|Year : 2019 | Volume
| Issue : 2 | Page : 109-115
The effect of binocular peripheral vision blocks (partial and complete), on balance in healthy young Indian adults: An experimental study
Apeksha Besekar, Vimal Telang
Department of Physiotherapy, All India Institute of Physical Medicine and Rehabilitation, Mumbai, Maharashtra, India
|Date of Submission||07-Feb-2019|
|Date of Decision||14-May-2019|
|Date of Acceptance||14-Oct-2019|
|Date of Web Publication||30-Dec-2019|
Dr. Apeksha Besekar
Department of Physiotherapy, All India Institute of Physical Medicine and Rehabilitation, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
QUESTION: How does the dynamic balance during functional tasks change with partial and complete peripheral vision blocks (CPVBs) as compared to full vision and no vision?
DESIGN: Randomized, within-participant experimental study.
PARTICIPANTS: Sixty young Indian adults (18–39 years) with normal 6/6 vision.
METHODS: Dynamic balance was tested and compared in functional activities on a long force plate (Neurocom Smart Version 8.6 Balance Master) with eyes open (EO), partial peripheral vision blocks (PPVB), Complete peripheral vision blocks (CPVB), and eyes closed (EC).
OUTCOME MEASURES: Center of gravity (COG) sway velocity in Sit to Stand (STS); Movement Time in Step up and Over (SUO); Step length, Step width and Speed in Walk Across (WA).
RESULTS: (1) Walk across: A significant linear trend was observed in the reduction of step length when the visual alterations were intensified, and there was no significant difference between EO versus PPVB (d = 0.06, 95% confidence interval [CI] - 1.78–3.41). With CPVB versus EC (d = 0.35), walking speed showed a considerable decrease. (2) Step quick turn: No significant difference between (a) turn time (EC vs. CPVB: d = 0.28; EO vs. PPVB: d = 0.13) and (b) turn sway (EC vs. CPVB: d = 0.24; EO vs. PPVB: d = 0.09). (3) Sit to stand: The sway velocity was least with CPVB with a nonsignificant linear trend (P = 0.71). (4) Step up and over: A clinically significant difference was obtained in EO versus EC, EC versus CPVB and EC versus PPVB but not with EO versus PPVB, EO-CPVB and PPVB versus CPVB.
CONCLUSION: These results reveal that in the normal young population, balance performance deteriorates as the availability of peripheral vision decreases, to the extent that in some functional activities, dynamic balance with CPVB is similar to the EC condition.
Keywords: Binasal occlusion, central vision, dynamic balance, peripheral vision, static balance
|How to cite this article:|
Besekar A, Telang V. The effect of binocular peripheral vision blocks (partial and complete), on balance in healthy young Indian adults: An experimental study. Physiother - J Indian Assoc Physiother 2019;13:109-15
|How to cite this URL:|
Besekar A, Telang V. The effect of binocular peripheral vision blocks (partial and complete), on balance in healthy young Indian adults: An experimental study. Physiother - J Indian Assoc Physiother [serial online] 2019 [cited 2020 May 28];13:109-15. Available from: http://www.pjiap.org/text.asp?2019/13/2/109/274289
| Introduction|| |
Numerous studies have shown that the stimulation of visual, proprioceptive, or vestibular systems evoke body sway. The availability of visual information can reduce postural sway by as much as 50%. On a firm surface, healthy controls rely 70% on somatosensory information, 20% vestibular, and 10% on vision; but on an unstable surface, they rely 60% on vestibular information, 30% visual and 10% on somatosensory information. Mechanism by which vision helps postural stabilization is the detection of visual motion. Visual motion can be either efferent, i.e., objects are moving in the environment, or efferent, i.e., consecutive to movements of the eyes, body, or head. The sensory system and the development of the individual senses occur in the afferent and efferent motion perception. The afferent motion perception consists of the focal system, also known as central vision which specializes in object motion perception and object recognition and ambient or peripheral vision which is sensitive to movement scene and is thought to dominate both perceptions of self-motion and postural control.
The peripheral visual field is defined as the visual field minus the foveal part. Central/foveal vision is about static details and outcome. Peripheral vision is the lion's share of vision and is at the heart of awareness of, and response to, the total space volume of our visual environment and all its inhabitants. The visual system, led by peripheral vision, also gives information about our posture and state of motion. However, unlike the vestibular system, the visual system also gives information about our state of motion at constant speeds and the status of our surroundings, i.e., the volume of space around us and the inhabitants of that space. What is it? How big is it? What distance (and therefore time) separates us from it? In which direction is it moving? What relationship does it have to the immediate circumstances? These types of questions can be accurately answered by well-tuned peripheral awareness.
