Cranial nerve 3, the oculomotor nerve, allows the eye to track the movement of objects by supplying nerve impulses to the muscles around the eye. It also supplies nerve function to the eye itself, allowing the lens to change shape, to facilitate focusing, and the iris to contract, to regulate the amount of light affecting the optic nerve. Damage to the oculomotor nerve can cause problems with any of these functions.
Trauma
Trauma to the head, due to a motor vehicle accident or fall, can result in damage to the oculomotor nerve. In the ophthalmic journal Klinika Oczna, Z. Mariak has stated that oculomotor nerve is the most frequently damaged cranial nerve. Closed head trauma can cause partial or complete tearing of the nerve root or nerve fibers, but Mariak notes that the nerve is capable of regeneration within 3 to 5 months.
Congenital Palsy
In rare cases, pediatric patients experience nerve palsies involving the oculomotor nerve. A palsy can manifest as muscle paralysis or uncontrollable tremors. In the British Journal of Ophthalmology, A Langmann MD, of the Department of Ophthalmology at the Medical University of Graz in Austria, describes a number of cases of oculomotor palsy. In such cases the nerve may be underdeveloped, causing visual disturbances, involuntary eye movement or the inability to coordinate the movements of both eyes simultaneously. This type of oculomotor disturbance could be genetic in nature, or could be caused by prenatal trauma, infection or exposure to toxins.
Cranial Mononeuropathy
Mononeuropathies are pathologies that affect a single nerve. Medline Plus cites two types of mononeuropathies affecting the oculomotor nerve.
Cranial mononeuropathy III--compression type--occurs when the oculomotor nerve is exposed to pressure from an external source. This could occur when a blood vessel wall weakens and balloons outward, causing an aneurysm that presses on the nerve. Tumors, trauma and infections could also cause compression to the oculomotor nerve. This condition can manifest in symptoms such as double vision, headaches, pain in the eye, or droopy eyelids.
Cranial mononeuropathy III--diabetic type--occurs when diabetes damages a nerve via the diabetic influences on blood sugar and blood flow. When diabetes damages the oculomotor nerve, the patient may experience the same symptoms as in compression type mononeuropathy.
Both of these conditions may cause the eyes to misalign and the pupils to react in abnormal ways.
