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At least 757 records · Page 42Linked to original sources
PubMed1997

Blindness and low vision in Jimma Zone, Ethopia: results of a population-based survey.

A population-based study on the prevalence of blindness and low vision was carried out in Jimma Zone, south-western Ethiopia between November 1994 and January 1995. A total of 7423 people from a sample of 8215 (90.4%) was examined. Sixty-three (0.85%) were blind (visual acuity less than 3/60 in the better eye) and 125 people (1.7%) had low vision (less than 6/18-3/60). Cataract and aphakia (52.4%), corneal opacity and phthisis bulbi (25.4%), and glaucoma (9.5%) were the major causes of blindness. Cataract (56.8%), refractive errors (28.8%), and corneal opacity (12.8%) were the major causes of low vision. Corneal opacity from trachoma was responsible for 20.6% of all blindness and 10.4% of low vision. The prevalence of visual impairment due to refractive errors was 5.1/1000 population. Almost 25% of the study population had active trachoma, and 0.9% of pre-school children had signs of vitamin A deficiency. Out of a total population of 2 million an estimated 17,000 people are blind and 34,000 have low vision (i.e., a total of 51,000 people with visual impairment). Approximately 20,000 people require cataract surgery, 52,000 require lid surgery for trichiasis, 24,000 require spectacles (excluding presbyopia), including 10,000 for significant refractive errors, half a million require treatment for active trachoma and 4,000 require glaucoma treatment. Effective and feasible eye care programs need to be established in the zone and the available ophthalmic services have to be strengthened. These may be achievable through joint efforts of the community and the Ministry of Health in collaboration with non-governmental organizations. The available eye services are briefly described and recommendations made to meet the important needs for prevention of blindness in the region.

Adolescent↗
PubMed1991

Evaluation of congenital colour vision deficiencies.

Three hundred patients who have congenital colour vision deficiencies were examined at the author's eye clinic for 3 years (1987-1990) using 5 types of colour vision tests: Hahn's, TMC's, Okuma's (new), H-R-R's colour vision tests and Double 15 Hue Test (Hahn). The results obtained from each test were quite different in type and grade, and the summarized results were considered to be the best: Type: protan 23.3%, deutan 76.0%, unclassified 0.7% Grade: mild 20.3%, medium 25.3%, strong 54.4% The frequency of coincidence both in type and grade between the summarized results and those of each test were compared, and the highest was 62.3% in Double 15 Hue Test. The efficiency of the author's colour vision test and Double 15 Hue Test were evaluated with the data in this clinical trial, and they were found to be useful for classifying the type and estimating the grade of the congenital and also acquired colour vision deficiencies.

Adolescent↗
PubMed1996

[Effects of the peripheral vision on visually induced vertigo].

Visually induced vertigo, or motion sickness, is thought to be mainly influenced by motion perception, not by shape perception. We examined this point by comparing the effect of the foveal vision on the visually induced vertigo with that of the peripheral vision. We set up three kinds of display conditions: Foveal vision (F), peripheral vision (P), and foveal + peripheral vision (F + P). Videotaped motion was presented on the display. The results showed that a drifting eye movement was larger after the experiment than before the experiment in the (P) and the (F + P) conditions, but not in the (F) condition. In addition, the mirror drawing was improved only in the (F) condition. Subjective ratings for the vertigo were higher in both the (P) and the (F + P) conditions than in the (F) condition. These results indicate that some visual units concerning low spatial frequencies participate in the visually induced vertigo.

Adult↗
PubMed1995

Adaptation to macular scotomas in persons with low vision.

Persons with scotomas in their central 20 degrees of vision often do not notice these blind spots within their visual field and have visual performance difficulties far exceeding what would be expected from standard vision tests. Before persons with macular scotomas can be assisted to optimally use their remaining vision for a better quality of life, more must be known about how the visual system adapts to a macular scotoma. Important issues include spatial and temporal characteristics of perceptual completion and metamorphopsia, development of preferred retinal loci for fixation and visual search, and dynamics of the preferred retinal locus development in terms of the changes in the eye movement system. With a full understanding of the visual system's adaptation to macular scotomas, new low vision devices and training techniques can be proposed to promote independence in activities of daily living for the person with low vision.

