Assessment of visual problems after acquired brain injury: a survey of current practice in Danish hospitals.

OBJECTIVES: To explore current hospital practice in relation to the assessment of vision problems in patients with acquired brain injury. DESIGN: A survey study. SUBJECTS: A total of 143 respondents from hospital settings, with background in occupational therapy and physical therapy, participated in the survey. METHODS: The survey questionnaire, developed collaboratively by Danish and Norwegian research groups, encompassed 22 items categorically covering "Background information", "Clinical experience and current practice", "Vision assessment tools and protocols", and "Assessment barriers". It was sent out online, to 29 different hospital departments and 18 separate units for occupational therapists and physiotherapists treating patients with acquired brain injury. RESULTS: Most respondents worked in acute or subacute hospital settings. Few departments had an interdisciplinary vision team, and very few therapists had formal education in visual problems after acquired brain injury. Visual assessment practices varied, and there was limited use of standardized tests. Barriers to identifying visual problems included patient-related challenges, knowledge gaps, and resource limitations. CONCLUSION: The study emphasized the need for enhanced interdisciplinary collaboration, formal education, and standardized assessments to address visual problems after acquired brain injury. Overcoming these challenges may improve identification and management, ultimately contributing to better patient care and outcomes in the future.

Health Needs Assessment in Home-Living Older Adults: Protocol for a Pre-Post Study.

BACKGROUND: Conducting a health needs assessment for older adults is important, particularly for early detection and management of frailty. Such assessments can help to improve health outcomes, maintain overall well-being, and support older adults in retaining their independence as they age at home. OBJECTIVE: In this study, a systematic approach to health needs assessment is adopted in order to reflect real-world practices in municipal health care and capture the nuances of frailty. The aim is to assess changes in frailty levels in home-living older adults over 5 months and to examine the observable functional changes from a prestudy baseline (t1) to a poststudy period (t2). Additionally, the study explores the feasibility of conducting the health needs assessment from the perspective of home-living older adults and their informal caregivers. METHODS: Interprofessional teams of registered nurses, physiotherapists, and occupational therapists will conduct 2 health needs assessments covering physical, cognitive, psychological, social, and behavioral domains. The study includes 40 home-living older adults of 75 years of age or older, who have applied for municipal health and care services in Norway. A quantitative approach will be applied to assess changes in frailty levels in home-living older adults over 5 months. In addition, we will examine the observable functional changes from t1 to t2 and how these changes correlate to frailty levels. Following this, a qualitative approach will be used to examine the perspectives of participants and their informal caregivers regarding the health needs assessment and its feasibility. The final sample size for the qualitative phase will be determined based on the participant's willingness to be interviewed. The quantitative data consist of descriptive statistics, simple tests, and present plots and correlation coefficients. For the qualitative analysis, we will apply thematic analysis. RESULTS: The initial baseline assessments were completed in July 2023, and the second health needs assessments are ongoing. We expect the results to be available for analysis in the spring of 2024. CONCLUSIONS: This study has potential benefits for not only older adults and their informal caregivers but also health care professionals. Moreover, it can be used to inform future studies focused on health needs assessments of this specific demographic group. The study also provides meaningful insights for local policy makers, with potential future implications at the national level. TRIAL REGISTRATION: ClinicalTrials.gov NCT05837728; https://clinicaltrials.gov/study/NCT05837728. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/55192.

Academic performance and musculoskeletal pain in adolescents with uncorrected vision problems.

