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PubMed1998

[Visual information processing and the mechanism of vision. Clinical application].

Psychogenic disturbance of vision includes various abnormalities such as low vision, abnormal visual field, abnormal color sense and disturbance of binocular function, although there are no abnormalities either in the eyeball or optic nerve, and no organic changes in brain computed tomography (CT) or magnetic resonance imaging (MRI). To clarify these abnormalities, it is necessary first to study the mechanism of visual information processing. In this report, the mechanism of visual information processing such as visual acuity, visual field, vision and attention and binocular function was studied by standard electrophysiological methods as well as by new techniques including electroencephalography (EEG) topography, visual evoked response imaging system (VERIS), and magnetoencephalogram (MEG). The following four items and the possibilities for clinical application were studied and discussed. The subjects were normal adults and child volunteers, patients with disturbance of vision of psychogenic origin, and patients with abnormal visual fields caused by organic changes in the visual pathway. 1. Visual acuity (form vision). 1) Visually evoked potemtial (VEP), early receptor potential (ERP), and MEG examination were carried out for normal subjects and patients with psychogenic disturbance of vision. 2) The P 100 of pattern reversal VEP of the patients showed a significantly higher response. 3) In normal subjects, the P 300 was observed widely around the Pz in the ERPs during Landolt's ring stimulation. 4) In normal children, the P 300 was observed slightly temporal to the Pz. 5) In some patients maximum amplitude of P 300 was observed in the occipital or temporal region, but in other patients there was no P 300 response in any derivation. 6) MEG in patients with the conversion type of psychogenic disturbance of vision showed only 2 small dipolar patterns around 117 ms during flash stimulation. It was quite different from that of normal subjects. 2. Visual field. 1) Multifocal VEP using VERIS could detect experimental artificial hemianopia caused by conclusion of the half visual field in normal subjects. 2) Multifocal VEP could detect hemianopia or quadratanopia. 3) In multifocal VEP in normal subject, off-latency time was about 36 ms longer than on-latency time both in the center and at the periphery of the retina. The ratio of on/off response decreased from the center to the periphery. 4) In MEG using flash stimulation, hemianopia could be detected even in patients with fixation difficulties. 5) As the subjective visual field was not always in accord with the objective field, objective visual field evaluation is important. 3. Vision and attention. 1) To confirm the influence of attention on visual information processings in patients with disturbance of vision of psychogenic origin, a hypothetical 'island of attention' was postulated. 2) The 'spiral visual field' and the 'Inazuma-type visual field' could be explained by application of this hypothesis for patients with disturbance of vision. 3) Three kinds of waves in VEF, W 1, W 2, and W 3, were detected by MEG after the stimulation of line motion illusion. There was a tendency for the latency time on the attention side to be shorter than on the non-attention side in waves W 2 and W 3. 4) There was a tendency for the amplitude of the attention side to be higher than that of the non-attention side in wave W 3. 5) Attention may influence vision. 4. Binocular vision. 1) A stimulus target was devised which did not elicit N 75, P 100, or N 140 waves. When this target was used for stereoptic stimulation, a negative wave was elicited with a latency of 170 to 280 ms. 2) When the same stimulus target without parallax was used, this negative wave was elicited but the amplitude was small. 3) When evoked potentials were measured under the same conditions, an electric dipole was elicited from the occipital to the temporal region by the electric current source. (ABSTRACT TRUNCATED)

Adolescent↗
PubMed1993

The distribution and nature of colour vision among the mammals.

