الفهرس 
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Abstract
About 347 million people worldwide suffering diabetes mellitus (DM), and these numbers are predicted to be increase to 430 million patients by 2030. Diabetic retinopathy (DR) is the leading cause of vision loss among working-age adults, and diabetic macular edema (DME) is the main responsible for the vision loss related to DR.
DME occurs in nearly 12% of patients with DR and causes more than 10,000 new cases of blindness per year. Duration and type of diabetes directly affect the prevalence rate of DME. Patients can develop DME in the first five years following diagnosis of type I diabetes. The prevalence rate gradually reaches up to 40% within 30 years. About 5% of patients with type II diabetes already have DME at the time of diagnosis.
The Early Treatment Diabetic Retinopathy Study group (ETDRS) defined DME (based on clinical grounds) as an increase in retinal thickness at or within one-disc diameter of the foveal center whether focal or diffuse, with or without hard exudates, sometimes associated with cysts. Diabetic retinopathy (DR) is classified as nonproliferative DR (NPDR) or proliferative one (PDR) based on the presence of neovascularization on the optic disc or elsewhere.
The pathogenesis of DME has not been thoroughly defined because there are complex processes with various contributing factors. chronic hyperglycemia, hypercholesterolemia, free oxygen radicals, advanced glycation end-products, and protein kinase C are involved in the pathologic process.
Refractory persistent DME is challenging issue as it can cause irreversible visual loss due to chronic tissue stress and permanent disruption of retinal architecture from macular edema, ultimately causing photoreceptor damage. OCT is a digital optical instrument that generates cross sectional images (tomograms) of the retina by optical-coherence interferometry, a procedure analogous to ultrasound, except for using light (a broad bandwidth near infrared light beam at 840 nm) rather than sound, and measures the echo delay time of light reflected and backscattered from the retina.