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At least 559 records · Page 31Linked to original sources

PubMed1988

Effect of chromatic dispersion of a lens on visual acuity.

Materials with a high refractive index have a considerable level of chromatic dispersion which, around the periphery of corrective lenses, may affect the wearer's visual acuity. By measuring visual acuity through prisms of increasing chromatic power we have established the relation between chromatic power and visual acuity. The maximum chromatic dispersion of materials useable in ophthalmic optics can be deduced from these results.

Adult↗

PubMed1999

[Visual acuity and ocular diseases in aged residents of nursing homes: study of 219 persons in Orléans].

PURPOSE: To measure the visual acuity and to determine the etiological causes of visual impairment in the elderly residing in nursing homes. METHODS: 219 elderly persons residing in nursing homes were examined in the residence. The ophthalmological examination consisted in a visual acuity measurement, a slit-lamp examination and a fundus examination. RESULTS: This study included 145 women and 74 men. Mean age was 79.1 years (range 41-101 years). Visual acuity could be measured in 181 subjects (82.6%): it was 1/10 or worse in the better eye in 23 of them (13%) and 2/10 to 3/10 in 36 patients (20%). In 21 (17.6%) out of the 119 patients aged over 74 years, visual acuity was 1/10 or worse in the better eye. Visual impairment significantly increased with age (p < 0.05). There was no difference between men and women in the prevalence of visual impairment. Among the 55 subjects with visual impairment, the main causes of vision loss were: cataract in 36 patients (66%), age-related macular degeneration in 9 patients (16%) and optic neuropathies in 5 patients (9%). Only one (2.8%) out of the 36 patients with cataract could be operated. CONCLUSION: The rate of visual impairment of people in nursing homes was higher than in corresponding age groups in the general population. The main cause of vision loss was cataract; however, only a few patients could benefit from an operation. These results confirmed that a systematic ophthalmologic examination should be performed before general health problems prevent patients from being operated.

Adult↗

PubMed1985

A simple grating visual acuity test for impaired children.

Twenty-five developmentally delayed or neurologically impaired nonverbal children, aged 2 to 15 years, referred for visual acuity assessment, were beyond the age at which standard preferential-looking techniques are considered to be effective and none could be tested with Snellen letters, illiterate Es, or Allen pictures. Our method, in which the children learn to point to grating stimuli, enabled us to obtain monocular visual acuity estimates in 19 of the 25 patients. When indicated, patching therapy was begun and was monitored with this method. Similar testing of 31 unimpaired children showed good prediction of recognition visual acuities except in patients with visual acuities worse than 20/160. The grating method accurately identified or excluded amblyopia in 26 of 31 children (84%). We consider this a clinically useful test of visual acuity in nonverbal impaired children.

Adolescent↗

PubMed1999

Refractive errors and visual acuity impairment among self-selected Hispanic, white, and black adults examined by the UCLA Mobile Eye Clinic.

BACKGROUND: Occurrence of refractive errors and uncorrected visual acuity impairment among self-selected, indigent, medically underserved Hispanic, white, and black adults examined by the staff of the UCLA Mobile Eye Clinic (MEC) are described in this study and compared to population-based studies. METHODS: The study sample consisted of all 2,970 Hispanic, 1,228 white, and 1,028 black participants, for a total of 5,226 self-selected adults, ages 25 to 74 years, who received vision screenings and eye examinations by the staff of the UCLA MEC from 1987 to 1997. Tests consisted of visual acuity, refractive error, intraocular pressure, retinoscopy, slit-lamp biomicroscopy, direct ophthalmoscopic examination, and indirect ophthalmoloscopy with pupillary dilation. Levels of visual acuity impairment were defined as mild (20/50-20/80), moderate (20/100), or severe (20/200 or worse) in either eye. RESULTS: Self-selected whites in this study had higher rates of astigmatism, anisometropia, and hyperopia, while myopia was higher among self-selected blacks. Myopia and hyperopia occurred more frequently among younger age groups for all ethnic groups. Whites had a higher occurrence of mild, moderate, and severe visual acuity impairment, as compared with Hispanics and blacks. CONCLUSIONS: Both refractive errors and impaired visual acuity of this self-selected sample are similar to those of adults from the National Health and Nutrition Examination Survey, Hispanic Health and Nutrition Examination Survey, and the Baltimore Eye Survey. The data presented in this study provide a crude estimate of the occurrence of refractive errors and impaired visual acuity among self-selected, medically underserved, indigent Hispanic, white, and black adults in the Los Angeles area.