The enhancement of peripheral visual awareness can be achieved with binasal occlusion, which incorporates typically placing the tapes in the nasal visual fields so that they do not go past the limbus. A case study on an adult with cerebral palsy reported successful use of binasal occlusion, as by occluding the middle of the binocular nasal field, there was an effect on binocular integration. This acts as a persistent change in the individual's central visual space forcing them to alter the way they handle the world. It also makes one more dependent on peripheral clues. It reduces confusion and helps stabilize the image, helping the patient to understand where they are in their personal visual space and how to adjust to changes regarding that space.
To avoid the interference of the age-related degenerative changes occurring in the sensory system, young participants were selected for the study. Hence, the question which arises here is, does the dynamic balance during functional tasks change with partial and complete peripheral vision blocks (CPVB) when compared to full vision (FV) and no vision (NV) while keeping the somatosensory and the vestibular inputs as the independent variables?
| Methods|| |
This study was a randomized, within-participant experimental study.
Flow of participants
The study included a onetime assessment with the four visual field modifications for each subject. Each protocol was performed thrice, and the average of the three readings was statistically analyzed.
On approval by the institutional ethical committee and after a written informed consent, 60 normal young Indian adults (18–39 years) (30 males and 30 females) with 6/6 vision tested by Snellen's Optometric chart were assessed in the Physiotherapy Department of All India Institute of Physical Medicine and Rehabilitation (AIIPMR), Mumbai, India.
Young adults with congenital acquired or symptomatic musculoskeletal, neurological, cardiovascular, vestibular or visual impairments or with any current or past medical diagnosis of injury or medications affecting balance were excluded from the study.
All the tests were performed by the same evaluator and standardized in terms of positioning and testing.
Centers through the study
Physiotherapy Department, AIIPMR, Mumbai, India.
How does dynamic balance during functional tasks change with partial and CPVBs as compared to FV and NV?.
Testing of the static and dynamic balance in functional activities was done with four visual field conditions, namely eyes open (EO), eyes closed (EC), complete peripheral vision blocks (CPVB). [Figure 1], and partial peripheral vision block (PPVB) [Figure 2]. For restricting the peripheral vision completely pinhole lenses with an aperture of 1.2 mm were used. The focus was set after making the subject wear the trial frame and adjusting the inter-pupillary distance using the trial frame. For restricting the peripheral vision partially, binasal occluders were placed on the trial frame in the form of the black paper applied just nasal to the pupil or Hirschberg reflex. Care was taken to provide the “adaptation period” after blocking visual fields prior to each assessment. The balance was assessed using the NeuroCom Balance Master® force platform system on a long force plate.
The following dynamic balance protocols were tested with each of the above-mentioned four visual field conditions.
Walk across: Participants were asked to walk across the force plate, which measured the average step length and the subject's gait speed. Step-Quick-Turn (SQT): The participant was instructed to take two forward steps on command, and then quickly turn 180° to either the left or right direction and return to the starting point, this separately measured, the time required to execute the turn, velocity of center of gravity (COG) sway during the turn for each direction of turning. Sit to Stand (STS) activity documented control of the COG over the base of support during the rising phase and for 5 s thereafter. Step-up-and-over (SUO): This test quantifies the participant's ability to control their body weight and postural stability while stepping up onto a 20 cm height curb with one foot and swinging the other foot over the curb while lifting the body through an erect standing position as quickly as possible, and then lower the bodyweight to land the swing leg as gently as possible. Movement Time was obtained which quantifies the number of seconds required to complete the maneuver, beginning with the initial weight shift to the nonstepping (lagging) leg and ending with the impact of the lagging leg onto the surface.
The outcome measures to compare the effect of four visual conditions were subjected to tests for normality distribution using Shapiro–Wilk test, and as the data came out to be normally distributed, repeated measures ANOVA was performed. Post hoc analysis was done using Test for Linear trend, and significance was established (P < 0.05). Effect size (Cohen's d) was calculated with 95% confidence interval (CI).
| Results|| |
During the activity of walk across, a significant linear trend was observed in the reduction of step length when the visual alterations were intensified (reduced). It is worth mentioning that there was no significant difference between the EO and the PPVBs (Cohen's d = 0.06, 95% CI − 1.78–3.41) conditions [Figure 3]; [Graph 1] and [Table 1].
|Figure 3: Participant performing the walk across activity wearing blindfolds, i.e., eyes closed|
Click here to view
The step width did not show any significant linear trend and difference with the visual conditions. Cohen's d ranged from 0.03 to 0.14 [Graph 2] and [Table 2].
