Accommodative and pupillary dysfunctions in concussion/mild traumatic brain injury: A Review.

BACKGROUND: Visual dysfunctions are common in individuals following concussion/mild traumatic brain injury (C/mTBI). Many deficits have been uncovered in their oculomotor system, such as in the pupil and accommodation. OBJECTIVE: To describe the static and dynamic abnormalities in the pupillary and accommodative systems in those with C/mTBI. This includes both diagnostic and therapeutic aspects, with emphasis on objectively-based test findings, as well as their basic and clinical ramifications. METHODS: PubMed, Google Scholar, and Semantic Scholar databases were searched from 1980-2020, using key words of accommodation, pupil, vision therapy, vision rehabilitation, and objective testing, for peer-reviewed papers, as well as related textbooks in the area, in those with C/mTBI. RESULTS: For both systems, most static and dynamic response parameters were abnormal: they were typically reduced, slowed, delayed, and/or more variable. Most of the abnormal accommodative parameters could be significantly improved with vision therapy. CONCLUSIONS: For both systems, most response parameters were abnormal, which could explain their visual symptoms and related problems. For accommodation, the improvements following vision therapy suggest the presence of considerable visual system plasticity, even in older adults with chronic brain injury.

Objectively-based vergence and accommodative dynamics in mild traumatic brain injury (mTBI): A mini review.

Vergence and accommodation have been critical areas of investigation in those with mild traumatic brain injury (mTBI). In this mini-review, the major laboratory studies in the area using objective assessment of vergence and accommodative dynamics in this population are discussed. These include the basic findings, their diagnostic and therapeutic implications, potential study limitations, and suggested future research directions. All studies provided important new information, and insights, into the area. There were two key outcomes of the reviewed studies common to both the vergence and accommodative systems in those with mTBI. First, most dynamic parameter's responsivity at baseline was abnormal: it was slowed, delayed, and/or inaccurate as compared to the normative control data. Second, most of the abnormal dynamic parameter's responsivity could be remediated, at least in part, following a short period of oculomotor-based vision therapy, thus demonstrating considerable residual neuroplasticity in the damaged, human brain.

A Novel Computer Oculomotor Rehabilitation (COR) Program for Mild Traumatic Brain Injury (mTBI).

Individuals with traumatic brain injury (TBI) manifest a wide range of visual dysfunctions. One of the most prevalent involves the oculomotor system, which includes version, vergence, and accommodation. However, until recently, there has been no comprehensive, computer-based program for remediation of these oculomotor deficits. We present such an oculomotor rehabilitation program that has been tested in a clinical trial in patients having TBI with a high degree of success based on before-and-after objective system recordings, performance measures, and related visual symptomotology. The basic program components include a versatile stimulus package incorporating the attentional paradigm of rapid serial visual presentation (RSVP), the ability to add a visual and/or auditory distractor to the training to increase difficulty level ("task loading"), automated assessment of RSVP errors, and automated assessment of visual performance over the training period. Program limitations and future directions are also considered.

Short-term persistence of oculomotor rehabilitative changes in mild traumatic brain injury (mTBI): A pilot study of clinical effects.

PRIMARY OBJECTIVE: In our earlier published studies, oculomotor therapy (OMT) was performed in 15 individuals with mild traumatic brain injury (mTBI) and over 90% of the clinical oculomotor parameters abnormal at baseline significantly improved immediately following the OMT. There was no placebo (P) effect on any of the parameters. The purpose of the present pilot study was to assess the short-term persistence of the previously obtained positive OMT findings. RESEARCH DESIGN: Upon completion of the OMT, clinical oculomotor parameters were re-assessed at 3-month and 6-month periods. No subsequent training was performed during this 6-month period. METHODS AND PROCEDURES: Clinical measures were repeated in eight of the 15 subjects who subsequently completed both the 3-month and 6-month follow-up assessments. All measures were assessed using conventional clinical testing methods. MAIN OUTCOMES AND RESULTS: Eight of the 13 (62%) clinical oculomotor parameters exhibited either persistence of, or delayed, improvement at the 3 and 6 month follow-up intervals. CONCLUSIONS: Findings demonstrate both the presence and persistence of oculomotor-based changes, suggestive of neural plasticity even in the adult, compromised brain. Further studies are warranted to confirm and extend the present pilot findings.