Adolescent↗

PubMed2005

Visual acuity change and mortality in older adults.

PURPOSE: Several studies indicate an increased mortality rate in older adults who have visual impairment, but few have attempted to address a potential causal mechanism. The goals of this study are to determine whether visual acuity loss increases the risk of dying and to examine whether depressive symptoms act as a mediator in this relationship. METHODS: Data were derived from the 2520 older adults who participated in the Salisbury Eye Evaluation project, a population-based prospective 8-year cohort study. Presenting binocular visual acuity was measured with the Early Treatment Diabetic Retinopathy Study [ETDRS] eye chart and depressive symptoms with the General Health Questionnaire Part D subscale. Mortality data were collected by staff follow-up. Analyses were performed with the Cox proportional hazards regression. RESULTS: Worse baseline acuity was associated with a higher mortality rate (hazard ratio [HR] = 1.05; 95% confidence interval [CI], 1.01-1.09). Also, those who gained two or more lines of visual acuity over 2 years had a lower adjusted risk of dying (HR = 0.47; 95% CI, 0.23-0.95). An interaction was detected, in that women who lost > or =3 lines of visual acuity over a 2-year period had a higher adjusted risk of dying (HR = 3.97; 95% CI, 2.21-7.15), whereas men did not (HR = 1.32; 95% CI, 0.66-2.63). Depressive symptoms did not mediate these relationships. CONCLUSIONS: If the relationship between visual acuity and mortality is indeed causal, it most likely acts via numerous pathways through a variety of intervening variables. The identification of these intervening variables could give additional targets for intervention if acuity cannot be restored.

Aged↗

PubMed1998

Standardized measurement of visual acuity.

The authors reviewed the main aspects of visual acuity evaluation such as the characteristics of the test devices, the notation employed in recording the visual acuity level and the procedures for V.A. assessment, in both distance and near tests. In addition, new ten-letter charts, that tend to follow strictly the standardization guideline suggested by NAS-NRC, are described.

Contrast Sensitivity↗

PubMed1989

Peripheral visual acuity with monovision and other contact lens corrections for presbyopia.

We have conducted two experiments to investigate the effect of monovision and other contact lens corrections for presbyopia upon peripheral visual acuity. In the first study, we measured binocular peripheral visual acuity using Landolt rings with seven subjects wearing a monovision correction. The Landolt rings were presented at eccentricities of 10, 20, 40, and 70 degrees on each side of the subject, with near additions of +1.50 D, +2.50 D, and no addition. We found no significant effect of monovision correction on peripheral visual acuity. In the second experiment we measured the peripheral visual acuity of 11 presbyopic subjects wearing distance contact lenses with lookover spectacles, soft progressive bifocal contact lenses, soft concentric bifocal contact lenses, monovision contact lenses, modified monovision contact lenses, and hard bifocal contact lenses using Koenig bar targets. There were no significant differences in peripheral visual acuity between any of the contact lens corrections for presbyopia.

Adolescent↗

PubMedDate not supplied

Physiological basis of visual acuity and its development in kittens.