BACKGROUND: Undetected vision problems are common in school children, and a prevalence of up to 40% has previously been reported. Uncorrected vision and lack of optimal eye wear can have a significant impact on almost all aspects of everyday life, such as development and learning, academic performance, pain and discomfort, and quality of life. This study aimed to analyze the relationship between uncorrected vision problems, educational outcomes, and musculoskeletal pain symptoms. METHODS: A total of 152 school children (15.1 ± 0.8 years, mean ± SD; 40% males) were included in the study. All participants were recruited from a free-of-charge school vision testing program in Kathmandu, Nepal. Academic grades were collected from the school records of the participants' nationwide final grade examinations. A questionnaire was used to record the use of digital devices, screen time, and associated symptoms, including musculoskeletal pain (Wong-Baker FACES Pain Rating Scales). RESULTS: A total of 61 children (40%) had uncorrected vision, with a cycloplegic refraction of SER - 0.53 ± 0.52 (mean ± SD). Children with uncorrected vision had significantly more third division grades (26 vs. 9%, p = 0.004) and shoulder pain in general/during screen use (66 vs. 43/40%, p = 0.008/0.003; 2.1/1.9 vs. 1.1/1.0 mean pain score, p = 0.002/0.001) compared with children with normal vision. Sex based subanalyses showed that only girls with uncorrected vision had more third division grades (25 vs. 4%, p = 0.006), and only boys with uncorrected vision had more shoulder pain in general/during screen use (76 vs. 28/31%, p < 0.001; 2.2/2.4 vs. 0.7 mean pain score, p < 0.001), compared with children with normal vision. CONCLUSIONS: The results of this study showed that even small refractive errors may impact educational outcomes and musculoskeletal pain in adolescents. Most of the participating children had low myopia, easily corrected with glasses. This suggests that regular eye examinations are important in school children, and there is a need for raised awareness among parents, and school- and healthcare personnel.

Use and underuse of mobility aids in individuals with visual impairment: a cross-sectional study of a Norwegian sample.

PURPOSE: To examine the use and underuse of mobility aids in individuals with visual impairment. METHODS: A telephone survey including a probability sample of 736 adults who were members of the Norwegian Association of the Blind and Sighted (response rate: 61%). The interviews took place between January and May 2017, collecting information about access, use, underuse and training in five types of mobility aids (white cane, guide dog, GPS, door-to-door transport and sighted guide). For each mobility aid, we obtained data for underuse defined as non-use despite expecting benefits of use in terms of increased mobility or safety. Participants also answered questions about loneliness (Three-Item Loneliness Scale) and life satisfaction (Cantril's Ladder of Life Satisfaction). RESULTS: Of the participants, 69% reported using at least one type of mobility aid. Use of specific aids ranged from 12% for the GPS to 52% for door-to-door transport. Estimates of underuse ranged between 14% for door-to-door transport and 28% for GPS. Underuse was not related to lack of resources, as many non-users expecting benefits had access to mobility aids and had undergone training in its use. For example, 81% of non-users of the white cane had access to a cane. In post hoc analyses, non-users who expected benefits from use had lower life satisfaction compared with users. CONCLUSIONS: Many individuals with visual impairment do not use mobility aids. Strategies that help visually impaired individuals overcome barriers to the use of mobility aids may improve their sense of safety, mobility and quality of life.Implications of rehabilitationThe best mobility aids are those being used. Rehabilitation professionals involved in the provision of mobility aids should be sensitive to the user's lived experiences, and be alert of the cultural meanings of mobility aids and on disability in general.Rehabilitation professionals, social service workers and others need more knowledge of the psychosocial and cultural aspects related to why people do not use their mobility aids.A successful integration of mobility aids in people's daily life cannot be achieved by sufficient accessibility alone. Structured routines for follow-up of those who receive aids should be implemented, so that the aids are actually used.Due to the high rates of underuse and its possible relation to quality of life, promoting regular use of mobility aids should be prioritized.

'If we don't assess the patient's vision, we risk starting at the wrong end': a qualitative evaluation of a stroke service knowledge translation project.

BACKGROUND: Visual impairments (VIs) affect 60% of stroke survivors and have negative consequences for rehabilitation and quality of life poststroke. Symptoms of VIs post stroke are difficult to identify for stroke survivors and health care professionals without using a structured vision assessment. In this study, we qualitatively evaluate the implementation outcomes after implementing a structured visual assessment with the Competence, Rehabilitation of Sight after Stroke Vision (KROSS) assessment tool in stroke care services. METHODS: This is a qualitative study comprising four focus group interviews. The health care personnel (HCP) involved in the implementation or with experience using the KROSS assessment tool in practice were invited to participate. We used Proctor et al.'s definitions of implementation outcomes as a framework, which informed the interview guide and analysis. We used a deductive - inductive content analysis, as described by Elo and Kyngäs. RESULTS: The participants found the structured vision assessment with the KROSS tool as being acceptable; they expressed a motivation and intention to use the new routine in practice. They believed it was important to assess their patient's visual function because it influenced other rehabilitation activities and activities of daily living. Most of the participants reported having adopted the vision assessment in their practice, except for those participants from the home care services who experienced that they have few stroke survivors to follow up on. The assessment was believed to be more appropriate to perform within the rehabilitation services where there is more of a focus on functional assessments. Although vision assessment was new to all the participants, they felt that they improved their vision assessment skills by regularly using the assessment tool. Together with sufficient instructions and supervision, they believed that vison assessment was feasible for their practise. Including the vison assessment in the existing routines and systems was important to promote sustainable implementation. CONCLUSION: Implementing a structured vision assessment with the KROSS tool in health care services was experienced as acceptable and feasible. The new routine led to increased attention towards poststroke VIs and increased collaboration with vision experts. Tailoring the routine to each practice and how they organise their work can support the integration of a vision assessment in their routines. To promote better vision care poststroke vision assessment and follow up should be included in the stroke care pathways.

