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

516 CHAPTER 16 Neuro-ophthalmology

Anatomy and physiology (2)

Ocular motor nerves

Third nerve

The CN III nucleus lies in the midbrain anterior to the periaqueductal gray matter at the level of the superior colliculus. It consists of a single central nucleus innervating both levator palpebrae superioris (LPS) muscles, and separate subnuclei for each superior rectus (SR) (contralateral innervation), medial rectus, inferior rectus (MR), and inferior oblique (IO) (all ipsilateral innervation).

The CN III fasciculus travels anteriorly through the medial longitudinal fasciculus (MLF), the red nucleus, and the cerebral peduncle. On leaving the midbrain, it emerges within the interpeduncular fossa and passes anteriorly beneath the posterior cerebral artery, above the superior cerebellar artery, and lateral to the posterior communicating artery (Fig. 16.1). It travels within the lateral wall of the cavernous sinus, dividing into superior and inferior branches that enter the orbit via the superior orbital fissure and annulus of Zinn.

The superior branch innervates LPS and SR, whereas the inferior branch innervates MR, IR, IO, and the pupillary sphincter. Parasympathetic fibers from the Edinger–Westphal nucleus travel in the IO branch as far as the ciliary ganglion and then in the short ciliary nerves to the globe, where they innervate the ciliary muscle and pupillary sphincter.

Fourth nerve

The CN IV nucleus lies just below the CN III nucleus in the lower midbrain at the level of inferior colliculus. The fasciculus decussates within the anterior medullary velum and exits the midbrain posteriorly.

It then curves round the midbrain, passes anteriorly between the posterior cerebral and superior cerebellar arteries, and travels within the lateral wall of the cavernous sinus (inferolateral to CN III, superior to CN V1). It then enters the orbit through the superior orbital fissure (but superior to the annulus of Zinn) and terminates in the superior oblique muscle.

Sixth nerve

The CN VI nucleus lies in the lower pons anterior to the fourth ventricle at the level of the facial colliculus. Although most axons innervate the ipsilateral LR, about 40% of axons project via the MLF to the contralateral MR subnucleus. The fasciculus travels anteriorly through the medial leminiscus and corticospinal tract, just medial to the trigeminal nuclear complex and vestibular nuclei.

After emerging at the pontomedullary junction, it ascends in the subarachnoid space between the pons and the clivus, before turning anterior over the petrous apex of the temporal bone and under the petroclinoid ligament to enter the cavernous sinus. Here it runs within the sinus itself just lateral to the ICA and inferomedial to CN III, IV, and V1, which run in the sinus wall. It then enters the orbit via the superior orbital fissure and annulus of Zinn to terminate in the LR muscle.

518 CHAPTER 16 Neuro-ophthalmology

Anatomy and physiology (3)

Autonomic supply

Sympathetic

The first-order neurons originate in the posterior hypothalamus and descend through the brainstem to synapse in the spinal cord at the ciliospinal center of Budge (C8-T2).

The second-order neurons emerge anteriorly in the ventral root (close to the lung apex) and then ascend in the sympathetic chain to synapse at the superior cervical ganglion.

The third-order neurons ascend along the ICA to the cavernous sinus and then via the nasociliary branch of CN V1 into the orbit and subsequently the long ciliary nerves, terminating in the dilator pupillae.

Parasympathetic

The light and near reflexes are both mediated by the parasympathetic supply from the Edinger–Westphal nucleus. The afferent arm for the light reflex is by 1) retinal ganglion cells that synapse in the ipsilateral pretectal nucleus and then 2) interneurons that innervate bilateral Edinger– Westphal nuclei. The inputs for the near reflex are less well-defined but probably include cortical influences (frontal and occipital lobes) mediated by a midbrain center (anterior to the pretectal nucleus).

The efferent arm for both reflexes comprise 1) preganglionic neurons from the Edinger–Westphal nucleus that travel in CN III and then the inferior division of CN III to the inferior oblique before synapsing at the ciliary ganglion, and 2) postganglionic neurons that run via the short ciliary nerves to terminate in the constrictor pupillae and ciliary muscle.

Cerebrospinal fluid (CSF)

CSF is produced by the choroid plexus in the lateral ventricles and the third ventricle. It flows from the lateral ventricles via the foramen of Munro to the third ventricle and then via the aqueduct of Sylvius to the fourth ventricle. From there, it leaves either via the lateral foramina of Luschka or the medial foramen of Magendie to bathe the spinal cord and cerebral hemispheres in the subarachnoid space.

CSF is then absorbed into the cerebral venous system by the arachnoid granulations. The subarachnoid space is continuous with the optic nerve sheath.

