1) The pupil forms from the absorption of the central pupillary membrane during development. It regulates the amount of light entering the eye and focuses vision by changing size. 2) The pupil constricts in bright light to reduce retinal illumination and dilates in dim light to maximize photons reaching the retina. Constriction also improves image quality by reducing aberrations. 3) Pupillary reflexes include light, near, darkness, and psychosensory reflexes. Abnormalities can indicate lesions in the afferent or efferent pathways. Tonic pupils are caused by damage to the ciliary ganglion and show slow, sustained constriction to light and near stimuli.

1. Pupillary pathway
Sumit Singh Maharjan

2. 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.

5. Pupil
• Number
• Location
• Size
i. Variation with age
ii. Physiological changes
iii. Isocoria-anisocoria
iv. Pupillary unrest
v. hippus
• Shape
• colour

6. Functions of pupil
• Pupil movement in response to changing light
intensity helps in optimizing retinal illumination to
maximize the visual perception.
Dim light Bright light
Dilatation 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

7. • 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 .

8. Clinical aspect of pupil function
• Pupil movement as an objective indicator of afferent and
efferent pathway.
• Pupil diameter as an indicator of wakefulness
helps 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 eye
Photophobia, glare and abberations following refractive
surgery or cataract.
• Pupil response to drugs as a mean of monitoring
pharmacologic effect.

9. Pupillary reflexes
• Light reflex
• Near reflex
• Darkness reflex
• Psychosensory reflex

10. Light reflex

11. Near reflex

12. Darkness reflex
Dilatation has 2 causes:
• Simply abolition of light reflex with consequent
relaxation of the sphincter pupillae
• Contraction of dilator pupillae supplied by
sympathetic nervous system

13. 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 pupillae
Inhibition of parasympathetic discharge to the
sphincter pupillae.

14. Abnormalities of pupillary reflexes
Afferent 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

15. TAPD or Amaurotic pupil

16. RAPD-Marcus Gunn pupil

17. 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.

18. Efferent pupillary defects
Common 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

19. 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 tonic
Accomodative paresis
Cholinergic supersensitivity of the denervated
muscle
Affected pupil is larger

20. Causes of tonic pupil
• Local tonic pupil
Viral ciliary ganglionitis e.g. herpes zoster
Orbital or choroidal trauma or tumors
• Neuropathic tonic pupil
Diabetes, alcoholism
• Idiopathic tonic pupil with benign areflexia (Adie’s
tonic pupil)

21. 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

22. • May be associated with mild regional impairment
of corneal sensations
• May be associated with absent knee jerk

23. Pupillary light –near dissociation

24. 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

26. Sympathetic supply of the eye

27. 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.

28. Pharmacology
Miotics
• Parasympathomimetics (sphincter stimulators):
i. Direct acting: pilocarpine
ii. Indirect acting or cholinesterase inhibitors:
physostigmine, ecothiophate iodide,
demecarium
• Sympatholytics
1. Alpha adrenergic blocker: thymoxamine,
phenoxybenzamine, dibenamide and tolazoline
• Others miotics: histamine, morphine

29. mydriatics
• Sympathomimetics: adrenaline, phenylephrine,
hydroxyamphetamine, cocaine
• Parasympatholytic: atropine, homatropine,
tropicamide, cyclopentolate.

30. 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

31. Thank
you