Vertebral-Basilar Case 6: Blindsided
The patient had no other neurologic deficit except a complete left homonymous hemianopsia: when his eyes were stationary, he could not see to the left side with either eye. He was very aware of his visual loss and compensated by moving his eyes in order to bring objects in his blind field into view. By this means, he was able to see objects on both sides of pictures and read across a whole page of written text without hesitation. Pupillary light reflexes were normal.
Diagrams
DX
Occlusion PCA Branch to Left Occipital Lobe
Note
Expert Note Case 6.
Blindsided
This patient suffered an infarction of the medial aspect of the right occipital lobe. The patient realized that he could not see to his left, and purposefully did not neglect objects even if they were in his blind regions.
By contrast, patients with a larger lesion in the lateral aspect of the right occipital lobe involving neighboring parts of the right parietal and temporal lobes may neglect objects on the left because they have lost the 'concept' of the left side, whether of themselves and of their world.
The central (macular) visual fields are usually represented in far posterior occipital lobe cortex that lies in the MCA/PCA border zone. Central vision is therefore largely spared in most PCA infarcts because there is enough blood flowing in MCA cortical branches to supply the border zone cortex.. Unfortunately, that was not the case for this patient, and there was no macular sparing. The patient's pupillary light reflexes were normal, however, because neither the retina, the optic tract or the upper brainstem depend on the cortical branches of the PCA.