Barriers and facilitators to the implementation of a structured visual assessment after stroke in municipal health care services.

BACKGROUND: Stroke is a leading cause of disability worldwide. Visual impairments (VIs) affect 60% of stroke survivors, and have negative consequences for rehabilitation and post-stroke life. VIs after stroke are often overlooked and undertreated due to lack of structured routines for visual care after stroke. This study aims to identify and assess barriers and facilitators to the implementation of structured visual assessment after stroke in municipal health care services. The study is part of a larger knowledge translation project. METHODS: Eleven leaders and municipal interdisciplinary health care professionals participated in qualitative interviews. During two workshops, results from the interviews were discussed with 26 participants from municipal health care services and user representatives. Data from interviews and workshops were collected before the intervention was implemented and analyzed using content analysis. RESULTS: The analysis identified individual and contextual barriers and facilitators. The individual barriers were related to the participants' experiences of having low competence of visual functions and vision assessment skills. They considered themselves as generalists, not stroke experts, and some were reluctant of change because of previous experiences of unsuccessful implementation projects. Individual facilitators were strong beliefs that including vision in stroke care would improve health care services. If experienced as useful and evidence based, the new vision routine would implement easier. Contextual barriers were experiences of unclear responsibility for vision care, lack of structured interdisciplinary collaboration and lack of formal stroke routines. Time constraints and practical difficulties with including the vision tool in current medical records were also expressed barriers. Contextual facilitators were leader support and acknowledgement, in addition to having a flexible work schedule. CONCLUSIONS: This study shows that improving competence about VIs after stroke and skills in assessing visual functions are particularly important to consider when planning implementation of new vision routines in municipal health care services. Increased knowledge about the consequences of living with VIs after stroke, and the motivation to provide best possible care, were individual facilitators for changing clinical practice. Involving knowledge users, solutions for integrating new knowledge in existing routines, along with easily accessible supervision in own practise, are essential facilitators for promoting a successful implementation.

Headache and musculoskeletal pain in school children are associated with uncorrected vision problems and need for glasses: a case-control study.

Musculoskeletal pain and headache are leading causes of years lived with disability, and an escalating problem in school children. Children spend increasingly more time reading and using digital screens, and increased near tasks intensify the workload on the precise coordination of the visual and head-stabilizing systems. Even minor vision problems can provoke headache and neck- and shoulder (pericranial) pain. This study investigated the association between headaches, pericranial tenderness, vision problems, and the need for glasses in children. An eye and physical examination was performed in twenty 10-15 year old children presenting to the school health nurse with headache and pericranial pain (pain group), and twenty age-and-gender matched classmates (control group). The results showed that twice as many children in the pain group had uncorrected vision and needed glasses. Most children were hyperopic, and glasses were recommended mainly for near work. Headache and pericranial tenderness were significantly correlated to reduced binocular vision, reduced distance vision, and the need for new glasses. That uncorrected vision problems are related to upper body musculoskeletal symptoms and headache, indicate that all children with these symptoms should have a full eye examination to promote health and academic performance.

"Invisible" visual impairments. A qualitative study of stroke survivors` experience of vision symptoms, health services and impact of visual impairments.

BACKGROUND: Visual impairments (VIs) have a negative impact on life and affect up to 60% of stroke survivors. Despite this, VIs are often overlooked. This paper explores how persons with VIs experience vision care within stroke health services and how VIs impact everyday life the first 3 months post stroke. METHODS: Individual semi-structured interviews were conducted with 10 stroke survivors 3 months post stroke, and analyzed using qualitative content analysis. RESULTS: The main theme, "Invisible" visual impairments, represents how participants experience VIs as an unknown and difficult symptom of stroke and that the lack of attention and appropriate visual care leads to uncertainty about the future. VIs were highlighted as a main factor hindering the participants living life as before. The lack of acknowledgement, information, and systematic vision rehabilitation leads to feelings of being unsupported in the process of coping with VIs. CONCLUSION: VIs are unknown symptoms pre stroke and sequelas after stroke that significantly affect everyday life. VIs and vision rehabilitation needs more attention through all phases of stroke health services. We request a greater awareness of VIs as a presenting symptom of stroke, and that visual symptoms should be included in stroke awareness campaigns. Further, we suggest increased competence and standardized evidence-based clinical pathways for VIs to advance all stroke health services including rehabilitation in order to improve outcomes and adaptation to future life for stroke survivors with VIs.

Discomfort glare and psychological stress during computer work: subjective responses and associations between neck pain and trapezius muscle blood flow.

PURPOSE: Exposure to additional environmental stress during computer work, such as visual and psychological demands, is associated with increased eye and neck discomfort, altered moods, and reduced well-being. The aim of this study is to elucidate further how subjective responses in healthy, young females with normal binocular vision are affected by glare and psychological stress during computer work, and to investigate possible associations between trapezius muscle blood flow and neck pain development. METHODS: 43 females participated in a laboratory experiment with a within-subject design. Four 10-min computer work conditions with exposure to different stressors were performed at an ergonomically optimal workstation, under the following series of conditions: no additional stress, visual stress (induced as direct glare from a large glare source), psychological stress, and combined visual and psychological stress. Before and immediately after each computer work condition, questionnaires regarding different visual and eye symptoms, neck and shoulder symptoms, positive and negative state moods, perceived task difficulty, and perceived ambient lighting were completed. Associations between neck pain and trapezius muscle blood flow were also investigated. RESULTS: Exposure to direct glare induced greater development of visual/eye symptoms and discomfort, while psychological stress exposure made participants feel more negative and stressed. The perception of work lighting during glare exposure was closely related to perceived stress, and associations between visual discomfort and eyestrain, and neck pain were observed in all conditions. Furthermore, participants with high trapezius muscle blood flow overall reported more neck pain, independent of exposure. CONCLUSIONS: Exposure to visual and psychological stresses during computer work affects the development of symptoms and negative moods in healthy, young females with normal binocular vision, but in different ways. The results also demonstrate the complex interactions involved in symptom development and lighting appraisal during computer work. When optimizing computer workstations, the complexity of the field must be taken into account, and several factors, including visual conditions, must be considered carefully.

Vision status of children aged 7-15 years referred from school vision screening in Norway during 2003-2013: a retrospective study.

BACKGROUND: Undetected vision problems is an important cause of reduced academic achievement, performance in everyday life and self-esteem. This receives little attention in national health care services in Norway even though most of these vision problems are easily correctable. There are no published data on how many Norwegian schoolchildren are affected by correctable vision problems. This study aims to determine the vision status in primary and secondary schoolchildren referred from vision screening during the 10 year period of 2003-2013. METHODS: Of the 1126 children (15%) aged 7-15 years referred to the university eye clinic by the school screening program, all 782 who attended the eye clinic were included in the study. Patient records were retrospectively reviewed with regard to symptoms, refractive error, best corrected visual acuity (BCVA) of logMAR, binocular vision, ocular health and management outcomes. RESULTS: Previously undetected vision problems were confirmed in 650 (83%) of the children. The most frequent outcomes were glasses (346) or follow-up (209), but types of treatment modalities varied with age. Mean refractive errors were hyperopic for all age groups but reduced with age (ANOVA, p < 0.001). Overall, 51% were hyperopic, 32% emmetropic and 17% myopic. Refractive errors did not change across the decade (linear regression, all p > 0.05). Mean logMAR BCVAs were better than 0.0 and improved with age (ANOVA, p < 0.001). The most prevalent symptoms were headaches (171), near vision problems (149) and reduced distance vision (107). CONCLUSIONS: The vision screening identified children with previously undetected visual problems. This study shows that the types of visual problems varied with age and that most problems could be solved with glasses. Our results stress the importance of regular eye examinations and that vision examinations should be included in primary health care services. Furthermore, there is a need for raised awareness among parents and teaching staff regarding vision problems in children.