1. An oft-cited view, derived principally from the writings of Gordon L. Walls, is that relatively few mammalian species have a capacity for colour vision. This review has evaluated that proposition in the light of recent research on colour vision and its mechanisms in mammals. 2. To yield colour vision a retina must contain two or more spectrally discrete types of photopigment. While this is a necessary condition, it is not a sufficient one. This means, in particular, that inferences about the presence of colour vision drawn from studies of photopigments, the precursors of photopigments, or from nervous system signals must be accepted with due caution. 3. Conjoint signals from rods and cones may be exploited by mammalian nervous systems to yield behavioural discriminations consistent with the formal definition of colour vision. Many mammalian retinas are relatively cone-poor, and thus there are abundant opportunities for such rod/cone interactions. Several instances were cited in which animals having (apparently) only one type of cone photopigment succeed at colour discriminations using such a mechanism. it is suggested that the exploitation of such a mechanism may not be uncommon among mammals. 4. Based on ideas drawn from natural history, Walls (1942) proposed that the receptors and photopigments necessary to support colour vision were lost during the nocturnal phase of mammalian history and then re-acquired during the subsequent mammalian radiations. Contemporary examination of photopigment genes along with the utilization of better techniques for identifying rods and cones suggest a different view, that the earliest mammals had retinas containing some cones and two types of cone photopigment. Thus the baseline mammalian colour vision is argued to be dichromacy. 5. A consideration of the broad range of mammalian niches and activity cycles suggests that many mammals are active during photic periods that would make a colour vision capacity potentially useful. 6. A systematic survey was presented that summarized the evidence for colour vision in mammals. Indications of the presence and nature of colour vision were drawn both from direct studies of colour vision and from studies of those retinal mechanisms that are most closely associated with the possession of colour vision. Information about colour vision can be adduced for species drawn from nine mammalian orders.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2002

Assessment of vision-related function in patients with age-related macular degeneration.

OBJECTIVE: To investigate the validity of the visual function index (VF-14) in assessing visual function in patients with age-related macular degeneration (AMD). DESIGN: Prospective noncomparative observational case series. PARTICIPANTS: One hundred fifty-nine consecutive patients attending a sole practitioner's academic retina-only clinic from May 1998 through August 1998 and from May 1999 through August 1999. MAIN OUTCOME MEASURES: Correlations were calculated between the VF-14 scores and the medical outcomes study 36-item short form (SF-36), weighted comorbidity scale, visual acuity and clinical AMD severity (stage), and vision self-assessment scales. Documentation of the severity of macular degeneration was performed by a sole examiner. RESULTS: There was a moderately strong correlation between visual acuity and trouble with vision (r = 0.51), satisfaction with vision (r = -0.50), and overall quality of vision (r = -0.56). A strong correlation was noted between VF-14 score and patients' self-rating of amount of trouble with vision (r = -0.67), satisfaction with vision (r = 0.62), and overall quality of vision (r = 0.67). In comparison, correlations between SF-36 score and patients' self-rating of amount of trouble with vision, satisfaction with vision, and overall quality of vision ranged from r = 0.37 to r = -0.40. Linear regression analysis for the overall study population indicated that AMD severity was not an independently significant predictor of VF-14 score after adjusting for visual acuity. However, among patients with 20/20 vision in the better eye, AMD severity was an independently significant predictor of VF-14 score after adjusting for visual acuity in the worse eye. CONCLUSIONS: The VF-14 exhibits a considerable degree of validity as a measure of functional impairment in patients with AMD. Age-related macular degeneration severity was an independently significant predictor of VF-14 score in the group of patients with 20/20 vision in the better eye, but this did not hold true for the overall study population. Age-related macular degeneration is associated with substantial impairment in reported visual function.

Aged↗
PubMed1998

Assessing the predictive ability of the test-positive findings of an elementary school vision screening.

