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Quebec model for low vision rehabilitation.

The increase in longevity (and secondary morbidity) in the Quebec population adds social and financial pressure to society, as it does elsewhere in Canada and in many western countries. This article gives a brief history of the evolution of vision rehabilitation services in Quebec and describes how services are provided for people with low vision throughout the province. Although numerous groups, associations, centres, and resources are available to assist people with vision impairments, such as the Canadian National Institute for the Blind-Québec, the majority of visual rehabilitation services are provided by government-sponsored rehabilitation centres, namely the Centres régionaux de réadaptation en déficience physique that are located strategically throughout the province. Low vision clinical evaluations in these centres are shared by 36 optometrists throughout the province. Between 5 and 7 ophthalmologists are involved in low vision care, half in university-affiliated hospitals, primarily in Montreal. There may be delays of up to 6 months to be seen in a funded low vision clinic. Statistics obtained from la Régie de l'assurance maladie du Québec show that there are approximately 8,000 requests for low vision aids every year, and that 80% of clients retain at least some level of visual function. Services are covered by Medicare and low vision aids are provided at no cost, although ophthalmologists cannot prescribe low vision aids through the Medicare-funded system. We must ensure that the capacity of our system continues to provide adequately for clientele in the future.

Health Resources↗

Prevalence and causes of blindness and low vision in southern Sudan.

BACKGROUND: Blindness and low vision are thought to be common in southern Sudan. However, the magnitude and geographical distribution are largely unknown. We aimed to estimate the prevalence of blindness and low vision, identify the main causes of blindness and low vision, and estimate targets for blindness prevention programs in Mankien payam (district), southern Sudan. METHODS AND FINDINGS: A cross-sectional survey of the population aged 5 y and above was conducted in May 2005 using a two-stage cluster random sampling with probability proportional to size. The Snellen E chart was used to test visual acuity, and participants also underwent basic eye examination. Vision status was defined using World Health Organization categories of visual impairment based on presenting visual acuity (VA). A total of 2,954 persons were enumerated and 2,499 (84.6%) examined. Prevalence of blindness (presenting VA of less than 3/60 in the better eye) was 4.1% (95% confidence interval [CI], 3.4-4.8); prevalence of low vision (presenting VA of at least 3/60 but less than 6/18 [corrected] in the better eye) was 7.7% (95% CI, 6.7-8.7); whereas prevalence of monocular visual impairment (presenting VA of at least 6/18 [corrected] in better eye and VA of less than 6/18 [corrected] in other eye) was 4.4% (95% CI, 3.6-5.3). The main causes of blindness were considered to be cataract (41.2%) and trachoma (35.3%), whereas low vision was mainly caused by trachoma (58.1%) and cataract (29.3%). It is estimated that in Mankien payam 1,154 persons aged 5 y and above (lower and upper bounds = 782-1,799) are blind, and 2,291 persons (lower and upper bounds = 1,820-2,898) have low vision. CONCLUSIONS: Blindness is a serious public health problem in Mankien, and there is urgent need to implement comprehensive blindness prevention programs. Further surveys are essential to confirm these tragic findings and estimate prevalence of blindness and low vision in the entire region of southern Sudan in order to facilitate planning of VISION 2020 objectives.

Adolescent↗

[Binocular vision after cataract surgery in children--long-term results].

