Pupillary pathway

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