Stepping accuracy and visuomotor control among older adults: effect of target contrast and refractive blur

Reduced corticospinal drive and inflexible temporal adaptation during visually guided walking in older adults

Corticospinal drive during walking is reduced in older adults compared with young adults, but it is not clear how this decrease might compromise one's ability to adjust stepping, particularly during visuomotor adaptation. We hypothesize that age-related changes in corticospinal drive could predict differences in older adults' step length and step time adjustments in response to visual perturbations compared with younger adults. Healthy young (n = 21; age 18-33 yr) and older adults (n = 20; age 68-80 yr) were tested with a treadmill task, incorporating visual feedback of the foot position and stepping targets in real-time. During adaptation, the visuomotor gain was reduced on one side, causing the foot cursor and step targets to move slower on that side of the screen (i.e., split-visuomotor adaptation). Corticospinal drive was quantified by coherence between electromyographic signals in the beta-gamma frequency band (15-45 Hz). The results showed that 1) older adults adapted to visuomotor perturbations during walking, with a similar reduction in error asymmetry compared with younger adults; 2) however, older adults showed reduced adaptation in step time symmetry, despite demonstrating similar adaptation in step length asymmetry compared with younger adults; and 3) smaller overall changes in step time asymmetry was associated with reduced corticospinal drive to the tibialis anterior in the slow leg during split-visuomotor adaptation. These findings suggest that changes in corticospinal drive may affect older adults' control of step timing in response to visual challenges. This could be important for safe navigation when walking in different environments or dealing with unexpected circumstances.NEW & NOTEWORTHY Corticospinal input is essential for visually guided walking, especially when the walking pattern must be modified to accurately step on safe locations. Age-related changes in corticospinal drive are associated with inflexible step time, which necessitates different locomotor adaptation strategies in older adults.

Salient Targets and Fear of Falling Changed the Gait Pattern and Joint Kinematic of Older Adults

BACKGROUND

Fear of falling and environmental barriers in the home are two major factors that cause the incidence of falling. Poor visibility at night is one of the key environmental barriers that contribute to falls among older adult residents. Ensuring their visual perception of the surroundings, therefore, becomes vital to prevent falling injuries. However, there are limited works in the literature investigating the impact of the visibility of the target on older adults' walking destinations and how that impact differs across them with different levels of fear of falling.

OBJECTIVE

The purpose of the study was to examine the effects of target salience on older adults' walking performance and investigate whether older adults with varying levels of fear of falling behave differently.

METHODS

The salient target was constructed with LED strips around the destination of walking. Fifteen older adults (aged 75 years old and above), seven with low fear of falling and eight with high fear of falling, volunteered for the study. Participants walked from the designated origin (i.e., near their beds) to the destination (i.e., near the bathroom entrance), with the target turned on or off around the destination of the walking trials. Spatiotemporal gait variables and lower-body kinematics were recorded by inertial sensors and compared by using analysis of variance methods.

RESULTS

Data from inertial sensors showed that a more salient target at the destination increased older adults' gait speed and improved their walking stability. These changes were accompanied by less hip flexion at heel strikes and toe offs during walking. In addition, older adults with low fear of falling showed more substantial lower-body posture adjustments with the salient target presented in the environment.

CONCLUSIONS

Older adults with a low fear of falling can potentially benefit from a more salient target at their walking destination, whereas those with a high fear of falling were advised to implement a more straightforward falling intervention in their living areas.