PURPOSE: To evaluate quality of binocular vision in dependence on type of cataract, time of surgery and type of aphakic correction with minimal 5 years follow up. METHODS: 127 children divided into 3 groups: Group A--24 children with monolateral congenital cataract, Group B--56 children with bilateral congenital cataract, Group C--47 children with traumatic cataract. Binocular vision results were evaluated 5-10 years after cataract surgery subordinated on the type of aphakic correction-PC IOL, contact lenses, spectacles, type of cataract (congenital mono or bilateral, traumatic) and time of cataract surgery. RESULTS: Group A: Binocular vision in 56% children with cataract surgery in the first 3 months of age and only 20% of binocular vision in children operated later. Binocular vision results in dependence on aphakic correction (46% in contact lens subgroup, 44% in PCIOL subgroup without statistically significant differences. Group B: Binocular vision in 76% of children operated in the first 3 months of age, and 79% of children operated later. Binocular vision in 68% of children in spectacle aphakic correction subgroup, 67% of children in contact lenses subgroup, and 75% of children in primary or secondary implanted PC IOL subgroup. Group C: Binocular vision in 80% of children with contact lenses subgroup, and in 84% of children with implantation PC IOL. CONCLUSION: Better results of binocular vision quality have children with cataract extraction in the first three months of age then children operated later in group with monolateral congenital cataract. Primary or secondary implantation of PC IOL was find to the better aphakic correction for the binocular visual results in the groups with bilateral congenital cataract and traumatic cataract than other types of aphakic correction. Amblyopia is a major determinate of visual outcome in childhood cataract. The timing of surgery--the early cataract removal will continue to be more important than the method of aphakic optical correction, especially in the case of monolateral congenital cataract.

Cataract↗

Causes of low vision and blindness in children in a blind school in Lagos, Nigeria.

A descriptive study to determine the causes of low vision and blindness in children attending the Pacelli School for the Blind in Lagos State, Nigeria. A standardised methodology was used with structured and semi-structured questioinaires. Twenty-six children aged below 16 years who were identified as having low vision and blindness were examined to determine the causes of the low vision and blindness. The anatomical sites of diseases leading to low vision and blindness in these children were retina (30.8%), lens (23.1%), glaucoma (19.2%), cornea (11.5%) and optic nerve (7.7%). Aetiologically, 38.5% of low vision was due to hereditary factors, 23.1% intra-uterine, 15.4% others and unknown in 23%. Retinal dystrophy was the most common cause of low vision and blindness, while congenital cataract and glaucoma were the major causes of avoidable blindness. Very few cases of corneal scar (Measles/Vitamin A deficiency) were seen. The causes of low vision appeared to be different from those of blindness as hereditary and intra-uterine factors were mainly responsible for low vision. It is recommended that these children be identified early, through low vision care programmes and those with avoidable causes treated accordingly.

Adolescent↗

Biomimetic machine vision system.

Real-time application of digital imaging for use in machine vision systems has proven to be prohibitive when used within control systems that employ low-power single processors without compromising the scope of vision or resolution of captured images. Development of a real-time machine analog vision system is the focus of research taking place at the University of Wyoming. This new vision system is based upon the biological vision system of the common house fly. Development of a single sensor is accomplished, representing a single facet of the fly's eye. This new sensor is then incorporated into an array of sensors capable of detecting objects and tracking motion in 2-D space. This system "preprocesses" incoming image data resulting in minimal data processing to determine the location of a target object. Due to the nature of the sensors in the array, hyperacuity is achieved thereby eliminating resolutions issues found in digital vision systems. In this paper, we will discuss the biological traits of the fly eye and the specific traits that led to the development of this machine vision system. We will also discuss the process of developing an analog based sensor that mimics the characteristics of interest in the biological vision system. This paper will conclude with a discussion of how an array of these sensors can be applied toward solving real-world machine vision issues.

Algorithms↗

Prevalence and causes of low vision and blindness in northern KwaZulu.

A survey of the prevalence of blindness and low vision was conducted in the Ingwavuma district of KwaZulu to assess the effectiveness of existing eye care facilities in the prevention and treatment of impaired vision and blindness. One hundred subjects from each of 60 randomly selected clusters (N = 6,090) were screened. Of these, 293 were identified and referred to an ophthalmologist for examination. Of the 268 (91,5%) examined, 241 were found to have visual impairment. Sixty-one of these people were blind, 85 had low vision, 61 were blind in one eye but had normal vision in the other, and 34 had low vision in one eye but normal vision in the other. The prevalence of blindness was 1,0% (95% confidence interval 0,7-1,2%), and the prevalence of impaired vision was 1,4% (95% confidence interval 1,1-1,7%). Age-related cataract (59,0%) and chronic glaucoma (22,9%) were the two main causes of blindness. Age-related cataract (75,3%), refractive error (10,0%) and chronic glaucoma (4,7%) were the main causes of impaired vision. Existing eye care services for the region have reduced the prevalence of blindness by only 7,0%. The training of ophthalmic nurses and the establishment of a sight-saver clinic in the area are necessary to reduce the prevalence of low vision and blindness.

