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What is Oculomotor nerve palsy and explain in detail?
Oculomotor nerve palsy or oculomotor neuropathy is an eye condition resulting from damage to the third cranial nerve or a branch thereof. As the name suggests, the oculomotor nerve supplies the majority of the muscles controlling eye movements (four of the six extraocular muscles, excluding only the lateral rectus and superior oblique). Damage to this nerve will result in an inability to move the eye normally. The nerve also supplies the upper eyelid muscle (levator palpebrae superioris) and is accompanied by parasympathetic fibers innervating the muscles responsible for pupil constriction (sphincter pupillae). The limitations of eye movement resulting from the condition are generally so severe that patients are often unable to maintain normal eye alignment when gazing straight ahead, leading to strabismus and, as a consequence, double vision (diplopia).

Presentation
A complete oculomotor nerve palsy will result in a characteristic displacement outward (exotropia) and downward (hypotropia). The outward displacement occurs because the lateral rectus muscle (innervated by the sixth cranial nerve) maintains muscle tone in comparison to the paralyzed medial rectus. The downward displacement occurs because the superior oblique muscle (innervated by the fourth cranial or trochlear nerve) is unantagonized by the paralyzed superior rectus, inferior rectus and inferior oblique. The affected individual will also have a ptosis, or drooping of the eyelid, and mydriasis (pupil dilation).

Causes
Oculomotor palsy can arise as a result of a number of different conditions. Non traumatic pupil-sparing oculomotor nerve palsies are often referred to as a "medical third," with those affecting the pupil being known as a "surgical third."

Congenital oculomotor palsy
The origins of the vast majority of congenital oculomotor palsies are idiopathic. There is some evidence of a familial tendency to the condition, particularly to a partial palsy involving the superior division of the nerve with an autosomal recessive inheritance. The condition can also result from aplasia or hypoplasia of one or more of the muscles supplied by the oculomotor nerve. It can also occur as a consequence of severe birth trauma.

Acquired oculomotor palsy
Vascular disorders such as diabetes, heart disease, atherosclerosis and aneurysm, particularly of the posterior communicating artery
Space occupying lesions or tumours, both malignant and non-malignant
Inflammation and infection
Trauma
Demyelinating disease (multiple sclerosis)
Autoimmune disorders such as myasthenia gravis
Post-operatively as a complication of neurosurgery
Cavernous sinus thrombosis

Mechanism
As the pair of oculomotor nerves arises from different subnuclei in the midbrain, courses through different structures in the brain and branches into superior and inferior divisions after exiting the cavernous sinuses, any lesions along its path will produce different pathological features of the third nerve palsy. The parasympathetic aspect of the nerve (which constricts pupils and thicken the lens) is located on the nerve surface, supplied by pial blood vessels. The nerves core contains the main trunk of the oculomotor nerve, supplied by vasa vasorum. Thus pathologies affecting the nerves core without affecting the superficial part of the nerve (thus sparing the pupillary reflex) are known as "medical" oculomotor nerve palsy