Download Neuro-ophthalmic disorders

Neuro-ophthalmic
Disorders
Relative Afferent Pupillary Defect
• seen in optic nerve lesion and severe retinal disease
• lesion of the optic nerve on one side blocks the afferent limb
of the pupillary light reflex
• pupils are equal and of normal size but the pupillary
response to light directed to the affected side is reduced
• sign observed during the swinging-flashlight test
• seen as both pupils dilation when light is swung from normal
to abnormal eye
• the affected side will constrict less therefore appearing to
dilate
Visual Pathway
• The optic nerve is formed by the axons arising from the retinal
ganglion cell layer.
• It passes out of the eye though the lamina cribrosa of the sclera.
• It is surrounded by dura, arachnoid and pia mater, continuous with
that surrounding the brain.
• The optic nerves extend from the posterior pole of the eye to cross
at the optic chiasm.
• The fibers travel as the optic tract - most of them go to the lateral
geniculate body in the thalamus (visual)
• Another population sends information to the tectum in midbrain
(afferent fibers of the pupillary light reflex)
• T
hey leave the lateral geniculate body forming the optic radiations
to the visual cortex.
• P
rimary visual cortex responsible for processing visual
information is located in the occipital lobe.
Optic Nerve
• Intraocular
• Orbital
• Intracanalicular
• Intracranial
Intraocular portion of the Optic Nerve
• Visible on the ophthalmoscopy as the optic disc.
• Central retinal vessels enter and leave the eye here.
• There is a complete absence of photoreceptors and is
known as the blind spot.
• Normally slightly vertically oval with an average area
dimensions of 1.76mm horizontally and and 1.92mm
vertically.
• Normal color is yellowish-orange.
• Sharply defined margin and the nasal side is slightly less
distinct due to the greater density of nerve fibers.
• There is a central depression called optic cup.
• Optic cup is the pale center of the disc and is devoid of
neuroretinal tissue.
• It is important to document the size of the cup.
• This is specified as the horizontal and vertical cup to disc
ratio.
• Normal cup to disc ratio is 0.3 mm.
• Increased cup to disc ratio indicates a decrease in the
quantity of healthy neuroretinal tissue and hence,
glaucomatous change.
Disturbances of the Visual Pathway
Optic Nerve
Swollen Optic Disc
• Papilloedema
• Space-occupying lesions of the optic nerve head
o Optic disc drusen (calcified axonal material)
o Gliomas
o Sarcoidosis
o Leukemia
• Papillitis
• Accelerated (malignant hypertension)
• Ischemic optic neuropathy
• Central retinal vein occlusion
• Pseudopapilloedema
• Myelinated nerve fibers around the nerve head
• Peripapillary atrophy in myopia
Optic disc drusen
Myelinated nerve fibers around the nerve head
Peripapillary atrophy in myopia
Papilloedema due to raised ICP
1. Optic nerve sheath is continuous with the subarachnoid
space of the brain.
2. As the CSF pressure increases, the pressure is transmitted
to the optic nerve.
3. The sheath acts as a tourniquet and leads to a buildup of
material at the level of lamina cribrosa.
4. This results in characteristic swelling of the nerve head.
5. Papilloedema may be absent in cases of prior optic atrophy
most likely secondary to a decrease in the number of
physiologically active nerve fibers.
Causes
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Idiopathic intracranial hypertension
Intracranial tumors (60%)
Craniosynostosis
Cerebral edema
Encephalitis
Obstruction of the ventricular system
Decreased CSF resorption
Increased CSF production
Medications - tetracycline, nalidixic acid, steroids
History
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Associated visual loss is rare
Transient visual obscurations
Blurred vision
Constriction of the visual field
Decreased color perception
Diplopia (sixth nerve palsy)
Headache, worse on waking and made worse by coughing
Nausea, retching, vomiting
Pulsatile tinnitus
History of trauma
Medications
Signs
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Swollen optic disc with blurry margins
Dilated and prominent superficial capillaries
No spontaneous venous pulsation of the CRV
Hemorrhages over and/or adjacent to the disc
Paton's lines
Normal color vision
No RAPD
Visual field testing
o large blind spot
o constricted filed in chronic cases
• Abnormal neurological signs
Investigations
• CT scan and MRI of the brain with contrast to identify space
occupying lesions
• MR venography to detect venous sinus thrombosis
• B-scan ultrasonography to rule out disc drusen
• Fluorescein angiography
• Lumbar puncture
Treatment
• Treat the underlying disorder
• Papilloedema will resolve within few weeks once ICP has
been normalized
• Optic atrophy usually remains
• Neurosurgery is required for space-occupying lesions and
hydrocephalus
Idiopathic Intracranial Hypertension
• Elevated ICP and presence of disc swelling with no
evidence of intracranial abnormality and no dilation of the
