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Results for “Visual Acuity”

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At least 145 records · Page 8Linked to original sources

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

New standardized visual acuity charts in Hindi and Gujarati.

Conventional Snellen visual acuity chart has unequal difficulty score and irregular progression in letter size causing jumping effect at different visual acuity levels. There is also increase in number of letters from above downwards. Consequently one or two mistakes per line has different meaning of visual acuity at different levels. We designed a new visual acuity chart of fourteen lines in Hindi and Gujarati to facilitate standardization in visual acuity measurement. These charts are designed for use at six meter distance, and the illumination is provided from front. These charts provide a standardized way of measuring visual acuity using local languages.

Humans↗

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↗

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↗

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↗