Ngee Jin Yap & Nathan Ng
Diabetic retinopathy is a serious sight-threatening complication of diabetes (1), where high blood glucose damages the small blood vessels throughout the body, including in the retina. These damaged blood vessels are prone to blood and fluid leakage resulting in retinal tissue swelling. In order to compensate for these blocked vessels, the eye facilitates growth of new abnormal blood vessels that tend to leak and bleed easily (2).
Diabetic retinopathy is the most common cause of visual impairment and blindness in patients aged over 20 years in industrialised countries (1). As of 2010, diabetic retinopathy has affected over 100 million patients worldwide and is continuing to rise (3).
The most important risk factor of diabetic retinopathy is the duration of diabetes and metabolic control. Good glycaemic control can help present and slow the progression of diabetic retinopathy (1).
Other risk factors include hypertension, hypercholesterolaemia, being pregnant or of Asian or Afro-Caribbean background (4).
Diabetic retinopathy can be classified into the following 2 types:
- Non-proliferative diabetic retinopathy (NPDR)
This occurs in the early stages of diabetic retinopathy. In NPDR, the walls of the blood vessels in the retina weaken, occasionally leading to leakage of fluids and blood into the retina. However, there is no new growth of blood vessels in this stage (5). Ophthalmoscopic features includes micro aneurysms, retinal haemorrhages, hard exudates (2,6).
- Proliferative diabetic retinopathy (PDR)
This is a relatively severe stage of diabetic retinopathy. In PDR, the damaged blood vessels are obstructed and hence result in the growth of new but abnormal blood vessels. These new blood vessels are fragile and cause leakage of blood into the vitreous resulting in vitreous haemorrhage (5). Ophthalmoscopic features in PDR includes neovascularisation and vitreous haemorrhage (2,6).
Early stages of diabetic retinopathy are largely asymptomatic. As the disease progress, symptoms such as blurred vision, having dark spot in the centre of your vision field, poor night vision and having spots or floaters might develop (1).
Poor glycaemic control result in disruption to blood vessel walls, blood flow and blood composition (7). These changes result in retinal capillary leakage and poor perfusion of the retina. Central vision is affected when the macula area of the retina is involved, as it is the area responsible of central visual acuity. Diabetic macular oedema can occur in both PDR and NPDR and is a major cause of vision loss in diabetes (8). Clinically significant macular oedema Is defined as the thickening of the retina and/or hard exudates within 500 μm of the centre of the macula (6). Centre involved macular oedema is at higher risk of developing vision loss.
The pathophysiological mechanism of diabetic retinopathy and macular oedema is likely multifactorial and complex. Of the different signalling pathways, it is important to know about the vascular endothelial growth factor (VEGF) pathway as anti-VEGF treatments have become a mainstay treatment for diabetic retinopathy. Hypoxia upregulates VEGF expression, which plays an important role in ocular neovascularisation and the increase of capillary permeability (9).
Diabetic retinopathy is mainly asymptomatic in the early stages. Therefore, regular eye screening for patients with diabetes is essential to enable timely diagnosis and management of the condition. Screening for diabetic eye problems includes:
- History to determine any visual problems or difficulties
- Measurement of visual acuity
- Evaluation of ocular structure
- Measurement of pressure within the eye (5,6)
- Fluorescein angiography – A dye is injected into a vein in the arm. Photographs are taken as the dye travels through the blood vessels in the eye. This helps identify blood vessels that are occluded and leaking (6)
- Optical Coherence Tomography – This provides a cross-sectional image of the retina which helps assess the thickness of the retina and determine the amount of fluid leaked into the retinal tissue (10)
Treatment and Prevention
Treatment of diabetic retinopathy varies depending on the severity of the disease.
Several measures can be taken to help prevent and slow the progression of diabetic retinopathy. These include
- Risk factor modification – Compliance to prescribed medication, regular monitoring of blood sugar levels, adhere to a balanced and healthy diet, regular exercise, controlling blood pressure and cholesterol levels, reduce alcohol intake and avoid smoking (3,6).
- Laser treatment (photocoagulation) – Argon laser is used to burn tissue and replace it by glial scar which consumes less oxygen. Capillaries disappear, hence eliminating neovascularisation proliferative factors. (1,6) Laser therapy is highly effective. The rate of severe visual loss can be reduced by 60% in 2 years (11).
- Antiangiogenic drugs such as Ranibizumab, Aflibercept and Bevacizumab – These are Anti-VEGFs that are injected into the vitreous of the eye in order to prevent growth of new vessels and decrease accumulation of fluid (1).
- Vitrectomy – This is a surgical procedure aiming to improve vision in patients with no clearing vitreous haemorrhage or retinal detachment (5,12).
Prevalence of diabetic retinopathy has increased dramatically over the years and will no doubt result in substantial burden to the healthcare system. Optimal screening and appropriate early interventions are of vital importance in preventing disease progression.
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