Why does third nerve palsy dilate pupils?

Why does third nerve palsy dilate pupils?

Pupil: In compressive third-nerve palsy, the pupil becomes fixed and dilated due to paralysis of sphincter pupillae. Ciliary muscle paralysis also leads to loss of accommodation. However, in ischemic lesions, the pupil is spared, and there is no loss of accommodation.

What cranial nerve dilates the pupil?

The oculomotor nerve (the third cranial nerve; CN III) has three main motor functions: Innervation to the pupil and lens (autonomic, parasympathetic)

What happens when the oculomotor nerve is damaged?

Damage to any of these nerves or the muscle or muscles they innervate causes dysconjugate gaze, which results in characteristic patterns of diplopia (double vision). In addition, with oculomotor nerve damage, patients also lose their pupillary constriction to light as well as the elevation of their eyelid.

What clinical signs are expected in case of damage to oculomotor nerve?

Symptoms and signs include diplopia, ptosis, and paresis of eye adduction and of upward and downward gaze. If the pupil is affected, it is dilated, and light reflexes are impaired.

Can third nerve palsy be corrected?

What can be done to correct third nerve palsy? Unfortunately, there is no treatment to re-establish function of the weak nerve if it is a congenital case. An acquired third nerve palsy may resolve, depending on the cause.

What pupil dilation means?

Muscles in the colored part of your eye, called the iris, control your pupil size. Your pupils get bigger or smaller, depending on the amount of light around you. In low light, your pupils open up, or dilate, to let in more light. When it’s bright, they get smaller, or constrict, to let in less light.

What does 3rd nerve palsy look like?

Older children and adults with third nerve palsy usually have double vision (diplopia) due to misalignment of the eyes. If a droopy eyelid (ptosis) covers the pupil, diplopia may not be noticeable. Ptosis of the eyelid or an enlarged pupil may be the first sign of a third nerve palsy.

What type of sickness is palsy?

Palsy means weakness or problems with using the muscles. CP is caused by abnormal brain development or damage to the developing brain that affects a person’s ability to control his or her muscles. The symptoms of CP vary from person to person.

Is the oculomotor nerve responsible for pupillary constriction?

Therefore, the oculomotor nerve is responsible not only for a wide variety of eye movements but also for pupillary constriction and lens accommodation. A variety of pathologies may affect this nerve, but it will result in ptosis, the eye rotated downward and outward and with a fixed, dilated pupil.

What causes non traumatic pupil sparing oculomotor palsy?

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’.

Why is damage to the oculomotor nerve called down and out?

Since the oculomotor nerve controls most of the eye muscles, it may be easier to detect damage to it. Damage to this nerve, termed oculomotor nerve palsy, is known by its down and out symptoms, because of the position of the affected eye (lateral, downward deviation of gaze).

What does acquired oculomotor nerve palsy ( OMP ) mean?

Acquired oculomotor nerve palsy (OMP) is an ocular pathology resulting from damage to third cranial nerve. It can presents in different ways causing somatic extraocular muscle dysfunction (superior, inferior, and medial recti; inferior oblique; and levator palpebrae superioris) and autonomic (pupillary sphincter and ciliary) muscles.