- Dr. Tamal Kanti Roysarkar
Diabetic Retinopathy (DR) is a vascular disease of the retina which affects patients with diabetes mellitus. Diabetes mellitus is extremely common, so it is not surprising that DR affects 3.4% of the population. Of the millions of people with DR, nearly one-fourth have vision-threatening disease.Time since diagnosis and extent of hyperglycemia are the most significant risk factors for the DR, but other risk factors for development and progression include hypertension, dyslipidemia, smoking, nephropathy and pregnancy.
PATHOPHYSIOLOGY: The retina is a light sensitive multi-layered sheet composed of neurons, photoreceptors, and support cells. Hyperglycemia is thought to cause endothelial damage leading to leaky, incompetent blood vessels of the retina.
NPDR: Early disease without neovascularization is called non-proliferative diabetic retinopathy (NPDR). Leaking capillaries give rise to dot-blot hemorrhages in the retinaandalso causes fluid deposition under the macula causing macular edema (ME),which isthe commonest cause of vision loss in DR. Resolution of fluid lakes leave behind waxy, yellow deposits called hard exudates (HEX). With time, there is obstructionand death of the nerve fiber layer, resulting in fluffy, white patches called cotton wool spots (CWS).
PDR: Proliferative diabetic retinopathy (PDR)is characterized by the presence of neovascularization (abnormal blood vessel growth) and this hasa great potential for severe visual loss. Angiogenicfactors, like VEGF, stimulate growth of new retinal blood vessels (neovascularization) to bypass the damaged vessels. However, these new vessels are leaky, fragile, andoften misdirected resulting in a vitreous hemorrhage and sudden vision loss. These vessels may also scar down, causing pull on the retina and eventual tractional retinal detachment which causes severe vision loss if it involves the macula.
SYMPTOMS: Decreased vision from macular edema or retinal detachment is the commonest symptom. Patients usually do not experience symptoms until late in the course of the disease. Bleeding into the vitreous can cause sudden loss of vision.
SCREENING: Screening for DR is incredibly important since most patients do not experience any symptoms until advanced stages of disease. If recognized early, the vision-threatening side-effects of DR can often be prevented with appropriate management. It is recommended Type 2 diabetics have their annual dilated eye exams begin shortly after the diagnosis of diabetes is made. Type 1 diabetics should begin annual eye exams 3-5 years after their diabetes diagnosis. Pregnant women with diabetes should have a dilated eye exam prior to conception, early in the first trimester, and then every 3 months until delivery
EXAMINATION: A proper diabetic eye exam should always begin by gathering a thorough history from the patient. Status of glucose control, dyslipidemia, anemia and BP control should be assessed. Examination should begin with visual acuity, intraocular pressure measurements, and a slit-lamp exam, including careful inspection of the iris for neovascularization and gonioscopy if required.Finally, the patient should have his or her pupils dilated for a thorough fundus exam.
INVESTIGATIONS: Fluorescein angiography (FA) may be used to definitively document retinal vessel occlusion and/or leakage. Macular edema appreciated and documented using optical coherence tomography (OCT). Ultrasound is useful to detect retinal detachment when the fundus cannot be clearly seen on exam due to a dense cataract, vitreous hemorrhage, or other reasons.
TREATMENT OPTIONS: The best treatment for DR is prevention of its development and progression with tight glucose control.Glucose control also has the added benefit of decreasing risk for other end-organ complications of diabetes. Patients should maintain a HbA1c ≤7%. Blood pressure, anemia, dyslipidemia should be controlled.Smoking is to be avoided. The causative micro aneurysms are localized, often using fluorescein angiography, and then directly treated with laser therapy. If the leakage is more diffuse, a grid of light laser burns in the area of leakage can decrease the edema. Currently, intra-vitreal injections of anti-VEGFsuch as Lucentis® or Avastin® (off label) and steroids are recommended for treatment of diabetic macular edema. For PDR, the mainstay of treatment is panretinal photocoagulation (PRP), in which peripheral portions of retina are destroyed using thousands of laser burns while sparing the central macula. This reduces the risk of severe vision loss by 50% and results in regression of neovascularization in 30-55% of patients.Patients with non-resolving vitreous hemorrhages or severe traction causing retinal detachment will benefit from a vitrectomy. In this procedure, the vitreous gel and hemorrhage and membranes on the retina are carefully removed from the eye and replaced with a saline solution.
The writer is the Consultant, Vitreo-retinal Services, Ophthalmology of Asgar Ali Hospital. He can be reached at firstname.lastname@example.org.