John G Buckley

University of Bradford, Bradford, England, United Kingdom

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Publications (53)122.27 Total impact

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    ABSTRACT: Falls sustained when descending stairs are the leading cause of accidental death in older adults. Highly visible edge highlighters/friction strips (often set back from the tread edge) are sometimes used to improve stair safety, but there is no evidence for the usefulness of either. To determine whether an edge highlighter and its location relative to the tread edge affect foot placement/clearance and accidental foot contacts when descending stairs. Sixteen older adults (mean±1SD age; 71±7years) with normal vision (Experiment 1) and eight young adults (mean±1SD age; 24±4years) with a visual impairment due to simulated age-related cataract (Experiment 2) completed step descent trials during which a high contrast edge highlighter was either not present, placed flush with the tread edge, or set back from the edge by 10mm or 30mm. Foot placement/clearance and the number of accidental foot contacts were compared across conditions. In experiment 1, a highlighter set back by 30mm led to a reduction in final foot placement (p<0.001) and foot clearance (p<0.001) compared to a highlighter placed flush with the tread edge, and the percentage of foot clearances that were less than 5mm increased from 2% (abutting) to 17% (away30). In experiment 2, a highlighter placed flush with the tread edge led to a decrease in within-subject variability in final foot placement (p=0.004) and horizontal foot clearance (p=0.022), an increase in descent duration (p=0.009), and a decrease in the number of low clearances (<5mm, from 8% to 0) and the number of accidental foot contacts (15% to 3%) when compared to a tread edge with no highlighter present. Changes to foot clearance parameters as a result of highlighter presence and position suggest that stairs with high-contrast edge highlighters positioned flush with the tread edge will improve safety on stairs, particularly for those with age-related visual impairment.
    Experimental gerontology 04/2014; · 3.34 Impact Factor
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    Alan R De Asha, John G Buckley
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    ABSTRACT: Background:Minimum toe clearance is a critical gait event because it coincides with peak forward velocity of the swing foot, and thus, there is an increased risk of tripping and falling. Trans-tibial amputees have increased risk of tripping compared to able-bodied individuals. Assessment of toe clearance during gait is thus clinically relevant. In able-bodied gait, minimum toe clearance increases with faster walking speeds, and it is widely reported that there is synchronicity between when peak swing-foot velocity and minimum toe clearance occur. There are no such studies involving lower-limb amputees.Objectives:To determine the effects of walking speed on minimum toe clearance and on the temporal relationship between clearance and peak swing-foot velocity in unilateral trans-tibial amputees.Study design:Cross-sectional.Methods:A total of 10 trans-tibial participants walked at slow, customary and fast speeds. Minimum toe clearance and the timings of minimum toe clearance and peak swing-foot velocity were determined and compared between intact and prosthetic sides.Results:Minimum toe clearance was reduced on the prosthetic side and, unlike on the intact side, did not increase with walking speed increase. Peak swing-foot velocity consistently occurred (~0.014 s) after point of minimum toe clearance on both limbs across all walking speeds, but there was no significant difference in the toe-ground clearance between the two events.Conclusion:The absence of speed related increases in minimum toe clearance on the prosthetic side suggests that speed related modulation of toe clearance for an intact limb typically occurs at the swing-limb ankle. The temporal consistency between peak foot velocity and minimum toe clearance on each limb suggests that swing-phase inter-segmental coordination is unaffected by trans-tibial amputation.Clinical relevanceThe lack of increase in minimum toe clearance on the prosthetic side at higher walking speeds may potentially increase risk of tripping. Findings indicate that determining the instant of peak swing-foot velocity will also consistently identify when/where minimum toe clearance occurs.
