SEARCH · PubMed Health

Results for “Visual Acuity”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources

PubMed2002

An expanded nystagmus acuity function: intra- and intersubject prediction of best-corrected visual acuity.

The Nystagmus Acuity Function (NAF) provides an objective measurement of the foveation characteristics of nystagmus waveforms and an assessment of potential visual acuity for subjects with congenital (CN) or latent/manifest latent (LMLN) nystagmus. It is based on the subjects' ability to maintain fixation within a physiologically based 'foveation window' of +/- 0.5 degrees and +/- 4.0 degrees/s. However, some subjects are incapable of controlling fixation well enough to remain within this window with duration sufficient for good foveation. To obtain a measure of the CN waveforms of these individuals, we are proposing an eXpanded Nystagmus Acuity Function (NAFX) that relaxes either the position limit, the velocity limit, or both. Data used in this study comes from 11 human subjects with CN (10 idiopathic and 1 with achiasma) and a Belgian sheepdog with achiasma. Visual acuity was tested with a standard Snellen chart and eye movements recorded with infrared oculography or scleral search coil. For the NAFX to be useful, it must not only be applicable for subjects who cannot maintain fixation within the standard limits of the NAF, but also must yield results equivalent to those obtained with the NAF when testing subjects who are capable of maintaining good fixation control. For the latter subjects, the amount of time when position and velocity fell within the expanded limits was measured, the standard deviations of the position and velocity during these times were calculated, and a tau-surface for the exponential function was generated to guarantee the equivalence between the NAF and the NAFX. We developed an automated NAFX equivalent to the original NAF. We demonstrated that equivalence in 10 subjects and the use of the NAFX on two additional (1 human and 1 canine) subjects who were incapable of maintaining fixation within the standard position and velocity limits. We demonstrated the effects of surgery and related the results to visual acuity. We found the results to be comparable to those seen when applying the NAF to subjects who had good fixation control. The NAFX can be determined for CN and LMLN subjects with poor control of fixation by extending the standard NAF position and/or velocity limits for foveation. The resulting function can be used along with the longest foveation domain (derived from the NAFX to measure breadth of a high-NAFX region) to identify the gaze or convergence angles with the best waveform and to predict the best-possible visual acuity that could be achieved with the reduction of their nystagmus.

Algorithms↗

PubMed2005

A nationwide population-based survey on visual acuity, near vision, and self-reported visual function in the adult population in Finland.

PURPOSE: To estimate the prevalence rates of habitual visual acuity (VA) levels and visual impairment in Finland and to assess their correlation with self-reported visual function. DESIGN: Cross-sectional population-based study. PARTICIPANTS: Subjects were selected randomly from the Finnish population aged 30 years or older. Of 7979 eligible people, 7393 (93%) were interviewed, 6771 (85%) were examined, and 6663 (84%) had distance VA assessed. METHODS: Participants underwent a home interview and a comprehensive examination including measuring binocular VA for distance and for near with the participants' current spectacles, if any. MAIN OUTCOME MEASURES: The level of VA for distance and for near with current spectacle correction. The self-reported capability to read newsprint and television text and the ability to move about without being restricted by reduced vision. RESULTS: The prevalence of good to moderate VA for distance (VA> or =0.5 [> or =20/40]) measured with current spectacles was 95.9%, and 87.4% had a VA level of 0.8 (20/25) or better. The prevalence of habitual visual impairment (VA< or =0.25 [< or =20/80]) was 1.6%, and 0.5% were blind (VA<0.1 [<20/200]). The prevalence of visual impairment increased significantly with age (P<0.001), especially in the age group of 65 to 74 years and upward. There was no gender difference in VA for distance, but decreased near vision (VA< or =0.25 [< or =20/80]) was significantly more common in men than in women (P<0.01). By applying the imputated numbers of visually impaired and blind participants to the Finnish population (approximately 3 million aged 30 years or older), there were approximately 65000 (2.1%) visually impaired and 17000 (0.6%) blind adult persons in the country in 2000. The correlation between self-reported visual ability and measured visual function was moderate but statistically significant (r = 0.27-0.40; P<0.0001). The proportion of people with reading difficulties or who were unable to read newsprint has decreased 7% during the last 2 decades. CONCLUSIONS: Functional visual impairment increased with age especially in the age group of 65 to 74 years and upward and was as prevalent in women as in men. The prevalence of people with reading difficulties has decreased considerably since 1980.

Adult↗

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↗

PubMed1999

[Clinical application of a new method for the objective estimation of minimum visual acuity].