Activities of Daily Living↗
PubMed1998

[Individual variations in color vision and its molecular biology].

Individual variations in normal color vision and congenital red-green color vision defects in Japanese males were investigated using both psychophysics and molecular biology techniques. 1. Normal color vision. We studied 72 Japanese males who were diagnosed as having normal color vision using the Ishihara plates test and Nagel model I anomaloscope. The structure of the gene arrays of the X-linked L- and M-pigment genes was determined using quantitative PCR-SSCP (polymerase chain reaction-single strand conformation polymorphism). We found the following variations of the number of M-pigment genes: 27 (38%) of these men had only one M-pigment gene, 29 (40%) had two, 13 (18%) had three and 3 (4%) had four. Two common polymorphisms were found at amino acid residue 180 of both L- and M-opsin, of the total 56 (78%) were Ser and the other 16 (23%) were Ala in the L-pigment and of the total 65 (90%) were Ala and the other 7 (10%) were Ser in the M-pigment. The Rayleigh match midpoints fell within the normal range, however there were two fairly distinct groups with consistent differences in each group. The mean values of the proportion of red in a mixture of red and green were 0.564 +/- 0.026 (mean +/- standard deviation). Correlation was found only between the Rayleigh match midpoint and the polymorphism at residue 180 of L-pigment. In order to estimate the variations of L/M cone ratio in the retinae the spectral sensitivities using heterochromatic flicker method were measured. Using the hypothesis that the luminosity function is proportional to the sum of L- and M-cone spectral sensitivity (k L (lambda) + M (lambda)), the constant k values were obtained. The k values for the subjects with Ser180 and Ala180 L-pigment were 1.89 +/- 1.44 and 1.85 +/- 1.02 respectively. Furthermore, in order to study the variation of information processing system, the spectral sensitivities for 1 degree, 200-ms test flash on a white background were measured. Using the hypothesis that the spectral sensitivity is proportional to the difference of L- and M-cone spectral sensitivity (L (lambda) - k' M (lambda)), the k' values were obtained. The k' values for the subjects with Ser180 and Ala180 L-pigment were 1.38 +/- 0.06 and 1.49 +/- 0.07 respectively. As a result, it was suggested that there are individual variations in both the L/M cone ratio and the color opponent system. 2. Congenital red-green color vision deficiencies. We studied the structure of the gene arrays of the X-linked L- and M-pigment genes and investigated the relationship between genotype and phenotype in 21 Japanese males comprising 4 protanopia, 6 protanomaly, 7 deuteranopia and 4 deuteranomaly. All of the protan subjects had 5' L-M fusion gene with/without the M gene. All of the deutan subjects had a normal L gene with/without 5' M-L fusion gene. Genotype agreed with phenotype in 8 of 10 protan subjects and 10 of 11 deutan subjects. Two of them were diagnosed as abnormal trichromatism in spite of having only one gene. One of them was diagnosed as dichromatism in spite of having two genes that encoded spectrally different pigments. As a result, it was felt that the diagnosis of dichromacy and abnormal trichromacy with an anomaloscope has limitations.

Asian People↗
PubMedDate not supplied

Managing low vision patients.

1. The ophthalmologist and staff are ultimately responsible for identifying low vision patients. 2. Most low vision patients who have a professional low vision evaluation are able to use vision enhancing devices. 3. In addition to optical magnifyers, new computer and television technology enhances use of residual vision.

Communication Devices for People with Disabilities↗
PubMed1976

A new screening method for detecting colour vision deficiencies.

Diagnostic colour vision examinations are generally administered with the anomaloscope. But this instrument requires a lot of time and experience for the tests as well as for the interpretation of the results. In practical use, it will be sufficient in most cases to know whether normal colour vision is present or not, and it is not necessary to use sophisticated devices. So it was considered desirable during the TCU conference on colour vision defects held in London in March 1973 [1] to have a testing method for practical use which is both accurate and time saving. At the time when this demand was brought up, a new colour vision test was being developed by Rodenstock [2]. It enables semi-skilled personnel to perform the test independently of ambient light condition in only 20-30 sec and to effect a classification of the type of colour vision at the same time [3].

