Technical Note: grading the vertical cup:disc ratio and the effect of scaling.
OBJECTIVE
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%).


CONCLUSIONS
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.
Bennett
Ruth
R
Ophthalmology Department, Nottingham University Hospitals NHS Trust, Nottingham NG7 2UH, UK.
Spry
Paul G D
PG
Fenerty
Cecilia H
CH
Harper
Robert A
RA
D002983:Clinical Competence / Q000592:standards*; D016001:Confidence Intervals; D003941:Diagnostic Techniques, Ophthalmological; D005901:Glaucoma / Q000175:diagnosis*; D006801:Humans; D015588:Observer Variation; D009898:Optic Disk / Q000473:pathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity