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BACKGROUND: Walking down ramps is a demanding task for transfemoral-amputees and terminating gait on ramps is even more challenging because of the requirement to maintain a stable limb so that it can do the necessary negative mechanical work on the centre-of-mass in order to arrest (dissipate) forward/downward velocity. We determined how the use of a microprocessor-controlled limb system (simultaneous control over hydraulic resistances at ankle and knee) affected the negative mechanical work done by each limb when transfemoral-amputees terminated gait during ramp descent. METHODS: Eight transfemoral-amputees completed planned gait terminations (stopping on prosthesis) on a 5-degree ramp from slow and customary walking speeds, with the limb's microprocessor active or inactive. When active the limb operated in its 'ramp-descent' mode and when inactive the knee and ankle devices functioned at constant default levels. Negative limb work, determined as the integral of the negative mechanical (external) limb power during the braking phase, was compared across speeds and microprocessor conditions. FINDINGS: Negative work done by each limb increased with speed (p < 0.001), and on the prosthetic limb it was greater when the microprocessor was active compared to inactive (p = 0.004). There was no change in work done across microprocessor conditions on the intact limb (p = 0.35). INTERPRETATION: Greater involvement of the prosthetic limb when the limb system was active indicates its ramp-descent mode effectively altered the hydraulic resistances at the ankle and knee. Findings highlight participants became more assured using their prosthetic limb to arrest centre-of-mass velocity.

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PURPOSE: To examine foveal structure in amblyopia using spectral-domain optical coherence tomography (SD-OCT). DESIGN: Prospective, cross-sectional study. PARTICIPANTS AND CONTROLS: Two subject groups were recruited to the study: 85 amblyopes (34 adults, 51 children) and 110 visually normal controls (44 adults, 66 children). METHODS: A detailed eye examination, including an SD-OCT scan, was performed in all participants. A total of 390 eyes of 195 subjects were imaged using a 3-dimensional (3D) macula scan covering a nominal 6 × 6-mm area with a resolution of 256 × 256 (65,536 axial scans). Data from the B-scans bisecting the fovea both horizontally and vertically were fitted with a mathematical model of the fovea to determine a range of foveal parameters. MAIN OUTCOME MEASURES: Foveal thickness, foveal pit depth, and foveal pit slope. RESULTS: Bilateral differences between the eyes of amblyopes compared with visually normal controls were found. The difference between foveal structure in amblyopic participants relative to structure in subjects with normal vision persisted even when variables such as age, ethnicity, axial length, and sex were taken into account. Amblyopes showed increased foveal thickness (+8.31 µm; P = 0.006) and a reduction in pit depth in the horizontal meridian (-10.06 µm; P = 0.005) but not in the vertical meridian (P = 0.082) when compared with subjects with normal vision. Foveal pit slopes were found to be approximately 1 degree flatter in the nasal (P = 0.033) and temporal (P = 0.014) meridians in amblyopes, but differences between amblyopes and controls in the superior (P = 0.061) and inferior (P = 0.087) meridians did not reach statistical significance. No statistically significant interocular differences were found in the foveal structure between amblyopic and fellow eyes. CONCLUSIONS: Differences were found in the foveal structure in both eyes of amblyopes compared with subjects with normal vision. These differences consisted of increased foveal thickness, reduced pit depth when measured along the horizontal meridian, and flattening of the nasal and temporal sides of the foveal pit.

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BACKGROUND: 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. METHODOLOGY/PRINCIPAL FINDINGS: 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. CONCLUSION/SIGNIFICANCE: 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.

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PURPOSE: Intervention trials that reduce visual impairment in older adults have not produced the expected improvements in reducing falls rate. We hypothesised that this may be caused by adaptation problems in older adults due to changes in magnification provided by new spectacles and cataract surgery. This study assessed the effects of ocular magnification on adaptive gait in young and older adults. METHODS: Adaptive gait was measured in 10 young (mean age 22.3 ± 4.6 years) and 10 older adults (mean age 74.2 ± 4.3 years) with the participants' habitual refractive correction (0%) and with size lenses producing ocular magnification of ±1%, ±2%, ±3%, and ±5%. Adaptive gait parameters were measured when participants approached and stepped up onto a raised surface. RESULTS: Adaptive gait changes in the young and older age groups were similar. Increasing amounts of magnification (+1% to +5%) led to an increased distance of the feet from the raised surface, increased vertical toe clearance and reduced distance of the lead heel position on the raised surface (p < 0.0001). Increasing amounts of minification (-1% to -5%) led to the opposite of these changes (p < 0.0001). Adaptation to ocular magnification did not occur in the short term in young or older adults. CONCLUSION: The observed adaptive gait changes were driven by the magnification changes provided by the size lenses. The raised surface appeared closer and larger with magnification and further away and smaller with minification and gait was adjusted accordingly. Magnification may explain the mobility problems some older adults have with updated spectacles and after cataract surgery.