Color Perception Tests↗
PubMed2000

An event-related brain potential study of cross-modal links in spatial attention between vision and touch.

Event-related potential (ERP) evidence for the existence of cross-modal links in endogenous spatial attention between vision and touch was obtained in an experiment where participants had to detect tactile or visual targets on the attended side and to ignore the irrelevant modality and stimuli on the unattended side. For visual ERPs, attentional modulations of occipital P1 and N1 components were present when attention was directed both within vision and within touch, indicating that links in spatial attention from touch to vision can affect early stages of visual processing. For somatosensory ERPs, attentional negativities starting around 140 ms poststimulus were present at midline and lateral central electrodes when touch was relevant. No attentional somatosensory ERP modulations were present when vision was relevant and tactile stimuli could be entirely ignored. However, in another task condition where responses were also required to infrequent tactile targets regardless of their location, visual-spatial attention modulated somatosensory ERPs. Unlike vision, touch apparently can be decoupled from attentional orienting within another modality unless it is potentially relevant.

Adult↗
PubMed2001

Modeling the L4 neuron of the fly (Musca domestica) vision system.

Vision systems based on digital image processing techniques are limited in a variety of areas, particularly speed and memory. Contrast enhancement, image segmentation, object recognition, and object tracking require extensive processing. Biological vision systems drastically outperform computer based digital vision systems in these areas. The animal retina is composed of processing layers with specialized neural cells designed to enhance contrast, segment images, and even produce temporal information. In the vision system of the fly, Musca domestica, the L1, L2, and L4 monopolar cells are of particular interest. The photoreceptor terminals R1 through R6 and L1 and L2 form a cartridge with current shunting inhibition that enhances contrast at the first synaptic contact. L1 and L2 cells are thought to exaggerate contrast while also providing a data reduction encoding scheme to increase communication efficiency with L4 cells and the inner plexiform layer. Research conducted by the authors attempts to simulate the encoding scheme of L1, L2, and L4, and the interactions of these three monopolar cells. This paper proposes that L1 and L2 encode edge information and orientation related to a single cartridge via a sinusoidal modulation scheme. L4 mediates information processing between cartridges via three bi-directional dendritic communication with adjacent L4 cells. Finally, we propose that L4 also synthesizes and forwards the edge orientation information and image movement information to the medulla. A single cartridge simulation was conducted using Matlab. Simulation results will be compared to actual signals taken from the fly eye. Because the fly eye is modular, the goal of this research is to implement the L1, L2, and L4 cell function in analog hardware--the result being a real-time parallel analog vision system.

Animals↗
PubMedDate not supplied

The virtual retinal display as a low-vision computer interface: a pilot study.

This pilot study examined the performance of an alternative computer visual interface, the Virtual Retinal Display (VRD), for low-vision use. The VRD scans laser light directly onto the retina, creating a virtual image. Since visually impaired individuals can have difficulty using computer displays, a matched comparison study was done between the VRD and the standard cathode ray tube (CRT) monitor. Reading speed and acuity tests were collected from 13 low-vision volunteers selected to represent the broad range of partially sighted individuals actively involved in the work force. Forty-six percent of subjects had highest visual acuity while viewing the VRD; 30% of subjects had highest acuity viewing the CRT; and 24% of subjects had equal acuity across the two displays. Although mean reading speed across all 13 subjects indicated no significant difference between displays, individual subjects with predominantly optical causes of low vision exhibited clinically important increases in reading speed versus the CRT. However, most subjects with predominantly retinal damage showed a slight disadvantage using the VRD. We give theoretical explanation to the bifurcated results and conclude that for a subset of low-vision users, the VRD technology is very promising as a basis for future low-vision aids.

Adult↗
PubMed2001

[First results of the IOBA low vision unit].

