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Eric B. Papas; Key Factors in the Subjective and Objective Assessment of Conjunctival Erythema. Invest. Ophthalmol. Vis. Sci. 2000;41(3):687-691.
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© ARVO (1962-2015); The Authors (2016-present)
purpose. To establish objectively measurable characteristics of the conjunctival
vasculature that correspond with the judgment of erythema by human
methods. Color images of bulbar conjunctiva from 21 subjects were
digitally analyzed to extract the following variables characteristic of
the scene: vessel width (W), number of vessels
(V), proportion of area occupied by vessels
(PA), relative redness both in vessels
(RRV) and in the whole image
(RRI), red-green difference both in vessels
(RGV) and in the whole image
(RGI), red-blue difference both in vessels
(RBV) and in the whole image
(RBI), and red hue value
(RHV). These data were compared with subjective
judgments by a panel of seven trained observers who independently rated
erythema in the same images, using a 0 to 4 scale with decimal
interpolation between grades.
results. Correlation analysis indicated significant associations
(P < 0.05) between the mean response of the human
observers and all the objective variables except RHV.
Associations with the morphometric variables PA (R 2 = 0.93) and V (R 2 = 0.90) were markedly stronger than
for the best colorimetric variable RBV (R 2 = 0.62).
conclusions. Judgments of erythema made by human observers do not rely primarily on
color but can be closely approximated by a univariate, linear model
involving only the proportion of the scene occupied by vessels. Under
the conditions of this study, grading of erythema by trained observers
can be considered to constitute measurement to at least an interval
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