Walking speed showed a considerable decrease and a significant linear trend when the participants walked with CPVBs and EC, with Cohen's d = 0.35 and 95% CI − 7.9 to − 2.9 [Graph 3] and [Table 3].
Step quick turn
When the participants performed SQT activity, a significant linear trend with turn sway and turn time was observed. It is found that there was no significant difference between the EC and CPVB as well as between EO and PPVB for (a) as (b). turn time (EC and CPVB: Cohen's d = 0.28 with 95% CI 0.04–0.28; EO and PPVB: Cohen's d = 0.13 with 95% CI − 0.07–0.18) and (b) turn sway (EC and CPVB: Cohen's d = 0.24 with 95% CI 1.64–5.90; EO and PPVB: Cohen's d = 0.09 with 95% CI − 0.70–4.24) [Graph 4] and [Graph 5]; [Table 4].
Sit to stand
After completion of the STS activity, the sway velocity was least with the CPVB, and this was significantly lower than with EO, PPVBs, and as well as with EC. Linear trend was not found significant (P = 0.71) [Graph 6] and [Table 5].
Step up and over
During the performance of SUO activity results showed a significant linear trend and a clinically significant difference was obtained in conditions: EO versus EC (Cohen's d = 0.72 with 95% CI − 0.26 to − 0.11), EC versus CPVB (Cohen's d = 0.5 with 95% CI 0.06–0.22) and EC-PPVB (Cohen's d = 0.48 with 95% CI 0.05–0.22) but no clinical significance in the EO-PPVB (Cohen's d = 0.18 with 95% CI − 0.10–0.01), EO-CPVB (Cohen's d = 0.19 with 95% CI − 0.09–0.007), and PPVB-CPVB (Cohen's d = 0 with 95% CI − 0.05–0.06) [Figure 4]a and [Figure 4]b and [Graph 7]; [Table 6].
|Figure 4: (a and b) Step up and over with complete peripheral vision blocks|
Click here to view
| Discussion|| |
Postural control is no longer considered one system or a set of righting and equilibrium reflexes. Rather, postural control is considered a complex motor skill derived from the interaction of multiple sensorimotor processes. Previous studies, consider the effects of altered visual and somatosensory information only on static balance; however, most of the functional day-to-day activities require dynamic balance.
The aim of this study was to observe the effect of binocular partial and CPVBs, FV, and NV on dynamic balance in young healthy Indian adults. In the following sections, the results of this experiment are discussed.
When the participants performed the walk across activity, step length with EC was significantly less than that in the EO, PPVB, and CPVB conditions. As the visual alterations were intensified (reduced) a significant linear trend showed a consistent reduction in the step length. It is worth mentioning that there was no significant difference between the EO and the PPVBs.
Concomitant with the reduced step length, there was a reduction of speed along with a similar linear trend. Nonsignificant change in step width with progressive reduction in visual fields was probably because participants were young, and the test distance (length of the force plate) was only 1.5 m. Furthermore, the reduction of step length and speed was sufficient to maintain the dynamic balance. This emphasizes the role of peripheral vision in functional activities such as walking even on level ground.
Similarly, there was a significant linear trend and increase in the turn sway and turn time in the CPVB versus PPVB for SQT: This again emphasizes the role of peripheral vision in performing dynamic tasks such as turning in day-to-day activities. Studies were done by Lenoir and Mazyn (2005) on discus throwing, state that while turning it might be that there is simply no time to process the information from the central visual field in a conscious way, and that information from the periphery is more suitable in this task. Surprisingly, it is seen that after performing the STS activity the sway velocity was least with the CPVB. Moreover, this was significantly lower than the EC and PPVB. With only central vision available, participants could be probably freezing on standing still after STS. Reduction in the sway velocity measured at the end of activity could be explained because of the probable stress reaction of only pinhole vision and the vertical acceleration from sitting position to a standing one.
