The pupil is a hole located in the centre of the iris that allows light to enter the retina. The iris contains muscles that control the size of the pupil in response to light and focusing. Anisocoria is when the pupils are unequal sizes and can be caused by physiological factors, trauma, inflammation, or neurological issues. Examining the pupils' reaction to light and focusing is important for evaluating eye and neurological function.

1. By Saptarshi Mehta

2. The pupil is a hole located in the centre of the iris of
the eye that allows light to enter the retina.

3. Light rays entering the pupil are either absorbed by the
tissues inside the eye directly, or absorbed after diffuse
reflections within the eye that mostly miss exiting the
narrow pupil.

4. The iris is a contractile structure, consisting manly of smooth muscle,
surrounding the pupil.
Iris contain two groups of smooth muscles :
I. A circular group called the sphincter pupillae
II. A radial group called dilator pupillae.

6.  The dilator pupillae innervated by sympathetic nerves from superior cervical
ganglion, cause the pupil to dilate when they contract.
 The sphincter pupillae is supplied by the parasympathetic system through the
3rd cranial nerve, when this muscle contracts, it reduces the size of the pupil.

8. The resting pupil size is influenced by several factors, most important are :
 The amount of ambient light.
 The status of retinal adaptation.
 The level of arousal, excitement or startle.
 The patient age.

9. The pupil gets wider in dark but narrower in light
 When wide, the diameter is 4 – 9 mm.
 When narrow, the diameter is 3 – 5 mm.

10.  The pupil serves two important functions - to control the illumination in the
eye, and to improve the optical quality of the image on the retina.
 The second function is very important because as the pupil gets larger, more
aberrations are created and the image on the retina gets "messier".
 To increase depth of focus. This basically increases the range (distance) over
which things appear sharp.

11. The pupillary light reflex (PLR) is a reflex that controls the diameter
of the pupil, in response to the intensity (luminance) of light that falls
on the retina of the pupil and the eye, thereby assisting
in adaptation to various levels of lightness/darkness.

12. • Light reflex.
• Near reflex.

13. Retina. Short ciliary nerves Iris sphincter
muscle
Optic nerve Ciliary ganglion
Optic chiasma Parasympathetic root of ciliary ganglion
Optic tract Oculomotor nerve
Pretectal nucleus Edinger–Westphal nucleus
Afferent Pathway
Efferent Pathway

14. Afferent Pathway Efferent Pathway

16. Retina  Optic nerve  Optic chiasma
 Optic tract  Lat geniculate body
 Optic radiations  visual cortex 
cortical association areas  mid brain
 occipitomesencephalic tract  E.W.
nucleus  3rd nerve  accessory
ciliary ganglion along short ciliary
nerves  ciliary muscle and pupil
constrictor

17. Pupils should be circular, central and equal in size. They should constrict to
light and accommodation equally
There are four steps in the examination of the pupils:
 Inspection
 Light reaction
 Swinging light test
 Accommodation reflex

18.  Inspection :
 Look for irregularity, inequality in size or eccentricity

19.  Light reaction:
 With one eye shielded from a pen torch beam
observe the constriction of the illuminated
pupil (the direct response) and the
constriction in the shielded pupil (the
consensual response)

20.  Swinging light test:
 The pen torch beam should be passed
rapidly from one eye to the other
 The normal response is sustained
constriction of both pupils
 If one pupil dilates upon illumination
there is an relative afferent pupillary
defect (Marcus Gunn pupil) in that eye
 This is a simple test of optic nerve
function.

21.  Accommodation reflex:
 The patient is asked to look at a distant object and then at
an object close to his face.
 Both pupils should constrict and dilate again when distant
gaze is resumed

22. Any disorder that physically damages the mechanical compliance
of the iris or iris musculature can result in an irregular pupil.

23. Blunt trauma to the eye can cause
focal tears in the sphincter muscle.

24. Iridodialysis occurs when the outer edge of the
iris is torn away from its ciliary attachment.

25. Intraocular inflammation can damage the iris or
cause it to adhere to the lens or cornea (synechiae).

26. Neovascularizatio can also distort the
iris and impair pupillary reactivity.

27. Iris malformation such as coloboma and
aniridia will affect pupil size and function.

28. The leading cause of a misshapen pupil
in an adult is probably cataract surgery.

30. This disorder is uniformly benign and occurs in healthy individuals, often with
a history of migraine. The pupil undergoes sectoral dilation lasting for a few
minutes before returning to normal. This phenomenon may occur multiple
times for several days or a week and then disappears. It is thought to
represent segmental spasm of the iris dilator muscle.

31. In rare cases, eccentric or oval pupils are seen in patients with rostral
midbrain disease. This abnormality is presumably caused by
incomplete damage of the pupillary fibers leading to selective
inhibition of iris sphincter tone.

