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Results for “Visual Acuity”

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At least 127 records · Page 7Linked to original sources

PubMed1985

Maturation of the visual evoked response and its correlation with visual acuity in preterm infants.

Visual evoked responses (VERs) were elicited in 70 infants with postmenstrual ages between 30 and 39 weeks. On the basis of neurological and ultrasound examinations, 30 of the infants were classed as neurologically normal and 40 as abnormal: 26 of the latter had periventricular haemorrhage. Initially the VER consisted of a negative deflection only, and the appearance of a positive wave immediately preceding the negative deflection was taken to indicate maturation of the VER. Maturation was significantly delayed in the neurologically abnormal infants, and the delay was related to the degree of neurological insult. The visual acuity of 32 infants was estimated within seven days of the VER recording. There was a correlation of 79 per cent between the VER and the data for visual acuity.

Birth Weight↗

PubMedDate not supplied

Visual acuity measurements by swept spatial frequency visual-evoked-cortical potentials (VECPs): clinical application in children with various visual disorders.

Previous studies have indicated that visual acuities of normal infants can be estimated with good accuracy using swept spatial frequency visual-evoked-potentials (VECPs). In this report we describe acuity measurements obtained with this technique from 304 examinations performed on 135 children having various visual disorders. When possible, two or more different stimulation frequencies (8, 12, 15 or 24 contrast reversals/sec) were used in each patient, and three to eight sweep VECPs were obtained from each patient under each simulation and recording condition. High correlation coefficients (0.94 - 0.96) between the acuity estimated on each patient from either the single sweep giving the best visual acuity (BSS) or from vector averages (VeA) of the EEG data obtained from several sweeps confirmed previous findings in normal infants. We also found high correlation coefficients among BSS recorded at different temporal frequencies (0.79-0.97) and among comparisons of BSS or VeA acuity to optotype visual acuity (0.6-0.89). Children with clinically undetectable optokinetic responses showed lower visual acuity estimated by BSS than those who demonstrated optokinetic nystagmus. We conclude that the sweep VECP is a valid method, giving estimates of acuity which correlate well with optotype acuity and correspond well to other clinical findings, and that it can be useful in the clinical management of nonverbal patients.

Child↗

PubMed1986

Subfoveal choroidal neovascular membranes in age-related macular degeneration. Visual prognosis in eyes with relatively good initial visual acuity.

We determined the visual prognosis of 94 eyes in 92 patients having age-related macular degeneration, a discrete choroidal neovascular membrane directly under the center of the foveal avascular zone (subfoveal), and an initial visual acuity of 20/100 or better. Of the patients who were reexamined 24 months following their initial presentation, 77% had lost at least four lines of vision and 64% had lost at least six lines. Estimation of visual loss using a conservative assessment procedure showed four-line visual loss in 65% of the patients and six-line loss in 50%. In general, the better the visual acuity at the initial examination, the more likely the patient was to have a smaller choroidal neovascular membrane. These results suggest that it may be reasonable to consider a randomized clinical trial of laser photocoagulation for this group of patients with a relatively poor visual prognosis.

Age Factors↗

PubMed1992

[Visual acuity perimetry. Detection of glaucomatous visual field defects].

50 eyes of 50 patients with different types of glaucoma (27 eyes with POAG, 14 eyes with glaucoma due to pseudoexfoliation, 8 eyes with chronic narrow-angle glaucoma, 1 eye with normal-tension glaucoma) were examined with light-sense perimetry (Humphrey-Field-Analyzer, program 30-2) and resolution perimetry according to Frisén [2-7]. As the field area tested by Frisén's ring perimeter is smaller than that of the HFA, the comparison was restricted to the area of the ring perimeter, so that 50 out of 77 test locations of the HFA were included. In addition to a quantitative comparison with statistical criteria based on age-corrected normal values, a subjective qualitative assessment was established. The quantitative comparison of all hemifields showed good agreement in 61% of eyes, the ring perimeter indicating moderately and markedly increased numbers of defects in 13% and 4% of eyes and the HFA in 18% and 4% of eyes, respectively. Qualitative comparison of the entire fields revealed good agreement in 46% of eyes, with moderately and markedly more defects in 18% and 10% for the ring perimeter and 12% and 14% for the HFA, respectively. The average time needed for examination was 6.0 +/- 1.1 min for the ring perimeter and 17.2 +/- 2.7 min for the HFA. The Global Deviation of the ring perimeter correlates linearly with the Mean Deviation of the HFA (r = 0.4824, P < 0.001).

Adult↗

PubMed1996

Visual acuity impairment in patients with retinitis pigmentosa.

