Karolina Skorkovska, M.D., Ph.D, holds a dual appointment in the Department of Ophthalmology and Optometry at St. Anne’s University Hospital in Brno, Czech Republic, and is on the Faculty of Medicine in the Department of Optometry and Orthoptics at Masaryk University in Brno. She has edited a slim but valuable volume on a subject that rarely receives more than a few pages in ophthalmic textbooks and at most its own chapter in books on visual fields.
The first chapter, an overview of the human visual pathway, begins with a reminder that there are approximately one million axons in the optic nerve, constituting almost 40% of the total number of axons in all cranial nerves. That’s an astounding figure, so consider it again: The optic nerve accounts for almost 40% of the total number of neurons in all of the cranial nerves! Another fact worth emphasizing is that visual information processing begins before information is relayed through the optic nerve. This occurs through interneurons in the retina – specifically amacrine and horizontal cells, modulating activity of the bipolar and ganglion cells.
Before addressing reading and driving specifically, permit me to share a quick review of the sites of damage to afferent visual pathways and their corresponding homonymous field defects:
Location 4: Right incomplete homonymous hemianopia with poor congruence due to a left optic tract lesion.
Location 6: Right superior homonymous quadrantanopia from damage to the left temporal lobe (inferior portions of the optic radiation).
Location 7: Right inferior homonymous quadrantanopia from damage to the left parietal lobe (superior portions of the optic radiation).
Location 8: Left complete homonymous hemianopia due to widespread damage of the right optic radiation in the vicinity of the occipital lobe.
Location 9: Right homonymous hemianopia with macular sparing from damage to the left occipital lobe.
Reading poses particular problems for patients with right homonymous hemianopia, and we discussed this extensively in a blog six years ago. The patient involved at the time has subsequently passed away, and we can now identify her as Ruth Ann Bray. Her best friend Nancy is still a patient in our practice, and comments each time she comes in about how appreciative Ruth was that we preserved her quality of life for several years before she died. Ruth is emblematic of increasing numbers of senior citizen rehabilitation patients for whom the subject matter in Homonymous Visual Field Defects is germane. More coming in Part 2 …