Pupil Functions PDF

Pupil functions: aid in light control, depth perception, improving image quality The pupil is an objective indicator of the amount of light transduction by the visual system. The pupil can be used to monitor retinal light sensitivity In clinical settings, the amount of pupil constriction to a light...

Pupil functions: aid in light control, depth perception, improving image quality The pupil is an objective indicator of the amount of light transduction by the visual system. The pupil can be used to monitor retinal light sensitivity In clinical settings, the amount of pupil constriction to a light stimulus or the steady-state diameter of the pupil under constant illumination can reflect the health of the retina or optic nerve It is crucial to evaluate pupils since they provide great information regarding neurologic functions. Pupillary abnormalities can be the only sign of a dysfunction of the eye or the brain Pupil response is mediated by the sympathetic and the parasympathetic system. Pupil size is determined by a balanced tone in the autonomic nervous system (ANS). Afferent and Efferent ○ Afferent: carries sensory information towards the CNS ○ Efferent: carries motor impulses from CNS to the muscles Iris muscles 2 agonist muscles in the iris: ○ Sphincter: miosis, constriction Under parasympathetic innervation ○ Dilator (radial): mydriasis, dilation Under sympathetic innervation Afferent Pathway Cranial nerve II (optic nerve) perceives light and takes the message to the brain ○ A defect in the afferent pathway does not necessarily have to be in the optic nerve, it could be in the retina or in the chiasm The response of the pupils to light is produced when the brain receives the message and cranial nerve III (oculomotor nerve) causes both pupils to constrict if the pathway is intact ○ Both pupils will constrict, even if only one eye is receiving the light information Pupillary Light Reflex (parasympathetic-constriction) This a four-neuron arc: ○ 1st neuron arc: connect the retina (retina ganglion cells) to the pretectal nucleus in the midbrain at the level of the superior colliculus ○ 2nd neuron arc: connects each pretectal nucleus to both Edinger-Westphal nuclei (EWN), therefore a unilateral light stimulus evokes a bilateral pupil constriction ○ 3rd neuron arc: connect the EWN to the ciliary ganglion The EWN gives rise to preganglionic parasympathetic fibers that exit the midbrain with CNIII and synapse with the postganglionic parasympathetic fibers of the ciliary ganglion ○ 4th neuron arc: leaves the ciliary ganglion and innervates the sphincter muscle Oculosympathetic pupillary pathway (sympathetic-dilation) Interruption of the sympathetic pathway at any level, will produce Horner’s Syndrome This is athree-neuron arc: ○ 1st neuron (central): starts in the posterior hypothalamus and ends in the ciliospinal center of Budge (in C8-T2) ○ 2nd neuron (preganglionic): leaves the ciliospinal center of Budge and travels over the apical pleura of the lung and into the superior cervical ganglion (SCG) at the level of the carotid bifurcation ○ 3rd neuron (postganglionic): joins the ophthalmic division of the trigeminal nerve (CN V) to reach the ciliary body and the pupil dilator muscle via the nasociliary and long ciliary nerves Near reflex and Accommodation Pathway When an object at near is fixated both eyes: ○ Converge, the intraocular lens accommodates and both pupils constrict ○ This is known as the near response ○ Even though they are associated movement, they are not dependent on one another Pupillary constriction for both parasympathetic pathway and near reflex have a final common efferent pathway from the EWN to the iris sphincter ○ They differ in the origin of the supranuclear input They also have slightly different pathways in the midbrain ○ Near reflex passing ventrally in the EWN ○ Light reflex passing dorsally in the EWN Examiner will always test: direct, consensual, near/accommodative and afferent pupillary reaction as well as pupil size, shape and integrity Pupil testing: Measure pupils in bright and dim light, Pupil response (direct and consensual), near/accommodative response, swinging flashlight test or Marcus Gunn test (testing for APD) Most common errors in APD testing: too slow a swing, using too low light level, blocking