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Results for “Visual Acuity”

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PubMed1980

Visual acuity following binocular deprivation in the cat.

Threshold visual acuity for three cats which were reared from birth to 4--12 months of age with bilateral lid closure was measured and compared to visual acuity in three cats which had the use of a non-deprived eye. The results indicate that binocular deprivation (BD) results in significant deficits in visual acuity which are proportional to the duration of deprivation. Threshold visual acuities were 3.7 cycles/deg. following 4 months of BD, 3.25 cycles/deg. following 7 months of BD and 2.55 cycles/deg. following 12 months of BD compared to acuities of 6.0, 6.5 and 6.8 cycles/deg9 for cats using a non-deprived eye. All BD cats had recovered from the initial visuomotor deficits, seen in these cats and reported in the literature, following lid-parting. The implication of such deficits in visual acuity on visual discrimination learning in BD cats is discussed.

Animals↗

PubMed1991

Visual acuity and contrast sensitivity in cataract: summation and inhibition of visual performance.

Patients exhibiting uniocular cataract often report an improvement in vision on closing their cataractous eye. Such qualitative evidence suggests the presence of binocular inhibition--the converse of binocular summation (that is the normal superiority of binocular over monocular vision). To quantify the extent of inhibition in cataract, binocular and monocular visual acuity and contrast sensitivity were measured in 28 patients. Twelve patients showed binocular inhibition for visual acuity whilst 11 showed inhibition for contrast sensitivity measured at four cycles per degree (c.deg-1). Contrast sensitivity for 8 c.deg-1 targets was further recorded in a subset of 14 patients in whom seven showed inhibition. In patients who demonstrated inhibition, the mean decrement in performance for visual acuity was 13%. For contrast sensitivity at 4 and 8 c.deg-1 the mean decrement was 25% and 32% respectively. The clinical significance of these findings is discussed with respect to the assessment of visual function and management of the cataract patient.

Adult↗

PubMed2004

Optotype and grating visual acuity in patients with ocular and cerebral visual impairment.

PURPOSE: To investigate the discrepancy between grating and optotype visual acuity in children with visual impairment due to brain and/or ocular abnormalities. METHODS: Better eye acuity at 114 cm was studied in 81 patients (ages, 5-24 years) attending special schools for the visually handicapped. Fourteen patients had a brain abnormality, 48 had an ocular disorder, and 19 had both. Three acuity tasks were administered: detecting gratings in one of two positions, discriminating the orientation of single gratings, and discriminating the orientation of uncrowded Landolt-C optotypes. The three paradigms were similar in stimulus contrast, luminance, presentation mode, and psychophysical procedure. RESULTS: Overall, grating acuity was better than optotype acuity, and the disparity increased with poorer optotype acuity. The largest discrepancies occurred in patients with brain abnormality, but disparities were also large in patients with optic nerve disorder. In patients with ocular and brain abnormality, grating acuities were only mildly better and not different from patients with only ocular abnormality. Grating orientation and grating detection tasks yielded similar thresholds, except in patients with cerebral visual impairment and with optic nerve disorder, whose grating detection acuity was better than grating orientation acuity. CONCLUSIONS: Grating-to-optotype acuity superiority is typically large in visual disorders involving the brain. The closely matched test paradigms point to stimulus characteristics as the explanation. However, because the discrepancy decreased with grating orientation acuity instead of grating detection acuity, the complexity of the response required also plays a role.

Adolescent↗

PubMed1996

Transillumination of iris and subnormal visual acuity--ocular albinism?

BACKGROUND: A common clinical sign in children with subnormal visual acuity or slow visual development was iris transillumination. This was used as the inclusion criterion in a study of children shown to have a subnormal visual acuity in a general health examination at age 4 years. METHODS: Refraction values, stereopsis, fundus photography, macular and nerve head appearance, and visual evoked response (VER) recordings were studied in 18 children. The clinical results were compared with 64 controls referred to the eye clinic because of subnormal vision from the general health examination or from school health care. RESULTS: Eight children had VERs showing asymmetry typical for albinism. Another four had only small asymmetries on the VER, indicating a lower degree of decussation abnormality. No simple correlation of visual acuity, degree of iris transillumination, stereopsis, or macular pathology and VER asymmetries were found. However, marked iris transillumination in all four quadrants, absence of a foveal reflex, and low visual acuity were weakly correlated. CONCLUSIONS: In a rather homogeneous group of children with iris transillumination and subnormal visual acuity eight of 18 had typical albino VERs. The findings of small atypical VER asymmetries in four children and no asymmetry in six children suggest that albinism may be considered as a description of a heterogeneous group of conditions including maximal decussation rate (100%) in the chiasma to a condition with almost normal (> or = 50%) decussation rate.