PURPOSE: To verify the efficacy a treatment for the rehabilitation of vision in our Unit for Clinical Low Vision in the testing of improvements in patient's efficiency for daily life activities. MATERIAL AND METHOD: 80 patients were studied. Ophthalmologic and optometric evaluation followed by a customised vision rehabilitation program were performed according to patient's immediate needs. In a second stage a telephoned questionnaire was filled in order to record efficacy of prescribed visual aids in their own environment. RESULTS: Rehabilitation training resulted in 89% of patients showing improvement in their quality of life in both fields; functional and psychological. 85% of patients showed improvement in near activities and 35% in far activities. DISCUSSION: A correct and specialised low vision refraction and a posterior vision rehabilitation training in the use of optical and non optical aids show increase in quality of life in patients with severe visual deficiencies.

Activities of Daily Living↗
PubMed2001

Ophthalmology. Screening and treatment of age-related and pathologic vision changes.

In the older adult, deterioration of normal vision is caused by age-related physiologic and pathologic changes. Vision impairment undermines quality of life by reducing independence, mobility, and the enjoyment that goes with seeing clearly. The most common causes of vision impairment are age-related macular degeneration (AMD), glaucoma, cataract, and diabetic retinopathy. Key to successful management of vision impairment is early detection of signs and symptoms, patient education regarding preventive strategies, and swift medical or surgical intervention for established or emerging conditions. Vision rehabilitation is an important management option.

Age Factors↗
PubMed2002

Effects of brief periods of unrestricted vision on the development of form-deprivation myopia in monkeys.

PURPOSE: To characterize the temporal integration properties of the mechanisms responsible for form-deprivation myopia (FDM), the effects of brief daily periods of unrestricted vision on the degree of FDM were investigated in infant monkeys. METHODS: Starting at approximately 3 weeks of age, unilateral form deprivation was produced in 24 infant rhesus monkeys by securing a diffuser spectacle lens in front of one eye and a clear, zero-powered lens in front of the fellow eye. During the treatment period (17 +/- 2 weeks), six infants wore the diffuser lenses continuously. In the other experimental infants, the diffuser lenses were removed each day and replaced with clear, zero-powered lenses for 1 (n = 7), 2 (n = 7), or 4 hours (n = 4). Refractive development was assessed by retinoscopy and A-scan ultrasonography. Control data were obtained from 11 normal infants and 3 infants reared with zero-powered lenses over both eyes. RESULTS: The degree of FDM varied significantly with the duration of unrestricted vision. Continuous form deprivation produced -5.2 +/- 3.6 D of relative axial myopia. However, 1 hour of unrestricted vision was sufficient to reduce the degree of axial FDM by more than 50% (-1.7 +/- 3.2 D). The infants that were allowed 4 hours of unrestricted vision exhibited only -0.4 +/- 0.5 D of FDM. CONCLUSIONS: As observed in chickens and tree shrews, relatively long periods of form deprivation can be counterbalanced by quite short periods of unrestricted vision. These results indicate that the processes or signals that promote axial elongation in monkeys are comparatively weak or easily overridden by factors that slow ocular growth.

Animals↗
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↗
PubMedDate not supplied

Assessment of educational services available to blind and low vision school children in Lagos, Nigeria.

A descriptive study to assess the educational services available to children attending the Pacelli School for the Blind in Lagos, Nigeria. A standardised methodology was used with structured and semi-structured questionnaires. Observations were also made in some areas. Of the 26 children aged 10-15 years who were identified as having low vision, 15 (57.7%) of them had significant improvement in distance and near vision after refraction while one third (31%) had improvement in their reading with low power magnifying lenses. All except 4 (25%) teachers were well educated but none seemed to have appreciable knowledge about the teaching of low vision children as all these children were taught Braille like their blind peers. While educational facilities available were reasonably adequate for blind children, no visual aids were available for low vision children. It is recommended that appropriate educational facilities, optical and non-optical devices should also be provided particularly for low vision children to enable them achieve their optimal potential in life.

