Diabetes Mellitus is a general health problem which affects approximately 1-2% of the population. It is caused by either a failure to produce insulin, or a decrease in the effect of the insulin produced. This causes an inability of the body to regulate blood glucose levels, causing them to rise. Diabetes is the most common cause of legal blind registrations between the ages of 20 and 65 years.
Diabetes causes changes in the blood vessel walls- damaging their internal lining, which can reduce the diameter of the vessel, and cause an increase in leakiness. It also causes a reduction in the oxygen carrying capability of the red blood cells and an increase in stickiness of clotting agents, which is most likely to affect small and medium sized blood vessels.
The eye can be affected by diabetes in a number of ways.
Because an increased blood sugar level causes fluid to be drawn into the blood stream from the surrounding tissues, the eye, and the lens in particular can become slightly dehydrated, which can cause a change in the prescription- usually an increase in myopia, or a decrease in hyperopia. These prescription changes are transient, and should settle back down as the blood sugars are brought under control. However, no matter how well a diabetic controls their blood sugar levels, it will not be as good as a normal person- it will fluctuate more. This constant slight swelling and de-swelling of the lens can damage the proteins inside it, leading to cataract- age related cataracts can come at a younger age and there are also specific diabetic cataracts. However the type of cataract an individual develops doesn’t matter, and the treatment is the same- a surgical procedure can replace the cloudy lens with a new plastic version.
An eye with low grade diabetic changes- the red blotches in the upper right are small haemorrhages. To the right of the macula (the red bit near the centre) is a yellowish spot, with another lower right- these are exudates. This eye would not require treatment.
Diabetic retinal disease (retinopathy) can be classified in a number of ways, but simply put, it can be broken down into changes which do not, and others which do require specific treatment.
Background Diabetic retinopathy does not require eye treatment.
On examination, the retina can show subtle transient changes-Microaneurysms (ballooning of the tiny capillary walls) and small haemorrhages (called dot/blot haemorrhages) may be seen. An increased leakiness of the vessels, causing retinal swelling- which may show up as exudates- yellow fatty deposits within the retina, may be noted, but unless situated close to central vision, does not require specific treatment.
Damage to the small blood vessels at the back of the eye can cause significant areas of the retina to become hypoxic (lacking in oxygen) which will cause an immediate effect that this part of the retina will not function as well as it did. This causes characteristic changes, which again usually do not require specific treatment.
If enough of the retina becomes hypoxic (lacking oxygen), new blood vessels may begin to grow to supplement the insufficient normal supply. These new blood vessels are unfortunately weaker than normal, and grow in the wrong place. They also have a tendency to produce a fibrous “support” structure. Over time, these vessels can rupture, and the fibrous elements can contract, causing a pull on the retina. This can lead to retinal detachment either by the traction produced pulling it off or by tearing. These blood vessels normally signify to the specialist that treatment will be necessary.
As previously mentioned, new vessels grow (probably in response to chemicals released) because the retina is not getting enough oxygen- hypoxia. If the retina was getting no oxygen at all (anoxia), it appears that it merely ceases to function, but does not release these chemicals. The specialists can use a laser to treat hypoxic areas of the retina. This causes damage to the area treated, but can prevent further release of the chemicals, stopping continued new vessel growth and hopefully the existing ones to regress. This Laser photocoagulation is the most common treatment for Diabetic Retinopathy.
The aim of laser therapy is to prevent further damage to the eye by these new vessels, or vessels which are leaking, but the laser itself does actually damage the retina- it burns. For this reason, “prevention is much better than cure”- some people believe that no matter what state their eyes get to, they can be fixed back to normal with a laser. This is unfortunately not the case. This is why in the above explanations “no specific eye treatment” keeps cropping up- the ophthalmologist does not intervene at that stage, but any improvement in general diabetic control would be beneficial, to prevent or slow advancement of the eye changes.
If the central sight area called the macula is affected, focal (small area) laser treatment may be used to prevent further damage- but some types of maculopathy are not treatable.
Advanced Diabetic Eye Disease
Advance Diabetic eye disease occurs when the proliferative stage has gone untreated, or rarely if treatment has failed to control it, and at this stage, the eye generally cannot be treated by laser alone. Persistent large haemorrhages in the Vitreous jelly at the back of the eye can cause changes which may lead to retinal detachment, which is catastrophic and difficult to treat, or opaque membranes can grow in the jelly. Both of these conditions may require surgery, where necessary the jelly may be removed, fibres pulling on the retina cut, and the retina reattached if at all possible.
Good diabetic control is imperative to the eye’s health, but even the most conscientious diabetic may eventually have problems- the likelihood of problems increases with the number of years the person has been diabetic.
If the diabetic patient is not having formal Diabetic Retinopathy screening done by their GP or a specialist, they should attend for a sight test at least every year, and sooner if advised or if they develop problems, allowing the Optometrist to check the back of the eye for those who require further follow up, or treatment.
Pregnant ladies who are diabetic should be checked very carefully- many experts would recommend every three months during the pregnancy, and a follow up check 6 – 8 weeks after the birth. Pregnancy is a definite risk factor for retinopathy development and/or progression.
It is advisable to inform the optometrist at the time of booking the test that you are diabetic- often it is beneficial to be able to dilate the pupils to ensure as good a view of the back of the eye as possible. Dilation is done using eye drops, which are painless (maybe a little sting?), and take about half an hour to take effect. Because the vision may be temporarily poorer following dilation, it is advisable not to drive or operate machinery during this time. Bring sunglasses, as the brightness may bother you when the pupils cannot constrict. These effects can last 6 to 9 hours, before gradually wearing off, so we would suggest afternoon appointments to avoid disrupting your whole day.