Q4 LONG ANSWER 10M ★ High-yield

Describe the ischaemic, toxic, nutritional and hereditary optic neuropathies.

Ophthalmology · 3rd Professional

Ischaemic Optic Neuropathy

Anterior ischaemic optic neuropathy (AION) is infarction of the anterior optic nerve supplied by the short posterior ciliary arteries. It divides sharply into a non-arteritic and an arteritic form, and distinguishing them is among the most urgent tasks in ophthalmology

Feature	Non-arteritic (NAION)	Arteritic (AAION) — giant cell arteritis
Age	Over 50, typically 55 to 70	Over 70; rare below 50
Visual acuity	Moderately reduced; often 6/12 to 6/60	Severe — counting fingers or worse in the majority
Preceding symptoms	None; often noticed ON waking	Amaurosis fugax, jaw claudication, scalp tenderness, temporal headache, polymyalgia, weight loss, fever, malaise
The disc	Segmental, hyperaemic swelling with splinter haemorrhages; the fellow disc is characteristically small and crowded — a "disc AT risk" with a cup-disc ratio under 0.2	Chalky white, pallid swelling — a highly characteristic appearance; the fellow disc is normal
ESR and CRP	Normal	Markedly raised, with thrombocytosis
Other eye	About 15% within 5 years	30 to 50% within days to weeks if untreated
Associations	Nocturnal hypotension, sleep apnoea, diabetes, hypertension, PDE5 inhibitors, amiodarone	Systemic vasculitis; aortic aneurysm; stroke
Treatment	None proven; control risk factors; avoid nocturnal hypotension by shifting antihypertensives to the morning	Immediate high-dose systemic steroid — an emergency

Giant cell arteritis must be excluded in every patient over 50 with sudden visual loss. The eye already affected is beyond help; the treatment is given to save the fellow eye, and the window is days
Start steroid immediately on clinical suspicion — intravenous methylprednisolone or oral prednisolone 1 mg/kg — before the biopsy and before the result. The temporal artery biopsy remains positive for 1 to 2 weeks after steroid is begun, so nothing is lost by treating first
The biopsy should take a segment of 2 to 3 cm, because the arteritis has skip lesions and a short specimen may be falsely negative; and a negative biopsy does not exclude the diagnosis where the clinical picture is convincing

Compressive and Traumatic Optic Neuropathy

Compressive optic neuropathy is characteristically slow, progressive and painless, with pallor exceeding any cupping and colour vision affected out of proportion to acuity. Any unexplained progressive optic neuropathy requires imaging
Optic nerve sheath meningioma — a middle-aged woman with the classical triad of slow visual loss, optic atrophy and optociliary shunt vessels on the disc, with a "tram-track" appearance of the enhancing sheath on imaging
Optic nerve glioma — a child, often with neurofibromatosis type 1, presenting with proptosis and visual loss; indolent, and often observed rather than treated
Other compressive causes — pituitary adenoma, craniopharyngioma, aneurysm, sphenoid wing meningioma, metastasis, and thyroid eye disease, in which apical crowding by enlarged muscles is a sight-threatening emergency requiring urgent steroid, radiotherapy or decompression
Traumatic optic neuropathy — indirect, from a blow to the brow or forehead transmitting force to the tethered nerve in the optic canal. There is immediate profound visual loss with a relative afferent pupillary defect and a normal-looking disc, pallor appearing weeks later
Its management is controversial: high-dose steroid is NO longer recommended, following the crash trial, which showed increased mortality with steroids in head injury; and surgical decompression of the canal is of unproven benefit. Most units observe, treat any compressive haematoma, and manage the head injury
Treat giant cell arteritis to save the fellow eye; the affected eye is beyond help and the window is measured in days
Steroid does not invalidate the biopsy for a week or two, so there is no reason ever to wait for histology before treating
Take two to three centimetres of artery, since skip lesions make a short specimen falsely negative
A negative biopsy does not exclude the diagnosis where the clinical picture and inflammatory markers are convincing
Send both ESR and CRP; CRP is the more sensitive and either may be raised alone
Thrombocytosis supports the diagnosis of arteritis, and is a useful additional pointer on the full blood count

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