Mei Ying Boon

Risk of Falls, Injurious Falls, and Other Injuries Resulting from Visual Impairment among Older Adults with Age-Related Macular Degeneration

PURPOSE Age-related macular degeneration (AMD) is the leading cause of irreversible visual impairment among older adults. This study explored the relationship between AMD, fall risk, and other injuries and identified visual risk factors for these adverse events. METHODS Participants included 76 community-dwelling individuals with a range of severity of AMD (mean age, 77.0 ± 6.9 years). Baseline assessment included binocular visual acuity, contrast sensitivity, and merged visual fields. Participants completed monthly falls and injury diaries for 1 year after the baseline assessment. RESULTS Overall, 74% of participants reported having either a fall or a non-fall-related injury. Fifty-four percent of participants reported a fall and 30% reported more than one fall; of the 102 falls reported, 63% resulted in an injury. Most occurred outdoors (52%), between late morning and late afternoon (61%) and when navigating on level ground (62%). The most common non-fall-related injuries were lacerations (36%) and collisions with an object (35%). Reduced contrast sensitivity and visual acuity were associated with increased fall rate, after controlling for age, sex, cognitive function, cataract severity, and self-reported physical function. Reduced contrast sensitivity was the only significant predictor of non-fall-related injuries. CONCLUSIONS Among older adults with AMD, increased visual impairment was significantly associated with an increased incidence of falls and other injuries. Reduced contrast sensitivity was significantly associated with both increased rates of falls and other injuries, while reduced visual acuity was only associated with increased fall rate. These findings have important implications for the assessment of visually impaired older adults.

Postural stability and gait among older adults with age-related maculopathy

PURPOSE To assess the postural stability and gait characteristics of adults with age-related maculopathy (ARM) and to identify the visual factors associated with postural stability and gait in this clinical population. METHODS Participants included 80 individuals with a range of severity of ARM (mean age, 77.2 years). Binocular visual function measures included visual acuity, contrast sensitivity, and merged binocular visual fields. Postural stability was assessed on both a firm and a foam surface using center-of-pressure measures derived from a force platform. Forty three of the participants underwent a three-dimensional motion analysis to quantify gait characteristics, including walking velocity, proportion of time spent with both feet in contact with the ground (double-support time), stride length, and step width. RESULTS After adjustment for age, sex, self-reported physical function, and cataract severity, all the vision measures were significantly associated with postural stability on the foam surface, with contrast sensitivity being the strongest correlate. In the analysis of the gait measures, only contrast sensitivity was significantly associated with walking velocity, step width, or stride length, whereas contrast sensitivity and visual field loss were both significantly associated with double-support time. CONCLUSIONS Impaired contrast sensitivity was associated with postural instability, slower walking velocity, increased step width, and reduced stride length. Impairments in either contrast sensitivity or visual fields were associated with increased double-support time. This result suggests that loss of contrast sensitivity and visual fields in patients with ARM can lead to balance and mobility problems.

What is the appropriate age cut-off for cycloplegia in refraction?

To investigate the age range for which cycloplegia provides additional information compared with non‐cycloplegic refraction in teenagers and young adults.

The correlation dimension: a useful objective measure of the transient visual evoked potential?

Visual evoked potentials (VEPs) may be analyzed by examination of the morphology of their components, such as negative (N) and positive (P) peaks. However, methods that rely on component identification may be unreliable when dealing with responses of complex and variable morphology; therefore, objective methods are also useful. One potentially useful measure of the VEP is the correlation dimension. Its relevance to the visual system was investigated by examining its behavior when applied to the transient VEP in response to a range of chromatic contrasts (42%, two times psychophysical threshold, at psychophysical threshold) and to the visually unevoked response (zero contrast). Tests of nonlinearity (e.g., surrogate testing) were conducted. The correlation dimension was found to be negatively correlated with a stimulus property (chromatic contrast) and a known linear measure (the Fourier-derived VEP amplitude). It was also found to be related to visibility and perception of the stimulus such that the dimension reached a maximum for most of the participants at psychophysical threshold. The latter suggests that the correlation dimension may be useful as a diagnostic parameter to estimate psychophysical threshold and may find application in the objective screening and monitoring of congenital and acquired color vision deficiencies, with or without associated disease processes.

Transient VEP and psychophysical chromatic contrast thresholds in children and adults

It has been found that humans are able to distinguish colours without luminance cues by about 2-4 months of age and that sensitivity to colour difference develops during childhood, reaching a peak around adolescence. This prolonged period of maturation is reflected by improvements in psychophysical threshold measures and by the VEP characteristics of morphology, latency and amplitude. An intra-individual comparison of VEP and psychophysical responses to isoluminant colour stimuli has not been made in children, however, and this was the aim of the present study. VEPs were recorded from 49 subjects, children (age range: 4.8-12.6 years) and adults (age range: 25.7-33.2 years). Psychophysical and VEP thresholds were both measured in 40 of those subjects. Nominally isoluminant chromatic (L-M) sinewave gratings were presented in onset-offset mode and identical stimuli were used for psychophysical and VEP recordings to allow comparison. In agreement with previous reports, morphology of the transient VEP in response to this stimulus differed considerably between children and adults. There was a significant difference between psychophysical and VEP thresholds in children, but not in adults. Our findings support and expand on previous work on maturation of the L-M chromatic pathway and indicate a larger discrepancy between VEP and psychophysical chromatic thresholds in children than in adults.

