Pupillary pathways reactions Dr C R Thirumalachar Pupillary

Pupillary pathways & reactions Dr. C. R. Thirumalachar

• Pupillary constrictor/ spincter-innervated by parasympathetic • Pupillary dilator – innervated by sympathetic • Evaluation of pupil- Diagnostic clue to ocular, neurological, medical, surgical and paediatric diseases

Light reflex: Direct & Consensual – Afferent pathway • Initiated by retinal photoreceptors • Transmitted along optic nerve • Undergo a hemidecussation at the optic chiasma (nasal fibres cross over) • Proceeds along optic tract • Short of lateral geniculate body- enters midbrain via sup. Brachium of sup. Colliculus • Synapses at pre- tectal nucleus • Ends in both Edinger westpal nucleui

• A second decussation occurs around aqueduct of sylvius • Decussation at chiasma & midbrain level between pretectal nucleus & Edinger Westpal nucleus accounts for consensual light reflex • E. W. nucleus (pupillo motor constrictor centre) • Efferent fibres tract along 3 rd nerve-nerve to inf. Obl. • Enter the ciliary ganglion through its short motor root • Synapse & relay at ciliary ganglion • Post ganglionic fibres reach ciliary muscle and iris spincter through short ciliary nerves

Light Reflex

Near relex • Accomodation reflex: • Stimulus : Blurring of retinal images when object is near • Retina- Optic nerve – Optic chiasma- Optic tract. Optic radiations- Lat geniculate body- visual cortex – cortical association areas- occipito mesencephalic tract- mid brain- E. W. nucleus- 3 rd nerve- accessory ciliary ganglion along short ciliary nerves- ciliary muscle and pupil constrictor

Near reflex- convergence relex • Co contraction of both medial recti • Proprioceptive impulses originate and travel along 5 th nerve • Reach mesencephalic root of 5 th nerve • Transmitted to EWP nucleus in midbrain via convergence centre (Perlias N) • From EWP efferent pathway same as accomodation reflex

Accomodation Reflex

• Dilator pathway • Hypothalamic dilator centre - part of sympathetic system • Descends through brainstem to the spinal cord • C 8 - T 2 segments of spinal cord cilio spinal centre of Budge

• Emerge out of spinal cord – enter paravertebral symp chain & synapses sup cervical ganglion • Symp plexus around carotid artery • Enter cranial cavity along internal carotid artery • Trigeminal ganglion – ophthalmic division – nasociliary nerve- long ciliary nerves- ciliary muscle and dilator pupillae

Sympathetic Pupillary system

Abnormal pupillary reactions • RAPD • RAPD seen in optic nerve & retinal diseases with extensive retinal damage , gross macular lesions. • Accurate quantification of RAPD (using neutral density filters)– is accomplished by determination of the log unit difference needed to balance the pupil reaction between the 2 eyes

Marcus Gunn Pupil -When the contralateral/normal eye is covered, pupil on the affected side dilates -When the affected eye is covered pupil of the normal eye remains unaffected. – Light is thrown on ipsilateral side(affected side); Ipsilateral direct reflex & contralateral consensual reflex- sluggish and ill sustained. – Light thrown on contralateral side (normal side) direct & consensual (affected side) is normal & well sustained

-If light is kept persistently on affected side, pupil may show initial sluggish contraction but contraction is ill sustained & gradually shows paradoxical dilatation -Indicates conduction defect along efferent pathway (Optic nerve, Optic chiasma, part of optic tract, dorsal mid brain )

• Argyll Robertson pupil(ARP) – Occurs in neurosyphilis, Tabesdorsalis, G. P. I. – Pupil is usually constricted ( involvement of descending sympathetic dilator fibres) – Light reflex is absent – Accomodation reflex , near reflex retained – Site of lesion –Pretectal nucleus. (dorsal mid brain)

• Horner’s syndrome : – Involvement of cervical sympathetic – Miosis, partial ptosis, enophthalmos & anhydrosis – Iris heterochromia

• Pourfour de Petit Syndrome – This syndrome is the clinical opposite of Horner syndrome. It represents oculosympathetic overactivity – unilateral mydriasis, lid retraction, apparent exophthalmos, and conjunctival blanching – Seen after trauma, brachial plexus anesthetic block or other injury, and parotidectomy

• Hemianopic pupil ( wernicke’s pupil ) – Seen in optic tract lesions with hemianopia – Stimulating the blind half of retina pupil shows no reaction – Stimulating seeing half of retina pupil shows reaction – Difficult to elicit – due to scattering & diffusion of light – Use a narrow streak of light

Hutchinson’s pupil • Useful in assessment of head injuries • Stage 1 : Ipsilateral pupil (on the side of head injury shows contraction due to irritation, Contralateral (normal) pupil –normal • Stage 2 : Ipsilateral pupil shows dilatation due to paralysis , contralateral pupil constricts (irritation spreads to normal side)

• Stage 3 : Both pupils dilate. Stage of bilateral paralysis. To assess pupil repeatedly is important, therefore mydriatics should be avoided in case of head injuries

• Adie’s tonic pupil: Characterised by – large unilaterally dilated pupil – Absent / poor light response – In near response , there is slow / tonic contraction of the iris – May be associated with loss of deep tendon reflexes (Adie’s syndrome) – Seen in young women

• Pupil in 3 rd nerve palsy – Dilated – Non reactive – Absolute motor paralysis – Associated with ptosis, deviation of eyeball

• Pupil in diabetes – Constricted – Sluggishly reactive due to • Glycogen infiltration of spincter • Autonomic denervation • Arteriosclerosis of radial iris vessels

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