Neuroopthalmology of chiasm: Pearls

1. a prefixed chiasm can result in deficit resembling congruous visual field loss
2. A postfixed chiasm can resemble bilateral optic neuropathy
3. Fixation blindness: attempts to focus on a near target results in overlap of 2 nonseeing temporal fields, and everything beyond fixation appears to disappear.
4. See saw nystagmus seen with masses or trauma cause one eye and other alternately elevating, intorting, and then depressing and extorting, in a pendular fashion
5. Gliomas of chiasm are similar to optic nerves, presenting with decreased vision, optic atrophy and strabismus
6. In pituitary apoplexy, pain is frequently retroorbital, and field defect is classically bitemporal superior quadrantanopsias, due to upward expansion of the tumor, 70 % vomit, LP is abnormal, MRI is diagnostic test of choice, and substantial medicolegal risk resides therein. Men have nmore than women
7. Aneurysms causing chiasmal compression include supraclinoid ICA, the ICA-opthalm a junction, and occassionally cavernous or ACOM arteries. Nonruptured aneurysms causing compression require treatment usually with clipping rather than coiling (Continuum 2009).