Technical Note: grading the vertical cup:disc ratio and the effect of scaling

Ruth Bennett, Paul G D Spry, Cecilia H Fenerty, Robert A Harper

    Research output: Contribution to journalArticlepeer-review


    PURPOSE: To evaluate the effect of scaling on sensitivity to change for grading the vertical cup:disc ratio (CDR).

    METHODS: Vertical CDR was assessed by six observers (three ophthalmologists and three optometrists) on 43 stereo disc photographs. Repeated observations were made for both 0.1 and 0.05 interval scales. Paired differences were calculated for all observers and each observer separately. Mean and standard deviation of differences and agreement statistics were used to compare scales.

    RESULTS: Five observers demonstrated a reduction in the spread of differences (mean difference 0.19 to 0.15) and all observers demonstrated a reduction in concordance using the finer scale (mean concordance 54% to 39%).

    CONCLUSION: The use of a finer scale reduces test-retest variability and increases sensitivity to change when estimating the vertical CDR. Use of this scale does not require any additional resource and it may be easily implemented in routine clinical practice.

    Original languageEnglish
    Pages (from-to)619-25
    Number of pages7
    JournalOphthalmic & physiological optics : the journal of the British College of Ophthalmic Opticians (Optometrists)
    Issue number6
    Publication statusPublished - Nov 2007


    • Clinical Competence
    • Confidence Intervals
    • Diagnostic Techniques, Ophthalmological
    • Glaucoma
    • Humans
    • Observer Variation
    • Optic Disk
    • Reproducibility of Results
    • Sensitivity and Specificity
    • Journal Article


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