Daiabetes can cause a lot of problems with the eye and can go on to cause blindness. I have written a recent list in my blog if you are interested. One of the complications less known about but which is quite rare is that diabetes can cause double vision, medically termed diplopia. There are three cranial nerves that supply the muscles around the eye that are responsible for eye movement. For instance, the movement of the right eye towards the nose requires the third cranial nerve to act on the appropriate muscle to pull it to the required direction. Diabetes causes damage to the cranial nerves as the blood supply is damaged that supply these nerves. Sometimes these patients can have pain in the eye where the nerve damage has occured.

If the third nerve is affected which supply the muscles that pull the eye up and in, the affected eye falls in the opposite direction so you get the eye turning down and out. This means that one of the eyes is looking where it is supposed to be looking but the affected eye is looking down and out so the patient will see a double image (one image above and to the side of the other). The third nerve also supplies the lids so if there is total nerve defect then the eye that has moved down and out can be completely covered up by the lid (ptosis). In this instance the patient will not complain of diplopia until the lid is pulled up.

To correct this problem will depend on how large the double vision is. When the angle is small then use of prisms ( which shift the image rather than the muscles having to do the work) incorporated in glasses can help. If the diplopia is from a large-angle divergence of the visual axis then patching the affected eye is the only short term solution.

Diabetes can affect the sixth nerve which supplies the muscle that pulls the eye out. The eye on the side where the nerve has been affected will move in towards the nose as the nerve supply has been damaged. The diplopia worsens with gaze in to the field of the weakened muscle.

Treatment of the condition is complicated and can only be applied once it is certain that there are no other underlying causes like injuries, tumours or another vascular event. The double vision is a rare condition with diabetes but of the 140 odd patients turning up to London eye emergency department with diplopia, about 35 had diabetes.

This gives an extra reason to keep your diabetes under control or even try to prevent yourself getting it by good diet, exercise and weight control.