Diabetic retinopathy is traditionally considered a disease of the posterior pole, primarily early in the disease course. However, recent advances in imaging technology have allowed for improved evaluation of peripheral pathologic changes. Ultra-widefield retinal imaging is a relatively new tool to assess the progression of DR with up to a 200° field of view in a single image, allowing visualization of more than 80% of the retina.
58 Covering the entire field of the retina can be achieved but requires a combination of multiple images of the patient gazing in the cardinal directions. This approach has been used in conjunction with FA to evaluate the peripheral retinal vasculature.
59 Limitations due to the spherical nature of the eye and the flat representation of the fundus image have led to the development and validation of methods to account for distortions.
60 Among these studies, follow-up work defined a specific method to accurately measure retinal lesions in the peripheral region, properly accounting for image distortions.
61 A major limitation of ultra-widefield imaging is that it measures reflectance of retinal structures at narrow bands around specific wavelengths (488, 532, and 633 nm) rather than from multi-wavelength white light. Thus, the resulting images are pseudocolor images, with each color representing the reflectance for that narrow band. Many tissues do not have high reflectance at these specific wavelength bands. According to some authors, ultra-widefield imaging, with or without FA, may lead to significant underestimation of DR levels in 10% to 20% of patients when compared to the standard seven-field ETDRS images.
37,62 In another study, a single ultra-widefield image captured aspects of DR such as nonperfusion, neovascularization, and panretinal photocoagulation scars that were underestimated in the standard seven-field ETDRS images and missed in 10% of cases.
63 Similarly, a subsequent study, using three widefield Optomap (Dunfermline, Scotland) images, reported neovascularization outside of the standard seven-field images in 11% of cases with neovascularization.
64 These studies thus suggest that ultra-widefield imaging may detect more severe DR or a higher rate of neovascularization relative to standard field imaging. The clinical significance of these findings remains unclear, as no studies to date have shown that the detection of these peripheral lesions impacts visual outcomes. However, subsequent studies have suggested that lesions in the peripheral retina are strongly associated with disease progression, as demonstrated by a 4.7-fold increased risk of progression to PDR over 4 years, independent of baseline severity and hemoglobin A1c (HbA
1c).
36 Further study is needed to determine the other factors involved in disease progression, including the possible effects of aging and other cardiovascular risk factors, on progressive ischemia. There is conflicting data regarding any association between peripheral lesions as detected by ultra-widefield imaging and DME. While a correlation between DME and peripheral ischemia demonstrated by nonperfusion area has been suggested by Wessel et al.,
63 a subsequent study by Silva et al.
36 found no association. Currently, several studies to determine whether ultra-widefield images can contribute to grading and risk assessment of DR are under way,
65 including the Diabetic Retinopathy Clinical Research (DRCR) Network Protocol AA.