PURPOSE: The purpose of this study is to assess the predictive ability of the test-positive findings of an elementary school vision screening program, conducted by 2nd-year optometry students, in identifying children with eye or vision disorders. METHODS: A modified version of the Modified Clinical Technique (MCT) vision screening was administered to elementary children from a below-average socioeconomic neighborhood in Houston, Texas. Comprehensive eye and vision examinations were provided to the available children who failed the vision screening. The screening was administered by groups of 2nd-year optometry students with the assistance of a 4th-year optometry student, and supervised by a faculty member licensed to practice optometry. The follow-up examinations were provided by supervised 4th-year optometry students in a clinical setting based at the elementary school. Positive predictive values calculated from the screening and examination findings estimate the probability that a failure on one or more of the screening tests would identify children with eye or vision disorders. RESULTS: Sixty-nine percent of the test-positive children examined were found to be true positives by the criteria developed in a study of vision screening methods in Orinda, California from 1954 through 1956. CONCLUSIONS: The predictive ability of this study's test-positive findings for identifying eye and vision disorders was found to be less than the predictive ability of the Orinda Study findings. This reduced predictive ability of the present study resulted in a larger number of children being overreferred for examinations than had occurred in the Orinda Study. The reduction in the ability of the test-positive findings of the current study's screening program to identify accurately children with eye and vision problems is most likely due to the limited experience of the optometry students conducting the screening program. The inability of this retrospective study to evaluate the accuracy of the test-negatives is a major limitation in assessing the total effectiveness of this vision screening program. Although the present study may indicate some value in optometry students conducting elementary vision screening programs, a prospective study which could assess the predictive ability of both test-positive and test-negative findings, as well as determine the sensitivity and specificity of the screening program, is needed to assess more fully the effectiveness of school vision screening programs using professional students.

Adolescent↗
PubMed2006

Prevalence and correlates of children's diagnosed eye and vision conditions.

PURPOSE: Little is known about the distribution of eye and vision conditions among children and about possible disparities in the distribution of these conditions. The purpose of this report is to describe the prevalence of diagnosed eye and vision conditions among children younger than 18 years in the United States. DESIGN: Repeated population-based cross-sectional study. PARTICIPANTS: Forty-eight thousand three hundred four members of randomly selected households in the U.S. who were younger than 18 years in the years 1996 through 2001 were analyzed. METHODS: The prevalence of children with diagnosed eye and vision conditions was estimated using self-reported information from the nationally representative Medical Expenditure Panel Surveys (MEPS) for 1996 through 2001. Descriptive statistics are presented, and the associations between the likelihood of diagnosed eye and vision conditions and child and family characteristics were assessed using logistic regression analyses adjusted for the complex survey design of MEPS. MAIN OUTCOME MEASURES: Prevalence of diagnosed eye and vision conditions and measures of the association between diagnosed eye and vision conditions and child and family characteristics. RESULTS: On average, approximately 6.8% (95% confidence interval [CI], 6.4%-7.2%) of children < 18 years in the U.S. have a diagnosed eye and vision condition, ranging from 8.6% (95% CI, 7.8%-9.5%) in 1996 to 5.8% (95% CI, 5.2%-6.4%) in 2001. Excluding conjunctivitis, the 4 most common conditions were refractive disorders, potentially blinding disorders, trauma or injury, and other disorders not elsewhere classified. White children, children with more educated mothers, and children living in higher income families were more likely to have a diagnosed eye and vision condition. Hispanic children, children in very good or excellent health, and uninsured children were less likely to have any self-reported diagnosed eye and vision condition. CONCLUSIONS: This article presents a method for using MEPS to identify children younger than 18 years with eye and vision conditions. Although this method does not identify all children with eye and vision conditions, it does identify children with diagnosed eye and vision conditions. Results provide some evidence that underprivileged children may be underdiagnosed, undertreated, or both, placing them at risk for future problems.

Adolescent↗
PubMed2005

Emergence of a rehabilitation medicine model for low vision service delivery, policy, and funding.

BACKGROUND: A rehabilitation medicine model for low vision rehabilitation is emerging. There have been many challenges to reaching consensus on the roles of each discipline (optometry, ophthalmology, occupational therapy, and vision rehabilitation professionals) in the service delivery model and finding a place in the reimbursement system for all the providers. METHODS: The history of low vision, legislation associated with Centers for Medicare and Medicaid Services coverage for vision rehabilitation, and research on the effectiveness of low vision service delivery are reviewed. RESULTS: Vision rehabilitation is now covered by Medicare under Physical Medicine and Rehabilitation codes by some Medicare carriers, yet reimbursement is not available for low vision devices or refraction. Also, the role of vision rehabilitation professionals (rehabilitation teachers, orientation and mobility specialists, and low vision therapists) in the model needs to be determined. In a recent systematic review of the scientific literature on the effectiveness of low vision services contracted by the Agency for Health Care Quality Research, no clinical trials were found. The literature consists primarily of longitudinal case studies, which provide weak support for third-party funding for vision rehabilitative services. CONCLUSIONS: Providers need to reach consensus on medical necessity, treatment plans, and protocols. Research on low vision outcomes is needed to develop an evidence base to guide clinical practice, policy, and funding decisions.

