A1. Disorders of the innervation of pupils Flashcards
Pupil is innervated by
- Sympathetic:
*sympathetic chain
*dilator pupillae m (part of iris) - parasympathetic:
*oculomotor nerve
*sphincter pupillae (part of iris)
List the location of Injuries to the sympathetic innervation of pupil
- In the hypothalamus and brainstem
- In the spinal cord
- Within the chest (paravertebral
sympathetic ganglia) - On the neck (sy. fibers that run
with ICA) - In the orbita
normal pupil size
what does it depend on
normal 2–6 mm
depends on the balance
between sympathetic and
parasympathetic tone
iris controls the —-
what does it consist of
size of the pupil.
It contains two groups of smooth muscle fibre
1. Sphincter pupillae: a circular constrictor (parasym)
- Dilator pupillae: a radial dilator (sym)
ciliary muscle, innervated
by
parasympathetic,
controls the degree of convexity of the
lens through the ciliary zonule
Pathway of pupillary constriction and the light reflex is controlled by which system
parasympathetic
list Pathway of pupillary constriction and the light reflex
- A stimulus, such as a bright light
shone in the left eye
-> will send an
afferent impulse along the optic
nerve to the midbrain (superior
colliculus) - a second order
fibre passes to the Edinger-Westphal
nucleus (part of the III nerve nucleus) on the same and opposite
side (through the posterior
commissure). - Efferent fibres leave
in the oculomotor nerve -> pass to
the ciliary ganglion and thence, in
the short ciliary nerve, to the
constrictor fibres of the sphincter
pupillae muscle.
If all pathways of pupillary constriction and the light reflex are intact- what happen if you shine light in one eye
shining a light in one eye will constrict both pupils at an equal rate and to a
similar degree.
lesion in sympathetic pathway leads to
Horner-triad ( ptosis, miosis, and anhidrosis)
what symptom is seen when there’re a lesion in parasympathetic pathway
->Mydriasis : pupil dialation
parasympathetic pathway is responsible for which reflexes
- Response to light (light reflex)
- Part of accommodation-convergence reflex
(response to focusing on near object that involves
accommodation, miosis and convergence)
what to check when examining intraocular muscles (pupils and pupillary reflexes):
-
Size and shape of pupils - dilation, constriction, pinpoint, anisocoria (unequal size), oval/irregular
shape, postoperative coloboma - Direct pupillary light reflex - Illuminate one pupil and it will constrict (cover the other)
-
Consensual/indirect pupillary light reflex - Illuminate one pupil and observe constriction of the
other -
Accommodation-convergence reflex -
When focusing on near object,
medial rectus muscles contract (convergence),
pupils constrict and
lenses accommodate for near vision.
Causes of mydriasis
- Complete oculomotor nerve lesion -
- Adie’s pupil (Tonic pupil)
May also have reduced/absent limb reflexes
( Holmes-Adie syndrome ). - Migraine - A few hours of mydriasis may accompany headache.
- Drugs - Anticholinergic drugs, TCA, NSAIDs, antihistamines, oral contraceptives.
Mydriasis can precipitate attack of acute angle-closure glaucoma
Complete oculomotor nerve lesion symptoms VS partial
● Complete oculomotor nerve lesion
* Mydriasis
* ptosis
* impaired eye movements on affected side.
Loss of direct pupillary reflex and accommodation reaction = Fixed pupil.
● External/partial oculomotor lesion → No parasympathetic involvement
(-ptosis
-lateral and downward deviation on affected side,
-diplopia)
what is Adie’s pupil (Tonic pupil)
-benign or malignant
-etiology
-acute or chronic
-unilateral or bilateral
- Benign, usually in young women.
- Acute onset, 80% bilateral,
- unknown cause.
- Mydriasis, often absent direct or indirect pupillary light reflex
- but may have slow pupillary constriction/dilation with accommodation.
- May also have reduced/absent limb reflexes ( Holmes-Adie syndrome ).
drugs causing mydriasis
Anticholinergic drugs
TCA
NSAIDs
antihistamines
oral contraceptives.
Mydriasis can precipitate attack of acute angle-closure glaucoma.
Causes of miosis:
- Horner’s syndrome - From sympathetic damage
- Argyll-Robertson pupil - Irregular shaped, small pupils that do not react to light, but can accommodate
- Drugs - Parasympathomimetics
Horner’s syndrome causes
can you distinguish between central VS peripheral cause?
- tumor (e.g. Pancoast)
- vascular lesions
- congenital (e.g. syringomyelia)
Can distinguish between central and peripheral cause (if lesion is preganglionic, cocaine in eyes
will still cause dilation)
Horner’s syndrome occurs due to damage at
sympathetic damage at
* brainstem,
* cervical cord,
* middle fossa,
* internal carotid artery,
* cervical sympathetic chain
* or anterior roots of C8 and T1
Horner’s syndrome symptoms
● Ptosis - Weakness of superior and inferior tarsal muscles.
Less marked than with CN3 palsy.
● Miosis - Weakness of dilator pupillae muscle.
● Disturbance of sweating (depends on lesion site)
Marcus Gunn pupil
(Relative afferent pupillary defect) -
* Impaired optic nerve causes
decreased response to swinging-flashlight test: Less constriction (= apparent dilation) when bright light is
swung from unaffected eye to affected eye.
The affected eye still senses the light and produces constriction to some degree (but reduced).
etiology of anisocoria
- Fixed and dilated pupil
indicates oculomotor nerve lesion. - May be caused by transtentorial herniation of the uncus gyri hippocampi due to hemispherical space occupying lesions, compressing the oculomotor nerve.
