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PubMed2003

Color vision at low light intensity, dark adaptation, Purkinje shift, critical flicker frequency and the deterioration of vision at low illumination. Neurophysiology at the nanometer range of neural structure.

The discovery that color vision extends to low illumination reported in this communication eliminates the duplicity theory as an explanation of vision differing at high and low illumination. Instead, an explanation of the difference was found when analyzing synaptic interaction between retinal neurons, made possible by revealing the synaptic connections between the neurons through three-dimensional reconstruction of the outer plexiform layer and by applying information communicated by published recordings of the potential of retinal neurons. The synaptic connections revealed the existence of a large horizontal cell network and of cone networks. The networks contribute continuous information regarding average light intensity over an area of the retina. The opposite sign of the network input maintains bipolar cell threshold constant when illumination varies. When at low illumination the network potential approaches a minimum the consequent extensive increase of transmitter release at network synapses eliminates fine tuning of synaptic transmission at these synapses. This accounts for the deterioration of vision at low illumination by eliminating spatial brightness contrast enhancement and also accounts for the difference in critical flicker frequency at high and low illumination. Network interference accounts for the two phases of dark adaptation and for the Purkinje shift. The analysis revealed conditions for particularly fast synaptic transmission leading to cascade like transmission at sequences of synapses. The overall design of the neural circuits establishes conditions for fast processing of information. This is the consequence of the neurons responding with graded changes of the membrane potential and conducting potentials electrotonically. Such neurons are therefore particularly suitable for processing of information.

Animals↗
PubMed1998

Need for vision rehabilitation in India. Survey of a private eye hospital.

PURPOSE: To determine the visual success outcomes following treatment in an urban private eye hospital in India. METHODS: A retrospective survey was done of 4122 consecutive files of fee-paying patients admitted to a private eye hospital in Hyderabad during a 3-month period in 1996. Data obtained a minimum of 4 months after completion of treatment included age, sex, diagnosis and distance visual acuity in the best eye. RESULTS: After completion of treatment 86.5% of patients had normal vision, 10.9% had low vision and 2.5% were blind. Of the people with low vision or blindness after treatment, 81.7% had a best corrected visual acuity of between 6/18 and 6/60. The 4 most common causes of low vision after treatment were unoperated cataract (20.4%), glaucoma (13.3%), diabetic retinopathy (12.4%) and retinitis pigmentosa (10.2%). CONCLUSION: The visual success rates in an urban Indian private eye hospital appear high with nearly 90% of patients achieving normal vision after the completion of treatment.

Adolescent↗
PubMed1985

[Practical experiences with very young children with vision disorders].

Very low vision or blindness affects the sensori-motor development of children. During infancy other exteroceptive stimuli like tactile and auditory stimuli, are being used as a substitute for the loss of vision. The very early motor signs of young neurologically normal infants, are based on this phenomenon. From a retrospective study of 30 very young low vision and blind infants some early motor signs are mentioned, as they can be used in diagnosis and treatment programs.

Acoustic Stimulation↗
PubMed1996

Psychophysics of reading--XIV. The page navigation problem in using magnifiers.

Most people with low vision require magnification to read. A magnifier's field of view often contains only a few letters at a time. Page navigation is the process by which the reader moves the magnifier from word to word, and from the end of one line to the beginning of the next line. Page navigation takes time and reduces reading speed. The major questions addressed in this paper are: (1) What role does page navigation play in limiting reading speed? and (2) Are the window width requirements for reading (number of characters in the field for a criterion performance level) increased by the need for page navigation? We measured the reading speeds of three normal-vision and seven low-vision subjects in two ways: with drifting-text requiring no page navigation, and with a closed-circuit TV (CCTV) magnifier which required page navigation. We built special hardware to record the location of the CCTV's magnified field in the text. These recordings were used to separate forward-reading time (left-to-right movement through the text) from retrace time (navigational movement). For normal-vision subjects, forward-reading and retrace times were about equal. For low-vision subjects, retrace times were shorter than forward-reading times, indicating that the forward-reading performance was limited by visual, not navigational, demands. The retrace time did have an impact, however, ranging from 17 to 50% of the overall time. The window requirements for reading with page navigation (CCTV) were larger than those for reading without page navigation (drifting-text). The difference was more than a factor of three for normal-vision subjects and close to a factor of two for low-vision subjects (10 characters for CCTV vs 5.2 characters for drifting-text for 85% of maximum reading speed.