ventricles on the scan
• Overweight women in the second and third decades
• Exposure to drugs such as contraceptive pills and
tetracyclines
• Headache, obscurations of vision, sixth nerve palsies
• No other neurological problems
• Progressive contraction of the visual field if the nerve
remains swollen for weeks
• Treatment by reducing the ICP
o medications (oral acetazolamide)
o ventriculoperitoneal shunting
o optic nerve decompression
Optic Neuritis
• Inflammation or demyelination of the optic nerve
• Papillitis - optic nerve head is affected
• Retrobulbar neuritis - nerve is affected more posteriorly with
no disc swelling
• Many are associated with multiple sclerosis
• Age 20 - 45, more in females and Caucasian
Causes
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Multiple sclerosis (50%)
Syphilis
Lyme disease
Herpes zoster
Autoimmune disorders (lupus)
IBD
Drugs (chloramphenicol, ethambutol)
Vasculitis
Diabetes
History
• Usually affects one eye
• Acute loss of vision that progress over a few days and then
slowly improve (some are permanent)
• Varies from a small area of blurring to complete blindness
• Distorted vision and reduced color vision
• Pain on eye movement in retrobulbar neuritis
• Preceding history of viral illness
• 40-70% develop other neurological symptoms to suggest
MS
Examination
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Reduced visual acuity
Reduced color vision
RAPD due to reduced optic nerve conduction
Central scotoma on field testing
Normal disc in RN, swollen disc in papillitis
Papillitis
• MRI scan can identify additional silent plaques of
demyelination
• Diagnosis of MS is essentially clinical
• Treatment with steroid may speed up visual recovery
• Immunosuppressive therapy in case of MS
• Vision slowly recovers over several weeks but not quite as
good as before the attack
• Repeated episodes may lead to optic atrophy and decline
in vision
• Vision may not recover in atypical cases
Ischemic Optic Neuropathy
Degenerative vaso-occlusive or vasculitic
disease of the arterioles
Compromise posterior ciliary vessels
Ischemia of the anterior optic nerve
Types
• Arteritic ischemic optic neuropathy
o giant cell arteritis
o advanced age
o mostly involving nearly complete vision loss
• Non-arteritic ischemic optic neuropathy
o results from the coincidence of cardiovascular risk factors
in a patient with "crowded" optic discs
o more common
o younger age group
o few near total loss of vision cases
Symptoms
• Sudden loss of vision or visual field, often on waking
• Vision in that eye is obscured by a dark shadow, often
involving just the upper or lower half of vision, usually the
area towards the nose
• Pain or scalp tenderness (giant cell arteritis)
Giant Cell Arteritis
• Autoimmune vasculitis in patients over the age of 60
• Affects arteries with an internal elastic lamina
• Present with any combination of:
o sudden loss of vision
o scalp tenderness (e.g. on combing)
o pain on chewing (jaw claudication)
o shoulder pain
o malaise
Signs
• Reduction in visual acuity
• Field defect, absence of the lower or upper half of the visual
field (altitudinal scotoma)
• Swollen and hemorrhagic disc, normal retina and retinal
vessels
• Pale disc in arteritic ION
• Small normal disc with small cup in non-arteritic ION
• Tender temporal artey in GCA
Investigations
• Elevated ESR and CRP in GCA (1 in 10 normal)
• Temporal artery biopsy
• Color duplex ultrasound - hypoechoic halo around the
temporal artery lumen
• Full blood count to exclude anemia
• Blood pressure
• Blood sugar
Treatment
• IV and oral high-dose steroids if GCA is suspected
• Dose is tapered over the ensuing weeks according to
symptoms and the response of ESR and CRP
• Steroids will not reverse the visual loss but can prevent the
involvement of the other eye
• No treatment for non-arteritic ION other than management
of underlying conditions
Prognosis
• Second eye may rapidly become involved if untreated
(GCA)
• Steroid therapy may have to be continued on a prolonged
basis and monitored
• Significant rate of involvement of the second eye in nonarteritic form (40 - 50%)
• Unusual for the vision to get progressively worse in nonarteritic form
• Vision lost does not recover in both conditions
Optic Chiasm
Causes
• pituitary tumor
o symptoms related to hormonal disturbance
• Meningioma
• Craniopharyngioma
Presentation
• Bitemporal hemianopia
• Missing objects in the periphery of visual field
• Difficulty in fusing images, causing the patient to complain of
diplopia although eye position and movement are normal
• Difficulty with tasks requiring stereopsis such as pouring
water into a cup or threading a needle
Optic Tract, Radiation & the
Visual Cortex
Causes
• tract - vascular or neoplastic
• radiation - neoplasia
• cortex - cerebrovascular accident
Presentation
• Homonymous hemianopic field defect
• tract - incongruous
• radiation or cortex - congruous
• Visual loss is of rapid onset; a slower onset suggests a
space-occupying lesion