Pupillary responses to light in chronic non-blast-induced mTBI.

PURPOSE: To evaluate objectively and quantitatively human pupillary responses to a light stimulus under photopic conditions in individuals with non-blast-induced, chronic, mild traumatic brain injury (mTBI). METHODS: Seventeen individuals with chronic, non-blast-induced mTBI and 15 visually-normal (VN) controls were tested (aged 21-45 years). Pupillary responsivity to a brief step-input light stimulus was assessed objectively in each eye for 5 seconds using the Neuroptics PLR-200 monocular, hand-held pupillometer with its pre-set and automated eight parameter analysis. RESULTS: Five of the eight parameters assessed were significantly reduced (p ≤ 0.05) in the mTBI group as compared to the VN control group: maximum (or peak) constriction velocity, average constriction velocity, average dilation velocity, maximum diameter and amplitude of constriction. The remaining three parameters were similar in each group (p > 0.05): constriction latency, 75% dilation recovery time and minimum diameter. CONCLUSIONS: The slowed dilation dynamics and reduced maximum pupillary diameter in mTBI suggest deficiency primarily of the sympathetic control system. The reduced peak velocities and related amplitudes suggest subtle parasympathetic involvement.

Proposed objective visual system biomarkers for mild traumatic brain injury.

The challenge and search for objectively based biomarkers to assess for the presence of concussion/mild traumatic brain injury is a high priority for the military establishment. We present a documented overview of specific test areas and related targeted, high-yield, objectively based parameters that may be potential "vision biomarkers" for the detection of concussion/mild traumatic brain injury based on results from our laboratory and others, with emphasis on oculomotor aspects. These findings have military relevance with respect to the initial diagnosis in the battlefield and in the far-forward medical facilities, pre-/postdeployment issues, pre-/postvisual rehabilitation evaluation, fitness-for-duty assessment, and establishment of a return-to-duty timeline.

Effect of oculomotor rehabilitation on accommodative responsivity in mild traumatic brain injury.

Accommodative dysfunction is a common oculomotor sequelae of mild traumatic brain injury (mTBI). This study evaluated a range of dynamic (objective) and static (subjective) measures of accommodation in 12 nonstrabismic individuals with mTBI and near vision-related symptoms before and after oculomotor training (OMT) and placebo (P) training (6 wk, two sessions per week, 3 h of training each). Following OMT, the dynamics of accommodation improved markedly. Clinically, there was a significant increase in the maximum accommodative amplitude both monocularly and binocularly. In addition, the near vision symptoms reduced along with improved visual attention. None of the measures were found to change significantly following P training. These results provide evidence for a significant positive effect of the accommodatively based OMT on accommodative responsivity. Such improvement is suggestive of oculomotor learning, demonstrating considerable residual brain-visual system plasticity in the adult compromised brain.

Versional eye tracking in mild traumatic brain injury (mTBI): effects of oculomotor training (OMT).

OBJECTIVE: To evaluate a range of objective measures of versional eye movements before and after oculomotor training (OMT) in individuals with mTBI. The results were compared with placebo (P) training. METHODS: Twelve individuals with mTBI (mean age = 29 ± 3 years) having oculomotor-based near-vision symptoms participated in the study. Versional eye movements were recorded objectively before and after OMT (fixation, predictable saccades, simulated reading) and P training (6 weeks each, two sessions/week, 45 minutes/session). RESULTS: Following OMT, there was a significant (p < 0.05) reduction in the horizontal fixational error. Saccadic gain increased both horizontally and vertically (p < 0.05). The saccade ratio for the simulated reading, multiple-line paradigm reduced significantly (p < 0.05). None of the measures changed significantly following the P training. CONCLUSIONS: The versional-based OMT had a significant, positive effect on most aspects of versional tracking. These findings are suggestive of improved rhythmicity, accuracy and sequencing of saccades following OMT in mTBI as a result of oculomotor learning.

