Effects of Age-Related Macular Degeneration on Postural Sway

Ageing changes the proprioceptive contribution to balance control under different types of mastoid vibration: A cross-sectional study

Ageing-related sensory deteriorations are significantly associated with poor balance control among older individuals, resulting in a higher risk of falling in a dark environment. In particular, the proprioceptive system plays a critical role in maintaining balance. This study aimed to determine how ageing-related sensory deteriorations contributed to balance control during standing under various sensory conflicts. Twenty healthy, active adults (10 young and 10 older) participated in this study. Balance control was quantified through two sensory organization test conditions (SOT-1: unblindfolded standing; SOT-2: blindfolded standing). Mastoid vibration (MV) was applied unilaterally (Uni) or bilaterally (Bi) to mastoid processes, for perturbing vestibular inputs. A total of six trials were assigned to each participant in a random order. Dependent variables included traveling route (TR), performance index (PI) and sample entropy (SaEn) in the anterior-posterior (AP) and medial-lateral (ML) directions. Our results showed that (1) compared to without MV, applying MV significantly increased TR_AP (Uni: P = 0.003; Bi: P < 0.001) and TR_ML (Uni: P = 0.009; Bi: P = 0.011) of all participants during blindfolded standing; (2) the application of Uni and Bi significantly increased PI_AP, PI_ML, SaEn_AP and SaEn_ML of young and older adults when standing in the SOT-1 and SOT-2 conditions (P < 0.05); and (3) older adults demonstrated significantly higher PI_AP, PI_ML and SaEn_ML than young adults in standing. This study indicated the potential risk of imbalance attributed to ageing-related proprioceptive and vestibular deteriorations even in healthy older adults. Furthermore, unilateral MV had a stronger effect on disturbing ML balance control than bilateral MV.

Utilisation of patient-centred outcome measures in age-related macular degeneration research and clinical practice: A systematic review

BACKGROUND

To identify the utilisation, type, and psychometric properties of patient-centered outcome measures (PCOMs) associated with the performance-based assessment of visual function (VF) in age-related macular degeneration (AMD) in clinical care and research.

METHODS

A systematic literature search identified studies, available in English, that used PCOMs to assess VF in patients with any AMD severity, published from January 2015 to November 2023. Two researchers screened studies for quality using the Mixed Methods Appraisal Tool (MMAT) 2018 and assessed the psychometric properties of the PCOMs with the guidance of Consensus-based Standards for the selection of health Measurement Instruments (COSMIN).

RESULTS

Of 514 studies shortlisted in the literature, 31 were eligible with the majority (77.4%) fulfilling all the MMAT criteria, indicating good quality. The most used PCOM was reading (14/31 = 45.1%), with 5 of the 14 studies (35.7%) showing that the increasing severity and/or progression of AMD were associated with a worsening reading ability. AMD also negatively affected mobility and physical activity levels (7/31 = 22.6%), and visual search and exploration (4/31 = 12.9%). Based on the COSMIN checklist, apart from reading and physical activity measured with the accelerometer, the other PCOMs had 'inadequate' psychometric properties.

CONCLUSIONS

Limited published studies include PCOMs as an assessment of VF in AMD patients. Apart from reading, there is a lack of robust validation data to support the widespread use of other PCOMs. Hence, well-designed, robustly validated, and simple to use PCOMs are required for more widespread implementation in AMD clinical care and research.

The effects of age and central field loss on maintaining balance control when stepping up to a new level under time-pressure

Objective

To investigate the effects of age and central field loss on the landing mechanics and balance control when stepping up to a new level under time-pressure.

Methods

Eight older individuals with age-related macular degeneration (AMD), eight visually normal older and eight visually normal younger individuals negotiated a floor-based obstacle followed by a 'step-up to a new level' task. The task was performed under (1) no-pressure; (2) time-pressure: an intermittent tone was played that increased in frequency and participants had to complete the task before the tone ceased. Landing mechanics and balance control for the step-up task was assessed with a floor-mounted force plate on the step.

Results

Increased ground reaction forces and loading rates were observed under time-pressure for young and older visual normals but not for AMD participants. Across conditions, loading rates and ground reaction forces were higher in young normals compared to older normals and AMD participants. Young visual normals also demonstrated 35-39% shorter double support times prior to and during the step-up compared to older normals and AMD participants. All groups shortened their double support times (31-40%) and single support times (7-9%) in the time-pressure compared to no-pressure condition. Regarding balance control, the centre-of-pressure displacement and velocity in the anterior-poster direction were increased under time-pressure for young and older visual normals but not for AMD participants. The centre-of-pressure displacement and velocity in the medial-lateral direction were decreased for the AMD participants under time-pressure but not for young and older visual normals.

Conclusions

Despite walking faster, AMD participants did not adapt their landing mechanics under time-pressure (i.e., they remained more cautious), whilst older and young adults with normal vision demonstrated more forceful landing mechanics with the young being most forceful. A more controlled landing might be a safety strategy to maintain balance control during the step-up, especially in time-pressure conditions when balance control in the anterior-posterior direction is more challenged.

Vision, Eye Disease, and the Onset of Balance Problems: The Canadian Longitudinal Study on Aging

PURPOSE

To understand the relationship between visual impairment, self-reported eye disease, and the onset of balance problems.

DESIGN

Population-based prospective cohort study.

