الفهرس 
BASIS OF OPTICAL COHERENCE TOMOGRAPHY
Evaluation of DME by Retinal Thickness MapOnly 14 pages are availabe for public view
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Abstract
Diabetic macular edema (DME) is a common complication of diabetic retinopathy (DR). It is a collection of intra-retinal fluid in the macula with or without lipid exudates and with or without cystoid changes. This is usually caused by leakage of intra retinal fluid from abnormal retinal capillaries and micro-aneurysms .
The clinical diagnosis of macular edema is made by slit lamp biomicroscopy, indirect ophthalmoscopy, as well as diagnostic tests.These diagnostic tests include fluorescein angiography for evaluating the retinal circulation and optical coherence tomography (OCT) for cross sectional high-resolution imaging of ocular tissues.
OCT is a relative new non –invasive diagnostic tool for obtaining cross-sectional high-resolution imaging of tissues. Its use in ophthalmology was first reported in 1990. It has been used to study the anatomy and pathogenesis of various ocular disorders affecting the posterior segment. These include vitreomacular traction syndrome, macular hole, and macular edema .
The first systems of OCT were based on Time Domain OCT (TD-OCT) technology and the examination was time consuming and could reach a resolution of only 10µm. Recent machines use the Spectral Domain OCT (SD-OCT) technology and image acquisition is dramatically less and the resolution reaches 3µm.
Since the landmark paper by Hee et al. in 1998 reporting the use of OCT to measure retinal thickness in DME studies have found it to be highly sensitive and specific in detecting DME and clinical significant macular edema (CSME) compared to other diagnostic modalities. OCT has enabled us to identify three basic types of structural changes in DME, namely retinal swelling, cystoid macular edema, and serous retinal detachment. Those changes correlate well with histopathologic studies and may be present in combinations in any individual patient.
A major advance in retinal thickness mapping is due to the application of SD-OCT. This new technology enables the generation of a cube of data from each point in the macula and enabling proper three-dimensional imaging data collection as opposed to the map generated from only 6 radial scans in TD-OCT machines.
Different lines of treatment for DME are present, and these include laser photocoagulation, Intravitreal triamcinolone (IVTA) injection, and the recently introduced vascular endothelial growth factor (VEGF) antagonists.
The introduction of anti-VEGF has revolutionized the management of DME and is considered by many one of the greatest advances in ophthalmology in the past decade. At present different types of anti-VEGF drugs are available. All these drugs inhibit VEGF angiogenic activity binding to VEGF protein and thus preventing its activation/ interaction. Bevacizumab (Avastin, Genetech Inc., San Francisco, CA), Ranibizumab (Lucentis, Genentech, Inc., South San Francisco, CA) , and Pegaptanib Sodium (Macugen, Eyetech Pharmaceuticals, Inc., New York, NY) are examples of drugs in this class .
Pars plana vitrectomy, with or without internal limiting membrane peeling, is effective in relieving macular edema caused by traction by taut posterior hyaloid or an epiretinal membrane. Thus decreasing macular thickening and improving VA.
OCT is also used for quantitative follow up of the effects of treatment of CSME. Studies of changes in macular thickness and volume allow tracking response to therapy.
Thus, studies show that OCT is a valuable tool in the diagnosis, management, and follow-up of patients with DME. It provides a highly accurate and reproducible method to diagnose macular edema that compares well to the standard clinical examination, ETDRS photos, and fluorescein angiography. Although it is an excellent anatomical study, it has not been shown to be an effective surrogate for functional tests such as VA in the assessment of macular edema.
Future research in OCT imaging will likely result in more improvements in resolution, speed, image registration, 3D imaging, and the ability to combine OCT with other various diagnostic modalities that will further our ability to evaluate DME.