Optic nerve
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Optic atrophy
Classification
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Primary: occurs without antecedent swelling of the optic nerve head. It may be caused by lesions from the retrolaminar optic nerve to the lateral geniculate body; disease anterior to the chiasm gives rise to unilateral atrophy, that of the chiasm and optic tract causes bilateral changes.
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Secondary: preceded by disc swelling (e.g. chronic papilloedema, anterior ischaemic optic neuropathy, papillitis).
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Consecutive: caused by disease of the inner retina or its blood supply (e.g. retinitis pigmentosa, central retinal artery occlusion).
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Diagnosis
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Symptoms: varied and dependent on cause.
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Signs: (a) white, flat disc with clearly delineated margins in primary ( Fig. 19.1 ) and consecutive atrophy, and (b) white or dirty grey, slightly raised disc with poorly delineated margins and occasionally surrounding ‘water marks’ in secondary atrophy ( Fig. 19.2 ). There is also reduction in the number of surface disc vessels in all types. In primary atrophy, changes may be sectoral depending on the lesion (e.g. temporal pallor from papillomacular bundle damage, band atrophy with sparing of the superior and inferior portions in lesions of the chiasm or optic tract).
Fig 19.1
Fig 19.2
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Classification of optic neuritis
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Ophthalmoscopic: (a) retrobulbar neuritis, in which the optic nerve head is not primarily involved and so appears normal, (b) papillitis, characterized by disc oedema and hyperaemia, that may be associated with flame-shaped peripapillary haemorrhages ( Fig. 19.3 ), and (c) neuroretinitis (see below).
Fig 19.3
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Aetiological: (a) demyelination (most common), (b) parainfectious, following viral infection or immunization, (c) infectious, which may be sinus-related or associated with systemic infections (e.g. syphilis, Lyme disease), and (d) other (e.g. sarcoidosis, systemic lupus erythematosus).
Demyelinating optic neuritis
Definition: demyelination is a pathological process by which nerve fibres lose their insulating myelin layer, disrupting nervous conduction within the white matter tracts of the brain, brainstem and spinal cord.
Classification: demyelinating diseases that may cause ocular problems include the following:
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Isolated optic neuritis: in a high proportion of cases, generalized disease subsequently develops; the overall 10-year risk of developing multiple sclerosis (MS) following an acute episode of optic neuritis is approximately 40%.
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Multiple sclerosis: most common by far.
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Devic disease (neuromyelitis optica): bilateral optic neuritis and subsequent transverse myelitis (spinal cord demyelination).
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Diagnosis
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Presentation: in 3rd to 6th decades with (a) monocular blurring, (b) occasionally phosphenes (tiny light flashes), (c) discomfort or pain in or around the eye frequently exacerbated by ocular movements, and (d) tender globe.
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VA: 6/18–6/60, occasionally worse.
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Other signs of optic nerve dysfunction: (see above).
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Disc appearance: normal in the majority of cases (retrobulbar neuritis), remainder show papillitis.
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Perimetry: diffuse visual field depression with superimposed focal defects, typically central, altitudinal, or arcuate.
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Course: vision worsens over several days to 2 weeks and then begins to improve; initial recovery is fairly rapid and then there is slow improvement over months.
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Prognosis: 75% recover to 6/9 or better; residua include (a) abnormal colour vision and light brightness appreciation, (b) optic atrophy, and (c) a mild RAPD.
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Treatment
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Indications: treatment may speed recovery but does not influence eventual visual outcome. It may be considered in some circumstances such as poor vision in the fellow eye or for occupational requirements.
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Intravenous methylprednisolone: for 3 days followed by a reducing course of oral prednisolone.
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Immunomodulation therapy: (e.g. interferon-beta) at the first episode of optic neuritis may reduce the risk of clinical MS in higher risk patients.
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Miscellaneous optic neuritis
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Parainfectious: may follow various viral infections (e.g. measles, mumps, chickenpox, glandular fever), as well as immunization; prognosis is usually good and treatment is not required in the majority.
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Sinus-related: may be due to direct spread of infection, occlusive vasculitis, and mucocele; treatment is with antibiotics and surgical drainage.
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Cat-scratch fever (benign lymphoreticulosis): (see Chapter 11 ) typically causes neuroretinitis (see below).
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Syphilis: acute papillitis or neuroretinitis may occur during primary or secondary stages (see Chapter 11 ).