Gallop has stated that peripheral vision is intimately related to the brainstem areas which control vital functions such as blood pressure, heart rate, and respiration. Therefore, peripheral vision can be considered as a survival mechanism, letting us know if our surroundings are threatening to us. Stressful situations arouse the sympathetic nervous system, which among other things causes dilation of the pupils. This allows for more light to enter and reach a greater area of the retina which may provide a wider range of information about the environment. If peripheral awareness is at a desirable level of functioning in the first place, two things may occur. First, there will be fewer stressful events since there will be fewer surprises in the environment, and second, the ability to react to and make closure with such events will be more efficient.
In the activity of SUO, which is akin to crossing obstacles no significant reduction in movement time was observed as long as some form of vision was present, i.e., central (CPVB) or peripheral (PPVB, EO) as soon as the total vision was blocked the movement time increased.
The results of this study indicate that the adaptations occurred to increase kinesthetic information and compensate for unreliable/incomplete visual information. These adaptations may be associated with the risk or fear of falls since the dynamic balance can be greatly impaired by the loss of afferent visual information.,,
Retinal neuroanatomy reveals the importance of peripheral function. The overall ratio of rods to cones is 17:1 with a concentration of rods in the near periphery equaling that of the cones in the fovea (150,000/mm2). In the fetal development, peripheral retina develops in advance of central retina. 20% of the fibers that make up the optic nerve go directly to the lower (postural) centers in the brain rather than to visual centers as do the other 80%. However, those 20% represent up to 80% of the area of the retina-the peripheral retina.
Gallop stated that because of reduced peripheral awareness, there is more likeliness to bump into things, lose track of the context in information-gathering activities, and have difficulty with athletic performance.
In the present study, balance performance changed by blocking the visual fields and changing the somatosensory input in the young adult population, thus indicating that the tasks become challenging with the reduction of visual and somatosensory input. Hence, change of visual field conditions and somatosensory input can be used for training balance.
The loss of peripheral vision is seen commonly in patients with ophthalmic conditions such as glaucoma and retinitis pigmentosa. Kotecha et al. published a study titled “Balance Control in Glaucoma” where postural stability was examined in glaucoma patients and participants with no ocular disease. The difference in sway between firm and foam standing evaluated the relative somatosensory contribution to balance. Results showed that glaucoma patients had a lower visual contribution to sway, and higher relative somatosensory contribution to sway. These patients displayed differences in their visual and somatosensory contributions to quiet standing balance compared with controls, associated with the degree of binocular visual field loss. This suggested that balance control may be compromised in this patient group.
The young participants were aware of the test conditions in advance, allowing the anticipatory postural adjustments and strategies with the reduction of visual inputs. However, with an unanticipated perturbation internal or external, the reactive adaptations may be different, which needs to be studied separately. Furthermore, degenerative changes with aging in the different systems are expected to reflect on the dynamic balance of the individuals in their functional activities along with the reduction in the visual fields which need to be examined.
The results of the present study open a door for physiotherapists in considering the development of specialized balance training programs for patients suffering from Glaucoma and other visual field defects.
Studies reported so far, consider the effects of altered visual and somatosensory information only on static balance; however, most of the functional tasks require dynamic balance. This study presents the baseline results which imply, partial binasal peripheral vision blocks were akin to FV and CPVBs were akin to NV during the performance of dynamic balance functional tasks. With PPVB, sensory reweighting permitted the functional activities in the normal fashion as in EO condition.
Peripheral vision training should gain recognition beyond advanced sports, and cost-effective methods such as binasal occlusion and CPVBs described in this study should be considered for assessing and then training the activities which are performed indoors (home environment) and outdoors. This, in turn, will result in improved confidence for participation in social and personal events by patient as well as general populations.
In the current scenario of the physiotherapy practice in India, we do not cater to an influx of patients affected with visual defects. However, this present study can serve as a basis for developing age-wise balance and vision training programs, which will help us to reach this untapped vast population of the patients.
| Conclusion|| |
The results reveal the importance of peripheral vision in dynamic balance during functional activities in the normal population. Even in the young population, balance deteriorated as the availability of peripheral vision decreased, to the extent that in some functional activities dynamic balance with CPVBs was similar to the EC condition and with PPVB, it was as good as with EO condition.
Further studies to assess and train the balance performance with binocular partial and CPVBs can be carried out in the different age groups and persons affected with peripheral vision loss conditions.
We are grateful to all the participants involved in the study for their cooperation without which this work was not possible.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]