Diabetic Retinopathy: Old Disease, New Strategies
BY LEO SEMES, OD, FAAO
The recent American Academy of Optometry (AAO) meeting focused on diabetic patient care. AAO President Dr. Robert Newcomb encouraged all attendees when seeing a diabetic patient to communicate with that patient's treating physician. As primary care providers, eyecare practitioners can intervene positively in the health care of diabetics.
Diabetic retinopathy ranks as one of the four leading causes of blindness in the United States, and many diabetics are brought to attention through an eye examination. This column will review some of the newer treatment strategies.
Published Clinical Practice Guidelines and other resources offer staging scales for diabetic retinopathy. The devastating consequences of proliferative retinopathy (PDR) are well known (50 percent blind within five years of diagnosis), but PDR is not the major cause of diabetic retinopathy vision loss. Clinically significant macular edema (CSME) holds that title. While this condition is difficult to diagnose at times, be suspicious whenever the foveal reflex is absent. Visual acuity may be affected only minimally, or patients may be asymptomatic. Pupillary dilation and careful stereoscopic evaluation may reveal macular thickening or other loss-of-contour changes. Fluorescein angiography or other imaging techno logies may help direct treatment and further specify the location of leakage within the macula.
Contemporary treatment includes focal and grid laser for specific and diffuse CSME, respectively. Vitrectomy also reportedly shows some promise.
Octreotide is in the statin class. A three-year study (Boehm 2001) showed that this long-acting somatostatin reduced the incidence of vitreous hemorrhage and the need for vitrectomy in a pilot study of nine diabetics vs. nine controls. Dosing was 100µg (subcutaneous) tid.
Protein kinases act on endothelial cells. They increase vascular permeability, among other actions. A Phase III clinical trial is currently investigating protein kinase C (PKC) inhibition, based on decreased peripheral neuropathy, using a Lilly proprietary compound.
In a similar approach to PKC inhibitors, researchers are evaluating aldose reductase inhibition for its ability to reduce vascular proliferation.
Antioxidants have also re-emerged to treat the effects of hyperglycemia. Conflicting reports suggest that no one antioxidant has a clear advantage over others, but some preliminary animal studies are concentrating on Vitamin C.
Finally, blood rheology (selective membrane filtration) is being revisited. A recent study (Luke 2001) evaluated 11 eyes of 11 patients before and after three treatment cycles over 18 weeks. Re searchers reported two indicators of improvement: decreased mean deviation (MD) on threshold static perimetry and 1.2-line mean improvement in visual acuity.
Improved diagnostic imaging technology (optical coherence tomography [OCT], scanning laser ophthalmoscopy [SLO] and retinal thickness analysis [RTA]) will better identify macular edema. Newer means of treatment may reduce the devastating complications associated with this cause of severe vision loss.
Dr. Semes is an associate professor at the University of Alabama at Birmingham School of Optometry.