Ординатура / Офтальмология / Английские материалы / Oxford American Handbook of Ophthalmology_Tsai, Denniston, Murray_2011

526 CHAPTER 16 Neuro-ophthalmology

Anterior ischemic optic neuropathy (2)

Nonarteritic AION

Nonarteritic AION comprises 90–95% of AION cases (see Table 16.5). It is proposed that an insufficient circulation to a crowded optic nerve head may lead to local edema, causing further vascular compromise and subsequent infarction. Identified vascular risk factors should be modified to prevent further ophthalmic and systemic complications.

Risk factors

The main risk factors appear to be diabetes, hypertension, and optic disc morphology (“disc at risk”—crowded disc with a small cup). Other proposed risk factors include smoking, hyperlipidemia, hypotension, anemia, hypermetropia, and obstructive sleep apnea.

Clinical features

•dVA (usually sudden but can be progressive; VA >20/200 in 61%;20/40 in 18%); commonly occurs overnight; occasional pain.

•RAPD, field loss (45% inferior altitudinal; 15% superior altitudinal), swollen optic disc (typically hyperemic, ± segmental, telangiectasia).

•Associations: “disc at risk” in fellow eye.

Investigations

•First rule out GCA (assessment, p. 524).

•If nonarteritic, then obtain BP, glucose, lipids, CBC. If patient is <50 years of age, then consider also vasculitis screen.

Treatment

There is no proven benefit for any treatment (including steroids, optic nerve sheath fenestration, hyperbaric oxygen, dopamine, and aspirin); however, aspirin (e.g., 81 mg/day) is commonly prescribed.

Refer to the physician for vascular assessment and treatment.

Prognosis

The risk of second eye involvement is around 19% over 5 years, with an increased risk after cataract surgery. Additionally, cardiovascular and cerebrovascular diseases are more common, possibly with increased mortality.

Posterior ischemic optic neuropathy

This rare condition describes ischemia of the more posterior (retrolaminar) optic nerve. It appears to result from watershed infarction, associated with hypotension or low hematocrit (typically after back surgery). Clinically, there is sudden visual loss with an RAPD (if unilateral) but normal optic disc; bilateral involvement is common.

ANTERIOR ISCHEMIC OPTIC NEUROPATHY (2) 527

Table 16.5 Arteritic and nonarteritic AION

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Other optic neuropathies and atrophies

Leber’s hereditary optic neuropathy (LHON)

This rare condition is maternally inherited, arising from point mutations in mitochondrial DNA. It may present at almost any age but typically in young adult males (M:F 3:1). Family history is present in around 50%. The mutations identified are 11,778 (the most common comprising 95%), 3460, and 14,484, all of which affect complex I of the respiratory chain.

Clinical features

•Sudden painless sequential dVA (usually affects second eye within 2 months; typically 20/200–HM).

•Large, dense, centrocecal scotoma, dcolor vision; disc may show peripapillary telangiectasia and peripapillary nerve fiber layer swelling (early) and temporal pallor (late). Pupillary reactions usually normal.

Investigations and treatment

Perform mitochondrial DNA analysis for LHON mutations (peripheral blood); consider also screening for differential diagnosis, including toxins and deficiencies. There is no effective treatment. Most patients have a poor visual prognosis, although some spontaneous recovery is seen with the uncommon 14,484 mutation.

Nutritional and toxic optic neuropathies

These uncommon acquired optic neuropathies all behave in a similar manner, probably because of a common disruption of mitochondrial oxidative phosphorylation. Tobacco-alcohol amblyopia may represent a combination of toxin (cyanide in tobacco smoke) and nutritional deficiency (low B12 associated with alcohol excess). Numerous other agents have been identified (Table 16.6).

Clinical features

•Subacute painless bilateral dVA (typically 20/30–20/200).

•Small central/centrocecal scotomas, dcolor vision; ±swelling of disc or peripapillary nerve fiber layer (early) and temporal pallor (late).

Investigations and treatment

A detailed history may reveal the cause. Consider obtaining B1, B2, B12, and folic acid levels (peripheral blood) and heavy metal screening (including 24-hour urine).