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INTRODUCTION: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

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AIM: To evaluate repeatability and reproducibility of macular thickness measurements in visually normal eyes using the Topcon 3D OCT-1000. METHODS: Phase 1 investigated scan repeatability, the effect of age and pupil dilation. Two groups (6 younger and 6 older participants) had one eye scanned 5 times pre and post- dilation by 1 operator. Phase 2 investigated between-operator, within and between-visit reproducibility. 10 participants had 1 un-dilated eye scanned 3 times on 2 separate visits by 2 operators. RESULTS: PHASE 1: No significant difference existed between repeat scans (p=0.75) and no significant difference was found pre- and post-dilation (p=0.54). In the younger group variation was low (95% limits +/- 3.62microm) and comparable across all retinal regions. The older group demonstrated greater variation (95% limits +/- 7.6microm). PHASE 2: For a given retinal location, 95% confidence limits for within-operator, within-visit reproducibility was 5.16microm. This value increased to 5.56microm for the same operator over two visits and to 6.18microm for two operators over two visits. CONCLUSION: A high level repeatability, close to 6microm, of macular thickness measurement is possible using the 3D OCT- 1000. Measured differences in macular thickness between successive visits that exceed 6microm in pre-presbyopic individuals are therefore likely to reflect actual structural change. OCT measures are more variable in older individuals and it is advisable to take a series of scans so that outliers can be more easily identified.

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When stepping down from one level to another, the leading limb has to arrest downward momentum of the body and subsequently receive and safely support bodyweight before level walking can begin. Such step downs are performed over a wide range of heights and predicting when and where contact between the landing limb and the lower level will be made is likely a critical factor. To determine if visual feedback obtained after movement initiation is habitually used in guiding landing behaviour, the present study determined whether pre-landing kinematics and the mechanics of landing would be modulated according to the type of visual feedback available during the stepping down phase. Ten healthy participants (32.3 +/- 7.9 years) stepped, from a standing position, down from three different heights onto a forceplatform, either coming immediately to rest or proceeding directly to walking across the laboratory. Repeated trials were undertaken under habitual vision conditions or with vision blurred or occluded 2-3 s prior to movement initiation. Pre-landing kinematics were assessed by determining, for the instant of landing, lead-limb knee and ankle angle, stepping distance, forwards positioning of the body CM within the base of support and the forwards and downwards body CM velocity. Landing mechanics for the initial contact period were characterized using lead limb vertical loading and stiffness, and trail limb un-weighting. When vision was occluded movement time, ankle plantarflexion and knee flexion were significantly increased compared to that determined for habitual vision, whereas forwards body CM positioning and velocity, vertical loading and stiffness, and trail limb un-weighting, were significantly reduced (p < 0.05). Similar adaptations were observed under blurred conditions, although to a lesser extent. Most variables were significantly affected by stepping task and step height. Subjects likely reduced forwards CM position and velocity at instant of landing, in order to keep the CM well away from the anterior border of the base of support, presumably to ensure boundary margins of safety were high should landing occur sooner or later than expected. The accompanying increase in ankle plantarflexion at instant of landing, and increase in single limb support time, suggests that subjects tended to probe for the ground with their lead limb under modified vision conditions. They also had more bodyweight on the trail limb at the end of the initial contact period and as a consequence had a prolonged weight transfer time. These findings indicate that under blurred or occluded vision conditions subjects adopted a cautious strategy where by they 'sat back' on their trail limb and used their lead limb to probe for the ground. Hence, they did not fully commit to weight transfer until somatosensory feedback from the lead limb confirmed they had safely made contact. The effect of blurring vision was not identical to occluding vision, and led to several important differences between these conditions consistent with the use of impoverished visual information on depth. These findings indicate that online vision is customarily used to regulate landing behaviour when stepping down.

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PURPOSE: Epidemiologic studies have indicated that elderly people who wear multifocal spectacles have an increased risk of tripping, particularly on stairs. Yet no studies have experimentally examined how wearing multifocal spectacles affects stair and step negotiation. The purpose of this study was to determine the effects of wearing multifocal compared with single-distance vision spectacles on minimum toe clearance and risk of tripping during step negotiation in the elderly. METHODS: Nineteen healthy subjects (mean age, 71.4 years) performed a single step up to a new level (heights, 7.5, 15, and 22 cm) while wearing multifocal (bifocals and progressive addition lenses) or single-distance vision spectacles. Minimum horizontal and vertical toe clearance were assessed by analyzing data collected with a five-camera, three-dimensional motion-analysis system. RESULTS: There was no difference in mean minimum toe clearance in subjects when wearing multifocal compared with single-distance vision spectacles. However, there was greater within-subject variability in vertical toe clearance when wearing multifocal spectacles (variance ratio, 1.53; P = 0.0004). Subjects were also significantly more likely to trip when wearing multifocal compared with single-vision spectacles (one-sided Fisher's exact test P = 0.025). CONCLUSIONS: Because of increased within-subject variability in vertical toe clearance when wearing multifocal spectacles, elderly individuals may be at greater risk of falling when negotiating steps and stairs if they do not also consistently increase margins of safety (mean vertical toe clearance). This suggests that some elderly who are at high risk of falling may benefit from wearing single-distance vision rather than multifocal spectacles when walking.

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