Purchase this article with an account.
S.B. Flynn, J. Dhaliwal, T. Realini, J. Pittenger, T. Redens; Is Cup–Disc Ratio Perceivable? . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5589.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: The clinical utility of cup–disc ratio (CDR) estimation presupposes a basic cognitive–perceptual capacity to assess the spatial relationship of nested figures. The present study evaluated this presupposition. Methods: 42 medical students participated as observers. In the estimation task, observers were presented 7 schematic stimuli consisting of 2 concentric circles. The outer circle’s size was kept constant, while the inner circle’s size varied across stimuli. For each stimulus, half of the observers estimated the area ratio of the circles, and half estimated the vertical–height ratio. In the production task, the same observers were given 7 sheets of paper, each with a single circle the same size as the outer circle above. On each sheet, observers drew a circle, centered within the outer circle, to produce a specified area or height ratio ranging from 0.05 to 0.95. The drawings were digitized, and actual ratios were calculated via image–analysis software. Results: Data were analyzed via linear and polynomial regression. In the area–ratio condition, the relationship between actual and perceived ratio was strongly nonlinear; polynomial regression yielded significant (p<0.001) first– and second–order trends. Thus, on average, observers were unable to accurately ascertain the area ratio of nested figures. In contrast, for the vertical–ratio condition, the pooled data were strongly and reliably linear, with an overall slope and intercept of 1.01 and 0.015, respectively. Thus, on average, observers were able to ascertain the vertical ratio of nested figures. However, there were considerable differences among individual observers, with regression slopes for individuals ranging from 0.76 to 1.16. Conclusions: The basic cognitive–perceptual mapping between actual and perceived area ratio is nonlinear. Because of this, area–based CDR estimates are likely to be inaccurate. In contrast, the mapping between actual and perceived vertical ratio is, on average, highly accurate. However, substantial individual differences exist and likely contribute to interobserver variability in clinical estimates of CDR.
This PDF is available to Subscribers Only