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Lyme disease (borreliosis): (see Chapter 11 ) may cause neuroretinitis and occasionally acute retrobulbar neuritis, which may be associated with neurological manifestations that can mimic MS.
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Cryptococcal meningitis: (see Chapter 11 ) may be associated with acute optic neuritis, which may be bilateral.
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Varicella zoster virus: may cause papillitis by spread from contiguous retinitis (e.g. acute retinal necrosis, progressive retinal necrosis; see Chapter 11 ), in herpes zoster ophthalmicus or chickenpox.
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Sarcoidosis: optic neuritis affects a minority of patients with neurosarcoid; the optic nerve head may exhibit a lumpy appearance suggestive of granulomatous infiltration ( Fig. 19.4 ), and there is often associated vitritis.
Fig 19.4
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Autoimmune optic nerve involvement: retrobulbar neuritis or anterior ischaemic optic neuropathy are the usual manifestations.
Neuroretinitis
Causes: cat-scratch fever is responsible for 60%, and approximately 25% are idiopathic (Leber idiopathic stellate neuroretinitis); other causes include syphilis, Lyme disease, mumps, and leptospirosis.
Diagnosis
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Presentation: gradual onset of painless unilateral visual impairment.
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VA: variable reduction.
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Signs of optic nerve dysfunction: usually mild.
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Progression of fundus signs: (a) papillitis associated with peripapillary and macular oedema ( Fig. 19.5a ), (b) macular star develops as the disc swelling is resolving ( Fig. 19.5b ), and (c) macular star resolves with return to normal or near-normal VA in 6–12 months.
Fig 19.5
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Treatment: varies according to cause; recurrent idiopathic cases may require steroids and/or other immunosuppressants.
Non-arteritic anterior ischaemic optic neuropathy
Pathogenesis: occlusion of the short posterior ciliary arteries resulting in partial or total infarction of the optic nerve head. Predispositions include (a) structural crowding of the optic nerve head so that the physiological cup is either very small or absent, and (b) cardiovascular risk factors, particularly hypertension.
Diagnosis
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Presentation: in 6th and 7th decades with sudden painless monocular visual loss, often altitudinal.
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VA: normal or only slightly reduced in approximately 30%; remainder have moderate to severe impairment.
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Perimetry: typically inferior altitudinal defect.
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Signs: (a) diffuse or sectoral hyperaemic disc swelling, often associated with a few peripapillary splinter haemorrhages ( Fig. 19.6 ); (b) swelling gradually resolves and pallor ensues; involvement of the fellow eye occurs in approximately 10% of patients after 2 years.
Fig 19.6
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Investigations: (a) blood pressure, (b) fasting lipid profile and blood glucose; (c) it is critical to exclude occult giant cell arteritis (GCA see below).
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Treatment: systemic predispositions should be addressed; aspirin is frequently prescribed, but it does not appear to reduce involvement of the fellow eye.
Arteritic anterior ischaemic optic neuropathy
Pathogenesis: GCA, a granulomatous necrotizing arteritis with a predilection for large and medium-sized arteries, including the superficial temporal. The disease is strongly associated with polymyalgia rheumatica, characterized by pain and stiffness in proximal muscle groups. Rare complications of GCA include dissecting aneurysms, myocardial infarction, and stroke; 30–50% of patients develop arteritic anterior ischaemic optic neuropathy (AAION).
Diagnosis
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Presentation of GCA: in old age.
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Symptoms of GCA: (a) scalp tenderness, (b) headache, (c) jaw claudication (pain on speaking and chewing), and (d) nonspecific symptoms such as neck pain, weight loss, fever, night sweats, malaise, and depression.
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Superficial temporal arteritis: thickened, tender, inflamed, and nodular arteries; absent pulsation is strongly suggestive of GCA.
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Presentation of AAION: (a) sudden profound unilateral visual loss (commonly light perception) that may be preceded by transient visual disturbance; (b) without treatment the fellow eye becomes involved in 30% of cases, usually within 1 week.
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Signs of AAION: (a) strikingly pale oedematous disc ( Fig. 19.7 ); (b) swelling resolves over 1 or 2 months and atrophy ensues.
Fig 19.7
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Investigations: (a) ESR is often very high (60 mm/hr or more), although normal in approximately 20%, (b) C-reactive protein is invariably raised and may be helpful when ESR is equivocal, and (c) platelet levels may be elevated.
