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At least 1,207 records · Page 67Linked to original sources
PubMed1996

Effect of naturally occurring visual acuity differences between two eyes in stereoacuity.

Stereoacuity was measured in 30 subjects with a naturally occurring visual acuity (VA) difference between the eyes. The stereoacuity was measured by a modified Howard's apparatus using the staircase method and VA was measured with log MAR charts. Stereoacuity was worse in subjects with a large VA difference between the two eyes; the correlation between stereoacuity and VA difference was significant (r = 0.76, P < 0.001). Neither the VA of the worse eye nor of the better eye contributed to the reduction in stereoacuity. The deterioration was more obvious if VA difference between the two eyes was one line or more (correlation coefficient, r= 0.88, P < 0.001). This study also reinforces the use of a > or = 70% stereothreshold when attempt stereoacuity results to compare with other studies.

Adolescent↗
PubMedDate not supplied

Long-term visual acuity after argon green laser photocoagulation of juxtafoveal choroidal neovascularization in highly myopic eyes.

PURPOSE: To evaluate visual outcomes in patients with high myopia afterjuxtafoveal choroidal neovascularization (CNV) treated with argon green laser photocoagulation. PATIENTS AND METHODS: We retrospectively analyzed 23 eyes of 21 patients with high myopia (>6.0 diopters and/or axial length >26 mm) with juxta foveal CNV treated with direct Argon green laser photocoagulation. Mean age at diagnosis was 49.08+/-12.20 years (range, 29 to 71). Mean follow-up was 54.26+/-26.18 months (range 18 to 96). RESULTS: Best corrected visual acuity (BCVA) before treatment was 0.09+/-0.10 (range, 0.01 to 0.40). Two months after treatment it was 0.14+/-0.12 (0.01 to 0.6), significant difference (p=0.02, Student's t-test forpaired data) and aftersix months 0.19+/-0.14 (0.01 to 0.5) (p=0.0002). Mean BCVA decreased with follow-up, to 0.19+/-0.15 (0.01 to 0.4) after two years, 0.16+/-0.15 (0.01 to 0.5) after three years and 0.16+/-0.19 (0.01 to 0.7) after four years, with no significant improvement after the third year (p=0.04). In two cases CNV reappeared. CONCLUSIONS: Direct argon green laser photocoagulation in high-myopia juxtafoveal CNV can improve BCVA initially for between two and 24 months. The improvement fades with time, and is no longer significant after the third year.

Adult↗
PubMed1996

Scanning laser densitometry in visual acuity loss of unknown origin.

AIM: To assess foveal cone photoreceptor function in patients with unexplained loss of central visual acuity. METHODS: Testing of foveal cone photoreceptor function was performed using scanning laser densitometry, colour matching (Rayleigh equation), and pattern electroretinography (ERG). Standard tests included full field ERG, electrooculography, visual evoked potentials, static perimetry, and fluorescein angiography. RESULTS: Decreased foveal cone photopigment density and abnormal pattern ERG were found in three patients. Results of colour matching were not unequivocal. CONCLUSION: Testing of foveal cone photoreceptor function using scanning laser densitometry may determine the location of pathological changes in certain patients with unexplained visual loss.

Adolescent↗
PubMed1982

Effects on visual acuity of neonatal or adult tectal ablation in rats.

Tectal ablation in neonatal rats leads to retrograde degeneration of retinal ganglion cells whereas similar damage in adults does not. We show here that the behavioral effects are comparably different. When rats with neonatal tectal ablation are tested as adults they are impaired in learning a discrimination between vertical and horizontal stripes and their visual acuity for square-wave gratings is slightly but significantly reduced.

Aging↗
PubMed1984

A comparison of the Snellen chart and the S-chart for visual acuity assessment in amblyopia.

A standard Snellen chart and a chart that controls contour interaction effects and gives equal numbers of acuity trials for all letter sizes (the S-chart) were used to compare visual acuities for 30 amblyopic patients (17 with central fixation, 13 with eccentric fixation). No statistically significant difference appeared between S-chart and Snellen acuity in the acuity range 20/30 to 20/80. When amblyopic acuity was below 20/100, S-chart and Snellen acuities differed significantly.

Amblyopia↗
PubMed1984

Visual motor co-ordination and dynamic visual acuity.

