Comparison of Two, Three and Four 45-degree Image Fields with the Topcon CRW6 Non-mydriatic Camera for the Screening of Diabetic Retinopathy

Abstract

Abstract: : Purpose: To evaluate the optimal number and positioning of photographic fields necessary to screen for diabetic retinopathy (DR) with the Topcon CRW6 45-degree non-mydriatic camera. Methods: A prospective, masked, cross-sectional, comparative study of DR grading using two, three and four non-mydriatic 45^o fundus images compared to the ETDRS seven standard stereoscopic 30^o photographic fields. Results: The addition of one or two non-mydriatic 45^o image fields to two fields centred respectively on the disc and the macula did not augment the sensitivity or the specificity of screening either for detection of any DR or clinically significant one. Screening for detection of any DR (ETDRS > 10) using only the two central fields centred on the disc and on the macula resulted in a 95.7% sensitivity and a 78.1% specificity while detection using additional image fields resulted in sensitivities and specificities of respectively 97.6% and 71.9% using 3 image fields and 97.6% and 65.6% using 4 image fields. Compared to the 35 mm seven standard stereoscopic fields, detection of clinically significant DR disease (ETDRS grade≥35) had sensitivities of respectively 87.5%, 88.9% and 88.9% and specificities of respectively 92.3%, 84.6% and 91.9%. The use of additional image fields resulted in a 6.2% augmentation of the referral rate to an ophthalmologist because of unmet image quality requirements. Concomitantly, the rate of detected pathology decreased with the use of additional fields causing a net global increase of the referral rate of 3.2%. Conclusions: The use of additional image fields to the two non-mydriatic 45^o image fields centred on the disc and the macula with the Topcon CRW6 non-mydriatic camera did not significantly increase neither the sensitivity nor the specificity of screening for DR. Contrary to the desired effect, the addition of fields resulted in a diminished utility and cost efficiency of this screening approach for DR. In a non-mydriatic camera screening strategy where the Topcon CRW6 camera is chosen, the capture of two 45^o image fields centred on the disc and on the macula is the most efficient approach.

Keywords: diabetic retinopathy • clinical (human) or epidemiologic studies: sys • imaging/image analysis: clinical