May/June 2021

Dynamic Vision
By James Deom, OD, FAAO, MPH, and Cedrick Noel, DC, DACNB, FABCDD
Today’s Geriatric Medicine
Vol. 14 No. 3 P. 14

When eye movement is diminished, musculoskeletal health is compromised. Improving dynamic vision in aging patients benefits balance and posture.

The link between vision, balance, and posture—a crucial factor when it comes to rehabilitation following severe brain injuries and stroke—is often overlooked in aging patients with mobility issues. Identifying impairments in dynamic vision can provide important clues about how the musculoskeletal system behaves. The strong connection between the visual system, the brain, and the spine leads patients to compensate for shortcomings in eye movement by adjusting their body positions or posture.

To successfully treat musculoskeletal problems and balance issues in older patients, an understanding of the visual system that affects the control of the spine is essential. Assessing eye movements gives a window into the brain and plays a key role in ensuring these patients can maintain their independence and autonomy.

Dynamic Vision and Vestibular Function
Visual acuity can be either static or dynamic. Static visual acuity is the ability to distinguish the details of static objects whose images are formed on the retina when the observer is also stationary, whereas dynamic acuity is the ability to visually resolve subtle spatial details of an object when the object, the observer, or both are moving. Both static and dynamic acuity decline with increasing age and changes in reaction time, speed, and agility.1

For clinicians, it’s important to understand that posture and balance go hand in hand. Good posture and good balance rely in part on accurate vision, which encompasses not just static visual acuity but also eye movement control—dynamic vision. Posture is a response to balance, making eye movement particularly important to evaluate. For good balance and, therefore, good posture, a functioning vestibular system—the part of the brain that perceives head movement—is required, as well as an accurate somatosensory system. When balance is poor, an individual’s posture compensates to try to improve stability. Aspects of this multifaceted system may deteriorate with age and, sometimes, with severe consequences, such as falls.2

Age-related vestibular dysfunction and associated imbalance has a major impact on morbidity, mortality, and health care resources. According to the National Institute of Deafness and Other Communication Disorders of the National Institutes of Health, falls account for more than 50% of all accidental deaths in older adults.3 Moreover, a 2006 analysis calculated the medical costs associated with fatal and nonfatal falls in the United States to be more than $19 billion per year.4

Testing the Key Systems
Balance and eye movement tests can be used to identify vestibular imbalances, and comparing the two can assist in diagnosing the concern. Available vision technology can be used to quickly and objectively identify eye movement-related impairments through eye tracking. Combining ocular testing with body positional changes helps lead to a better understanding of vestibular and balance issues. Eye tracking assessments can be simple for clinicians to administer, and most can report real-time illustrative graphics, making it easy to communicate results to patients and improve the understanding of their diagnoses. This improved understanding can lead to increased commitment to treatment. Illustrative reports make it easy to track progress and validate pre- and postrehabilitation program results.

Studies have shown that decreased ocular motor function can be an early sign of Parkinson’s and other neurodegenerative disorders .5 Assessing eye movement can not only reveal the signs of disease, dysfunction, or degeneration that might have otherwise been missed but also monitor some of those neurodegenerative conditions known to be present.

Other exams performed in this setting include cranial nerve function—comparing right with left—to determine the integrity of the brainstem. Reflexogenic eye movements should be compared with volitional eye movements. Reflexes that involve eye movements are the optokinetic reflex and the vestibular ocular reflex. As patients move their heads in different positions, their eyes are assessed to determine whether they move in an equal and opposite direction—this is the vestibular ocular reflex. The optokinetic reflex reveals whether the eyes have a quick and a slow phase. It’s seen when individuals’ eyes track a moving object that then moves out of the field of vision, at which point their eyes move back to the positions they were in when they first saw the object.

This is important because when people walk, their heads bob up and down, requiring their eyes to adjust vertically in order to maintain clear vision. When vertical eye control is compromised, the body stiffens to prevent too much bobbing. This eventually leads to the patients crouching down and slouching forward. Dynamic eye movement training is used as a large piece of rehabilitation protocol to improve eye movement behavior and control as well as posture.

Eye Movement Training
From a clinical perspective, the health care provider must seek to identify the best rehabilitation approach for each patient and how therapy and treatment should be delivered. First the vestibular system must be corrected, and vestibular imbalances can be identified either through balance or eye movement testing.

Specifically, as it relates to aging patients, it’s imperative that health care providers ask questions and determine goals for therapy, such as which activities the patients want to be able to do that they can’t do now. Eye movement training should be individualized based on the patients’ presentations. For example, a dynamic vision test may reveal that a person's short-range saccade eye movements are normal but that long-range saccades, such as looking from the bottom of a computer screen to the top, fall short of the target. This is common in older adults. If patients can perform short saccades, then over time, the saccades can be optimized to be longer, so that the patients are increasingly looking up (see sidebar “Types of Eye Movements”).

Eye movement exercises can be combined with a working reflex. Every time the eyes move up to a new target that’s a little higher than the previous target, the patients are also bending their heads down, causing their eyes to be pushed up by the vestibular reflex. When the eyes move up for the next saccade, they have been primed by the reflex that works to push the eyes upward, making it easier. The idea is to use the reflexes that are intact to reinforce volitional eye control. Eye movement testing systems can be used to evaluate different training strategies to immediately determine which offers the best outcome (see sidebar “Classification of Saccadic Eye Movements”).

Dynamic vision training can be safely and easily used at home on any large tablet or computer. If patients’ underlying neural networks are intact, improvements in balance—and therefore posture—can be seen immediately. Greater changes will take more time. With daily diligence, significant changes can even be seen a week later. In the older adult population, there can be other factors in play such as structural changes in the spine. Although those may not be able to be changed, balance still can be improved. In many instances, improved balance will result in improved posture, too.