Effect of oculomotor vision rehabilitation on the visual-evoked potential and visual attention in mild traumatic brain injury.

PRIMARY OBJECTIVE: The purpose of the experiment was to investigate the effect of oculomotor vision rehabilitation (OVR) on the visual-evoked potential (VEP) and visual attention in the mTBI population. RESEARCH DESIGN AND METHODS: Subjects (n = 7) were adults with a history of mild traumatic brain injury (mTBI). Each received 9 hours of OVR over a 6-week period. The effects of OVR on VEP amplitude and latency, the attention-related alpha band (8-13 Hz) power (µV(2)) and the clinical Visual Search and Attention Test (VSAT) were assessed before and after the OVR. RESULTS: After the OVR, the VEP amplitude increased and its variability decreased. There was no change in VEP latency, which was normal. Alpha band power increased, as did the VSAT score, following the OVR. CONCLUSIONS: The significant changes in most test parameters suggest that OVR affects the visual system at early visuo-cortical levels, as well as other pathways which are involved in visual attention.

Oculomotor neurorehabilitation for reading in mild traumatic brain injury (mTBI): an integrative approach.

BACKGROUND: Considering the extensive neural network of the oculomotor subsystems, traumatic brain injury (TBI) could affect oculomotor control and related reading dysfunction. OBJECTIVE: To evaluate comprehensively the effect of oculomotor-based vision rehabilitation (OBVR) in individuals with mTBI. METHODS: Twelve subjects with mTBI participated in a cross-over, interventional study involving oculomotor training (OMT) and sham training (ST). Each training was performed for 6 weeks, 2 sessions a week. During each training session, all three oculomotor subsystems (vergence/accommodation/version) were trained in a randomized order across sessions. All laboratory and clinical parameters were determined before and after OMT and ST. In addition, nearvision-related symptoms using the Convergence Insufficiency Symptom Survey (CISS) scale and subjective visual attention using the Visual Search and Attention Test (VSAT) were assessed. RESULTS: Following the OMT, over 80% of the abnormal parameters significantly improved. Reading rate, along with the amplitudes of vergence and accommodation, improved markedly. Saccadic eye movements demonstrated enhanced rhythmicity and accuracy. The improved reading-related oculomotor behavior was reflected in reduced symptoms and increased visual attention. None of the parameters changed with ST. CONCLUSIONS: OBVR had a strong positive effect on oculomotor control, reading rate, and overall reading ability. This oculomotor learning effect suggests considerable residual neuroplasticity following mTBI.

The effect of retinal defocus on simple eye-hand and eye-foot reaction time in traumatic brain injury (TBI).

PRIMARY OBJECTIVE: The purpose of the experiment was to assess the effect of retinal defocus on simple eye-hand (E-H) and eye-foot (E-F) reaction time (RT) in traumatic brain injury (TBI). DESIGN AND METHODS: Sixteen subjects with traumatic brain injury (five males and 11 females; aged 22-34 years) participated in the experiment. These were compared with 16 visually-normal, age/gender-match subjects. Retinal defocus was introduced optically (plano, +1, +2, +3, +4, +10D and +2D × 90) in the spectacle plane with binocular viewing. E-H and E-F RT were assessed binocularly using the RT-2S Simple Reaction Time Tester (Advanced Therapy Products, Glen Allen, VA). The test target colour and angular subtense simulated a conventional red/green traffic signal at 120 feet. RESULTS: There was no significant effect (p > 0.05) of retinal defocus on either E-H or E-F RT in each population. There was a significant effect (p < 0.05) of TBI on both E-H and E-F RT as compared with the normative data, with it being longer and more variable in TBI. Each RT condition was longest in those with moderate TBI. CONCLUSIONS: Both RTs were robust to retinal defocus, thus suggesting central nervous system insensitivity for this simple RT task. However, the increased RTs and related variability found in TBI, especially in moderate TBI, have potential safety implications (e.g. driving a car, ambulating).

Visual fatigue effects on vergence dynamics in asymptomatic individuals.

