Other risk factors, such as nephropathy, anemia, sleep apnea, and thiazolidinedione (glitazone) use, may also affect the development of DME. Patients with microalbuminuria have a lower serum protein concentration and thus, a reduced plasma colloidal osmotic pressure. This decreased osmotic pressure allows fluid to exit the retinal blood vessels and causes DME. 7 Serum osmolarity may also play a role in DME. Some patients were noted to have decreased DME after receiving hemodialysis. 19 Retinal vascular permeability can be increased by ischemia caused by hypoxia from anemia or sleep apnea. 7 Glitazones have been associated with an increased risk of developing DME, although the cause is unclear. 7
Examination
The American Academy of Ophthalmology recommends annual diabetic retinopathy screening for all patients with DM. Screening exams should start at the time of diagnosis for patients with T2DM and at 5 years after diagnosis for patients with T1DM. Currently, patients without a history of diabetic retinopathy can be screened via an ophthalmologic exam or review of color fundus photographs, which can be taken by trained personnel in the primary care or subspecialty settings.
Unfortunately, only 60% of patients with DM are screened annually. It is important to emphasize to patients the importance of a screening eye exam. Many patients do not understand that diabetic retinopathy may be present even if they are not experiencing any changes in vision. The patient should be referred to an ophthalmologist immediately if he or she reports blurry vision, wavy lines, or dark spots in the vision, especially if those symptoms are acute. The goal of a screening program is early detection: to identify those patients who are at risk for vision loss from DM and to provide close follow-up and timely treatment. Any patient with a history of diabetic retinopathy should be followed at the interval recommended by the eye care provider. 11
Patient history is an important part of the screening exam, including symptoms, duration of DM, A1c, medications, medical history (hypertension, nephropathy, dyslipidemia, obesity, pregnancy), and ocular history. If there is evidence of diabetic retinopathy or DME, recommendations for better systemic control of DM or its comorbidities can be made based on the patient history. During the screening exam, the patient’s visual acuity and intraocular pressure are measured. A basic examination of the anterior segment looking for neovascularization of the iris is also completed. Iris neovascularization is a sign of proliferative diabetic retinopathy that would indicate laser treatment, also known as panretinal photocoagulation, or intravitreal injection.
The patient’s pupils are dilated, which enables the eye care provider to examine the retina. Patients often dislike this portion of the examination, because the dilation drop causes their vision to be blurry for 4 to 6 hours. However, dilation ensures that the provider has a view of the entire retina and can detect early stages of diabetic retinopathy.
If the screening is taking place via color fundus photographs, a nonmydriatic fundus camera, which does not require dilation, can be used. The purpose of the screening examination is to assess changes that can lead to vision loss. Important features that must be detected if present are macular edema, extensive microvascular changes, vitreous hemorrhage, and neovascularization of the optic nerve, retina, or iris. 11 It is important to remember that the diabetic screening examination does not take the place of a complete ophthalmologic examination for other ocular disease, such as glaucoma. The patient may need to schedule additional appointments with an eye care provider if other eye problems exist.