Data on the effect of an antihistamine (triprolidine 10 mg) on visuo-motor coordination and dynamic visual acuity were used to establish interactions between these skills. Analysis of covariance and principal component analysis were used. The analyses suggested two main effects--an effect on the activity of the neuromuscular system and one which impaired ability to anticipate target movement. Detection of impaired performance by any task may have wider implications to the effectiveness of the individual than that obviously suggested by the skill itself.

Humans↗
PubMed1992

Impairment of high-contrast visual acuity in Parkinson's disease.

Several studies have shown that the visual system is affected in Parkinson's disease (PD) with reduced contrast sensitivity, low-contrast acuity, and flicker sensitivity, as well as altered electroretinograms (ERGs) and pattern visual evoked potentials (VEPs). Apparently, however, no study has yet specifically determined whether visual acuity to high-contrast stimuli is impaired in PD. Visual acuity was measured in a group of 16 patients with PD, both on and off drugs (for 24 h), and 16 age- and sex-matched normal control subjects. Acuity was impaired in the PD group both on standard Snellen chart and on a screen in a computerized test of visual resolution. The degree of impairment was 24 and 25%, respectively, in the two tests. The PD patients had marginally better acuity on both tests while receiving drugs, but the differences were not significant. The difference between the two groups was consistent with impaired resolution and could not be accounted for by any perceptual dysfunction that may also have been present in the PD group. Conversely, however, impaired acuity may be implicated in studies that have reported mild deficits of visuospatial/visuoperceptual function in PD. Reduced acuity appears to be a subtle sequela of dopaminergic deficiency in the visual system.

Adult↗
PubMed2005

Visual acuity measurement of prosthetic vision: a virtual-reality simulation study.

A virtual-reality simulation tested prosthetic visual acuity for both rectangular and hexagonal phosphene grids. Thirteen normally sighted, untrained subjects were required to identify the Landolt C optotype over ten sessions. Overall performance, performance by filter setting (image analysis), and performance by size and orientation of the Landolt C optotype are reported. The results indicated that the hexagonal grid had a slight (4.1%) but statistically significant (p < 0.0001) performance advantage over the rectangular grid for correct identification of the testing symbol. It was also observed that both the phosphene grids had distinct performance profiles relating to their respective spatial orientation. Over the course of the ten sessions, learning afforded subjects an averaged improved performance of 10%.

Artificial Intelligence↗
PubMed2002

Distant visual acuity in chronic psychiatric patients. A pilot study.

BACKGROUND: There is a paucity of systematically collected data on visual impairment in patients with chronic psychiatric disorders. The aim of this pilot study was to estimate the magnitude of impairment of distant visual acuity (DVA) including refractive and non-refractive errors in institutionalized psychiatric patients awaiting resettlement in the community in Hong Kong. METHOD: DVA was tested using the Snellen method in a randomly selected cohort of 428 institutionalized psychiatric patients from the four long-stay rehabilitation units in Hong Kong. The pinhole method was employed to differentiate between refractive and non-refractive impairment of DVA. RESULTS: Seventy-five percent of the sample had impaired DVA; 39 % of the subjects had refractive error (myopia). Only a small percentage of patients wore spectacles and had adequately corrected vision. Patients with impaired DVA were significantly older than those with normal DVA. CONCLUSION: While the frequency of myopia corresponds to that found in the general population in Hong Kong, the nature of non-refractive impairment needs further investigation including systematic eye examination, and examination of medication and life-style factors. Periodical eye examinations should be part of comprehensive health assessment for chronic psychiatric patients.

Chronic Disease↗
PubMed1997

Visual acuity in children with colobomatous defects.

Examining a child with a colobomatous defect can be challenging. The most important predictor of visual outcome is identification of normal foveal anatomy. The clinician should first evaluate the child for the associated systemic conditions. The next step is to identify the presence of normal foveal structures in the involved eye(s). If present, a trial of amblyopia treatment should be initiated. Anisometropic amblyopia is common and should be addressed. Retinal detachments are common and add uncertainty to predicting visual acuity.

Child↗
PubMed1976

A simple relationship between the probability distribution of visual acuity and the density of retinal output channels.