In addition to rehabilitation, eye movement exercises can also be used as maintenance programs through which patients can reap the benefits of activity. Just as body movement and aerobic exercise are important to well-being, eye movement exercises are important to living life dynamically. By identifying ocular motor dysfunction and instituting a plan with foundational principles that can be monitored, patients can maintain their dynamic vision and improved well-being through frequent eye movement exercises.

Conclusion
Whether with respect to physical therapy, vision therapy, or chiropractic care, all specialists need to consider vestibular imbalances first because they’re central to neurological function. The system is predominant, making it essential for survival. The visual system is also very dominant: Cognitively we will believe our eyes before we believe our other senses.

Too often, older patients with progressive neurological dysfunction get left behind. It’s extremely meaningful to give them back the ability to live life dynamically so they can enjoy their daily activities. Through strengthening the visual system and improving eye movements, patients can be empowered to have some independence and better navigate their environment safely. We have a big opportunity to truly make a difference in people's lives.

— James Deom, OD, FAAO, MPH, is passionate about eye and overall health care. He has a special interest in brain injury and vision and received his MPH in this area. He works tirelessly on educating other health care providers and payors on the advantages of including vision specialists such as optometrists as members of the interdisciplinary teams at brain injury rehabilitation hospitals. He’s is a RightEye advisor and hosts a podcast called Try Not To Blink (trynot2blink.com). He practices at Hazleton Eye Specialists in Hazleton, Pennsylvania.

— Cedrick Noel, DC, DACNB, FABCDD, is a chiropractor, nutritionist, and specialist in brain rehabilitation at Noel Brain & Spine (Absolute Chiropractic & Wellness). He’s committed to providing chiropractic solutions to address patients' unique needs, whether pain relief after an accident or injury, or from a specific condition. He treats patients with brain-based conditions such as a mild traumatic brain injury or a developmental disorder. Noel is a RightEye advisor and offers videos on eye movement therapy at tinyurl.com/yydm48tn.

[Sidebars]
TYPES OF EYE MOVEMENTS
Saccades are rapid eye movements that allow us to scan a scene quickly. They are largely automatic and happen even when we focus on a single spot. Smooth pursuit visual behavior is when the eye tracks an object in linear fashion. Vergence allows the eyes to focus on different objects in three dimensions. This movement can be broken down into convergence (in which the eyes point closer together) and divergence (in which the eyes point farther apart). Convergence allows us to focus on near objects and divergence on those that are farther away. Vestibulo-ocular movements compensate for movement, allowing us to see clearly by keeping our eyes on the intended visual target. To follow a target at high speed, one employs all four of these types of eye movements.

SOURCE: BRIDGEMAN B. EYE MOVEMENTS. IN: RAMACHANDRAN VS, ED. ENCYCLOPEDIA OF HUMAN BEHAVIOR. 2ND ED. CAMBRIDGE, MA: ACADEMIC PRESS; 2012:160-166.

CLASSIFICATION OF SACCADIC EYE MOVEMENTS
• Reflexive and voluntary saccades: Orienting to a newly appearing target by means of a saccadic eye movement is a natural response. A saccade made to a target is a "reflexive" or "stimulus-elicited" saccade, vs a situation in which there is voluntary or endogenous cognitive control, eg, when a person is directed to look to the left. All saccades are essentially voluntary in nature. If the time and place of a target’s appearance can be predicted, an anticipatory saccade often occurs before the target itself appears.

• Delayed saccades and memory-guided saccades: Delayed saccade involves the ability to suppress making a response and has been used to investigate the underlying deficits in conditions such as Parkinson’s disease and schizophrenia. Memory-guided saccade is when a target is only flashed briefly so that saccades are directed to a remembered location. Such saccades show a decrease in accuracy in normal individuals and especially in patients with damage to the basal ganglia and regions of the frontal lobe involved in processes of working memory.

• Antisaccades: An antisaccade is a response directed away from a peripheral target to the opposite (mirror image) location. Antisaccades require the suppression of a response to the target and the voluntary control over saccade direction to make the response in the opposite direction. Antisaccades have longer latency than do saccades made toward a target. Damage to regions of the frontal cortex dramatically increases error rates.

• Microsaccades: When the eyes fixate an object, they are in continual small-scale motion, showing irregular drift and tremor, interspersed by miniature saccadic movements. These eye movements are essential to prevent our visual percept from fading, and they occur at a rate of around one per second.

SOURCE: FINDLAY J, WALKER R. HUMAN SACCADIC EYE MOVEMENTS. SCHOLARPEDIA. 2012;7(7):5095.

References
1. Long GM, Crambert RF. The nature and basis of age-related changes in dynamic visual acuity. Psychol Aging. 1990;5(1):138-143.

2. Allen D, Ribeiro L, Arshad Q, Seemungal BM. Age-related vestibular loss: current understanding and future research directions. Front Neurol. 2016;7:231.

3. Rauch SD, Velazquez-Villaseñor L, Dimitri PS, Merchant SN. Decreasing hair cell counts in aging humans. Ann N Y Acad Sci. 2001;942:220-227.

4. Stevens JA, Corso PS, Finkelstein EA, Miller TR. The costs of fatal and non-fatal falls among older adults. Inj Prev. 2006;12(5):290-295.

5. Pretegiani E, Optican LM. Eye movements in Parkinson’s disease and inherited Parkinsonian syndromes. Front Neurol. 2017;8:592.