ANATOMYANATOMYThe optic nerve extends from the The optic nerve extends from the lamina cribrosa up to lamina cribrosa up to the optic chiasmathe optic chiasma . The nerve is covered by meningeal . The nerve is covered by meningeal sheathes –the dura, the arachnoid and the pia . The sheathes –the dura, the arachnoid and the pia . The subarachanoid space of the nerve is continuous with subarachanoid space of the nerve is continuous with that of the brain .that of the brain .The optic nerve consists of the axons of the ganglion The optic nerve consists of the axons of the ganglion cells of the retina i.e at the optic disk the fibers of the cells of the retina i.e at the optic disk the fibers of the nerve fiber layer of the retina pass into the optic nerve fiber layer of the retina pass into the optic nerve .Behind the lamina cribrosa the nerve fibers are nerve .Behind the lamina cribrosa the nerve fibers are myelinated (or medullated).In front of the lamina myelinated (or medullated).In front of the lamina cribrosa , the nerve fibers lose their myelin sheath and cribrosa , the nerve fibers lose their myelin sheath and become transparent in the nerve fibers layer of the become transparent in the nerve fibers layer of the retina.retina.The central retinal artery and vien pierce the memingeal The central retinal artery and vien pierce the memingeal sheathes around the optic nerve 10-12 mm behind the sheathes around the optic nerve 10-12 mm behind the globe and then come to lie in the center of the nerveglobe and then come to lie in the center of the nerve.

DISEASES OF THE OPTIC NERVE :DISEASES OF THE OPTIC NERVE : Papilloedema Papilloedema (choked disk)

:

it is purely hydrostatic non inflammatory swelling of the optic disk (or nerve head) resulting from increased intracranial pressure and from obstruction to the orbital venous outflow . The condition is usually bilateral. However:

1)One eye may be effected before the other . 2)Degree of swelling may differ considerably in

the two eyes.

Normal optic nerve

An optic nerve with mild swelling An optic nerve with mild swelling ((papilledemapapilledema). ).

Another example of an optic nerve with mild papilledema.

The halo of edema now surrounds the optic disc.

Etiology: Increased intracranial pressure forces C.S.F into

subarachnoid space around the optic nerve .Consequently the central retinal vien is compressed as it crosses the subarachnoid space while the thicker walled central retinal artery continues to transmit blood. As a result oedema of disk develops .

I) Intracranial causesI) Intracranial causes::1)Tumours of brain (mid brain,barieto-occipital region

and cerebellum ) are much the commonest cause and 80% of these are associated with papilloedema . The site of tumour is more important than its size. In general those tumours which tend to produce internal hydrocephalus will cause papilloedema .

Foster-Kennedy Syndrome :unilateral papilloedema with primary optic atrophy on the other side suggest a tumour of the opposite alfactory lobe or orbital surface of front lobe.

2) Cerebral abscess3) Tuberculous or syphilitic meningitis4) Cavernous sinus Thrombosis5) Head injury with subarachnoid

hemorrhage II)SystemicII)Systemic::• 1)Malignant hypertension • 2)Leukaemia

Leukaemia

II) II) SystemicSystemic::1)Malignant hypertension 2)Leukaemia

III)OrbitalIII)Orbital::1)Meningioma of optic nerve sheath2)Orbital cellulites

IV)OcularIV)Ocular::1)Hypotony 2)Raised intraocular pressure as in acute

congestive glaucoma..

Symptoms:1) For long vision – particularly central vision

may be unimpaired.

2) Transient attacks of blurred vision due to spasm of retinal arteries.

3) When secondary optic atrophy sets in there is fall of vision and progressive contraction of visual field.

SignSign

The fundus picture is as follow :

1) in the early stage there is blurring and hyperaemia of the upper and lower margins of the optic disc: this extends around the nasal side then over the disc filling up The physiological cup the disc becomes elevated over the surrounding retina .

By direct ophthalmoscopy adifference of 2-6d may be found between the focuss of the vessel at the top of the disc and those on the retina alittil way off 2) the veins are dilicated and tortuous their pulsation may be absent even on pressure Upon the globe .

3) flame shaped haemorrhage and soft exudates are seen on and around the disc .

4) The radiating oedematos foldes around the macula take on the appearance of amacular fan or star .

5) post neurotic or secondary optic atrophy : the nerve fiber es unableto withstand the pressure degenerate 0 the disc become pale grey there is proliferation of fiberous tissue on the disc as aresult the margin are blurred and there is sheating of vessels.