To answer the questions, (1) Which cells in the visual system are responsible for high visual acuity and (2) Does the function of the cells which provide high visual acuity develop postnatally; single cell studies have been made in the retina, lateral geniculate nucleus (LGN) and visual cortex of cats of different ages. Sustained-X retinal ganglion cells in the area centralis (the equivalent retinal position to the human fovea) set the upper limit of visual acuity. The cellular acuity develops postnatally until it reaches the adult level at 3--4 months-of-age. The improvement of acuity is associated with an increase in the strength of the inhibitory surround mechanism of the receptive field of sustained cells in the area centralis. The maturation of cellular acuity coincides with maturation of retinal and LGN synaptic organisation and of optic nerve myelination.

Age Factors↗

PubMed2004

Using the KM visual acuity chart for more reliable evaluation of amblyopia compared to the HVOT method.

PURPOSE: To evaluate a new letter matching visual acuity (VA) chart (the KM chart) for children aged 5-7 years, designed as a Monoyer-based chart, in order to obtain a better consistency between school and preschool VA recordings. METHODS: Visual acuities were assessed using three methods: the HVOT, KM and Monoyer charts. Comparisons were made between the KM method versus the HVOT and Monoyer methods, respectively. Children with normal vision and with different degrees of amblyopia were investigated. RESULTS: Visual acuity levels appeared significantly higher in children with amblyopia when tested with the HVOT chart than when tested with the KM chart. Visual acuities obtained with the Monoyer and KM methods were comparable. The difference between the Monoyer and KM methods on the one hand, and the HVOT method on the other, can be explained by the fact that the HVOT chart elicits less crowding effect than the other two charts. CONCLUSIONS: Visual acuity in children with amblyopia might be overestimated if the HVOT test alone is used to assess vision. Use of the HVOT chart, therefore, should be restricted to the 3.5-4.5 years age group, for whom the KM chart is somewhat too difficult. In our opinion the KM chart should be preferred for use with older preschool children because it shows good consistency with the Monoyer chart.

Amblyopia↗

PubMed2006

Effect of cytomegalovirus retinitis on the risk of visual acuity loss among patients with AIDS.

PURPOSE: To describe the prevalence and incidence of reduced visual acuity in eyes of patients with AIDS and without cytomegalovirus (CMV) retinitis at enrollment and estimate the proportion of incident vision loss attributable to new-onset CMV retinitis in this cohort. DESIGN: Multicenter prospective observational study. PARTICIPANTS: Three thousand fourteen eyes of 1507 patients with AIDS and without CMV retinitis at enrollment. METHODS: Medical history, ophthalmologic examination, and laboratory testing collected at enrollment and at follow-up visits every 6 months thereafter. MAIN OUTCOME MEASURES: Loss of visual acuity across the < or =20/50 and < or =20/200 thresholds and doubling of the visual angle; potential causes of this vision loss. RESULTS: For eyes of patients without CMV retinitis at enrollment, the proportions with best-corrected visual acuity of < or =20/50 and of < or =20/200 were 3.9% and 1.8%, respectively. The incidence rates of vision loss to < or =20/50, < or =20/200, and to a doubling of the visual angle were 1.5/100 eye-year (EY), 0.8/100 EY, and 2.1/100 EY, respectively. Approximately 40% of the incident vision loss was attributable to CMV retinitis diagnosed during the follow-up period, and approximately 25% was attributable to cataract. CONCLUSIONS: Although the development of CMV retinitis was the most common reason for visual acuity loss in eyes of our patients with AIDS, it accounted for less than half of the vision loss in our population (approximately 40%). Newly diagnosed cataract during the follow-up period accounted for a substantial amount of incident vision loss as well.

Acquired Immunodeficiency Syndrome↗

PubMed1992

Effect of induced fixation disparity on binocular visual acuity.

Fixation disparities were artificially created for distance vision by prisms, and the monocular and binocular visual acuities were measured. The normal approximate 10% improvement in binocular visual acuity compared to monocular visual acuity, deteriorated in proportion to the amount of fixation disparity created by the prisms. This was true in both eso- and exo-disparity, although not to the same extent.

Adult↗

PubMed1981

Clinical use of visual acuity measured with pupil responses.

