The destructive effects of diabetes mellitus (DM) are far reaching, and optometrists see patients with diabetes in their chairs every day.
Ocular effects include changing vision, dryness, diabetic retinopathy, diabetic macular edema, cataracts and glaucoma. Vision changes may include reduction in visual acuity, refractive error, color vision and accommodative dysfunction. Dryness is usually the end results of a neurotrophic cornea in addition to sluggish glands leading to tear deficiency.
Diabetic retinopathy (DR) is a disease of the retina caused by diabetes that involves damage to tiny blood vessels in the back of the eye. Diabetic retinopathy afflicts 93 million people worldwide, and 28 million of these have vision-threatening DR.1-3 These numbers are expected to increase as the prevalence of type 2 diabetes continues to climb.4
DR is a major cause of blindness in the United States.5 Diagnosis and treatment of DR focus on vascular abnormalities that appear at later stages of the disease.
DR is diagnosed in five stages.
The first stage is “no apparent retinopathy.” As the name implies, there are no diabetic fundus changes.
The second stage is “mild non-proliferative retinopathy” (NPDR). This stage is characterized by the presence of a few microaneurysms.
The third stage is “moderate NPDR,” which is characterized by the presence of microaneurysms, intraretinal hemorrhages, or venous beading (VB) that do not reach the severity of the standard photographs 2B, 6A and 8A.
The fourth stage—severe NPDR—is the key level to identify. Data from the Early Treatment Diabetic Retinopathy Study (ETDRS) has shown that eyes in patients with T2DM that reach severe NPDR have a 50 percent chance of developing high risk characteristics if laser treatment is not instituted.6
The diagnosis of severe NPDR is based on the 4:2:1 rule of the ETDRS.7 Using standard photographs 2B, 6A and 8A to compare with fundus findings, ODs can easily diagnose severe NPDR.7
If hemorrhages of at least the magnitude of standard photograph 2B are present in all four quadrants, then by definition severe NPDR is present. If two or more quadrants have venous beading (VB) of the same magnitude or greater than standard photograph 6A, then by definition severe NPDR is present. If one or more quadrants has intraretinal microvascular abnormalities (IRMA) of the same magnitude or greater than standard photograph 8A, then by definition severe NPDR is present.
The final stage is “proliferative diabetic retinopathy” (PDR). PDR is characterized by neovascularization of the disc, neovascularization of the retina, neovascularization of the iris, neovascularization of the angle, vitreous hemorrhage or tractional retinal detachment.
Diabetic macular edema
Diabetic macular edema (DME), defined as a retinal thickening involving or approaching the center of the macula, represents the most common cause of vision loss in patients affected by DM.8 DME results when fluid accumulation increases retinal thickness and causes light-distorting fluid-filled cysts within retinal tissue and serous detachments separating the neural retina from the underlying pigmented epithelium.9
The ETDRS defined clinically significant diabetic macular edema as edema satisfying any one of the following three criteria:10
• Any retinal thickening within 500 µm of the center of the macula
• Hard exudates within 500 µm of the center of the macula with adjacent retinal thickening
• Retinal thickening at least one disc area in size, any part of which is within 1 disc diameter of the center of the macula.
When present, DME was subclassified into mild, moderate, or severe depending on distance of the thickening and exudates from the fovea.11
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