Adolescent↗

Interocular transfer of the movement aftereffect in central and peripheral vision of people with strabismus.

PURPOSE: To compare binocularity in central and peripheral vision of people with early-onset strabismus and people with normal binocular vision. METHODS: Ten subjects with early-onset strabismus, and nine subjects with normal binocular vision were tested. To assess binocularity, interocular transfer (IOT) of a rotary movement aftereffect (MAE) was measured. The MAE stimuli were either confined to the central 2.8 degrees of the visual field or were presented 10 degrees into peripheral vision. RESULTS: In peripheral vision, there was no significant difference in IOT for the two groups of subjects. In central vision, there was a significant decrease of IOT in subjects with early-onset strabismus. Their IOT was, however, significantly greater than zero. CONCLUSIONS: Early-onset strabismus appears to spare binocularity in peripheral vision but reduces it in central vision. It does not abolish binocularity assessed by IOT of MAE, suggesting that some binocular connections survive early-onset strabismus, even in central vision.

Adolescent↗

Improvements in clinical and functional vision and perceived visual disability after first and second eye cataract surgery.

AIMS: To determine the improvements in clinical and functional vision and perceived visual disability after first and second eye cataract surgery. METHODS: Clinical vision (monocular and binocular high and low contrast visual acuity, contrast sensitivity, and disability glare), functional vision (face identity and expression recognition, reading speed, word acuity, and mobility orientation), and perceived visual disability (Activities of Daily Vision Scale) were measured in 25 subjects before and after uncomplicated cataract surgery (10 first eye surgery and 15 second eye surgery) and in 10 age matched controls. RESULTS: Significant improvements were found after surgery in clinical and functional vision and perceived visual disability. Greater improvements were found after first eye surgery than after second eye surgery. However, first eye surgery did not return all scores to age matched normal levels. There were significant improvements in several of the tests measured after second eye surgery, and all postoperative values were similar to those from age matched normals. CONCLUSIONS: Significant improvements in clinical, functional, and perceived vision are obtained by cataract surgery. The improvements in objective measures of functional vision found in this study support previous findings of improvements in patients' perceived functional vision. In addition, these data provide support to the necessity of second eye surgery in some patients to improve certain aspects of visual function to age matched normal levels.

Aged↗

[Long-term vision follow-up after vitrectomy in diabetic retinopathy].

BACKGROUND: We investigated whether visual acuity remained stable in the long run after vitrectomy for complications of diabetic retinopathy and which risk factors for a decrease in vision could be identified. MATERIALS AND METHODS: The charts of 389 patients who had undergone vitreous surgery for complications of diabetic retinopathy between 1990 and 1994 were retrospectively reviewed. The median follow-up was 26 months with a minimum of 6 months. RESULTS: Seventy-two percent of the eyes with a vision of 20/200 or better within 6 months after surgery retained this vision after 2 years. The percentage of eyes with vision of less than 5/200 was 25% after 6 months and increased to 41% after 4 years. After 2 years 24% of the eyes had lost two or more lines compared to the best vision within the first 6 months after surgery. The main cause for a decrease of vision in type-I diabetics was retinal detachment, in type-II diabetics a progression of maculopathy and opticopathy. Risk factors for a detachment were pre-existing retinal detachment before surgery and reduced postoperative vision. The risk factor for a progression of maculopathy and opticopathy was a silicone tamponade. CONCLUSIONS: Eyes with good vision soon after surgery remain stable in the long run. Eyes with advanced stages of diabetic retinopathy and only ambulatory vision after surgery have an increased risk for new loss of visual function in the long run.

