Vol. 15 Issue 20
Post Trauma Vision Syndrome
Disruption affects language and cognition
Post trauma vision syndrome (PTVS) results when traumatic brain injury (TBI), stroke, whiplash or other brain injury disrupts the balance between the ambient and focal visual systems. Visual details become prominent but spatially disorganized, while ambient, or peripheral, input is distorted. The normal balance of visual, proprioceptive, kinesthetic and vestibular input is disrupted, preventing information about balance and posture from being integrated with input from the peripheral visual system at the level of the midbrain.
Post trauma vision syndrome impacts language and cognition in a number of ways. The motor and sensory visual systems contribute to each communicative modality, as well as to language-related functional activities like telling time, counting money, and using the telephone.
"The increased time and effort that a person expends trying to process visual input becomes a distraction, and the visual system actually becomes over-stimulated," according to Heidi McMartin, MS, CCC-SLP, on staff at Chelsea Community Hospital in Chelsea, MI. "It's almost like there is noise in the system." Television and certain environments that contain a combination of sound, light and motion can be over-stimulating, she noted.
Attention, response latency, visual memory and thought organization also are affected in PTVS because of delays in language and thought processing and the distraction that results from an imbalance in the peripheral and central visual systems. "Patients appear to be distracted, and they have lapses in attention, even if they're just speaking or looking around their environment," McMartin said. "This resulting delay in processing negatively affects the storage and recall of what they've read, heard or seen."
Among the common symptoms of PTVS are esotropia, a loss of fusion or eye alignment caused by the inward turn of one eye, and exophoria, in which the eyes diverge and aim at a point beyond the point of focus, causing objects to become blurry even though the eyes are in alignment.
PTVS also may result in convergence insufficiency, or difficulty rotating the eyes medially to sustain focus for near tasks such as reading and writing. Symptoms of convergence insufficiency may include blurred vision, eye fatigue, and loss of place during reading and writing.
Another symptom of PTVS is a low blink rate, according to McMartin. "Blinking helps maintain our focus when we're performing sustained visual activities. A low blink rate can decrease the speed of processing by interfering with sustained focus and leading to longer fixations that hinder visual language processing."
Problems and confusion related to vision include the perception of moving words and objects. When patients read, words may appear to move at the margins. When they turn their head, objects may appear to move," said McMartin. These perceptions may be misinterpreted as cognitive deficits or a psychological disturbance.
"If the client complains of visual hallucinations, we're sometimes too quick to assume that it's a psychological impairment," she told ADVANCE. "But, in fact, these symptoms can occur in post trauma vision syndrome, because of an unstable peripheral visual system, or macular degeneration."
Problems focusing on stationary objects, such as words, as well as moving objects are only some of the many challenges faced by patients with PTVS. One of the more common impairments is a disrupted scanning pattern. Impaired scanning may be due to eye muscle imbalance, impaired eye alignment, or an imbalance between the peripheral and central visual systems.
Typically, when we read, our eyes fixate on one point, while our peripheral vision works to help us prepare to read the following words. In reading and writing, letter and word sequences often are perceived in a disordered manner or may overlap one another. PTVS may disrupt other visual functions as well, including depth perception and the ability to track a moving object and judge its distance and speed. This is crucial in situations such as crossing a road.
A lack of visual organization causes persons with PTVS to have difficulty orienting themselves within an environment, even a familiar one such as the home. "Their scanning pattern and spatial orientation are disrupted, so they have difficulty recalling the location of objects and places," explained McMartin.
PTVS also can occur in conjunction with visual midline shift syndrome (VMSS), where the vertical midline of the body is perceived as having shifted to the right or left. This can occur in an anterior or posterior direction as well, causing the person to lean forward or backward. Patients with right-hemisphere stroke and VMSS frequently will neglect their left visual field and functions on the left side of the body, such as arm and leg movement.
"Because our eyes direct our head movements, we will often cue right-hemisphere stroke clients to point their eyes at a target, rather than cueing them to turn their head, since their eyes don't always move when they turn their head," McMartin said.
Patients with neurogenic communication disorders can recover some level of function through neural reorganization, in which the unaffected areas of the brain adopt the functions of the damaged areas to recover lost skills.
"Vision rehabilitation seeks to improve visual-motor and visual-perceptual function through a combination of exercises and compensatory strategies," she said. Referral to a vision specialist such as a neuro-optometrist or neuro-ophthalmologist for a functional vision examination may be beneficial. This exam includes measuring eye movement abilities, eye focusing, eye aiming, binocular vision, eye-hand coordination, visual perception and visual-motor integration. Prescribed treatments may include the use of prism lenses, partial occlusive patching, and eye exercises to achieve optimal functional visual processing.
Post trauma vision syndrome often is overlooked by the interdisciplinary treatment team. When problems with vision are raised, professionals usually are concerned with visual acuity. "PTVS patients often don't even complain directly of visual problems," said McMartin. "Some people who have double vision will never mention it. They'll just say, 'My glasses don't work since I had the stroke.'" Information about the visual system and PTVS typically is not included in the academic curriculum for speech-language pathology.
Treatment by a vision therapist or occupational therapist for PTVS consists of strengthening the eye muscles, retraining the working parts of the visual system, and learning compensatory strategies.
"PTVS clients use their cognitive skills to make sense of distorted visual input," said McMartin. "For example, a person with double vision sometimes sees a ghost image of a word, but they can learn strategies to differentiate between what's real and what's not." Spontaneous recovery of visual function can occur up to 12 months after the brain injury. Recovery through rehabilitation is based on severity of the damage, overall patient health, and patient compliance with treatment recommendations.
Because PTVS impacts all aspects of independent functioning, treatment must be provided by an interdisciplinary team that includes a physician, neuro-optometrist or neuro-ophthalmologist, speech-language pathologist, and occupational, physical and recreational therapists. Early intervention for PTVS can reduce its impact on language function, cognition and independent living.
The speech-language pathologist can make a significant contribution to the rehabilitation of visual function by expanding and modifying traditional speech and language treatment materials and methods. Language activities that direct attention to visual detail, improve visual discrimination, and retrain scanning for reading are helpful, as is adjusting font size and spacing between letters and words.
By recognizing the signs and symptoms of PTVS, the speech-language pathologist can distinguish the deficits caused by language and cognitive impairments from those due to PTVS and identify error patterns in near-vision tasks.
Because one of the symptoms of PTVS is intolerance to light, rehabilitation therapists can help optimize lighting and monitor the degree of visual stimulation. Some patients also may have impaired contrast sensitivity, the inability to see object borders and differentiate objects from a background. For example, they may have difficulty seeing white potatoes on a white plate or white bathroom fixtures against a white wall. Each therapy discipline can modify the physical environment to enhance visual processing in all aspects of daily living.
"It's important that the entire rehabilitation team recognize visual impairments as they affect functional language, daily living skills, balance and mobility," said McMartin.
For More Information
• Heidi McMartin, (734) 222-8385, e-mail: firstname.lastname@example.org
• Neuro-Optometric Rehabilitation Association, online: www.nora.cc
Jason Mosheim is an Assistant Editor at ADVANCE. He can be contacted at email@example.com.