Throughout the retina, the parameters of the probability distribution of visual acuity for monochromatic interference fringes are closely proportional to the number of retinal ganglion cells per degree of visual angle. There are no simple relationships to receptor spatial frequencies. These findings suggest that neuro-retinal acuity is determined principally by the spatial frequency of neural output channels.

Humans↗
PubMed1976

Prognosis of primary rhegmatogenous retinal detachments. 2. Accounting for and predicting final visual acuity in surgically reattached cases.

Multiple linear regression-analysis of variance was used to define relationships between final visual acuity and several parameters in 31 patients with reattached primary rhegmatogenous retinal detachments. Older patient age, preoperative macular detachment, clinically visible macular lesions, greater detachment duration and extent, and higher subretinal fluid butyrylcholinesterase activity were all inversely related to final acuity. The relationship of each parameter to final acuity, in conjunction with and apart from all the other parameters, was defined. Collectively the parameters accounted for 85% of the variation about the mean of the clinically observed finally acuities. The parameters could be weighted to give a generally, reasonably accurate prediction of final acuity at the time of surgery. The findings are consistent with a pathophysiological sequence involving alterations in the choroidal circulation and the blood-ocular barrier of the posterior segment.

Adolescent↗
PubMed1997

Graphical representation of visual acuity data.

Accurate graphical depiction of data requires that distances between points map precisely to the quantitative differences they represent. In the case of Snellen visual acuity, consecutive line sizes do not generally correspond to equal increments in visual angle, hence scores plotted against axes marked off in equal intervals provide a false representation of the relation between plotted values. A worked example illustrates the nature of this problem and its solution.

Humans↗
PubMed1990

Form perception and visual acuity in a chimpanzee.

A 6.5-year-old female chimpanzee learned to distinguish perfectly every letter of the alphabet in a matching-to-sample task with 26 letters as choice alternatives. Confusion of letters during the initial training was used to scale them in a multidimensional similarity space and to associate them in hierarchical clusters. The results resembled those obtained from similarity judgements by humans. Using letters of various sizes, a visual acuity test revealed that the chimpanzee's acuity was about 1.5, comparable to that in normal humans. The chimpanzee also readily learned to use letters as names of individual humans and chimpanzees. A species-typical feature was identified in the perceptual processes associated with complex forms, such as those involved in individual recognition.

Algorithms↗
PubMed2005

[The visual acuity impairment as the only sign of cerebral aneurysms--case report].

Cerebral aneurysms are the most common reason of subarachnoid haemorrhage at the age of 50-60. Though the results of such haemorrhage are severe (high morbidity and mortality), it is quite often, the first noticeable sign of the problem. Previous symptoms i. e. headache, ophthalmic disturbances, temporary neurological symptoms are often passed over. The authors present the case of a young woman with cerebral aneurysms, in which the visual acuity impairment was the only symptom of the disease.

Adult↗
PubMed1987

Visual acuity in a diabetic population.

In a population study of all insulin-treated diabetics and a random sample of those treated with oral antihyperglycaemic agents (OHA) in Gotland, Sweden, the visual acuity (VA) was determined. The prevalence rates of visual impairment (VA 0.1-0.2) and blindness (VA less than 0.1) in the insulin-treated group were 4.9 and 4.4%, respectively, and in OHA-treated diabetics 7.2 and 1.4%. The impairment and blindness were due to diabetic retinopathy (Rp) in 72% of the insulin-treated group, but only in 14% of the OHA-treated diabetics in whom cataract and age-related maculopathy were the predominant causes. Blindness was four times more frequent among insulin-treated females than males. On simple logistic regression test VA correlated with Rp, age at examination, age at onset of diabetes, duration of diabetes and sex. However, on multiple logistic regression analysis the only significant relationships with VA were in the insulin-treated group, a correlation with Rp and age; and in the OHA-treated group, a correlation with age only. Thus the higher frequency of blindness in insulin-treated women was explained by Rp and age. When standardizing for age, the fraction of blind patients was found to be significantly higher among the insulin-treated than in the OHA-treated diabetics (6.7 vs 1.4%).

Adult↗
PubMed1981

Visual acuity and test performance.

Evaluation of scholastic achievement (American College Testing Service) test scores confirms previous reports that persons with poor visual acuity perform better on these tests than individuals with normal or superior acuity.

Adolescent↗