Adult↗
PubMed1997

Demographic characteristics of the vision-disabled elderly.

PURPOSE: To profile certain demographic features of the low-vision population in Ontario, Canada. METHODS: Sixty-six optometrists or optometry centers, 8 ophthalmologists, and 23 Canadian National Institute for the Blind rehabilitation worker teams were recruited to the study. They were required to report on their low-vision examinations during a 3-year period. RESULTS: Reports from 4744 low-vision examinations were received. Of the patients examined, 71% were over age 65 (subsequently called seniors or elderly), and 55% were over age 75. Ninety percent of all the patients lived in households and 10% lived in institutions. Seniors made up 71% of the patients living in households and 88% of the patients living in institutions. Most of the seniors were women (65%), and 57% had functional limitations in addition to low vision, most commonly limitations in mobility, hearing, or agility. Age-related maculopathy was the primary diagnosis in 75% of seniors, and the most common secondary diagnosis was cataract (46%). The main objective for most elderly low-vision patients was to gain improvement in personal reading (75%). CONCLUSIONS: The vast majority of low-vision patients were elderly, the largest number being 75 to 84 years old. When older senior low-vision patients (> or = 85 years) were compared with younger seniors (65 to 74 years), the older seniors were more likely to be women, more likely to have additional functional limitations, more likely to live in an institution, and more likely to have age-related maculopathy and cataract. Whether some elderly low-vision patients may be helped by cataract surgery needs to be determined.

Adolescent↗
PubMed1990

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↗
PubMed1988

Effect of magnification and field of view on reading speed using a CCTV.

Reading speeds were measured in 18 subjects with normal vision and 10 with low vision for each of 20 experimental conditions with different magnifications and field sizes on the Closed Circuit Television System (CCTV). There was a significant difference between the results for the two groups of subjects. These results suggested that in low-vision patients with faster reading speeds, minimum magnification for maximum field size on the CCTV would be valid advice. For low-vision patients who read more slowly, reading speed may improve at higher magnifications despite reduced field size.

Adult↗
PubMed1997

[Use of a new optoelectronic vision aid for highly visually handicapped patients].

UNLABELLED: A new low vision aid (LVA)-the Low Vision Enhancement System or LVES, which were as developed at the Johns Hopkins University in Baltimore, is now commercially available. This instrument allows a magnification up to 10 times with control of contrast and luminance while the field of view is very large: 60 x 40 degrees. We present first results concerning LVES in comparison to conventional LVAs. PATIENTS AND METHODS: 60 consecutive patients suffering from macular dystrophy, macular degeneration, optic atrophy, tapetoretinal degeneration, or diabetic retinopathy were included in this study. We compared visual acuity with glasses, with telescope and using LVES. Furthermore we compared contrast acuity by the use of the Pelli-Robson-charts as well as the subjective impression of the patients. RESULTS: Improvement of visual acuity with LVES compared to correction with glasses was 8 log steps on average and up to 3 steps as compared to the use of telescopes. More important is the improvement of contrast sensitivity (0-16 steps) and the reduced glare. Despite the subjective improvement of visual acuity and contrast sensitivity the majority of patients could not imagine to use LVES regularly. A significant improvement as compared to conventional low vision aids is possible for special applications such as office work, recognition of faces or images or for looking at a blackboard. CONCLUSION: In addition to traditional LVAs, the Low Vision Enhancement System opens up possibilities for a very small group of patients. Especially patients suffering from macular dystrophy or Lebers optic atrophy may benefit from this new system. The most important advantage of LVES is the improvement of contrast sensitivity and the significantly decreased glare sensitivity. Additionally the near working distance is changeable. The variable magnification allows an easier fitting to various tasks. Prior to the prescription of LVES a detailed and time consuming testing is necessary.