the patient’s view of target (leading to accommodation), forgetting to check pupil reflexes prior to instilling mydriatics/cycloplegics With + APD, the affected eye perceives light dimmer ○ The affected eye constricts less in direct and re-dilates more than normal or than the fellow eye ○ The affected eye ahs a greater consensual response coming from the normal eye than direct Affected pupil: its consensual reaction > direct reaction Normal pupil: its direct reaction > consensual reaction Pupil Hiccup: rhythmic fluctuations in pupillary size when there is a steady illumination, because of unbalance between the sympathetic and parasympathetic innervation (normal phenomenon) May sometimes be observed during a CN III Palsy Recovery This is NOT an APD Measuring an RAPD: +1 RAPD (mild): initial constriction, early re-dilation +2 RAPD (moderate): no initial movement of the pupil, then dilation +3 RAPD (severe): immediate dilation +4 RAPD: amaurotic pupil Can be also measure using neutral density filters (NDF) over the normal eye, until both eyes have equal pupil constriction Reverse/Inverse APD testing A patient that has a pupil that is distorted or unreactive (trauma or surgery) and the opposite eye has a condition that affects the afferent pathway (ex: optic neuritis) When testing: ○ Perform the swinging flashlight test, while observing the functioning pupil ○ Observe for constriction when both eyes are shined Cause for APD Lesions anterior to the chiasm: ○ Optic nerve Optic neuritis Retrobulbar neuritis Optic atrophy Anterior Ischemic Optic Neuropathy (AION) Asymmetric Primary Open Angle Glaucoma (POAG) Optic nerve trauma Chiasm compression by mass ○ Retina Marked retinal detachment Extensive retinal pathology Major retinal vascular occlusions Central retinal artery occlusion (CRAO) Central retinal vein occlusion (CRVO) Pupillary Recording PERRLA (-) APD OD/OS ○ Pupils are Equally Round and Reactive to Light and Accommodation, no Afferent Pupillary Defect in OD and OS (+) RAPD or (+) MG ○ Relative Afferent Pupillary Defect (RAPD) ○ Marcus Gunn ○ Always need to specify the affected eye APD can quantified by using NDF ○ Record log units where pupillary constriction was the same for both eyes Ex: +RAPD OS, 0.3 log ND filter PERRLA (-) APD OD/OS, OD brisk OS brisk PERRL (-) APD OD/OS OD+4 OS+2 (sluggish) PRRL (-) APD OD/OS OD>OS 1 mm in dim and bright OD RRL (-) APD, OS irregular, sluggish D (direct) and C (Consensual) Record abnormalities ○ OD is round, reactive to light. OS is distorted by surgery and sluggish in direct (D) and consensual (C) OD RRL (-) APD; OS irregular, sluggish D and C Key Points Pupils sizes (OD/OS) should be equal in both eyes at both dim and bright illumination ○ If in doubt, ask the patient for photos and evaluate them carefully If the afferent arc is intact, the direct response should be equal to the consensual response ○ Always evaluate both direct and consensual response For direct and consensual evaluation the light source should not be shined directly into the patient’s eye, it should be directed from slightly inferior ○ Avoid bleaching the retina If pupil sizes are unequal: ○ Is the direct/consensual response equally strong in both eyes? ○ If the pupil size difference larger in dim or in bright illumination? ○ Is the near/accommodative reflex the same for both eyes? ○ Amplitude of accommodation equal in both eyes? Anisocoria If there is anisocoria present: ○ Does it vary in different illuminations? ○ Is the difference more significant in dim illumination? ○ If the difference more significant in bright illumination? Anisocoria that is equal in dim and bright, without ptosis: Physiological anisocoria Anisocoria more pronounced in dim illumination, with mild ptosis in the ipsilateral side of the miotic pupil: Horner’s Syndrome (oculosympathetic syndrome) Anisocoria more pronounced in bright illumination: characteristic of parasympathetic dysfunction Light-near dissociation, refers to conditions where the light reflex is absent or abnormal, but the near response is intact There is no clinical condition in which the light reflex is present and the near response is absent For bilateral ON disease, no RAPD will be seen, unless disease is asymmetric Pharmacological mydriasis and miosis Sympathomimetics can cause 1-2 mm of dilation, stimulating