Neuro-Ophthalmology





Optic nerve


Optic atrophy


Classification





  • 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 ( Fig. 19.1A ). Disease anterior to the chiasm gives rise to unilateral atrophy, while that of the chiasm and optic tract causes bilateral changes.




    Fig. 19.1


    Optic atrophy: (A) primary due to compression, showing shunt vessels, (B) primary due to nutritional neuropathy, (C) secondary due to chronic papilloedema, showing Paton lines, (D) papillitis.



  • Secondary: preceded by disc swelling (e.g. chronic papilloedema, anterior ischaemic optic neuropathy, papillitis).



  • Consecutive: caused by disease of the inner retina or its blood supply (e.g. retinitis pigmentosa, central retinal artery occlusion).



Diagnosis





  • Symptoms: varied and dependent on cause.



  • Signs: (a) white, flat disc with clearly delineated margins in primary ( Fig. 19.1B ) and consecutive atrophy, (b) white or dirty grey, slightly raised disc with poorly delineated margins and occasionally surrounding ‘water marks’ in secondary atrophy ( Fig. 19.1C ). 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).



Classification of optic neuritis





  • Ophthalmoscopic: (a) retrobulbar neuritis, in which the optic nerve head is not primarily involved and so it appears normal, (b) papillitis, characterized by disc oedema ( Fig. 19.1D ) and hyperaemia, that may be associated with flame-shaped peripapillary haemorrhages, (c) neuroretinitis (see below).



  • 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), (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:




  • Isolated optic neuritis: in a high proportion of cases, generalized disease subsequently develops. The overall 15-year risk of developing multiple sclerosis (MS) following an acute episode of optic neuritis is approximately 50%, but with no lesions on MRI the risk is 25%



  • Multiple sclerosis: most common by far.



  • Devic disease (neuromyelitis optica): bilateral optic neuritis and subsequent transverse myelitis (spinal cord demyelination).



Diagnosis





  • 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, (d) tender globe, (e) worsening of vision on exercise or increase in body temperature (Uhthoff phenomenon).



  • VA: 6/18–6/60, occasionally worse.



  • Other signs of optic nerve dysfunction: (see Box 19.1 ).



    Box 19.1

    Signs of optic nerve dysfunction





    • Reduced VA



    • Relative afferent pupillary defect



    • Dyschromatopsia: impairment of colour vision, mainly red and green



    • Diminished light brightness sensitivity



    • Diminished contrast sensitivity



    • Visual field defects, varying with the underlying pathology





  • Disc appearance : normal in the majority of cases (retrobulbar neuritis), remainder show papillitis.



  • Perimetry: diffuse visual field depression with superimposed focal defects, typically central, altitudinal, or arcuate.



  • MRI: shows changes in the optic nerve on STIR imaging ( Fig. 19.2A ) and characteristic lesions in the white matter of the brain.




    Fig. 19.2


    (A) Axial T2-weighted image of optic neuritis secondary to MS, (B) sarcoid granuloma of the optic nerve head (arrow).



  • 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.



  • Prognosis: 90% recover to 6/9 or better. Residual signs include: (a) abnormal colour vision and light brightness appreciation, (b) optic atrophy, (c) a mild RAPD.



Treatment





  • 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.



  • Intravenous methylprednisolone: 1 g daily for 3 days, followed by a reducing course of oral prednisolone (1 mg/kg daily for 11 days).



  • Immunomodulation therapy: (a) interferon-beta at the first episode of optic neuritis to reduce the risk of clinical MS, (b) glatiramer acetate to reduce the frequency of relapses, (c) natalizumab may be used for highly active relapsing-remitting MS if there has been a poor response to interferon beta or glatiramer acetate, (d) ocrelizumab may be used for highly active disease and primary progressive MS, (e) alemtuzumab may be the most cost-effective of the monoclonal antibodies because of the favourable dosing strategy.



Miscellaneous optic neuritis (see Chapter 12 )





  • Parainfectious: may follow various viral infections (e.g. measles, mumps, chickenpox, glandular fever), as well as immunization. The prognosis is usually good and treatment is not required in the majority.



  • Sinus-related: may be due to direct spread of infection, occlusive vasculitis and mucocoele; treatment is with antibiotics and surgical drainage.



  • Cat-scratch fever (benign lymphoreticulosis): typically causes neuroretinitis (see below).