Improved indoor lighting improved healthy aging at home - an intervention study in 77-year-old Norwegians.

Introduction: Healthy aging and good quality of life is important to allow older people to live at home. Lighting is a significant environmental attribute promoting visual, physical, and mental health. Due to normal visual age changes, older people need more light, but improving indoor lighting levels receives little attention. Objective: To investigate the impact of improved home lighting on abilities to perform activities of daily living (ADLs) and quality of life in healthy older people. Methods: Sixty healthy 77 years old living at home participated during the 4-month dark winter period. In the intervention group (IG, n=30), the living room lighting was optimized by providing lamps and a basic control system with three preset levels (normal, medium, low). Participants chose the light level and kept a diary. No change was implemented for the control group (CG, n=30). A questionnaire measured self-reported visual and general health and ability to perform ADL in regards to lighting before and after the intervention in both groups. Results: In the IG, lighting levels significantly improved self-assessed lighting levels, abilities to perform ADLs, and read and write in the living room (all p<0.03). In the CG the only change was a deterioration in performing ADLs ( p<0.05). The difference in change was significant between the IG and CG (all p<0.02). "Normal" lighting was the preferred level and increased comfort and well-being. The IG also resumed visually demanding tasks, and acknowledged that avoiding these tasks were mainly due to poor lighting. Conclusions: Good vision is essential in promoting healthy aging at home and require adequate lighting. This can easily be achieved using a basic light system. Adopting to higher lighting levels evolves quickly. Our results suggest that improved quality of light could improve quality of life, and lighting should be included as a factor promoting healthy aging at home.

Visual and psychological stress during computer work in healthy, young females-physiological responses.

PURPOSE: Among computer workers, visual complaints, and neck pain are highly prevalent. This study explores how occupational simulated stressors during computer work, like glare and psychosocial stress, affect physiological responses in young females with normal vision. METHODS: The study was a within-subject laboratory experiment with a counterbalanced, repeated design. Forty-three females performed four 10-min computer-work sessions with different stress exposures: (1) minimal stress; (2) visual stress (direct glare); (3) psychological stress; and (4) combined visual and psychological stress. Muscle activity and muscle blood flow in trapezius, muscle blood flow in orbicularis oculi, heart rate, blood pressure, blink rate and postural angles were continuously recorded. Immediately after each computer-work session, fixation disparity was measured and a questionnaire regarding perceived workstation lighting and stress was completed. RESULTS: Exposure to direct glare resulted in increased trapezius muscle blood flow, increased blink rate, and forward bending of the head. Psychological stress induced a transient increase in trapezius muscle activity and a more forward-bent posture. Bending forward towards the computer screen was correlated with higher productivity (reading speed), indicating a concentration or stress response. Forward bent posture was also associated with changes in fixation disparity. Furthermore, during computer work per se, trapezius muscle activity and blood flow, orbicularis oculi muscle blood flow, and heart rate were increased compared to rest. CONCLUSIONS: Exposure to glare and psychological stress during computer work were shown to influence the trapezius muscle, posture, and blink rate in young, healthy females with normal binocular vision, but in different ways. Accordingly, both visual and psychological factors must be taken into account when optimizing computer workstations to reduce physiological responses that may cause excessive eyestrain and musculoskeletal load.

Development of radial optic flow pattern sensitivity at different speeds.

The development of sensitivity to radial optic flow discrimination was investigated by measuring motion coherence thresholds (MCTs) in school-aged children at two speeds. A total of 119 child observers aged 6-16years and 24 young adult observers (23.66+/-2.74years) participated. In a 2AFC task observers identified the direction of motion of a 5° radial (expanding vs. contracting) optic flow pattern containing 100 dots with 75% Michelson contrast moving at 1.6°/s and 5.5°/s and. The direction of each dot was drawn from a Gaussian distribution whose standard deviation was either low (similar directions) or high (different directions). Adult observers also identified the direction of motion for translational (rightward vs. leftward) and rotational (clockwise vs. anticlockwise) patterns. Motion coherence thresholds to radial optic flow improved gradually with age (linear regression, p<0.05), with different rates of development at the two speeds. Even at 16years MCTs were higher than that for adults (independent t-tests, p<0.05). Both children and adults had higher sensitivity at 5.5°/s compared to 1.6°/s (paired t-tests, p<0.05). Sensitivity to radial optic flow is still immature at 16years of age, indicating late maturation of higher cortical areas. Differences in sensitivity and rate of development of radial optic flow at the different speeds, suggest that different motion processing mechanisms are involved in processing slow and fast speeds.