Delivery of Health Care↗
PubMed2006

Frequency of colour vision deficiencies in melanoma patients: results of a prospective comparative screening study with the Farnsworth panel D 15 test including 300 melanoma patients and 100 healthy controls.

Patients with melanoma may experience a variety of different vision symptoms, in part associated with melanoma-associated retinopathy. For several melanoma patients with or without melanoma-associated retinopathy, colour vision deficiencies, especially involving the tritan system, have been reported. The frequency of colour vision deficiencies in a larger cohort of melanoma patients has not yet been investigated. The aim of this study was to investigate the frequency of colour vision deficiencies in melanoma patients subject to stage of disease, prognostic factors such as tumour thickness or Clark level, S100-beta and predisposing diseases that may have an impact on colour vision (hypertension, diabetes mellitus, glaucoma or cataract). Three hundred melanoma patients in different tumour stages and 100 healthy age-matched and sex-matched controls were examined with the saturated Farnsworth panel D 15 test. Seventy out of 300 (23.3%) melanoma patients and 12/100 (12%) controls showed pathologic results in colour testing. This discrepancy was significant (P < 0.016; odds ratio = 2.23, 95% confidence interval 1.15-4.32). Increasing age was identified as a highly significant (P = 0.0005) risk factor for blue vision deficiency. Adjusting for the age and predisposing diseases, we could show that melanoma was associated with the risk of blue vision deficiency. The frequency of blue vision deficiency in 52/260 melanoma patients without predisposing diseases (20%) compared with 4/78 controls without predisposing diseases (5.1%) differed significantly (odds ratio 4.441; confidence interval 1.54-12.62; P < 0.004). In 260 melanoma patients without predisposing diseases, blue vision deficiency, as graded on a 6-point scale, showed a weak positive correlation (Spearman) with tumour stage (r = 0.147; P < 0.01), tumour thickness (r = 0.10; P = 0.0035), Clark level (r = 0.12; P = 0.04) and a weak negative correlation with time since initial diagnosis (r = -0.11; P = 0.0455). Blue vision deficiency is associated with melanoma, but is only weakly related to stage of disease. Although we saw a positive correlation with well-known prognostic markers, such as tumour thickness and Clark level, blue vision deficiency as assessed by the Farnsworth panel D 15 test in general is inappropriate as a marker of tumour progression. For the use of blue vision deficiency in melanoma patients without predisposing diseases, a diligent test performance and interpretation is very important.

Adult↗
PubMed2005

The Glenn A. Fry Award Lecture 2003: Vision in elders--summary of findings of the SKI study.

PURPOSE: To assess a broad range of vision functions in a large older population, to investigate the impact of vision function loss on visual performance measures, and to determine whether low contrast vision measures can predict future loss of visual acuity. METHODS: A large battery of vision functions, including spatial vision measures, glare tests, visual fields, stereopsis, color vision, temporal sensitivity, reading performance, and face recognition, was administered to a population of 900 community-living older observers (mean age, 75.5 years; SD, 9.3 years; range, 58 to 102 years). A subsample (N = 596) was retested on average 4.4 years later (SD, 1.0 years). RESULTS: Each vision function is affected differentially by aging. Some functions show little change with age (e.g., standard clinically measured high contrast visual acuity), whereas others demonstrate drastic losses with increasing age. For the oldest age group (>90 years), vision function losses ranged from 1.2 times worse than young observers (critical flicker/fusion frequency) to 18 times worse than young observers (low contrast acuity in glare). Visual performance measures, such as reading or face recognition, are also significantly affected by aging even in those with intact visual acuity. The results demonstrate that low contrast vision functions can successfully predict subsequent loss of high contrast visual acuity. CONCLUSION: Nonstandard vision function measures show significant losses with age that cannot be predicted by standard clinical measures. Measures of low contrast vision function allow clinicians to identify and monitor those patients at high risk for future vision loss.

