The pupil is a circular aperture located in the center of the iris that regulates the amount of light entering the eye. It has two muscles - the sphincter pupillae and dilator pupillae - that control its size. The pupillary reflex causes involuntary constriction or dilation of the pupil in response to light and near focus. There are several pupillary reflexes, including the light reflex which causes constriction when light hits the eye, and the near reflex which causes constriction during near vision due to convergence and accommodation of the eye. The pathways involve the retina, optic nerve, pretectal nucleus, and Edinger-Westphal nucleus.

1. Anatomy and Physiology of Pupil
Presented by –
MAAZ UL HAQ
C.L GUPTA EYE INSTUTUTE MORADABAD
5/20/2021 1

2. Introduction
• Aperture at centre of iris
• Regulates the amount of light reaching the retina
• Controls the amount of chromatic & spherical
aberration in retinal image
5/20/2021 2

3. Anatomy of Pupil
 Number
• Normally one
• Rarely more than one is called polycoria
5/20/2021 3

4. Cont.
 Location
• Almost in centre of iris, rarely congenitally eccentric
(corectopia)
 Shape : circular
 Colour : greyish black
5/20/2021 4
Leukocoria

5.  Size: 3-4 mm
• Variation with age : small at birth, largest during
adolescent, slowly smaller with increasing age
• Physiological changes :
Dilate –emotional stress, Constrict – sleep
• Isocoria : both of equal size
5/20/2021 5

6. • Muscles : Sphincter pupillae and dilator pupillae
controlling the pupil size
5/20/2021 6

7. Pupillary reflex
• The size of the pupil is controlled by
involuntary constriction and dilation of the iris
in order to regulate the intensity of light
entering the eye.
This is known as the pupillary reflex.
5/20/2021 7

8. Pupillary Reflexes
Light reflex
Near reflex
Darkness reflex
Psychosensory reflexes
5/20/2021 8

9. Light reflex
• Direct light reflex : constriction of pupil to
which light is shone
• Consensual light reflex : constriction of other
pupil when light is shone one eye
• Light reflex is initiated by rods &cones
5/20/2021 9

10. 5/20/2021 10
Afferent Pathway
information from the rods & cones
reaches the ganglion cells
Nasal Fibers decussate in optic
chiasma
Travels centrally along the optic
nerve to the chiasma
Terminate in the contralateral
pretectal nucleus
Travel along the opposite optic tract

11. Internuncial pathway
• Fibres connect each pretectal nucleus with Edinger –
Westphal nucleus
5/20/2021 11

12. Efferent Pathway
The axons of the EW nucleus extend
into the IIIrd CN.
5/20/2021 12
Pupilloconstricitor fibres are situated
on surface of 3rd nerve
Preganglionic fibres enter the inferior
division of 3rd nerve
Reach the ciliary ganglion
Post ganglion fibres along short ciliary
nerves innervate shincter pupillae

13. 5/20/2021 13

14. Near reflex
• Near reflex is occur looking near object.
• It consists of two components
1. Convergence reflex
2. Accomodation reflex
Near reflex triad consist of
• Increased accommodation
• Convergence of visual axis
• Constriction of the pupils
5/20/2021 14

15. Pathway of Convergence reflex
5/20/2021 15
Fibers from medial recti via 3rd CN
Mesencephalic nucleus Of 5th CN
Convergence Center in tectal or Pretectal region
Internuncial fibres go to the EW Nucleus
Efferent fibers travel along 3rd CN
Relay in Accessory Ganglion
Sphincter Pupillae

16. 5/20/2021 16

17. Pathway of Accommodation reflex
5/20/2021 17
Via Optic nerve,Chiasma,Optictract, Lateral Geniculate
Body, Striate Cortex
Afferent impulses extend retina to parastriate cortex
Internuncial fibre relay impulses parastriate cortex to
EWN
Via Occipitomesencephalic tract & pontine centre
From EW Nucleus efferent impulses travels
Via 3rd CN to Sphincter Pupillae and ciliary muscles

18. Darkness reflex
• Abolition of light reflex – relaxation of
sphincter pupillae
• Contraction of dilator pupillae – supplied by
sympathetic nervous system
5/20/2021 18

19. Psychosensory reflex
• Dilatation of pupil in response to sensory and psychic
stimuli.
• The mechanism of psychosensory reflexes is a
cortical one and pupillary dilatation results from
 A sympathetic discharge to the dilator pupillae
 Inhibition of parasympathetic discharge to the
sphincter pupillae
5/20/2021 19

20. Lid closure reflex
• Non specific term (may be accompanied by pupillary
contraction or dilatation).
• Used for the following entities –
• Constriction of pupil associated with blinking
– type of darkness reflex
• Pupillary dilatation associated with lid-closure on
touching the cornea (oculopupillary reflex) – type of
psychosensory reflex
5/20/2021 20

21. 5/20/2021 21