====== Visual field deficit ======

Depends in part on location of [[chiasm]] with respect to [[sella turcica]]: the chiasm is located above the [[sella]] in 79%, posterior to the sella turcica ([[postfixed chiasm]]) in 4%; in front of the sella (pre-fixed) in 5 %.

1. compression of the [[optic chiasm]]:

a) [[bitemporal hemianopsia]] that obeys the vertical meridian: classic visual field deficit
associated with a [[pituitary tumor]]. Due to impingement on crossing nasal fibers in the chiasm

b) other reported patterns that occur rarely: [[monocular temporal hemianopsia]].

2. optic nerve compression: more likely in patients with a [[postfixed chiasm]].

a) [[loss of vision]] in the ipsilateral eye. If carefully sought, there is usually a superior outer (tem-
poral) [[quadrantanopsia]] in the contralateral eye 
((Walsh FB, Hoyt WF. Clinical Neuro-Ophthalmology. Baltimore 1969))
(so-called [[junctional scotoma]] AKA “pie in the sky” defect) from compression of the anterior [[Wilbrand's knee:]]; may also be an early finding even without a post-fixed chiasm

b) may produce central scotoma or monocular reduction in visual acuity

3. compression of the optic tract: may occur with a pre-fixed chiasm. Produces homonymous
hemianopsia