  • Syphilis : acute papillitis or neuroretinitis may occur during primary or secondary stages.



  • Lyme disease (borreliosis): may cause neuroretinitis and occasionally acute retrobulbar neuritis, which may be associated with neurological manifestations that can mimic MS.



  • Cryptococcal meningitis: may be associated with acute optic neuritis, which may be bilateral.



  • Varicella zoster virus: may cause papillitis by spread from contiguous retinitis (e.g. acute retinal necrosis, progressive retinal necrosis), in herpes zoster ophthalmicus or chickenpox.



  • Sarcoidosis: optic neuritis affects a minority of patients with neuro-sarcoid. The optic nerve head may exhibit a lumpy appearance suggestive of granulomatous infiltration ( Fig. 19.2B ) and there is often associated vitritis.



  • Autoimmune optic nerve involvement: retrobulbar neuritis or anterior ischaemic optic neuropathy are the usual manifestations.



Neuroretinitis


Causes:


cat-scratch fever (which is quite rare) is responsible for 60% and approximately 25% are idiopathic (Leber idiopathic stellate neuroretinitis); other causes include syphilis, Lyme disease, mumps and leptospirosis.


Diagnosis





  • Presentation: gradual onset of painless unilateral visual impairment.



  • VA : variable reduction.



  • Signs of optic nerve dysfunction: usually mild.



  • Progression of fundus signs: (a) papillitis associated with peripapillary and macular oedema, (b) macular star develops as the disc swelling is resolving ( Fig. 19.3A ), (c) macular star resolves with return to normal or near-normal VA in 6–12 months.




    Fig. 19.3


    Neuroretinitis: (A) macular star, (B) papillitis.



  • FA: shows subtle optic disc hyperfluorescence secondary to swelling ( Fig. 19.3B ).



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, (b) cardiovascular risk factors, particularly hypertension.


Diagnosis





  • Presentation: in 6th and 7th decades with sudden, painless, monocular visual loss, that is usually altitudinal in appearance.



  • VA: normal or only slightly reduced in approximately 30%; remainder have moderate to severe impairment.



  • Perimetry: usually inferior altitudinal defect.



  • Signs: (a) diffuse or sectoral hyperaemic disc swelling, often associated with a few peripapillary splinter haemorrhages ( Fig. 19.4A ), (b) swelling gradually resolves and pallor ensues.




    Fig. 19.4


    Anterior ischaemic optic neuropathy: (A) disc swelling and flame-shaped haemorrhages, (B) thickened temporal artery, (C) pale swelling of the upper half of the optic disc in temporal arteritis, (D) lower altitudinal visual field defect.

    (Figure 19.4B courtesy of S Farley, T. Cole, and L. Rimmer.)



  • Involvement of the fellow eye occurs in approximately 10% of patients after 2 years and 15% at 5 years. Risk factors include bilateral optic disc drusen and non-compliance with CPAP in patients with moderate/severe obstructive sleep apnoea.



  • Investigations: (a) blood pressure, (b) fasting lipid profile and blood glucose, (c) it is critical to exclude occult giant cell arteritis (GCA see below).



Treatment:


there is no definitive treatment, but predisposing systemic factors should be addressed. Aspirin reduces the short-term risk of involvement of the fellow eye, but does not appear to reduce the long-term risk.


Arteritic anterior ischaemic optic neuropathy


Pathogenesis:


giant cell arteritis (GCA), a granulomatous necrotizing arteritis with a predilection for large and medium-sized arteries, including the superficial temporal. 30–50% of patients develop arteritic anterior ischaemic optic neuropathy (AAION). The disease is strongly associated with polymyalgia rheumatica, characterized by pain and stiffness in proximal muscle groups. Rare complications of GCA include dissecting aneurysm, myocardial infarction and stroke.


Diagnosis





  • Presentation of GCA: in old age.



  • Symptoms of GCA: (a) scalp tenderness, (b) headache, (c) jaw claudication (pain on speaking and chewing), (d) nonspecific symptoms such as neck pain, weight loss, fever, night sweats, malaise and depression.



  • Superficial temporal arteritis: thickened, tender, inflamed and nodular temporal arteries ( Fig. 19.4B ). Absent pulsation is strongly suggestive of GCA.



  • 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.