Activities of Daily Living↗
PubMed1999

[Use of visual aids for vision of disabled children].

OBJECTIVE: To discuss the effect of using distance and near optical low vision devices for children in low vision clinic. METHOD: 139 subjects from age 6 to 14 years were provided with 2.5 X telescopes and + 8.00D to + 40.00D glasses for improving far and near sight respectively. RESULT: 22.3% subjects' distance visual acuity was >or= 0.5 and 53.2% subjects' near visual acuity was >or= 0.5 after using distance and near low vision aids. CONCLUSIONS: Low vision aid is essential and effective in low vision clinic. It not only improves the visual acuity of visual disabled children, but also helps the development of special education through visual rehabilitation.

Adolescent↗
PubMed2004

Racial variations in causes of vision loss in nursing homes: The Salisbury Eye Evaluation in Nursing Home Groups (SEEING) Study.

OBJECTIVE: To determine the prevalence and causes of low vision in a large sample of nursing home residents. METHODS: Twenty-eight nursing homes on the Eastern Shore of Maryland and Delaware were enrolled in a clinical trial to assess the impact of vision restoration/rehabilitation on nursing home residents. Visual acuity was measured using both recognition charts and preferential looking techniques. An ophthalmologist examined all residents with visual acuity worse than 20/40 in the better-seeing eye and determined the primary cause for decreased vision. Results are reported for the better-seeing eye. RESULTS: Of 2544 eligible residents, 1591 (63%) participated, but 286 residents were unable to respond to visual acuity testing. Of the remaining 1307 residents, 496 (37%) had best-corrected visual acuity worse than 20/40 in the better-seeing eye. Causes were ascribed for 412 subjects. Rates of low vision were similar between African American subjects and white subjects (39% and 38%, respectively; age-adjusted P =.18). Cataract was the leading cause of low vision, responsible for 37% of low vision among white subjects and 54% of low vision among African American subjects. Macular degeneration was responsible for 29% of low vision among white subjects but only 7% among African American subjects. Glaucoma caused low vision in 4% of white subjects and 10% of African American subjects. Refractive error was not a frequent cause of low vision in nursing home residents. CONCLUSIONS: Low vision is highly prevalent among nursing home residents, with 37% having visual acuity worse than 20/40 in the better-seeing eye. Differences in causes of low vision between African American subjects and white subjects were noted, with African American subjects more likely to have vision loss on the basis of cataract, a readily treated condition. Appropriate interventions for nursing home residents, who face significant obstacles in accessing eye care services, have the potential to improve the quality of life of this at-risk older population.

Aged↗
PubMed2005

The effect of rehabilitation on depression among visually disabled older adults.

There has been a great deal of interest in identifying the impact of rehabilitation on psychological well-being, as well as functional ability, among elders with disabilities, but empirical data remain limited. This descriptive study of participants in vision rehabilitation service examines the effect of specific vision rehabilitation services (low vision clinical services, skills training, counseling, optical device use, and adaptive device use) on change in depression among a sample of older adults with age-related vision impairments. Participants (N = 95) were interviewed at application for services and then approximately two years later. Findings from hierarchical regression analyses indicated that low vision clinical services, counseling, and use of optical devices, in separate models, each significantly contributed to a decline in depression, after controlling for age, health status, vision status, functional disability, as well as baseline depression. When all service variables were entered into the same equation, they explained an additional 10% of the variance in change in depression. Given the well documented robust relationship between disability and depression, findings point to the influence of vision rehabilitation interventions on both physical and psychological functioning, and underscore the need for future, controlled research on rehabilitation service models that address mental health issues.

Adaptation, Psychological↗
PubMed1991

Geriatric optometry questionnaire.