PURPOSE: To evaluate objectively changes in vergence dynamics following intentional visual fatiguing tasks using congruent (C) and non-congruent (NC) vergence stimulus demands. METHODS: Pre- and post-task vergence dynamics to a 10.3° disparity stimulus were recorded objectively in 12 adult, asymptomatic individuals for both convergence and divergence. There were two fatigue-inducing tasks: Congruent or C-task: Subjects altered bifixation (50 cycles) between reduced Snellen charts at 2 m and at 20 cm every 3 s. Non-congruent or NC task: Subjects performed 50 cycles of vergence flipper (7Δ BO/BI), while bifixating a reduced Snellen chart at 40 cm. Pre- and post-task mean amplitude, time constant, peak velocity, and steady-state response variability were compared. RESULTS: There was a significant increase in mean post-task, steady-state response variability for both the C and NC tasks. However, there were no significant group differences for either convergence or divergence between the pre- and post-mean amplitude, time constant, and peak velocity parameters for both the C and NC tasks, although post-task peak velocity was consistently reduced. CONCLUSIONS: Steady-state vergence response variability was found to be the critical objective parameter to demonstrate significant fatigue effects in the group. Peak velocity was also consistently reduced to a small extent in the NC task. We speculate that these fatigue effects are of a central, and not of peripheral, origin.

Visual fatigue and accommodative dynamics in asymptomatic individuals.

PURPOSE: To evaluate accommodative dynamics immediately before and after visual fatigue-inducing tasks with congruent (C) and noncongruent (NC) visual stimuli. METHODS: Accommodative dynamics for a 2-diopter (D) step (2.5 ↔ 4.5 D) stimulus were assessed using the WAM-5500 open-field autorefractor in 10 visually normal, asymptomatic, young-adult subjects before and after C and NC tasks performed on different days in a counterbalanced manner. For the C task, subjects altered binocular fixation (50 cycles) between reduced Snellen charts at 50 and 20 cm every 3 seconds to the beat of a metronome. For the NC task, subjects performed 50 cycles of accommodative flipper (± 1.5 D) as rapidly as possible while binocularly fixating on a reduced Snellen chart at 40 cm. RESULTS: Mean steady-state (SS) response level reflecting its accuracy was significantly (p ≤ 0.05) reduced post-NC task for both increasing (4.5-D level) and decreasing (2.5-D) accommodation. Although the SS response variability was significantly (p ≤ 0.05) increased post-NC task at the 4.5-D stimulus level, it did not change significantly (p > 0.05) for the C task. There were no significant differences between the pretask and posttask group mean initial amplitude, time constant, and peak velocity for either the C or the NC task for both increasing and decreasing accommodation. CONCLUSIONS: The accommodative system exhibited consistent fatigue effects with respect to SS variability and response accuracy. There was no objective evidence of oculomotor learning for these specific tasks.

Effect of oculomotor rehabilitation on vergence responsivity in mild traumatic brain injury.

A range of dynamic and static vergence responses were evaluated in 12 individuals with mild traumatic brain injury (age: 29 +/- 3 yr) having near vision symptoms. All measures were performed in a crossover design before and after oculomotor training (OMT) and placebo (P) training. Following OMT, peak velocity for both convergence and divergence increased significantly. Increased peak velocity was significantly correlated with increased clinically based vergence prism flipper rate. Steady-state response variability for convergence reduced significantly following OMT. The maximum amplitude of convergence, relative fusional amplitudes, and near stereoacuity improved significantly. In addition, symptoms reduced significantly, and visual attention improved markedly. None of the measures were found to change significantly following P training. The significant improvement in most aspects of vergence eye movements following OMT demonstrates considerable residual brain plasticity via oculomotor learning. The improved vergence affected positively on nearwork-related symptoms and visual attention.

Vergence in mild traumatic brain injury: a pilot study.

Vergence dysfunction in individuals with mild traumatic brain injury (mTBI) may have a negative effect on quality of life, functional abilities, and rehabilitative progress. In this study, we used a range of dynamic and static objective and subjective measures of vergence to assess 21 adult patients with mTBI and nearwork symptoms. The results were compared with 10 control adult subjects. With respect to dynamic parameters, responses in those with mTBI were slowed, variable, and delayed. With respect to static parameters, reduced near point of convergence and restricted near vergence ranges were found in those with mTBI. The present results provide evidence for the substantial adverse effect of mTBI on vergence function.

