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. 2004 Nov;88(11):1434-8.
doi: 10.1136/bjo.2004.045534.

Incremental nature of anterior eye grading scales determined by objective image analysis

J S Wolffsohn  1
Affiliations

Incremental nature of anterior eye grading scales determined by objective image analysis

J S Wolffsohn. Br J Ophthalmol. 2004 Nov.

Abstract

Aim: To use previously validated image analysis techniques to determine the incremental nature of printed subjective anterior eye grading scales.

Methods: A purpose designed computer program was written to detect edges using a 3 x 3 kernal and to extract colour planes in the selected area of an image. Annunziato and Efron pictorial, and CCLRU and Vistakon-Synoptik photographic grades of bulbar hyperaemia, palpebral hyperaemia roughness, and corneal staining were analysed.

Results: The increments of the grading scales were best described by a quadratic rather than a linear function. Edge detection and colour extraction image analysis for bulbar hyperaemia (r2 = 0.35-0.99), palpebral hyperaemia (r2 = 0.71-0.99), palpebral roughness (r2 = 0.30-0.94), and corneal staining (r2 = 0.57-0.99) correlated well with scale grades, although the increments varied in magnitude and direction between different scales. Repeated image analysis measures had a 95% confidence interval of between 0.02 (colour extraction) and 0.10 (edge detection) scale units (on a 0-4 scale).

Conclusion: The printed grading scales were more sensitive for grading features of low severity, but grades were not comparable between grading scales. Palpebral hyperaemia and staining grading is complicated by the variable presentations possible. Image analysis techniques are 6-35 times more repeatable than subjective grading, with a sensitivity of 1.2-2.8% of the scale.

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Figures

Figure 1
Figure 1
Example of edge detection and colour extraction techniques applied to a selected (dashed rectangle) area of an image of bulbar hyperaemia.
Figure 2
Figure 2
Edge detection (filled symbols) and relative red colouration (open symbols) with grading scale images of bulbar hyperaemia. Error bars = 1 SD.
Figure 3
Figure 3
Edge detection (filled symbols) and relative red colouration (open symbols) with grading scale images of palpebral hyperaemia. Error bars = 1 SD.
Figure 4
Figure 4
Edge detection (filled symbols) and relative red/green colouration (open symbols) with grading scale images of palpebral roughness. Error bars = 1 SD.
Figure 5
Figure 5
Edge detection (filled symbols) and relative green colouration (closed symbols) with grading scale images of corneal staining. Error bars = 1 SD.
See this image and copyright information in PMC

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