Higher
Optic Pathway Lesion Introduction Depending on
where an interruption (medically called"lesion") of the optic
pathway takes place, there would be a different, but very characteristic
visual field defect. For instance, as the link shows,an interruption of the right
optic nerve from a right-sided orbital cavity fracture would lead to total blindness
in the right eye.
However,
a right-sided basal skull fracture behind the optic chiasm would lead to a field
defect in both outer (=temporal) visual field halves (called "bitemporal
hemianopia"). On the other hand, if a skull fracture in the very back of
the right skull or a stroke just to the right of the midline damages the visual
cortex of the brain (number 4 lesion in the illustration of the above link), about
2/3 of the inner (nasal) half of the visual field of the right eye and 2/3 of
the temporal half of the left eye visual field would have disappeared.The
neurologist and eye specialist can pinpoint through detailed visual field testing
where in the higher visual pathways the lesion would be. A CT or MRI scan can
be used to confirm the clinical findings. Signs
and symptoms: The signs and symptoms depend on the underlying pathology
on the one hand and on the type of lesion that causes the interruption of the
visual pathway on the other hand. If, for instance, a pituitary tumor causes
the lesion there could be headaches, vomiting, weakness from lack of ACTH etc.
and, depending on whether the pressure occurs in front or behind the optic chiasm,
there would be different findings as mentioned under "introduction"
above (see lesion B and C of this optic
pathway link). With a stroke
there would be other associated symptoms and symptoms would be different again
following a skull fracture where there would be a history of trauma prior to the
visual loss. Diagnostic test: A thorough history
and physical examination is done first including a visual field test. Depending
on the findings it may be necessary to do other tests such as a CT scan, MRI scan
or even a PET scan in some special cases. Special views of the pituitary gland
or of the orbital cavity may have to be requested from the radiologist. Treatment: Depending
on what the diagnosis is after the testing has been completed, the treatment will
be specifically directed at the underlying lesion that has been identified. This
may involve several specialists such as an eye specialist, a neurologist, a neurosurgeon
and in case of a pituitary tumor an endocrinologist as well.
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