Development of sampling efficiency and internal noise in motion detection and discrimination in school-aged children.

The aim of this study was to use an equivalent noise paradigm to investigate the development and maturation of motion perception, and how the underlying limitations of sampling efficiency and internal noise effect motion detection and direction discrimination in school-aged children (5-14 years) and adults. Contrast energy thresholds of a 2c/deg sinusoidal grating drifting at 1.0 or 6.0 Hz were measured as a function of added dynamic noise in three tasks: detection of a drifting grating; detection of the sum of two oppositely drifting gratings and direction discrimination of oppositely drifting gratings. Compared to the ideal observer, in both children and adults, the performance for all tasks was limited by reduced sampling efficiency and internal noise. However, the thresholds for discrimination of motion direction and detection of moving gratings show very different developmental profiles. Motion direction discrimination continues to improve after the age of 14 years due to an increase in sampling efficiency that differs with speed. Motion detection and summation were already mature at the age of 5 years, and internal noise was the same for all tasks. These findings were confirmed in a 1-year follow-up study on a group of children from the initial study. The results support suggestions that the detection of a moving pattern and discriminating motion direction are processed by different systems that may develop at different rates.

The development of global motion discrimination in school aged children.

Global motion perception matures during childhood and involves the detection of local directional signals that are integrated across space. We examine the maturation of local directional selectivity and global motion integration with an equivalent noise paradigm applied to direction discrimination. One hundred and three observers (6-17 years) identified the global direction of motion in a 2AFC task. The 8° central stimuli consisted of 100 dots of 10% Michelson contrast moving 2.8°/s or 9.8°/s. Local directional selectivity and global sampling efficiency were estimated from direction discrimination thresholds as a function of external directional noise, speed, and age. Direction discrimination thresholds improved gradually until the age of 14 years (linear regression, p < 0.05) for both speeds. This improvement was associated with a gradual increase in sampling efficiency (linear regression, p < 0.05), with no significant change in internal noise. Direction sensitivity was lower for dots moving at 2.8°/s than at 9.8°/s for all ages (paired t test, p < 0.05) and is mainly due to lower sampling efficiency. Global motion perception improves gradually during development and matures by age 14. There was no change in internal noise after the age of 6, suggesting that local direction selectivity is mature by that age. The improvement in global motion perception is underpinned by a steady increase in the efficiency with which direction signals are pooled, suggesting that global motion pooling processes mature for longer and later than local motion processing.

Reduction in direction discrimination with age and slow speed is due to both increased internal noise and reduced sampling efficiency.

PURPOSE: Sensitivity to moving structure decreases with age and slow speeds may be selectively impaired. This loss could be caused by elevated internal noise in the responses of motion sensors or a reduction in the efficiency with which motion responses are integrated. We adapt an equivalent noise paradigm to analyze the perception of slow and fast speed motion as a function of normal aging. METHODS: A total of 70 observers (20 to 89 years) identified the direction of global motion in a two-alternative forced choice task. In a central 8° aperture, 100 dots of 10% Michelson contrast were moving at 1.6 or 5.5°/s. The direction of each dot was drawn from a Gaussian distribution whose mean and SD were adaptively changed. Internal noise and sampling efficiency were estimated from direction discrimination thresholds as a function of external direction noise, speed, and age. RESULTS: Direction sensitivity was significantly worse for slow speeds at all ages (paired t-test, P < 0.05) and decreased approximately 2% per year (linear regressions, P < 0.01). This aging deficit was due to significant changes in internal noise (5.5°/s) and sampling efficiency (1.6°/s) (linear regression, P < 0.05). CONCLUSIONS: There is motion sensitivity loss with age that arises from an increase in internal noise in the responses of directional sensors and a decrease in responses that contribute to the global decision. Differences in the rates of progression at each speed indicate that motion is processed by independent systems tuned to different speeds, and that the channel for slow speed may be more vulnerable to normal age-related changes.

