Understanding Sensory Impairments and Brain Disorders
Why might an optometrist be interested in dementia, Alzheimer’s disease, stroke, vestibular sensory loss and other vestibular and sensory impairments, the proprioceptive system, even cerebral hypoxia, and birth asphyxia?
Because an increasing number of studies are demonstrating the role of the eye’s retina in diagnosing these disorders, mitigating many of their symptoms, and generally improving patients’ quality of life. Researchers are finding that the retina, which is composed of brain tissue, plays a critical role in the central nervous system, and 21st century optometrists are taking advantage of this information in helping patients manage neurological disease and injury. That eyeglasses and contact lenses can influence central nervous system activity is slowly becoming public knowledge.
“Eyeglasses and contact lenses can influence the central nervous system."
Brain trauma and neurological disorders disrupt sensory circuitry and the ability to mentally map space. When central and peripheral eyesight fail to interact as a team and/or inputs from eye and ears are out of synchronization -- in other words, auditory and visual maps do not match, then patients often become confused about their environment. This confusion can manifest itself symptomatically as:
- Visual processing problems
- Constricted perception and awareness
- Inappropriate reactions and responses to the surrounding environment
- Difficulties with executive functioning and decision-making
- Postural instability
- Anxiety
- Mood disorders caused by changes to the limbic system
- Disruptions to circadian rhythm
Use of Light to Stimulate the Retina
I have described on numerous occasions the clinical work of the Mind-Eye Institute in addressing these connections. Our team uses highly individualized, therapeutic lenses, filters, and other optometric interventions to stimulate the retina by changing the intensity, amount, or angle of entering light.
As I have explained previously, changes in the way light passes through the retina can promote development of new brain pathways in patients struggling with the symptoms of traumatic head injury, concussion, stroke, and autonomic and neurological disorders. Retinal stimulation also has proven effective in building undeveloped visual processing skills in children – and adults – on the autism spectrum or people labeled with attention deficit hyperactivity disorder and other learning difficulties.
Environmental feedback signals (in the form of light) enter the retina and convert into electrical signals, which propagate through neurons and interact with key brain structures. These retinal signals affect not only the visual cortex but other, significant regions of the brain as well, linking with structures like the limbic system, the cerebellum, and brainstem.
Mind-Eye Brainwear™ and Hypoxic Ischemic Encephalopathy (HIE)
Case in point: a 20-year-old woman who has struggled all her life with sensory overload, depth perception impairments, cerebral palsy, and epilepsy due to birth asphyxia (her brain deprived of oxygen for several minutes at birth) most recently experienced what her mother calls “dramatic, transformative improvement” in quality of life, thanks to the Mind-Eye Brainwear™ eyeglasses prescribed by my associate Carla Adams, OD. The patient herself says the Mind-Eye glasses have broadened her world in terms of what she can do – without fear.
For example, the patient’s mother talked about the overwhelming terror that firework displays had caused her daughter – “she would hold onto me and bury her face into my chest.” She also discussed her daughter’s reluctance to walk among a grove of trees behind the family’s house because the filtered sunshine, which creates dappled light patterns on the ground, confused her depth perception. Yet, after receiving and wearing her Mind-Eye glasses, the patient told her mother how much she now enjoys the lights and colors of fireworks and can often be found walking easily within the grove of trees.
I have been on the medical advisory board of www.hopeforhie.org, seeing many of the babies whose brains were deprived of oxygen at birth. The type of overwhelming stimulation from peripheral eyesight as described by the mother and her daughter is common among these patients.
Sensory impairments can make everyday activities like walking difficult. Scientists writing in a 2021 issue of Current Opinion in Physiology state that “even small head movements can produce postural and perceptual instability” when the vestibular system – a structural labyrinth located in the inner ear -- is affected. The diagnosis of PPPD (persistent postural perceptual dizziness) has many visual components. Indeed, the authors add, “Vestibular information is integrated with proprioceptive and other sensory inputs to generate our senses of motion."
Exactly How is the Retina Involved?
So back to the question, “What does this all have to do with the retina?”
When the brain is injured due to trauma like birth asphyxia or neurological disease, including Alzheimer’s, dementia, and Parkinson’s, communication among neuron signals can become disrupted. And this disruption may then disturb the integration of these neurons with other body sensors involving touch, sensation, pressure, and movement.
Proprioceptors? What Are They?
Proprioceptors are mechanosensory neurons found in muscles, tendons, ligaments, and joints. They transmit information to the central nervous system and, in turn, activate feedback loops. These feedback loops allow the body to move without conscious attention.
At the same time, they communicate with other sensory systems, including the ears and eyes. The integrated function and coordination of these neurons are what stabilize posture and prompt body movement. The proprioceptors help with balance, stair climbing, and core posture control, thereby lessening clumsiness.
Visual Processing
The Mind-Eye Institute has been studying the retina’s role in integrating various sensory maps, including eye-ear coordination, to process visual space and achieve proper spatial awareness. This synchronization of perceived auditory and visual space with proprioceptors optimizes performance.
For instance, people can be scared of walking on stairs or through doorways. As another example, picking up objects is an action requiring subconscious planning of the amount of energy to exert. If the eyes send signals indicating something is going to be heavy, a person readies his or her arms to lift in a manner much differently than when anticipating picking up a small cardboard box of inconsequential weight.
Visual processing involves a complex network of communication signals between the central nervous system (which includes the retina, brain, and spinal cord) and other circuitry.
The Answers May Be in the Eyes
In my blog last month and at the July 2023 Alzheimer’s Association International Conference, I discussed studies showing how the retina is a key in the diagnosis of Alzheimer’s and other neurodegenerative disorders and how it could eventually become an important structure for slowing progression of these diseases. The retina is the only part of the brain that is readily accessible to non-invasive techniques, including stimulation using light, in order to change – and improve -- brain function.
Whether discussing the mysteries of visual processing amidst the hustle-bustle of a crowded grocery store, diagnosing Alzheimer’s disease early in its development, overcoming the effects of neonatal hypoxic ischemic encephalopathy, or simply walking normally in a grove of light-dappled trees, the eyes hold many of the answers, serving as biomarkers for multiple systemic diseases.
