Download MBBS (Bachelor of Medicine and Bachelor of Surgery) Pupillary Reflex Pathway and Abnormalities PowerPoint PPT presentation
Light Reflex
When light is shown in one eye both pupils
constrict .Constriction of pupil to which light is
shown is called direct light reflex and that of
other pupil is called consensual or indirect reflex.
Light reflex is initiated by rods and cones.
Pathway of light reflex :
Afferent fibers extend from retina to the pretectal nucleus in
the midbrain. Internuncial fibers connect each pretectal
nucleus with Edinger Westphal nuclei of both sides .This
connection forms the basis of consensual light reflex. Efferent
pathway consists of parasympathetic fibers which arise from
the Edinger Westphal nucleus in midbrain and travel along the
oculomotor cranial nerve.The preganglionic fibers enter the
inferior division of third nerve and via the nerve to inferior
oblique reach the ciliary ganglion to relay.post ganglionic
fibres travel along the short ciliary nerves to innervate the
sphincter pupillae.
NEAR REFLEX
Near reflex occurs on looking at a near object.It consists of
two components.
a)Convergence reflex-contraction of pupil on convergence
b)Accommodation reflex-contraction of pupil associated with
accommodation.
PATHWAY OF CONVERGENCE REFLEX:
Afferents from medial recti travel centrally via the third
nerve to the mesencephalic nucleus of the 5th nerve to
a presumptive convergence center in the tectal or
pretectal region.From this the impulse is relayed to the
Edingher-Westphal nucleus and subsequent efferent
pathway of near reflex is along the third nerve.The
efferent fibres relay in the accessory ganglion before
reaching the sphincter pupillae
PATHWAY OF ACCOMODATION REFLEX
The afferent impulses extend from the retina to the parastriate
cortex via the optic nerve,chiasma,optic tract,lateral
geniculate body,optic radiation and striate cortex.From the
parastriate cortex the impulses are relayed to the Edingher-
Westphal nucleus of both sides via the occipito mesencephalic
tract and the pontine center.From the Edingher-Westphal
nucleus efferent impulses travel along the 3rd nerve and reach
the sphincter pupillae and ciliary muscle after relaying in the
accessory and ciliary ganglion.
EXAMINATION OF PUPILLARY REFLEX
DIRECT LIGHT REFLEX:
To elicit this reflex,patient is seated in a dimly lighted
room.With the help of a palm,one eye is closed and a narrow
beam of light is shown to other pupil and its response is
noted.the procedure is repeated for the second eye.A normal
pupil react briskly and its constriction to light is well maintained.
CONSENSUAL LIGHT REFLEX:
Patient is seated in a dimly lighted room and the two eyes are
separated from each other by an opaque curtain kept at the
level of nose.(either hand of examiner or a piece of
cardboard).Then one eye is exposed to a beam of light and
pupillary response is observed in the other eye.The same
procedure is repeated for the second eye.normally the
contralateral pupil should also constrict briskly when light is
thrown on to other pupil.
SWINGING FLASH LIGHT TEST
It is performed when relative afferent pathway defect or
Marcus Gunn Pupil is suspected in one eye.
To perform this test a bright flash light is shown on to one
pupil and constriction of that pupil is noted.Then after
3sec, the flash light is quickly moved to the contralateral
pupil and response is noted.This swinging to and fro of
flash light is repeated several times while observing the
pupillary response.
Normally both pupils constrict equally and the pupil to which
light is transferred remains tightly constricted.
In the presence of RAPD in one eye the affected pupil will dilate
when the flash light is moved from normal eye to the abnormal
eye.This response is called Marcus gunn pupil or RAPD.It is the
earliest indication of optic nerve disease.
NEAR REFLEX - EXAMINATION
To determine the near reflex, patient is asked to
focus on a far object and then instructed suddenly
to focus at an object (pencil or tip of index
finger) held about 15 cm from patient's eye.
While the patient's eye converges and focuses the
near object, observe the constriction of pupil.
ABNORMALITIES OF PUPILARY
REACTIONS
Amaurotic light reflex
It refers to the absence of direct light reflex on the
affected side (say right eye) and absence of
consensual light reflex on the normal side (i.e., left
eye). This indicates lesions of the optic nerve or
retina(optic neuritis or ischaemic optic neuropathy)
on the affected side (i.e., right eye), leading to
complete blindness. In diffuse illumination both
pupils are of equal size.
Efferent pathway defect.
Absence of both direct and consensual light reflex on the
affected side (say right eye) and presence of both direct and
consensual light reflex on the normal side (i.e., left eye)
indicates efferent pathway defect (sphincter paralysis).
Near reflex is also absent on the affected side.
Its causes include: effect of parasympatholytic drugs (e.g.,
atropine, homatropine), internal ophthalmoplegia, and third
nerve paralysis.
Wernicke's hemianopic pupil
It indicates lesion of the optic tract. In this condition,
light reflex (ipsilateral direct and contralateral
consensual) is absent when light is thrown on the temporal
half of the retina of the affected side and nasal half of the
opposite side; while it is present when the light is thrown
on the nasal half of the affected side and temporal half of
the opposite side.
Marcus Gunn pupil
It is the paradoxical response of a pupil to light in the presence
of a relative afferent pathway defect (RAPD).
Causes of Marcus Gunn pupil include incomplete optic nerve
lesions and severe retinal diseases.
If a patient with mild optic nerve lesion in left eye,shine light
into affected eye and a seemingly normal response noted.After
2sec,move torch briskly to shine the normal right eye.the right
pupil which is already constricted due to consensual response
will stay constricted.now when torch is moved to the left
side,because of the subtle afferent defect ,signal strength of
input to midbrain pupilloconstrictor or Edingher Westphal nuclei
is reduced,resulting in apparently paradoxical dilatation of left
pupil.
Argyll Robertson pupil (ARP)
Here the both pupils are slightly small in size and reaction
to near reflex is present but light reflex (both direct and
consensual) is absent, i.e., there is light near dissociation
(to remember, the acronym ARP may stand for
`accommodation reflex present').Both pupils are involved
and dilate poorly with mydriatics.
It is caused by a lesion (usually neurosyphilis,multiple
sclerosis,syringobulbia,autonomic neuropathy) in the region
of tectum.
Adie's tonic pupil
In this condition, reaction to light is absent and to near reflex is
very slow and tonic. The affected pupil is larger (anisocoria).
It is caused by post ganglionic parasympathetic pupillomotor
damage. It is usually unilateral, associated with absent knee
jerk and occurs more often in young women.
Adie's pupil constricts with weak pilocarpine (0.125%) drops,
while normal pupil does not, because the denervated iris
sphincter is supersensitive to topical parasympathomimetics.
LIGHT NEAR DISSOCIATION
ARGYLL ROBERTSON PUPIL
HOLMES ADIE PUPIL
PARINAUD'S SYNDROME
ABERRANT THIRD NERVE REGENERATION
MYOTONIC DYSTROPHY
DIABETES MELLITUS
THANK YOU...
This post was last modified on 12 August 2021