Estimating chromatic contrast thresholds from the transient visual evoked potential

Chromatic contrast thresholds may be estimated from transient VEPs by measuring the peak-to-peak amplitude at a range of stimulus levels followed by extrapolation to zero amplitude. However, there have been reports of failure of this technique when applied to the transient chromatic VEP due to variability of amplitude, difficulties with component identification and poor correlation of amplitude with stimulus level. The aim of our study was to compare methods of transient VEP chromatic contrast threshold estimation in terms of success rate and comparison with psychophysical threshold. We found each of the methods we investigated to have a high success rate, and in most cases VEP and psychophysical thresholds did not differ significantly.

Contrast-response functions of the multifocal steady-state VEP (MSV)

OBJECTIVES To measure contrast-response functions (CRFs) for 9 visual field (VF) regions and nonlinear interactions between regions using a multifocal steady-state VEP (MSV). METHODS Ten normal adults were tested (51.7 ± 16.9 yr, 5 females). Stimuli resembling those of the Frequency Doubling Technology (FDT) perimeter were presented in 9 VF regions simultaneously, which were modulated at incommensurate temporal frequencies (mean 19.7 Hz). Responses were recorded to 11 contrasts from 3% to 89%, using 8 scalp electrodes. Two repeats of a 20s duration stimulus were averaged for each contrast. RESULTS The CRFs were log-linear except for a depression near 7% contrast (p=0.0008), which was prominent in the central VF. The effects of VF region, stimulus frequency and recording electrode were significant (all p<0.016). Significant responses at frequencies corresponding to interactions between VF regions also appeared. Electrodes that were best for the interactions and second harmonic responses differed, suggesting different cortical sources. CONCLUSIONS Despite short recording durations the saturating CRFs meant that significant responses could be measured to low contrasts, and be distinguished from nonlinear interactions. SIGNIFICANCE Recording MSVs to low contrast FDT-like stimuli might be useful for quantifying damage by glaucoma and other visual disorders.

The short‐sighted perspective of long‐term eye health‐care

Eye health‐care in Australia encompasses patients with chronic disorders being referred to ophthalmologists for detailed assessment and subsequent management. An increasing case load and relative decrease in ophthalmologists predicted over the next few years portend of an upcoming bottleneck in care delivery. To improve the efficiency and effectiveness of patient care within a rapidly changing health system, we propose that minor adjustments to existing services could improve the proficiency of resources. Such changes will require service providers to rethink their positions and roles and actively collaborate with each other for improved patient outcomes.

Development and validation of the 21‐item Children's Vision for Living Scale (CVLS) by Rasch analysis

The aim was to develop and validate an instrument called the ‘Childrens Vision for Living Scale’ (CVLS) for the assessment of vision‐related quality of life in Saudi Arabian children with and without amblyopia.

Home modification guidelines as recommended by visually impaired people

Purpose – The purpose of this paper is to provide an evidence-base for home modification guidelines for people with visual impairment due to age-related macular degeneration (AMD), from the perspective of people with AMD, by exploring the home modifications they find useful and would recommend to other people with visual impairment due to AMD as being effective. Design/methodology/approach – People with impairments may not be aware of their own coping with inability strategies until they are asked to express their strategies. A qualitative approach using semi-structured individual interviews was used to elicit the perspectives of people with AMD with regards to their preferred home modification interventions. Interviews were recorded and then transcribed verbatim into text for thematical analysis using Nvivo 8. Findings – In total, 31 individuals (aged 79.1 ^ 5.6 years) with AMD and no other ocular diseases were recruited from a low vision clinic or the Macular Degeneration Foundation database in a metropolitan city. Interviewees had not received any formal home modification assessment from a government provider. Nevertheless, 70 per cent of participants stated that they undertook home modifications themselves or with the assistance of family and friends. The most important functional modifications as perceived by the participants concerned the installation of hand rails, non-slip matting, colour contrasting safety stair nosing, single lever taps, slip resistant flooring, lift chairs and motion sensors that activated pathway lighting. Kitchens, steps and bathrooms were perceived as hazardous locations. Most participants had difficulties with reading fine-print material on kitchen appliances, washing machines, microwave ovens and remote controls for electronic devices in the home. Originality/value – An evidence-base for useful home modifications as suggested by people with visual impairment was perceived to be a valuable resource for other people with visual impairment who may not yet have developed adaptive strategies. Industrial and interior designers and low vision rehabilitation services who aim to improve functionality of the home environment will also find these suggestions useful.