Aged↗
PubMed2003

Low vision and blindness in adults in Gurage Zone, central Ethiopia.

AIM: To determine the magnitude and causes of low vision and blindness in the Gurage zone, central Ethiopia. METHODS: A cross sectional study using a multistage cluster sampling technique was used to identify the study subjects. Visual acuity was recorded for all adults 40 years and older. Subjects who had a visual acuity of <6/18 were examined by an ophthalmologist to determine the cause of low vision or blindness. RESULTS: From the enumerated population, 2693 (90.8%) were examined. The prevalence of blindness (<3/60 better eye presenting vision) was 7.9% (95% CI 6.9 to 8.9) and of low vision (6/24-3/60 better eye presenting vision) was 12.1% (95% CI 10.9 to 13.3). Monocular blindness was recorded in 16.3% of the population. Blindness and low vision increased with age. The odds of low vision and blindness in women were 1.8 times that of the men. The leading causes of blindness were cataract (46.1%), trachoma (22.9%), and glaucoma (7.6%). While the prevalence of vision reducing cataract increased with age, the prevalence of trachoma related vision loss did not increase with age, suggesting that trichiasis related vision loss in this population might not be cumulative. CONCLUSION: The magnitude of low vision and blindness is high in this zone and requires urgent intervention, particularly for women. Further investigation of the pattern of vision loss, particularly as a result of trachomatous trichiasis, is warranted.

Adult↗
PubMed2006

Perspectives on low vision service in Canada: a pilot study.

BACKGROUND: A review of the literature and current practice patterns for vision rehabilitation care in Canada provide a basis for this pilot study, which was undertaken to explore related issues from the perspectives of older adults and low vision service providers. The pilot study was overseen by a number of collaborators whose names are listed at the end of this paper. METHODS: Thirty people aged 60 years or older who had vision impairments and were clients of the Canadian National Institute for the Blind were surveyed by telephone. Ophthalmologists, optometrists, and opticians completed a mail questionnaire. Vision rehabilitation practitioners and nurses, ophthalmic technicians, and service providers for low vision technical aids were surveyed by e-mail. RESULTS: Ophthalmologists are a primary source of referrals to low vision services, but low functional vision does not always trigger such referrals, nor are referrals always timely. Optometrists are primary providers of low vision services, including dispensing of low vision aids, but such aids are expensive, and inadequate training in their use may contribute to noncompliance. Costs associated with providing low vision assessments and services are higher than compensation to vision service providers, whose capacity to meet increasing demand is limited. In addition, there are disparities between rural and urban areas and among provinces in the availability of, and funding for, services and aids. INTERPRETATION: On the basis of the findings, an emergent theory is proposed on the consequences resulting from lack of planning and standards for vision rehabilitation care. The implications of this study form the basis for further research.

Aged↗
PubMed1995

Vision testing and the elderly driver: is there a problem meriting policy change?

BACKGROUND: The number of elderly drivers is increasing. The primary purpose of public policy requiring vision screening for driver's license renewal is to identify, and, when necessary, restrict drivers with functional vision impairments. Because of age-related ocular conditions, elderly drivers, as a group, have a higher incidence and prevalence of functionally impaired vision. To date, there is no empirical evidence of a significant predictive relationship between changes in vision function and automobile crashes. METHODS: Most states require vision screening for driver's license renewal, whereas some do not. Among those states requiring vision screening, there is considerable variation in the frequency and level of testing. Efforts to determine the role of vision in driving, while suggestive, have not been useful in identifying at-risk older drivers. RESULTS: Researchers have observed that older drivers are often aware of their decreased functional capacity and voluntarily adjust their driving patterns by driving less frequently, for shorter distances, during daylight hours, more slowly, and during non-rush hours. However, although not statistically significant, the decline in the mean annual traffic fatality rates with increased state vision screening requirements suggests a possible beneficial effect of vision screening. CONCLUSIONS: Because older drivers are at risk for sight-threatening conditions, they are most affected by vision screening requirements for driver's license renewal. Since a loss of driving privileges represents a major loss of mobility and independence, there is a pressing need to better understand the relationship between age-related vision changes and the frequency and severity of traffic crashes.