    Prosthetics & Orthotics International 01/2014; · 0.56 Impact Factor
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    ABSTRACT: Most clinically available prosthetic feet have a rigid attachment or incorporate an "ankle" device allowing elastic articulation during stance, with the foot returning to a "neutral" position at toe-off. We investigated whether using a foot with a hydraulically controlled articulating ankle that allows the foot to be relatively dorsiflexed at toe-off and throughout swing would increase minimum toe clearance (MTC). Twenty-one people with unilateral transtibial amputa-tion completed overground walking trials using their habitual prosthetic foot with rigid or elastic articulating attachment and a foot with a hydraulic ankle attachment (hyA-F). MTC and other kinematic variables were assessed across multiple trials. When using the hyA-F, mean MTC increased on both limbs (p = 0.03). On the prosthetic limb this was partly due to the device being in its fully dorsiflexed position at toe-off, which reduced the "toes down" foot angle throughout swing (p = 0.01). Walk-ing speed also increased when using the hyA-F (p = 0.001) and was associated with greater swing-limb hip flexion on the pros-thetic side (p = 0.04), which may have contributed to the increase in mean MTC. Variability in MTC increased on the prosthetic side when using the hyA-F (p = 0.03), but this did not increase risk of tripping.
    The Journal of Rehabilitation Research and Development 01/2014; 51(3). · 1.78 Impact Factor
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    ABSTRACT: Background If a prosthetic foot creates resistance to forwards shank rotation as it deforms during loading, it will exert a braking effect on centre of mass progression. The aim of the present study was to determine whether the centre of mass braking effect exerted by a unilateral amputee’s habitual rigid ‘ankle’ foot was reduced when they switched to using an ‘Echelon’ hydraulic ankle-foot device. Methods Nineteen lower limb amputees (eight trans-femoral, eleven trans-tibial) walked overground using their habitual dynamic-response foot with rigid ‘ankle’ or ‘Echelon’ hydraulic ankle-foot device. Analysis focussed on determining changes in how the centre of mass was transferred onto and above the prosthetic-foot, freely chosen walking speed, and spatio-temporal parameters of gait. Findings When using the hydraulic device both groups had a smoother/more rapid progression of the centre of pressure beneath the prosthetic hindfoot (p ≤ 0.001), and a smaller reduction in centre of mass velocity during prosthetic-stance (p < 0.001). As a result freely chosen walking speed was higher in both groups when using the device (p ≤ 0.005). In both groups stance and swing times and cadence were unaffected by foot condition whereas step length tended (p < 0.07) to increase bilaterally when using the hydraulic device. Effect size differences between foot types were comparable across groups. Interpretation Use of a hydraulic ankle-foot device reduced the foot’s braking effect for both trans-femoral and trans-tibial amputees. Findings suggest that attenuation of the braking effect from the foot in early stance may be more important to prosthetic-foot function than its ability to return energy in late stance.
    Clinical Biomechanics. 01/2014;
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    ABSTRACT: The present study introduces four event detection algorithms for defining touch-down and foot-off during stair descent and stair ascent using segmental kinematics. For stair descent, vertical velocity minima of the whole body center-of-mass was used to define touch-down, and foot-off was defined as the instant of trail limb peak knee flexion. For stair ascent, vertical velocity local minima of the lead-limb toe was used to define touch-down, and foot-off was defined as the local maxima in vertical displacement between the toe and pelvis. The performance of these algorithms was determined as the agreement in timings of kinematically derived events to those defined kinetically (ground reaction forces). Data were recorded while 17 young and 15 older adults completed stair descent and ascent trials over a four-step instrumented staircase. Trials were repeated for three stair riser height conditions (85mm, 170mm, and 255mm). Kinematically derived touch-down and foot-off events showed good agreement (small 95% limits of agreement) with kinetically derived events for both young and older adults, across all riser heights, and for both ascent and descent. In addition, agreement metrics were better than those returned using existing kinematically derived event detection algorithms developed for overground gait. These results indicate that touch-down and foot-off during stair ascent and descent of non-instrumented staircases can be determined with acceptable precision using segmental kinematic data.