Adolescent↗
PubMed2002

[A study on examination of color vision with pattern-visual evoked potential].

OBJECTIVE: To understand the specific nature of the color and brightness components of the human visual evoked potential and explore the possibility of an objective method for examining the color vision. METHOD: The transient VEP was measured in normal subjects and persons with deficient color vision by multichannel electro-physiological apparatus. In the experiment, four kinds of reversal checkerboard patterns are simulated by the computer software technology as stimuli. The patterns included black-white (95% contrast), isoluminance chromatic checkerboards red-white, green-white, red-green (100% saturation), which were 25 ' in visual angle and alternated at a rate of 0.8 Hz. The main component, P (1) wave, was analyzed. RESULTS: (1) The normal subject group: The P (1) latencies in four conditions were obtained in terms of the length of latencies, the ordinal of P (1) latencies (from short to long) was as follows: red-white < black-white < red-green < green-white. There were very significant differences among the four latencies (P < 0.01). The P (1) amplitudes elicited with the black-white were higher than those with chromatic ones. But among the P(1) amplitudes elicited with chromatic checkerboards there were no difference. (2) The group with deficient color vision: There were no significant differences in the P(1) latencies and amplitudes elicited with the four stimuli. The length of latencies with black- white stimulus was the shortest. Red-green blindness as well as deuteranopia had no response to green stimulus but did to red or red-green stimulus. (3) Between the two groups, there were no differences in the P (1) latencies, but the P (1) amplitudes of persons with deficient color vision elicited with the chromatic stimuli were obviously lower. CONCLUSION: The results show that it is feasible to use chromatic VEP for examining congenital color vision deficiency, especially for red-green blindness and deuteranopia. At present, there is lack of quantitative and qualitative results of color VEP examination.

Adolescent↗
PubMedDate not supplied

Prevalence and causes of blindness and low vision in Dambatta local government area, Kano State, Nigeria.

In 1995 a population based cross sectional blindness prevalence survey was conducted in Dambatta local government area (LGA). 3596 people were examined. The prevalence of blindness was 1.14% with 95% confidence limit of (0.8-1.48%). The causes of blindness are cataract 54%, Trachoma 17%, Glaucoma 15%, Corneal opacity 7%, other blinding conditions 7%. The prevalence of low vision was 2.05% with 95% confidence limit (1.60-2.50%). One percent of the population were severely visually impaired (WHO category 2). The causes of low vision are cataract 55%, corneal opacity 14%, uncorrected aphakia 11%, Glaucoma 7%, Refractive error 5%, other conditions 8 percent. Cataract was the leading cause of uniocular blindness with 53%, others were phthisis bulbi 17%, Trauma 14%, corneal opacity 10%, and others 7 percent. Cataract was the single most important cause of blindness, low vision and uniocular blindness accounting for 54%, 55%, and 53%, respectively. Uncorrected aphakia accounted for 11% of the low vision group, 80% of these had couching. This study showed that 93% of the blindness was avoidable in the sense that it could have been primarily prevented or, is treatable. 92% of the causes of low vision are avoidable.

Blindness↗
PubMed2003

[Vision analysis of cataract extraction with intraocular lens implantation in venerable aged patients].

PURPOSE: To evaluate possible diseases affecting visual acuity in cataract extraction with intraocular lens implantation in venerable aged patients. METHODS: 387 patients (425 eyes) over 80 years old were performed cataract extraction and intraocular lens(IOL) implantation, The postoperative vision was observed and affecting factors were analysed. RESULTS: After the operation, there were 221 eyes (52.0%) of which corrected vision was better than 1.0, Ninty-eight eyes (23.8%) of which was 0.5-0.9, 106 eyes (24.9%) of which was less than 0.5. The main diseases that affect vision restoration were aged-related macular degeneration, glaucoma, retinal vein occlusion and optic atrophy. CONCLUSION: The vision of venerable aged patients who had the operation of cataract extraction and IOL implantation were greatly increased. The various fundus diseases in senile patients are mains reason affecting vision restoration.

Age Factors↗