Optic Nerve Injury

As such optic nerve is a direct continuation of brain, has all the three meningeal layers covering it- the pia, arachnoid and dura. The optic nerve can be divided into 3 segments: the intraorbital segment, the intracanalicuair segment, and the intracranial segment. Intracanalicular portion is most important for Otolaryngologist as this is the site frequently involved, where Optic nerve decompression is most beneficial and this is the site where an Otolaryngologist can reach endoscopically. The intracanalicular portion passes through the canal formed by the two struts of the lesser wing of the sphenoid and carries the optic nerve and the ophthalmic artery.

The trauma may be direct or indirect. In direct trauma, the optic nerve may be compressed, partially injured or lacerated or even completely transected by the displaced bony fragments or chips. The intracanalicular portion is most frequently involved in indirect trauma such as blunt trauma resulting in intrasheath or orbital haematoma. These haematoma may compress and compromise the blood supply to optic nerve resulting in loss of vision.

latrogenic trauma during functional endoscopic sinus surgery can occur in cases where Onodi cells or Sphenoethmoid cells are present.

Both Coronal and Axial CT images are important to assess optic nerve injury.

Fig. : Coronal Section: Fracture lesser wing of the Sphenoid associated with blunt of the optic nerve and blindness.

Fig. : Axial Section: Fracture (R) lateral wall of the orbit with blunt of the optic nerve and blindness. Co-incidentally this patient also had transverse fracture of the temporal bone and facial paralysis.

Fig. :Axial Section: Fracture of Basi sphenoid and medial as well as lateral walls of the obrit (Black arrow) with haematoma in the posterior ethmoids (white arrow) can be seen.

Fig. :Axial Section: Fracture of lesser wind of the sphenoid (Arrow), posterior ethmoid, with haeatoma in the posterior ethmoids, orbital apex and surgical emphysema of the anterior orbit is seen of the (R) side.

Fig. Axial Section: Fracture of the ethmoids, lamina papyracea and obrital haematoma is seen on (R) side.