The response of the pupil was measured to a foveally fixated small field in which a checkerboard was alternated with a blank field of equal luminance. Visual acuity was assessed with pupil responses in 70 subjects who visited our clinic. A high correlation was found between the visual acuity as measured with pupil responses and the subjective acuity, using the same checkerboard stimuli. We also compared the visual acuity as measure with with pupil responses with the Snellen acuity. The method of obtaining pupil visual acuity seems to compare favourable with other objective methods of measuring visual acuity.

Adolescent↗

PubMed2005

Comparison of visual acuity levels in pediatric patients with amblyopia using Wright figures, Allen optotypes, and Snellen letters.

PURPOSE: To compare and correlate the clinical performance of Wright figures in visual acuity assessments of pediatric patients with amblyopia to those obtained through Allen cards and Snellen letters. SUBJECTS AND METHODS: Best-corrected visual acuity of 26 amblyopic children were measured with the Wright figures(c), Snellen letters, and isolated Allen optotypes, respectively. Amblyopia was defined as two lines of visual acuity difference or a visual acuity level of 20/30 or lower as determined by Snellen chart. The results were evaluated for statistical intergroup differences using the Wilks' Lambda multivariate analysis of variance and for correlation using the Pearson correlation coefficient test. RESULTS: The mean age of the subjects was 8.27 +/- 2.46 years (range: 5 to 15 years). The mean logMAR values for the Wright figures(c), Snellen letters, and Allen optotypes were 0.40 +/- 0.20, 0.47 +/- 0.23, and 0.29 +/- 0.28, respectively. When compared with Snellen letters, the Wright figures correlated to a higher degree ( r = 0.46, P < 0.001) than Allen optotypes ( r = 0.67, P < 0.001). With a visual acuity of 20/40 or worse on Snellen letter testing, the sensitivity of Wright figures(c) and Allen cards in diagnosing amblyopic eyes was 87.0 and 56.5%, respectively ( P = 0.016). CONCLUSIONS: Wright figures, designed primarily to evaluate the vision in the preliterate pediatric population, correlate more closely to Snellen letters and have a higher rate of correctly identifying amblyopia than isolated Allen optotypes in pediatric patients.

Adolescent↗

PubMed2006

Prevalence of high astigmatism, eyeglass wear, and poor visual acuity among Native American grade school children.

PURPOSE: The purpose of this study was to examine the prevalence of astigmatism and poor visual acuity and rate of eyeglass wear in grade school children who are members of a Native American tribe reported to have a high prevalence of large amounts of astigmatism. METHODS: Vision screening was conducted on 1,327 first through eighth grade children attending school on the Tohono O'odham Reservation. Noncycloplegic autorefraction was conducted on the right and left eye of each child using the Nikon Retinomax K+ autorefractor, and monocular recognition acuity was tested using ETDRS logarithm of the minimum angle of resolution (logMAR) letter charts. RESULTS: Tohono O'odham children had a high prevalence of high astigmatism (42% had > or = 1.00 D in the right or left eye) and the axis of astigmatism was uniformly with-the-rule. However, only a small percentage of children arrived at the vision screening wearing glasses, and the prevalence of poor visual acuity (20/40 or worse in either eye) was high (35%). There was a significant relation between amount of astigmatism and uncorrected visual acuity with each additional diopter of astigmatism resulting in an additional 1 logMAR line reduction in visual acuity. CONCLUSIONS: Uncorrected astigmatism and poor visual acuity are prevalent among Tohono O'odham children. The results highlight the importance of improving glasses-wearing compliance, determining barriers to receiving eye care, and initiating public education programs regarding the importance of early identification and correction of astigmatism in Tohono O'odham children.

Adolescent↗

PubMed2004

The effect of optical defocus on the test-retest variability of visual acuity measurements.