Adult↗

Suppressive and facilitatory spatial interactions in amblyopic vision.

Amblyopic vision is characterized by reduced spatial resolution, and inhibitory spatial interactions ("crowding") that extend over long distances. The present paper had three goals: (1) To ask whether the extensive crowding in amblyopic vision is a consequence of a shift in the spatial scale of analysis. To test this we measured the extent of crowding for targets that were limited in their spatial frequency content, over a large range of target sizes and spatial frequencies. (2) To ask whether crowding in amblyopic vision can be explained on the basis of contrast masking by remote flanks. To test this hypothesis we measured and compared crowding in a direction-identification experiment with masking by remote flanks in a detection experiment. In each of the experiments our targets and flanks were comprised of Gabor features, thus allowing us to control the feature contrast, spatial frequency and orientation. (3) To examine the relationship between the suppressive and facilitatory interactions in amblyopic contrast detection and "crowding". Our results show that unlike the normal fovea [Levi, Klein, & Hariharan, Journal of Vision 2 (2002a) 140] crowding in amblyopia is neither scale invariant, nor is it attributable to simple contrast masking. Rather, our results suggest that suppressive spatial interactions in amblyopic vision extend over larger distances than in normal foveal vision, similar to peripheral vision of non-amblyopic observers [Levi, Hariharan, & Klein, Journal of Vision 2 (2002b) 167], for targets of the same size. Observers can easily detect the features that comprise our targets (Gabor patches) under conditions where crowding is strong. Thus, our speculation is that crowding occurs because the target and flanks are combined or pooled at a second stage that is coarse in the amblyopic visual system, following the stage of feature extraction. In amblyopic vision, this pooling takes place over a large spatial distance.

Adult↗

Molecular patterns of X chromosome-linked color vision genes among 134 men of European ancestry.

We used Southern blot hybridization to study X chromosome-linked color vision genes encoding the apoproteins of red and green visual pigments in 134 unselected Caucasian men. One hundred and thirteen individuals (84.3%) had a normal arrangement of their color vision pigment genes. All had one red pigment gene; the number of green pigment genes ranged from one to five with a mode of two. The frequency of molecular genotypes indicative of normal color vision (84.3%) was significantly lower than had been observed in previous studies of color vision phenotypes. Color vision defects can be due to deletions of red or green pigment genes or due to formation of hybrid genes comprising portions of both red and green pigment genes [Nathans, J., Piantanida, T.P., Eddy, R.L., Shows, T.B., Jr., & Hogness, D.S. (1986) Science 232, 203-210]. Characteristic anomalous patterns were seen in 15 (11.2%) individuals: 7 (5.2%) had patterns characteristic of deuteranomaly (mild defect in green color perception), 2 (1.5%) had patterns characteristic of deuteranopia (severe defect in green color perception), and 6 (4.5%) had protan patterns (the red perception defects protanomaly and protanopia cannot be differentiated by current molecular methods). Previously undescribed hybrid gene patterns consisting of both green and red pigment gene fragments in addition to normal red and green genes were observed in another 6 individuals (4.5%). Only 2 of these patterns were considered as deuteranomalous. Thus, DNA testing detected anomalous color vision pigment genes at a higher frequency than expected from phenotypic color vision tests. Some color vision gene arrays associated with hybrid genes are likely to mediate normal color vision.

Color Perception↗

Effects of changes in self-reported vision on cognitive, affective, and functional status and living arrangements among the elderly.

