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Screening for Sight-threatening Retinopathy: Comparison of Fundus Photography with Automated Color Contrast Threshold Test

journal contribution
posted on 2023-06-07, 22:49 authored by Gek L Ong, Lionel G Ripley, Richard S Newsom, Matthew Cooper, Anthony G Casswell
Purpose: To compare tritan contrast threshold (TCT) with fundus photography in screening for sight-threatening diabetic retinopathy (STDR), before significant visual loss. Design: Prospective, comparative study. Methods: A total of 510 consenting diabetic patients attending a hospital-based photographic screening clinic were recruited over a 2-year period. Exclusion criteria included visual acuity of worse than 6/9, previous photocoagulation, and a history of previous eye disease known to affect color vision. The automated TCT test was performed using a computerized cathode ray tube-based technique. Retinal photography was performed using a Polaroid mydriatic fundus camera with a 45 degrees field. Grading of diabetic retinopathy was carried out by an ophthalmologist using slit-lamp biomicroscopy and a 78-diopters lens. Assessments of sensitivity, specificity, and predictive values for both fundus photography and the TCT test were made. Results: Both the fundus photography and TCT test correlated significantly with the presence of STDR (P < .0001, 2 test). The TCT test yielded a sensitivity of 94% (95% confidence interval [CI], 73%¿ 100%) and a specificity of 95% (95% CI, 92%¿ 96%) for detection of STDR compared with a sensitivity of 88% (95% CI, 66%-97%) and a specificity of 95% (95% CI, 93%¿97%) with fundus photography. Combined modality improved overall screening performance. Conclusion: The TCT assessment is an effective and clinically viable technique, in comparison with fundus photography, to screen for STDR among a diabetic population. Additionally, our results also showed that combining the TCT test with fundus photography greatly increases the performance of screening for STDR.


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American Journal of Ophthalmology







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  • Engineering and Design Publications


Colour-vision deficit is identified as a better basis for screening for sight-threatening diabetic retinopathy than the currently preferred fundus photography which is improving with the advent of modern digital cameras but these and the SGM/SCS are relatively expensive, static apparatus and this has led to the development of the Trafford Anomaloscope (red/green) and the Sussex Anomaloscope (tritan) which are cheap, portable, desk-top instruments for colour-vision assessment. Clinical trials are proving successful and have led to industrial sponsorship from Peca Electronics ( and to the adoption of these new machines for a retinopathy screening programme in the Australian outback. (Patent GB2411010).

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