Cranial Nerve Palsies

Three cranial nerves control the muscles that move the eye, the third, fourth and sixth. There is a complex control mechanism from the mid-brain that coordinates eye movements so that you can read, follow a moving object, and adjust to different light conditions whilst maintaining binocular vision the whole time. This is no mean feat and tiny changes to the nerves and control mechanism can cause significant symptoms.

Sometimes the nerves fail to work. If any one of these nerves fails to function, the eyes will not move normally and you will notice double vision. It will either be horizontal, or vertical, depending upon which nerve(s) are involved.

Details of the individual symptoms and findings associated with each nerve palsy are beyond the scope of this discussion. If, however, you experience double vision and have been diagnosed with nerve palsy there will be a system of investigations to rule out potential causes that may include the following:

  • Vascular nerve palsy – blood vessels to nerve affected – conditions such as diabetes and vasculitis need to be excluded
  • Head injury
  • Aneurysms
  • Pituitary problems
  • Raised intracranial pressure – tumours, benign variants

In order to exclude these possible causes the following investigations may be requested:

  • CT scan
  • MRI scan
  • Xray
  • Angiogram (Dye injected into vessels to demonstrate their patency)
  • Ultrasound
  • Blood tests

In many cases a precise cause may not be identified.

Most cranial nerve palsies get better after a month or so.

If you have double vision you should not drive.

Courtesy Mr Graham Duguid

Binocular single vision is essential for certain tasks….

It may be possible to attach a Fresnel Prism to glasses to eliminate the worst of the double vision straight ahead. If the problem persists for more than a few months, prisms can be incorporated into your glasses.

If there s no recovery, and no prospect of improvement; surgery to the eye muscles can be considered. This is particularly helpful with reducing double vision in the straight-ahead direction, but may not address the issue in all positions of gaze.

Banner image: Bilateral sixth nerve palsy in a cat

This man has a 6th nerve palsy affecting the left eye. This stops the left eye from turning outwards.
The picture on the left shows him trying to look left, the right eye can do it the left cannot.
In the middle he looks at a near object without problem.  On the right he is looking to the right
and he can do this as well.  He just gets double-vision looking to the left in the distance .