Neuro-ophthalmic Disorders

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Neuro-ophthalmic Disorders
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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

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Visual Pathway

• The optic nerve is formed by the axons arising
  from the retinal ganglion cell layer.
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• It passes out of the eye though the lamina
  cribrosa of the sclera.
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• It is surrounded by dura, arachnoid and pia
  mater, continuous with that surrounding the
  brain. 
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• 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)

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• Another population sends information to
  the tectum in midbrain (afferent fibers of the
  pupillary light reflex) 
• ?They leave the lateral geniculate body forming
  the optic radiations to the visual cortex. 
• ?Primary visual cortex responsible for processing
  visual information is located in the occipital
  lobe. 

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Optic Nerve

• Intraocular
• Orbital
• Intracanalicular
• Intracranial

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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.

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• 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. 

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Disturbances of the Visual Pathway

•  

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Optic Nerve
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Swollen Optic Disc

• Papilloedema
• Space-occupying lesions of the optic nerve head
• Optic disc drusen (calcified axonal material)
• Gliomas
• Sarcoidosis
• Leukemia
• Papillitis
• Accelerated (malignant hypertension)
• Ischemic optic neuropathy
• Central retinal vein occlusion
• Pseudopapilloedema
• Myelinated nerve fibers around the nerve head
• Peripapillary atrophy in myopia

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Optic disc drusen
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Myelinated nerve fibers around the nerve head
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Peripapillary atrophy in myopia
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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. 

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Causes

• 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

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History

• 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

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Signs 

• 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
• large blind spot
• constricted filed in chronic cases
• Abnormal neurological signs

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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 

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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

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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

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• Treatment by reducing the ICP
• medications (oral acetazolamide)
• ventriculoperitoneal shunting
• optic nerve decompression

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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

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Causes

• Multiple sclerosis (50)
• Syphilis 
• Lyme disease
• Herpes zoster
• Autoimmune disorders (lupus)
• IBD
• Drugs (chloramphenicol, ethambutol)
• Vasculitis
• Diabetes

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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

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Examination

• 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

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Papillitis
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• 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

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Ischemic Optic Neuropathy

• Degenerative vaso-occlusive or vasculitic 
• disease of the arterioles
• Compromise posterior ciliary vessels
• Ischemia of the anterior optic nerve

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Types

• Arteritic ischemic optic neuropathy
• giant cell arteritis
• advanced age
• mostly involving nearly complete vision loss
•  Non-arteritic ischemic optic neuropathy
• results from the coincidence of cardiovascular
  risk factors in a patient with "crowded" optic
  discs
• more common
• younger age group
• few near total loss of vision cases

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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) 

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Giant Cell Arteritis

• Autoimmune vasculitis in patients over the age of
  60
• Affects arteries with an internal elastic lamina
• Present with any combination of
• sudden loss of vision
• scalp tenderness (e.g. on combing)
• pain on chewing (jaw claudication)
• shoulder pain
• malaise

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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

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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

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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

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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 non-arteritic form (40 - 50) 
• Unusual for the vision to get progressively worse
  in non-arteritic form
• Vision lost does not recover in both conditions

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Optic Chiasm
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Causes

• pituitary tumor
• symptoms related to hormonal disturbance
• Meningioma
• Craniopharyngioma 

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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

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Optic Tract, Radiation the Visual Cortex
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Causes

• tract - vascular or neoplastic
• radiation - neoplasia
• cortex - cerebrovascular accident

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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