the dilator muscle ○ Phenylephrine: Preparation H (cream to treat hemorrhoids, non-clinical: to decrease eye bags) ○ Naphazoline: Naphcon-A, Clear Eyes ○ Cocaine, crack ○ Jimsonweed (gardening and touch eyes -> cross-contamination) Parasympatholitics: can cause mydriasis of up to 8 mm, inhibits the sphincter muscle ○ Tropicamide, Atropine, Scopolamine (Dramamine- specifically the patch), Plants (deadly nightshade or belladonna) Miotics: ○ Pilocarpine, pesticides, flea powder ○ Narcotics and opioids cause pinpoint pupils Heroin Codeine Morphine Usually tend to be by accident (pharmacologic mydriasis): phenylephrine, naphazoline, tropicamide, atropine Patient will have poor or no light or near response ○ Very important to differentiate from aneurysm affecting CN III Diagnosis ○ Pilocarpine 1% instillation Pharmacologic mydriasis: will NOT constrict Non-pharmacolgic mydrias: will constrict Important to rule out aneurysm Amaurotic pupil This is caused by an afferent defect, essentially this is a “blind eye” ○ Grade 4 APD ○ No light perception (NLP) as a result of an optic nerve lesion Pupils will have no light reaction in direct evaluation ○ Positive consensual evaluation reaction (fellow is stimulated) The fellow eye will have no consensual reaction (when affected eye is stimulated) Near reflex will be present in both eyes (-) D, (+) C, other eye (+) D and (-) C, (+) Near OU Argyll Robertson Pupil Light-near dissociation ○ Sluggish or no reaction to light but brisk response to near stimuli Pupils tend to be small and irregular in shape (1-2mm) ○ Poor dilation in darkness Bilateral and symmetrical presentation Pupils do NOT constrict when exposed to bright light but DO constrict on a near object (accommodative reflex) Poor dilation after instillation of mydriatics Hallmark of neurosyphilis (tertiary syphilis) ○ But may occur with DM, chronic alcoholism, MS, CNS degenerative disease, midbrain tumors Cause: site of lesion is the region of the sylvian aqueduct in the rostral midbrain ○ In this location the damage interferes with the light reflex fibers but it spares the fibers subserving pupillary constriction for near viewing Adie’s Tonic Pupil Unilateral or bilateral tonically reacting pupils developing in otherwise healthy patients ○ 80% unilateral Pupil appears abnormally dilated with sluggish reaction to light but better reaction to near stimuli, but still sluggish ○ Impaired parasympathetic ciliary ganglion, though to be caused by denervation of the postganglionic nerve supply to the sphincter and ciliary muscle This lead to pupillary and accommodative changes After fixating the near stimuli, there is slow re-dilation of the affected pupil Slit lamp examination of the pupil often revealed sectoral palsy with vermiform movements of the margin Mostly idiopathic, benign condition More commonly seen in between 20-50 years of age 70% of the cases are in females May be accompanied by hyporeflexia or areflexia ○ Reduction in reflexes Accommodative response, may be initially affected, but tends to improve with time ○ Tonicity to light response tends to get worse There is no treatment, reassurance is key Diagnostic tests: ○ Dilute one part Pilocarpine 1% with 8 parts of saline solution to achieve Pilocarpine 0.125% ○ Instill 1 gtt of Pilocarpine 0.125% OU and wait 30 min. Adie’s Tonic pupil will constrict, normal pupils will not be affected by such a low concentration ○ This is due to denervation and hypersensitivity Horner’s Syndrome If sympathetic innervation to the eye is interrupted this results in: ○ Retractor muscles in the eyelids are weakened: ptosis ○ Dilator muscle of the iris is weakened: miosis ○ Vasomotor and sudomotor control of parts of the face are lost: anhidrosis A lesion of the ocular sympathetic fibers will produce Horner’s Syndrome ○ Anisocoria is more apparent in dark, and may even disappear in bright conditions ○ Triad: Ptosis, miosis, and anhidrosis Ipsilateral Lesions can be located anywhere along the sympathetic pathway Differential diagnosis between: ○ Central lesions (1st order) ○ Preganglionic lesions (2nd order) ○ Postganglionic lesions (3rd order) May be congenital or acquired ○ If congenital, iris depigmentation (heterochromia) may be present in the affected eye ○ If acquired may be due: trauma, malignancy Anisocoria more