Sex Differences in the Visuomotor Control of Obstacle Crossing When Walking are not Age-Related

To ensure stable obstacle crossing when walking, visual information is required two steps before reaching the obstacle. As possible age-related sex differences in visuomotor control have not been investigated, we assessed sex differences in obstacle crossing while walking, as examined by toe clearance (TC) and postural stability. Participants were 14 younger and 14 older adults (equal numbers of men and women) who wore goggles for visual field adjustment while obstacle crossing during gait. We manipulated three visual field occlusion conditions (total, lower, and no visual field occlusions) two steps before the obstacle and analyzed the TC of the lead limb, and the participants’ step width and root mean square of trunk acceleration as indices of postural stability. We found a significant interaction between sex and visual condition in step width, with men showing larger step width values than women in all visual field conditions. Moreover, while women showed no step-width differences across visual field conditions, men had a larger step width with the lower visual field occluded than in the other visual conditions. We found no other significant sex differences. Our results suggest that men may be more dependent than women on the upper visual field for postural stability during obstacle crossing. Sex differences in visuomotor control were not affected by age.

Correcting Presbyopia With Autofocusing Liquid-Lens Eyeglasses

OBJECTIVE

Presbyopia, an age-related ocular disorder, is characterized by the loss in the accommodative abilities of the human eye. Conventional methods of correcting presbyopia divide the field of view, thereby resulting in significant vision impairment. We demonstrate the design, assembly and evaluation of autofocusing eyeglasses for restoration of accommodation without dividing the field of view.

METHODS

The adaptive optics eyeglasses comprise of two variable-focus liquid lenses, a time-of-flight range sensor and low-power, dual microprocessor control electronics, housed within an ergonomic frame. Subject-specific accommodation deficiency models were utilized to demonstrate high-fidelity accommodative correction. The abilities of this system to reduce accommodation deficiency, its power consumption, response time, optical performance and MTF were evaluated.

RESULTS

Average corrected accommodation deficiencies for 5 subjects ranged from -0.021 D to 0.016 D. Each accommodation correction calculation was performed in ∼67 ms which consumed 4.86 mJ of energy. The optical resolution of the system was 10.5 cycles/degree, and featured a restorative accommodative range of 4.3 D. This system was capable of running for up to 19 hours between charge cycles and weighed ∼132 g.

CONCLUSION

The design, assembly and performance of an autofocusing eyeglasses system to restore accommodation in presbyopes has been demonstrated.

SIGNIFICANCE

The new autofocusing eyeglasses system presented in this article has the potential to restore pre-presbyopic levels of accommodation in subjects diagnosed with presbyopia.

Multifocal Spectacle and Monovision Treatment of Presbyopia and Falls in the Elderly

Presbyopia is an age-related condition that affects approximately 1.8 billion people worldwide. Strategies to correct presbyopia include both nonsurgical and surgical approaches. Although eye care providers assume that multifocal spectacles and monovision have lower risks than surgical interventions, there is evidence to suggest that the use of these nonsurgical approaches in the older population increases the risk for trips and falls. Each year, fall-related injuries and deaths are reported in a substantial portion of the population, both globally and in the United States. Previous studies have shown a link between visual acuity, contrast sensitivity, stereoacuity, and visual field impairments and falls. More recent mechanistic and epidemiological studies have shown that multifocal spectacles and monovision can increase the risk for falls as well. Although evidence on the financial burden of falls related to multifocal spectacles or monovision is limited, total direct medical costs related to falls associated with multifocal spectacles are estimated to be approximately $11 billion annually in the United States. Therefore, it is important that eye care providers consider the risk for falls associated with multifocal spectacles and monovision when making decisions on the best strategy for correcting presbyopia in older adults. [J Refract Surg. 2021;37(6 Suppl):S12-S16.].

Spectacle non-tolerance in clinical practice - a systematic review with meta-analysis

PURPOSE

Spectacle non-tolerance or adverse events to spectacle wear are serious concerns for both patients and practitioners. Non-tolerance may contribute to a negative impact on the practitioner's ability and practice. Therefore, a detailed understanding of frequency and causes of spectacle non-tolerance in clinical ophthalmic practice is essential. This review aimed to determine the prevalence and causes of non-tolerance to spectacles prescribed and dispensed in clinical practice.