Treat deficiency with oral supplementation, except for B12 (IM and must be given with folate). In alcoholics, consider prophylactic vitamin supplementation. Identify and prevent route of toxin exposure (which may affect others, e.g., family members).

Inherited optic atrophy

Autosomal dominant

Kjer syndrome is the most common isolated optic atrophy and is due to a mutation in 3q. Bilateral symmetrical dVA (usually 20/30–20/120) occurs insidiously in midto late childhood.

OTHER OPTIC NEUROPATHIES AND ATROPHIES 529

Autosomal recessive

•Isolated: this is rare, severe, and presents early (age <4 years).

•Behr syndrome: optic atrophy ± nystagmus, ataxia, spasticity, dIQ.

•Wolfram syndrome (DIDMOAD): diabetes insipidus, diabetes mellitus, optic atrophy, deafness.

Table 16.6 Causes of nutritional and toxic optic neuropathies

Table 16.7 Causes of optic atrophy

530 CHAPTER 16 Neuro-ophthalmology

Papilledema

Papilledema describes optic disc swelling (usually bilateral) arising from raised intracranial pressure (ICP); the term should not be used to describe other causes of disc edema (see Table 16.8). Raised ICP is transmitted from the subarachnoid space via the optic nerve sheath to cause axoplasmic hold-up and consequent disc edema.

The urgent priority is to rule out an intracranial mass (e.g., tumor, abscess, hemorrhage); however, the most common cause of papilledema is idiopathic intracranial hypertension (see Table 16.9).

Clinical features

•Visual obscurations (transient dVA, few seconds duration, up to 30x/ day, unior bilateral, may be precipitated by posture, straining, etc.); diplopia; field defects (usually enlarged blind spot). Sustained dVA is a serious sign of irreversible damage—it may occur early in aggressive disease or late in chronic papilledema.

•iICP leads to headache (often worse lying down or straining), nausea, vomiting, and pulsatile tinnitus.

•Disc swelling is usually bilateral; however, swelling may not occur in an already abnormal optic disc or nerve sheath (e.g., congenital anomaly, optic atrophy, high myopia).

Staging of papilledema

•Early: hyperemic, blurred + elevated margin, subtle peripapillary nerve fiber layer edema, dilated disc capillaries, distended retinal veins, absent spontaneous venous pulsation (SVP).

•Acute: as listed above + peripapillary hemorrhages, cotton wool spots, increased nerve fiber layer edema (may obscure retinal vessels).

•Chronic: dhyperemia, dcotton-wool spots or hemorrhages, variable swelling, usually still elevated; ±drusen-like deposits and optociliary shunt vessels at the disc (in which case this is sometimes called vintage papilledema).

•Atrophic/late: pale atrophic disc, dswelling, attenuated arterioles.

Investigation

Urgent neuroimaging (preferably MRI with gadolinium enhancement) may reveal primary pathology, hydrocephalus, or empty sella; consider the following:

•MRV: check cerebral venous sinuses.

•LP: check opening pressure (normal <20 cmH2O or <25 cmH2O in the obese), glucose, protein, protein electrophoresis, microscopy, culture.

•FA (if diagnostic uncertainty): late leakage from dilated disc capillaries.

Treatment

Intervention depends on the underlying cause and severity and may range from weight loss to extensive neurosurgery. Shared care with another specialty (neurosurgery, neurology, oncology, medicine) is often necessary. However, regular ophthalmic assessment of acuity, color vision, fields, and optic disc status is invaluable to preserving vision.

Table 16.9 Causes of raised intracranial pressure

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Pseudopapilledema

A number of optic disc anomalies may resemble papilledema.

Disc drusen: may cause the most diagnostic confusion as they may not be clinically obvious (buried) and may cause visual loss. Their prevalence is around 0.5% in Caucasians. They may be inherited (autosomal dominant). They are usually bilateral and become more obvious throughout life.

The disc has a lumpy appearance and absent cup and the vessels emerge centrally and then show abnormal branching (trifurcation); opto-ciliary shunt vessels may be present. VA is usually normal, but field defects occur in 75% of cases (arcuate, blind spot enlargement, generalized constriction). They are associated with CNV. Their presence may be demonstrated by their autofluorescence or on B-scan US or CT.

Hypermetropic discs may appear crowded and elevated.

