OPTIC NERVE DISORDERS

Papilledema, i.e. swelling of optic nerve head, secondary to raised intracranial pressure (ICP), is commonest optic nerve lesion, characterized by:

• Loss of spontaneous venous pulsations (earliest),

• Hyperemia and edematous blurring of disc margins,

• Obliteration or fullness of optic disc cup,

• Peri-discal retinal edema, hemorrhages, exudates or concentric retinal wrinkling (Paton lines) in severe cases (Fig.

Etiologically, papilledema indicates raised ICP due to cerebral edema, obstructed CSF flow or increased CSF production (Table 26.12). Elevated CSF pressure in subarachnoid space leads to similar pressure-rise within the optic nerve sheath, consequent vascular stasis and nerve edema. Infants with open fontanels and sutures are less likely to develop papilledema due to outward release of CSF pressure. Presence of papilledema has to be excluded before lumber puncture, to avoid risk of sudden brain-stem herniation, i.e. coning.

Clinically, these cases present with features of raised ICP, e.g. headache, vomiting, bradycardia, hypertension and false localizing signs, e.g. lateral-rectus (Vi nerve) palsy. (Ch 18.4) Vision is normal in acute papilledema but may be impaired in late stages due to secondary optic atrophy, macular scarring and pressure damage on optic nerve.

D/D of papilledema includes other causes of similar fundal changes, e.g. acute optic neuritis (vision impaired in early stages), hypertensive retinopathy, diabetic retinopathy and rare pseudopapilledema-a structural disc abnormality.

Treatment of papilledema is essentially the treatment of raised ICP (Chapter 18.4). Acute papilledema is completely reversible within 6-8 weeks, if CSF pressure is relieved in initial stages. However, long-standing cases are irreversible due to secondary neurovascular changes. Optic neuritis, i.e. “inflammation, demyelination and/or degeneration of optic nerve with loss of visionquot; is usually

TABLE 26.12: Common causes of papilledema

• CNS infections: Meningitis, encephalitis

• ICSOLs: Brain tumors, tuberculoma

• Head injury

• Intracranial hemorrhage

• Toxic encephalopathy: Poisonings, metabolic

• Developmental: Hydrocephalus, craniosynostosis

ICSOL: Intracranial space occupying lesions an acute illness in children, which may be unilateral or bilateral. Depending on the portion of nerve affected, it is termed as Retrobulbar neuritis (posterior segment), Papillitis (nerve-head) or Neuroretinitis (associated retinal involvement).

Etiologically, it is seen in: (a) viral nerve-head infections,

(b) toxic neuritis, e.g. lead, vincristine, (c) CNS infections, e.g. meningitis, and (d) demyelinating diseases, e.g. multiple sclerosis.

Neuromyelitis optica (Devic disease) is a rare disease with sudden blindness due to bilateral optic neuritis and paraplegia due to transverse myelitis.

Treatment of optic neuritis depends on primary cause. IV or local steroids have been demonstrated to speed­up the recovery in young adults, but do not affect the final outcome. In most cases of primary optic neuritis, recovery begins after 1-4 weeks though complete vision may not be restored.

Optic atrophy, i.e. irreversible degeneration of optic nerve axons with attendant loss of vision, is characterized by: (a) disc pallor, and (b) deepening of optic cup on fundoscopy.

Etiologically, it may be primary, i.e. without preceding papilledema, due to familial or hereditary degeneration; or more likely secondary, following optic neuritis or prolonged papilledema. Disc margins are well defined in primary and obscure in secondary optic atrophy.

Optic nerve glioma is the commonest but benign tumor of optic nerve, which may develop in intra-orbital or intra-cranial portion of nerve.

Clinically, intra-orbital tumor presents with unilateral blindness and proptosis, while intra-cranial tumor usually involves optic chiasma and manifests with bitemporal hemianopia, raised ICP and hypothalamic/ pituitary dysfunction.

As these tumors are very slowly progressive, best therapeutic approach is periodic observation, followed by surgery for intraorbital tumor (if vision is completely lost) or radiotherapy/chemotherapy for intracranial tumor.

Congenital abnormalities of optic nerve are rare and include optic nerve aplasia/hypoplasia, which is typically unilateral and frequently missed due to normal vision in other eye; and tilted or funnel-shaped (morning-glory) disc with significant visual impairment or astigmatism.

26.2.13