32. Anisocoria is a condition characterized by an unequal size of the eye's pupils.
Affecting 20% of the population

33. (A) Physiological
(B) Mechanical
(C) Pharmacological
(D) Horner syndrome
(E) Adie tonic pupil
(F) III nerve palsy

35.  Anisocoria Equal in Dim and Bright light.
 Anisocoria Greater in Dim Light. (Problem in
dilator pupillae sympathetic nerves)
 Anisocoria greater in bright light. (Problem in
sphincter pupillae supplied by the
parasympathetic system through the 3rd cranial
nerve)

36. Causes of anisocoria range from benign (normal) to life-threatening conditions.
Clinically, it is important to establish whether anisocoria is more apparent in
dim or bright light:
 Anisocoria which is greater in dim light suggests Horner's syndrome or
mechanical anisocoria.
 Anisocoria which is greater in bright light suggests Adie tonic pupil,
pharmacologic dilation, Oculomotor nerve palsy, or damaged iris.

37.  It is the most common cause of a difference in pupil size of 0.4
mm or more.
 About 20% of individuals have noticeably asymmetric pupil
diameters.
 The difference in pupil diameters is less than 1.0 mm.

38. Occasionally previous trauma (including surgery) or inflammation can
lead to adhesions between the iris and the lens or intraocular lens.
These adhesions may prevent dilation in conditions of dim
illumination. Posterior synechiae should be visible with a magnifying
lens or slit lamp.

39. The use of pilocarpine may result in a
small, poorly reactive pupil. Anisocoria
will not be present if both eyes are
treated, but the unilateral use of
medication may cause confusion.
When mydriatic medications are instilled
in the eye accidentally or intentionally,
the pupil becomes dilated and reacts
poorly to light and near stimulation.

40. A lesion at any point along the oculosympathetic pathway results in Horner
syndrome.
Which includes :
 Ptosis
 Miosis
 Enophthalmos
 Anhidrosis on the same side.
 With Horner syndrome, anisocoria is more apparent in dim illumination,
and the affected pupil shows dilation lag when the room light is abruptly
turned off.
 Light and near pupillary reactions are intact, but the eyelid is ptosis due to
paresis of Muller muscle.

41. Tonic pupils include sluggish, segmental pupillary responses to light and
better response to near effort followed by slow redilation. A tonic pupil is
caused by postganglionic parasympathetic pupillomotor damage.
 70% patients are female.
 Tonic pupils are unilateral in 80% of cases, although the second pupil may
later become involved (4% per year).

42. The pupil is not round; the sphincter contracts
from the 11 o'clock to 1 o'clock areas, Where
the sphincter is paralyzed, the regions of iris
stroma are relatively flat.
The arrow indicates
the junction of the normal sphincter (NS) and
the atonic sphincter (AS)

43.  Dilated
 Non reactive
 Absolute motor paralysis
 Associated with ptosis, deviation
of eyeball

45.  Involvement is usually bilateral but asymmetrical.
 The pupils are small in size and irregular in shape.
 The light reflex is absent, but near reflex is present.
 The pupils dilate very poorly with mydriatics like atropine

46.  Constricted
 Sluggishly reactive due to :
 Glycogen infiltration of spincter
 Autonomic denervation
 Arteriosclerosis of radial iris vessels

47.  Seen in optic tract lesions with hemianopia
 Stimulating the blind half of retina pupil shows no reaction
 Stimulating seeing half of retina pupil shows reaction
 Difficult to elicit – due to scattering & diffusion of light
 Use a narrow streak of light

48. Useful in assessment of head injuries
 Stage1 : Ipsilateral pupil (on the side of head injury shows contraction due
to irritation, Contralateral (normal) pupil –normal
 Stage2 : Ipsilateral pupil shows dilatation due to paralysis , contralateral
pupil constricts (irritation spreads to normal side)
 Stage3 : Both pupils dilate. Stage of bilateral paralysis. To assess pupil
repeatedly is important, therefore mydriatics should be avoided in case of
head injuries

49. Hippus, also known as pupillary athetosis, is spasmodic,
rhythmic, but irregular dilating and contracting pupillary
movements between the sphincter and dilator muscles

50. oThe involved eye is completely blind.
oThe near reflex is normal in both eyes.
oBoth pupils are equal in size.
oAbsence of direct light reflex on the
affected side and absence of consensual
light reflex on the normal side.

52. The Relative Afferent Pupillary Defect (RAPD), or Marcus-Gunn
Pupil is an extremely significant and highly objective clinical
finding in the examination of the visual system.

53.  When the normal eye is stimulated
both pupils constrict.
 Then when the light is swung to
the diseased eye, both pupils dilate
instead of constricting.

54. The "swinging flashlight test" is probably the best test for identifying an
RAPD. In this test, a strong, steady light is used.
 No Relative Afferent Pupillary Defect (I): Both pupils constrict equally without evidence
of pupillary re-dilation with the "swinging flashlight test", except possibly for "hippus".
 Mild Relative Afferent Pupillary Defect (II): The affected pupil shows a weak initial
constriction, followed by dilation to a greater size.
 Moderate Relative Afferent Pupillary Defect (III): The affected pupil shows a stable or
unchanged level of constriction, followed by dilation to a greater size.
 Severe Relative Afferent Pupillary Defect (IV): The affected pupil shows an immediate
dilation to a greater size.