Optic nerve

COLOBOMA OF THE OPTIC DISC results from failure in closure of the

embryonic Fissure

Congenital and developmental disorders1. Anomalies of the optic disc Include crescents, congenital

pigmentation, coloboma, drusen and hypoplasia of the optic disc

2. Anomalies of the nerve fibres Like medullated (opaque) nerve fibres

3. Anomalies of vascular elements such as persistent hyaloid artery,

congenital tortuosity of retinal vessels

MEDULLATED NERVE FIBRES also known as opaque nerve fibres represent myelination of nerve fibres of

the retina Normally medullation of optic nerve

proceeds from brain downwards to the eyeball and stops at the level of lamina cribrosa

PERSISTENT HYALOID ARTERY Congenital remnants of the hyaloid arterial

system persist in different forms Bergmester’s papilla refers to flake

of glial tissue projecting from the optic disc

Vascular loop or a thread of obliterated vessel sometimes is seen running forward into the vitreous

Mittendorf dot represents remnant of the anterior end of hyaloid artery, attached to the posterior lens capsule

OPTIC NEURITIS

includes inflammatory and demyelinating disorders of optic nerve

Etiology◦ Idiopathic.◦ Hereditary optic neuritis (Leber’s disease)◦ Demyelinating disorders multiple sclerosis,

neuromyelitis optica

Parainfectious optic neuritis is associated with measles, mumps, chickenpox, whooping cough and glandular fever

Infectious optic neuritis sinus related (with acute ethmoiditis) or associated with cat scratch fever, syphilis (during primary or secondary stage), lyme disease and cryptococcal meningitis in patients with AIDS

Toxic optic neuritis

Clinical profile Anatomical types. three types: Papillitis. refers to involvement of optic

disc Neuroretinitis refers to combined

involvement of optic disc and surrounding retina in the macular area

Retrobulbar neuritis characterized by involvement of optic nerve behind the eyeball

Symptoms. Asymptomatic or associated with following

symptoms:

Visual loss. Sudden, progressive and profound visual loss is the hallmark

Dark adaptation is lowered

Impairment of colour vision

Episodic transient obscuration of vision

Depth perception is impaired

Pain. mild dull eyeache

Signs are as follows: Visual acuity reduced markedly

Colour vision severely impaired

Pupil shows ill-sustained constriction to light

Marcus Gunn pupil sign

4. Ophthalmoscopic features. hyperaemia of the disc and blurring of

the margins Retinal veins are congested and tortuous Splinter haemorrhages and fine exudates

on the disc inflammatory cells in the vitreous

Retrobulbar neuritis fundus appears normal

Visual field changes. Common relative central or

centrocaecal scotoma Contrast sensitivity is impaired

Visually evoked response (VER) shows reduced amplitude and delay in the transmission time

Differential diagnosis papilloedema and pseudo-papilloedema

Acute retrobulbar neuritis must be differentiated from malingering, hysterical blindness, cortical blindness etc.

Treatment Efforts made to find out and treat the

underlying cause Corticosteroid therapy shorten the period

of visual loss, but will not influence ultimate level of visual recovery in patients with optic neuritis

LEBER’S DISEASE Hereditary optic neuritis affects males around age of 20 years transmitted by the female carriers characterised by progressive visual

failure fundus is initially normal or in the acute

stage disc may be mildly hyperaemic with telangiectatic microangiopathy

Eventually bilateral primary optic atrophy ensues

TOXIC AMBLYOPIAS includes conditions wherein visual loss

results from damage to optic nerve fibres due to effects of exogenous or endogenous poisons

Tobacco amblyopia men who are generally pipe smokers, heavy

drinkers and have a diet deficient in proteins and vitamin B complex

hence also labelled ‘tobacco-alcohol-amblyopia

Pathogenesis

Clinical features. men between 40 and 60 years

characterised by bilateral gradually progressive impairment in central vision

fogginess and difficulty in doing near work

bilateral centrocaecal scotomas

Fundus examination essentially normal or slight temporal pallor of disc

Treatment. complete cessation of tobacco and alcohol

consumption Hydroxycobalamine 1000 μg intramuscular

injections weekly for 10 weeks and care of general health and nutrition

Prognosis. It is good, if complete abstinence from

tobacco and alcohol is maintained Visual recovery is slow and may take

several weeks to months

Methyl alcohol amblyopia results in optic atrophy and permanent

blindness

Pathogenesis. Oxidised into formic acid and formaldehyde They cause oedema followed by

degeneration of the ganglion cells of the retina, resulting in complete blindness due to optic atrophy

Clinical features. Headache, dizziness, nausea, vomiting,

abdominal pain, delirium, stupor and even death

characteristic odour due to excretion of formaldehyde in the breath or sweat is a helpful diagnostic sign

Ocular features. Patients are usually brought with almost

complete blindness, which is noticed after 2-3 days, when stupor weans off.

