It travels through the cavernous sinus and close to the posterior communicating artery. The oculomotor nerve travels directly from the brainstem to the eye in a straight line. Therefore third nerve palsy causes a dilated fixed pupil. The oculomotor nerve also contains parasympathetic fibres that innervate the sphincter muscle of the iris. Therefore third nerve palsy causes a ptosis. It also supplies the levator palpebrae superioris, which is responsible for lifting the upper eyelid. Therefore when these muscles are no longer getting signals from the oculomotor nerve, the eyes moves outward and downward due to the effects of the lateral rectus and superior oblique still functioning without resistance. It supplies all of the extraocular muscles except the lateral rectus and superior oblique. The third cranial nerve is the oculomotor nerve. It causes a “ down and out” position of the eye. Divergent strabismus (squint) in the affected eye.Argyll-Robertson pupil (in neurosyphilis).This is usually temporary and associated with migraines. Tadpole pupil is where there is spasm in a segment of the iris causing a misshapen pupil. This can cause a hole in the iris causing an irregular pupil shape. This is usually associated with poorly controlled diabetes and diabetic retinopathy.Ĭoloboma is a congenital malformation in the eye. Rubeosis iridis (neovascularisation in the iris) can distort the shape of the iris and pupil.
This could be caused by cataract surgery and other eye operations.Īnterior uveitis can cause adhesions (scar tissue) in the iris that make the pupils misshapen.Īcute angle closure glaucoma can cause ischaemic damage to the muscles of the iris causing an abnormal pupil shape, usually a vertical oval. Trauma to the sphincter muscles in the iris can cause an irregular pupil. They are stimulated by the sympathetic nervous system using adrenalin as a neurotransmitter. The dilator muscles of the pupil arranged like spokes on a bicycle wheel travelling straight from the inside to the outside of the iris. The fibres of the parasympathetic system innervating the eye travel along the oculomotor (third cranial) nerve. They are stimulated by the parasympathetic nervous system using acetylcholine as a neurotransmitter. There are circular muscles in the iris that cause pupil constriction. The pupil is formed by a hole in the centre of the iris.
There are a number of conditions that can cause abnormally shaped or sized pupils.
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