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Sensitivity and reliability of objective image analysis compared to subjective grading of bulbar hyperaemia
  1. Rachael Claire Peterson1,
  2. James Stuart Wolffsohn2
  1. 1
    Centre for Contact Lens Research, University of Waterloo, Canada
  2. 2
    School of Life and Health Sciences, Ophthalmic Research Group, Aston University, Birmingham, UK
  1. Dr J Wolffsohn, Ophthalmic Research Group, Aston University, Birmingham, B4 7ET, UK; j.s.w.wolffsohn{at}


Aims: To establish the sensitivity and reliability of objective image analysis in direct comparison with subjective grading of bulbar hyperaemia.

Methods: Images of the same eyes were captured with a range of bulbar hyperaemia caused by vasodilation. The progression was recorded and 45 images extracted. The images were objectively analysed on 14 occasions using previously validated edge-detection and colour-extraction techniques. They were also graded by 14 eye-care practitioners (ECPs) and 14 non-clinicians (NCLs) using the Efron scale. Six ECPs repeated the grading on three separate occasions

Results: Subjective grading was only able to differentiate images with differences in grade of 0.70–1.03 Efron units (sensitivity of 0.30–0.53), compared to 0.02–0.09 Efron units with objective techniques (sensitivity of 0.94–0.99). Significant differences were found between ECPs and individual repeats were also inconsistent (p<0.001). Objective analysis was 16× more reliable than subjective analysis. The NCLs used wider ranges of the scale but were more variable than ECPs, implying that training may have an effect on grading.

Conclusions: Objective analysis may offer a new gold standard in anterior ocular examination, and should be developed further as a clinical research tool to allow more highly powered analysis, and to enhance the clinical monitoring of anterior eye disease.

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  • Competing interests: None.

  • Abbreviations:

    coefficient of reliability


    eye-care practitioners


    edge detection




    relative colour extraction