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.
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.
3.
4.
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.
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
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
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
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
Aperture present in the center of the iris
Controls the amount of light reaching the retina
And also controls the amount of chromatic and spherical aberration of the retinal image.
patients with a fixed immobile pupil are usually symptomatic during an abrupt change in illumination, photophobic in sudden increase to light and defective dark adaptation in dim lighting conditions.
Function:
Protects against excessive bleaching of the visual pigments
Helps in light and dark adaptation,maximizing visual acquity at diff levels
Caused by complete optic nerve or retinal lesion leading to total blindness on affected side
Caused by an incomplete optic nerve lesion or a severe retinal disease.
And best tested by swinging flash light.
RAPD is the earliest sign of optic nerve disease even if the visual acquity is normal.
Sec to previous surgery or grossly elevated IOP
Blunt trauma to globe may injure branches of short ciliary nerves at iris root
Miosis, ptosis , anhydrosis, dilatation lag, pupillary reactions are normal
Increasing norepinephrine release, preventing its uptake and directly stimulating dilator fibres
Parasympatholytics compete with Ach at myoneural junction and blocks sphincter activity