A national survey of American Optometric Association Low Vision Section members was conducted by the newly formed Geriatrics and Low Vision Committee during the fall of 1989. The "Geriatric Optometry Questionnaire" was designed to establish a greater understanding of the nature of comprehensive professional services for the unique needs of visually impaired older persons. Of the 481 surveys mailed, 289 were returned for a response rate of 60 percent. Seventy-eight percent of the respondents had completed their formal optometric education after 1970. Results indicated that geriatric optometric care is predominantly delivered in private practices and in low vision agencies. Approximately 69 percent of the patients are above the age of 65, with the majority of those being under 85. Although the average initial low vision appointment lasts 60-90 minutes, this generally represents the low vision examination and evaluation of low vision devices only. Complete ocular health assessments combined with low vision evaluations are provided by only 33.5 percent. While 80 percent of the optometrists responding take psychosocial histories, only 60 percent routinely refer patients for social services and rehabilitative training. Similarly, 57 percent of those responding referred patients for independent daily living skills instruction and only 53 percent for orientation and mobility training. These data suggest that optometrists have not yet completely incorporated the multidisciplinary approach to geriatric health care and that continuing education in this area is needed.

Aged↗
PubMed2005

Short-term in-office practice improves reading performance with stand magnifiers for people with AMD.

PURPOSE: People with low vision often use optical low vision aids to assist reading. There have been numerous training programs recommended to train people using magnifiers for reading. However, most of the programs are time consuming and labor intensive. In this study, we investigated the effects of home-based large print reading practice on reading performance when stand magnifiers (STM's) are first prescribed. METHODS: Thirty-two subjects with age-related macular degeneration (AMD) and with minimal experience in using magnifiers for reading were recruited. They were divided into three groups: control, practice 1 (P1), and practice 2 (P2). Before the prescription of STM's, all the subjects were given the same amount of in-office practice with the STM (weeks 0 to 2). In addition, in these 2 weeks, P1 and P2 subjects were given large print books to read daily at home. P2 subjects were required to read the large print books through a reduced field of view. The control group subjects received no additional reading practice. Reading rates with and without STM's on passages of text were assessed for all the subjects regularly for 20 weeks. RESULTS: There were no significant differences between the control, P1, and P2 groups in the increase in reading rate with STM (p = 0.29). At week 0, reading rate for small print with STM was significantly slower than reading rate on the equivalent-sized large print (p = 0.004); however, as time went on, reading rate with STM's increased significantly (p = 0.02). After 2 weeks of in-office magnifier practice and repeated measures of reading rate with STM, reading rate with STM had improved such that it was not significantly different from reading rate on large print (p = 0.11). CONCLUSION: Supervised, short-term, in-office practice with the magnifier was effective in improving magnifier reading performance to achieve maximum reading rate. Additional large print reading practice did not result in any greater improvement in reading rate than in-office magnifier practice alone.

Aged↗
PubMed1999

[Data analysis on epidemiologic survey of cataract in China].

OBJECTIVE: To approach the prevalence of age-related cataract and its relationships with the condition of examination, diagnostic criteria and geographical environment in various areas. METHODS: According to the WHO's criteria of blindness and low vision, a statistical analysis of a national sample survey of blindness and low vision was carried out over the country. RESULTS: The number of patients with age-related cataract and visual acuity < 0.3 in both eyes calculated in the whole population was more than 5 million, the prevalence being 0.46%. The prevalence of blindness and that of low vision were 0.43% and 0.58% respectively. Among the blind, 41.06% was caused by cataract, and the low vision caused by cataract was 49.38%. Among elderly of >or= 60 years, the proportion of the blind and low vision caused by cataract was 73.13%. When the cataract standard was defined as lens opacity with visual acuity < 0.7, the prevalence of cataract was 5.99% in Beijing sample survey at the suburb area. The incidence of age-related cataract in females was significantly higher than that in males. In a survey of Beijing suburb in 1997, the prevalence of cataract among 5,084 elderly people of >or= 50 years with bilateral corrected visual acuity < 0.1 was 2.22%. In the southern part of China, the area of low latitude, especially in the plateau, such as in Guangdong Province (0.69%) and in Tibet (1.04%), the prevalence of cataract is much higher than that in northern part, high latitude areas, such as Heilongjiang Province (0.26%). A comparative study of the cataract prevalence of elderly >or= 40 years in the areas of different levels above the sea and sunshine times, it shows that the higher level above the sea and longer sunshine time the higher cataract prevalence. CONCLUSIONS: A longer sunshine time and a larger amount of ultraviolet irradiation are considered as the risk factors of cataract. Age-related cataract is the leading cause of blindness and the low vision in China.