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Temporal artery biopsy: should be performed urgently if GCA is suspected; steroids (see below) should not be withheld pending biopsy.
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Treatment
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Aims: mainly to prevent blindness of the fellow eye; very rarely, prompt treatment may result in improvement in the primary eye.
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Regimen: (a) intravenous methylprednisolone for 3 days followed by long-term oral prednisolone, (b) oral prednisolone alone in some circumstances, (c) antiplatelet therapy (e.g. aspirin), and (d) immunosuppressants in steroid-resistant cases or as steroid-sparing agents.
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Posterior ischaemic optic neuropathy
Ischaemia of the retrolaminar portion of the optic nerve is much less common than the anterior variety; it is a diagnosis of exclusion and may be of the following types:
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Operative posterior ischaemic optic neuropathy (PION): develops following a variety of surgical procedures (e.g. cardiac, spinal); bilateral involvement is common and the visual prognosis often poor.
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Arteritic PION: associated with GCA and carries a poor visual prognosis.
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Non-arteritic PION: associated with the same systemic risk factors as the anterior variety apart from crowded optic discs.
Diabetic papillopathy
Pathogenesis: occurs in both type 1 and type 2 diabetics, probably due to small-vessel disease but is milder than AION.
Diagnosis
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VA: 6/12 or better.
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Signs: (a) unilateral or bilateral mild disc swelling and hyperaemia; (b) disc surface telangiectasia is common ( Fig. 19.8 ).
Fig 19.8
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Course: usually several months.
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Treatment: systemic steroids are of questionable benefit.
Leber hereditary optic neuropathy
Genetics: maternally inherited mitochondrial DNA mutation that typically affects males; asymptomatic female relatives may show telangiectatic microangiopathy.
Diagnosis
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Presentation: between the 2nd and 4th decades with acute or subacute severe painless unilateral loss of central vision; the fellow eye is affected within weeks or months.
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Acute signs: (a) often subtle disc hyperaemia with obscuration of margins ( Fig. 19.9 ), (b) surface telangiectasia, (c) swelling of the peripapillary nerve fibre layer, (d) dilatation and tortuosity of posterior pole vasculature; FA shows absence of leakage; papillary light reactions may remain brisk.
Fig 19.9
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Course: vessels regress, swelling resolves, and severe optic atrophy supervenes with a final VA of 6/60 or less.
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Perimetry: central or centrocaecal scotomas.
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Treatment: generally ineffective; smoking and excessive consumption of alcohol should be discouraged.
Nutritional optic neuropathy (tobacco–alcohol amblyopia)
Pathogenesis: deficiency in protein and B vitamins after dietary neglect, particularly affecting heavy drinkers and cigar smokers; some also have defective B 12 absorption and may develop pernicious anaemia.
Diagnosis
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Presentation: insidious onset of progressive, usually symmetrical, bilateral visual impairment associated with dyschromatopsia.
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Discs: normal at presentation in most cases, although some show subtle pallor.
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Perimetry: bilateral centrocaecal scotomas, easier to plot and larger with a red target.
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Treatment: abstention from drinking and smoking; intramuscular hydroxocobalamin and oral multivitamins, including thiamine and folate.
Papilloedema
Pathogenesis: swelling of the optic nerve head secondary to raised intracranial pressure. It is nearly always bilateral, although may be asymmetrical. Causes of raised intracranial pressure: (a) idiopathic intracranial hypertension (pseudotumour cerebri), (b) space-occupying intracranial lesions, (c) cerebral venous sinus thrombosis, and (d) severe systemic hypertension.
Diagnosis
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General symptoms: (a) headache occurs early in the morning and may wake the patient from sleep; may intensify with head movement, bending, or coughing, (b) sudden nausea and vomiting, often projectile, and sometimes (c) deterioration of consciousness.
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Visual symptoms: (a) transient obscurations lasting a few seconds, (b) horizontal diplopia (due to stretching of one or both 6th nerves over the petrous tip), a false localizing sign, and (c) persistent visual loss in long-standing papilloedema with secondary optic atrophy (see below).
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Early papilloedema: (a) mild disc hyperaemia with preservation of the optic cup, (b) indistinct peripapillary retinal nerve striations and disc margins ( Fig. 19.10a ), and (c) loss of previous spontaneous venous pulsation (also absent in 20% of normals).