Adolescent↗

PubMed1990

Binocular summation in visually evoked responses and visual acuity.

Monocular and binocular transient visually evoked responses (VER) were recorded on 50 adult subjects using a pattern reversal stimulus (check size 5.5 min arc). The peak-to-trough amplitude of the VER wave was measured and compared with the subjective visual acuity (Landolt C). The binocular amplitude enhancement over the monocular amplitude was around 26% across the acuity range studied, whereas the mean binocular subjective visual acuity improvement was around 11.3%, but this varied from 1% at the high acuity end to 17% at the low acuity end of the range.

Adolescent↗

PubMedDate not supplied

Assessment of visual acuity in children with severe neurological impairments.

We used the Teller Acuity Cards to assess visual acuity in children with severe neurological handicaps (N = 12), all of whom had been previously untestable. With every child we were able to obtain at least one estimate of visual acuity, even with those described as likely having little or no visual function. However, in all cases, performance was poorer than that of unimpaired children of the same age. Our results confirm that the test is useful for assessing visual acuity in populations who, because of significant cognitive, linguistic, and motor deficits, cannot be assessed by more traditional techniques.

Adolescent↗

PubMedDate not supplied

Visual acuity in a community-dwelling Japanese population and factors associated with visual impairment.

PURPOSE: The aim of this study was to describe the distribution of visual acuity and investigate the predictors of visual impairment in a Japanese population. METHODS: Best-corrected visual acuity was measured in 2263 subjects aged 40-79 years randomly selected from a local community. Relations between visual impairment and possible risk factors were investigated. RESULTS: Among these subjects, 41 individuals (1.8%) were identified as visually impaired (best-corrected visual acuity in the better eye <0.5). Both sexes in the older age groups had a higher frequency of visual impairment (Mantel-Haenszel chi-square test: P<0.001). A multiple logistic regression indicated that an increase in age of 10 years [odds ratio (OR) 3.9; 95% confidence interval (CI) 2.3-6.7] and myopia (OR 2.9; 95%CI 1.4-6.0) were independent risk factors for visual impairment. Individuals with the highest level of education (college or higher) had a lower risk of visual impairment (OR 0.1; 95%CI 0-0.7) compared to individuals with the lowest level of education. CONCLUSIONS: As expected, visual impairment increased with advancing age, although the prevalence of visual impairment in our population was lower than in other surveys. Racial and regional differences and differences in study design may be responsible for discrepancies between surveys. It is noteworthy that myopia was a significant risk factor for visual impairment, although the reasons for this association are uncertain and need further investigation.

Adult↗

PubMed2005

Clinical outcomes of phacoemulsification cataract surgery in diabetes patients: visual function (VF-14), visual acuity and patient satisfaction.

PURPOSE: To evaluate the visual outcomes (visual acuity [VA] and visual function) after phacoemulsification cataract surgery in patients with diabetic retinopathy (DR), and assess patient satisfaction with final surgical outcome. METHODS: This prospective study comprised 74 eyes of 74 patients with different stages of DR. One surgeon (AW) performed all cataract surgery in a standardized fashion. Patients were assessed using the VF-14 (Visual Function-14) questionnaire. The following groups of patients were compared: those with no apparent retinopathy; those with mild non-proliferative DR (NPDR); those with severe NPDR, and those with proliferative DR (PDR). Visual acuity and visual function questionnaire (VF-14) responses were recorded preoperatively and 3 months postoperatively, during which the non-operated fellow eye showed no progression in retinopathy. RESULTS: Improvements in visual outcomes were significantly higher in groups 1 and 2 compared to groups 3 and 4 (Tukey-Kramer, p < 0.001). Comparisons between groups 1, 2 and 3, 4 showed significant differences in improvements in VA (Tukey-Kramer, p < 0.01), yet no statistically significant differences in functional (VF-14) improvements emerged between these groups. CONCLUSIONS: Patients with more advanced levels of DR showed no functional improvements despite improvements in VA. This emphasizes the relevance of patient education prior to surgery. In particular, it should be explained to patients with more advanced DR that, although surgery may be required, their functional improvement may be limited.

