Clinical evaluation of 'local contrast enhancement' for oral fluorescein angiograms

Purpose To describe and assess the clinical impact of 'local contrast enhan cement' on oral fluorescein angiograms. Methods Oral fluorescein angiograms (OFA) were performed on 12 patients wit h a range of diabetic retinopathy. The digital images were processed using two enhancement techniques: histogram equalisation, a widely available meth od; and 'local contrast enhancement'. Twelve control images and 24 enhanced images were randomised and subjectively graded for clarity between 1 and 1 00 on a visual analogue scale by two masked observers. A score of 50% was c hosen as the cat-off for clinically useful images. Results The mean score for the unenhanced images was 38.8% (SD 19.4); the h istogram equalisation performed better at 54.7% (SD 10.0) (p = 0.016) and l ocal contrast enhancement' at 69.4% (SD 13.6) (p < 0.001). These results eq uate to a 14.7% improvement in comparison with histogram equalisation and a 30.3% improvement with the 'local contrast enhancement' technique. All the local contrast enhancement' images were clinically useful, compared with 5 8.3% Of the histogram equalisation images (chi(2) 2.08, p = 0.2), and 33.3% of the control images (chi(2) = 6.75, P = 0.01). Conclusion This pilot study has demonstrated the power of local contrast en hancement' techniques for low-contrast fluorescein angiograms. Using local contrast enhancement' oral fluorescein angiograms can give high-quality ima ges and may allow safer patient investigation.