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PubMed1981

Development alterations in binocular competitive interactions and visual acuity in visually deprived cats.

The purpose of the present study was to determine the effects of developmental alterations in binocular competitive interactions between the eyes on visual acuity. Comparisons were made between animals which were monocularly deprived (MD) of patterned visual input, binocularly lid-sutured cats (BD), and animals which had the lids of one eye sutured closed and the other eye removed prior to natural eye opening (MDE). Thus, each group differed in the degree of competitive imbalance between the eyes during postnatal development. Threshold visual acuity for high contrast, squarewave gratings was measured in a jumping stand. Mean visual acuities for each group using a single deprived eye were: group MD, 0.65 cycles/deg; group BD, 3.2 cycles/deg; group MED, 3.72 cycles/deg. These results indicated that the greater the competitive disadvantage an eye is placed at during development, the greater the acuity (sensory) deficits. Further, comparisons made between MD and MDE animals indicated that the acuity deficits using effects of deprivation per se.

Animals↗
PubMed1997

Radiologists and visual acuity.

Visual acuity (VA) and potential risks to the radiologist's eyesight have been relatively neglected subjects in the radiological literature. This study comprises two parts, the first consisting of a questionnaire on this subject sent to a random sample of 480 practising radiologists in the United Kingdom, and the second, a spot check of the VA of radiologists in our department. Of questionnaires, 73 %were returned. Of respondents, 76 % felt that ionising radiation could affect their vision, but only 13 % used lead glasses on a regular basis. A total of 71 % felt that regular monitoring of eyesight should be required. Of 25 tested radiologists, 5 had suboptimal VA and could benefit from further correction. The pertinent literature is reviewed, and a case for periodic eyesight testing is presented, including VA and grey-scale discrimination.

Adult↗
PubMed1999

Longitudinal changes in visual acuity and visual ability in a cohort followed from the age of 70 to 88 years.

PURPOSE: To assess the change in visual acuity (VA) for distance and near and to correlate VA to changes in visual ability in a longitudinal study group followed from 70 to 88 years. METHODS: In the population-based study H70 in Gothenburg, Sweden, 958 subjects from the original cohort were eye examined at age 70 and the surviving subjects were reexamined at age 82 (n=203) and at 88 years (n=129). Evaluation of change in visual function between age 82 and 88 was made in 66 subjects who took part in all three eye examinations. RESULTS: The VA in the subsample (n=66) showed minimal difference compared to the cross-sectional groups. At age 70 nearly 100% of both sexes had VA> or =0.8. At age 82 about 50% and at age 88 about 25% had this VA level. Males retained a slightly better visual acuity compared to women. VA< or =0.3 was found in about 10% at age 82 and in >20% at age 88. Reading ability remained high, but at 82 years 1.6% and at 88 years 10.5% could benefit from adjustment of their near glasses. Visual ability corresponded well to VA at age 82, but not at 88 years. Women lost the ability for most tasks, whereas men showed small changes. CONCLUSIONS: The majority of old people had good distance and near vision. A deterioration in visual acuity did not necessarily mean a negative change in visual ability. This emphasizes the importance of relating objective and subjective findings regarding VA and visual impairment to functional ability of the oldest of the elderly.

Activities of Daily Living↗
PubMed1977

Optic nerve hypoplasia with good visual acuity and visual field defects: a study of children of diabetic mothers.

Seventeen children, born of severely diabetic mothers, exhibited segmental optic nerve hypoplasia with normal visual acuity and altitudinal or sector field defects corresponding to the hypoplastic areas of the disc. This is the first group of patients with optic nerve hypoplasia in which a possible cause has been identified. Optic nerve hypoplasia is neither a rare abnormality usually associated with serious central nervous system defects, nor is it always accompanied by decreased visual acuity.

Abducens Nerve↗
PubMed2005

[Objective measurements of visual acuity by visual evoked potentials].

Electrophysiological measurements of the threshold spatial frequency were conducted in 26 healthy subjects by using visual evoked potentials with the purpose of objective determination of the visual acuity. For that we proposed a universal method of the visual stimulation and EEG processing (using ICA decomposition in particular) to minimize errors arising on account of individual differences in the visual system functioning. As a result, a correlation of 0.74 and a logarithmic dependence were obtained between spatial resolution measured by electrophysiological and psychophysical methods. The proposed methods of objective measurement of visual resolution has a high effectiveness, does not depend on specificity of individual EEG and domination of different channels in the visual system. Therefore it is possible to determinate objectively the visual acuity in humans independently of their responses.

Adolescent↗
PubMed2000

[Pattern visual evoked potentials visual acuity--the evaluation of visual acuity of less than 0.1].

