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Abstract
The retinal microangiopathy caused by diabetes leads to ischemic retinopathy with sight-threatening neovascularization when a critical number of capillaries becomes nonperfused and obliterated. The process begins in individual capillaries and then involves group of capillaries and advances centripetally to the arterioles and their branches.
VEGF is a potent vasopermeability factor which is a growth factor that is highly expressed under diabetic conditions and thought to induce neovascularization and blood-retinal barrier breakdown. It acts on endothelial cell tight junctions and decreases their protein contents or increases phosphorylation which leads to increase paracellular permeability.
Diabetic macular edema is swelling of the retina in diabetes mellitus due to leaking of fluid from blood vessels within the macula which is believed to be the result of retinal microvascular changes that occur in patients with diabetes. Thickening of the basement membrane and reduction in the number of pericytes lead to increased permeability and incompetence of retinal vasculature. It is classified into focal and diffuse. Clinically significant macular edema is considered if edema is close enough to the center of the retina to pose a risk to vision. Risk factors of developing DME are type 1 and 2 DM with long duration of diabetes up to 10 years, poor control of hyperglycemia, renal diseases, systemic hypertension and serum hyperlipidemia.
Diagnosis of DME is done by visual acuity, Amsler grid, fundus biomicroscopy, fundus angiography, optical coherence tomography and scanning retinal thickness analyzer.
Treatment of DME is done by laser photocoagulation either focal, grid or modified grid laser, vitrectomy specially if there is taut posterior hyaloid membrane causing traction on the macula, medically through intravitreal injection of steroids or new anti-VEGF drugs.
Intravitreal triamcinolone is a synthetic glucocorticoid, has been shown to deliver high initial concentrations to the target tissue and provide effective levels for at least 3 months. It has antiangiogenic, antifibrotic and antipermeability properties, also decrease levels of vascular endothelial growth factor (VEGF) and improve BRB function. Action in many studies showed that therapeutic effect of triamcinolone is typically seen with in 1 month, though it often fades by 6 months, thus requiring re-injection.
Side effects of intravitreal triamcinolone are increased intraocular pressure which can be treated medically by antiglaucomatous drugs or surgically by trabeculectomy or trabeculoplasty. Some cases require vitrectomy to remove the drug if the IOP elevation is very high and the optic nerve is felt to be susceptible to damage in a short period of time. Posterior subcapsular cataract and nuclear cataract lead to cataract surgery in about 15-20% of elderly patients within 1 year of injection. Endophthalmitis which is either infectious or non-infectious.