Visual pathway consists of Retina / optic nerve / optic ...

Students:

Rahaf Hasanein

Mohammad Jomaa

Heba Abu Khalaf

Nebras abu abed

Reviewed and Modified: Dr Mohammad Abusamak FRCS

Collected by: Rahaf Jereisat

Visual pathway consists of :

Retina / optic nerve / optic chiasm / optic tracts / lateral geniculate

bodies/optic radiations / visual cortex

Control of retinal Illumination.

Reduces optical aberrations.

Depth of focus by miosis (pinhole effect(

In dim light, pupil dilates maximizes the number of photons to

enhance dark adaptation.

A small pupil reduces spherical and chromatic aberration.

After Refractive surgery, patient with large pupil have more

bothersome symptoms (glare at night)

In light adaptation, pupil constricts and enhances light adaptation.

When the eye focus on near object, they converge and the pupils

constrict (the near response)

are controlled by parasympathetic and sympathetic nervous system.

Sympathetic -> mydriasis

Parasympathetic -> miosis

Constriction of pupil

more Light on >> optic nerve crossing >> optic tract>> activate

both pretectal nucleus >>Edinger-Westphal

nucleus>>occulomotor (parasympathatic)>>ciliary ganglion>>

short ciliary nerves

dilation of pupil

Originate in post. hypothalmus >>ciliospinal center (c8-

T2)>>superior cervical ganglion>>trigeminal nerve>> ophthalmic

nerve >>nasociliary N<<LONG ciliary nerve

Anisocoria….. Inequality of pupils sizes.

Drugs.

Trauma.

Sympathetic lesions (Horner’s).

Parasympathetis lesions (Adie’s, Third nerve Palsy).

20% of people may have anisocoria

Measure afferent input. (RAPD)

Indicates awakefulness.

Excited individuals - larger pupil.

Slept , on narcotics - smaller pupil.

Central inhibition (parasympathomimetic) at level of

midbrain.

Autonomic functions.

Pupil diameter and optical aberrations.

Pharmacological response.

1.ocular disease

2.disorders of the controlling neural pathway;

3.pharmacological action

1.Ocular diseases

anterior uveitis due to Ocular synechiae.

intraocular surgery

blunt trauma to the eye, which may rupture the sphincter muscle,

causing irregularity or fixed dilation (traumatic mydriasis)

an acute and severe rise in ocular pressure – as in acute

glaucoma.

2. Neurological Causes

Best detected by swinging light torch:

light is repeatedly shone into the affected eye alternating with the

good side. When the light is shining on the unaffected eye, both

pupils constrict. When it’s transferred to the diseased side, there

is bilateral pupillary dilation. While the near reflex is intact.

A lesion of the optic nerve on one side blocks the afferent limb of

the pupillary light reflex.

Testing for an RAPD is critical in a patient suspected of having an

optic nerve lesion, such as optic neuritis .

An RAPD may be seen in very severe disease of the retina but not

with opacities of the cornea or lens.

**Interruption of the sympathetic pathway manifestations:

Miosis on the affected side.

Dilation Lag (pupil dilates slowly in dark room, anisocria greatest

first 4-5 seconds after light it turned off)

A slight ptosis on the affected side. “up-side down ptosis”

Enophthalmos, The reduced palpebral aperture size gives an

impression of recession.

Anhydrosis on the affected side, if the sympathetic pathway is

affected proximal to the base of the skull.

conjunctival injection

**Due to its extended pathway, The sympathetic pathway may be

affected by a multitude of pathologies Examples include:

Syringomyelia , an expanding cavity within the spinal cord,

sometimes extending into the medulla (syringobulbia), which

compresses the pathway. Typically, it also causes wasting of the

hand muscles and loss of sensation.

Small - cell carcinoma at the lung apex which catches the cervical

sympathetic chain. Involvement of the brachial plexus gives rise to

pain and to T1 wasting of the small muscles of the hand in

Pancoast’s syndrome.

Neck injury, disease or surgery .

Cavernous sinus disease – catching the sympathetic carotid plexus

in the sinus.

Right Horner’s Syndrome before and after Cocaine

test

Diagnosis of Horner’s

Cocaine (prevents reuptake of Norepinephrine) , 4% or 10%.

After application by 40-60 minutes , check pupils.

Presence of >=1 mm aniosorocia after cocoaine is positive test.

Hydro

xyamphetamine (differentiates pre- from post-ganglionic lesions).

Apraclonidine (reversal of anisocoria , alpha-1 supersensitivity)

1. Adie’s tonic pupil

2. The Argyll Robertson pupil

3. peri- aqueductal brainstem lesions such as Parinaud’s syndrome .

4. Other causes include diabetes, multiple sclerosis, severe optic

nerve disease and midbrain lesions.

1.Adie's Tonic Pupil

neurological disorder that causes one or both pupils to be abnormally

dilated (mydriasis) with delayed constriction in response to exposure to

light but better response to accomodation(chronic stage(

Heterochromia

Horner ’s syndrome may also be congenital, in which case the iris colour may be altered when compared to the fellow eye (heterochromia).

Due to ciliary ganglionitis which denervates the parasympathetic

supply to the iris and ciliary body (immune mediated)

Women, youngs and it’s benign.

Segmental denervation (sectoral palsy(

50% bilateral in 10 years.

The consequences are

Unilateral enlarged pupil that can become bilateral overtime.

