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© 2003 by the American Diabetes Association, Inc.
Letters: Comments and Responses |
Response to Merin and Reeves
1 Ocular Diabetes and Medical Retina Unit, Division of Ophthalmology, Department of Surgery, School of Medicine, University of Santiago de Compostela and Complejo Hospitalario Universitario de Santiago de Compostela, Santiago de Compostela, Spain
2 Department of Physiology, School of Medicine, University of Santiago de Compostela and Complejo Hospitalario Universitario de Santiago de Compostela, Santiago de Compostela, Spain
3 Supercomputation Center of Galicia (CESGA), Santiago de Compostela, Spain
4 Department of Ophthalmology, Hospital Meixoeiro, Vigo, Spain
5 Division of Endocrinology, Department of Medicine, School of Medicine, University of Santiago de Compostela and Complejo Hospitalario Universitario de Santiago de Compostela, Santiago de Compostela, Spain
6 Clinical Epidemiology Unit, School of Medicine, University of Santiago de Compostela and Complejo Hospitalario Universitario de Santiago de Compostela, Santiago de Compostela, Spain
We appreciate the comments of Merin and Reeves (1) concerning our article (2). There is no doubt that image quality is the most crucial aspect of diabetic retinopathy screening. Both spatial and color resolution play an important role in both the acquisition and display devices.
In our study we used the fundus camera Canon CR5-45NM with a Sony video camera (DXC950). Unfortunately, at that time, the system mentioned by the authors of the letter (CR6-45 NM fundus camera with a Canon digital camera) was not available; indeed, though, it offers a relevant improvement over the older configuration.
The system we have used may not be able to provide enough image quality to detect every retinal lesion. It generated image files in JPEG format from a digital image of 800x600 pixels, which is lower than the recommended 1,300x1,000 and much lower than the new cameras that may reach 2,600x2,300 pixels. To minimize image degradation, we used the lowest JPEG compression available in our image grabber (1:3 ratio). However, despite these limitations, our data show that the grading of the retinopathy made after digital image inspection and after direct eye fundus examination shows agreement in the vast majority of cases and, therefore, an adequate follow-up or treatment of most patients could be made. Although JPEG compression may not have been the best choice, a recent article (3) shows that higher compression ratios than the one we used do not produce serious degradation of the images.
We mentioned in our article that we lost image features in high-grade diabetic retinopathy. This was not because of the resolution of our system but because hemorrhages and media opacifications deteriorated the visibility of the retina. We believe they would have been missed even with a higher resolution camera.
The review by Aiello et al. (4) suggests that, at the time their article was written, digital images obtained with nonmydriatic fundus cameras were not a replacement of standard seven-field stereoscopic 30° fundus photography. We did not compare our digital images with standard fundus photography; therefore, we cannot suggest such a replacement. Instead, we showed that there is agreement between digital image inspection and direct fundus examination in grading diabetic retinopathy. Thus, we believe that digital fundus images may be adequate for this purpose. We expect, as Merrin and Reeves mention, that new advances in technology will improve image quality, and will increase not only spatial and color resolution but also time resolution and stereoscopic viewing from which patients may benefit.
Footnotes
Address correspondence to Francisco Gómez-Ulla or Francisco Gonzalez, Department of Ophthalmology, Hospital Provincial de Conxo, C/Ramón Baltar s/n, E-15706, Santiago de Compostela, Spain. E-mail: ciulla{at}usc.es or francisco.gonzalez{at}usc.es.
References
- Merin LM, Reeves D: Technical issues in retinopathy screening (Letter). Diabetes Care 26:965–966, 2003
[Free Full Text]
- Gómez-Ulla F, Fernandez MI, Gonzalez F, Rey P, Rodriguez M, Rodriguez-Cid MJ, Casanueva FF, Tome MA, Garcia-Tobio J, Gude F: Digital retinal images and teleophthalmology for detecting and grading diabetic retinopathy. Diabetes Care 25:1384–1389, 2002
[Abstract/Free Full Text]
- Eikelboom RH, Yogelsan K, Barry CJ, Constable IJ, Tay-Kearney M-L, Jitskaia L, House PH: Methods and limits of digital image compression of retinal images for telemedicine. Invest Ophthalmol Vis Sci 41:1916–1924, 2000
[Abstract/Free Full Text]
- Aiello LP, Gardner TW, King GL, Blankenship G, Cavallerano JD, Ferris FL, Klein R: Diabetic retinopathy. Diabetes Care 21:143–156, 1998[Medline]
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