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Vision Challenges with Vestibular Disorders

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Vision Challenges with Vestibular Disorders 5018 NE 15TH AVE · PORTLAND, OR 97211 · FAX: (503) 229-8064 · (800) 837-8428 · [email protected] · VESTIBULAR.ORG Vision Challenges with Vestibular Disorders By Michael C. Schubert, PT, PhD with the Vestibular Disorders Association, and contributions by Kenneth Ciuffreda, O.D., PhD, FCOVD-A and Allen H. Cohen, O.D., FCOVD A common complaint for people with patients consult with an optometrist who vestibular disorders is that they have specializes in Neuro-optometric difficulty with their vision. They may Rehabilitation. The neuro-optometric experience problems focusing on an object evaluation specifically assesses the visual, or perceive that objects are moving from ocular motor and focusing skills important side to side or revolving around them for stabilizing the sensory motor (vertigo). They may see their visual field components of the vestibule-ocular reflex jiggle or bounce during head motion (or “VOR”). (oscillopsia) or have double vision (diplo- pia). When they hold their heads still, HOW DO VESTIBULAR DISORDERS these visual instability problems might AFFECT VISION? resolve. The vestibular system and the visual Many people with vestibular disorders system coordinate with each other through consult an eye care professional due to brain pathways in order to control visual their visual symptoms. The typical eye fixation. The ‘ear to eye’ connection is examination is done while the patient’s known as the vestibulo-ocular reflex head is resting against a head rest, (VOR). The VOR has a critical role of thereby reducing the head motion, which keeping the eyes still during head motion. may mask the visual symptoms. With a This is known as gaze stability. The VOR vestibular disorder, the eyes may not be also sends a signal down to the postural the primary cause of the problem; muscles of the trunk/arms/legs, which is therefore the typical eye exam will not crucial for maintaining balance. identify any eye pathology or routine optical problems that would explain the Another way to explain this is to consider patient’s reported symptoms. the video camera. Video cameras have motion stabilizing equipment built into Visual acuity issues and/or functional them. This equipment stabilizes the visual visual skills deficits, such as focusing, eye world in order to capture a clear visual tracking and fixation and eye teaming scene even though natural motions of the coordination, may often trigger or hand holding the video camera would exacerbate vestibular symptoms. otherwise blur the image. In the case of a Therefore, it is recommended that these © Vestibular Disorders Association ◦ vestibular.org ◦ Page 1 of 6 deficient VOR, the eyes move during head reflexive motion of the eyes that includes motion, when they should instead be still. a fast and slow rotation; the eyes will appear to jerk one direction (fast) and HOW DOES THE VESTIBULO- then slowly reset in the opposite direction. OCULAR REFLEX WORK? Patients with a disrupted VOR commonly experience vertigo due to the asymmetry The inner ear includes a unique type of in firing rate between the left and right sensory hair cell that responds to head ear. They may also experience oscillopsia motion. When the head rotates, the hair during head motion, where objects in the cells move and this triggers the firing rate visual world appear to bounce/move in the vestibular (inner ear) nerve, which because the VOR is not able to keep the sends this signal to the brain, eye, and eyes still during head motion and the postural muscles. In the absence of objects therefore do not remain fixed on motion, both inner ears are still sending a the same point of the retina. Imbalance is signal to the brain, and the amount of also commonly experienced by those with signal from the left and right ears should a VOR deficit. be similar. Normally, this signal becomes asymmetric when the head rotates to one Interestingly, some patients with a side. For example, when the head turns vestibular disorder may also experience toward the right the firing rate from the photosensitivity (discomfort with bright right vestibular nerve increases while the light) and other vision problems such as: firing rate from the left vestibular nerve intense discomfort with flickering lights, decreases. The difference in firing rate is particularly fluorescent, sodium, or interpreted by the brain as a rotation (or mercury vapor lights, moving objects, motion) of the head and is used to provide rows of similar objects, such as in grocery stability to the eyes and postural muscles store aisles or lines of text on a page, or (i.e. balance) during head motion. busy, high contrast patterns, such as Therefore if the vestibular system is not polka dots or sunlight filtering through working properly in 1 ear (or both), then mini-blinds. Environments with a the brain does not receive correct combination of fluorescent lighting and information about head motion from