The Importance of Eye Movement Analysis in Functional Neurology Therapy

Neurological Disorders can be tricky to assess or diagnose as there are often very little outward signs of trouble until the condition becomes severe.

There’s a lot that we don’t understand about how neurological disorders work and what causes them. In functional neurology, eye movement studies have been conducted extensively not only in healthy human subjects but also in patients with neurological disorders.

These tests were designed by trained neuroscientists from specialized clinics such as Chicago Neuro in order to get a glimpse of possible neurological diseases or disorders brewing beneath the surface.

Let’s discuss how eye movements are related to neurology, as well as how we can use this to benefit patients who suffer from neurodegenerative diseases.

Importance of Eye Movement Analysis in Functional Neurology Therapy

What does observing our eye movements tell us about our brain?

Humans have evolved to be inherently more visually attuned, meaning we use our eyes as the primary sensory organ upon which we observe and interact with the outside world. 

The inner workings of our brain and what it is currently processing is, to some extent, reflected by the focus of our gaze.

On a daily basis, we deliberately or instinctively observe other people’s gaze as a way to gauge their thoughts or intentions.

In neurology, eye movement is a useful indication of our current neurological state.

Eye movements (usually in saccades) allow us to examine the outside environment.

A saccade is a fast, simultaneous movement of both eyes in the same direction between two or more phases of fixation.

Smooth pursuit motions, on the other hand, the eyes appear to move slowly rather than in jumps. We then fixate on objects one at a time. 

Intuitively, we believe that we can get the gist of a situation in a single glance, even if it is only for a brief while before making any eye movements, but this is an illusion. When we read a text, this becomes evident.

We cannot gain even a basic concept of the meaning of what is written until we look at each word (or two words, if one of the words is short enough) one at a time.

A “single glance” is not enough for our brain to absorb everything.

This is due to the fact that just 1–2 degrees of the retina’s visual field (central vision) is capable of high resolution, requiring us to use regular eye movements to carefully scrutinize each word in the text.

If eye movement isn’t possible, we shift our sight by moving our head.

Our brain’s inclination for sparse coding may contribute to the illusion of acquiring the gist of a scene at a look.

With central vision, we acquire visual information from the essential areas of the scene, but we rely on guesswork to fill in the gaps.

Types of Eye Movement Disorders

Strabismus, or misalignment of the eyes, is one of the most frequent eye abnormalities in children, affecting about 4% of children under the age of six years. Strabismus can cause visual loss (amblyopia) and have serious psychological consequences.

To avoid permanent vision impairment, strabismus must be detected and treated early. Amblyopia affects 30–50% of children with strabismus.

To give these youngsters an opportunity to develop normal binocular vision, appropriate alignment of the visual axis must be restored at an early stage of visual development.

Many terminologies are used to discuss and characterize strabismus, which literally means “to squint or look obliquely.”

Orthophoria refers to the ideal state of perfect ocular equilibrium. It means that the oculomotor apparatus is perfectly balanced, allowing the eyes to remain coordinated and aligned in all gaze positions and distances.

True orthophoric individuals maintain perfect alignment even when binocular vision is disrupted, such as when one eye is occluded. Because the majority of people have a minor latent deviation, orthophoria is uncommon (heterophoria).

Heterophoria is a repressed inclination for the eyes to wander. Fusional processes that provide binocular vision or prevent diplopia generally govern this latent deviation (double vision).

Only under particular circumstances, such as weariness, illness, or stress, or during testing, does the eye stray from its regular fusional ability (such as covering 1 eye).

If there is a lot of heterophoria, it might cause annoying symptoms such temporary diplopia (double vision), migraines, and asthenopia (eyestrain).

Normal people have some degree of heterophoria, which is normally asymptomatic.

Heterotropia is a permanent misalignment of the eyes. It happens because the fusional process is unable to control the deviation.

Depending on the subject, tropias might be unilateral or alternating between both eyes.