Adolescent↗
PubMed2003

The prevalence and incidence of visual impairment in people of age 20-59 years in industrialized countries: a review.

BACKGROUND: Reviews on the prevalence of blindness and low vision in persons of age 20 to 59 years are lacking. We have therefore carried out a review based on a Medline search. METHODS: The review was confined to epidemiological studies performed in Western Europe, North America and Australia covering the age group 20 to 59 years where there were comparable definitions of blindness and low vision according to the IAPB and WHO classification of blindness and low vision. RESULTS: Three surveys, four register studies and two studies based on multiple sources matched our selection criteria. Blindness and low vision are described separately. Blindness: Only one study, based on multiple sources, covered the whole age group 20 to 59 years. In this study the overall prevalence of blindness was 0.08%. The prevalence of blindness was 0.04% among those 20-39 years old, whereas in the age group 40-59 years it was 0.1% in two surveys and one study on multiple sources. However, the prevalence was higher, 0.5% among whites and 0.7% among colored, in The Baltimore Eye Study. The definition of blindness was similar in all three studies. Low vision: Three studies provided data on the prevalence of low vision in the age group 20-59 years, although the number of cases was very small. In one study the prevalence of a visual acuity < or = 6/24 to 6/48 was 0.07% and in another the prevalence was 0.17% using < 6/18 to 0.5/60. No person with low vision was found in the third study. CONCLUSIONS: The existing epidemiological data on blindness and low vision among adults aged 20 to 59 years are insufficient. Epidemiological studies based on multiple sources are needed for the study of rare conditions such as blindness and low vision.

Adult↗
PubMed2005

A randomized controlled trial to determine the effectiveness of prism spectacles for patients with age-related macular degeneration.

OBJECTIVE: To determine the effectiveness of prism spectacles in people with age-related macular degeneration by relocating the retinal image. METHODS: We implemented a randomized, placebo-controlled, double-masked trial. Participants with age-related macular degeneration received a standard low-vision assessment and the prescription of conventional low-vision aids 6 weeks before the study intervention. Participants were randomized to receive 1 of the following, including the optimal refractive correction: (1) custom, incorporating bilateral prisms to match participants' preferred power and base direction; (2) standard, incorporating standard bilateral prisms (6 prism diopters [Delta] base up for logMAR [logarithm of the minimum angle of resolution] visual acuity (VA) of 0.48-1.00 and 10Delta base up for logMAR VA of 1.02-1.68); or (3) placebo, consisting of spectacles matched in weight and thickness to prism spectacles but without prism. MAIN OUTCOME MEASURES: Outcomes measured binocularly at baseline and 3-month follow-up included distance logMAR VA, reading speed, critical print size, visual functioning questionnaires, and observed visual task performance. Scores on the 25-item National Eye Institute Visual Functioning Questionnaire and the Melbourne Low-Vision ADL (Activities of Daily Living) Index were converted to linear estimates using Rasch analysis. The Manchester Low Vision Questionnaire was used to collect descriptive data. RESULTS: A total of 225 participants completed the trial (median age, 81 years). We found no significant effect of treatment group on any of the outcome measures, including VA, the primary outcome (adjusted for baseline) (P = .63). Participants' responses to the Manchester Low Vision Questionnaire suggested that the prism spectacles added to their problems. CONCLUSIONS: Prism spectacles are no more effective than conventional spectacles for people with age-related macular degeneration.

Activities of Daily Living↗
PubMed2000

Traditional couching is not an effective alternative procedure for cataract surgery in Mali.

