title: Neural rim characteristics of healthy South Indians: the Chennai Glaucoma Study.
abstract: OBJECTIVE
  To report neural rim dimensions for South Indians and examine rim shape with relevance to clinical evaluation.
  
  
  METHODS
  Healthy phakic participants (n = 623) of the Chennai Glaucoma Study with normal frequency-doubling perimetry underwent complete eye examinations including optic disc digital stereophotography. Planimetry was performed under stereoviewing conditions using custom software. Rim area, shape, and associations were examined. Rim area asymmetry was studied in a subgroup of 565 subjects.
  
  
  RESULTS
  Mean neuroretinal rim area was 2.29 +/- 0.39 mm(2). Disc area (P < 0.001) and type of cupping (P < 0.001) were associated with rim area. Mean rim area asymmetry was 0.18 +/- 0.15 mm(2); 95% of subjects had asymmetry < 0.5 mm(2). Disc area asymmetry (0.359, P < 0.0001) and intraocular pressure (IOP) asymmetry (P = 0.004) were related to rim area asymmetry. On average, the inferior rim was thickest and the temporal was thinnest. Mean inferior by superior rim width was 1.18 +/- 0.17; 2.5 percentile, 0.9. Thirty-eight (7.1%) subjects had the superior rim thicker than the inferior rim, the occurrence of which was associated with disc torsion (P = 0.002) and male sex (P = 0.04). Of the clinically relevant rim width measures in glaucoma (i.e., inferior, superior, and temporal) the temporal rim was thinnest in 469 (87.8%) eyes. Horizontally oval disc shape (P < 0.0001), type of cupping (P = 0.006), and astigmatism (P = 0.001) were associated with the presence of thicker temporal than superior/inferior rims.
  
  
  CONCLUSIONS
  The report provides hitherto unreported neural rim measurements among healthy South Indians. The ISNT rule (inferior rim thicker than superior rim, thicker than nasal rim, thicker than temporal rim) was violated in a significant minority. Physiological associations with such violations are described.
authors.affiliation: Medical and Vision Research Foundations, Sankara Nethralaya, Chennai, India.
authors.forename: Hemamalini
authors.initials: H
authors.lastname: Arvind
authors.forename: Ronnie
authors.initials: R
authors.lastname: George
authors.forename: Prema
authors.initials: P
authors.lastname: Raju
authors.forename: Ramesh S
authors.initials: RS
authors.lastname: Ve
authors.forename: Baskaran
authors.initials: B
authors.lastname: Mani
authors.forename: Prashanth
authors.initials: P
authors.lastname: Kannan
authors.forename: Lingam
authors.initials: L
authors.lastname: Vijaya
mesh_terms: D001369:Axons / Q000502:physiology*; D005260:Female; D006801:Humans; D007194:India; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D009898:Optic Disk / Q000033:anatomy & histology*; D012165:Retinal Ganglion Cells / Q000166:cytology*; D058609:Visual Field Tests