BeyHealth Quarterly Journal (BHQJ) BHQJ 2018: 001:1 (May 2018) - Page 6

CPD Hot Topic Type 2 Diabetes & Eye Disease - Focus on Diabetic Retinopathy Ogugua Okonkwo MD. FRCS FWACS Dr Ogugua Okonkwo is Consultant Ophthalmic Surgeon & Vitreoretina Specialist at the Eye Foundation Retina Institute, Lagos, Nigeria. Introduction Diabetes Mellitus is a metabolic disorder characterised by impairment of the body’s ability to handle glucose. This occurs as a result of a relative or absolute lack of insulin, resulting in a state of hyperglycemia (or high blood sugar). There is an expected 55% increase in the global prevalence of diabetes by 2035. Africa is projected to have the highest percentage increase in prevalence, ahead of all other regions of the world, with an estimated 110% increase by 2035[1]. The World Health Organization estimates that by 2030, there will be 18,234,000 diabetic cases in Africa, of which 4,835,000 will reside in Nigeria alone[2]. Diabetic retinopathy, acceleration of cataracts, glaucoma, anterior ischaemic optic neuropathy, diabetic papillopathy, and neuropathy involving the 3rd, 4th or 6th cranial nerves are some of the main ocular complications of diabetes. Diabetes is best known for its microvasculopathy or effects on the small arteries and blood vessels (microcirculation) of organs, notably the kidney, eyes, neurons and brain among others. Diabetic Retinopathy (DR) is the most common ocular microvascular complication of type 2 diabetes. Risk factors for DR include long duration of diabetes, poor or unsatisfactory glycemic control, hypertension, anaemia, hyperlipidemia, nephropathy, pregnancy, smoking and obesity. Diabetic retinopathy is an insidious disease and often manifests in the form of vision loss arising CPD UPDATE • Diabetic Macula Oedema (DMO), is the commonest cause of vision loss in diabetic patients • Screening for Diabetic Retinopathy (DR) can result in early detection, intervention and prevention of blindness • An ischaemic retina produces VEGF, which stimulates new vessel growth, hence term Proliferative Diabetic Retinopathy (PDR) • Subsequent vitreous haemorrhage, from diabetic macula oedema (exudative change), which is the commonest cause of vision loss overall. Ischaemia-induced vision loss will also result in proliferative complications, which include bleeding into the vitreous humour (vitreous haemorrhage), tractional retinal detachment (causing pulling ‘stress’ on the macula), and severe ischemia involving the macula. Ischemia can also be severe enough to cause abnormal new vessel formation or rubeosis, evolving into a state of rubeotic or neovascular glaucoma. The macula is the functional centre of the light-sensitive retina, responsible for sharp, high- resolution colour vision. Located within the macula is a tiny ‘pit’ called the fovea centralis, at which the layers of the retina are neatly parted to allow rays of light gain direct access to photo-sensitive receptor cells (cones), thereby creating the clearest vision possible for the individual in bright light. Damage to this important part of the retina results in visual impairment and distortion of vision. Pathogenesis The origin and development these microvascular complications can be explained by the following tractional retinal detachment and 3 proposed theories. vision loss may result from new 1. Hyperglycemia, a state of elevated blood glucose altering the expression of genes vessel growth • Leakage of lipoproteins into the retina (hard exudates) are visible as distinct white or yellowish deposits of varying sizes • Retinal ischaemia is often visible as ‘cotton wool spots’ and areas of new vessel formation in the eye and leading to increased or decreased amounts of certain gene products capable of altering cellular function. 2. Glycosylation of proteins giving rise to a series of reactions, leading to considerable alteration of proteins. 3. Chronic hyperglycemia resulting in oxidative stress in cells, leading to the formation of an excess of toxic end products of oxidation, including peroxides, nitric oxide and oxygen free radicals. Histologically, loss of hugely important supporting cells called pericytes is known to be responsible • The consequence of an oedematous for the damage caused to vascular endothelial cells observed in the eyes of many diabetic patients. or ischaemic retina is often loss of Pericytes are irregularly arranged contractile cells that wrap themselves around the retinal capillary vision if the macula is involved • PDR may be a highly specific endothelial cells and in the walls of capillaries and tiny venules in other parts of the body. Damage to these cells (and the consequent destruction of retinal endothelial cells) leads almost indicator for diabetic nephropathy as inevitably to a picture of dilated capillaries and venules (microaneurysms) and breakdown of the both are microvasculopathy-related all-important blood-retinal barrier, normally responsible for regulating the flow of nutrients and metabolic waste products in and out of a healthy retina. 6 | MAY 2018 | Issue 1