Binocular Vision Lecture 9 - Pupils PDF

Binocular Vision Lecture 9 – Pupils Professor Phillip Buckhurst By the end of the session I will be able to Identify the afferent and efferent pathways that control pupil size Describe the parasympathetic and sympathetic nerve innovations Identify how to test for pupil function Re...

Binocular Vision Lecture 9 – Pupils Professor Phillip Buckhurst By the end of the session I will be able to Identify the afferent and efferent pathways that control pupil size Describe the parasympathetic and sympathetic nerve innovations Identify how to test for pupil function Recognize a series of pupil function abnormalities Terms you need to know Afferent – Nerve that carries information towards the central nervous system Efferent – nerve that carries information away from the central nervous system Sympathetic – “Fight and flight” Parasympathetic – “Rest and Digest” Cholinergic receptors (muscarinic) – stimulated by Acetylcholine Adrenergic receptors (alpha 1) – stimulated by Noradrenaline The Afferent pathway pretectal nuclei Afferent pathway – Nerve LGN carrying information towards the central nervous system The pathway from the retina to optic the pretectile nuclei (in the brain) tract Very important to understand the what a lesion along is afferent pathway will do to the corneal reflexes (lets come back to this Optic in a minute) Optic nerve chiasm LIGHT The Afferent pathway Retinal Ganglion cells Via the optic nerve, optic chiasm and optic tract Pretectal nucleus Central processing occurs at this point Edinger-Westphal nucleus Efferent Pathway Efferent pathway -- Nerve carrying impulses away from the central nervous system towards the muscles controlling the pupil size Sphincter muscle – Parasympathetic – “rest and digest” Dilator Muscle – Sympathetic – “fight and flight”  The muscles controlling pupil size The dilator muscle The sphincter muscle Sphincter Muscle The pupil size is mainly determined by the contraction or relaxation of the sphincter muscle thin circumferential ring of smooth muscle fibres The sphincter muscle responds to signals coming from the short ciliary nerve and constricts the pupil It is innervated by cholinergic parasympathetic fibers Dilator Muscle The dilator muscle has a secondary effect on pupil size The dilator muscle responds to signals coming from the long ciliary nerve and dilates the pupil It is innervated by adrenergic sympathetic fibers The sphincter and Dilator muscle are antagonistic muscles  In dark lighting conditions The sphincter muscle relaxes – This muscle has the biggest effect on pupil size The dilator muscle contracts  In bright lighting conditions The sphincter muscle contracts – This muscle has the biggest effect on pupil size The dilator muscle relaxes  Effects of pharmaceutical innovation You can make the pupil either contract or dilate through pharmaceutical methods Pupil mydriasis Pupil miosis (dilated pupil) (Constricted pupil) Tropicamide Cyclopentolate Anti-muscarinics Atropine Pilocarpine Parasympathomimetic Phenylepherine Sympathomimetic Pupil terminology Anisocoria Miosis Mydriasis Normal Pupils They are round in shape and relatively equal in size Their size vary from 1 to 8mm in diameter – Normal pupils range from 3 to 5mm in ambient light conditions – Miotic pupils are less than 3mm – Mydriatic pupils are greater than 7mm Efferent Pathway The parasympathetic pathway Edinger-Westphal nucleus Cranial nerve III Ciliary Ganglion Short ciliary nerve Note: Within the orbit, the nerve axons leave the inferior division Iris sphincter Muscle of the oculomotor nerve and travel to the inferior oblique muscle before going to the ciliary ganglion  The Afferent and Efferent pathway together Edinger-Westphal nucleus Central processing occurs at this point Cranial nerve III Pretectal nucleus Ciliary Ganglion Via the optic nerve, optic Short ciliary nerve chiasm and optic tract Retinal Ganglion cells Iris sphincter Muscle The Afferent and Efferent pathway together Efferent Pathway The Sympathetic pathway Postero-lateral hypothalamus Within the spinal chord Ciliospinal centre of Budge-Waller Over the apex of the lung Superior cervical ganglion The long ciliary nerve Travels along the ophthalmic division of the 5th nerve for a while Dilator muscle The Efferent pathway The sympathetic pathway Testing pupil function Pupil Testing Purpose – To examine the afferent and efferent neurological pathways