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Autonomic Innervation of ocular
structures and Pupillary Reflexes
Dhanyasree NairM Optom
Autonomic nervous system (ANS)
▪ A type of motor nervous system
▪ Innervates smooth muscles, glands, and the heart and consists of
▪ Sympathetic system - prepares the body to face an emergency
▪ Parasympathetic system - restores the resting state.2
Autonomic nervous system (ANS)
Ocular structures innervated by the ANS are Iris musclesCiliary muscle Smooth muscles of the eyelidsChoroidal and conjunctival blood vessels Lacrimal gland.
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Sympathetic Innervation
▪ Sympathetic innervation for ocular structures originates in segments T-1 through T-3.
▪ Ocular structures supplied by the sympatheticsystem are the iris dilator, ciliary muscle, smoothmuscle of the lids, lacrimal gland, and choroidaland conjunctival blood vessels.
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Autonomic nervous system (ANS)
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SYMPATHETIC
Autonomic nervous system (ANS)
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SYMPATHETIC
Parasympathetic Innervation
▪ Parasympathetic innervation of ocular structures originates in the midbrain and pons.
▪ Ocular structures supplied by the parasympathetic system are the iris sphincter, ciliary muscle, lacrimal gland, and blood vessels.
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Autonomic nervous system (ANS)
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PARASYMPATHETIC
Autonomic nervous system (ANS)
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PARASYMPATHETIC
Autonomic nervous system (ANS)
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Neurotransmitters When an action potential reaches the terminal end of an axon, a
neurotransmitter is released
The neurotransmitter activates either the next fiber in the pathway or the target structure, the effector.
The neurotransmitter binds to effector sites on the muscle and initiates a contraction.
After contraction, it is released from the muscle and is either inactivated or taken back up by the nerve ending, thus preventing muscle spasm
Neurotransmitters
In the sympathetic pathway the neurotransmitter released by the preganglionic fiber is acetylcholine, and the neurotransmitter released by the postganglionic fiber is norepinephrine.
In the parasympathetic system both preganglionic and postganglionic fibers secrete acetylcholine.
Fibers that release acetylcholine are called cholinergic, and fibers that release norepinephrine are called adrenergic.
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Autonomic nervous system (ANS)
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Sympathetic
Parasympathetic
Neurotransmitters
Adrenergic Cholinergic
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DRUGS: AGONISTS AND ANTAGONISTS
Agonist: drug that replicates the action of a neurotransmitter
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Agonist
Direct acting
Indirect acting
Direct-acting agonist : structurally similar to the transmitter and duplicates the action of the neurotransmitter by acting on the receptor sites of the effector.
Adrenergic agonists, eg: Epinephrine and phenylephrine
Cholinergic agonists, eg: Pilocarpine
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Direct-acting agonists
Adrenergic agonist Cholinergic agonist
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Indirect-acting agonist: Excites the nerve fiber
release of transmitter prevents the reuptake of
neurotransmitter
Adrenergic indirect-acting agonists, eg: Hydroxyamphetamine, Cocaine
Cholinergic indirect-acting agonists, eg: Physostigmine
Indirect-acting agonists -Adrenergic
Hydroxyamphetamine Cocaine
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Indirect-acting agonist - Cholinergic
Action of Acetylcholinesterase (AChe) Action of Physostigmine
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Antagonists: Either block the receptor sites or block the release of the neurotransmitter, thus preventing action of the effector.
Adrenergic antagonists, eg: Dapiprazole
Cholinergic antagonists , eg: Atropine, cyclopentolate, andtropicamide 21
Antagonists
Adrenergic antagonist Cholinergic antagonist
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Pupillary Reflexes
▪ LIGHT REFLEX
▪ NEAR REFLEX
▪ DARKNESS REFLEX
▪ PSYCHOSENSORY REFLEXES
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Light Reflex
When light is shone in one eye both the pupils constrict
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Pathway of light reflex (Afferent) The light reflex is mediated by the retinal photoreceptors and carried out by four neurons1. First (sensory) connects each retina with both pretectal nuclei in
the midbrain at the level of the superior colliculi.
- Impulses originating from the nasal retina are conducted by fibres which decussate in the chiasm and pass up the opposite optic tract to terminate in the contralateral pretectal nucleus.
- Impulses originating in the temporal retina are conducted by uncrossed fibres (ipsilateral optic tract) which terminate in the ipsilateral pretectal nucleus.25
Pathway of light reflex (Afferent)
2. Second (internuncial) connects each pretectal nucleus to both Edinger-Westphal nuclei.
-Thus a uniocular light stimulus evokes bilateral and symmetrical pupillary constriction.
-Damage to internuncial neurons is responsible for light-near dissociation in neurosyphilis and pinealomas.
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Pathway of light reflex
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Pathway of light reflex (Efferent)
3. Third (pre-ganglionic motor) connects the Edinger-Westphal nucleus to the ciliary ganglion.
-The parasympathetic fibres pass through the oculomotor nerve, enter its inferior division(the nerve supplying the inferior oblique) and reach the ciliary ganglion.
