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Pupillary reflexes
The document discusses normal and abnormal pupillary reflexes. It describes the anatomy and physiology behind the light reflex and near reflex. The light reflex involves transmission of signals from the retina through the optic pathway to the Edinger-Westphal nucleus which controls the iris sphincter and dilator muscles. The near reflex involves a triad of accommodation, convergence, and pupillary constriction. It also discusses various pupil abnormalities that can occur due to lesions in the afferent or efferent pathways as well as pharmacologic agents that cause miosis or mydriasis. Specific conditions mentioned include Horner's syndrome, Adie's tonic pupil, and Argyll Robertson pupil.
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Pupillary reflexes
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- 2. Normal pupil • Functions: •Limits the amount of light reaching retina • Controls spherical & chromatic aberrations • Number • Location • Size 3-4 (bright)… 4-8 (dark) • The same for different genders & iris colours • Variation with age • Physiologic anisocoria
- 3. • Pupillary unrest:constant symmetrical fluctuation… detected by magnification • Hippus: exaggerated.. Detected on visual inspection • No diagnostic significance • Colour: depend on the structures behind it • Greyish black • Jet black • leukocoria
- 4. • Pupillary constrictor/spincter-innervated by parasympathetic • Pupillary dilator – innervated by sympathetic • Evaluation of pupil- Diagnostic clue to ocular, neurological, medical, surgical and paediatric diseases
- 5. Light reflex • Whenlight is shown to one eye.. Both pupils constrict • Direct vs consensual • Almost identical in time, course & magnitude • If both pupils illuminated at once summation • Dependant the state of adaptation of the retina, emotions, alertness, … • Maximum frequency of stimuli is 5 Hz
- 6. Light reflex • Initiatedby retinal photoreceptors • Transmitted along optic nerve • Undergo a hemidecussation at the optic chiasma (nasal fibres cross over) • Proceeds along optic tract • Synapses at pre- tectal nucleus • Ends in both Edinger westpal nucleui • Any given pretectal neuron behaves functionally as though it recieves similar inputs from each eye & projects equally in each EW nucleus • Ipsilateral around periaqueduct • Contralateral via the posterior commissure
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- 8. • Efferent fiberstravel on the surface of CN-III • to inf. Obl. • &/ due to long course unilateral defecits can be of localizing significance in unilateral pathology • Synapse & relay at ciliary ganglion • Post ganglionic fibres reach ciliary muscle and iris spincter through short ciliary nerves to reach the sphincter pupillae • Cerebral cortex sends inhibitory signals to EW nucleus absence leads to meiosis during sleep
- 9. • Functions: • Protectsagainst excessive bleaching of the visual pigments • Light/Dark adaptation to maximize VA
- 10. Near reflex • Triad: •Inc. accomodation • Convergence of visual axes • Constriction of the pupils
- 11. Near reflex • Accomodationreflex: • 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- 3rd nerve- accessory ciliary ganglion along short ciliary nerves- ciliary muscle and pupil constrictor
- 12. Near reflex- convergence reflex •Co contraction of both medial recti • Proprioceptive impulses originate and travel along 5th nerve • Reach mesencephalic root of 5th nerve • Transmitted to EW nucleus in midbrain via convergence centre (in the tectal or pretectal area) • From EW efferent pathway same as accomodation reflex
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- 14. Darkness reflex • Fromlighted to dim environment • Physiology • Abolition of light reflex relaxation of sphincter pupillae • Contraction dilator pupillae
- 15. Psychosensory reflexes • Dilationin response to psychological stimuli • Not seen in newborn • Fully developed at 6 months of age • Cortical mechanism
- 16. Ciliospinal reflex • Pupildilation in response to painful stimulus in the neck • Indicates that some of the psychosensory reflex is mediated at the spinal cord
- 17. Lid-closure reflex • Nonspecificterm 1.Meiosis with blinking • Constrict transiently with blinking • Absent in darkness maybe darkness reflex 1.Homolateral meiosis with lid closure • Constrict with forced prohibited lid closure • Absent if distant gaze unconscious attempt at near gaze 1.Oculopupillary reflex (mydriasis on corneal touch)
