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F. Pan, W.H. Swanson, M.W. Dul; Evaluation of the Cortical Pooling Model of Glaucomatous Defects . Invest. Ophthalmol. Vis. Sci. 2003;44(13):56.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: A quantitative model of perimetry in glaucoma predicts that both low test-retest variability and good sensitivity to defect can be achieved with stimuli that maximize the number of ganglion cells whose responses are pooled by the cortical mechanisms which mediate visual thresholds. Here we evaluate predictions of the model. Methods: To maximize the number of ganglion cells whose responses are pooled by cortical mechanisms, two new types of stimuli were used: a 0.5 cycle/deg luminance Gabor stimulus and circular equiluminant chromatic (L-M) stimuli close in size to the critical area of the L-M mechanism. A standard stimulus (luminance increment 0.43° in diameter) was also used. Stimuli were displayed temporally as Gaussian pulses on a 21" monitor driven by a VSG2/5 video controller. The background was an equal-energy white subtending 27° by 21°. Background luminance was 50 cd/m2 for the Gabor and the chromatic stimuli, and 10 cd/m2 for the standard stimulus. Thresholds were measured at 8 locations in the visual field at 9.5°, 15° and 21° eccentricity. Nineteen patients with glaucoma and twenty age-similar normal observers were each tested twice within a 2-week period. Results: Contrast sensitivities of patients were transformed into depth of defect using normative data. Mean depth of defect was slightly lower for the chromatic stimuli but this was not statistically significant (F=2.54, p>0.08), and lower normal variability for the chromatic stimuli (F=2.73, p<0.05) actually resulted in more abnormal points for the chromatic stimuli than for the standard stimulus (Chi-square=73.3, p<0.0005). A one-way within-subjects ANOVA found a significant effect of stimulus on test-retest variability (F=5.54, p<0.005); Tukey’s HSD test showed variability was lower for the chromatic stimuli than for the standard stimulus (p<0.05). In areas with defects greater than 4dB, test-retest variability was significantly lower for the Gabor stimulus than for the standard stimulus (t=2.69, p<0.02). Conclusions: As predicted, the two new types of stimuli have advantages over the standard stimulus in that test-retest variability can be reduced, and at the same time sensitivity to defect can be maintained.
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