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Pathway of light reflex (Efferent)
4. Fourth (post-ganglionic motor) leaves the ciliary ganglion and passes in the short ciliary nerves to innervate the sphincter pupillae.
-The ciliary ganglion is located within the muscle cone, just behind the globe.
-Only the parasympathetic fibers synapse in the ciliary ganglion.
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Near Reflex
Occurs on looking at near objects
Consists of two components – a) Convergence reflex : comprises convergence of visual axes and
associated constriction of the pupils
b) Accommodation reflex : Includes increased accommodation and associated pupillary constriction
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Pupillary Reflexes
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Pathway of convergence reflex
Simultaneous contraction of both medial recti
Afferent fibres from the recti muscles travel along the third nerve
Reach the Mesencephalic root of the fifth nerve
Travel to the Edinger-Westphal nucleus via the convergence centre (Perlia’s nucleus)
From Edinger-Westphal nucleus, pathway same as that of light reflex.
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Pathway of accommodation reflex
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Retina
Via Optic nerve, Chaisma Optic Tract
Lateral Geniculate Body
Striate Cortex
Para Striate Cortex
Via Occipitomesencephalic
Tract and Pontine center
EW Nucleus
Via III n. to Sphincter Pupillae
Darkness Reflex
Light to dark Pupil dilates
Has 2 causes: -Abolition of light reflex relaxation of sphincter pupillae
-Contraction of dilator pupillae
Pathway same as that of light reflex
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Darkness Reflex
Light to dark Pupil dilates
Has 2 causes: -Abolition of light reflex relaxation of sphincter pupillae
-Contraction of dilator pupillae
Pathway same as that of light reflex
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Psychosensory reflexes Dilatation of pupil in response to sensory and psychic stimuli.
▪ Absent in a newborn, but appear in the first few days of life and well developed by the age of six months.
▪ Mechanism of psychosensory reflexes is at the cortical level and pupillary dilatation in these results from two components :
-sympathetic discharge to the dilator pupillae
-inhibition of the parasympathetic discharge to the sphincter pupillae.37
Psychosensory reflexes Lid-closure reflex
May occur in 3 forms – ▪ Following a blink, either voluntary or spontaneous, both pupils
constrict. It is assumed to be a type of darkness reflex.
▪ Constriction occurs if the lid is held open while trying to close it. It is also referred to as lid-closure reflex.
▪ Pupillary dilatation associated with lid-closure on touching the cornea (oculopupillary reflex). It is assumed to be a type of psychosensory reflex.38
ABNORMALITIES OF
PUPILLARY REFLEXES
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AFFERENT PATHWAY DEFECTSTOTAL AFFERENT PATHWAY DEFECT (TAPD) OR AMAUROTIC PUPIL
Caused by a complete optic nerve or retinal lesion leading to total blindness on the affected side.
Characterized by the following : Involved eye is completely blind (i.e no light perception)
Absence of direct light reflex on the affected side and absence of consensual light reflex on the normal side.
When the normal eye is stimulated, both pupils react normally.40
Amaurotic pupillary response
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RELATIVE AFFERENT PATHWAY DEFECT (RAPD) OR MARCUS GUNN PUPIL
Caused by an incomplete optic nerve lesion or a severe retinal disease.
Paradoxical response of a pupil to light
Tested by ‘swinging flashlight test’
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EFFERENT PUPILLARY DEFECTS
Characterized by
Absence of both direct and consensual light reflex on the affected side (say right eye)
Presence of both direct and consensual light reflex on the normal side (i.e left eye).
▪ On the affected side, near reflex is also absent and pupils remains fixed and dilated.43
EFFERENT PUPILLARY DEFECTS
Common causes are Brainstem lesions
Fascicular third nerve lesions
Lesions of the ciliary ganglion
Secondary iris damage
Inadvertent exposure to mydriatic drugs44
EFFERENT PUPILLARY DEFECTS TONIC PUPIL
Caused by damage to ciliary ganglion or short ciliary nerves
Clinical features- Affected pupil is larger Reaction to light is absent Near reflex is slow Accommodative paresis
Eg: Adie‘s Tonic pupil (due to denervation of postganglionic supply of sphincter pupillae and ciliary muscle of unknown aetiology)45
PUPILLARY LIGHT-NEAR DISSOCIATIONRefers to any situation in which the pupillary near reaction is present and the light reaction is absent.
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PUPILLARY LIGHT-NEAR DISSOCIATION
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PUPILLARY LIGHT-NEAR DISSOCIATIONARGYLL ROBERTSON PUPIL ( ARP )
Most important cause of pupillary light-near dissociation Caused by neurosyphilis in the region of tectum Clinical features-
------Bilateral, miotic pupil with irregular margins and are asymmetrical.
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SYMPATHETIC PARESISHORNER‘S SYNDROME
Paresis of the oculosympathetic innervation due to a lesion in its pathwayClinical features- Ptosis Upside down ptosis Miosis Normal light and near pupillary reflexes Dilation lag Facial anhydrosis Heterochromia irides49
THANK YOU
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