WAHT IS DIABETIC RETINOPATHY
Diabetic retinopathy is a leading cause of visual impairment in working-age adults. While defects in neurosensory function have been demonstrated in patients with diabetes mellitus prior to the onset of vascular lesions, the most common early clinically visible manifestations of diabetic retinopathy would include microaneurysm formation and intraretinal hemorrhages. Microvascular damage leads to retinal capillary nonperfusion, cotton wool spots, increased numbers of hemorrhages, venous abnormalities, and intraretinal microvascular abnormalities (IRMA). During this stage, increased vasopermeability can result in retinal thickening (edema) and/or exudates that may lead to a loss in central visual acuity.
The proliferative stage results from closure of arterioles and venules with secondary proliferation of new vessels on the disc, retina, iris, and in the filtration angle. These new vessels then lead to traction retinal detachments and neovascular glaucoma respectively. Vision can be lost in this stage from capillary nonperfusion or edema in the macula, vitreous hemorrhage, and distortion or traction retinal detachment.
RATIONALE FOR SCREENING
Screening for DR is important because the majority of patients who develop DR have no symptoms until macular edema (ME) and/or proliferative diabetic retinopathy (PDR) are already present. The efficacy of laser photocoagulation and/or vascular endothelial growth factor (VEGF) inhibitors in preventing visual loss from PDR and ME is well established in randomized trials. However, these therapies are more beneficial in preventing visual loss than reversing diminished visual acuity. Thus, early detection through screening programs and appropriate referral for therapy are important to preserve vision in individuals with diabetes. (See “Diabetic retinopathy: Prevention and treatment”.)
Diabetic retinopathy can occur at any age. The primary prevention and screening process for diabetic retinopathy varies according to the age of disease onset. Several forms of retinal screening with standard fundus photography or digital imaging, with and without dilation, are under investigation as a means of detecting retinopathy. Appropriately validated digital imaging technology can be a sensitive and effective screening tool to identify patients with diabetic retinopathy for referral for ophthalmic evaluation and management. Digital cameras with stereoscopic capabilities are useful for identifying subtle neovascularization and macular edema. At this time, it is not clear that photographic screening programs achieve a greater reduction in vision loss than does routine community care in areas where access to ophthalmologists is straightforward. Studies have found a positive association between participating in a photographic screening program and subsequent adherence to receiving recommended comprehensive dilated eye examinations by a clinician. Of course, such screening programs have great value in circumstances in which access to ophthalmic care is limited. Future research should also include establishing standardized protocols and satisfactory performance standards for diabetic retinopathy screening programs.
At this time, these technologies are not considered a replacement for a comprehensive eye evaluation by an ophthalmologist experienced in managing diabetic retinopathy.
The Ophthalmic Technology Assessment on Single Field Fundus Photography for Diabetic Retinopathy Screening states15:
A variety of techniques can be used to detect and classify diabetic retinopathy, including direct and indirect ophthalmoscopy, stereoscopic color film fundus photography, fluorescein angiography, and mydriatic or nonmydriatic digital color or monochromatic photography.16 Ophthalmoscopy is the most commonly used technique to screen for diabetic retinopathy. However, undilated ophthalmoscopy, especially that done by nonophthalmologists, has poor sensitivity relative to 7-field stereoscopic color photography. Under typical clinical conditions, direct ophthalmoscopy done by nonophthalmologists has a sensitivity of approximately 50% for the detection of proliferative retinopathy.17 The gold standard for the detection and classification of diabetic retinopathy is stereoscopic color fundus photographs in 7 standard fields, as defined by the Early Treatment Diabetic Retinopathy Study (ETDRS) group.18 Although this technique is accurate and reproducible, it is labor intensive and requires skilled photographers; skilled photograph readers; and sophisticated photography equipment, film processing, and archiving. The turnaround time from acquisition of the data to interpretation can take weeks in clinical trials. Finally, from the patient’s perspective, it can be time consuming and uncomfortable. In short, 7-field stereoscopic fundus photography is not an ideal screening technique, but it can serve as the standard with which to compare other screening technologies.
There is level I evidence that single-field fundus photography with interpretation by trained readers can serve as a screening tool to identify patients with diabetic retinopathy for referral for ophthalmic evaluation and management, but it is not a substitute for a comprehensive ophthalmic examination. The advantages of single-field fundus photography interpreted by trained readers are ease of use (only one photograph is required), convenience, and ability to detect retinopathy. The disadvantage is that reported sensitivity values are less than ideal when compared with 7–standard field photography. When compared with ophthalmoscopy, however, single-field fundus photography has the potential to improve the quality of the evaluation and the numbers of patients evaluated. The use of nonmydriatic fundus photography systems represents a compromise. Although it is apparent that mydriasis improves image quality and sensitivity, particularly in older patients, it is uncertain whether this is outweighed by the disadvantage of dilation related to patient compliance. In other words, the diminished sensitivity of a nonmydriatic photograph may be acceptable if more patients complete the process.
Whether any of the systems discussed can accommodate the tens of thousands of photographs necessary to appreciably improve detection rates for diabetic retinopathy in the general population is unknown. Caution should be exercised in strictly applying the test characteristics from the reported studies; most tests perform less well in the real-world setting. Further studies will be required to assess the implementation of programs that are based on single-field fundus photography in a real clinical setting to confirm the clinical effectiveness and cost-effectiveness of these techniques in improving population visual outcomes. Future research also should include establishing standardized protocols and satisfactory performance standards for diabetic retinopathy screening programs.
Ophthalmologists can play an important role in the total care of the patient with diabetes. At the time of the eye examination, patients can be counseled about the importance of maintaining near-normal blood glucose and blood pressure and monitoring serum glycosylated hemoglobin levels, which may lessen the risk of retinopathy developing and progressing. It is recommended that an HbAlc of 7.0% or lower is the target for glycemic control in most patients while in selected patients there may be benefit to setting a target of 6.5%. Aspirin may be used without concern for worsening diabetic retinopathy by patients with diabetes who require aspirin for other medical indications and have no contraindications. Intravitreal injections of anti-vascular endothelial growth factor (VEGF) agents have been shown to be an effective treatment for center-involving diabetic macular edema. Treating physicians should note that the use of betadine antiseptic drops is recommended during intravitreal injections. At this time, laser photocoagulation remains the preferred treatment for non-center-involving diabetic macular edema.
Physicians that care for patients with diabetes, and patients themselves, need to be educated about indications for ophthalmologic referral. Referral to an ophthalmologist is required when there is any non-proliferative diabetic retinopathy, proliferative diabetic retinopathy (PDR), or macular edema. Ophthalmologists should communicate the ophthalmologic findings and level of retinopathy with the primary care physician as well as the need for optimizing metabolic control. It is reasonable to encourage patients with diabetes to be as compliant as possible with therapy of all medical aspects of their disease.