Eye diseases related to diabetes include a range of conditions such as refractive changes, double vision, cataract, glaucoma and diabetic retinopathy. Of these conditions, diabetic retinopathy is the only one that is directly caused by diabetes and that most frequently results in vision loss.
What is Diabetic Eye Disease?
Diabetic retinopathy occurs as a direct result of chronic hyperglycaemia causing damage to the retinal capillaries, leading to capillary leakage and capillary blockage. It may lead to loss of vision and eventually blindness. While diabetes may also cause conditions such as cataract, glaucoma, loss of focusing ability and double vision, there needs to be a focus on diabetic retinopathy given the rapidly rising incidence of this largely avoidable form of vision loss.
All people with diabetes are at risk of developing retinopathy. The major risk factors for developing and progression of retinopathy are:
- The duration of diabetes
- High glucose levels
- High blood pressure
An eye condition that is caused by diabetes – diabetic retinopathy:
Diabetic retinopathy results from damage to the small blood vessels of the retina through changes in the blood flow. Initially diabetic retinopathy may cause few or mild symptoms but, as the disease progresses, it can lead to blindness. Diabetic retinopathy can cause changes in the eye including:
• Microaneurysms – small bulges in the blood vessels of the retina that can leak fluid into the retina.
• Retinal haemorrhages – tiny spots of blood that leak into the retina.
• Hard exudates – lipid deposits.
• Cotton wool spots – swollen ischaemic axons in the nerve fibre layer.
• Venous dilation and beading.
• Intraretinal microvascular abnormalities – abnormal branching or dilation of existing blood vessels.
• Abnormal new vessels – depending on the location of the new vessels, these are classified as either “neovascularisation of the disc” or “neovascularisation elsewhere”.
Non-proliferative Diabetic Retinopathy:
The early stage of diabetic retinopathy is known as “non-proliferative diabetic retinopathy”. During this stage the microvascular abnormalities are limited to the retina.
Proliferative Diabetic Retinopathy:
Proliferative diabetic retinopathy occurs as a result of microvascular abnormalities that restrict blood flow to the retina which deprives it of oxygen. In an attempt to supply blood to the deprived areas, new blood vessels grow from the retina into the vitreous cavity. Proliferative diabetic retinopathy can cause severe vision loss via vitreous haemorrhage, tractional retinal detachment and neovascular glaucoma.
Diabetic Macular Edema:
Diabetic maculopathy affects the central part of the retina—the macula— which is important for central vision. This may be through lack of blood flow or swelling and the most common form is diabetic macular edema (DME).
In clinical practice the presence and severity of DME is assessed and documented separately from the stage of diabetic retinopathy. DME is potentially sight threatening. If there are signs of DME particularly involving the centre of the macula, the patient should be seen as soon as possible by an ophthalmologist.
Eye conditions that may be exacerbated by diabetes:
These eye conditions are not caused by diabetes but are more prevalent and, in some cases, deteriorate faster in people with diabetes. While these conditions are less likely to cause vision loss they are still of concern and should be kept in mind by primary health professionals.
Variations in blood glucose levels may cause changes in the refractive power of the eye. If a person presents to an eye care practitioner with substantial refractive changes, this may indicate substantial changes in the level of blood glucose.
Diplopia (double vision) is the simultaneous perception of two images of a single object that is caused by damage to the nerves that control eye movement coordination. Diabetes is the leading cause of the nerve damage that disrupts normal eye movement.
Cataracts are characterised by clouding of the lens that affects vision and can appear in one or both eyes. Snowflake cataracts with white opacities may affect people with type 1 diabetes and sub-optimal metabolic control. Age-related cataract tends to occur earlier among people with diabetes than people without diabetes.
Glaucoma is a group of progressive conditions that results in damage to the optic nerve. It usually occurs when fluid builds up in the front part of the eye. Glaucoma can permanently damage vision in the affected eye(s), reducing peripheral vision and resulting in irreversible visual loss.
• Open-angle chronic glaucoma develops slowly over time and often is asymptomatic until the disease has progressed significantly.
• Closed-angle glaucoma is characterised by sudden eye pain and other symptoms, and is treated as a medical emergency.
• Neovascular glaucoma can be seen in advanced cases of proliferative diabetic retinopathy.