The pupil is a small aperture in the center of the iris that regulates the amount of light entering the eye. Its diameter changes in response to different light levels, ranging from about 1.5 mm in bright light to 8 mm in dim light. The size of the pupil also decreases with age. It constricts during sleep and dilates during emotional stress. The pupil functions to control the light entering the retina and the amount of aberration in the retinal image.

2.  The pupil is an aperture present in the
centre of the iris.
 Normall one pupil in each eye, more than
one pupil this congenital anomaly is called
polycoria
 Located in slightly nasal of the iris

3.  In normal room light, a healthy human
pupil has a diameter of about 3-4 mm
 In bright light, the pupil has a diameter of
about 1.5 mm
 In dim light the diameter is enlarged to
about 8 mm

4.  The size of the pupil small at birth, largest
during adolescence ,and smaller with
increasing age
 Tends to dilate during emotional stress and
constrict during sleep
 Isocoria : two pupil are equal in size

5.  Functions of pupil:
1. limit the amount of light reaching to the
retina.
2. Contol the amount of chromatic abberation &
spherical abberration in the retinal image

6.  Colour:
 It appears greyish black ( deppending upon
the condotion of the structure located
behind it
 Aphakia : jet black
 Leukocoria: white coloured pupil

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.
 Pupillary reflex divided in to two
1.light reflex
2.near reflex

8. 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

9. Pathway of light reflex
 Afferent pathway : extend from the retina to the
pretectal nucleus in the mid brain
 information from the rods & cones reaches the
ganglion cells travels optic nerve to the
optic chiasma optic tract pretectal
nucleus

10.  Internuncial pathway: connect each
pretectal nucleus with Edinger – Westphal
nucleus
 Half of the postsynaptic fibers from the
pretectal area terminate in the
ipsilateral Edinger-Westpal nucleus and
other half cross to the contralateral EWN

11. Efferent pathway :
EWN 3rd cranial nerve
(oculomotor) cilliary ganglion
innervate the sphincter pupillae

12. Near reflex pathway
 Near reflex is occur looking near object.
 consists of two components
1.convergence reflex
2. accomodation reflex

13. Pathway of convergence reflex
Afferent path way : medial rectus
mesencephalic nucleus of the 5th nerve
convergence centre in the tectal or pretectal region
 Internuncial pathway : convergence centre
EWN

14.  Efferent pathway : EWN 3rd cranial nerve
(oculomotor) cilliary ganglion
innervate the sphincter pupillae

15. Pathway of accomodation reflex
 Afferent path way : extend from retina to
optic nerve optic chiasma optic tract
lateral geniculate body
optic radiation striate cortex
Parastriate cortex

16.  Internuncial pathway : parastriate cortex
EWN (via occipito-mesencephalic tract & pontine
centre)
 Efferent pathway : EWN 3rd cranial nerve
(oculomotor) cilliary ganglion
innervate the sphincter pupillae

18. Thank you