    Gait & posture 11/2013; · 2.58 Impact Factor
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    ABSTRACT: Passive prosthetic devices are set up to provide optimal function at customary walking speed and thus may function less effectively at other speeds. This partly explains why joint kinetic adaptations become more apparent in lower-limb amputees when walking at speeds other than customary. The present study determined whether a trans-tibial prosthesis incorporating a dynamic-response foot that was attached to the shank via an articulating hydraulic device (hyA-F) lessened speed-related adaptations in joint kinetics compared to when the foot was attached via a rigid, non-articulating attachment (rigF). Eight active unilateral trans-tibial amputees completed walking trials at their customary walking speed, and at speeds they deemed to be slow-comfortable and fast-comfortable whilst using each type of foot attachment. Moments and powers at the distal end of the prosthetic shank and at the intact joints of both limbs were compared between attachment conditions. There was no change in the amount of intact-limb ankle work across speed or attachment conditions. As speed level increased there was an increase on both limbs in the amount of hip and knee joint work done, and increases on the prosthetic side were greater when using the hyA-F. However, because all walking speed levels were higher when using the hyA-F, the intact-limb ankle and combined joints work per meter travelled were significantly lower; particularly so at the customary speed level. This was the case despite the hyA-F dissipating more energy during stance. In addition, the amount of eccentric work done per meter travelled became increased at the residual knee when using the hyA-F, with increases again greatest at customary speed. Findings indicate that a trans-tibial prosthesis incorporating a dynamic-response foot reduced speed-related changes in compensatory intact-limb joint kinetics when the foot was attached via an articulating hydraulic device compared to rigid attachment. As differences between attachment conditions were greatest at customary speed, findings indicate a hydraulic ankle-foot device is most effectual at the speed it is set-up for.
    Journal of NeuroEngineering and Rehabilitation 10/2013; 10(1):107. · 2.57 Impact Factor
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    ABSTRACT: In this paper we use multivariate statistical techniques to gain insights into how adaptive gait involving obstacle crossing is regulated in lower-limb amputees compared to able-bodied controls, with the aim of identifying underlying characteristics that differ between the two groups and consequently highlighting gait deficits in the amputees. Eight unilateral trans-tibial amputees and twelve able-bodied controls completed adaptive gait trials involving negotiating various height obstacles; with amputees leading with their prosthetic limb. Spatiotemporal variables that are regularly used to quantify how gait is adapted when crossing obstacles were determined and subsequently analysed using multivariate statistical techniques. There were fundamental differences in the adaptive gait between the two groups. Compared to controls, amputees had a reduced approach velocity, reduced foot placement distance before and after the obstacle and reduced foot clearance over it, and reduced lead-limb knee flexion during the step following crossing. Logistic regression analysis highlighted the variables that best distinguished between the gait of the two groups and multiple regression analysis (with approach velocity as a controlling factor) helped identify what gait adaptations were driving the differences seen in these variables. Getting closer to the obstacle before crossing it appeared to be a strategy to ensure the heel of the lead-limb foot passed over the obstacle prior to the foot being lowered to the ground. Despite adopting such a heel clearance strategy, the lead-foot was positioned closer to the obstacle following crossing, which was likely a result of a desire to attain a limb/foot angle and orientation at instant of landing that minimised loads on the residuum (as evidenced by the reduced lead-limb knee flexion during the step following crossing). These changes in foot placement meant the foot was in a different part of swing at point of crossing and this explains why foot clearance was considerably reduced in amputees. These results highlight that trans-tibial amputees use quite different gait adaptations to cross obstacles compared with controls (at least when leading with their prosthetic limb), indicating they are governed by different constraints; seemingly related to how they land on/load their prosthesis after crossing the obstacle.