Adult↗

PubMed2000

Relationship between visual acuity and eye position variability during foveations in congenital nystagmus.

Visual acuity in congenital nystagmus has proven to be primarily related to the duration of foveation periods, during which the image of a target falls onto the fovea and eye velocity slows down. It was found that the longer the foveation time the higher the visual acuity. However, the cycle-to-cycle variability of the eye position and velocity during foveation periods also contribute to visual acuity. A high variability of the eye position during the foveations hinders a stable placement of the target image on the centralmost fovea and consequently decreases visual acuity. To investigate the relationship between different nystagmus features and visual acuity, infrared- oculographic and electro-oculographic eye position recordings of 20 patients affected by congenital nystagmus were analysed in different gaze positions. In several patients' recordings, a high variability of the eye position during foveations (i.e. greater than 0.5 degrees) was detected. Correspondingly, low visual acuity was measured, in spite of sufficiently long foveation periods. The standard deviation of eye positions during foveation periods was used to measure this variability and it was found to be correlated to visual acuity, in conjunction with the mean duration of the foveation periods. On the basis of the data analysis, an exponential relationship is proposed to relate visual acuity and the standard deviation of the eye position during foveations.

Adolescent↗

PubMed1994

Visual outcome after laser photocoagulation for subfoveal choroidal neovascularization secondary to age-related macular degeneration. The influence of initial lesion size and initial visual acuity. Macular Photocoagulation Study Group.

OBJECTIVE: To provide detailed information specific to the initial visual acuity and initial lesion size on the outcome of patients with subfoveal choroidal neovascularization (CNV) secondary to age-related macular degeneration. DESIGN AND PATIENTS: The 189 eyes assigned to laser photocoagulation and the 184 eyes assigned to observation in the Subfoveal New CNV Study were divided into nine subgroups based on initial visual acuity and initial lesion size. MAIN OUTCOME MEASURES: The pattern of visual acuity loss for both treated and untreated eyes through 4 years of follow-up was compared among the subgroups. Reading speed and contrast thresholds also were examined. RESULTS: Four patterns (A, B, C, D) of visual acuity loss in treated eyes relative to untreated eyes were identified. Eyes in group A (small lesion and moderate or poor initial visual acuity or medium lesion and poor visual acuity) had the best visual outcome with treatment; treated eyes were better throughout follow-up. Eyes in group B (small lesion and good initial visual acuity or medium lesion and moderate or good visual acuity) had substantial treatment benefit by 12 months, but were worse immediately after treatment. Eyes in group C (large lesion and poor initial visual acuity) had a small treatment benefit throughout follow-up. Eyes in group D (large lesion and moderate or good visual acuity) had the worst visual outcome with treatment; treated eyes were substantially worse for the first 18 months and were not appreciably better through 4 years of follow-up. CONCLUSIONS: Recommendations for treatment of subfoveal CNV should take account of the initial visual acuity and lesion size. Eyes in group D are poor candidates for laser treatment.

Aged↗

PubMedDate not supplied

Treating myopia with acoustic biofeedback: a prospective study on the evolution of visual acuity and psychological distress.

OBJECTIVE: The effects of a visual training technique on changes in myopia, visual acuity, and psychological distress were studied in a controlled prospective study. METHOD: A group of 33 female students with myopia < or = 3.50 diopters (D) underwent visual training using an acoustic biofeedback technique. A group of 22 female students with myopia and a group of 27 students with emmetropia formed the two control groups, matched for school, age, sex, and refractive error. Manifest and cycloplegic refraction, visual acuity, personality profile (CPI), and psychological distress (SCL-90) were measured at the baseline (T0), at 10 weeks (T1), and after 12 months (T2). RESULTS: At T2, myopia significantly progressed both in the treated and in the untreated students with myopia. Visual acuity improved only in the treated myopia group (despite refraction objectively being worse). No differences were found among the personality profiles in the three groups. All items indicative of psychological suffering improved in the group treated for myopia whose visual acuity was ameliorated. CONCLUSIONS: The visual training technique led to no improvement in objective measures of visual acuity, but did lead to an improvement in one relatively subjective measure of visual acuity and a parallel improvement in psychological conditions. The students with myopia who were treated consequently had a greater sense of general well-being.