PURPOSE: We previously developed a new method for estimating objective visual acuity by means of pattern visual evoked potentials (PVEP). In this study, this method was applied to the evaluation of visual acuity of 0.05 and 0.01. METHODS: Ten subjects with visual acuity of 0.05 and ten normal subjects with visual acuity of 0.01 were examined. The visual acuity of the subjects was decreased step by step by means of plus spherical lenses of increasing power. In the PVEP study, the stimulus consisted of black and white checkerboards with a visual angle of 8 degrees (central stimulus) and a global field with a 5 degrees central circular scotoma (peripheral stimulus), contrast level of 15%, and a frequency of 0.7 Hz. One hundred PVEP responses were averaged per session. We reported that there was a linear relation between log subjective visual acuity of 0.1-1.0 and log check size of the patterns with PVEP. In reference to that, the check sizes of the patterns were estimated at 66' with visual acuity of 0.05, and 107' with visual acuity of 0.01. Each visual acuity was then used with other check sizes of three patterns. RESULTS: With central stimulus the P100 components of O1, O2, and Oz were recorded with 66' and 82' patterns at visual acuity of 0.05(central stimulus). The P100 components of O1, O2, and Oz were 107', 137' and 161' at visual acuity of 0.01(central stimulus). There was no P100 component at visual acuity of 0.05 and 0.01(peripheral stimulus). CONCLUSION: This method of PVEP is a useful tool as an objective estimation of visual acuity less than 0.1 and is presumed to stimulate preferentially the X retinal ganglion cell to parvocellular pathway.

Adult↗
PubMed1999

Information from false statements concerning visual acuity and visual field in cases of psychogenic visual impairment.

BACKGROUND: If visual acuity (VA) and/or visual field (VF) is claimed to be worse than in reality, it can be difficult to estimate the actual VA/VF. This paper describes a method of proving malingering and of estimating the actual VA by statistical evaluation of the subjective responses to discrete visual stimuli. METHODS: VA is measured by using a Landolt or Snellen optotype with four possible directions. There are n (> or = 16) questions at each acuity level. Each direction of the optotype occurs with the same frequency. The sequence is not predictable. In testing the VF, the stimulus is presented in an unpredictable sequence but with the same frequency at each of four distinct locations outside the claimed field at the horizontal and the vertical meridian. The field is divided into four quadrants defined by the 45 degrees-225 degrees and 135 degrees-315 degrees meridians. The candidate is requested to search for the light. The target quadrant of the first eye movement is recorded. At each VA level, the distribution function of the binomial formula allows estimation of the probability Pc of < or = kc and > or = kc correct answers to n questions by mere accident. Regarding the VF, the direction of the first saccade at each stimulus presentation can be processed accordingly. RESULTS: If n = 32 and kc = 0,1,2, the chance P that this pattern is merely accidental is about 0.0001, 0.001, 0.007. Values of P < or = 0.01 strongly suggest that the answers were voluntarily wrong. Preference for the opposite direction can also point to psychogenic influence: If ko = 15,16,17,18, P is about 0.006, 0.002, 0.0006, 0.0002. CONCLUSION: Systematically false statements can yield valuable information about the actual visual functions.

Adult↗
PubMed1995

Correlating preferential looking visual acuity and visual behavior in severely visually handicapped children.

We developed a series of questions that reflects the functional abilities of severely visually handicapped children. The study population comprised 100 patients aged 30 to 60 months (mean 43.23), mostly afflicted with retinopathy of prematurity. Visual acuity was measured by preferential looking. Preferential looking acuities of the patients ranged from 20/25 (0.8) to 20/6400 (0.003) (mean 20/470 (0.04)). Ten activities were analyzed and correlated with preferential looking acuity. Among the selected visual activities, when children are not interested in television (p = 0.0001), toys (other than those that make sounds (p = 0.0001), and people (p = 0.001)), their preferential looking acuities were very low. For example, 73 out of 100 patients who were visually interested in television had preferential looking acuities (mean 20/245 (0.082)) that were significantly higher (p = 0.001) than 21 patients not interested in television (mean 20/2806 (0.007)). Patients with nystagmus (n = 79) had significantly lower preferential looking acuities (p = 0.0001) (mean 20/1114 (0.018)) than patients with no nystagmus (mean 20/57 (0.35)). When evaluating visual function in young, severely visually impaired patients, in addition to preferential looking testing, analyzing visual behavior within the environment is important to accurately evaluate their remaining visual abilities.

Child, Preschool↗
PubMed2000

Visual system in a diurnal marsupial, the numbat (Myrmecobius fasciatus): retinal organization, visual acuity and visual fields.

The visual system of the numbat (Myrmecobius fasciatus), a highly endangered diurnal marsupial, has been investigated both anatomically and behaviorally. The ganglion cell layer, examined in cresyl-violet stained wholemounts, contained 832,800 ganglion cells; the number of ganglion cells corresponded to optic axon counts. An area centralis was located in the mid-temporal retina, where cells formed a bilayer, but there was no evidence of a visual streak. Visual acuity, estimated from counts of peak ganglion cell density (8,100/mm(2)) and measurements of posterior nodal distance (7.84 mm), was found to be 6.3 cycles per degree. The value was similar to that of 5.2 cycles per degree estimated by behavioral tests. Sectioned material revealed the presence of numerous oil-droplets in a cone-dominated retina. A rich retinal vasculature of the end-artery type of paired arteries and veins formed beds in the ganglion cell and inner nuclear layers. Measurements of visual fields revealed a binocular overlap of 80 degrees in the horizontal plane, and a total field of view approaching 240 degrees of visual angle. Monitoring of pupillary responses with an infrared video camera showed that the numbat possesses a remarkably wide, static pupil. Our results are discussed in relation to the ecology of the species and its phylogeny.