    Journal of NeuroEngineering and Rehabilitation 08/2013; 10(1):98. · 2.57 Impact Factor
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    ABSTRACT: Large changes in spectacle prescription can increase falls risk in older people. We investigated the effect of induced astigmatism (a common cause of distorted or blurred vision in older people) on locomotor stepping patterns to determine whether the orientation of astigmatic changes could have differential effects on gait safety when negotiating steps and stairs. 10 older adults (mean age 76.0±6.4 years) walked up to and stepped onto a raised block whilst wearing their spectacle prescription and when blurred with ±3.00D cylinders at axes 45°, 90°, 135° and 180°. Gait measurements included foot placement before the block, toe clearance over the block edge and foot placement on the block. Induced astigmatism with axes at 90°, providing magnification in the horizontal meridian only, caused no change in stepping pattern. Induced astigmatism with axes at 180° caused foot placement changes in the anterior or posterior direction according to whether magnification was positive or negative in the vertical meridian (block perceived higher or lower respectively). Induced astigmatism with axes oblique at 45° and 135° (causing the block to be perceived as a parallelogram sloping downwards either to the right or left) caused gait changes in the anterior and posterior, vertical and lateral directions. Changes in lateral foot placement appeared to be an attempt to maintain constant foot clearance levels over the block edge by stepping over the perceived 'lower' side of the 'sloping' block. Astigmatic changes with oblique axes had the greatest effect on gait. Clinicians, including optometrists, physiotherapists, occupational therapists and nurses should counsel older patients about the effects of astigmatism on gait safety. Furthermore, partial prescribing of astigmatic corrections should be considered to reduce the risk of falling.
    PLoS ONE 01/2013; 8(5):e63351. · 3.53 Impact Factor
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    ABSTRACT: BACKGROUND: Disruptions to the progress of the centre-of-pressure trajectory beneath prosthetic feet have been reported previously. These disruptions reflect how body weight is transferred over the prosthetic limb and are governed by the compliance of the prosthetic foot device and its ability to simulate ankle function. This study investigated whether using an articulating hydraulic ankle attachment attenuates centre-of-pressure trajectory fluctuations under the prosthetic foot compared to a fixed attachment. METHODS: Twenty active unilateral trans-tibial amputees completed walking trials at their freely-selected, comfortable walking speed using both their habitual foot with either a rigid or elastic articulating attachment and a foot with a hydraulic ankle attachment. Centre-of-pressure displacement and velocity fluctuations beneath the prosthetic foot, prosthetic shank angular velocity during stance, and walking speed were compared between foot conditions. FINDINGS: Use of the hydraulic device eliminated or reduced the magnitude of posteriorly directed centre-of-pressure displacements, reduced centre-of-pressure velocity variability across single-support, increased mean forward angular velocity of the shank during early stance, and increased freely chosen comfortable walking speed (P≤0.002). INTERPRETATION: The attenuation of centre-of-pressure trajectory fluctuations when using the hydraulic device indicated bodyweight was transferred onto the prosthetic limb in a smoother, less faltering manner which allowed the centre of mass to translate more quickly over the foot.
    Clinical biomechanics (Bristol, Avon) 12/2012; · 1.76 Impact Factor
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    ABSTRACT: When descending stairs bodyweight becomes supported on a single limb while the forwards-reaching contralateral limb is lowered in order to make contact with the step below. This is associated with lowering of the centre of mass (CoM), which in order to occur in a controlled manner, requires increased ankle and knee joint torque production relative to that in overground walking. We have previously shown that when descending steps or stairs older people operate at a higher proportion of their maximum eccentric capacity and at, or in excess of the maximum passive reference joint range of motion. This suggests they have reduced and/or altered control over their CoM and we hypothesised that this would be associated with alterations in muscle activity patterns and in the CoM vertical acceleration and velocity profiles during both the lowering and landing phases of stair descent. 15 older (mean 75yrs) and 17 young (mean 25yrs) healthy adults descended a 4-step staircase, leading with the right limb on each stair, during which CoM dynamics and electromyographic activity patterns for key lower-limb muscles were assessed. Maximum voluntary eccentric torque generation ability at the knee and ankle was also assessed. Older participants compared to young increased muscle co-contraction relative duration at the knee and ankle of the trailing limb so that the limb was stiffened for longer during descent. As a result older participants contacted the step below with a reduced downwards CoM velocity when compared to young participants. Peak downwards and peak upwards CoM acceleration during the descent and landing phases respectively, were also reduced in older adults compared to those in young participants. In contrast, young participants descended quickly onto the step below but arrested their downward CoM velocity sooner following landing; a strategy that was associated with longer relative duration lead-limb plantarflexor activity, increased peak upwards CoM acceleration, and a reduced landing duration. These results suggest a reduced ability to generate high eccentric torque at the ankle in the forward reaching limb is a major factor for older participants adopting a cautious movement control strategy when descending stairs. The implications of this CoM control strategy on the incidences of falling on stairs are discussed.
