BLOG: Use VEP to understand processing dysfunctions
Click Here to Manage Email Alerts
Visual evoked potentials testing has been used for more than 75 years to look for conditions that interfere with afferent nerve transmission — the one-way communication of visual information from each retina to the brain.
While it is effective for this purpose, the visual evoked potentials (VEP) can also tell us a great deal about whether the brain’s visual processing systems are working and, more importantly, guide treatment when they are not.
There are two visual processing pathways in the brain. The first to develop in humans is the spatial visual process (SVP). It sends information from the peripheral visual system to the superior colliculus in the mid-brain, where it is matched up with incoming data from the motor and proprioceptive systems, including muscles and joints. Once integrated, peripheral visual and proprioceptive information is rapidly transmitted to the frontal, parietal and occipital lobes of the brain, pre-programming the brain with the spatial context it needs to anticipate visual stimuli.
The SVP serves as the base of support for the second visual processing pathway, the focal visual process (FVP), which is used to fixate on a specific target, such as a pen on a desk or a moving car. It is the FVP that requires binocular fusion of images from each eye.
Years ago, I noticed that traumatic brain injury (TBI) patients presented with what seemed to be binocular vision problems (convergence insufficiency, exophoria and problems with tracking and quick eye movements), but that traditional vision therapy approaches didn’t help. We have been able to show that TBI patients have a significant drop in VEP amplitude, and that the SVP is compromised following TBI. And when there is SVP dysfunction, engaging the focal processes to work harder at fixating is not at all helpful. The FVP is already working overtime because it has lost its SVP base of support. The problem lies not with the eyes or eye muscles, but within the brain.
When prisms are used to support the SVP, our studies have shown an increase in the amplitude of the VEP in TBI patients, but not in normal controls (Padula et al.). When the neurological connection between the SVP and the proprioceptive system has been damaged, lenses and prisms can help to re-ground the SVP, thereby rebalancing the brain’s dual visual processing systems. We can see this reflected in VEP after treatment with prisms. The SVP essentially releases the visual system back to a state of readiness, allowing it to re-focus when the VEP checkerboard pattern changes. Without this release, the brain is not ready to fixate on or respond to the visual stimulus.
I now use VEP on every patient I examine because it provides so much insight into how the visual systems anticipate change, respond to stimuli and re-ground with the proprioceptive system – or fail to. If I can get a brain wave change on the VEP with lenses and prisms, then I know they should be my first approach to treatment rather than vision therapy. With VEP to help us understand processing dysfunctions, we as neuro-optometrists can better design therapeutic interventions to influence and rebalance these TBI-induced dysfunctions.
Reference:
For more information:
William V. Padula, OD, SFNAP, FAAO, FNORA, is in private practice at the Padula Institute of Vision Rehabilitation in Guilford, Conn. He is the co-founder of the Neuro-Optometric Rehabilitation Association (NORA) and was the founding chair of the Low Vision Section for the American Optometric Association. He has served as a consultant to the Committee on Vision for the National Academy of Sciences. Padula lectures and consults internationally on visual consequences of tick-borne disease, children’s vision related to learning and development, and adult vision problems related to stroke and traumatic brain injury. He will be teaching the course, “Visual evoked potential (VEP) the final frontier: What does the VEP tell us?” at the 2022 NORA conference. For more information and to register, visit https://noravisionrehab.org/about-nora/annual-conferences/2022-annual-conference
Disclaimer: The views and opinions expressed in this blog are those of the authors and do not necessarily reflect the official policy or position of the Neuro Optometric Rehabilitation Association unless otherwise noted. This blog is for informational purposes only and is not a substitute for the professional medical advice of a physician. NORA does not recommend or endorse any specific tests, physicians, products or procedures. For more on our website and online content, click here.
Collapse