PURPOSE: To determine the effect of optical defocus on the test-retest variability (TRV) of visual acuity measurements in normal subjects. METHODS: Normal subjects underwent repeated visual acuity measurement with optical defocus of 0, 0.50, and 1.00 D. All measurements were taken using the Early Treatment Diabetic Retinopathy Study (ETDRS) version of the Bailey-Lovie logMAR chart. TRV was quantified in terms of its 95% range, both empirically and using the approach of Bland and Altman. RESULTS: According to the Bland and Altman approach, the estimated 95% TRV ranges were +/-0.11 logarithm of the minimum angle of resolution (logMAR) for 0-D defocus, +/-0.18 logMAR for 0.50-D defocus, and +/-0.25 logMAR for 1.00-D defocus. CONCLUSIONS: Optical defocus has a considerable effect on the TRV of visual acuity measurements. These findings have important implications for both clinical practice and clinical research. Uncorrected refractive errors as small as 0.50 D may compromise the detection of visual change in individuals, and contribute to unnecessarily large sample sizes in clinical trials in which visual acuity is used as a primary outcome measure.

Adult↗

PubMed1999

Visual acuity after cycloplegia in children: implications for atropine penalization.

BACKGROUND: Atropinization of the sound eye is an alternative to patching in the treatment of amblyopia. Whether atropine treatment can induce a switch in fixation depends on the refractive error of the sound eye, visual acuity of the amblyopic eye, distance from the fixation target, and presence of any optical correction or penalization. General guidelines are needed on the basis of refractive error and visual acuity in the amblyopic eye to predict which patients may potentially benefit from atropine penalization. METHODS: Refractive error and visual acuity at distance (6 m) and/or at near (33 cm) were recorded in a normal eye of 126 consecutive children (mean age, 8.2 years), 30 to 60 minutes after receiving cyclopentolate 1%. Visual acuity was plotted versus refractive error at distance and at near, and best-fit curves were calculated. RESULTS: There was a consistent, reproducible relationship between refractive error and visual acuity after cycloplegia at both distance and near in healthy children. CONCLUSIONS: The results of this study can be used to quickly determine whether atropine penalization has the potential for success on the basis of a patient's visual acuity in the amblyopic eye and refractive error in the sound eye. When adequate hyperopia is present in the sound eye, one should consider testing for fixation preference or initiating a therapeutic trial of atropine. Those children with insufficient hyperopia in the sound eye relative to visual acuity in the amblyopic eye can be spared the time, expense, and potential side effects of atropine penalization.

Adolescent↗

PubMed1989

Visual acuity after the repair of pseudophakic retinal detachments involving the macula.

Postoperative visual acuities were retrospectively evaluated in a series of 100 pseudophakic eyes in which rhegmatogenous retinal detachments involved the macula and in which reattachment surgery was anatomically successful. Preoperative visual acuity and duration of macular detachment were related to visual outcome. Eyes in which extracapsular surgery had been followed by posterior chamber lens implantation had significantly better postoperative visual acuities than cases in which older iris-fixation intraocular lenses (IOLS) were placed after intracapsular procedures. Retinal detachments associated with posterior chamber IOLs have a relatively favorable anatomical and visual prognosis.

Adult↗

PubMedDate not supplied

Operative correction of ocular aberrations to improve visual acuity.

PURPOSE: Optical aberrations of the human eye degrade the quality of the retinal image and may, therefore, represent a major limit of visual acuity. METHODS: In 15 eyes, ocular aberrations were corrected in addition to myopia and astigmatism by means of wavefront-guided laser in situ keratomileusis (LASIK). RESULTS: At 1 month after surgery, a supernormal visual acuity of 20/10 and better was obtained in 4 eyes (27%). The increase in root mean square wavefront error ranged from 0.6 to 2.3 and was significantly correlated with the increase in visual acuity (R2 = 0.79; P = .03). CONCLUSION: Although the correction of aberrations was not yet optimal, these results show that ocular optical aberrations limit visual acuity in humans and supernormal visual acuity can be achieved by operative correction.

Adult↗