    Experimental gerontology 11/2012; · 3.34 Impact Factor
  • Matthew A Timmis, John G Buckley
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    ABSTRACT: Although gaze during adaptive gait involving obstacle crossing is typically directed two or more steps ahead, visual information of the swinging lower-limb and its relative position in the environment (termed visual exproprioception) is available in the lower visual field (lvf). This study determined exactly when lvf exproprioceptive information is utilised to control/update lead-limb swing trajectory during obstacle negotiation. 12 young participants negotiated an obstacle wearing smart-glass goggles which unpredictably occluded the lvf for certain periods during obstacle approach and crossing. Trials were also completed with lvf occluded for the entirety of the trial. When lvf was occluded throughout, foot-placement distance and toe-clearance became significantly increased; which is consistent with previous work that likewise used continuous lvf occlusion. Both variables were similarly affected by lvf occlusion from instant of penultimate-step contact, but both were unaffected when lvf was occluded from instant of final-step contact. These findings suggest that lvf (exproprioceptive) input is typically used in an online manner to control/update final foot-placement, and that without such control, uncertainty regarding foot placement causes toe-clearance to be increased. Also that lvf input is not normally exploited in an online manner to update toe-clearance during crossing: which is contrary to what previous research has suggested.
    Gait & posture 03/2012; 36(1):160-2. · 2.58 Impact Factor
  • Graham J Chapman, Andy Scally, John G Buckley
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    ABSTRACT: This study investigated the importance of binocular vision to foot placement accuracy when stepping onto a floor-based target during gait initiation. Starting from stationary, participants placed alternate feet onto targets sequentially positioned along a straight travel path with the added constraint that the initial target (target 1) could move in the medio-lateral (M-L) direction. Repeated trials when target 1 remained stationary or moved laterally at the instant of lead-limb toe-off (TO) or 200 ms after TO (early swing) were undertaken under binocular and monocular viewing. Catch trials when target 1 shifted medially were also undertaken. Foot-reach kinematics, foot trajectory corrections and foot placement accuracy for the step onto target 1 were determined via 3D motion analyses. Peak foot-reach velocity and initial foot-reach duration were unaffected by vision condition but terminal foot-reach duration was prolonged under monocular conditions (p = 0.002). Foot trajectory alteration onsets were unaffected by vision condition, but onsets occurred sooner when the target shifted in early swing compared to at TO (p = 0.033). M-L foot placement accuracy decreased (p = 0.025) and variability increased (p = 0.05) under monocular conditions, particularly when stepping onto the moving target. There was no difference between vision conditions in A-P foot placement accuracy. Results indicate that monocular vision provides sufficient information to determine stepping distance and correctly transport the foot towards the target but binocular vision is required to attain a precise M-L foot placement; particularly so when stepping onto a moving target. These findings are in agreement with those found in the reaching and grasping literature, indicating that binocular vision is important for end-point precision.
