pupillary pathway
TRANSCRIPT
Pupillary pathway
Sumit Singh Maharjan
Development of the pupil• Pupil is formed by the complete absorption of the
central part of pupillary membrane.• pupillary membrane is formed by the mesodermal
tissue surrounding the margin of the optic cup and tunica vasculosa lentis. • The peripheral part of the pupillary membrane gets
vascularised. • The central part is eventually completely absorbed
forming the pupil.
Pupil • Number• Location• Sizei. Variation with ageii. Physiological changesiii. Isocoria-anisocoriaiv. Pupillary unrestv. hippus• Shape• colour
Functions of pupil• Pupil movement in response to changing light
intensity helps in optimizing retinal illumination to maximize the visual perception.
Dim light Bright lightDilatation of pupil provides an immediate means for maximizing the number of photons reaching the retina.
Pupil constriction can reduce retinal illumination by up to 1.5 log units within 0.5 seconds
Helps in dark adaptive mechanisms
Helps in light adaptation
• Improves the image quality of the retina when the steady state pupil diameter is small.
It minimizes optical aberration in the lens and cornea by limiting the light rays entering the eye.
Glare and aberrations commonly occurs with a large pupil in darkness or after mydriasis.
• Depth of focus of the eye’s optical system: Small pupil increases the depth of focus of the
eye’s optical system similar to pinhole effect of camera .
Clinical aspect of pupil function• Pupil movement as an objective indicator of afferent and
efferent pathway.• Pupil diameter as an indicator of wakefulnesshelps in monitoring sleep disorders, monitoring of fatigue,
anesthesia level, response to noxious stimuli.• Pupil inequality as a reflection of autonomic nerve output to
each iris.direct damage to iris sphincter and pharmacologic miosis or
mydriasis.• Influence of pupil diameter on the optical properties of the eyePhotophobia, glare and abberations following refractive
surgery or cataract.• Pupil response to drugs as a mean of monitoring
pharmacologic effect.
Pupillary reflexes• Light reflex• Near reflex• Darkness reflex• Psychosensory reflex
Light reflex
Near reflex
Darkness reflexDilatation has 2 causes:• Simply abolition of light reflex with consequent
relaxation of the sphincter pupillae• Contraction of dilator pupillae supplied by
sympathetic nervous system
Psychosensory reflex• Dilatation of pupil in response to sensory and
psychic stimuli• Mechanism of psychosensory reflexes is a cortical
one and apparently the pupil dilatation in these results from 2 components-
Sympathetic discharge to the dilator pupillaeInhibition of parasympathetic discharge to the
sphincter pupillae.
Abnormalities of pupillary reflexesAfferent pathway defect• Total afferent pathway defect (TAPD) or Amaurotic
pupil• Relative afferent pathway defect (RAPD) or Marcus
Gunn pupil• Wernicke’s hemianopic pupil
Efferent pathway defects• Tonic pupil
TAPD or Amaurotic pupil
RAPD-Marcus Gunn pupil
Wernicke’s hemianopic pupil• Indicates lesion of the optic tracts• Light reflex is absent- temporal half of the retina of
affected side and nasal half on the opposite side
• Light reflex is present on nasal half of affected side and temporal half of opposite side.
Efferent pupillary defectsCommon causes:• Brainstem lesions at the level of sup colliculus and
red nucleus• Fascicular third nerve lesions• Lesions of the ciliary ganglion or short ciliary nerves• Iris damage• Drugs
Tonic pupil• Damage to the ciliary ganglion or short ciliary
nerves.• Characterized by:Reaction to light is absent and to near reflex is very
slow and tonicAccomodative paresisCholinergic supersensitivity of the denervated
muscleAffected pupil is larger
Causes of tonic pupil• Local tonic pupilViral ciliary ganglionitis e.g. herpes zosterOrbital or choroidal trauma or tumors• Neuropathic tonic pupilDiabetes, alcoholism• Idiopathic tonic pupil with benign areflexia (Adie’s
tonic pupil)
Adie’s tonic pupil• Caused by denervation of the post
ganglionic supply of the sphincter pupillae and ciliary muscle• Usually unilateral• Typically affects healthy young
women • Affected pupil is large and
irregular• Light reflex is absent• Near reflex is slow and tonic• Accomodative paresis
• May be associated with mild regional impairment of corneal sensations• May be associated with absent knee jerk
Pupillary light –near dissociation
Argyll Robertson pupil• Caused by the lesion in the region of tectum • Usually bilateral but asymmetrical • Pupils small in size and irregular• Light reflex is absent but near reflex is present• Pupils dilate very poorly with mydriatics
Sympathetic supply of the eye
Horner’s syndrome• Central horner syndrome: brainstem vascular
lesion, demyelination, tumors, syringomyelia, spinal cord lesion C8-T2.• Preganglionic horner syndrome: pancoast tumor of
the lung, carotid and aortic aneurysms, malignant cervical lymph node, trauma to neck• Postganglionic horner syndrome: benign vascular
headache syndrome affecting the internal carotid artery, head trauma, intra aural or retro parotid trauma and cavernous sinus lesions.
PharmacologyMiotics • Parasympathomimetics (sphincter stimulators): i. Direct acting: pilocarpineii. Indirect acting or cholinesterase inhibitors:
physostigmine, ecothiophate iodide, demecarium
• Sympatholytics1. Alpha adrenergic blocker: thymoxamine,
phenoxybenzamine, dibenamide and tolazoline• Others miotics: histamine, morphine
mydriatics• Sympathomimetics: adrenaline, phenylephrine,
hydroxyamphetamine, cocaine
• Parasympatholytic: atropine, homatropine, tropicamide, cyclopentolate.
References • Wolff’s anatomy of the eye and orbit-eighth edition• Anatomy and physiology of eye -2nd edition AK
Khurana• Adler’s physiology-9th edition• Clinical anatomy of the eye-2nd edition, snell’s
Thank you