She tried to read small and large printed items but could not comprehend them.
The neurological examination demonstrated a right homonymous hemianopsia but other cranial nerves, sensory systems and muscle strength were normal.
She understood information presented to her orally but could not name the letters of the alphabet shown to her visually, though she could identify them by touch.
When asked to write her insurance information she did so accurately but could not read back what she wrote.
Her post-chiasmal lesion on the left has deprived her left calcarine cortex of direct visual input. The left visual field and its visual pathway to the right calcarine area is intact (otherwise she would be blind).
Visual information from the right visual cortex is ordinarily transferred to the left, language dominant hemisphere via the splenium of the corpus callosum for
Visual information from the right visual cortex is ordinarily transferred to the left, language dominant hemisphere via the splenium of the corpus callosum for
1) integration of visual fields and
2) language functions.
Here callosal fibers are damaged so the left hemisphere gets neither direct visual input from the right visual field nor indirect input from the left visual field; hence she cannot comprehend written words through her speech, spoken or written, but is normal is response to information presented orally or by touch.
This is a case of pure alexia due to occlusion of branches of the posterior cerebral artery supplying the calcarine cortex and corpus callosum.
Extended Explanation
A homonymous hemianopsia is due to injury to the visual pathway behind the optic chiasm - a visual defect in the right visual field is due to injury on the left side.
Such a visual defect would not in itself cause an inability to read; the left visual field would be used instead.
Language functions are usually a property of the left hemisphere and injury could result in language difficulties of motor or receptive types.
She shows that her motor speech whether spoken or written is normal and information presented orally or by touch is handled well. She demonstrates a pure alexia - an inability to read.
The suddenness of the loss suggests a vascular etiology and the symptoms are referable to branches of the posterior cerebral artery.
Vascular studies demonstrated an occlusion in branches of the right posterior cerebral artery supplying the calcarine cortex and adjacent splenium of the corpus callosum.
Vascular studies demonstrated an occlusion in branches of the right posterior cerebral artery supplying the calcarine cortex and adjacent splenium of the corpus callosum.