    Experimental Brain Research 01/2012; 216(1):71-80. · 2.22 Impact Factor
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    ABSTRACT: Descending kerbs during locomotion involves the regulation of appropriate foot placement before the kerb-edge and foot clearance over it. It also involves the modulation of gait output to ensure the body-mass is safely and smoothly lowered to the new level. Previous research has shown that vision is used in such adaptive gait tasks for feedforward planning, with vision from the lower visual field (lvf) used for online updating. The present study determined when lvf information is used to control/update locomotion when stepping from a kerb. 12 young adults stepped down a kerb during ongoing gait. Force sensitive resistors (attached to participants' feet) interfaced with an high-speed PDLC 'smart glass' sheet, allowed the lvf to be unpredictably occluded at either heel-contact of the penultimate or final step before the kerb-edge up to contact with the lower level. Analysis focussed on determining changes in foot placement distance before the kerb-edge, clearance over it, and in kinematic measures of the step down. Lvf occlusion from the instant of final step contact had no significant effect on any dependant variable (p>0.09). Occlusion of the lvf from the instant of penultimate step contact had a significant effect on foot clearance and on several kinematic measures, with findings consistent with participants becoming uncertain regarding relative horizontal location of the kerb-edge. These findings suggest concurrent feedback of the lower limb, kerb-edge, and/or floor area immediately in front/below the kerb is not used when stepping from a kerb during ongoing gait. Instead heel-clearance and pre-landing-kinematic parameters are determined/planned using lvf information acquired in the penultimate step during the approach to the kerb-edge, with information related to foot placement before the kerb-edge being the most salient.
    PLoS ONE 01/2011; 6(4):e19079. · 3.53 Impact Factor
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    ABSTRACT: Purpose Prehension deficits exist in amblyopes when reaching for a single/isolated object in binocular viewing. Here, we examine prehension for objects that are flanked by nearby distracters.Methods Twenty amblyopes (36.4±11.7 yrs) & twenty visual normals (27.5±6.3 yrs) reached for a solid cylindrical object (height 12cm, diameter 3 or 4cm) located directly in front of the participant. The object was flanked by two similarly-sized distracters placed either side of the object, or in front and behind it. The spacing between the object and distracters was scaled according to finger-width of individual participants and was set at spacings of 2- and 4- finger-widths. Shutter-goggles prevented a view of spatial configuration until the movement was to be initiated. Opening the shutters provided the cue for participants to pick up the object in a singe, smooth movement. Movements of the arm, hand and object were recorded using an 8-camera, Vicon-IR recording system.Results Amblyopia affects both the ‘reach’ and the ‘grasp’ phases of prehension. Maximum grip aperture is the same in both groups suggesting that amblyopes are no worse at scaling their grip size to the size of object. But amblyopes show more cautious prehension behaviour. This is because maximum grip aperture and maximum reach velocity occur earlier in their reach, and because there is a longer time from the end of the reach to initial contact with object, and a longer time from contact to lift.Conclusion Our results suggest that amblyopes have more difficulty judging object distance than object size. However, the functional significance of these amblyopic versus visual-normal differences in prehension outside the laboratory is as yet unclear.
    Acta ophthalmologica 09/2010; 88(s246). · 2.44 Impact Factor
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    ABSTRACT: The aim of the present study was to determine adaptive gait changes in long-term wearers of monovision correction contact lenses by comparing gait parameters when wearing monovision correction to those observed when wearing binocular distance correction contact lenses. Gait and toe clearance parameters were measured in eleven participants (53.5 +/- 4.6 years, median monovision wearing time 5 years) as they repeatedly walked up to and onto a raised surface with either monovision or distance correction. Compared to distance correction, monovision resulted in a large reduction in stereoacuity from 17'' to 87'', a slower walking velocity (p = 0.001), a reduced horizontal toe clearance of the step edge (p = 0.035) and, for trials when monovision correction occurred first, a 33% greater variability in vertical toe clearance (p = 0.021). Variability in some gait data was large due to certain study design features and learning effects. A slower walking velocity with monovision correction suggests participants became more cautious, likely as a result of the significantly reduced stereoacuity. The decreased horizontal toe clearance and increased vertical toe clearance variability suggests that monovision correction may cause a greater likelihood of hitting step edges and tripping during everyday gait. Recommended study design features are suggested for future adaptive gait studies to increase the precision of the data and to attempt to minimize the effects of learning from somatosensory feedback.