Poor reaction to light with characteristic slow , worm-

like(vermiform) contraction of iris .(sectoral paresis)

Slow sustained miosis on accommodation (hence the name tonic),

results from muscarinic supersenitivity.

Constricts to dilute pilocarpine (0.1%), unlike the normal pupil.

Can be part of bigger syndrome: adie-holmes syndrome, Areflexia

The ciliary body is nine times more innervated than iris so it isn’t

affected as the iris.

Cholinergic Supersensitivity

0.125% Pilocarpine produces more constriction in the abnormal

pupil.

Develops in 5-7 days.

Can occur in CN III palsy as well

2.Argyll Robertson pupil

The pupils are bilaterally small and irregular. They do not react to light

but respond to accommodation

Seen in neurosyphilis, it’s suggested that a periaqueductal lesion on

dorsal aspect of edinger-westphal nucleus involves fibres associated

with response to light but spares those associated with near response .

3.Parinaud's syndrome

1. Pupils not reactive to light

2. Limited in elevation (upgaze palsy)

3. Convergence – retraction nystagmus

coma, both pupils may become miosed with preservation of the

light reflex if a pontine lesion is present.

Coma associated with a unilateral expanding supratentorial mass,

e.g. haematoma, results in pressure on the third nerve and

dilation of the pupil .

Midbrain lesions cause loss of the light reflex with mid-point

pupils

Intrinsic third nerve (Parasympathatic) lesions also cause a dilated

pupil.

Midbrain pupil:

Arises from lesions affecting the pretectal nuclear complex in dorsal

region of midbrain produces mydriasis and light near dissociation .

Causes include demyelination, infarction, enlargement of 3rd ventricle

and space occupying tumors such as pineloma .

3. Pharmacological Agents

1. Pathological miosis is seen in

a. Horner’s syndrome.

b. Third nerve palsy.

c. Argyll Robertson pupil.

d. Coma.

e. Systemic and topical atropine treatment.

2. Horner ’ s syndrome may be seen in

a. Syringomyelia.

b. Lung neoplasia.

c. Cavernous sinus disease.

d. Myasthenia gravis.

e. Carotid artery dissection.

3. Light – near dissociation

a. The reaction of the pupils is greater to light than accommodation.

b. May be seen in diabetes.

c. Is seen in Horner’s syndrome.

d. Is seen in patients with an Argyll Robertson pupil.

e. Is seen following administration of tropicamide drops.

4. Match the drop to its action: dilates (mydriasis) or constricts (miosis.)

a. Cyclopentolate.

b. Atropine.

c. Pilocarpine. (constricts)

d. Tropicamide.

e. Phenylephrine.

Differential diagnosis: pupil

Choose the most appropriate single diagnosis in the following abnormalities affecting the

pupils.

1. A 25 - year - old female comes into the surgery concerned that in a recent group

photograph it was pointed out to her that the right pupil looked bigger than the left.

She had no visual problems and no diplopia. On examination her eye movements

were full, no ptosis was present and the difference in pupil size was confirmed. The

right pupil constricted poorly to light.

=The poorly reacting pupil is the key to the diagnosis; on a slit - lamp examination

vermiform movements would be observed. Absent reflexes would help to confirm

the diagnosis.

2. A 67 - year - old man who had smoked all his life noted that his left pupil was smaller

than his right and his left lid drooped slightly. On examination the findings were

confirmed and both pupils reacted normally to light. The difference in pupil size was

more pronounced in the dark.

=Horner’s syndrome. The history of smoking makes the investigation for associated

chest neoplasia important.

3. An 80 - year - old man with a diagnosis of glaucoma for which he had been on the

same treatment for many years attended his optician. He was noted to have

bilaterally small pupils which did not appear to react to light.

=It is likely that he is taking pilocarpine to treat his glaucoma. This is an unusual drop

to prescribe to treat the condition today but was a mainstay of treatment in the

past.

4. A 45 - year - old man attended his GP with a frontal headache and reduced vision in

his left eye. The GP confirmed that the vision was reduced and noted that although

the pupils were equal, when a light was moved from the right to the left eye both

pupils appeared to dilate. The optic nerve on the left appeared pale, that on the

right was normal .

=This is a relative afferent pupillary defect. The pallor of the optic disc confirms the

likelihood of optic nerve disease.

5. A child suspected of having a squint had been taken to the eye hospital one

afternoon. The following morning his mother phoned the GP saying that his pupils

were dilated.

=Cyclopentolate drops are applied to dilate the pupil and allow an examination of

the fundus. The effect of the drops may last for some hours.

Differential diagnosis: field defect

Choose the most appropriate single field defect in the following situations

1. A 77 - year - old man with hypertension and diabetes notices that he is unable to see

on the left hand side. An MRI scan confirms a right cortical infarct.

=A posteriorly placed visual pathway lesion causes a congruous defect (similar

defect in both eyes); those affecting the optic tract are incongruous.

2. A 50 - year - old man presents to his GP saying that he feels his peripheral vision is

reduced and he often spilled the water when making a cup of tea. The GP notes that

although his acuity was normal he missed the temporal letters on the Snellen chart

with each eye.

=The symptoms suggest the possibility of a bitemporal hemianopia and the patient’s

performance on the Snellen chart helps to confirm the presence of this type of field

defect arising from a chiasmal lesion.

3. A 62 - year - old lady was found by her optometrist to have a raised intraocular

pressure in the right eye. He noted that the optic disc appeared cupped on the right

compared to the left. The eye otherwise appeared normal.

=An arcuate fi eld defect is typical of glaucoma.