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- 19. Parasympathomimetics • Cholinergic • Initiateor potentiate acetylcholine action 1.Direct acting • Pilocarpine; similar to acetylcholine 1.Indirect (cholinesterase inhibitors) • Cholinesterase is present in presynaptic axon • Block action or deplete stores 1. Reversible physostigmine 2. Irreversible ecothiophate iodide, demecarium, diisopropyl fluorophosphate 2.Dual action
- 20. Sympatholytics • Alpha-adrenergic blockers •By preventing dilator contraction by occupying alpha-receptor sites on the iris dilator • E.g: thymoxamine, phenoxybenzamine, dibenamine, tolazoline • Guane-thidine • commonly used in ophthalmology • Depletes norepinephrine stores & disrupts release • Continued topical drops lead to Horner’s syndrome
- 21. Other miotics • Histamine: •Direct action • Even in atropinized eyes • Morphine • Cutting off cortical inhibition of EW nucleus • Also direct action
- 22. Sympathomimetics • Ways ofaction: • Inc. norepinephrine release • Prevent reuptake • Direct action 1.Adrenaline (epinephrine) • Direct action • 4 drops of 0.1% q5m • Rapidly inactivated (not effective)
- 23. 2. Phenylephrine 5-10% •Synthetic analog • Direct action & inc. release 2. Hydroxyamphetamine & ephidrine • Inc. release 2. Cocaine • Prevents reuptake
- 24. Parasympatholytics 1. Atropine 1% •Strongest • Completely paralyses sphincter pupillae & ciliary muscles • Complete dilation in 30-40 m & cycloplegia in 2h • Duration 7+ d 1. Homatropine 2% • Quicker • Cycloplegia in 45-60 m • Duration 48 h
- 25. 3. Cyclopentolate 1% •Short acting • Cycloplegia 1 h • Duration 6-12 h 3. Tropicamide 1% • noncycloplegic
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- 27. Afferent pathway defects 1.TAPD (amaurotic pupil) • Complete retinal or nerve lesion • Total blindness • -ve ipsilateral direct & contralateral consensual light reflex • Isocoria in diffuse illumination • Near reflex is preserved
- 28. 2. RAPD (marcusgunn pupil) • Severe retinal or incomplete optic nerve lesion • Swinging flashlight test • Paradoxical response of the affected pupil by Swinging flashlight test • Earliest sign of optic nerve disease • VA maybe preserved
- 29. • 3. Wernicke’shemianopic pupil • Optic tract lesion • Ipsilateral temporal & contralateral nasal
- 30. Efferent pathway defects •Ipsilateral absence direct & consensual light reflexes • Ipsilateral absence of near reflex • Ipsilateral fixed & dilated pupil • Causes • Brainstem lesions • Fascicular 3rd nerve lesion • Ciliary ganglion lesion • Iris damage • Drugs • Pilocarpine to differentiate from neuro
- 31. Tonic pupil • -velight, accomodation & near reflexes • Cholinergic hypersensitivity (pilo 0.125%) • Causes • Local • Herpes zoster ganglionitis • Orbital or choroidal trauma or tumors • Blunt trauma resulting injury at the iris root • Neuropathic (DM, alcoholism) • Adie’s tonic pupil
- 32. • Adie’s tonicpupil: 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 as for the knee (Adie’s syndrome) • Seen in young women • Mild regional corneal impaired sensitivity
- 33. Light-Near dissociation 1. Bilateralcomplete afferent pathway defect 2. Lesion in the midbrain at the level of the pretectal area 3. CN-III palsy with regeneration of MR innervation into sphincter innervation pathway (pseudo-Argyll Robertson pupil) 4. Ciliary ganglion or short ciliary nerve with regeneration of accomodation fibers into sphincter pupillae 5. Aberrant regeneration in DM, alcoholism, amyloidosis
- 34. • Argyll Robertsonpupil(ARP) • Occurs in neurosyphilis, Tabesdorsalis,G.P.I. • Site of lesion: (dorsal mid brain) in the region of the tectum near the sylvian aqueduct interfering with light reflex fibers & supranuclear inhibitory fibers going down to EW nucleus • Characteristics: • Bilateral asymmetrical involvement • Small irregular pupils • Preserved vision • -ve light & +ve near reflexes • Poor dilation with atropine • Further constriction with physostigmine
- 35. • Horner’s syndrome: • Involvement of cervical sympathetic • Miosis, partial ptosis, enophthalmos & anhydrosis • Iris heterochromia
- 36. • Pourfour dePetit 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