  • Signs of AAION: (a) strikingly pale oedematous disc ( Fig. 19.4C ), (b) swelling resolves over 1 or 2 months and atrophy ensues, (c) altitudinal visual field defect ( Fig. 19.4D and Box 19.2 ).



    Box 19.2

    Visual field defects in optic neuropathies




    • 1.

      Central scotoma




      • Demyelination



      • Toxic and nutritional



      • Leber hereditary optic neuropathy



      • Compression



    • 2.

      Enlarged blind spot




      • Papilloedema



      • Congenital anomalies



    • 3.

      Respecting horizontal meridian




      • Anterior ischaemic optic neuropathy



      • Glaucoma



      • Disc drusen



    • 4.

      Upper temporal defects not respecting vertical meridian




      • Tilted discs






  • Investigations: (a) ESR is often very high (60 mm/hour or more), although normal in approximately 20%, (b) C-reactive protein is invariably raised and may be helpful when ESR is equivocal, (c) platelet levels may be elevated, (d) ultrasound of the temporal artery shows a hypoechoic halo around the temporal artery lumen in 75%.



  • Temporal artery biopsy: should be performed urgently if GCA is suspected. Steroids (see below) should not be withheld pending biopsy.



Treatment





  • Aims: mainly to prevent blindness of the fellow eye. Very rarely, prompt treatment may result in improvement in the primary eye.



  • Regimen: (a) intravenous methylprednisolone 500 mg–1 g/day for 3 days followed by long-term oral prednisolone, (b) oral prednisolone alone in some circumstances, (c) antiplatelet therapy (e.g. aspirin) to reduce the risk of stroke and visual loss, (d) immunosuppressants in steroid-resistant cases or as steroid-sparing agents.



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:




  • 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 is often poor.



  • Arteritic PION: associated with GCA and carries a poor visual prognosis.



  • 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





  • VA: 6/12 or better.



  • Signs: (a) unilateral or bilateral mild disc swelling and hyperaemia, (b) disc surface telangiectasia is common.



  • Course: usually several months.



Treatment:


systemic steroids are of questionable benefit.


Leber hereditary optic neuropathy


Genetics:


maternally inherited mitochondrial DNA mutation. Typically affects males, but asymptomatic female relatives may show telangiectatic microangiopathy.


Diagnosis





  • 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.



  • Acute signs: (a) often subtle disc hyperaemia with obscuration of margins ( Fig. 19.5A ), (b) surface telangiectasia ( Fig. 19.5B ), (c) swelling of the peripapillary nerve fibre layer, (d) dilatation and tortuosity of posterior pole vasculature, (e) FA shows absence of leakage; pupillary light reactions may remain brisk.




    Fig. 19.5


    Leber hereditary optic neuropathy: (A) acute stage showing hyperaemic disc swelling, (B) telangiectatic microangiopathy.



  • Course: vessels regress, swelling resolves and severe optic atrophy supervenes with a final VA of 6/60 or less.



  • Perimetry: central or centrocaecal scotomas.



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 vitamin B 12 absorption and may develop pernicious anaemia.


Diagnosis





  • Presentation: insidious onset of progressive, usually symmetrical, bilateral visual impairment associated with dyschromatopsia.



  • Discs: normal at presentation in most cases, although some show subtle pallor (see Fig. 19.1B )



  • Perimetry: bilateral centrocaecal scotomas, easier to plot and larger with a red target.



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 it may be asymmetrical. Causes of raised intracranial pressure: (a) idiopathic intracranial hypertension (pseudotumour cerebri), (b) space-occupying intracranial lesions, (c) cerebral venous sinus thrombosis, (d) severe systemic hypertension.


Diagnosis





  • 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.



  • Visual symptoms: (a) normal visual acuity, but transient obscurations lasting a few seconds, (b) horizontal diplopia (due to stretching of one or both 6th nerves over the petrous tip) is a false localizing sign, (c) persistent visual loss in long-standing papilloedema with secondary optic atrophy (see below).



  • Early papilloedema: (a) mild disc hyperaemia with preservation of the optic cup, (b) indistinct peripapillary retinal nerve striations and disc margins ( Fig. 19.6A ), (c) loss of previous spontaneous venous pulsation (also absent in 20% of normal individuals).




    Fig. 19.6


    Papilloedema: (A) early, (B) acute established, (C) chronic, (D) atrophic.