PURPOSE: To study effects of changes in self-reported vision on functional status, cognition, depressive symptoms, and living arrangements. DESIGN: Longitudinal analysis of household survey data. METHODS: A total of 6234 sample persons observed in the study of Assets and Health Dynamics Among the Oldest Old (AHEAD) 1995 were followed in 1998, 2000, and 2002 or until death or sample attrition. Effects of changes in self-reported vision and other factors were assessed by means of ordinary least-squares and logistic regression with panel data methods. Main outcome measures were limitations of instrumental activities of daily living (IADLs), activities of daily living (ADLs), and other, cognition, depressive symptoms, and living arrangements. RESULTS: A decline from excellent/good vision to fair/poor near and distance vision had statistically significant effects on several IADL limitations, and some ADL and other limitations. Largest effects were for driving (OR for no limitation: 0.55, P = .003), managing money (OR: 0.61, P < .001), and preparing hot meals (OR: 0.61, P < .001). Onset of fair-poor near vision increased the likelihood of onset of at least one IADL (OR for no limitation: 0.71, P < .01) and ADL (OR: 0.74, P = .003) limitation. Onset of legal blindness resulted in a 78% increase in the likelihood of an IADL limitation (OR for no limitation: 0.22, P < .001). Effects of vision declines on cognition and depressive symptoms were statistically significant but small. Decline in vision increased the probability of nursing home residence. CONCLUSIONS: Visual impairment has major impacts on functional status. Preventing vision loss is likely to appreciably improve the functioning of elderly persons.

Activities of Daily Living↗

Contrast sensitivity and other vision tests in the optic neuritis treatment trial.

PURPOSE: To determine the intercorrelation, prevalence of abnormality, and incremental detection value of vision tests in optic neuritis. METHODS: We calculated the linear correlation of paired vision tests and prevalence of abnormal test values from baseline and six-month measurements of Snellen visual acuity, Pelli-Robson contrast sensitivity, Humphrey Field Analyzer mean deviation, and Farnsworth-Munsell 100-hue color vision in 438 patients entered in the Optic Neuritis Treatment Trial from 1988 to 1991. The incremental detection value of nonvisual acuity tests was defined as their frequency of abnormality when visual acuity was 20/20 or better. RESULTS: All four vision-test results were highly intercorrelated at baseline and at six months. At baseline, contrast sensitivity had the highest prevalence of abnormality, but all vision tests were so often abnormal that differences were not clinically relevant. At six months, when visual recovery had occurred, contrast sensitivity was most often abnormal (2.2 X visual acuity; 1.8 X mean deviation; 1.5 X Farnsworth-Munsell 100-hue color vision test); when contrast sensitivity, mean deviation, or Farnsworth-Munsell 100-hue color vision was normal, visual acuity was 20/25 or better in 98% of patients. CONCLUSIONS: The high intercorrelation of four vision tests suggests that optic neuritis affects a broad range of visual functions. Among non-visual acuity tests, Pelli-Robson contrast sensitivity proved to be a particularly practical and sensitive indicator of visual dysfunction in optic neuritis.

Adolescent↗

Temporal integration for stereoscopic vision.

With normal binocular vision, maximal stereoacuity requires an extended viewing duration, but the relationship between the critical viewing duration for stereopsis and other variables affecting stereoacuity is unknown. The purposes of the study were to investigate the properties of normal temporal integration for stereoscopic vision with respect to the effects of contrast and spatial frequency of the stimuli and to determine whether the temporal summation of disparity is affected in deficient stereopsis caused by abnormal binocular vision during infancy. Psychophysical methods were used to measure stereothresholds in human and monkey subjects with either normal binocular vision or abnormal binocular vision. The results showed that the critical viewing duration for stereoscopic depth discrimination was independent of variations in basic stimulus parameters and/or the subject's stereoacuity. A critical duration of approximately 100 ms was found for both local (narrowband Gabor and broadband line targets) and global (dynamic random dots) stimuli. Although stereothresholds increased with decreasing stimulus contrast, the properties of temporal integration did not. Stereothresholds were substantially elevated for monkeys and humans with abnormal binocular vision, but the critical durations for these subjects were not significantly different from those of subjects with normal binocular vision. Overall, the results demonstrate that the general properties of temporal integration for stereopsis are similar to other detection and discrimination tasks that do not require binocular processing. In addition, increased integration time does not account for the elevated stereothresholds of subjects with abnormal binocular vision.

Animals↗

Optical treatment of residual vision in diabetic retinopathy.

