We all have 12 nerves that control the movement and sensation of everything in our head and neck. Actually, there are 24, because there is one on each side. Some of these nerves are very important in neuro-ophthalmology.
Cranial Nerve 2
Cranial nerve 2 is the optic nerve, which connects the eye to the brain. Damage to this nerve causes loss of vision, but we don’t call this a cranial nerve palsy. If the nerve is inflamed, then we call it optic neuritis. Other causes of damage, such as a tumour, loss of blood supply, or trauma is called an optic neuropathy.
Cranial Nerve 3
Cranial nerve 3 controls the position of the upper eyelid, the size of the pupil and many eye movements. A 3rd nerve palsy can cause any combination of double vision, unequal pupils and a droopy eyelid. Although this usually happens because of a temporary lack of blood flow to the nerve, there are other more dangerous causes that need to be looked for.
Cranial Nerve 4
Cranial nerve 4 moves the eyes up and down and also rotates them when you tilt your head. A 4th nerve palsy will cause double vision with the two images apart either diagonally or up and down. Straight lines may also look tilted. Many people with 4th nerve palsies were actually born with them, but didn’t realize it until they stop being able to compensate for it. Other common causes are a temporary lack of blood flow to the nerve or head trauma.
Cranial Nerve 6
Cranial nerve 6 moves the eyes outwards. A 6th nerve palsy will cause double vision with the two images side by side. The images usually get closer together when you look to one side and further apart when you look to the other side. Common causes of 6th nerve palsy are a temporary lack of blood flow to the nerve, high pressure inside the head, and temporal arteritis. There are many other rare causes that will also need to be screened for.
Cranial Nerve 7
Cranial nerve 7 controls most of the muscles in the face. A 7th nerve palsy is also called a Bell’s palsy, and causes half of the face to droop. This can look a lot like a stroke, and needs to be assessed immediately. Many people cannot close their eye because of the weakness. If the eye dries out, it can be very painful and cause blurred vision. A 7th nerve palsy often happens for no good reason, but may be related to an infection or other rare causes.