INTRODUCTION: In Mali, more cataract patients receive sight-restoring surgery using a traditional "couching" procedure (the lens inside the vitreous body) than by modern cataract surgery. In order to evaluate the relative effectiveness and other outcomes of the traditional procedure compared to the modern surgical intervention, we conducted a population-based survey in a rural district of Mali in 1996. METHOD: A total of 99,800 persons from 160 villages were eligible to be included in the sample. All individuals operated for cataract by a modern procedure were checked for visual acuity and questioned regarding their clinical history, the cost of the surgery and their satisfaction with the surgery immediately following the operation and presently. Each patient was paired with one person operated by a traditional cataract surgical procedure. RESULTS: From a total population of 99,800 we found 85 individuals (0.085%) who had been operated by intracapsular extraction (ICCE) without lens implantation and we paired these with 82 individuals operated by the traditional method and by a local healer. In both groups, males were predominant (74.4% in the modern group and 61.3% in the traditional) and the median age was 65 and 68 years, respectively. Men with a higher social status (defined as administrative or religious authority) were slightly more common among those operated by ICCE (18.9%) than among those operated by the traditional healer (4.4%). Nearly half (47.6%) of the patients operated by couching did not know that a modern alternative existed. The mean cost to the patient of the two procedures was similar; with traditional couching costing on average US$ 42.10 and modern surgery (including transport and drugs) costing US$ 52.40. The traditional healer was often paid partially in kind and the price paid varied according to the patient's ability to pay. The clinical results differed greatly between the two methods. After aphakic correction of eyes operated by ICCE, 5.3% had good vision (33/18), 76.8% had low vision (33/60 and <3/18) and 17.9% were still blind (<3/60). Of eyes operated by traditional couching, none had good vision, 29.1% had low vision and 70.9% were blind. The level of satisfaction was high (89.7%) among persons operated in an ophthalmic center by the modern method, and relatively low (22.6%) among persons operated traditionally. DISCUSSION: In Mali, two types of providers offer two different interventions to treat cataract-blind persons. This study suggests that the couching method used by traditional healers is relatively expensive and ineffective. It is also potentially dangerous although this study did not address this question specifically. It is important that health policy makers and medical authorities do what they can to prevent traditional healers from performing the couching procedure, as well as informing the population about the existence of a more-effective and safer alternative. However, while more effective and safer, the results obtained by ICCE are not excellent either. Further, it is important to improve the quality of ophthalmic services in order to provide cataract patients with the best, most accessible and least expensive services possible.

Aged↗
PubMed1997

Survey of visual impairment in an Indian tertiary eye hospital.

A retrospective survey of 4,122 consecutive patient records was performed in a tertiary care eye hospital in Hyderabad, India. Data collected included age, gender, visual acuity after completion of treatment and diagnosis. 62.8% of the patients were male. After completion of treatment, 10.8% had low vision (best corrected visual acuity < 6/18 to 3/60 in the better eye) and 2.6% were blind (best correct visual acuity < 3/60 in the better eye). Most cases of low vision were found in the 50 to 70 year age group (42.9%). The most common visual acuity range after treatment amongst patients with vision loss was < 6/18 to 6/60 (71%). The 4 main causes of low vision were cataract (21.4% of low vision group), glaucoma (14.0%), diabetic retinopathy (13.0%), and retinitis pigmentosa (10.7%). The 4 main causes of blindness were glaucoma (16.3% of blind group), diabetic retinopathy (13.2%), corneal opacities (11.6%) and retinitis pigmentosa (11.6%). It is suggested that patients with low vision at the conclusion of treatment be referred to a vision rehabilitation centre. Referral should be made in cases with a best corrected visual acuity < 6/18 to 3/60 or with visual field loss to within 15 degrees of fixation. Patients aged under 50 years of age are expected to achieve maximal rehabilitation success. Motivation and vocational requirements should be assessed in older or more complex cases before referral. The data of this study show that about 10% of patients seen at a tertiary care eye hospital in India could benefit from low vision rehabilitation.

Adolescent↗