  • Established papilloedema: (a) severe disc hyperaemia ( Fig. 19.6B ), (b) moderate disc elevation with absence of the cup, (c) venous engorgement, (d) peripapillary flame haemorrhages and cotton wool spots, (e) circumferential retinal folds (Paton lines), (f) hard exudates that typically radiate from the centre of the fovea.



  • Chronic papilloedema: (a) severe disc elevation ( Fig. 19.6C ), (b) absence of cotton wool spots and haemorrhage, (c) optociliary shunts, (d) drusen-like crystalline surface deposits (uncommon).



  • Atrophic papilloedema: (a) discs are dirty grey and slightly elevated, with (b) few crossing blood vessels, (c) indistinct margins (secondary optic atrophy; Fig. 19.6D ).



  • Perimetry: blind spot is enlarged in the early established stages; atrophy may be associated with constriction.



  • Investigations: to determine the cause. MR, CT and B-scan US show an enlarged optic nerve diameter in most cases.



Terson syndrome





  • 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.



  • Intraocular haemorrhage: frequently bilateral and typically intraretinal and/or preretinal (subhyaloid; see Fig. 17.1B ), although occasionally subhyaloid blood may break into the vitreous; probably caused by retinal venous stasis secondary to increased cavernous sinus pressure.



  • Prognosis: usually good as the blood commonly resolves spontaneously within a few months. Early vitrectomy may be considered for dense bilateral haemorrhage.



Congenital optic disc anomalies





  • 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. 19.7A ), (d) myopic astigmatic refractive error, (e) perimetry may show superotemporal defects that do not respect the vertical midline.




    Fig. 19.7


    (A) Tilted optic disc, (B) optic disc pit.



  • Optic disc pit: (a) large disc, (b) round or oval pit of variable size, usually located temporally ( Fig. 19.7B ), (c) perimetry may show glaucoma-like defects, (d) serous macular detachment (in 50%).



  • Optic disc drusen: (a) waxy pearl-like deposits of calcific material ( Fig. 19.8A ) 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, (e) complications (rare) include juxtapapillary CNV and progressive, but limited visual field defects, (f) drusen can be demonstrated on OCT ( Fig. 19.8B ), autofluorescent imaging, and B-scan US.




    Fig. 19.8


    Optic disc drusen: (A) clinical appearance, (B) OCT appearance.



  • Optic disc coloboma: unilateral or bilateral; (a) glistening white bowl-shaped excavation so that the inferior neuroretinal rim is thin or absent, (b) may be associated with an adjacent choroidal and iris coloboma ( Fig. 19.9A ), (c) perimetry shows a superior defect, (d) systemic associations (uncommon) include chromosomal and CNS anomalies and CHARGE syndrome.




    Fig. 19.9


    (A) Large disc coloboma, (B) ‘morning glory’ optic disc anomaly, (C) hypoplastic disc showing the double ring sign (arrowhead shows the edge of the disc and the arrow shows the edge of the visible sclera), (D) myelinated nerve fibres.

    (Figure 19.9A courtesy of P. Gili, Figure 19.9C courtesy of D. Hildebrand.)



  • Morning glory anomaly: unilateral; (a) large disc with a funnel-shaped excavation surrounded by an annulus of chorioretinal disturbance ( Fig. 19.9B ), (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.



  • Optic nerve hypoplasia: may occur as an (a) isolated anomaly in a normal eye, (b) in a grossly malformed eye, or (c) 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. 19.9C ), (d) retinal vascular tortuosity (common).



  • Myelinated nerve fibres: (a) white feathery streaks running within the retinal nerve fibre layer from the disc ( Fig. 19.9D ), (b) ocular associations of extensive myelination include high myopia, anisometropia and amblyopia, (c) systemic associations include NF1.



  • Aicardi syndrome: X-L dominant condition that is lethal in utero in males; (a) bilateral multiple depigmented chorioretinal lacunae clustered around the disc, (b) disc may be hypoplastic, colobomatous, or pigmented, (c) ocular associations include microphthalmos and iris colobomas, (d) systemic associations a range of severe CNS and skeletal anomalies.



  • Optic disc dysplasia: markedly deformed disc that does not conform to any recognizable category described above.



Pupils


Anatomy: The light reflex is mediated by the photoreceptors and is subserved by four neurons ( Fig. 19.10A ) .


Oct 30, 2022 | Posted by in OPHTHALMOLOGY | Comments Off on Neuro-Ophthalmology

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