Eye movement analysis is a complicated area in Neurology and multiple sclerosis (MS). We take eye movements for granted, placing them somewhere on the awareness scale between waving one's hand to say hello and automatically activating chest muscles that assist with respiration.
There is willful action when we cooperate with commands to: "Look over here". One consciously trains one's gaze to the requested site. On the other hand, when one "has a look around" Sherlock Holmes style at a crime scene, one's eye movements may be unrehearsed or relatively spontaneous. Additionally, there is the subconscious world of sleep, with rapid eye movements (REM) that predominate dreaming.
So you may be asking: What does the above have to do with vertigo? Precisely on point, my dear Watsons out there in cyberspace. Whether a doctor is evaluating an MS patient with vertigo or any patient for that matter, eye movement review is critical to ascertaining why the patient has the problem.
In a sense, eye movements are windows to the cause of the vertigo. This spinning affliction made famous by Hitchcock in film is not itself a disease but a symptom of a process affecting the brain and related nervous system structures. Although many patients with vertigo may complain of feeling faint or light headed, the key to an accurate depiction of this phenomenon is the sensation of movement or perceived motion, i.e. the patient and/or the world around him is moving when normally, he would not appreciate it as such.
Eye movements together with retinal and brain processing of position change help us "right ourselves" in our worlds of solar system spin punctuated by individual and environmental motion. Many find riding in cars or boats to be triggers of vertigo, but as a result of compensatory reflexes, most do not experience it. Could you imagine if walking alone induced vertigo or observing something in motion caused dizziness in the viewer? Eye movements linked to our vestibular system which begins in the inner ear with nerve connections to our brain stem, cerebellum, spinal cord and the gaze centers in our cerebral cortex, help us diminish our feelings of rotation by working together to stabilize our position in space.
When the eye movements show excessive or unusual jerking at rest or with head position change or in response to looking in one direction or another (up, down or to either side), they answer certain questions as to why vertigo exists.
In MS (as in stroke, toxin exposure or brain cancer), damage to a vestibular nucleus in the brain stem or a nerve branch entering the brain stem from the Vllth cranial nerve can cause dizziness. In these situations, the inner ear also crucially involved in preventing the stabilizing sensations of motion, is normal. However, that same inner ear (called the semicircular canal) can be damaged by a virus, a bacteria or another autoimmune disorder other than MS such as Meniere's disease (MD). In this latter disorder, (more commonly seen in MS patients) changes in the inner ear fluid can disturb equilibrium. In MD, not only is there episodic vertigo, but attacks of tinnitus (ringing) and hearing loss are also noted.
The defective eye movement jerking in MS or in other conditions involving vertigo or perceived visual field jitter is called nystagmus. These jerks seen by the physician on examination are imperfect attempts by the nervous system to correct an abnormal situation. Our eyes tend to move together in a given direction (conjugately). In MS, if connections to nerves that will eventually stimulate eye muscles to move smoothly or direct gaze are inflamed, limitations in eye movement and nystagmus can result. One classic example in MS is a brain stem plaque that can limit the movement towards the midline of one eye and nystagmus with eye movement away from the midline in the other eye. This is called Internuclear Ophthalmoplegia (INO) due to a Medial Longitudinal Fasciculus (MLF) lesion. With conjugate movements of the eyes to the left, a right INO would prevent the right eye from moving to the center and would reveal the left eye jerking when looking to the left.
Although not typically associated with vertigo, INO symptoms can include oscillopsia (moving vision), particularly with gaze in a certain direction or double vision (diplopia) that resolves when one eye is covered. Nystagmus may also not be associated with symptoms despite being noted on examination.
To summarize: If you are dizzy, your problem may be due to an MS attack on the nerves in the brain stem that connect to the inner ear. Your doctor, on evaluating this condition, may find that you have abnormal involuntary jerking eye movements called nystagmus in one or both eyes. Along with dizziness or vertigo, double vision, moving vision, gait imbalance, nausea, vomiting, hearing loss or tinnitus can complicate the presentation.