Fundus examination in early cases mild disc oedema and markedly narrowed blood vessels,

Finally bilateral primary optic atrophy

Treatment 1. Gastric lavage

2. Administration of alkali Soda bicarb given orally or intravenously (500 ml of 5% solution)

3. Ethyl alcohol. given in early stages. Is given in small frequent doses, 90 cc every 3 hours for 3 days

4. Eliminative treatment by diaphoresis in the form of peritoneal dialysis

5. Prognosis is usually poor; death may occur due to acute poisoning.

Blindness occurs in those who survive

Quinine amblyopia Clinical features. near total blindness

Deafness and tinnitus may be associated

pupils fixed and dilated

Fundus examination retinal oedema, marked pallor of the disc and extreme attenuation of retinal vessels

Visual fields markedly contracted

Ethambutol amblyopia Antitubercular drug toxicity usually occurs in patients who have

associated alcoholism and diabetes

Clinical features. optic neuritis with typical central scotoma Optic chiasma bitemporal hemianopia reduced vision & colour vision during

antitubercular treatment Fundus examination papillitis Recovery occurs following cessation

ANTERIOR ISCHAEMIC OPTIC NEUROPATHY

(AION) refers to segmental or generalised

infarction of anterior part of optic nerveEtiology. results from occlusion of short

posterior ciliary arteries Depending upon etiology it may be typified

as follows: Idiopathic AION.

Arteritic AION. occurs in association with giant cell arteritis

AION due to other causes. associated with severe anaemia, collagen

vascular disorders, following massive haemorrhage, papilloedema, migraine and malignant hypertension

Clinical features. Visual loss is usually marked and sudden Fundus examination during acute stage

reveal segmental or diffuse oedematous, pale or hyperaemic disc, usually associated with splinter haemorrhages

Visual fields altitudinal hemianopia

Treatment. Immediate treatment heavy doses of

corticosteroids (80 mg prednisolone daily) and tapered by 10 mg weekly

Steroids in small doses (5 mg prednisolone) continued for a long time (3 months to one year)

PAPILLOEDEMA ‘papilloedema’ passive disc swelling

associated with increased intracranial pressure which is almost always bilateral although it may be asymmetrical

‘disc oedema or disc swelling’ includes all causes of active or passive oedematous swelling of the optic disc

Causes of disc oedema1. Congenital anomalous elevation

(Pseudopapilloedema)

2. Inflammations Papillitis Neuroretinitis

3. Ocular diseases Uveitis Hypotony Vein occlusion

4. Orbital causes Tumours Graves’ orbitopathy Orbital cellulitis

5. Vascular causes Anaemia Uremia Anterior ischaemic optic neuropathy

6. Increased intracranial pressure

Etiopathogenesis of papilloedema Causes. secondary to raised intracranial pressure

which may be associated with following conditions:

Congenital conditions aqueductal stenosis and craniosynostosis

Intracranial space-occupying lesions (ICSOLs).

Intracranial infections such as meningitis and encephalitis

Intracranial haemorrhages.

Obstruction of CSF absorption via arachnoid villi which have been damaged previously

Tumours of spinal cord

Idiopathic intracranial hypertension (IIH)

Systemic conditions malignant hypertension, pregnancy induced hypertension (PIH) cardiopulmonary insufficiency, blood dyscrasias and nephritis

Diffuse cerebral oedema from blunt head trauma

swelling due to ocular and orbital lesions is usually unilateral

In majority of the cases with raised intracranial pressure, papilloedema is bilateral

1. Foster-Kennedy syndrome associated with olfactory or sphenoidal

meningiomata and frontal lobe tumours There occurs pressure optic atrophy on side

of lesion and papilloedema on other side (due to raised intracranial pressure)

Pseudo-Foster-Kennedy syndrome characterised by occurrence of unilateral

papilloedema with raised intracranial pressure (due to any cause) and a pre-existing optic atrophy (due to any cause) on other side

Pathogenesis. It has been a confused and

controversial issue

Hayreh’s theory is the most accepted one

states that develops as a result of stasis of axoplasm in the prelaminar region of optic disc, due to an alteration in the pressure gradient across the lamina cribrosa

Clinical features [A] General features. headache, nausea, projectile vomiting and

diplopia Focal neurological deficit

[B] Ocular features. history of recurrent attacks of transient

blackout of vision (amaurosis fugax) Visual acuity and pupillary reactions : normal Clinical features described under four

stages: early, fully developed, chronic and atrophic

1. Early (incipient) papilloedema Symptoms usually absent and visual acuity

normal Pupillary reactions normal Ophthalmoscopic features Obscuration of disc margins Absence of spontaneous venous pulsation

at the disc (appreciated in 80% of the normal individuals)

Mild hyperaemia of disc Splinter haemorrhages. Visual fields are fairly normal.

