Traumatic Optic Neuropathy- Prof. N. Karthikeyan (1)

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Traumatic Optic Neuropathy

By Prof. N. Karthikeyan.

Presentation at

CME on Neuro-Ophthalmic Disorders.

at Regional Institute of Ophthalmology and

Government Ophthalmic Hospital, Chennai.September 16, 2006.


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Traumatic Optic Neuropathy

Is a devastating potential complication of closed

head injury. The hall mark is a loss of visual function

subnormal visual acuity, visual field loss and colour

vision dysfunction and the presence of afferent

pupillary defect prechiasmatic location.

TON is seen in 2.5% of mid facial injury and 2.5% of

closed head injury.

At the Institute of Neurology, GGH, Chennai the

incidence is about 0.1%.


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History

18th century recognized the relation between frontal trauma, visionloss in the absence of ocular injury.

In 1879 Berlin described first the pathological examination of the optic

nerve after head trauma. In 1890 Battle distinguished penetrating from non penetrating indidect

optic nerve injury.

20th century definition, classification, pathophysiology and traumaticoptic nerve injury has been described.

1900 transcranial unroofing of the optic canal was the surgical

procedure for TON. In 1920 Sewell performed transethmoidal optic canal decompression.

Recently endoscopic instrumentation has gained popular support forendoscopic transnasal optic nerve decompression.


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Anatomy

Orbit is pyramidal, base is anterior. Orbital

walls converge posteriorly near SOF and OF. Optic canal is separated from the SOF by

optic strut. Optic canal is about 6.5 mm in

diameter and 8.1 mm in length.


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Anatomy


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Anatomy

Optic nerve is 3.4 mm in diameter, measures 35 50 mm fromthe retina to optic chiasm.- intraocular 1 mm, intraorbital 20

30 mm, intracanalicular 5

11 mm and intracranial 3

16 mm. axons of the nerve have their origin from the nerve fibre layer of

the Retina.

Except intraocular segment the axons of the Optic nerve aremyelinated. Pial branches of the ICA, ACA, Acom.

A perfuse intracranial optic nerve. Intraorbital Optic nerve issupplied by perforating branches of the Ophthalmic artery.


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Pathophysiology

TON can occur anywhere along the nerve intraorbital

or intracranial. It can be

Direct Optic nerve is avulsed, impinged, crushed

or transected by

penetrating wound with knife, pencil, bullets or

pellets

by extensive crush injuries displaced cranio orbital

fracture

by surgical repair of facial bone fractures



Pathophysiology

Indirect most common form after blunt trauma tosuperior orbital rim, lateral orbital wall or frontal area.

Compression force from trauma transmitted viaorbital bone to orbital apex and optic canal.

Elastic deformation of the sphenoid bone allows theforce to be transmitted to intracanalicular segment of

the Optic nerve. Contusion of the intracanalicular Optic nerve axons

and Pial vasculature produce localized Optic nerveischaemia and oedema.



Diagnosis

Essentially clinical.

Suspect if there is midfacial injury, orbital,frontal bone fracture.

A loss of best corrected V/A or VF

accompanied by ipsilateral RAPD.

Identify premorbid ocular condition that limits

visual recovery.



Diagnosis

Perform complete ophthalmic examination

Ocular adnexa orbital rim wall fracture, orbital oedema,

proptosis, EOM dysfunction, signs of penetrating injuries,extrusion of orbital contents.

Visual acuity serial assement

Pupillary reaction an afferent pupillary defect.

IOP increase due to orbital haematoma, diffuse orbital

haematoma, orbital emphysema, soft tissue oedema. Ophthalmoscopy evaluate Retinal, Choroidal, ONH

morphology and presence of Ring shaped haematoma adjacentto Optic nerve head.



Investigations



Investigations

PT, APTT, bleeding time

CT Scan of orbit Perimetry

Multifocal VEP

Multifocal ERG

Identify subclinical loss.



Treatment

Medical observation, steroids, antioxidants

Surgical

optic nerve decompression



Treatment

Indications for surgical treatment -

Clinical signs of optic nerve injury CT Scan / MRI Scan showing optic nerve

sheath haematoma, optic canal fracture

No improvement with high dose steroids


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Treatment

Surgical procedures

Intracranial subfrontal approach Extracranial external Ethmoidectomy

Extracranial endoscopic

Sphenoethmoidectomy


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Other independent Trauma induced optic

neuropathy

Optic nerve avulsion due to

severe orbital trauma

profound rotation of the globe fracture of the nerve at sclera-Lamina`cribrosa

Optic nerve transaction

Diffuse orbital haemorrhage diagnosed by CT /MRI

Localized orbital haemorrhage

Optic sheath haematoma

Orbital emphysema


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neuropathy


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neuropathy


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neuropathy


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Thank you

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Traumatic Optic Neuropathy- Prof. N. Karthikeyan (1)