11.3Fundus Camera

No commercially available fundus camera systems meet all of the outlined requirements. In particular, the cost of the equipment necessary to acquire digital images is a major barrier to wide spread use by primary care physicians. Furthermore, most existing cameras do not include automated data transfer or reporting modalities. The DigiScope® (EyeTel Imaging, Inc., Columbia, MD) was designed by the Johns Hopkins University Ophthalmic Physics Laboratory specifically to address, in the primary care arena, the challenge of detecting diabetic retinopathy requiring referral to an ophthalmologist. The DigiScope® has effective automated functions including pupil alignment, fundus focusing, adjustment of illumination, and image acquisition that alleviate the need for a trained photographer [2]. The instrument is manufactured in China and has several unique features that allow the production cost to remain significantly below that of other commercially available retinal cameras. The camera chip produces redfree, monochromatic images. While producing monochromatic images requires less expensive instrumentation than to obtain color images, it has also been demonstrated that red-free imaging enhances contrast and eases visualization of vascular lesions including microaneurysms, hemorrhages, and neovascularization (Fig. 11.1) which are characteristic of diabetic retinopathy [3]. Rather than using the typical 30° single image as is common with other fundus cameras, the instrument acquires a series of ten frames for each eye that are viewed as a mosaic with coverage of approximately 45–50° of the posterior pole and a total resolution of 1,840 by 1,220 pixels. By acquiring a series of small images which are viewed as a mosaic, utilization of a less expensive camera chip is possible.

The American Academy of Ophthalmology and the American Telemedicine Association stress the importance of validation of diabetic retinopathy assessment systems [4, 5]. The grading of Early Treatment Diabetic Retinopathy Study (ETDRS) seven standard field stereoscopic color fundus photographs using the modified Airlie House classification is considered

Fig. 11.1 Example of neovascularization at the disc with standard color fundus image (left image) and red-free DigiScope® image (right image) demonstrating enhancement of vascular features with red-free viewing

the gold standard for determining the severity of diabetic retinopathy [6]. The DigiScope® has been independently validated against this gold