Fig 19.10
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Established papilloedema: (a) severe disc hyperaemia, (b) moderate disc elevation with absence of the cup, (c) venous engorgement, (d) peripapillary flame haemorrhages and cotton wool spots ( Fig. 19.10b ), (e) circumferential retinal folds (Paton lines), and (f) hard exudates that typically radiate from the centre of the fovea.
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Chronic papilloedema: (a) severe disc elevation, (b) absence of cotton wool spots and haemorrhage ( Fig. 19.10c ), (c) optociliary shunts, and (d) drusen-like crystalline surface deposits (uncommon).
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Atrophic papilloedema: (a) discs are dirty grey and slightly elevated, with (b) few crossing blood vessels, and (c) indistinct margins (secondary optic atrophy; Fig. 19.10d ).
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Perimetry: blind spot is enlarged in the early established stages; atrophy may be associated with constriction.
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Investigations: to determine the cause; MR, CT, and B-scan US show an enlarged optic nerve diameter in most cases.
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Terson syndrome
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Definition: combination of intraocular and subarachnoid haemorrhage secondary to rupture of an intracranial aneurysm. Intraocular haemorrhage may also occur with subdural haematoma and acute elevation of intracranial pressure from other causes.
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Intraocular haemorrhage: frequently bilateral and typically intraretinal and/or preretinal (subhyaloid; Fig. 19.11 ), although occasionally subhyaloid blood may break into the vitreous; probably caused by retinal venous stasis secondary to increased cavernous sinus pressure.
Fig 19.11
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Prognosis: usually good as the blood commonly resolves spontaneously within a few months; early vitrectomy may be considered for dense bilateral bleeds.
Congenital optic disc anomalies
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Tilted optic disc: (a) oblique entry of the optic nerve into the globe, with (b) angulation of the cup axis and elevation of the neuroretinal rim, (c) associated findings include inferonasal chorioretinal thinning ( Fig. 19.12 ) and myopic astigmatic refractive error; (d) perimetry may show superotemporal defects that do not respect the vertical midline.
Fig 19.12
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Optic disc pit: (a) large disc, (b) round or oval pit of variable size, usually located temporally ( Fig. 19.13 ); (c) perimetry may show glaucoma-like defects; (d) serous macular detachment (in 50%).
Fig 19.13
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Optic disc drusen: (a) waxy pearl-like deposits of calcific material ( Fig. 19.14 ) present in approximately 0.3% of the population, (b) difficult to detect in early childhood because they lie deep to the disc surface and may mimic papilloedema, (c) anomalous vascular patterns; (d) associations include retinitis pigmentosa and angioid streaks, and (e) complications (rare) include juxtapapillary CNV and progressive but limited visual field defects; drusen are demonstrated well on B-scan US.
Fig 19.14
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Optic disc coloboma: unilateral or bilateral; (a) glistening white bowl-shaped excavation so that the inferior neuroretinal rim is thin or absent ( Fig. 19.15 ); (b) may be associated with an adjacent choroidal and iris coloboma; (c) perimetry shows a superior defect; (d) systemic associations (uncommon) include chromosomal and CNS anomalies, and CHARGE syndrome.
Fig 19.15
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Morning glory anomaly: unilateral; (a) large disc with a funnel-shaped excavation surrounded by an annulus of chorioretinal disturbance ( Fig. 19.16 ), (b) white tuft of glial tissue overlies the central portion, (c) blood vessels emerge radially from the rim of the excavation, (d) serous retinal detachment (in 30%); (e) systemic associations (uncommon) include frontonasal dysplasia (mid-facial anomalies, basal encephalocele, midline brain malformations), and NF2.
Fig 19.16
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Optic nerve hypoplasia: may occur as an isolated anomaly in a normal eye, in a grossly malformed eye, or in association with systemic disorders, typically involving midline brain structures (e.g. de Morsier syndrome—septo-optic dysplasia—in approximately 10%). Maternal ingestion of predisposing agents (e.g. steroids, alcohol, anticonvulsants) during pregnancy has been implicated. (a) VA ranges from normal to no light perception, (b) small grey disc, (c) surrounding yellow halo of hypopigmentation (double-ring sign; Fig. 19.17 ), and (d) retinal vascular tortuosity (common).
Fig 19.17
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Myelinated nerve fibres: (a) white feathery streaks running within the retinal nerve fibre layer from the disc ( Fig. 19.18 ); (b) ocular associations of extensive myelination include high myopia, anisometropia, and amblyopia, and (c) systemic associations include NF1.
Fig 19.18 
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