PURPOSE: The purposes of this study of diabetic retinopathy are to classify degree of vision impairment, determine the percentage of patients for whom vision can be improved by an accurate refraction, identify the most useful magnifying devices, and arrive at the success rate for the magnifiers. METHODS: Study of 101 consecutive subjects. RESULTS: Visual acuity was 20/200 (6/60) or better in 71% of subjects. Spectacle correction improved vision for 29%. High-add bifocal magnifiers improved vision for 30% of patients; half-eye spectacle magnifiers improved vision for 45%; and hand-held magnifiers improved vision for 11% of patients. Visolett magnifiers improved vision for 44%, and combination spectacle magnifiers and Visolett improved vision for 24% of patients. Multiple optical aids for 63% of patients resulted in a success rate of 68%. CONCLUSIONS: The ophthalmologist is obligated to ensure that eyes are refracted and appropriate magnifying devices are provided as part of treatment for diabetic retinopathy.

Diabetic Retinopathy↗

A new approach to vision screening in schools.

PURPOSE: To determine the prevalence of visual "defects" among a sample of young schoolchildren and evaluate a new system for vision screening in schools. METHODS: A new system for vision screening in schools has been developed. The system is based on a computer program which may be run on a low specification personal computer. Information about the child's symptoms, history and family history is acquired by means of a parental questionnaire and entered into the program prior to the vision screening. Distance visual acuity and stereopsis are measured directly on the computer screen and colour vision is assessed using a reduced Ishihara test. The program carries out an "expert" analysis of the questionnaire data and the vision test results and determines the most likely diagnosis. Reports for parents, teachers, optometrists, doctors can be generated automatically and statistics relating to the overall screening program are available. An evaluation of a prototype version of the system was carried out on 245 schoolchildren aged between 5 and 8 years. RESULTS: Overall, 48 children failed the screening (excluding colour vision deficiencies), 32 of whom were unaware of any problem with their eyes. Comparison of the result of the vision screening with the outcome of a full eye examination gave a sensitivity of 93.8% and a specificity of 96.1%. CONCLUSION: A significant number of young school children have unsuspected remediable visual defects. The computer-based vision screener provides an efficient, sensitive and specific method for screening in schools.

Child↗

Color vision characteristics of visually impaired children.

A classroom assessment of color vision characteristics of children with low vision was conducted using a battery of tests. The results showed 75% of the children failed one or more tests, although only 24% had a moderate or severe color vision defect. Comparisons with the low vision clinic color vision assessment showed that many of the children were not identified as being color vision defective. Considering the use of color-coded information in education, greater emphasis on color vision evaluations in routine low vision examinations is recommended.

Child↗

Vision loss in Australia.

OBJECTIVE: To assess the prevalence and causes of vision loss in Australia and to project these data into the future. DESIGN: Synthesis of data from two cross-sectional population-based cohort studies--the Melbourne Visual Impairment Project and the Blue Mountains Eye Study--and extrapolation to the entire Australian population. SETTING AND PARTICIPANTS: 8376 community and 533 nursing home residents recruited between 1992 and 1996 in urban and rural Victoria and New South Wales. MAIN OUTCOME MEASURES: Age-standardised prevalence of low vision (visual acuity < 6/12) and blindness (visual acuity < 6/60) (both measured in the best eye, with spectacles if usually worn for distance vision), and their causes for the Australian population for 2000 to 2024, projected from Australian Bureau of Statistics population data. RESULTS: In 2004, 480,300 Australians were estimated to have low vision, including 50,600 with blindness. The most common causes of low vision were undercorrected refractive error (62%), cataract (14%) and age-related macular degeneration (10%). The latter was responsible for almost half of all cases of blindness. The numbers of people with low vision and blindness are projected to almost double by 2024. CONCLUSIONS: Vision loss in Australia is a much bigger problem than is usually recognised; 76% of low vision is caused by uncorrected refractive error or cataract, both readily treatable. However, the prevention and treatment of macular degeneration poses a major challenge.

Adult↗