Neuro-Visual Processing Rehabilitation for Visual Dysfunction

William V. Padula and Jonathan Jenness

BACKGROUND

Definitions

• Doctors of optometry are “independent primary health care providers who specialize in the examination, diagnosis, treatment, and management of diseases and disorders of the visual system, the eye, and associated structures as well as the diagnostics of related systemic conditions” [1].

• Doctors of ophthalmology are “physicians who specialize in the medical and surgical care of the eyes and visual system and in the prevention of eye disease and injury” [2].

• Neuro-Visual Processing Rehabilitation (NVPR), also referred to as Neuro-Optometric Rehabilitation (NOR), refers to development of an individualized treatment regimen for patients with visual deficits as a direct result of physical disabilities due to traumatic brain injury (TBI) and other neurological insults [3].

• Vision therapy and orthoptics are “a sequence of neurosensory and neuromuscular activities individually prescribed and monitored by the doctor to develop, rehabilitate, and enhance visual skills and processing. The vision therapy program is based on the results of a comprehensive eye examination or consultation, and takes into consideration the results of standardized tests, the needs of the patient, and the patient’s signs and symptoms. The use of lenses, prisms, filters, occluders, specialized instruments, and computer programs is an integral part of vision therapy. The length of the therapy program varies depending on the severity of the diagnosed conditions, typically ranging from several months to longer periods of time. Activities paralleling in-office techniques are typically taught to the patient to be practiced at home, thereby reinforcing the developing visual skills” [4].

• Neuro-Visual Postural Therapy (NVPT) “Following a brain injury the spatial visual process is often compromised and this affects posture, balance and spatial orientation. NVPT is a series of therapeutic activities performed by a clinician in conjunction with prism lenses that facilitates visual-spatial organization affecting balance and binocularity in individuals who have had a neurological event. The weight shift movements in conjunction with the prisms organize and ground the visual-spatial process with the proprioceptive base of support (BOS). This stabilizes the bi-modal visual process (neuro-visual process) and supports organization of the vestibular and kinesthetic systems” [3].

Symptoms related to visual dysfunction following a TBI may include: headache, diplopia, homonymous hemianopsia, vertigo, asthenopia, difficulty with focusing the eyes, movement of print when reading, tracking difficulty, photophobia, and blurred vision [5].

• Diplopia, typically due to binocular vision dysfunction, is quite prevalent following a TBI [6,7]. Binocular dysfunction may result in difficulties with balance, posture, and spatial orientation [3].

• Visual field defect/visual neglect

Homonymous hemianopsia, field loss affecting either the entire left or right field, is often seen in the setting of TBI [8,9].

Visual neglect is a lack of spatial conscious awareness in the absence of a homonymous hemianopsia [10].

Homonymous hemianopsia or visual neglect can induce a shift in visual egocenter, resulting in visual midline shift syndrome (VMSS) [3,10,11].

Normal Visual Processing

The bimodal visual system is composed of two visual processes. The focal visual process is oriented toward detail, identification, attention, and concentration. It isolates figure from the ground, is conscious, and is related to the functioning of the occipital cortex and associated cortices. The ambient or spatial-visual process is oriented toward spatial orientation, balance, posture, and movement, and is preconscious. It is mediated primarily at the midbrain, although the occipital cortex also plays a role [12,13]. The ambient visual process integrates information with the sensorimotor system [14].

Development of Posture

• Vision supports organization of balance and posture through the following processes:

The visual concept of egocenter (i.e., one’s own midline) is a function of interaction between the ambient visual process and the sensorimotor system [11,15].

Developmentally, vision matches information with the sensorimotor systems to organize the visual midline or egocenter to reinforce postural alignment with the proprioceptive system [16].

Feed forward cooperation occurs between the ambient visual process and sensorimotor system. It is used to initiate movement within a closed-loop system between midbrain and the cortices. The closed-loop system depends upon the correction of errors and recognition from performance-related feedback [12].

The ambient visual process is preconscious and serves as an anticipatory or readiness process following organization with the proprioceptive BOS. Following a brain injury, the spatial or ambient visual process can become compromised, affecting the component of vision that serves to establish the platform or base for higher conscious visual processing and perception. A compromise to the spatial-visual process affects child development. The compromise interferes with matching spatial-visual and proprioceptive information affecting postural alignment and weight shift [3].

Visual Processing Dysfunction

Refers to visual compromise due to central pathology. Two clinical syndromes are recognized:

• Post-Trauma Vision Syndrome (PTVS)

Following a neurological event the spatial-visual process can become compromised, binding the focal process to the ambient or spatial-visual process. This has been termed focal binding [3]. The result causes a variety of symptoms and binocular dysfunctions that are characteristic of compromise in the spatial-visual process such as:

Exotropia and exophoria [17–19]

Diplopia [6]

Accommodative insufficiency [20]

Convergence insufficiency [20]

Deficiency in saccadic eye movements and pursuit tracking [20]

Photophobia [20]

Postural changes associated with compensation of vision dysfunction [11,15]

Although symptoms and characteristics of binocular dysfunction are logically related to oculomotor nerve palsy, the mechanism for the cause of binocular dysfunction in the setting of PTVS appears to be related to trauma affecting the bimodal visual processing systems. Changes in visual evoked potential amplitude occur following treatment though use of base-in prisms and binasal occlusion. Following such treatment, a rapid decline in symptoms and syndrome characteristics may be seen. This condition has been termed PTVS [21].

• VMSS—Bimodal visual processing dysfunction affecting posture, balance, and postural tone are common following a TBI.

TBI affects the balance of the bimodal visual process, which can alter the visual midline or egocenter [17].

Common symptoms include perceived tilting of the floor, walls appearing to shift/move, drifting/leaning during ambulation, and abnormal weight shift [17].