Sources of motion-sensitivity loss in glaucoma.

PURPOSE: Primary open angle glaucoma (POAG) is a leading cause of irreversible adult blindness and is characterized by progressive optic neuropathy and constriction of the visual field. Behavioral tests for POAG target retinal ganglion cell (RGC) classes that have reduced redundancy or that might be selectively damaged, but these tests cannot differentiate dysfunctional from nonfunctional RGC inputs to motion sensors. In this study, a signal-to-noise motion-sensitivity task was used to investigate the sources of motion-sensitivity loss in patients with POAG. METHODS: An equivalent noise paradigm was used to investigate sensitivity to the direction of radial optic flow patterns across the visual field in visually normal observers and patients with POAG. Internal noise and sampling efficiency were estimated from the direction of heading contrast-discrimination thresholds as a function of the level of added external noise. RESULTS: Contrast sensitivity to optic flow fell with retinal eccentricity for all observers, and decreased with both age and POAG. Equivalent noise analysis showed that the fall-off with eccentricity was primarily due to reduced sampling efficiency with relatively little increase in the level of internal noise and that the fall-off with age was attributable to both sources of error. Compared with age-matched control observers, patients with POAG have similar levels of internal noise but significantly lower sampling efficiency at all retinal loci. CONCLUSIONS: Motion-sensitivity losses with age, eccentricity, and POAG can arise from higher levels of internal noise and lower sampling efficiency. The central and peripheral glaucomatous neuropathy is mostly attributable to a reduction in sampling efficiency, suggesting that RGCs are nonfunctional rather than dysfunctional in this condition.

Contextual modulation of the motion aftereffect.

The authors examined center-surround effects for motion perception in human observers. The magnitude of the motion aftereffect (MAE) elicited by a drifting grating was measured with a nulling task and with a threshold elevation procedure. A surround grating of the same spatial frequency, temporal frequency, and orientation significantly reduced the magnitude of the MAE elicited by adaptation to the center grating. This effect was bandpass tuned for spatial frequency, orientation, and temporal frequency. Plaid surrounds but not contrast-modulated surrounds that moved in the same direction also reduced the MAE. These results provide psychophysical evidence for center-surround interactions analogous to those previously observed in electrophysiological studies of motion processing in primates. Collectively, these results suggest that motion processing, similar to texture processing, is organized for the purpose of highlighting regions of directional discontinuity in retinal images.

Acuity, crowding, reading and fixation stability.

People with age-related macular disease frequently experience reading difficulty that could be attributed to poor acuity, elevated crowding or unstable fixation associated with peripheral visual field dependence. We examine how the size, location, spacing and instability of retinal images affect the visibility of letters and words at different eccentricities. Fixation instability was simulated in normally sighted observers by randomly jittering single or crowded letters or words along a circular arc of fixed eccentricity. Visual performance was assessed at different levels of instability with forced choice measurements of acuity, crowding and reading speed in a rapid serial visual presentation paradigm. In the periphery: (1) acuity declined; (2) crowding increased for acuity- and eccentricity-corrected targets; and (3), the rate of reading fell with acuity-, crowding- and eccentricity-corrected targets. Acuity and crowding were unaffected by even high levels of image instability. However, reading speed decreased with image instability, even though the visibility of the component letters was unaffected. The results show that reading performance cannot be standardised across the visual field by correcting the size, spacing and eccentricity of letters or words. The results suggest that unstable fixation may contribute to reading difficulties in people with low vision and therefore that rehabilitation may benefit from fixation training.

Resolution of complex motion detectors in the central and peripheral visual field.

We examine how local direction signals are combined to compute the focus of radial motion (FRM) in random dot patterns and examine how this process changes across the visual field. Equivalent noise analysis showed that a loss in FRM accuracy was largely attributable to an increase in local motion detector noise with little or no change in efficiency across the visual field. The minimum separation for discriminating the foci of two overlapping optic flow patterns increased in the periphery faster than predicted from the resolution for a single FRM. This behavior requires that observers average numerous local velocities to estimate the FRM, which enables resistance to internal and external noise and endows the system with the property of position invariance. However, such pooling limits the precision with which multiple looming objects can be discriminated, especially in the peripheral visual field.