OPTIC NEUROPATHIES

1. Anatomy of optic nerve2. Clinical features3. Special investigations

6. Leber hereditary optic neuropathy

4. Optic neuritis

5. Anterior ischaemic optic neuropathy (AION)

• Retrobulbar neuritis• Papillitis• Neuroretinitis

Anatomy• The optic nerve is the second of twelve paired

cranial nerves but is considered to be part of the central nervous system .

• composed of retinal ganglion cells axons and Portort cells

• Most of the axon of the optic nerve terminate in the lateral geniculate nucleus from where information is relayed to the visual cortex.

• Its diameter increases from about 1.6 mm within the eye, to 3.5 mm in the orbit to 4.5 mm within the cranial space

• The optic nerve component lengths are :

1 mm in the globe, 24 mm in the orbit, 9 mm in the optic canal and 16 mm in the cranial space before joining the optic chiasm.

• partial decussation occurs and about 53% of the fibers cross to form the optic tracts.

Signs of optic nerve dysfunction

• Reduced visual acuity

• Diminished light brightness sensitivity

• Dyschromatopsia

• Afferent pupillary conduction defect

Applied anatomy of afferent conduction defect

Anatomical pathway Signs

• Equal pupil size

• Light reaction - ipsilateral direct is absent or diminished - consensual is normal

• Near reflex is normal in both eyes

• Total defect (no PL) = amaurotic pupil

• Relative defect = Marcus Gunn pupil

3rd

Visual field defectsCentral scotoma

Altitudinal Nerve fibre bundle

Centrocaecal scotoma

Optic disc changes

• Retrobulbar neuritis• Early compression

Normal

• Papilloedema• Papillitis and neuroretinitis

Swelling

• Optic nerve sheath meningioma• Occasionally optic nerve glioma

Optico-ciliary shunts

• Postneuritic• Compression

Atrophy• AION

• Hereditary optic atrophies

Special investigations

Orbital fat-suppression techniques in T1-weighted images

Assessment of electrical activity ofvisual cortex created by retinal stimulation

MRI Visually evoked potential

Classification of optic neuritisRetrobulbar neuritis (normal disc)

• Demyelination - most common• Sinus-related (ethmoiditis)

• Lyme disease

Papillitis (hyperaemia and oedema)

• Viral infections and immunization in children (bilateral)• Demyelination (uncommon)• Syphilis

Neuroretinitis (papillitisand macular star)

• Cat-scratch fever

• Lyme disease

• Syphilis

1-Retrobulbar neuritis,in which the optic disc appearance is normal,at least initially , because the optic nerve head is not involved.It is the most frequent type in adults and is frequently associated with multiple sclerosis.

2-Papillitis,it is characterized by variable hyperaemia and oedema of the optic disc.

It is the most common type of optic neuritis in children.

3-Neuroretinitis is characterized by Papillitis with macular star.It is the least common type of optic neuritis and is most frequently associated with varial infections and cat-scratch fever.Other causes include syphilis and lyme disease and resolve within 6-12 months.

by definition , papilloedema is swelling of the optic nerve head. Secondary to raised intracranial pressure. It is nearly always bilateral , although it may be asymmetrical. All other causes of disk oedema in the absence of raised intracranial pressure are referred to as ‘disk swelling ,and usually produce visual impairment. All patient with papilloedema should be suspected of having an intracranial mass unless proved otherwise.however not all patients with raised intracranial pressure will necessarily develop papilloedema .

Non-arteritic AION

• Pale disc with diffuse or sectorial oedema

• Eventually bilateral in 30% (give aspirin)

• Age - 45-65 years• Altitudinal field defect

Presentation

Acute signs

• Few, small splinter-shaped haemorrhages

• Resolution of oedema and haemorrhages• Optic atrophy and variable visual loss

Late signs

FA in acute non-arteritic AION

Generalized hyperfluorescenceIncreasing localizedhyperfluorescence

Localized hyperfluorescence

Superficial temporal arteritis

• Headache

• Age - 65-80 years• Scalp tenderness

Presentation

• Superficial temporal arteritis

• Jaw claudication• Polymyalgia rheumatica

• Temporal artery biopsy

• ESR - often > 60, but normal• in 20%• C-reactive protein – always• raised

Special investigations• Acute visual loss

Histology of giant cell arteritis

• High-magnification shows giant cells

• Granulomatous cell infiltration

• Disruption of internal elastic lamina

• Proliferation of intima

• Occlusion of lumen

Arteritic AION• Affects about 25% of untreated patients with giant cell arteritis• Severe acute visual loss• Treatment - steroids to protect fellow eye• Bilateral in 65% if untreated

• Pale disc with diffuse oedema• Few, small splinter-shaped haemorrhages• Subsequent optic atrophy

Leber hereditary optic neuropathy

Maternal mitochondrial DNA mutations

Signs• Disc hyperaemia and dilated capillaries (telangiectatic microangiopathy)• Vascular tortuosity• Swelling of peripapillary nerve fibre layer

Presents• Typically in males - third decade• Occasionally in females - any age• Initially unilateral visual loss• Fellow eye involved within 2 months• Bilateral optic atrophy

• Subsequent bilateral optic atrophy