PURPOSE: The authors evaluated visual acuity impairment in 906 patients from 742 families with either isolated or various identifiable genetic subtypes of retinitis pigmentosa (RP) to determine the severity of their visual acuity impairment. Emphasis was placed on the prevalence of total blindness and visual acuity of 20/200 or worse in this group of patients. METHODS: This cross-sectional retrospective study included all patients with RP who met certain entrance criteria and were examined by one of the authors (GAF). The authors analyzed the eye of each patient with the best-corrected visual acuity on their most recent visit. RESULTS: Seventeen patients with a sector form of RP were excluded from the authors primary analysis. In the remaining group of 889 patients, 710 (80%) had a visual acuity of better than 20/200, 648 (73%) showed a visual acuity of 20/70 or better, and 489 (55%) had a visual acuity of 20/40 or better in at least 1 eye. Seventy-five patients (8%) had visual acuity of count fingers or worse in their best eye. There was only one patient with no light perception in each eye. Patients with autosomal dominant RP, as a group, had the least severe and those with X-linked recessive RP had the most severe impairment in visual acuity. Those with autosomal recessive disease were intermediate in severity of visual impairment. CONCLUSIONS: Analysis of visual acuity in this large group of patients with RP, which genetically is representative of patients with RP seen in the United States by those who specialize in retinal disease, showed that it was rare for the patients to lose all visual acuity from the disease itself. Further, legal blindness from visual acuity loss, defined as best-corrected visual acuity that is no better than 20/200 in at least one eye, occurred in a relatively small percentage (20%) of our patient population, whereas approximately half of all patients and 42% of those older than 60 years had a visual acuity of 20/40 or better in at least one eye. The extent of impairment in visual acuity was associated with the genetic subtype of the disease.

Adolescent↗

PubMed1981

Ophthalmic changes from age of 10 to 18 years. A longitudinal study of sequels to low birth weight. II. Visual acuity.

Re-examination of corrected visual acuity was done in 137 18-year-old Danes, who were originally examined at the age of 10 years, as part of a study of sequels to low birth weight (LBW) (Fledelius 1976). Median values indicate that most adolescents are able visually to discriminate considerably above the customary 6/6 limit. As compared with low-birth-weighters (n=70), full-terms (n=67) show a significantly higher cumulated visual acuity score. Similarly, binocular median visual acuities are 1.2 (LBW) and 1.4 (in FT). The difference is neither explained by the ex-prematures' higher frequency of heterotropia, nor by their (minor) share of eyes with subnormal vision. The latter occurred especially in the subgroup of 'myopia of prematurity'. The exceptional cases with RLF-blindness were discarded from follow-up. Concerning visual acuity, the previously reported lagging behind of ex-prematures in childhood has proven to be not only a temporary delay, but a permanent (adult) feature.

Adolescent↗

PubMed1996

A new Arabic distance visual acuity chart.

BACKGROUND: A new Arabic visual acuity chart has been designed using the various recommendations made by vision scientists for achieving a standardized acuity chart. Our goal was to design a standardized Arabic distance visual acuity chart. METHOD: The chart is based on the design principle devised by Bailey and Lovie. Twelve Arabic letters of nearly equal legibility values, which could be constructed on a 5 by 5 Snellen framework, were used. The LogMAR method of scaling visual acuity was used, hence the size of letters in the rows progresses in a uniform step of 0.1 logarithm unit. RESULT: The size of letters in the chart ranged from 58.2 to 4.6 mm, corresponding to visual acuity of 4/40 to 4/3 (6/60 to 6/4) (20/200 to 20/15). The chart is designed for use at 4 m; acuity values for a 6-m testing distance are, however, provided on the chart. CONCLUSION: The chart will be useful for examining Arabic speaking patients.

Arabs↗

PubMed1988

The use of accurate visual acuity measurements in clinical anti-cataract formulation trials.

A standardized visual acuity technique is presented for use in anti-cataract drug trials. Ferris Logmar charts were used in repeatability studies of vision, visual acuity and pinhole visual acuity measurements for twenty normal subjects (mean (+/- SD) age 64 +/- 6.3 years). Visual acuity measurements were shown to be the most repeatable and thought to be the most suitable for monitoring cataract progression. Repeated visual acuity measurements were made on 29 cataractous eyes of 15 subjects (mean (+/- SD) age 67.8 +/- 7.2 years). A Logmar score change of 0.1 (one line) was shown to be a statistically significant change. This value can be used in statistical analyses of drug efficacy. The normal data gives a mean Logmar visual acuity of 1.15 (Snellen equivalent 6/5). This indicates the inadequacy of using 6/6 as a norm value for visual acuity, even for older patients. As the possibility of reversal of cataract theoretically exists in the early stages of cortical and capsular cataracts, patients with small amounts of these types of cataract are ideal patients for anti-cataract formulation trials. The normal visual acuity results indicate that the inclusion criteria for clinical trials can include patients with cataracts with visual acuity as good as 6/6.