the busy patterns or moving objects are vestibular nerves, and this results in especially problematic, which is why shop- symptoms such as vertigo, imbalance, or ping in large stores may be very difficult. oscillopsia. Even environments with subdued décor can be fatiguing if frequent head move- IMPACTS OF A DISRUPTED ments are required. Sometimes these VESTIBULO-OCULAR REFLEX symptoms of visual super-sensitivity are related to an unrecognized migraine A disrupted or impaired VOR can result in disorder1, and treatment aimed at abnormal vestibular nystagmus, a migraine prevention may be effective. © Vestibular Disorders Association ◦ vestibular.org ◦ Page 2 of 6 Other times, an abnormal vestibular such as by cupping their chin in their hand, system and migraine are the coupled in an effort to prevent tiny head culprits. movements—even those as small as are produced by a pulse. Reading text on a printed page can be difficult for people with an impaired VOR, People with vestibular disorders may also because the small head motion have an illusion of motion in their destabilizes gaze. The result is words and peripheral vision. A damaged VOR can also letters that appear to oscillate and shift cause nystagmus to worsen when the (see Figure 1). person looks to the right or left. In this case, looking over the shoulder while omit not a good backing up a car may be difficult. representation Peripheral vision distortions may especially Figure 1. For people with oscillopsia, tracking be problematic for a person who wears printed words on a page can require a great Progressive Add Lenses (PAL) and or deal of effort because of the distortion bifocals and has substituted eye rotation produced by even small head movements. instead of head motion in order to minimize those distortions. Although eyeglasses Reading text on a computer monitor may produce clear and consistent vision straight be a problem due to the heightened ahead, lens aberrations such as visual field sensitivity to screen flickering or scrolling curvature and distortion reduce visual pages of text. Many people with an clarity when a person looks through the impaired VOR resort to manually bracing side of a lens (Figure 2). Thus, if a person their head to reduce reading problems, A B C D Figure 2. Projection of a flat object (A) onto a curved surface causes straight lines to appear curved (B) as the power (curvature) of a lens increases, so does the correct farsightedness cause pincushion-type distortion (C) and glasses that correct nearsightedness cause a barrel-like distortion (D). © Vestibular Disorders Association ◦ vestibular.org ◦ Page 3 of 6 with glasses moves the eyes rather than water or air, known as the caloric test. The the head to scan, objects viewed to the side eye movements are recorded using small will appear to distort and move. Certain electrodes placed on the skin around the shapes of windshields in cars or vans eyes or with a video camera mounted to a may cause similar peripheral distortion goggle frame (known as video- at their edges. nystagmography or VNG). Rotation testing employs the same electrodes or goggles to Individuals with vestibular disorders often measure the relationship between the experience a visual dependence, where the velocity of the head and eyes during whole brain becomes extremely reliant on vision body rotation. to maintain balance. However, as a result Other tests measure function from the of a VOR defect, this may lead to vestibular system by exposing the subject symptoms when a person’s visual field is to a clicking noise, known as the vestibular overwhelmed (e.g., busy patterns on evoked myogenic potential (VEMP) test. wallpaper) or lacks a point of fixation (e.g. darkness, wide open spaces). Typical The vestibular function tests are comments from such patients include: administered and interpreted by trained . I cannot be in a crowd of people nor in specialists. Factors such as age, 2 wide-open spaces; both situations make medications, 3(p. 51) or systemic processes me feel disoriented and panicky. such as depression, 4 migraine, 5 or sleep . I often take a cart in a grocery store even deprivation6, 7 and even alertness can when I’m shopping for only one item. modify the VOR. I’ve become so frustrated I would rather just stay home. TREATMENT EVALUATION The first approach to resolving most of the vision problems affecting visual-vestibular The diagnosis of a vestibular disorder relies symptoms is to eliminate any ocular or on a combination of careful history of the functional visual problems such as eye problem, physical examination, and fixation and eye movement, focusing, and laboratory tests. The laboratory tests binocular teaming problems. An evaluation involve evaluation of the vestibular system by an optometrist (OD) is necessary to based on eye movements. For example, diagnose and treat these problems. electronystagmography (ENG) is a battery Depending on the vestibular diagnosis, of tests to measure brain and vestibular treatment may involve vestibular physical originated eye movements.
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