Accidents, Traffic↗
PubMed2005

Retrospective analysis of refractive errors in children with vision impairment.

PURPOSE: Emmetropization is the reduction in neonatal refractive errors that occurs after birth. Ocular disease may affect this process. We aimed to determine the relative frequency of ocular conditions causing vision impairment in the pediatric population and characterize the refractive anomalies present. We also compared the causes of vision impairment in children today to those between 1974 and 1981. METHODS: Causes of vision impairment and refractive data of 872 children attending a pediatric low-vision clinic from 1985 to 2002 were retrospectively collated. As a result of associated impairments, refractive data were not available for 59 children. An analysis was made of the causes of vision impairment, the distribution of refractive errors in children with vision impairment, and the average type of refractive error for the most commonly seen conditions. RESULTS: We found that cortical or cerebral vision impairment (CVI) was the most common condition causing vision impairment, accounting for 27.6% of cases. This was followed by albinism (10.6%), retinopathy of prematurity (ROP; 7.0%), optic atrophy (6.2%), and optic nerve hypoplasia (5.3%). Vision impairment was associated with ametropia; fewer than 25% of the children had refractive errors < or = +/-1 D. The refractive error frequency plots (for 0 to 2-, 6 to 8-, and 12 to 14-year age bands) had a Gaussian distribution indicating that the emmetropization process was abnormal. The mean spherical equivalent refractive error of the children (n = 813) was +0.78 +/- 6.00 D with 0.94 +/- 1.24 D of astigmatism and 0.92 +/- 2.15 D of anisometropia. Most conditions causing vision impairment such as albinism were associated with low amounts of hyperopia. Moderate myopia was observed in children with ROP. CONCLUSIONS: The relative frequency of ocular conditions causing vision impairment in children has changed since the 1970s. Children with vision impairment often have an associated ametropia suggesting that the emmetropization system is also impaired.

Adolescent↗
PubMed2001

Peripheral vision and back tuck somersaults.

Although vision appears to enhance performance of somersaulting skills, few studies have investigated the source (foveal or ambient) of useful visual cues that can potentially be used by gymnasts during a somersault. Therefore, the primary objectives were to investigate the possible role of peripheral vision in the control of orientation and landing balance in a back tuck somersault. 10 female gymnasts (age = 11.6 +/- 2.7 yr., competitive level = 8 +/- 1.2, training time in gymnastics = 5.9 +/- 1.6 yr.) performed back tuck somersaults under four visual conditions (full visual field, horizontal peripheral vision limited to 100 degrees, horizonal peripheral vision limited to 60 degrees, and no vision) while wearing electromagnetic sensors that allowed automatic digitizing. Analysis yielded no statistically significant difference on any of the kinematic variables among vision conditions. Despite limiting the gymnasts' available horizontal peripheral vision, joint angles, angular velocities, and timing remained very similar. There were no statistically significant differences in landing balance between the conditions of full vision, 100 degrees peripheral vision, and 60 peripheral vision. However, gymnasts were less stable at landing when vision was absent as compared to the three other vision conditions.

Adolescent↗
PubMed2000

Aircrew visors and color vision performance: a comparative and preliminary pilot study analysis.