Aged↗

PubMed1980

Visual acuity screening of preterm infants.

Visual acuity was screened in 36 healthy infants born 4 or more weeks prior to term. Preterm infants tested at 8 and 12 weeks of postnatal age showed significantly poorer performances than those shown by 8- and 12-week-old full-term infants. However, no differences in performance were found when the scores of preterm infants tested at 4, 8, and 12 weeks of postterm age (i.e., 4, 8, and 12 weeks from due date) were compared with scores of 4-, 8-, and 12-week-old full-term infants. The results suggest that visual acuity is more closely correlated with age from conception than with age from birth and that visual acuity screening in preterm infants should be carried out with acuity gratings appropriate for the infant's postterm age rather than with acuity gratings appropriate for the infant's postnatal age.

Age Factors↗

PubMed1992

Contrast visual acuities in cataract patients. II. After IOL implantation.

Contrast visual acuities were measured in 100 eyes of 75 patients who attained a best-corrected visual acuity of greater than or equal to 0.8 (20/25) after intraocular lens (IOL) implantation. The variable contrast visual acuity chart (VCVAC), with three contrast levels of 90, 15, and 2.5% and reverse polarity of 90% contrast, was used to measure contrast visual acuities. The follow-up period ranged from 3 to 35 months (mean 7.41). The mean visual acuities measured with the 90, 15, and 2.5% charts were 0.92 (SD = 0.11), 0.59 (SD = 0.13), and 0.33 (SD = 0.14), respectively. The mean visual acuity measured with the 90% reverse polarity chart was 0.97 (SD = 0.11). The decreases in visual acuities compared with the 90% contrast were 0.64 and 1.48 octaves in the 15% and the 2.5% contrast charts, respectively. The pattern of the contrast acuity profile was comparable to normal subjects, but in 28 of 100 (28%) eyes, the visual acuities measured with the reverse polarity chart were slightly better than those measured with the standard 90% contrast chart, suggesting that the glare effect still exists after IOL implantation, though to a lesser degree than in cataractous eyes.

Adult↗

PubMed1991

The significance of testing preoperative visual function in cataract using laser interferometric visual acuity and ERG.

Tests of preoperative visual function and prediction of postoperative E chart visual acuity (ECVA) using laser interferometric visual acuity (LIVA) and electroretinogram (ERG) were performed in 16 cases (19 eyes) of cataract. The results showed that the coincident rate between preoperative LIVA and postoperative ECVA was 63.2%, and there was a parallel correlation between preoperative amplitude of photopic ERG b-wave and postoperative ECVA in 79.0% of the eyes. Comparing these two methods, the test of LIVA is very simple, fast, and is easily accepted by the patients with cataract. ERG is an objective method, which is slightly influenced by dense lens, but the test is more complex. Therefore, the combined use of these two methods will provide a more comprehensive and correct evaluation of preoperative visual function and a more reliable prediction for postoperative visual acuity in patients with cataract.

Adolescent↗

PubMed1996

Changes in myopia, visual acuity, and psychological distress after biofeedback visual training.

The effects of auditory biofeedback training on myopia, visual acuity (VA), and psychological distress were evaluated in a controlled prospective study involving 55 mildly myopic (< or = -3.5 D) high school students. These myopes were divided into 2 groups, matched for age and dioptric defect: 33 were treated with visual training and 22 were not; 27 emmetropic subjects formed a further control group. Subjects were evaluated at the baseline (T0), at 10 weeks after the end of the treatment (T1), and after an interval of 12 months (T2) from the baseline for: (1) manifest and cycloplegic refraction, and the difference between them (cycloplegic tonus); (2) VA measured with a conventional optotype in all subjects, and also with a computer-generated optotype in the treated group; and (3) psychometric values and personality profile. At T2, myopia had significantly worsened both in the treated and in the control myopes; VA in the treated myopes appeared significantly improved when measured by the conventional optotype, but unchanged when measured by computer. Psychometric scores improved significantly in the treated myopes and in the emmetropic controls. Objectively the autorefractometer showed that 38% of the myopes had voluntary control of positive accommodation, i.e., the ability to increase spherical defect; no voluntary control of negative accommodation was observed. An increase in VA was associated with a significant increase in the foveation time (i.e., the period of time when the target is imaged on the fovea and the eye is motionless), and was partly attributable to a learning effect. In conclusion, biofeedback visual training had a positive effect on psychological distress and subjective VA improvement, but failed to reduce the existing myopia or delay its evolution.