Accommodation, Ocular↗

PubMed2005

Empiric determination of corrected visual acuity standards for train crews.

PURPOSE: Probably the most common visual standard for employment in the transportation industry is best-corrected, high-contrast visual acuity. Because such standards were often established absent empiric linkage to job performance, it is possible that a job applicant or employee who has visual acuity less than the standard may be able to satisfactorily perform the required job activities. For the transportation system that we examined, the train crew is required to inspect visually the length of the train before and during the time it leaves the station. The purpose of the inspection is to determine if an individual is in a hazardous position with respect to the train. In this article, we determine the extent to which high-contrast visual acuity can predict performance on a simulated task. METHODS: Performance at discriminating hazardous from safe conditions, as depicted in projected photographic slides, was determined as a function of visual acuity. For different levels of visual acuity, which was varied through the use of optical defocus, a subject was required to label scenes as hazardous or safe. RESULTS: Task performance was highly correlated with visual acuity as measured under conditions normally used for vision screenings (high-illumination and high-contrast): as the acuity decreases, performance at discriminating hazardous from safe scenes worsens. CONCLUSIONS: This empirically based methodology can be used to establish a corrected high-contrast visual acuity standard for safety-sensitive work in transportation that is linked to the performance of a job-critical task.

Adult↗

PubMed1989

[Statistical evaluation of visual acuity].

The statistical evaluation of the visual acuity has to be based on the non-parametric test as the decimal scale of the visual acuity forms a serial scale and not the intervallic one. From the theoretic point of view, the most advantageous approach uses the paremetric statistical tests. Visual acuity is measured on optotypic tables with log gradiation of the optotype size. At present time optotypes of this kind are not available in Czechoslovakia.

Humans↗

PubMed2001

New visual acuity chart for patients with macular hole.

PURPOSE: To evaluate the usefulness of a new multiple-letter visual acuity chart (MLAC) for the measurement of visual acuity in patients with macular hole. METHODS: Visual acuity was measured using a standard visual acuity chart (Landolt rings, also referred to as C's) and with the MLAC in normal subjects and in patients with a cataract or a macular hole. The MLAC has 14 plates (45 x 45 cm), and on one plate, many Landolt C's were printed with the gaps pointing in the same direction and all of one size. The sizes of the letters and gaps were made to give equivalent visual acuities of 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.5, and 2.0. The spacing between the letters was 33.3% of the diameter of the C's. Each chart projected many C's onto the macular area (5 degrees x 5 degrees ), which permitted the measurement of visual acuity at an extrafoveal point without the patient having to search for the extrafoveal point with the best acuity. RESULTS: There was no difference in the acuity measurement determined with the standard chart and the MLAC in normal subjects and patients with cataracts. Twelve of 16 patients with open macular hole, however, demonstrated higher acuity measurement (more than two lines) on the MLAC than on the standard chart. The improvement of visual acuity measurement after successful macular hole surgery was significantly less with the MLAC than with the standard chart. CONCLUSIONS: Our results suggest that the standard acuity chart, when administered before surgery, underestimates the patient's potential visual acuity after surgery, whereas the MLAC provides a better estimate of the patient's postoperative acuity. The MLAC can be a useful tool for measuring visual acuity in patients with macular hole.

Aged↗

PubMed2006

Comparison of logMAR ETDRS chart and a new computerised staircased procedure for assessment of the visual acuity of children.

The validity and repeatability of visual acuity measures are particularly important in the detection and monitoring of childhood visual anomalies such as amblyopia. The repeatability and sensitivity of a new computerised visual acuity test, 'Staircased Procedure' is compared with the now gold standard visual acuity test, the early treatment of diabetic retinopathy study (ETDRS). Twenty-seven visually normal children (mean age: 6.7 +/- 1.1 years) and 27 children with amblyopia (mean age: 6.1 +/- 0.7 years) were tested with the ETDRS and Staircased Procedure. A retest was administered 4-5 weeks later and 30 min later for the visually normal and the amblyopic children, respectively. The staircased procedure produced significantly better visual acuity than the ETDRS for visually normal and amblyopic children. Repeatability was similar for both tests (ETDRS: 0.11 log units; staircased procedure: 0.13 log units). In conclusion, the Staircased Procedure was an acceptable test with high repeatability and validity.