METHOD

The current systematic review included quantitative studies published in the English language that reported spectacle non-tolerance in clinical practice. A comprehensive search was conducted in PubMed, Scopus and the Web of Science database for studies published until 13 July 2020. An adapted version of the Newcastle-Ottawa Scale (NOS) modified for cross-sectional studies was used to assess the quality of each included study. Five investigations with 205,478 study participants were included in the review. The prevalence of spectacle non-tolerance from individual studies was pooled using MetaXL software. The pooled prevalence of spectacle non-tolerance was 2.1% (95% CI: 1.6-2.7) ranging from 1.6% to 3.0%. The papers were also reviewed to identify the potential causes of non-tolerances. Nearly half reported that non-tolerance (47.4%) was due to an error in refraction. Other causes identified were errors related to communication (16.3%), dispensing (13.5%), non-adaptation (9.7%), data entry (8.7%), binocular vision (7.4%) and ocular pathology (6.4%).

SUMMARY

This review improves our understanding of spectacle non-tolerance in clinical practice. This is important because non-tolerance may lead to spectacle wear discontinuation, which may deprive patients of optimal vision. Increased non-tolerance in clinical practice may affect a clinician's reputation and incur additional costs associated with reassessments and replacements. Spectacle non-tolerance occurred due to a multitude of factors related to optical dispensing and wearer adaptation. Therefore, there is a need for vigilance while prescribing spectacles. The limited evidence highlights the need for more studies, especially in limited-resource settings, to improve the quality of refractive error services.

Falls prevention interventions for older adults with low vision: A scoping review: Étude de portée sur les interventions visant à prévenir les chutes chez les aînés ayant une basse vision

BACKGROUND

Older adults with low vision are especially vulnerable to falls. There are no comprehensive reviews of fall prevention interventions for older adults with vision loss who live in the community.

PURPOSE

The aim of this study was to review the evidence regarding community-based falls prevention interventions that appear inclusive of and/or accessible to individuals with low vision.

METHOD

A scoping review was completed using the framework developed by Arksey and O'Malley, and the charted data were analyzed using sums and percentages and qualitative content analysis.

FINDINGS

Seventeen publications were selected for this review. The analysis allowed for a thorough description of the types of falls prevention interventions (multiple components, home safety/modification, tai chi, the Alexander Technique, improvement of vision through vision assessment and referral, vision/agility training, and yoga), how each intervention addresses vision impairment, and the relation of results to falls risk.

IMPLICATIONS

Falls prevention research targeting individuals with visual impairment is limited, and the intervention approaches available may not be effective for older adults with permanent vision loss.

The addition of stripes (a version of the 'horizontal-vertical illusion') increases foot clearance when crossing low-height obstacles

Trips over obstacles are one of the main causes of falling in older adults, with vision playing an important role in successful obstacle negotiation. We determined whether a horizontal-vertical illusion, superimposed onto low-height obstacles to create a perceived increase in obstacle height, increased foot clearances during obstacle negotiation thus reducing the likelihood of tripping. Eleven adults (mean ± 1 SD: age 27.3 ± 5.1 years) negotiated obstacles of varying heights (3, 5, 7 cm) with four different appearance conditions; two were obstacles with a horizontal-vertical illusion (vertical stripes of different thickness) superimposed on the front, one was a plain obstacle and the fourth a plain obstacle with a horizontal black line painted on the top edge. Foot clearance parameters were compared across conditions. Both illusions led to a significant increase in foot clearance when crossing the obstacle, compared to the plain condition, irrespective of obstacle height. Superimposing a horizontal-vertical illusion onto low-height obstacles can increase foot clearance, and its use on the floor section of a double-glazing door frame for example may reduce the incidence of tripping in the home. Practitioner Summary: Low-height obstacles such as the floor section of a double-glazing door frame are potential tripping hazards. In a gait lab-based study we found that a horizontal-vertical illusion superimposed onto low-height obstacles led to significantly higher foot clearances; indicating their potential as a useful safety measure.