520 CHAPTER 16 Neuro-ophthalmology

Diagnosis is more difficult in early symmetric disease where there may be no objective signs. Electrodiagnostic tests are often helpful in such cases. Also, typical optic neuropathy features may be seen in other diseases (e.g., central scotoma, dcolor vision, or secondary optic atrophy in retinal disorders). The challenge is thus first to recognize the optic neuropathy and then elucidate the cause (Tables 16.2 and 16.3).

Unexplained optic neuropathy requires urgent investigation (p. 523) to elucidate the cause and rule out serious disease such as compression secondary to a tumor.

Table 16.2 Clinical features of optic nerve vs. macular disease

522 CHAPTER 16 Neuro-ophthalmology

Optic neuritis: assessment

Inflammation of the optic nerve may be divided into papillitis (where the disc is swollen), retrobulbar neuritis (where the disc is spared), and neuroretinitis (with retinal involvement, “macular star”). The most common cause of optic neuritis is demyelination, although a number of important differential diagnoses must be considered.

Acute demyelinating optic neuritis

Incidence within the general population is around 5/100, 000/year, but it occurs in up to 70% of patients with known MS. Most of the patients are female (F:M 3:1) and are usually aged 20–50 years. The disease is usually unilateral, although bilateral involvement may be seen in children.

Clinical features

•Rapid dVA over hours or days (rarely become NPL); recovery starts within 2 weeks and may continue for a few months; dcontrast

sensitivity, dcolor vision, field loss (variable pattern), retrobulbar pain (present in 90%; often worse on eye movement, usually precedes dVA), photopsia.

•RAPD (may be absent if pre-existing contralateral disease), disc swelling (only 1/3 of cases); disc should not be pale in the acute stages of a first episode; may have few hemorrhages, retinal exudates, and mild vitritis.

Investigations

If the episode is entirely typical (Box 16.1), the diagnosis may be made on clinical grounds alone.

Box 16.1 Features of typical optic neuritis (from Optic Neuritis Treatment Trial)

•Ages 20–50 years

•Unilateral

•Worsens over hours/days

•Recovery starts within 2 weeks

•Retrobulbar pain (may be worse on eye movement)

•dColor vision

•RAPD

If the episode is atypical, investigate to rule out a progressive optic neuropathy (see below).

Treatment

This is indeed controversial. Intravenous methylprednisolone hastens visual recovery but does not affect long-term outcome (conclusion of Optic Neuritis Treatment Trial). On this basis, IV steroid treatment may be offered to those with poor vision in the other eye or with severe pain.

524 CHAPTER 16 Neuro-ophthalmology

Anterior ischemic optic neuropathy (1)

AION is a significant cause of acute visual loss in the elderly population, affecting up to 10/100,000/year of those over 50 years of age. In 5–10% of cases, the etiology is arteritic (giant cell arteritis); in 90–95% it is nonarteritic. Giant cell arteritis (GCA) is an ophthalmic emergency requiring immediate assessment and appropriate institution of systemic steroid treatment.

Arteritic AION

In arteritic AION, short posterior ciliary artery vasculitis leads to ischemic necrosis of the optic nerve head.

Clinical features

•Sudden dVA (<20/200 in 76%); headache, scalp tenderness, jaw claudication, weight loss, night sweats, myalgia (association with polymyalgia rheumatica); may have a warning episode of transient dVA (short obscurations or longer amaurosis fugax–like episodes).

•RAPD, swollen disc (typically pale; rarely segmental), ± peripapillary hemorrhages and cotton wool spots, abnormal temporal arteries (thickened, tender, nonpulsatile).

•Associations: CRAO, BRAO, cilioretinal artery occlusion, CN III, IV, VI palsy.

Investigations

•Immediate ESR, CRP, CBC: iESR, iCRP, and iPlt are all supportive of GCA (Table 16.4). Consider urgent temporal artery biopsy (aim to perform it within a few days, although positive results may be obtained

up to 7 days after corticosteroid treatment). ESR should be interpreted in context (Box 16.2). See also diagnostic criteria in Box 16.3.

Treatment

Give immediate adequate steroid treatment (e.g., 1 g methylprednisolone IV 1x/day for 1–3 days) followed by oral prednisolone 1–2 mg/kg 1x/day). Aspirin may have additional benefit. Once disease is controlled, steroids may be titrated according to symptoms and inflammatory markers (CRP responds more quickly than ESR).

Treatment may last several years so osteoporosis prophylaxis is important. The elderly are particularly vulnerable to the side effects of steroids.

Prognosis

The risk of second eye involvement ranges from 10% (if treated) to 95% (untreated). Other complications of GCA include TIA, stroke, neuropathies, thoracic artery aneurysms, and death.