II (Heidelberg, Germany) scanning laser ophthalmoscope. All contour lines were drawn by the same researcher on 2 occasions. The first drawing was made without optic disc photographs but using the 3-dimensional rotation assessment. The second drawing was made with the additional aid of digital monoscopic optic disc photographs.
  
  
  RESULTS
  There was a high correlation between the measurements taken with and without optic disc photographs. For the global disc area, the difference between the mean readings was 0.67 mm and the intraclass correlation (ICC) was 0.81 [95% confidence interval (CI) 0.73-0.86]. The mean difference for the global cup-to-disc ratio was 0.03 [ICC 0.86 (95% CI 0.80-0.90)]. The ICCs were high across almost all of the readings except rim volume, in which the ICC was 0.57 (95% CI 0.43-0.69).
  
  
  CONCLUSIONS
  This study shows minimal differences in HRT measured optic disc parameters when optic disc photos are used to aid in the definition of the scleral ring. Omitting the use of disc photographs in measuring HRT outputs may translate into significant savings in time and logistics in simultaneously obtaining HRT and optic disc photographs in large population-based studies.
authors.affiliation: Department of Ophthalmology, National University Hospital, Singapore National Eye Centre, London, UK. ploonsc@yahoo.com
authors.forename: Seng Chee
authors.initials: SC
authors.lastname: Loon
authors.forename: Louis
authors.initials: L
authors.lastname: Tong
authors.forename: Gus
authors.initials: G
authors.lastname: Gazzard
authors.forename: Yiong Huak
authors.initials: YH
authors.lastname: Chan
authors.forename: Ee Ling
authors.initials: EL
authors.lastname: Sim
authors.forename: Tin
authors.initials: T
authors.lastname: Aung
authors.forename: Donald T H
authors.initials: DT
authors.lastname: Tan
authors.forename: P R
authors.initials: PR
authors.lastname: Healey
authors.forename: Tien Yin
authors.initials: TY
authors.lastname: Wong
authors.forename: Victor
authors.initials: V
authors.lastname: Koh
authors.forename: Seang Mei
authors.initials: SM
authors.lastname: Saw
mesh_terms: D002648:Child; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D008297:Male; D009216:Myopia / Q000175:diagnosis / Q000209:etiology; D009412:Nerve Fibers / Q000473:pathology*; D009887:Ophthalmoscopy / Q000379:methods; D009898:Optic Disk / Q000473:pathology*; D010781:Photography; D012165:Retinal Ganglion Cells / Q000473:pathology*; D012307:Risk Factors; D014054:Tomography / Q000379:methods