pronounced in dark than in bright Pupillary light and near responses are unimpaired Triad: ○ Miosis ○ Ptosis: due to primary paralysis of the superior tarsal (Muller’s) muscles Sometimes the lower lid is slightly elevated due to the losing nerve supply as well, this will produce an upside-down ptosis (lower lid is slightly elevated) This will produce a narrowing of the palpebral fissure, apparent enophthalmos ○ Anhidrosis: due to vasomotor and sudomotor changes, ipsilateral to the affected eye Will only occur in central and preganglionic Horner’s syndrome, not in postganglionic Central Neuron (1st order): often accompanied by other hypothalamic, medullary or brainstem abnormalities ○ Example: vascular occlusion, intraparenchymal neoplasms, cervical spondylosis Preganglionic (2nd order): malignancy are the most common cause, especially lung (Pancoast tumor) and breast tumors. Accidental or surgical injury ○ Disc herniation at C8 or T1, trauma, pneumothorax, coronary artery bypass, pacemaker insertion Postganglionic (3rd order): lesions may be extracranial or intracranial ○ Tumors, inflammatory lesions and other masses in the neck, carotid dissections, aneurysms, infections and other lesion of the cavernous sinus, Cluster headaches, giant cell arteritis, skull base neoplasms or fractures Pharmacologic diagnostic testing is performed since it is important to differentiate between physiologic anisocoria Cocaine test is most commonly used: ○ Blocks reuptake of NE of the neuroeffector junction Normal eyes cocaine 4-10% causes dilation ○ In Horner’s Syndrome no NE is release (due to lesion) and cocaine will not dilate the pupil Cocaine 4-10% is very difficult to obtain clinically and it is not diagnostic of lesion location ○ Apraclonidine can be used to verify Horner’s diagnosis Apraclonidine 0.5-1% is an alpha-adrenergic agonist ○ In normal eyes dilation effect is very minimal ○ Acts on the delayed sensitivity of alpha 1 receptors in the dilator muscle ○ Will produce dilation of the Horner’s Syndrome pupil, due to hypersensitivity ○ Normal eye will not dilate, Horner’s pupil will dilate Lesion localization: ○ Hydroxyamphetamine 1% is clinically useful in differentiating between central and preganglionic lesions and postganglionic lesions No diagnostic test for central vs preganglionic ○ Hydroxyamphetamine releases NE from the stores in the adrenergic nerve ending, producing significant mydriasis in normal subjects If cocaine or apraclonidine test has been performed, hydroxyamphetamine cannot be performed until 24-48 hrs after Only performed when Horner’s has been diagnosed ○ If the lesion is central or preganglionic: will produce normal mydriasis ○ If the lesion is postganglionic: will not produce mydriasis Isolated III CN Palsy Sudden onset of unilateral ptosis with eye or head pain Eye is exotropic and hypertrophic (down and out) ○ Complaints of diplopia With & without pupil involvement Depending on where the lesion is located the pupillary fibers might or might not be affected Isolated III CN Palsy WITH pupil involvement Most common cause: Posterior communicating artery aneurysm Other causes: ○ Tumors ○ Trauma ○ Leukemia ○ Uncal herniation ○ Pituitary apoplexy ○ Ischemic vascular disease (rare with pupil involvement) Patients need to be referred for neurologic evaluation STAT. Isolated III CN Palsy WITHOUT pupil involvement Tend to be ischemic in nature, but this is not always the case Follow patient closely, this might develop pupil involvement soon after initial presentation ○ Vascular disease: can cause an infarct of CN III central fibers (pupil sparing) Causes: ○ Ischemic microvascular disease (diabetes, HTN) ○ Cavernous sinus syndrome ○ Giant Cell Arteritis (GCA) Isolated III CN Palsy Management If pupil involvement is present: referred for neuro consult in nearest ER STAT ○ Must rule out PCA aneurysm ○ MRI/MRA recommendation If pupil sparing (vasculopathy), patient has diabetes or HTN, follow the patient closely and monitor for possible pupillary involvement ○ Refer to PCO for medical/lab work-up ○ F/U in 5-7 days ○ Most ischemic causes resolve in 90 days, if not resolved, order neurotesting If pupillary sparing in younger than 50 y/o order neuro testing unless known vascular condition In children, less than 10 y/o regardless of pupils order neuro testing