title: Asymmetry in optic disc morphometry as measured by heidelberg retina tomography in a normal elderly population: the Bridlington Eye Assessment Project.
abstract: OBJECTIVE
  To define the normal range of asymmetry in optic disc parameters measured by the Heidelberg Retina Tomograph (HRT II; Heidelberg Engineering GmbH, Dossenheim, Germany) in a normal elderly population.
  
  
  METHODS
  Optic disc analysis of 918 eyes of 459 normal elderly patients was performed. All patients were consecutive in a cohort screened for eye disease. Normality was defined with a normal visual field on automated suprathreshold screening, intraocular pressure less than 22 mm Hg, and minimum corrected visual acuity of 6/12. Asymmetry measures were calculated by subtracting the values of the smaller disc from those of the larger disc.
  
  
  RESULTS
  Subjects' mean age (262 female and 197 male) was 72.6 years (range, 65.5-89.3). There was no significant difference in disc area or rim area between the right and left eyes. Neither rim-to-disc area ratio asymmetry nor rim measurement asymmetries were significantly affected by age or sex. Rim-to-disc area ratio asymmetry was much less affected by the increasing difference in disc size than was absolute rim asymmetry. The 2.5th and 97.5th percentile limits of normality for the rim-to-disc area ratio asymmetry in the global and temporal-inferior analyses were -0.212 and 0.154, and -0.331 and 0.261, respectively.
  
  
  CONCLUSIONS
  The normal range of parameter asymmetry in an age group relevant to glaucoma may be useful in the discrimination of normal from early glaucoma. Asymmetry analysis may improve discriminatory ability by reducing parameter variability based on disc size. The rim-to-disc area ratio asymmetry measure is likely to be the most useful parameter in describing normality with consistency.
authors.affiliation: Department of Ophthalmology, Queen's Medical Centre, Nottingham, UK.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Hawker
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Vernon
authors.forename: Gerard
authors.initials: G
authors.lastname: Ainsworth
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Hillman
authors.forename: Harmish K
authors.initials: HK
authors.lastname: MacNab
authors.forename: Harminder S
authors.initials: HS
authors.lastname: Dua
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D007834:Lasers; D008297:Male; D008403:Mass Screening; D009898:Optic Disk / Q000033:anatomy & histology*; D012016:Reference Values; D014054:Tomography / Q000379:methods; D006113:United Kingdom; D014794:Visual Fields / Q000502:physiology