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Orbit

  1. The orbit forms a quadrilateral pyramid: roof, floor, medial wall, and lateral wall.

    1. Roof: orbital process of the frontal bone, lesser wing of the sphenoid

    2. Floor: orbital plate of maxilla, orbital surface of zygoma, orbital process of the palatine bone

    3. Medial wall: frontal process of maxilla, lacrimal bone, sphenoid bone, lamina papyracea of the ethmoid bone

    4. Lateral wall: lesser and greater wings of the sphenoid, zygoma

  2. The trochlea, a pulley through which runs the tendon of the superior oblique muscle, is located between the roof and the medial wall.

    1. The trochlea is the only cartilage in the orbit.

    2. A displaced trochlea causes diplopia on downward gaze.

    3. Trochleitis is the inflammation of the trochlea or the paratrochlea region, causing pain and tenderness locally without extraocular movement deficit. It is diagnosed with CT scan. Treatments include oral NSAIDs, and oral or local steroid injection for cases non-responding to NSAIDs.

  3. The anterior and posterior ethmoid foramina are situated at the junction between the frontal and ethmoid bones, in the frontal side of the suture line.

  4. The inferior orbital fissure is in the floor of the orbit. It is bound by the greater wing of the sphenoid, orbital surface of the maxilla, and orbital process of the palatine bone. It transmits the two branches of the CN V2 (infraorbital nerve and the zygomatic nerve), fine branches from the sphenopalatine ganglion to the lacrimal gland, infraorbital artery and vein, and ophthalmic vein branch.

  5. The superior orbital fissure lies between the roof and the lateral wall of the nose. It is a gap between the lesser and the greater wings of the sphenoid bone.

    1. It transmits cranial nerves III, IV, V1, VI, the superior orbital vein, ophthalmic vein, orbital branch of the middle meningeal artery, and recurrent branch of the lacrimal artery.

    2. Compression of the structures in the superior orbital fissure by bony fragment or mass causes superior orbital fissure syndrome, which presents with ophthalmoplegia, ptosis, fixed and dilated pupil without vision loss.

  6. The optic canal runs from the middle cranial fossa into the apex of the orbit. It is formed by a curvilinear portion of the lesser wing of the sphenoid bone.

    1. The optic nerve and ophthalmic artery course through the optic canal.

    2. Orbital apex syndrome typically results from a compressive lesion near the orbital apex. It presents as complete ophthalmoplegia, ptosis, fixed and dilated pupil, visual function impairment, and ipsilateral upper face hypesthesia from CN II, III, IV, V1, and VI involvement.

  7. The cavernous sinus is not part of the orbit, nevertheless it is considered a crucial ophthalmic structure. It extends from the superior orbital fissure and is bordered by the sphenoid bone and temporal bone.

    1. CN III, IV, V1, and V2 travel through the two dural layers of the lateral wall. CN VI lies free in the cavernous sinus. Sympathetic fibers travel along the internal carotid artery into the cavernous sinus, where it joins CN V1 to enter the orbit. The ...

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