responsible for pupillary function – Abnormalities can be life threatening Pupil Testing Procedure consists of four steps 1. Observation (screen for anisocoria) 2. Direct and consensual response 3. Swinging flashlight test 4. Near reflex test (if there is a problem with any of the first three steps) 1. Observation In bright and dim illumination Look for asymmetries in pupil size Measure pupil size (to the nearest 0.5mm) 20% of eyes have some asymmetry in size – Anisocoria Physiological You need to investigate Pathological Important – If anisocoria is physiological then the difference in pupil size will be the same in bright light conditions as in dim conditions – If pathological then it will be different (more on this in a minute) 2. The direct Response Direct light reflex – If you shine your light into a healthy eye then the pupil should constrict – The constriction of the ipsilateral pupil to the light stimulus 2. Examining the Direct Response In dim illumination Instruct the patient to look at the distant target Shine the light into the patient’s right eye Observe the size and the speed of the pupil constriction of the patient’s right eye This is the direct response or direct light reflex of the right eye Repeat with the left eye 2. Results of the Direct Response Pentorch For the direct test we look at the response of the eye we are shining the light into (It should constrict) 2. The consensual Response Consensual light reflex – The constriction of the contralateral pupil to the light stimulus 2. Testing the Consensual Response In dim illumination Instruct the patient to look at the distant target Shine the light into the patient’s right eye Observe the size and the speed of the pupil constriction of the patient’s left eye This is the consensual response or consensual light reflex of the left eye 2. Results of the Consensual Response Pentorch For the consensual test we look at the response of the other eye (the one we are not shining the light into (It should also constrict) 3. Swinging Flashlight Test Also known as the Marcus Gunn test because it is a test for “pupillary escape” or the Marcus Gunn response 3. Swinging Flashlight Test In dim illumination Move the light between the eyes rapidly, leaving it on each eye for 3 seconds Observe the direction of response (constriction or dilation) and the size of each pupil at the moment that the light first arrives there and during the 3 second observation period  3. Results of the swinging flashlight test Step 1: You should Step 2: Move the Step 3: Both pupils shine the light into the torch across to should stay right eye. Both pupils the other eye fast constricted should constrict Pentorch 4. Near Reflex Test Instruct the patient to look at the distant target The examiner holds up a target containing fine detail approximately 25cm from the patient Ask the patient to fixate the near target and look for pupil constriction Note the speed of the constriction and the roundness of each pupil 4. Near Reflex Accommodation, convergence, and pupil constriction (miosis) occur at the same time Artificially induced convergence causes accommodation and miosis Artificially induced accommodation causes convergence and miosis Miosis is the weakest of the three responses so that it cannot induce accommodation and convergence Some accommodation fibers innervate the pupil The convergence pathway is located close to the Edinger- Westphal nucleus so that there may be some crossing over with accommodation and miosis Damage to the afferent pathway Reminder of the visual pathway The key thing to remember is that the nerve fibres serving the nasal retina (temporal visual field) cross over at the chiasm (from OPT201) 1 2 3 4 5 6  Damage to the afferent pathway pretectal nuclei light shone in one eye causes pupil contriction in both eyes i.e. LGN DIRECT and CONSENSUAL reflexes afferent pathway from retina to pretectal nuclei (towards brain) optic tract Fibres cross over at the chiasm A lesion of the optic nerve will affect the pupil reactions It is likely to cause an RAPD Optic Optic nerve chiasm LIGHT Damage to the afferent pathway pretectal nuclei lateral Light shone into the effected geniculate eye will cause: nucleus – A reduced direct response – A reduced consensual optic response tract Light shone into the non- effected eye will cause: – A normal direct response – A normal consensual Optic response Optic nerve The near response will be chiasm normal