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More than 9 percent of U.S. adults have diabetes, and those patients are sitting in your chair. Find out how diabetes affects your patients’ vision.
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
DME treatment may be evolving from a laser ablative approach into a pharmacotherapeutic approach. The exponential growth that has occurred over the past decade in the retinal pharmacotherapy field has led to the development of several pharmacotherapies for retinal vascular diseases including DME, such as pegaptanib (Macugen, Bausch + Lomb), bevacizumab (Avastin, Genentch), ranibizumab (Lucentis, Genentech) and aflibercept (Eylea, Regeneron). Many of these agents, in the form of intravitreal injections or sustained delivery devices, have already undergone clinical trial testing for safety and efficacy and others, such as avacincaptad (Zimura, Ophthotech) are currently being evaluated.
Gestational diabetes is a type of diabetes that is first seen in a pregnant woman who did not have diabetes before she was pregnant. Gestational diabetes usually manifests itself in the middle of a pregnancy. Doctors test for it between 24 and 28 weeks of pregnancy.
Women who have had gestational diabetes have a 35 percent to 60 percent chance of developing T2DM in the next 10 to 20 years.
Updated criteria for diagnosing gestational diabetes will increase the proportion of women diagnosed with gestational diabetes. Using these criteria, an international, multicenter study of gestational diabetes found that 18 percent of the pregnancies were affected by gestational diabetes.12
Gestational diabetes may be an independent risk factor for cataracts later in life, although the risks are greatest for women who subsequently develop T2DM.
The number of people with DM is increasing,13 and cataracts are one of the most common causes of visual impairment in these patients.14
The incidence of cataracts in insulin-dependent, non–insulin-treated, and insulin-treated non-insulin-dependent diabetics were 7.1, 11.7, and 17.8 per 1000 person-years, respectively. Cataract was four times more common in diabetics and twice more frequent in men.15
It was found that the risks for cortical cataracts (CC) and posterior subcapsular cataracts (PSC) were elevated for patients with T2DM.14
Advances in cataract surgical techniques and instrumentation have improved outcomes; however, surgery may not be safe and effective in certain individuals with pre-existing retinal pathology or limited visual potential, according to the Wisconsin Epidemiologic Study of Diabetic Retinopathy.16
The relationship between diabetes and open-angle glaucoma (the most common type of glaucoma), has intrigued researchers for years. People with diabetes are twice as likely to develop glaucoma as are non-diabetics, although current research is beginning to call this into question.17
Neovascular glaucoma, a rare type of glaucoma, is always associated with other abnormalities, diabetes being the most common. Neovascular glaucoma can occur if these new blood vessels grow on the iris close off the fluid flow in the eye and raise intraocular pressure (IOP).17
Patients with DM have an increased risk of dry eye. The diabetic patient has decreased tear break-up time, Schirmer’s test values, and corneal sensitivity as well as increased fluorescein and lissamine green staining.18,19
In diabetes, damage to the microvasculature feeding the lacrimal gland together with autonomic neuropathy of the lacrimal gland-both of which occur early in the course of diabetes-may contribute to impaired function of the gland.20
Sorbitol accumulation within cells can lead to cellular edema and dysfunction, which causes lacrimal gland damage and dysfunction and decreased tear secretion.21
Decreased corneal sensitivity is a clinical manifestation of diabetic keratoplasty. Furthermore, reduced corneal sensation can also lead to a reduced blink rate and increased tear evaporation.22 These potential mechanisms induce DED in diabetic patients.
Diabetes and eye care
A comprehensive eye examination by an optometrist or ophthalmologist annually or biannually at minimum to identify changes in the blood vessels of the retina is recommended for persons with diabetes.8
The number of patients with DM is increasing, and the need for proper diabetic eyecare will only escalate in the future. This situation presents an opportunity for optometrists to serve as primary eyecare providers for these patients. Optometrists need to be proactive in keeping up with new technology and treatment so they can serve these patients with the most up-to-date options.
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