Myopic discs are often elevated nasally and may show staining on FA. Tilted discs are usually elevated superotemporally.

IDIOPATHIC INTRACRANIAL HYPERTENSION 533

Idiopathic intracranial hypertension

Idiopathic intracranial hypertension (formerly known as benign intracranial hypertension and pseudotumor cerebri) is the most common cause of papilledema. It is a diagnosis of exclusion made in the presence of normal neuroimaging and CSF analysis, but with an elevated CSF opening pressure. The prevalence is around 0.9/100,000 in the general population but up to 19/100,000 in obese young women.

Risk factors

It typically affects obese young women, but there is a wide age range of presentation. The strongest risk factors are obesity and recent weight gain, although many other associations have been suggested (Table 16.10).

Clinical features

•Visual obscurations (transient dVA, few seconds duration, unior bilateral, up to 30x/day, may be precipitated by posture, straining, etc.); diplopia; field defects (usually enlarged blind spot); sustained dVA may be early in aggressive disease (usually an indication for shunting).

•Headache (in 94% of cases; often worse lying down or straining), retrobulbar pain, pulsatile tinnitus.

•Disc swelling (usually bilateral; p. 530).

Investigation

•MRI with gadolinium enhancement and MRV: aim to rule out all other causes of iICP.

•LP: check opening pressure, glucose, protein, protein electrophoresis, microscopy, and culture. Normal opening pressure in adults is usually

<20 cm H2O, or <25 cm H2O in the obese; in children, lower levels are normal.

Treatment

Titrate treatment against symptoms and risk of visual loss (monitor VA, color vision, fields, discs). The evidence base for treatment is weak. Treatment may include the following:

•Weight loss.

•Medical: acetazolamide (up to 500 mg 4x/day), or consider furosemide.

•Surgical: optic nerve sheath fenestration is effective for vision preservation but may not address headaches or tinnitus. Unilateral surgery occasionally positively affects the contralateral side.

•Neurosurgical: lumboperitoneal or ventriculoperitoneal shunting (but significant complications).

•If pregnant: acetazolamide appears to be safe after 20 weeks gestation; weight loss is not advised.

534 CHAPTER 16 Neuro-ophthalmology

Table 16.10 Associations of idiopathic intracranial hypertension

CONGENITAL OPTIC DISC ANOMALIES 535

Congenital optic disc anomalies

Congenital optic disc anomalies range from common variations with minimal sequele (e.g., tilted discs) to severe abnormalities associated with poor vision and CNS abnormalities (e.g., morning glory anomaly).

Tilted disc

In this common bilateral but often asymmetric condition, the optic nerves insert obliquely into the globe. It is often associated with myopia and oblique astigmatism. The bitemporal field defects are unlike chiasmal lesions: they do not respect the vertical midline, they are static, and in some cases they may be resolved with refractive correction.

Clinical features

•Normal VA; may have superotemporal field defects.

•Disc is usually orientated inferonasally with elevation of the superotemporal rim, thinning of the inferonasal RPE/choroid, and situs inversus of the retinal blood vessels.

Optic disc pit

This rare usually unilateral condition may cause significant visual problems. Its origin is unclear, but it represents a herniation of neurectodermal tissue into a depression within the optic nerve.

Clinical features

•Often asymptomatic; dVA if complications; visual field defects (commonly paracentral arcuate scotoma).

•Gray pit usually in the temporal part of the optic disc; disc itself is larger than in the unaffected eye.

•Complications: macular retinoschisis and subsequent serous retinal detachment may occur in up to 45% of cases; this can be treated with vitrectomy and gas tamponade.

Optic nerve hypoplasia

This describes a reduced number of axons within the optic nerve. Optic nerve hypoplasia is a significant cause of poor vision in childhood. It may be isolated or be associated with a range of CNS abnormalities (Table 16.11)

Clinical features

•Variable VA (normal to NLP), visual field defects, color vision, pupil reactions.

•Small, gray disc surrounded by an inner yellow ring of chorioretinal atrophy and an outer pigment ring (double-ring sign).

•Other features may include aniridia, microphthalmos, strabismus, and nystagmus.

Table 16.11 Associations of optic disc hypoplasia