    Ophthalmic and Physiological Optics 05/2010; 30(3):281-8. · 1.74 Impact Factor
  • John G Buckley, Matthew P Juniper
    Journal of Applied Physiology 04/2010; 108(4):1016; author reply 1019-20. · 3.48 Impact Factor
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    ABSTRACT: Epidemiologic research has shown that multifocal spectacle wearers (bifocal and progressive addition lenses [PALs]) are more than twice as likely to fall than are nonmultifocal spectacle wearers, with this risk further increasing when negotiating stairs. The present study investigated whether step and stair descent safety is improved by using single-vision distance lenses. From a stationary standing position on top of a block, 20 long-term multifocal wearers stepped down (from different block heights) onto a lower level wearing bifocal, progressive addition, or single-vision distance lenses. Use of single-vision distance spectacles led to an increased single-limb support time, a reduced ankle and knee angle and vertical center-of-mass velocity at contact with the lower level, and a reduced ankle angular velocity and vertical center-of-mass velocity during initial landing (P < 0.03). These findings indicate that landing occurred in a more controlled manner when the subjects wore single-vision distance spectacles, rather than tending to "drop" onto the lower level as occurred when wearing bifocals or PALs. Use of single-vision distance spectacles led to improvements in landing control, consistent with individuals' being more certain regarding the precise height of the lower floor level. This enhanced control was attributed to having a view of the foot, step edge, and immediate floor area that was not blurred, magnified, or doubled and that did not suffer from image jump or peripheral distortions. These findings provide further evidence that use of single-vision distance lenses in everyday locomotion may be advantageous for elderly multifocal wearers who have a high risk of falling.
    Investigative ophthalmology & visual science 03/2010; 51(8):3903-8. · 3.43 Impact Factor
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    ABSTRACT: Gait during obstacle negotiation is adapted in visually normal subjects whose vision is temporarily and unilaterally blurred or occluded. This study was conducted to examine whether gait parameters in individuals with long-standing deficient stereopsis are similarly adapted. Twelve visually normal subjects and 16 individuals with deficient stereopsis due to amblyopia and/or its associated conditions negotiated floor-based obstacles of different heights (7-22 cm). Trials were conducted during binocular viewing and monocular occlusion. Analyses focused on foot placement before the obstacle and toe clearance over it. Across all viewing conditions, there were significant group-by-obstacle height interactions for toe clearance (P < 0.001), walking velocity (P = 0.003), and penultimate step length (P = 0.022). Toe clearance decreased (approximately 0.7 cm) with increasing obstacle height in visually normal subjects, but it increased (approximately 1.5 cm) with increasing obstacle height in the stereo-deficient group. Walking velocity and penultimate step length decreased with increasing obstacle height in both groups, but the reduction was more pronounced in stereo-deficient individuals. Post hoc analyses indicated group differences in toe clearance and penultimate step length when negotiating the highest obstacle (P < 0.05). Occlusion of either eye caused significant and similar gait changes in both groups, suggesting that in stereo-deficient individuals, as in visually normal subjects, both eyes contribute usefully to the execution of adaptive gait. Under monocular and binocular viewing, obstacle-crossing performance in stereo-deficient individuals was more cautious when compared with that of visually normal subjects, but this difference became evident only when the subjects were negotiating higher obstacles; suggesting that such individuals may be at greater risk of tripping or falling during everyday locomotion.
