The pupil is a circular opening in the iris that regulates the amount of light entering the eye. It is normally centered and round, with sizes ranging from 2.5-4mm depending on lighting conditions. The pupil size is controlled by the dilator and sphincter muscles of the iris. Disorders of the pupil include anisocoria where the pupils are unequal sizes, mydriasis where the pupils are overly dilated due to paralysis of the parasympathetic fibers, and miosis where the pupils are overly constricted due to a lesion in the sympathetic pathway. Argyll Robertson pupils are small, irregular pupils that react to accommodation but not light, indicating a lesion in the periaqueductal region

1. PUPIL IN HEALTH AND
DISEASE

2. NORMAL PUPIL
The pupil is an opening located in the center of
the IRIS that allows light to enter the retina.
•The size of the pupil determines the amount of
light that enters the eye.
11 The pupil size is controlled by the dilator and
sphincter muscles of the iris.

3. Number
Normally there is one pupil.
More than one is called polycorla
Location
Normally almost centtal (slightly nasal).
Eccentric pupil Is called Correctopla.

4. May be variable in size but
should be equal
React to light
Central
Round
!
PUPIL
Unequal
Not reacting to light
Not central
Irregular
Dilated or Constricted

5. Size
Varies from 2.5mm to 4mm depending upon the
illumination.
Miotic pupils are less than 2mm.
Mydriatic pupils are more than 7mm.
dilat~d
pupil
cor1stricted
ptJJlil

6. Functions of pupil
•It regulates the amount of light entering the eye.
·It improves the visual acuity because it prevents the
irregular refraction by the periphery of the cornea
and lens, and increases the depth of focus.
·It allows the passage of aqueous humour from the
posterior chamber to the anterior chamber.

7. Relevant Anatomy
The IRIS contains 2 groups of smooth muscles :
; A circular group called sphincter pupillae.
r A radial group called dilator pupillae.

8. DISORDERS OF THE PUPIL

9. ANISOCORIA
•Anisocoria is defined as a difference of 0.4 mm or
more between the sizes of the pupils ofthe eyes.
•About 20% of normal people have a slight difference
in pupil size which is known as physiological
anisocoria. In this condition, the difference between
pupils is usually less than 1 mm.

10. Ifthe larger pupil is abnormal ( poor constriction),
the anisocoria is greatest in Bright illumination, as the
normal pupil becomes small. Caused by disruption of
Parasympathetic pupillary pathway.
Ifthe smaller pupil is abnormal ( poor dilatation),
the anisocoria is greatest in dark illumination, as the
normal pupil becomes large. Caused by disruption of
Sympathetic pupillary pathway.

11. MYDRIASIS
•This results from paralysis of the parasympathetic
fibers, either at their origin from the pretectal nuclei
and the EW nucleus in the midbrain, during the
course with the 111 C.N or at the ciliary ganglion at the
orbit.
• Most commonly such lesions are due to vascular
accidents in the mid brain, tentorial herniation ( due
to cerebral space occupying lesions) or aneurysms of
the carotid arte

12. MIOSIS
This indicates a lesion in the sympathetic pathway to
the pupillary dilator
Thus the lesion may be in the
• hypothalamus,
• brain stem,
• lateral aspect ( the spinal cord as far down as the
upper thoracic segments)

13. • the sympathetic chain,
• the cervical sympathetic ganglion,
• the precarotid plexus
• the sympathetic fibers which run to the orbit
accompanying the ophthalmic division of the V
Cranial Nerve

14. Argyll Robertson Pupil
•AR Pupils are small (miosis), irregular in outline and
have light near dissociation.
•They react poorly to light but very welI to near reflex.
•AR Pupils are usually bilateral and symmetrical.
•Vision grossly intact.

15. Argyll Robertson Pupil
•The lesion lies in the periaqueductal region,
pretectal area and rostral mid brain dorsal to the
EW nuclei.
•AR Pupils are a classical eye finding in neurosyphilis.
•Also seen in Tabes Dorso/is, G.P.I ( Paralytic
dementia) and Aortic Regurgitation.

16. R
,
everse Argyll Robertson Pupil
•Very rare.
• Pupils react to light but not to accommodation.
•Due to lesion in occipitotectaI tract eg., encephalitis
lethargica, Diphtheria.