Animals↗
PubMed2002

A longitudinal study of visual acuity and visual rehabilitation needs in an urban Swedish population followed from the ages of 70 to 97 years of age.

PURPOSE: To investigate the longitudinal change in visual acuity (VA) in the oldest members of the elderly population, to estimate future numbers of people with visual impairments, and to estimate needs for and the effects of visual rehabilitation. METHODS: In the Gerontological and Geriatric Population Studies in Gothenburg, Sweden (H 70), subjects underwent repeated eye examinations at the ages of 70, 82, 88, 95 and 97 years. Logistic regression analysis was used to estimate the probability of independent living as a function of distance VA at different ages. RESULTS: Rates of normal VA (>or= 0.8) declined from 86% of the study group at age 70 to 7% of the study group at age 95 (0% at age 97). The incidence of VA <or= 0.1 increased from 1.4% at age 70 to 27% (all women) at age 97. The deterioration was faster at higher ages. No statistically significant difference in best-corrected distance VA between genders was found. A substantial improvement was achieved by correcting refractive errors. There was a statistically significant correlation between distance VA and the probability of independent living at all ages except age 97. At ages 95 and 97, about 50% of the study group were able to read newspaper print with best-corrected glasses. CONCLUSIONS: The number of old people with impaired vision will increase. People aged 80 years and older should have regular eye-screening in order to preserve vision and present conditions of living. Cataract surgery and low vision rehabilitation should be offered when the subject can still benefit from it, preferably during their 80s at the latest.

Activities of Daily Living↗
PubMed2001

Comparison of contrast sensitivity, visual acuity, and Humphrey visual field testing in patients with glaucoma.

PURPOSE: To investigate the relationship between large-letter contrast sensitivity, high-contrast visual acuity, and visual field defects in patients with glaucoma. METHODS: Patients with a diagnosis of glaucoma, glaucoma suspect, or ocular hypertension whose visual acuity was 20/40 (logMAR = 0.3) on better were included in the study. Visual acuity was measured using the Lighthouse visual acuity charts. Contrast sensitivity was measured using the Pell-Robson (PR) chart. The mean depression (MD) score from the most recent Humphrey visual field was used to quantify the visual field defect. RESULTS: A total of 120 eyes were studied. The PR contrast sensitivity score correlated more strongly with the MD of the visual field (r = .589, P < .001) than did the logMAR visual acuity (r = .193, P = .035). When just the eyes with open-angle glaucoma were considered (N = 54), the correlation was even greater for the PR score (r = .638). In ocular hypertensive eyes (N = 25), the correlations to PR and logMAR were not that different (r = .394 for PR, r = .303 for logMAR). Pseudophakic eyes did not show as strong a correlation (r = .335) as did phakic eyes (r = .591). CONCLUSION: For glaucomatous eyes with visual acuity of 20/40 or better, a decrease in the contrast sensitivity correlates with increased visual field loss. We speculate that this decrease in contrast sensitivity in glaucoma patients may account for their complaints of poor vision despite normal or near normal visual acuity.

Contrast Sensitivity↗
PubMed2006

Influence of differences of visual acuity in various visual field conditions on spectral characteristics of the center of pressure sway.

This study examined the influence of visual acuity and visual field on the spectral characteristics of the center of pressure during standing. 17 men and 20 women participated in High and Low visual acuity groups. Both groups underwent center of pressure measurements under three visual field conditions: No vision: subjects were given no visual information, Central vision: they were given only central visual field information, and Full vision: they were given full visual information. To assess the spectral characteristics of center of pressure, mean power frequency and frequency of maximal power were calculated from medial-lateral and anterior-posterior center of pressure directions. The Friedman test and Scheffé pairwise comparison tests showed that frequency of maximal power was higher in the No vision than in the Central and Full vision conditions in the High visual acuity group. In conclusion, people with high visual acuity are more susceptible to visual field conditions than those with low visual acuity. It is suggested that postural control characteristics differ with visual acuity or resolution in the central visual field.

Adult↗
PubMed2003

[Calculating the mean visual acuity and the change in visual acuity with a decimal acuity chart].

The decimal visual acuity chart is not easy to use for statistical analysis and requires a transformation into LogMAR units (decimal logarithm of the Minimum Angle Resolution). In contrast to the decimal chart, the logarithmic chart has an arithmetic progression and a constant interval between lines. The LogMAR chart makes statistical analysis of visual acuity easy. Change in visual acuity is calculated directly by subtracting LogMAR data, while the average visual acuity is obtained with the arithmetic mean value of the LogMAR data. The mean acuity expressed in LogMAR units can be transformed into a decimal chart for a more comprehensive result. To calculate the average visual acuity directly from the decimal data, the geometric mean value must be used instead of the arithmetic mean value.

Calibration↗