BACKGROUND: A very important aspect of visual performance to consider, for present and future recommendations regarding aircrew visors, concerns their impact on color vision. The literature has remained mostly inconclusive with respect to the human perceptual process of colors during actual mission employment. OBJECTIVE: This study uses active duty military aircrews to provide objective and valuable information on the effects of Short Wavelength Absorbing Filters (SWAFs), such as the High Contrast Visor (HCV), and some selected waveband type Laser Eye Protection (LEP) visors on color vision. It provides a direct comparison of several current and proposed aircrew eye protective visors with respect to their effects on color vision. The data analyzed in this study will also be used to support a recommendation regarding a new optimal visor for aircrew wear during air to air (and ground) engagements, for sun protection, and possible visual enhancement in order to improve user compliance. METHODS: Seven volunteers on active flying status each underwent comprehensive color vision testing with and without seven of the U. S. Air Force's (USAF's) current or proposed aircrew visors/filters. Spectral transmissions of these visors/filters were obtained to identify and determine their individual characteristics which included their ability to induce acquired color vision decrements in "color normal" individuals. RESULTS: The widely utilized USAF HCV significantly degraded color vision more than luminosity matched neutral density visors. Abrupt color vision decrements for specifically fielded LEP visors were also noted. Their objective data supported theoretical and speculated color vision effects. Even though low transmittance neutral density visors did have some effect on color vision, decrement severity was not considered significant enough to affect overall performance during color vision testing. CONCLUSIONS AND DISCUSSION: Because of their ability to significantly affect color vision, concerns regarding the use of HCV and LEP visors should entail age, baseline color vision, environmental, and mission factors. Further testing should be done to evaluate the definitive effects that these visors actually have on the recognition of color symbology of Multi Function and Electronic Flight Information Displays. Findings in this study also support theoretical opinions that encourage the fielding of a neutral density filter (mildly tinted) with an overall transmission of 25-49%. Its use by flyers during low and bright illuminant conditions may greatly enhance visual performance by encouraging wearer compliance while allowing colors to be perceived normally.

Adult↗
PubMed2003

Vision and driving self-restriction in older adults.

OBJECTIVES: To assess driving self-restriction (vision related and nonvision related) in relation to vision test performance of older adults. DESIGN: Cross-sectional study. SETTING: Population-based cohort of community-dwelling older adults. PARTICIPANTS: Six hundred twenty-nine current drivers aged 55 and older had driving behavior, health, and physical function assessed and vision function tested in 1993-95. MEASUREMENTS: Self-report of driving restriction as vision or non-vision related and performance on a comprehensive battery of vision tests (visual acuity; contrast sensitivity; effects of illumination level, contrast, and glare on acuity; visual fields with and without attentional load; color vision; temporal sensitivity; and the effect of dim light on walking ability). RESULTS: Demographic, health, and functional characteristics differed significantly between restrictors and nonrestrictors but not between vision- and nonvision-related restrictors. Controlling for potential confounding, only vision-related driving self-restriction was significantly associated with reduced performance on nonstandard measures of acuity. Poor depth perception was significantly associated with restriction for both vision- and nonvision-related reasons. Poor performance on attentional visual field tests, analyzed individually and in combination with standard field tests, was not associated with driving self-restriction. CONCLUSION: Older adults with early changes in spatial vision function and depth perception appear to recognize their limitations and restrict their driving even if they do not acknowledge the visual impairment as the cause for restriction. Poor visual attention, a risk factor for crashes, may not be recognized. Additional studies of driving self-restriction in relation to risk factors for crashes in older adults may help refine this strategy of reducing driving-related injury and death.

Aged↗
PubMed2001

A weighted version of the Melbourne Low-Vision ADL Index: a measure of disability impact.