2. Established (fully developed) papilloedema

Symptoms. history of transient visual obscurations in

one or both eyes, lasting a few seconds, after standing

Visual acuity is usually normal, Pupillary reaction remain normal

Ophthalmoscopic features Apparent optic disc oedema is seen as its

forward elevation above the plane of retina

Physiological cup of the optic disc is obliterated.

Disc becomes hyperaemic and blurring of the margin is present all-around

Multiple soft exudates and superficial haemorrhages may be seen near the disc

Veins becomes tortuous and engorged Visual fields enlargement of blind spot

3. Chronic or long standing (vintage) papilloedema

Symptoms. Visual acuity is reduced ???? Pupillary reactions normal Ophthalmoscopic features acute haemorrhages and exudates resolve,

and peripapillary oedema is resorbed Optic disc gives appearance of the dome of

a champagne cork The central cup remains obliterated Visual fields Blind spot is enlarged and

the visual fields begin to constrict

4. Atrophic papilloedema Symptoms. develops after 6-9 months of chronic

papilloedema Severely impaired visual acuity Pupillary reaction. impaired

Ophthalmoscopic features greyish white discoloration and pallor of

the disc due to atrophy of the neurons and associated gliosis

Prominence of the disc decreases Retinal arterioles are narrowed Whitish sheathing develops around the

vessels. Visual fields Concentric contraction of

peripheral fields

Treatment and prognosis neurological emergency and requires

immediate hospitalisation

As a rule unless causative disease is treatable or cerebral decompression is done, the course of papilloedema is chronic and ultimate visual prognosis is bad

OPTIC ATROPHY refers to degeneration of the optic nerve occurs as an end result of any pathologic

process that damages axons

Classification Primary optic atrophy refers to simple

degeneration of the nerve fibres without any complicating process within the eye e.g., syphilitic optic atrophy.

Secondary optic atrophy occurs following any pathologic process which produces optic neuritis or papilloedema

Ophthalmoscopic classification. It is more useful

Common types are as follows: Primary (simple) optic atrophy Consecutive optic atrophy Glaucomatous optic atrophy Post-neuritic optic atrophy Vascular (ischaemic) optic atrophy

Ascending versus descending optic atrophy.

Ascending optic atrophy follows damage to ganglion cells or nerve fibre layer due to disease of the retina or optic disc

Descending or retrograde optic atrophy proceeds from the region of the optic tract, chiasma or posterior portion of the optic nerve towards the optic disc

Etiology 1. Primary (simple) optic atrophy. multiple sclerosis, retrobulbar neuritis

(idiopathic), Leber’s and other hereditary optic atrophies

2. Consecutive optic atrophy. occurs following destruction of ganglion

cells secondary to degenerative or inflammatory lesions of the choroid and/or retina

Its common causes are: diffuse chorioretinitis, retinitis pigmentosa,

pathological myopia and occlusion of central retinal artery

3. Postneuritic optic atrophy. It develops as a sequelae to long-standing papilloedema or papillitis

4. Glaucomatous optic atrophy. It results from the effect of long standing raised intraocular pressure

5. Vascular (ischaemic) optic atrophy. It results from the conditions (other than glaucoma) producing disc ischaemia

include: giant cell arteritis, severe haemorrhage, severe anaemia and quinine poisoning

Clinical features of optic atrophy 1. Loss of vision, may be of sudden or

gradual onset

2. Pupil is semidilated and direct light reflex is very sluggish or absent

Swinging flash light test depicts Marcus Gunn pupil

3. Visual field loss will vary with the distribution of the fibres that have been damaged

4. Ophthalmoscopic appearance of the disc will vary with the type of optic atrophy.

In general pallor of the disc and decrease in the number of small blood vessels (Kastenbaum index)

Ophthalmoscopic features of different types of optic atrophy are as described below:

Primary optic atrophy

Consecutive optic

atrophy

Post-neuritic optic atrophy

Glaucomatous optic atrophy

Ischaemic optic atrophy

chalky white or white with bluish hue

Disc appears yellow waxy

Optic disc looks dirty white in colour

Pale disc pallor of the optic disc

edges (margins) are sharply outlined

edges are not so sharply defined

edges are blurred,.

Edges well defined

Lamina cribrosa is clearly seen at the bottom of the physiological cup

physiological cup is obliterated and lamina cribrosa is not visible

deep and wide cupping of the optic disc and nasal shift of the blood vessels

Major retinal vessels and surrounding retina are normal

Retinal vessels are attenuated

vessels are attenuated and perivascular sheathing is often present

Normal attenuation of the vessels

Differential diagnosis 1. Non-pathological pallor of optic disc is

seen in: axial myopia, infants, and elderly people

sclerotic changes physiological

2. Pathological causes of pallor disc (other than

optic atrophy) include: hypoplasia, congenital pit,and coloboma

Treatment The underlying cause when treated help in

preserving some vision in patients with partial optic atrophy

once complete atrophy has set in, the vision cannot be recovered