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Visual Midline Shift Syndrome

April

Visual Midline Shift Syndrome

by Dr. April Eryou

Visual Midline Shift Syndrome (VMSS) can occur following an insult to the brain. It is generally seen when the patient also present with a hemiparesis, hemiplegia or neglect, but can also be seen in patients post traumatic brain injury (TBI), with multiple sclerosis and with cerebral palsy. There are varying reports regarding the prevalence of VMSS. In a 2016 retrospective study by Tong et al, prevalence of VMSS was measured in TBI patients and in controls. 93% of TBI patients had some sort of VMSS and 13% of controls exhibited VMSS2. A retrospective study by Bansal et.al found 40% of acquired brain injury patients (TBI and cerebral vascular accident (CVA)) has VMSS3. In a study of only CVA patients, Padula et.al found over 70% of patients had VMSS4. VMSS occurs because of a dysfunction in how the ambient visual process is matched with sensorimotor information from the tactile, kinesthetic, proprioceptive and vestibular systems. The Ambient visual process is an M cell pathway from retina to lateral geniculate body to mid brains that is involved in a feedback loop with the sensorimotor systems. The ambient visual process generally helps answer the questions of “where” a person is in space. When there is a mismatch between the ambient visual information and sensorimotor information the results is poor balance, poor locomotion and impaired coordination. After a neurological injury occurs, information (proprioceptive) from both sides of the body can become mismatched when the information is stronger from one side compared to the other, this specifically occurs in hemiparesis, hemiplegia and neglect. The ambient visual system can try to help re balance the body by re-adjusting the body’s sense of midline to better match the information coming from each side of the body. This process generally occurs several days after the insult. The resulting adaptation presents in the patient as a shift in posture. The patient may complain of mobility problems, balance difficulties and challenges walking in a straight line. Observations of the patient’s movements and posture is very helpful for the diagnosis of VMSS. One would look to see if the patient appeared tilted to one side or another or tilted front/back. You could also look to see if the patient walked as though the floor is tilted. There are instruments such as NeurOpTrek that can help a practitioner quantify gait and balance changes that can occur with VMSS. To test for a horizontal VMSS, the examiner sits to one side of the patient; at about 40 cm away, the examiner moves a fixation target (pencil or wolff wand) from left to right and then right to left. The patient follows the target with only their eyes. The patient tells the examiner when they perceive the target as being centered between their two eyes. Consistent centering left or right of midline is considered a positive finding. To test for an anterior/posterior midline shift, the examiner again sits off the side; a target parallel to the floor is move from below the face to above the face and then from above the face to below. This time, the patient alerts the examiner when they perceive the target to be at their eye level. Repeatable centering above or below eye level is a positive finding. VMSS tend to be away from the affected side. Treatment would be the use of yoked prisms. When a midline shift occurs, the ambient visual system expands space on one side of the body and contracts space on the other side. The prisms are positioned to negate this special distortion. They would be prescribed in glasses and also used during the rehabilitation period to help the patient reset their visual midline. Visual-Motor activities done during neuro-optometric rehabilitation would done to rehabilitate VMSS. If the patient was too sensitive to prismatic distortions for prism to be use them in the rehabilitation process, left and right translucent filters could be used instead. Before prisms or filters are prescribed, in office trials should be done because some patients exhibit paradoxical responses. Paradoxical responses occur because the patient does not go through the adaptation process described above following the insult. Additionally, because VMSS is present in the “normal” population, trialing treatment options is important because VMSS only needs to be treated if it is causing a patient problems with function and/or performance.

2. Tong D, Cao J, Amanda B, Lin E. High prevalence of visual midline shift syndrome in TBI: a retrospective study. Vision Development & Rehabilitation 2016; vol2 issue3: 176-182.

3. Bansal S, Han E, Ciuffreda K. Use of yoked prisms in patients with acquired brain injury: A retrospective analysis. Brain Injury 2014;28:1441-

4. Padula W, Nelson C, Benabib R, Yilmaz T, Krevisky S. Modifying postural adaptation following a CVA through prismatic shift of visuo-spatial egocenter. Brain Injury 2009;23:566-76.