Differential diagnosis :1) pseudo neuritis or pseudo papilloedema

seen in cases of high hypermetropia or in astigmatism

2) Papillitis

Pseudopapilledema

Papillitis

PapillitisPapillitis papilloedemapapilloedema 1. Unilateral

2. Sudden diminished of vision

3. Sustained papillary reaction marcus gunn pupil

4. Media might be hazy due to exudation into vitreous

5. Disc swelling rarely more than 2-3d

6. Field defect central or centrocaecal scotoma between the fixation and blined spot especially for red and green

7. x-ray skull : normal

8. condition temporary and recovers in afew weeks

1. Bilateral

2. For long central vision is unilateral

3. Pupil round and reacts briskly to light

4. Media clear

5. May be as high as 6d

6. Enlarged blined spot later contraction of the peripheral field

7. Shows silver beaten appearance erosion of posterior clinoid process and dorsum sellae

8. Condition progressively deteriorates and ends in blindness unless treated in

time

Treatment :

The ideal treatment is the removal of the cause of raised intracranial pressure i.e. surgical removal of brain tumour . If this is not possible to retain vision decompression of the skull remove rigidity of skull bone burr hole or shunt operation is done . Once optic atrophy sets in visual prognosis becomes poor .

Optic neuritisOptic neuritis : inflammation of the optic nerve

Classification :

1-papillitis: when the optic disc or nerve head is inflamed .

2- retrobulbar neuritis : when the optic nerve behind the eyeball is inflamed.

A -acute

b -chronic –toxic amblyopic .

papillitispapillitis

Papilloedema. The disc is swollen and the disc margin has disappeared. The veins are congested.

EtiologyEtiology : : 1-septic foci teeth tonsilis sinusitis particularly of sphenoidal

sinus and posterior ethmoidal cells since the optic nerve is closely related to them .

2- orbital cellulites3- meningitis –tuberculous syphilitic .4- choroio-retinitis –including sympathetic ophthalmitis 5- demyelinating diseases like disseminated or multiple

sclerosis neuromyelitis optica (or Devic's disease ). Since the lesion in these diseases appear where the nerve

fibers are myelinated the characteristic lesion in optic nerve is retrobulbar neuritis .

6- diabetes anaemia 7- lebers disease 8- exogenous toxins.

SymptomsSymptoms: it is usually unilateral.

1) Sudden diminision of vision.

2) Pain on moving the eye upwards because of the attachment of the sheath of the superior rectus muscle to the sheath of the optic nerve near the optic foramen.

SignsSigns::

1) Ill sustained papillary reaction (Marcus Gunn pupil) inability to maintain contraction on prolonged stimulation with light

2) Fundus shows following picture.A) Papillitis:1) Media is hazy due to exudation in vitreous. There is blurring and hyperaemia of the disc margin.

Te physiological cup is obscured. The disc swelling is rarely more than 2-3 D.

2) The veins are dilated and tortuous. 3) There may be flame – shaped hemorrhages and

soft exudates on and around the disc. 4) Post neurotic or secondary optic atrophy. Refer

papilloedema B) Retrobulbar neuritis: The fundus appears

normal. The condition may be truly defined as a disease wherein neither the ophthalmologist nor the patient sees anything!

Differential diagnosis: refer papilloedema.

Treatment:

1-Treatment of cause such as septic focus sinusitis .

2-Corticosteroids –orally or by posterior subtenons injection.

Recently, high dose of Methylprednisolone IV has been recommended.

3-Injection of high doses of vit. B1, B6, B12.

Chronic Retrobulbar Neuritis : (Toxic Amblyopic)

It includes a number of conditions in which the ganglion cells/optic nerve

fibers are damaged by the exogenous poisons. EtiologyEtiology::1-Tobacco-chewing or smoking. The causative

agent is nicotine, collidine or lutidine. 2-Ethyl and methyl alcohol.3-Lead 4-Arsenic 5-Quinine Predisposing factors: poor general health and

vitamin deficiency.

Symptoms: Symptoms: 1) radual diminision of vision – sharp vision i.e. vision

for fine work such as reading fine print, threading a needle ect. Is particularly affected.

2) Colour blindness.

SignSign: At first no changes are seen in the fundus.Later there

is blurring of the disc margin, pallor of the temporal side of the disc.

Central fields: shows central or centrocaecal scotoma

for white and coloured objects (red and green).