LIGHT Damage to the afferent pathway The direct response The effected eye The non-effected eye Pentorch Pentorch Damage to the afferent pathway The consensual response The effected eye The non-effected eye Pentorch Pentorch Damage to the afferent pathway The swinging flashlight test The non-effected eye The effected eye Pentorch Damage to the afferent pathway The near response The non-effected eye The effected eye H TE HMW What would cause this problem Very severe pathology that blocks the impulses from reaching the chiasm i.e. a blind eye – Very very dense amblyopia – Very very dense cataracts – Optic neuritis Damage to the parasympathetic arm of the efferent pathway  Damage to the parasympathetic arm ofpretectal the efferent pathway nuclei Damage to the parasympathetic arm Edinger-Westphal of the efferent pathway with result in Nuclei a more dilated pupil You need to work out if the lesion is prior to the ciliary ganglion or post ganglion Damage at the post ganglionic stage is known as Adie’s tonic pupil The pupil does not react to light 3rd nerve but does to a near target Ciliary Maximum response to ganglion Pilocarpine Damage at the pre-ganglionic stage (3rd nerve palsy) can cause: Absent accommodation Fixed dilated pupil Sphincter Paresis of some of the EOM muscle Adie’s pupil The pupil in bright conditions The non-effected eye The effected eye Adie’s pupilThe pupil in dim conditions The non-effected eye The effected eye Adie’s pupil The direct response The effected eye The non-effected eye Pentorch Pentorch Adie’s pupil The consensual response The effected eye The non-effected eye Pentorch Pentorch Adie’s pupil The swinging flashlight test The non-effected eye The effected eye Pentorch Adie’s pupil The near response The non-effected eye The effected eye H TE HMW Adie’s Tonic Pupil Damage to ciliary ganglion or postganglionic fibers of the short ciliary nerve (parasympathetic pathway problem) Usually unilateral, common in females The affected eye is dilated and reacts poorly to light (poor direct and consensual response) Near reaction is strong, slow, and tonic When the patient refixates at distance, the pupil redilates very slowly  Damage to the 3rd nerve pretectal nuclei Edinger-Westphal Nuclei Damage to the 3rd nerve can cause a fixed dilated pupil 3rd nerve Ciliary ganglion Sphincter muscle Damage to the sympathetic arm of the efferent pathway  Damage to the Efferent pathway The sympathetic arm Damage to the sympathetic system causes a miotic pupil – Affects the dilator muscle Known as Horner's syndrome Could have a life threatening aetiology Horner’s Syndrome Pupillodilator dysfunction Damage to the sympathetic pathway Common cause: lung cancer Pancoast tumor Signs: ptosis (droopy eyelid), miosis, facial anhydrosis (sweat gland denervation), iris heterochromia (congenital Horner’s) Pupil reacts normally to light and near Horner’s syndrome The pupil in bright conditions The non-effected eye The effected eye Horner’s syndrome The pupil in dim light conditions The non-effected eye The effected eye Horner’s syndrome The direct response The effected eye The non-effected eye Pentorch Pentorch Horner’s syndrome The consensual response The effected eye The non-effected eye Pentorch Pentorch Horner’s Syndrome The swinging flashlight test The non-effected eye The effected eye Pentorch Horner’s syndrome The near response The non-effected eye The effected eye H TE HMW Argyll Robertson pupil  Argyll Robertson Pupil pretectal nuclei Damage to the parasympathetic pathway Possible causes: neurosyphilis (lesion Edinger-Westphal around the Edinger-Westphal nucleus), long- Nuclei term diabetes, or alcoholism Presumed neurosyphilis until proven otherwise Both pupils are small and respond poorly or not at all to light (no direct and consensual response) 3rd nerve Normal response to near (light-near Ciliary dissociation) ganglion Sphincter muscle Recording If all the pupil responses are normal – Record PERRLA, No RAPD Pupils Equal Round and Responsive to Light and Accommodation Relative Afferent Pupillary Defect – Negative Marcus Gunn response (you tend to find this written less and less) Recording Describe any pupil abnormalities – Inequality of size (anisocoria) – Direct (D) and consensual (C) responses based on speed and amount of constriction on a scale of 0 to 4+ Binocular Vision Lecture 9 – Pupils Professor Phillip Buckhurst Session: OPT503 Pupils Lecturer: Phillip Buckhurst