METHODS

Baseline and 3-year follow-up data were used from the Canadian Longitudinal Study on Aging. The Comprehensive Cohort included 30,097 adults aged 45 to 85 years recruited from 11 sites across 7 provinces. Balance was measured using the 1-leg balance test. Those who could not stand on 1 leg for at least 60 seconds failed the balance test. Presenting visual acuity was measured using the Early Treatment of Diabetic Retinopathy Study chart. Participants were asked about a previous diagnosis of cataract, macular degeneration, or glaucoma. Logistic regression was used.

RESULTS

Of the 12,158 people who could stand for 60 seconds on 1 leg at baseline, 18% were unable to do the same 3 years later. For each line worse of visual acuity, there was a 15% higher odds of failing the balance test at follow-up (odds ratio [OR] = 1.15, 95% confidence interval [CI] 1.10, 1.20) after adjustment. Those with a report of a former (OR = 1.59, 95% CI 1.17, 2.16) or current cataract (OR = 1.31, 95% CI 1.01, 1.68) were more likely to fail the test at follow-up. Age-related macular degeneration and glaucoma were not associated with failure on the balance test.

CONCLUSION

These data provide longitudinal evidence that vision loss increases the odds of balance problems over a 3-year period. Efforts to prevent avoidable vision loss are needed, as are efforts to improve the balance of visually impaired people.

Effect of optical correction by fully corrected glasses on postural stability

Although various previous studies have reported that the experimentally induced refractive errors interfered with postural control, few studies have demonstrated the optical correction effect of wearing glasses. The purpose of this study was to investigate whether wearing full corrected glasses to correct myopia and hyperopia can have a positive effect on postural stability. To this end, a total of 34 subjects (19 males and 15 females) of an average age of 22.38 ± 2.41-years-old participated in this study. After measuring the full corrected powers of refractive errors of subjects through subjective refraction, updated glasses were provided to 17 myopic subjects and first time glasses were provided to 17 hyperopic subjects as full corrected glasses, respectively. Postural evaluation was carried out using the TETRAX biofeedback system, after which we compared and analyzed the postural instability index and sway power index before and after wearing full corrected glasses. When updated and old glasses for correcting myopia were worn, the postural instability index was significantly reduced, and the sway power index was statistically decreased only in the mid-high frequency region associated with the somatic system, compared to the no glasses state, respectively. However, after wearing first time glasses for hyperopia correction, no significant difference was found in the postural instability index or sway power index. We suggest that providing optimal visual information through the optical correction of myopic refractive error is a useful approach that can lead to synergistic effects of somatic functions involved in postural control. Consequently, we demonstrated that wearing glasses to fully correct the refractive errors has a positive effect on increasing postural control in static posture. Our results may have important clinical implications in the field of optometry and balance evaluation.

Effect of Visual Search Training on Saccades in Age-related Macular Degeneration Subjects

OBJECTIVE

To compare the impact of unilateral versus bilateral Age-related Macular Degeneration (AMD) on saccadic movements, and to show the effect of visual search training on these eye movement performances in AMD subjects. We hypothesized that unilateral and bilateral AMD subjects had abnormal saccadic performances, and that visual search training could improve their performances.

METHODS

Three groups participated in visual search training: 13 elderly unilateral AMD subjects (mean age: 74.6 ± 1.6 years), 15 elderly bilateral AMD subjects (mean age: 74.2 ± 1.2 years), and 15 healthy age-matched control subjects (mean age: 70.9 ± 1.3 years). Horizontal saccadic performances were recorded before and after visual search training (Metrisquare®) with the Mobile Eye Tracker (Mobile EBT®). We analyzed the saccadic movement performances: latency, mean velocity and gain. We measured the training performances for each exercise: the time, the number of omissions and the number of errors. We analyzed the performances with Kruskal-Wallis and posthoc tests.

RESULTS

The latency of saccades in AMD subjects is significantly longer compared to healthy elderly for 15° (p<0.03), 10° (p<0.003) and 5° (p<10-3). Unilateral and bilateral AMD subjects normalized their latency of saccades after training for small saccades (respectively p=0.30 and p=0.23 for 10°, and p=0.09 and p=0.52 for 5°). In elderly, performances depend on the saccade's amplitude.

CONCLUSION

AMD subjects' saccadic movements are disrupted: the execution needs more time but is efficient. The visual search training improved the saccadic performances in AMD subjects. Further studies will aim to improve knowledge on such issues and to explore the benefit of training over time in unilateral AMD subjects.

Postural Instability in Subjects With Usher Syndrome

This study investigated postural performances and vestibular impairment in Usher patients. The three groups studied were: 11 patients with Usher type I (with visual and vestibular impairment), 14 patients with Usher type II (with only visual impairment), and 14 healthy control subjects. Postural stability was measured with a Framiral Multitest Equilibre platform with three visual conditions: eyes open (EO), eyes closed (EC), and vision disturbed by optokinetic stimulation (OPT), and two different postural conditions: stable or unstable platform. The surface and mean velocity of the center of pressure displacement (CoP) were measured and a postural instability index (PII) was calculated. Usher type I and II patients were more unstable than control subjects, but only for the unstable platform. Patients with Usher type I (with severe vestibular impairment) were also significantly more unstable than patients with Usher type II (with normal vestibular function) on the unstable platform. The severity of the vestibular impairment was correlated with the surface of the CoP displacement. We suggest that poor postural control of Usher patients is due to the abnormalities in their visual and, when defective, vestibular inputs. Measurements of postural stability on an unstable platform can distinguish type I from type II Usher patients. We emphasize the importance of multisensory evaluation in these patients to guide development of personalized visuo-vestibular rehabilitation techniques to improve their postural stability and improve their quality of life.