When we think about our vision, we tend to think solely of our eyes. The way they seamlessly receive and instantaneously help us to translate information about the world around us is remarkable and easy to take for granted. However, the eyes do not do it alone. They are an extension of the brain and part of the central nervous system.
Visual information from the eyes travels deeper into the brain on fibers that make up . The visual pathway runs from the eyes to a part of the midbrain called the lateral geniculate nucleus or LGN and then from there it travels along fibers to the visual cortex, part of the brain in the back of the head just above the base of the skull. In the visual cortex, visual information is sorted, translated, and interpreted further. Since this visual pathway exists in the front, middle, and back of the brain with tracts or connecting fibers to each of these stops along the way, if a growth like a tumor puts pressure on any part of this pathway it can affect our vision. If the tumor pushes on a part of the visual pathway long enough, it may cause swelling of one or both of the optic nerves or eye nerves, which are examined during a routine eye exam. Besides swollen eye nerves, growths along the visual pathway may also result in visual field defects as well as other visual and non-visual symptoms.
Eye exams and visual field testing do not replace other diagnostic tests to check for brain tumors but are used in conjunction with those tests to see how the tumor is affecting your vision and whether or not those effects will likely be permanent. Getting regular eye exams and telling your eye doctor about any problems or issues you are having with your vision or in your daily life is important.
For the year 2020, the National Cancer Institute estimated that in the US there would be . In December of 2020, I personally lost one of my relatives to glioblastoma. She was 45. Although changes to her vision weren’t the first sign that something was wrong, she did experience many changes to her vision and visual field prior to her passing which I monitored through eye exams and visual field testing. It is true that when we are training as doctors we are told “when you hear hoofbeats look for the horses, not zebras” meaning that odds are when you are trying to diagnose a patient, the most common explanation or diagnosis is more likely to be favored over a rare one. However, having now seen a “rare” condition in my own family, I urge all doctors including eye doctors to remember that zebras still make hoofbeats. Early detection and treatments can prolong, if not save, a life.
by Dr. Cheryl G. Murphy, OD