Vergence dysfunction in mild traumatic brain injury (mTBI): a review.

Vergence eye movements are used to track objects that move in depth in one's binocular visual field to attain and maintain a fused and single percept. The mechanism and control of vergence eye movements involves complex neurological processes that may be compromised in individuals with traumatic brain injury, thus frequently resulting in a wide range of vergence dysfunctions and related near-work symptoms, such as oculomotor-based reading problems. This paper presents a review of the vergence system and its anomalies in mild traumatic brain injury, as well as their diagnostic and therapeutic clinical ramifications. Implications related to brain imaging and human neuroplasticity are also considered.

Accommodation in mild traumatic brain injury.

Accommodative dysfunction in individuals with mild traumatic brain injury (mTBI) can have a negative impact on quality of life, functional abilities, and rehabilitative progress. In this study, we used a range of dynamic and static objective laboratory and clinical measurements of accommodation to assess 12 adult patients (ages 18-40 years) with mTBI. The results were compared with either 10 control subjects with no visual impairment or normative literature values where available. Regarding the dynamic parameters, responses in those with mTBI were slowed and exhibited fatigue effects. With respect to static parameters, reduced accommodative amplitude and abnormal accommodative interactions were found in those with mTBI. These results provide further evidence for the substantial impact of mTBI on accommodative function. These findings suggest that a range of accommodative tests should be included in the comprehensive vision examination of individuals with mTBI.

Effect of vergence adaptation and positive fusional vergence training on oculomotor parameters.

PURPOSE: Clinical studies have shown that positive fusional vergence (PFV) can be trained through a program of orthoptic exercises. Models of accommodation and vergence predict that training PFV would require a reduction in the convergence accommodation (CA) cross-link. Recent investigations have found that the CA/C ratio is not changed in a clinical population after orthoptics. We hypothesized that such orthoptic programs may instead act to reduce CA through changes in the relationship between fast and slow vergence components. METHODS.: Eleven visually normal subjects were tested. Phoria adaptation to a 12-Delta base-out (BO) wedge prism and the resulting CA responses were monitored every 3 min for 15 min to a DoG target at 0.4 m. These measures were repeated after 2 weeks of orthoptics. Phorias, stimulus accommodative convergence (AC)/A and CA/C ratios, and PFV amplitudes at near were also determined. Before the orthoptics program, these measures were repeated under "adapted" conditions. RESULTS: Phoria adaptation following prolonged viewing through the 12-Delta BO wedge prism was associated with a concomitant reduction in the CA. These changes were asymptotic over time with 95% of the change occurring within the first 3 to 6 min. After 2 week of orthoptics, the rates and magnitudes of both phoria adaptation and CA reduction increased significantly (p < 0.01). PFV at 40-cm limits showed increases with orthoptics and under vergence adaptation. CA/C and AC/A ratios were unchanged after orthoptics, but the former was reduced, and the latter increased under the vergence adapted condition. CONCLUSIONS: Orthoptics acts to change the time constant and magnitude of vergence adaptation to BO prisms, which leads to a concomitant reduction of CA over a similar time course. This process appears to underlie the increase in positive fusion limits. Although reductions in CA/C ratio occur under the vergence adapted state, this ratio is not directly changed with orthoptics.

Static and dynamic aspects of accommodation in mild traumatic brain injury: a review.

Accommodation refers to the process of obtaining and maintaining a focused foveal retinal image of an object of interest. It involves optical, sensory, motor, perceptual, cognitive, pharmacologic, and biomechanical aspects, and hence represents a complex, multilevel neurologic control process. In patients with mild traumatic brain injury (mTBI), this process frequently is disrupted and compromised neurologically because of the pervasiveness of the coup-contrecoup, swelling, and shearing aspects of the brain injury. In this report, we review the earlier literature on accommodation in mTBI and then present several new findings from our clinical research unit, along with their clinical implications.