PURPOSE: Recently, a new method for the objective estimation of the minimum visual acuity (OEM) by means of suppression of the optokinetic nystagmus has been presented (Klin Monatsbl Augenheilkd 1998;212:196-202). This study reports on the clinical use of this method. METHODS: In 120 individuals referred to our clinic either to procure an ophthalmological expert opinion or for differential diagnosis of an unclear visual impairment, an OEM was performed. The result of the OEM was compared to the clinical findings (history, biomicroscopy of anterior and posterior segments, objective refractometry, pupillary responses, binocular alignment, motility, binocular vision, colour vision, applanation tonometry, electrophysiology, fluorescein angiography, neurologic, radiologic, psychiatric findings, reproducibility of visual acuity and visual field statements under different conditions, comparison of subjective and objective visual field data, statistical prove of false visual acuity and visual field statements) which were critically interpreted concerning the credibility of the subject's statements. RESULTS: As a result of the clinical examinations, the stated visual acuity of 62 individuals was credible. In one of these individuals, the OEM pointed to a slightly (1dB) better visual acuity. The statements of 7 individuals could not be categorized clinically. The OEM pointed to a better acuity in 3 cases. The stated vision of the remaining 51 individuals was not credible. In 38 of these cases, the OEM pointed to a better acuity, or false statements could be proven by the OEM. CONCLUSION: A significant rate (75%) of the individuals whose statements were not credible was detected by the computer-aided, nystagmographic method of OEM. The method allows an estimation of the actual minimum visual acuity and yields evidence of false statements concerning the detection acuity.

Biofeedback, Psychology↗

PubMed1999

The need for cataract surgery: projections based on lens opacity, visual acuity, and personal concern.

AIM: To assess the projected needs for cataract surgery by lens opacity, visual acuity, and patient concern. METHODS: Data were collected as part of the Melbourne Visual Impairment Project, a population based study of age related eye disease in a representative sample of Melbourne residents aged 40 and over. Participants were recruited by a household census and invited to attend a local screening centre. At the study sites, the following data were collected: presenting and best corrected visual acuity, visual fields, intraocular pressure, satisfaction with current vision, personal health history and habits, and a standardised eye examination and photography of the lens and fundus. Lens photographs were graded twice and adjudicated to document lens opacities. Cataract was defined as nuclear greater than or equal to standard 2, 4/16 or greater cortical opacity, or any posterior subcapsular opacities. RESULTS: 3271 (83% response) people living in their own homes were examined. The participants ranged in age from 40 to 98 years and 1511 (46.2%) were men. Previous cataract surgery had been performed in 107 (3.4%) of the participants. The overall prevalence of any type of cataract that had not been surgically corrected was 18%. If the presence of cataract as defined was considered the sole criterion for cataract surgery with no reference to visual acuity, there would be 309 cataract operations per 1000 people aged 40 and over (96 eyes of people who were not satisfied with their vision, 210 eyes of people who were satisfied with their vision, and three previous cataract operations). At a visual acuity criterion of less than 6/12 (the vision required to legally drive a car), 48 cataract operations per 1000 would occur and people would be twice as likely to report dissatisfaction with their vision. CONCLUSIONS: Estimates of the need for cataract surgery vary dramatically by level of lens opacity, visual acuity, and patient concern. These data should be useful for the planning of health services.

Adult↗

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↗

PubMed2002

Potential vision testing--the relationship between visual acuity and Vernier acuity in the presence of simulated cataract.

To evaluate the utility of a computer controlled two-bar Vernier acuity measurement as a predictor of visual function in the presence of cataract we measured logMAR visual acuity and Vernier acuity in a group of 40 young normal observers under various levels of dioptric blur (0-3 D in dioptre steps). The Vernier thresholds were resistant to dioptric blur up to 2 D, but performance degraded with blur of 3 D for non-optimised Vernier stimulus parameters. The stimulus parameters, bar length and bar separation, were further investigated in two subjects under conditions of blur. By extending the Vernier bar length and increasing the bar separation the effect of blur could be further reduced even under the most blurred condition. The relationship between visual acuity and Vernier acuity was determined. Vernier acuity was measured in the presence of Vistech cataract simulating lenses and a prediction of visual acuity was made for three observers, two with no ocular abnormality and one with age-related maculopathy. The cataract simulating lenses affected the measured visual acuity in all three subjects, but had less effect on Vernier acuity. Predicted visual acuities were all within six letters (0.12 log units) of the visual acuity without the simulated cataract. As expected, the subject sufferng from age-related maculopathy, whilst showing similar levels of Vernier acuity to the two ocularly healthy subjects at 1.5 degrees of retinal eccentricity, showed much poorer Vernier acuity for stimuli presented at fixation.

Adult↗

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↗