OPTIC NEUROPATHIES Anatomy of optic nerve Clinical features 3. Special investigations 4. Optic neuritis Retrobulbar neuritis Papillitis Neuroretinitis 5. Anterior ischaemic optic neuropathy (AION) 6. Leber hereditary optic neuropathy

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 Afferent pupillary conduction defect Dyschromatopsia Diminished light brightness sensitivity

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 defects Central scotoma Centrocaecal scotoma Altitudinal Nerve fibre bundle

Optic disc changes Normal Swelling Optico-ciliary shunts Atrophy Papilloedema Retrobulbar neuritis Papillitis and neuroretinitis Early compression AION Optico-ciliary shunts Atrophy Postneuritic Optic nerve sheath meningioma Compression Occasionally optic nerve glioma Hereditary optic atrophies

Special investigations MRI Visually evoked potential Orbital fat-suppression techniques in T1-weighted images Assessment of electrical activity of visual cortex created by retinal stimulation

Classification of optic neuritis Retrobulbar neuritis (normal disc) Papillitis (hyperaemia and oedema) Neuroretinitis (papillitis and macular star) Demyelination - most common Viral infections and immunization in children (bilateral) Cat-scratch fever Lyme disease Sinus-related (ethmoiditis) Demyelination (uncommon) Lyme disease Syphilis 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 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 Presentation Acute signs Late signs Age - 45-65 years Altitudinal field defect Eventually bilateral in 30% (give aspirin) Acute signs Late signs Pale disc with diffuse or sectorial oedema Resolution of oedema and haemorrhages Few, small splinter-shaped haemorrhages Optic atrophy and variable visual loss

FA in acute non-arteritic AION Localized hyperfluorescence Increasing localized hyperfluorescence Generalized hyperfluorescence

Superficial temporal arteritis Presentation Age - 65-80 years Scalp tenderness Headache Jaw claudication Polymyalgia rheumatica Superficial temporal arteritis Acute visual loss Special investigations ESR - often > 60, but normal in 20% C-reactive protein – always raised Temporal artery biopsy

Histology of giant cell arteritis Granulomatous cell infiltration High-magnification shows giant cells 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 Presents Typically in males - third decade Occasionally in females - any age Initially unilateral visual loss Fellow eye involved within 2 months Bilateral optic atrophy Signs Disc hyperaemia and dilated capillaries (telangiectatic microangiopathy) Vascular tortuosity Swelling of peripapillary nerve fibre layer Subsequent bilateral optic atrophy