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

Purpose To describe and assess the clinical impact of 'local contrast enhancement' on oral fluorescein angiograms. Methods Oral fluorescein angiograms (OFA) were performed on 12 patients with a range of diabetic retinopathy. The digital images were processed using two enhancement techniques: histogram equalisation, a widely available method; and 'local contrast enhancement'. Twelve control images and 24 enhanced images were randomised and subjectively graded for clarity between 1 and 100 on a visual analogue scale by two masked observers. A score of 50% was chosen as the cat-off for clinically useful images. Results The mean score for the unenhanced images was 38.8% (SD 19.4); the histogram equalisation performed better at 54.7% (SD 10.0) (p = 0.016) and local contrast enhancement' at 69.4% (SD 13.6) (p < 0.001). These results equate 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 58.3% 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 enhancement' techniques for low-contrast fluorescein angiograms. Using local contrast enhancement' oral fluorescein angiograms can give high-quality images and may allow safer patient investigation.