====== Ophthalmic segment aneurysm ======

The [[ophthalmic segment aneurysm]]s arise from the [[internal carotid artery]] (ICA) between the roof of the [[cavernous sinus]] and the origin of the [[posterior communicating artery]]. 

The ophthalmic segment of the [[internal carotid artery]] (C6) extends from the [[distal dural ring]] to the origin of the [[posterior communicating artery]].

The segment is known as the [[carotid ophthalmic segment]].

===== Classification =====


Ophthalmic segment aneurysms (OSAs) OSAs include (NB: nomenclature varies among authors):

1. [[ophthalmic artery aneurysm]]s:

2. [[superior hypophyseal artery aneurysm]]s:

a) [[Paraclinoid internal carotid artery aneurysm]]: usually does not produce visual symptoms

b) suprasellar variant: when giant, may mimic pituitary tumor on CT.

===== Clinical features =====

1. ≈45% present as [[SAH]]

2. ≈ 45% present as [[visual field defect]]:

a) as the aneurysm enlarges it impinges on the lateral portion of the [[optic nerve]] →inferior temporal fiber compression →[[ipsilateral monocular superior nasal quadrantanopsia]]

b) continued enlargement →upward displacement of the nerve against the [[falciform ligament]] (or fold) →superior temporal fiber compression →[[monocular inferior nasal quadrantanopsia]]

c) in addition to near-complete [[loss of vision]] in the involved eye, compression of the optic nerve near the [[chiasm]] may also produce a superior temporal quadrant defect in the contralateral eye ([[junctional scotoma]] AKA“[[pie in the sky]]” defect) from injury to the anterior knee of Wilbrand (nasal retinal fibers that course anteriorly for a short distance after they decussate in the contralateral optic nerve).

3. ≈ 10% present as both