Treatment:

1-Complete withdrawal of tobacco, alcohol

2-Administration of high doses of Vitamin B1 , B6 and B12 (hydrox-cobalamine)

3-Improvement of general health

4-Vasodilators – nicotinic acid.

OPTIC ATROPHY:It is a term usually applied to the condition of the optic

disc when the optic nerve is degenerated.Etiology:1-Syphilis – Tabes dorsalis, G.P.L.2-Pressure – pituitary tumour , glioma of optic nerve 3-Tuberculous meningitis. 4-Glaucomatous optic atrophy 5-Circulatory optic atrophy – due to occlusion of central

retinal artery, arterio- sclerosis.6-Consecutive optic atrophy – due to destruction of

ganglion cells in retina as in retinitis pigmentosa, choroiditis.

OPTIC ATROPHY

OPTIC ATROPHYCentral Field Loss

7-Traumatic optic atrophy: Avulsion of optic nerve. fracture of skull, heamorrhage into optic nerve sheath.

8-Toxic optic atrophy : exogenous toxins, tobacco alcohol , 9-Metabolic diabetes mellitus10- Demyelinating disease – disseminated sclerosis , 11-Hereditary – Liber's disease.

Pathology: 1-Columnar optic atrophy: occurs when degeneration and

regeneration are orderly and the proliferating astrocytes arrange themselves in longitudinal columns replacing the nerve fiber layers.

2-No pattern optic atrophy occurs when there is replacement of the nerve fibers with glial tissue which is excessive and is densely tangled.

3-Cavernous optic atrophy occurs when there is degeneration of nerve fibers without much replacement by glial tissue .

Symptoms:

1-Usually there is progressive diminished of vision .

2-Colour blidness.

Signs:

1-When atrophy is complete the pupil is dilated and fixed.

2-Fundus shows:

Primary or simple optic

atrophy Secondary or post neuritic

optic atrophy

• -seen in case of syphilis, pituitary tumor

•1-disc

•a) colour : white with a bluish tint

•b) edges: sharply defined and regular.

•c) lamina cribrosa seen (stippling).

•d) slight atrophic cupping seen

•2-Retina:

•a) vessels normal arteries may

be slightly attenuated . •b)surrounding retina is normal in appearance.

• Seen following papilloedema , papillitis.

• There is proliferation of fibrous tissue on the disc and along the retinal vessels.

• Dense white, chalky white or grayish white .

• Blurred and irregular

• Not seen

• No cupping seen (physiological cup obscured.

• Arteries are thin, veins are dilated , both show sheathing

with fibrous tissue

• Surrounding retina shows pigmentary disturbances which are most common at macula.

3)consecutive optic nerve atrophy : seen in retinitis pigmentosa, choroiditis.

Disc: Yellow, waxy appearance, edge are well defined.

Retina: vessels, show marked attenuation, particularly in case of retinitis pigmentosa. Surrounding retina shows evidence of retinitis pigmentosa, choroditis (pigmentary disturbance).

Peripheral Fields: show concentric contraction or irregular or sector shaped defects.

Treatment:1-Directed at the cause –anti-syphilitic treatment

penicillin in high doses , removal of pituitary tumour.

2-vasodilators: Tb. nicotinic acid.3-Injection Vitamins B1, B12 in high doses.

MEDULATED NERVE FIBERS OR OPAQUE MEDULATED NERVE FIBERS OR OPAQUE NERVE FIBERS:NERVE FIBERS:

Medullation of the optic nerve fibers Medullation of the optic nerve fibers starts centrally i.e. from the brain and at birth starts centrally i.e. from the brain and at birth reaches a level immediately behind the lamina reaches a level immediately behind the lamina cribrosa , normally the process ceases here . cribrosa , normally the process ceases here . But occasionally patches of nerve fibers on But occasionally patches of nerve fibers on the optic disc or in the retina region medullary the optic disc or in the retina region medullary sheath after they have passed through the sheath after they have passed through the lamina cribrosa . These are called medullated lamina cribrosa . These are called medullated nerve fibers or opaque nerve fibers.nerve fibers or opaque nerve fibers.

OPHTHALMOSCOPIC APPEARANCE:

They appear as white patches with a feathery outline on and around the disc. Usually the retinal vessels are covered in places by opaque nerve fibers.

Medullated nerve fibers disappear in cases of demyelinating diseases , optic atrophy due to pituitary tumour, glaucoma.

Field defects: Opaque nerve fibers produce an enlarged blind spot or an

arcuate scotoma.