Managing diabetic retinopathy in primary care
Diabetic retinopathy is a leading cause of blindness, making early detection of this condition crucial. Dr Yong Shao Onn from the Eagle Eye Centre at Mt Alvernia Hospital, Singapore, speaks to Roshini Claire Anthony on the diagnosis and treatment options.
Diabetes mellitus affects an estimated 415 million people worldwide, including approximately 600,000 individuals in Singapore. Diabetic retinopathy (DR) is a specific microvascular complication of diabetes and is the leading cause of blindness in working-aged persons in developed countries, including Singapore.
The prevalence of DR increases with the duration of diabetes, and nearly all persons with type 1 diabetes (T1D) and more than 60 percent of those with type 2 diabetes (T2D) have some retinopathy after 20 years. DR is a multifactorial disease and hyperglycaemia/glycated haemoglobin value, hypertension, hyperlipidemia, pregnancy, nephropathy/renal disease, obesity, smoking, moderate alcohol consumption, and physical inactivity have been identified as risk factors for the condition.
Tight glycaemic control reduces both the incidence and long-term progression of DR in both T1D and T2D, as demonstrated in the DCCT* and UKPDS** studies respectively. [Diabetes Care 2014;37:5-7; Br J Clin Pharmacol 1999;48:643-648] It should be noted, however, that tight control has been associated with paradoxical early worsening of DR, especially in patients with higher baseline HbA1c who have undergone a more rapid reduction of HbA1c in the first 6 months of treatment. Tight glycaemic control is also a known risk factor for hypoglycaemic episodes.
The retinal microangiopathy of DR is a result of hyperglycaemia-induced changes to the retinal capillary vessel walls, in both the central and peripheral areas of the retina. In diabetic macular oedema (DME), the impaired vessels leak fluid into the central part of the retina (macula), which causes structural and functional changes in the part of the retina that provides the sharp vision needed for reading and recognizing faces.
Prolonged damage to the retinal capillaries results in ischaemia of the peripheral retina and macula, prompting the development of growth factors that cause new abnormal blood vessels (neovascularization) and scar tissue to grow on the surface of the retina. This stage of the disease is known as proliferative diabetic retinopathy (PDR). Retinal neovascularization may result in bleeding into vitreous cavity (vitreous haemorrhage) or cause scar tissue formation and subsequent tractional detachment of the retina. Iris neovascularization may cause elevated intraocular pressure and pain due to a mechanical clogging of the aqueous drainage system of the eye.
All patients with diabetes should be screened annually for diabetic eye disease with fundus photography as a minimum requirement, with the aim of detecting DR before any vision loss has occurred. If diabetic changes are detected, referral to an ophthalmologist is then required.
The best way to diagnose DR is a dilated eye examination by an ophthalmologist, looking specifically for thickening of the macula (DME), evidence of retinal ischaemia, neovascularization of the iris, optic disc, or retina, or fibrotic tissue on the surface of the retina.
Regular dilated eye exams by an ophthalmologist are important, especially for those who are at a higher risk for DR or diabetes. For patients older than 50 years, a comprehensive dilated eye exam every 1–2 years can evaluate the patients’ vision and need for corrective lenses, intra-ocular pressure (looking for glaucoma), ocular adnexa and anterior segment (eyelids, cornea, checking for dry eye), and lens (looking for cataracts), as well as a complete examination of the retina and vitreous, in addition to checking for signs of diabetic eye disease.
Optical coherence tomography (OCT) uses a laser to scan the retina, providing highly detailed cross-sectional images of the retina that show its thickness and its composite layers, allowing visualization and detection of even trace amounts of intraretinal fluid and hard exudates within the retinal tissue. OCT angiography (OCTA) is a recent iteration of this technology which allows for detection of blood flow within the retinal vessels, including the capillary network that is damaged by diabetes. Ischaemic (non-perfused) areas can therefore be mapped, and serial scans performed to look for interval change.
Fundus photographs document DR severity and allow for easier and objective monitoring of the disease on follow-up visits to determine progression.
Fluorescein angiography is the intravenous injection of a fluorescein dye to evaluate retina blood vessel circulation. As the dye circulates through the eyes, both still and dynamic images (video) of the retina can be captured to accurately detect blood vessels that are closed, damaged, or leaking fluid.
With proper screening, DR can be identified before vision loss begins. Even if DR is diagnosed, early disease may only require observation. An appropriate schedule of follow-up examinations can then be planned, with the aim of early detection of further deterioration that might then warrant treatment.
Treatment of DR and DME can be broadly classified into three categories. Intravitreal injections of anti-vascular endothelial growth factor (VEGF) agents (bevacizumab, ranibizumab, aflibercept) into the vitreous cavity have been shown to result in better vision than laser treatment alone for patients with DME and PDR. [Ophthalmology 2012;119:789-801; Ophthalmology 2014;121:2247-2254] The key to these treatments is their ability to block VEGF, a chemical signal that stimulates leakage and abnormal blood vessel growth. Repeated doses of anti-VEGF medications may be needed to prevent blood vessels from leaking fluid and causing vision loss.
Intravitreal injections of corticosteroids (eg, dexamethasone implant, fluocinolone) have also been shown to benefit patients with DME due to the anti-VEGF and anti-inflammatory properties of these drugs. [Ophthalmology 2014;121:2473-2481] These procedures can be done in a clinic or hospital setting to prevent, treat, or reverse damage from diabetes in the retina.
Panretinal photocoagulation laser is used to ablate the ischaemic peripheral retina to reduce VEGF production. Focal laser of the macula is also used as an adjunct for treatment of DME. [Arch Ophthalmol 1985;103:1796-1806]
Vitreous and retinal surgery may be required in cases of advanced PDR to treat vitreous haemorrhage and relieve the fibrotic tissues that cause tractional retinal detachments.
Although DR remains the leading cause of preventable blindness in working adults, there are primary and secondary interventions proven effective in limiting visual loss. It is extremely important for diabetic patients to maintain the eye examination schedule put in place by their ophthalmologists. Through early detection, a treatment regimen to help prevent vision loss in almost all patients may be carried out.