Pupillary ReflexesOthman Al-Abbadi, M.D

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

• 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

• 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• When light 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

Light reflex• Initiated by 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

Light Reflex

• Efferent fibers travel 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

• Functions:• Protects against excessive bleaching of the visual pigments• Light/Dark adaptation to maximize VA

Near reflex• Triad:

• Inc. accomodation• Convergence of visual axes• Constriction of the pupils

Near reflex• 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- 3rd nerve- accessory ciliary ganglion along short ciliary nerves- ciliary muscle and pupil constrictor

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

Accomodation Reflex

Darkness reflex• From lighted to dim environment• Physiology

• Abolition of light reflex relaxation of sphincter pupillae• Contraction dilator pupillae

Psychosensory reflexes• Dilation in response to psychological stimuli• Not seen in newborn• Fully developed at 6 months of age• Cortical mechanism

Ciliospinal reflex• Pupil dilation in response to painful stimulus in the neck

• Indicates that some of the psychosensory reflex is mediated at the spinal cord

Lid-closure reflex

• Nonspecific term

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)

Pharmacology

• Miotics

• Mydriatics

Parasympathomimetics

• Cholinergic• Initiate or potentiate acetylcholine action1.Direct acting• Pilocarpine; similar to acetylcholine

1.Indirect (cholinesterase inhibitors)• Cholinesterase is present in presynaptic axon• Block action or deplete stores1. Reversible physostigmine2. Irreversible ecothiophate iodide, demecarium,

diisopropyl fluorophosphate

2.Dual action

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

Other miotics• Histamine:• Direct action• Even in atropinized eyes

• Morphine• Cutting off cortical inhibition of EW nucleus• Also direct action

Sympathomimetics • Ways of action:• Inc. norepinephrine release• Prevent reuptake• Direct action

1.Adrenaline (epinephrine)• Direct action• 4 drops of 0.1% q5m• Rapidly inactivated (not effective)

2. Phenylephrine 5-10%• Synthetic analog• Direct action & inc. release

2. Hydroxyamphetamine & ephidrine• Inc. release

2. Cocaine• Prevents reuptake

Parasympatholytics1. 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

3. Cyclopentolate 1%• Short acting• Cycloplegia 1 h• Duration 6-12 h

3. Tropicamide 1%• noncycloplegic

Abnormalities of pupillary reflexes

Afferent pathway defects1. 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

2. RAPD (marcus gunn 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

• 3. Wernicke’s hemianopic pupil• Optic tract lesion• Ipsilateral temporal & contralateral nasal

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

Tonic pupil• -ve light, 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

• 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 as for the

knee (Adie’s syndrome) • Seen in young women• Mild regional corneal impaired sensitivity

Light-Near dissociation

1. Bilateral complete afferent pathway defect2. Lesion in the midbrain at the level of the

pretectal area3. 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

• Argyll Robertson pupil(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

• 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