Diabetes and the eyes – prevention is better than cure

Diabetes nurse educator, Kate Bristow, educates us on the normal function of the eyes and how uncontrolled diabetes can damage this.

Before we can identify what is abnormal in the eyes, we need to know what is normal. This is why screening is so important. In eye care, this is a cardinal rule.

The prevalence of diabetes is increasing, especially in working age adults. Fifty percent of people with diabetes don’t know they have diabetes and out of that 50% will not receive treatment or inadequate treatment. Fifty percent of people with diabetes will develop diabetic retinopathy (DR).

What is diabetic retinopathy (DR) and how can we prevent it?

Retinopathy is a complication of diabetes that affects the eyes. DR is caused by damage to the blood vessels in nerve tissue at the back of the eye. If blood pressure and blood glucose levels are consistently high, it can cause serious damage to blood vessels. Blood vessels in your eyes supply blood to the seeing part of the eye which is called the retina.

Damage to blood vessels can cause blockage, leaking or unusual growth of random blood vessels. This means that the retina does not get sufficient blood.

Retinopathy usually develops in stages. Early stages have no symptoms but as the condition progresses you may develop:

• Floaters or spots in your visual field
• Blurred vision
• Dark or empty areas in your vision
• Loss of vision and difficulty perceiving colours
• Blindness can occur

What causes diabetic eye disease?

Too much glucose in the bloodstream over time can lead to damage of the very small blood vessels which take oxygen to the eye. This means no blood supply or reduced blood supply to the eye. The eye tries to compensate by growing new blood vessels, which don’t develop properly and leak or bleed into the retina or into the vitreous (gel-like fluid that fills your eye)  that leads to further damage of the retina.

Retinopathy can be early or advanced

Early diabetic retinopathy is called non-proliferative diabetic retinopathy (NDPR). This means new blood vessels are not yet growing in the eye but the walls of the retina weaken and can bulge and leak fluid or blood into the retina. Larger vessels can also dilate and swell. NPDR can progress from mild to severe as more and more blood vessels are damaged.

Sometimes damage to the retinal blood vessels leads to a build-up of fluid causing swelling in the centre of the retina, the macular. This is called macular oedema and if it affects vision, treatment is required to prevent permanent visual loss.

Advanced diabetic retinopathy is also known as proliferative retinopathy where damaged blood vessels lead to starvation of the retina of oxygen, causing growth of abnormal new vessels in the retina. The vessels are fragile and prone to leaking or bleeding into the vitreous.

Scar tissue from the growth of the new blood vessels can cause the retina to detach from the back of the eye. This is called tractional retinal detachment because the retina is pulled off the eye by scar tissue.

New blood vessels (neovascular) can also interfere with the normal function of the eye and pressure can build up in the eye. Raised intraocular pressure damages the main nerve in the eye (the optic nerve) which carries messages from the eye to the brain, resulting in a condition called glaucoma.

What are the risk factors for diabetic retinopathy?

It can be a complication for anyone who has diabetes especially if you have:

• Diabetes over a longer period
• Poor blood glucose control and bouncing blood glucose levels
• High blood pressure
• High cholesterol in pregnancy
• Smoking
• If you are of African descent or Hispanic, the risk is higher.

Complications associated with diabetic retinopathy include

• Vitreous haemorrhage is when the new abnormal blood vessels bleed into the vitreous of the eye causing floaters or visual disturbances. This is often not permanent and if the retina is not damaged, sight can return to normal after a few weeks or months. Laser treatment is required to regress the abnormal blood vessels and if laser is not possible, surgery to remove the gel (vitrectomy) is done and then laser performed.
• Retinal detachment happens when the scar tissue associated with abnormal blood vessel growth can pull the retina away from the back of the eye. This causes spots, flashes of light or severe loss of vision.
• Glaucoma is when new blood vessels grow on the iris of the eye which interfere with normal flow of fluid out of the eye and increased pressure in the eye. This causes damage to the optic nerve.
• Blindness occurs when diabetic retinopathy, macular oedema, glaucoma individually or in combination leads to complete loss of vision, especially if left untreated.

Prevention is better than cure

Although it is not always possible to prevent diabetic retinopathy, regular eye exams, good blood glucose and blood pressure control and early treatment for problems with your sight can go a long way to preventing severe loss of vision.

Patient education is essential, work with a diabetes nurse educator (DNE) to learn how to better manage other aspects of diabetes. Your DNE is your co-ordinator to the team approach to your diabetes care.

So, in short:

• Manage your diabetes with a healthy eating plan and a regular exercise routine.
• Take medications as prescribed and work with your doctors diabetes educator to improve/manage/maintain your blood pressure, cholesterol and glucose control
• Test your blood glucose levels regularly and aim for targets that you have set with your diabetes medical team.
• Have your HbA1c (glycosylated haemoglobin) tested regularly and aim for a reading of 7% or below. A decrease of 1% in HbA1c can reduce complications of diabetes, including DR by 33% (that’s a 1/3 decrease in risk because of better blood glucose).
• Manage weight and blood pressure; healthy lifestyle choices go a long way to helping with this.
• Quit smoking
• Reduce/stop alcohol use.
• If you have diabetes before or develop it during a pregnancy, the risk of retinopathy may be increased, and you may need more regular eye exams during this period.
• Be aware of visual changes and seek help immediately if you are concerned. This includes blurred vision, or spots.
• See your eye doctor/ophthalmologist for an annual examination even if your vision is fine. Your pupil will be dilated to allow careful examination of the back of your eye.

Diabetes does not always lead to loss of vision and being actively involved in your own diabetes management is the best way to prevent complications. There are team members out there to guide and support you in this. Ask for help from your diabetes team.

The Ophthalmology Society of South Africa (OSSA) developed the Screen For Life programme for early diagnosis of diabetic retinopathy.

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