Amblyopia↗

PubMed1992

Set shot shooting performance and visual acuity in basketball.

Common sense suggests that decreasing visual acuity will have a negative effect on basketball shooting performance. To test the hypothesis that basketball shooting performance monotonically decreases with decreasing acuity, 19 subjects attempted 25 set shots from a fixed location at each of 5 different acuity levels: 6/6 or better and vision blurred (by optical defocus) to visual acuities of 6/12, 6/24, 6/48, and 6/75. Our results revealed a small but statistically nonsignificant decrease in shooting performance between the 6/6+ and 6/12 conditions. For visual acuities between 6/12 and 6/75, the number of baskets made remained constant. We conclude that decreases in visual acuity over the range of 6/6+ to 6/75 resulting from defocus do not significantly reduce set shot shooting performance.

Adolescent↗

PubMedDate not supplied

Laser interferometric prediction of postoperative visual acuity in patients with genetic ectopia lentis.

PURPOSE: To compare preoperative laser interference visual acuity (LIVA) with postoperative Snellen visual acuity (SVA), and to evaluate clinical significance using laser interferometer in patients with genetic ectopia lentis. METHODS: We treated a series of 18 patients (34 eyes) with genetic ectopia lentis whose visual acuity did not improve with optical phakic or aphakic correction, or with modern microsurgery and automated suction-cutting devices. Laser interferometry and electroretinogram (ERG) were used for the examination of retinal function before surgery. RESULTS: There was not significant difference between the interferometric acuity before operation and the corrected visual acuity after operation (p > 0.05), and the coincidence rate between them was 80% (27 eyes). ERG examination showed normal function in most of the patients. CONCLUSIONS: The results showed that the laser interferometric acuity is a valuable method in evaluation of postoperative visual acuity in patients with ectopia lentis. In six eyes, the LIVA was lower than the initial corrected vision postoperatively, but ERG examination showed that the retinal function was normal in these patients. Therefore, in patients with genetic ectopia lentis, LIVA combined with ERG predicts visual acuity more accurately.

Adolescent↗

PubMed1999

Comparison of suppression, stereoacuity, and interocular differences in visual acuity in monovision and acuvue bifocal contact lenses.

PURPOSE: The relationship between visual acuity and stereoacuity has been well documented: as binocular visual acuity increases, stereoacuity improves. We compared interocular differences in visual acuity and stereoacuity in two presbyopic soft contact lens modalities, monovision and a new soft bifocal contact lens, the Acuvue Bifocal. The Acuvue Bifocal is hypothesized to show a smaller interocular acuity difference, increased stereoacuity, and decreased suppression over monovision at distance and near. METHODS: Monovision patients wearing Acuvue or Surevue soft contact lenses were tested for visual acuity, stereoacuity, and suppression at distance and near. Stereoacuity was tested with the Randot Stereotest (near) and the BVAT (distance). Suppression was evaluated with the Acuity Suppression Vectogram (near) and the BVAT (distance). Patients were then fit with the Acuvue Bifocal in each eye. After wearing the lenses for 1 week, the same tests of visual acuity, stereoacuity, and suppression were performed. RESULTS: The mean interocular acuity difference (IAD) at distance with monovision was 0.712 logarithm of the minimum angle of resolution (logMAR) (SD = 0.275) and 0.188 logMAR (SD = 0.252) (p < 0.001) with the Acuvue Bifocal. At near, the mean IAD with monovision was 0.420 logMAR (SD = 0.183) and 0.137 logMAR (SD = 0.147) (p < 0.001) with the Acuvue Bifocal. Of the monovision subjects, 89% (17 of 19) demonstrated suppression at near while only 26% (5 of 19) did with the bifocal lenses (statistically significant at p < 0.001). Stereoacuity at near improved from a median of 200 sec arc with monovision to 50 sec arc with the bifocal lenses. CONCLUSIONS: In this study, correcting presbyopia with the Acuvue Bifocal versus monovision resulted in a statistically significant decrease in the interocular difference in visual acuity at distance and near. The decreased interocular difference in visual acuity improved certain aspects of binocularity as demonstrated by a decrease in suppression and an increase in stereoacuity.

Contact Lenses, Extended-Wear↗