OBJECTIVE: To develop a version of the Melbourne Low-Vision ADL Index that measures the personal impact of disability in activities of daily living (ADL's). Also, to determine the relationship between clinical measures of vision impairment and disability impact. METHODS: The Melbourne Low-Vision ADL Index (MLVAI) is a desk-based clinical assessment of disability in ADL's. Ability to perform each item is rated on a five-level descriptive scale from zero to four. In this study, the original version of the MLVAI was modified to measure disability impact. The simple modification involved weighting each item by the importance of that item to the person being tested. Importance was also rated on a five-level scale from zero to four. The validity and reliability of the Weighted Melbourne Low-Vision ADL Index (MLVAI(W)) was determined for 97 vision-impaired subjects in a cross-sectional study. RESULTS: Cronbach's alpha coefficient indicated an internal reliability of 0.94, and an intraclass correlation coefficient indicated an overall reliability of 0.88. The standard error of measurement was 24.7 points (out of a possible score of 400). There was a statistically significant difference in test scores between normal subjects and vision-impaired subjects. All vision measures had a high, statistically significant correlation with MLVAI(W) score. Near-word acuity had the strongest correlation (r(s) = 0.78, p < 0.001), followed by Melbourne Edge Test contrast sensitivity (r(s) = -0.72, p < 0.001). Visual field had the weakest correlation (r(s) = -0.52, p < 0.001). The best predictive model of MLVAI(W) score incorporated the variables age, near-word acuity, and visual field. Together, these variables accounted for 65.1% of the variance in MLVAI(W) score. CONCLUSIONS: The MLVAI is highly valid and reliable when weighted by a scale that reflects the personal importance of ADL's. The MLVAI(W) can provide information over and above that obtained with the usual clinical vision measures and may be used to assess low-vision patients and to measure low-vision rehabilitation outcomes. It is suggested that the assessment of disability using the original MLVAI and the assessment of the impact of disability using the MLVAI(W) should be kept separate to facilitate the clear interpretation of the outcomes of low-vision rehabilitation.

Activities of Daily Living↗
PubMed2005

The magnitude of the effect of calf muscles fatigue on postural control during bipedal quiet standing with vision depends on the eye-visual target distance.

The purpose of the present experiment was to investigate whether, with vision, the magnitude of the effect of calf muscles fatigue on postural control during bipedal quiet standing depends on the eye-visual target distance. Twelve young university students were asked to stand upright as immobile as possible in three visual conditions (No vision, Vision 1m and Vision 4m) executed in two conditions of No fatigue and Fatigue of the calf muscles. Centre of foot pressure displacements were recorded using a force platform. Similar increased variances of the centre of foot pressure displacements were observed in the fatigue relative to the No fatigue condition for both the No vision and Vision 4m conditions. Interestingly, in the vision 1m condition, fatigue yielded: (1) a similar increased variance of the centre of foot pressure displacements to those observed in the No vision and Vision 4m conditions along the medio-lateral axis and (2) a weaker destabilising effect relative to the No vision and Vision 4m conditions along the antero-posterior axis. These results evidence that the ability to use visual information for postural control during bipedal quiet standing following calf muscles fatigue is dependent on the eye-visual target distance. More largely, in the context of the multisensory control of balance, the present findings suggest that the efficiency of the sensory reweighting of visual sensory cues as the neuro-muscular constraints acting on the subject change is critically linked with the quality of the information the visual system obtains.

Adult↗
PubMed2003

Is word recognition different in central and peripheral vision?

Peripheral vision plays an important role in normal reading, but its role becomes larger for visually impaired people with central-field loss. This experiment studied whether lexical processing differs in central and peripheral vision through the analysis of word-frequency effects in lexical decisions. We asked two main questions: (1) Do central and peripheral vision differ in the time course of lexical processing? and (2) do central and peripheral vision differ in the quality of lexical processing? To address the first question, we examined the time course of frequency effects in central and peripheral vision over a range from 25 to 500 ms. We found that significant frequency effects occurred for the shortest exposures, 25-50 ms, in central vision, whereas significant frequency effects did not occur in peripheral vision until 100 ms. To address the second question, we used word-frequency effects as a marker for the nature of lexical processing. We compared frequency effects in central and peripheral vision for data within matched ranges of percent accuracy (0-20%, 20-40%, 40-60%, 60-80%, and 80-100%). We found that there was no difference in the pattern of frequency effects in central and peripheral vision at equivalent performance levels. We conclude that lexical processing is slower in peripheral vision, but the quality of lexical processing is similar in central and peripheral vision.

Adolescent↗