    Investigative ophthalmology & visual science 03/2010; 51(5):2487-95. · 3.43 Impact Factor
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    Valentina Graci, David B Elliott, John G Buckley
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    ABSTRACT: To determine the relative importance to adaptive locomotion of peripheral visual cues provided by different parts of the visual field. Twelve subjects completed obstacle crossing trials while wearing goggles that provided four visual conditions: upper visual field occlusion, lower visual field occlusion (LO), circumferential peripheral visual field occlusion (CPO), and full vision. The obstacle was either positioned as a lone structure or within a doorframe. Given that subjects completed the task safely without cues from the lower or peripheral visual field, this suggests that subjects used exteroceptive information provided in a feed-forward manner under these conditions. LO and CPO led to increased foot placement distance from the obstacle and to increased toe clearance over the obstacle with a reduced crossing-walking velocity. The increased variability of dependent measures under LO and CPO suggests that exproprioceptive information from the peripheral visual field is generally used to provide online control of lower limbs. The presence of the doorframe facilitated lead-foot placement under LO by providing exproprioceptive cues in the upper visual field. However, under CPO conditions, the doorframe led to a further reduction in crossing velocity and increase in trail-foot horizontal distance and lead-toe clearance, which may have been because of concerns about hitting the doorframe with the head and/or upper body. Our findings suggest that exteroceptive cues are provided by the central visual field and are used in a feed-forward manner to plan the gait adaptations required to safely negotiate an obstacle, whereas exproprioceptive information is provided by the peripheral visual field and used online to "fine tune" adaptive gait. The loss of the upper and lower peripheral visual fields together had a greater effect on adaptive gait compared with the loss of the lower visual field alone, likely because of the absence of lamellar flow visual cues used to control egomotion.
    Optometry and vision science: official publication of the American Academy of Optometry 11/2009; 87(1):21-7. · 1.53 Impact Factor
  • John G Buckley, Steven F Jones, Louise Johnson
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    ABSTRACT: This study utilises a rarely examined biomechanical parameter--the free vertical moment--to determine age-related differences in rotational kinetics of the body about the vertical-axis when stepping down from a stationary position. Ten older and 10 young adults completed step-downs from three heights. Free vertical moment impulse and peak during step-initiation double-support and the subsequent step-execution phase, and vertical-axis pelvis angular displacement and velocity at instant of landing were compared. The free vertical moment during double-support was directed away from the intended lead-limb side, producing a change in vertical-axis rotational momentum that moved the lead-limb in a forwards-medial direction about the stationary support/trailing limb during the subsequent step-execution phase. The free vertical moment during step-execution was directed towards the lead-limb side and acted to slow/halt the body's vertical-axis rotation away from lead-limb side. Free vertical moment impulse and peak during double-support were similar between groups (P>0.05), but during step-execution were significantly reduced in older adults (P=0.002). As a result older adults had greater vertical-axis pelvis angular displacement and velocity at instant of landing (directed away from lead-limb side), with significant (P<0.001) group-by-step height interactions indicating that differences between groups became more pronounced with increasing step-height. These findings highlight that older adults were unable to exert the same vertical-axis control during single-support as young subjects did. Findings also highlight that the analysis of free vertical moment data can be a useful biomechanical tool to highlight age-related differences in how steps/stairs are negotiated.
    Clinical biomechanics (Bristol, Avon) 11/2009; 25(2):147-53. · 1.76 Impact Factor

Publication Stats

688 Citations
122.27 Total Impact Points


  • 2002–2014
    • University of Bradford
      • • Department of Optometry and Vision Science
      • • School of Health Studies
      • • School of Engineering, Design and Technology
      Bradford, England, United Kingdom
  • 2012
    • Anglia Ruskin University
      Cambridge, England, United Kingdom
    • University of Salford
      • School of Health Sciences
      Salford, ENG, United Kingdom
  • 2010
    • Laval University
      • Centre Interdisciplinaire de Recherche en Réadaptation et Intégration Sociale (CIRRIS)
      Québec, Quebec, Canada
  • 2008
    • University of Delaware
      • Department of Physical Therapy
      Newark, DE, United States
  • 2006–2007
    • University of Leeds
      • Centre for Sport and Exercise Sciences
      Leeds, ENG, United Kingdom
  • 1999–2004
    • Manchester Metropolitan University
      • • Institute for Biomedical Research into Human Movement and Health (IRM)
      • • Department of Exercise and Sport Science
      Manchester, ENG, United Kingdom