Disorders Of The Pupils And Eye Movements Flashcards
Learn all about disorders of the eyes
Pupil Disorders: Which two groups of smooth muscles within the iris determine pupil size?
- Sphincter pupillae: circular constricter muscle parasympathetically innervated
- Dilator pupillae: radial dilator sympathetically innervated
Anatomical pathway of fibres controlling the pupillary muscles?
- Parasympathetic fibres arise in Edinger-Westphal nucleus in the dorsal midbrain.
- Sympathetic fibres arise in the hypothalamus
What is the light reflex, when light is shone into the eye?
- Afferent stimulus travels via the retina, optic nerve and then both optic tracts. They synapse with the Edinger Westphal nuclei.
- Efferent fibres from this nuclei travel within third cranial nerve to innervate the sphincter pupillae.
- Effect in pupil where light has been shone called direct response, response in other eye called consensual response.
What is Aniscoria?
- Inequality of in size of pupil
- Pupillary response to light and accommodation are unaffected
- In pathological Aniscoria there is interruption of the pathways of light and or accomodation
To identify which pupil is abnormal in patients with Aniscoria?
- Pupillary response: abnormal pupil will have impaired response to light and accommodation.
- Evidence of ptosis: look for other signs eg Horner’s syndrome. If ptosis accompanied by large pupil look for other signs of third nerve palsy.
- Response to dark: Place patient in the dark, if pupil fails to dilate then probably pathological pupil
Describe Horner’s Syndrome
Interruption of sympathetic pathway characterised by:
- Pupil constriction: Pupil reaction to light and accommodation is reduced. Affected pupil dilates less than normal one in dim light.
- Partial ptosis
- Anhidrosis (lack of sweating)of ipsilateral side of face.
- Enophthalmos - Sunken eye
What is a Pontine lesion?
Bilateral unreactive pin point pupils in a comatose patient suggests a large intrapontine lesion, such as hemorrhage, causing bilateral interruptions of the sympathetic pathways within the brainstem
Causes of Horner’s Syndrome?
- Hypothalamic lesions eg craniopharyngioma
- Brainstem eg MS, infarction, tumour(glioma)
- Cervical cord eg syringomyelia ( cyst forming in spinal cord)
- T1 root eg pancoast tumour, cervical rib
- Sympathetic chain: neoplastic infiltration, surgical damage, carotid artery dissection
Causes of Horner’s Syndrome?
- Hypothalamic lesions eg craniopharyngioma
- Brainstem eg MS, infarction, tumour(glioma)
- Cervical cord eg syringomyelia ( cyst forming in spinal cord)
- T1 root eg pancoast tumour, cervical rib
- Sympathetic chain: neoplastic infiltration, surgical damage, carotid artery dissection
Describe Argyll Robertson pupils
- Small and irregular
- No response to light but response to accommodation
- Lesion thought to be in midbrain
- AR pupils associated with tertiary neurosyphillis
Causes of large mydriatic pupils
- Lesions of the eye: damage to the iris in acute glaucoma, trauma to the sphincter muscles
- Drugs: parasympathetic paralysis (atropine), sympathetic stim (adrenaline)
- Third nerve lesion
- Holmes Adie pupil
- Afferent pupillary defect
What aretypical third nerve lesions?
- Pupil is dilated both direct and consensual light responses on affected side are absent
- This is an efferent papillary so consensual response on unaffected side is present if light is shone on affected side
What are the characteristics of 3rd nerve palsy?
- Ptosis
- Opthalmoplegia: Levator palpebrae, superior, inferior, medial recti, and inferior oblique
3.
What ate common causes for third nerve palsys?
- Diabetic mononeuropathy
- Posterior communicating artery aneurysm
- Herniation of the uncus of the temporal lobe in raised intracranial pressure
