May 2004
Volume 45, Issue 13
ARVO Annual Meeting Abstract  |   May 2004
Morphological Determinants of Cup–Disc Ratio Estimation
Author Affiliations & Notes
  • T. Realini
    Ophthalmology, West Virginia University, Morgantown, WV
  • S.B. Flynn
    Ophthalmology, Louisiana State University, Shreveport, LA
  • J.B. Pittenger
    Psychology, University of Arkansas Little Rock, Little Rock, AR
  • Footnotes
    Commercial Relationships  T. Realini, None; S.B. Flynn, None; J.B. Pittenger, None.
  • Footnotes
    Support  none
Investigative Ophthalmology & Visual Science May 2004, Vol.45, 5578. doi:
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      T. Realini, S.B. Flynn, J.B. Pittenger; Morphological Determinants of Cup–Disc Ratio Estimation . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5578.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract: : Purpose: Significant inter–observer and intra–observer variability exists in judging cup–disc ratio (CDR). This study seeks to identify the morphological basis for C/D judgment: what aspect of the nerve determines observers’ clinical estimation of CDR? Methods: A series of 9 monoscopic photographs of optic nerves, representing the CDR spectrum from 0.1 to 0.9, were projected on a screen, and 20 ophthalmologists and 1 optometrist were asked to describe the CDR using a decimal between 0 and 1. Separately, we used image–analysis software to determine the CDR for each of the nine images by three different definitions: vertical CDR (VCDR—the ratio of the longest vertical dimension of the cup divided by the longest vertical dimension of the disc), horizontal CDR (HCDR—analogous to VCDR), and area CDR (ACDR—the two–dimensional cup area divided by the two–dimensional disc area). Linear regression of participant judgment against each of the three definitions was performed to determine which definition best captured the judgment strategy of the participants. Results: Of the three definitions of CDR, regression against VCDR gave the closest to ideal fit, with participants slightly underestimating CDR for smaller CDRs and overestimating CDR for larger CDRs. A similar pattern with greater error at both ends of the CDR spectrum was seen with the HCDR definition. By the ACDR definition, participant CDR judgments were overestimates for CDRs of all sizes. 

Conclusions: No single parametric definition of CDR fully described the participants’ strategies for judging CDR. The CDR estimation process likely differed among participants based on individual differences in both perception and description. These inter–individual differences may account for part of the inter–observer variability seen in existing studies of CDR estimation.

Keywords: optic disc • anatomy • perception 

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