Adolescent↗

PubMed1996

Objective measurement of contrast sensitivity and visual acuity with the steady-state visual evoked potential.

Since the appearance of Campbell and Maffei's and Harter and White's reports it has been well established that the visual evoked potential (VEP) can be used to predict psychophysical contrast sensitivity and visual acuity and is thus suited as an objective technique to assess these fundamental aspects of vision. Nevertheless, the technique has not become a standard diagnostic tool, being too time-consuming to apply and suffering from variable reliability under pathological visual conditions. In addition, there are problems of reliability in normal subjects. By using an unconventional stimulus--temporally sinusoidal 16-Hz on-off modulation of sinewave gratings--we demonstrated that these problems can be alleviated in normal subjects. This stimulus avoids the low signals in the visible range that frequently occur with conventional pattern-reversal stimuli, it leads to high correspondence between normal observers, and it is much faster to apply than are transient VEPs. Initial applications of this stimulus to amblyopes yielded promising results. The steady-state VEP could consequently turn into a viable diagnostic procedure in disturbances of visual contrast perception.

Contrast Sensitivity↗

PubMed1979

Assessment of the visual acuity of human color mechanisms with the visually evoked cortical potential.

The amplitude of the human visually evoked cortical potential (VECP), which has been shown to vary as a function of the dimensions of checks in a checkerboard pattern, was used to objectively assess the visual acuity of the blue-sensitive compared with the red- and green-sensitive mechanisms in the eye. The results agree with psychophysical measures which have indicated poorer acuity of the blue system compared with the red and green systems.

Adult↗

PubMed1992

Simulation of a phosphene-based visual field: visual acuity in a pixelized vision system.

A visual prosthesis for the blind using electrical stimulation of the visual cortex will require the development of an array of electrodes. Passage of current through these electrodes is expected to create a visual image made up of a matrix of discrete phosphenes. The quality of the visual sense thus provided will be a function of many parameters, particularly the number of electrodes and their spacing. We are conducting a series of psychophysical experiments with a portable "phosphene" simulator to obtain estimates of suitable values for electrode number and spacing. The simulator consists of a small video camera and monitor worn by a normally sighted human subject. To simulate a discrete phosphene field, the monitor is masked by an opaque perforated film. The visual angle subtended by images from the masked monitor is 1.7 degrees or less, depending on the mask, and falls within the fovea of the subject. In the study presented here, we measured visual acuity as a function of the number of pixels and their spacing in the mask. Visual acuity was inversely proportional to pixel density, and trained subjects could achieve about 20/26 visual acuity with a 1024 pixel image. We conclude that 625 electrodes implanted in a 1 cm by 1 cm area near the foveal representation of the visual cortex should produce a phosphene image with a visual acuity of approximately 20/30. Such an acuity could provide useful restoration of functional vision for the profoundly blind.

Blindness↗

PubMed1980

Automated clinical visual acuity testing.

We developed a method for testing visual acuity using a general-purpose microcomputer which displays visual acuity targets on a television monitor, controls a staircase psychophysical testing procedure, and provides a printed record of mean visual acuity and standard deviation. This automated procedure can be used to increase the precision of clinical visual acuity testing and to determine if changes in a patient's visual acuity are statistically significant.

Adolescent↗

PubMed1989

[Objective and subjective determination of visual acuity].

The results of the present study show that the normal human visual acuity is not 1 (30 c/dg) but a remarkably higher value, about 1.73 (55 c/dg). Many authors, who studied the problem of objective determination of the visual acuity using visual evoked cortical potentials, corrected their results under the assumption that the objective method overestimates the real visual acuity. Now it is clear that the conventional determination of the visual acuity leads to serious underestimation of the real visual acuity. So, the way toward a more precise objective estimation of the human threshold visual acuity is now open.

Adolescent↗

PubMed1970

Conditioned vocalizations as a technique for determining visual acuity thresholds in sea lions.

Aerial visual acuity and underwater visual acuity were measured in two sea lions (Zalophus californianus) by training them to emit click bursts if they saw a striped target or to remain silent if they saw a gray target. The closest grating spacings that could be resolved both in air and under water subtended a visual angle of 5.5 minutes of arc at a distance of 5.5 meters.

Animals↗