Pupils Flashcards
The light reflex is mediated by retinal photoreceptors and subserved by 4 neurons.
First (sensory) connects each retina with both pretectal nuclei in the midbrain at the level of the ____________. Impulses originating from the nasal retina are conducted by fibres that decussate in the __________ and pass up the contralateral optic tract to terminate in the contralateral pretectal nucleus. Impulses originating in the temporal retina are conducted by uncrossed fibres (ipsilateral optic tract) that terminate in the ipsilateral pretectal nucleus.
Second (internucleal) connects each pretectal nucleus to both __________. Thus, a monocular light stimulus evokes bilateral and symmetrical pupillary constriction. Damage to internucleal neurons is responsible for light-_____________ in neurosyphilis and pinealomas.
Third (preganglionic motor) connects the Edinger-Westphal nucleus to the ciliary ganglion. The parasympathetic fibres pass through the __________, enter its inferior division and reach the ciliary ganglion via the nerve to the inferior oblique muscle.
Fourth (postganglionic motor) leaves the ciliary ganglion and passes in the ___________ to innervate the sphincter pupillae. The ciliary ganglion is located within the muscle cone, just behind the globe. It should be noted that, although the ciliary ganglion serves as a conduit for other nerve fibres, only the parasympathetic fibres synapse there.
superior colliculus;
optic chiasm;
Edinger-Westphal nuclei;
near dissociation (LND);
oculomotor nerve (CN3);
short ciliary nerves
The sympathetic supply involves 3 neurons:
First (central) starts in the ____________ and descends, uncrossed, down the brainstem to terminate in the ___________, in the intermediolateral horn (IML horn) of the spinal cord, located between C8 and T2.
Second (preganglionic) passes from the ciliospinal centre to the superior cervical ganglion in the neck. During its long course, it is closely related to the __________where it may be damaged by bronchogenic carcinoma (Pancoast tumour) or during surgery on the neck.
Third (postganglionic) ascends along the __________ to enter the cavernous sinus where it joins the ophthalmic division of the trigeminal nerve (CN V1). The sympathetic fibres reach the ciliary body and the ____________ via the nasociliary nerve and the long ciliary nerves.
posterior hypothalamus;
ciliospinal centre of Budge;
apical pleura;
internal carotid artery (ICA);
dilator pupillae muscle
what are the causes of central (first order) horners?
- Brainstem disease – commonly stroke (e.g. lateral medullary infarction), but also tumour, demyelination (multiple sclerosis)
- Syringomyelia
- Lateral medullary syndrome (Wallenberg syndrome)
- Cervical spinal cord lesion
- Diabetic autonomic neuropathy
what are the causes of preganglionic (second order) horners?
- Pancoast tumour
- Carotid and aortic aneurysm and dissection
- Thoracic spinal cord lesion
- Miscellaneous neck lesions (thyroid tumour, enlarged lymph nodes, trauma, post-surgical)
what are the causes of postganglionic (third order) horners?
- Internal carotid artery dissection (painful)
- Nasopharyngeal tumour
- Cavernous sinus mass
- Otitis media
what is the presentation of horners?
Mild ptosis
- Usually only 1-2 mm
- Results from weakness of superior tarsal muscle/Muller’s muscle
Miosis (and anisocoria)
- Ptotic eye has smaller pupil (miosis)
- Due to unopposed action of the sphincter pupillae on affected side
- Dilator lag - smaller pupil takes a longer time to dilate when a bright source of light is moved away from the eye
- Anisocoria worse in the dark
+/- Anhidrosis
- Sudomotor fibres supplying the skin of the face run along the external carotid artery (ECA), so anhidrosis occurs only if the lesion is below the superior cervical ganglion (i.e. first or second order Horner’s)
- Anhidrosis is absent in third order Horner’s/postganglionic
Horner’s
Hypochromic heterochromia (iris of different colour; Horner being lighter)
- Seen in congenital or long-standing Horner’s
Isolated vs non-isolated
Isolated: no other neurologic or systemic deficits
what are the test to confirm the diagnosis of horner’s?
Topical apraclonidine 0.5% (alpha-2 adrenergic agonist)
- Aim: confirms Horner’s
- Causes pupillary dilation in the Horner’s pupil due to denervation supersensitivity (upregulation of adrenergic receptors in denervated dilator pupillae) + mild pupillary constriction in the normal pupil (presumably by downregulating the noradrenaline release at the synaptic cleft), i.e. reversal of anisocoria
Topical hydroxyamphetamine 1%
- Aim: differentiates preganglionic from postganglionic Horner’s
- A normal or preganglionic Horner pupil will dilate, but postganglionic Horner will not dilate. This is because hydroxyamphetamine potentiates the release of noradrenaline from functioning postganglionic nerve endings.
- In a lesion of the third order neuron (postganglionic), there is no release of noradrenaline from the dysfunctional nerve.
what are the investigations that should be done for a horners patient?
Seek urgent neurological assessment; acute Horner’s should be considered an emergency
CT/MR angiography, spanning circle of Willis to aortic arch to r/o neck (including carotid), apical lung, thyroid, and skull base lesions
Perform other relevant investigations, depending on the suspected aetiology, e.g. CXR, CT thorax, carotid doppler U/S, MRI brain/head/neck
what is adie’s tonic pupil?
- caused by denervation of the postganglionic parasympathetic supply to the sphincter pupillae and ciliary muscle, and may follow a viral illness
- tonically dilated pupil that reacts slowly to light but shows a more definite response to accommodation (i.e., light-near dissociation [LND]) + anisocoria worse in the light (because parasympathetic lesion)..
what is argyll roberston pupils?
bilateral small pupils that reduce in size on a near object (i.e., they accommodate), but do not constrict when exposed to bright light (i.e., they do not react to light)