In an alternating tropia, neither eye has a preference for fixation, and both eyes drift at the same rate. Because each eye is used on a regular basis, eyesight develops normally. Because only one eye is constantly misaligned, unilateral tropia is a more dangerous condition.

The preferred eye becomes the deviated eye, resulting in amblyopia or loss of vision in the deviated eye.

The term “type of deviation” is commonly used to characterize ocular misalignments. This aids in determining the cause and treatment of strabismus.

To further distinguish the kind of strabismus, the prefixes eso-, exo-, hyper-, and hypo- are added to the terms phoria and tropia.

Inward or convergent deviations of the eyes, sometimes known as crossed eyes, are esophoria and esotropia.

Exophoria and exotropia are outward-facing or divergent eye deviations, with walleyed being the common name.

Upward and downward deviations of the eye are referred to as hyperdeviations and hypodeviations, respectively.

In cases of unilateral strabismus, the deviating eye is frequently mentioned as part of the misalignment description (left esotropia).

How are neurological conditions diagnosed through eye movement analysis?

A neurologic examination can be an important diagnostic tool because the eye is an extension of the brain.

The neuro exam lets you to check structures that are related to vision and can help you decide how urgent a patient’s ocular findings, such as visual field defects, cranial neuropathies, double vision, optic neuropathy, ptosis, pupillary abnormalities, and loss of vision, should be treated.

It may raise your clinical suspicion for underlying causes such as stroke, space-occupying lesion, and demyelinating disease.

Many illnesses involving the central nervous system cause abnormal eye movements.

Typically, such anomalies are described solely on the basis of gross clinical observations, such as the following:

Pursuit movements are examined by having the patient follow a flashlight that is gently moved back and forth in front of his eyes.

By asking the patient to look swiftly between two objects held to the right and left before his eyes, the capacity to fixate and refixate laterally displaced targets (movement of regard, saccadic movement) is tested.

The existence or absence of spontaneous nystagmus is detected in various gaze locations, but the magnitude and frequency are difficult to assess in this method.

Observing the eyes during such examinations is unquestionably an adequate tool for detecting major eye movement irregularities.

However, it is evident that more advanced methods for analyzing eye movements are not only more likely to yield accurate results, but they are also more likely to provide more accurate results.

How do neurologists assess a patient’s eye movements in a clinical setting?

Neurologists will ask a patient to follow their finger as it moves to the left or right and back again, or from top to bottom and back again, to test smooth pursuit.

Pursuit is a gradual, smooth eye movement that allows the fovea (i.e., central vision) to acquire the object, and it may be measured rather reliably at the bedside.

Saccades intrude during attempted pursuit (saccadic chase) when eye movements are abnormal, as is common in neurological patients. In terms of diagnosis, this is a very “non-specific” finding.

Neurologists measure saccades by placing both hands’ index fingers side by side or on top of each other, bending one at a time, and asking the subjects to look at the bent (or extended) finger.

The purpose of this test is to assess if saccades are initiated promptly in response to finger movements. Saccadic eye movements, in contrast to chase, are so quick, reaching angular speeds of up to 500–600 degrees per second in some situations, that they are impossible to assess accurately with the naked eye.

As a result, we must record saccades in order to accurately analyze their speed and the latency with which they are initiated.

Important clues come from a detailed and appropriate history, as with all elements of the neurological examination.

Patients with eye movement disorders may complain of double vision, in which case they should be asked if it is constant or intermittent; if it occurs, or is it maximal, in certain directions of gaze; what is the relationship of one image to the other; and if they have tried covering one eye, did that relieve the symptom.

Oscillopsia, or the illusion of movement of stationary objects, is a less commonly reported symptom in which it is necessary to determine whether the movement is horizontal or vertical, and whether it is more noticeable in certain gaze positions, such as in downbeat nystagmus, where the oscillopsia is most noticeable on down gaze.