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Results for “Visual Acuity”

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At least 415 records · Page 23Linked to original sources

PubMed2001

Recovery of uncorrected visual acuity after laser in situ keratomileusis or photorefractive keratectomy for low myopia.

PURPOSE: To compare uncorrected visual acuity and refractive error in patients undergoing photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) between 1 week and 6 months after surgery. METHODS: All eyes underwent PRK or LASIK with the VisX StarS2 excimer laser. We retrospectively analyzed data from 77 random eyes of 77 patients in the PRK group and 76 eyes of 76 patients in the LASIK group. All eyes had a low myopic refractive error (spherical equivalent range, -0.88 diopters (D) to -5.13 D; mean PRK. -2.8 +/- 0.20 D: LASIK, -2.5 +/- 0.22 D). Uncorrected visual acuity and manifest refractive error were evaluated 1 week, 1 month, and 6 months after surgery. RESULTS: Each eye undergoing PRK was paired with an eye undergoing LASIK for a similar level of spherical equivalent. Mean uncorrected visual acuity after 1 week was 0.85 +/- 0.06 (20/25, logMAR 0.12 +/- 0.04) for the PRK group and 1.01 +/- 0.06 (20/20, logMAR 0.01 +/- 0.03) for the LASIK group (p < 0.001). Mean spherical equivalent after 1 week was 0.23 +/- 0.12 D for the PRK group and -0.02 +/- 0.07 D for the LASIK group (p = 0.02). Mean uncorrected visual acuity after 1 month was 1.03 +/- 0.05 (20/20, logMAR 0.02 +/- 0.03) for the PRK group and 1.05 +/- 0.05 (20/20. -0.02 +/- 0.03) for the LASIK group (p = 0.16). Mean spherical equivalent after I month was 0.19 +/- 0.10 D for the PRK group and -0.02 +/- 0.09 D for the LASIK group. This difference was statistically significant (p = 0.02), but was unlikely to be clinically significant. Mean uncorrected visual acuity after 6 months was 1.05 +/- 0.06 (20/20, logMAR -0.01 +/- 0.03) for the PRK group and 1.06 +/- 0.05 (20/20, logMAR -0.14 +/- 0.03) for the LASIK group (p = 0.41). Mean spherical equivalent after 6 months was 0.02 +/- 0.08 D for the PRK group and 0.00 +/- 0.08 D for the LASIK group (p = 0.35). CONCLUSION: Uncorrected visual acuity 1 week after surgery is significantly better in eyes undergoing LASIK than in eyes undergoing PRK. Both procedures provide functional vision by 1 week after surgery. The difference does not relate to refractive error, which was similar between the two groups, but to differences in healing of the epithelium. By 1 month after surgery, there is no difference in mean uncorrected visual acuity between eyes that undergo PRK or LASIK for low myopia.

Cornea↗

PubMed1995

[Measurement of temporal summation of visual acuity with the use of a trial tachistoscope].

Visual acuity was measured in eighteen normal eyes of 10 subjects ranging from 20 to 30 years of age, using a modified tachistoscope. We changed the exposure time of the target (1-1,000 msec) or background luminance (0.1-200 cd/m2). The visual acuity rose with increasing exposure time. At background luminance over 10 cd/m2, the critical duration time was about 500 msec. However, at low luminance below 10 cd/m2, the critical duration was prolonged. This tendency was also seen when the pupil diameter was fixed at 3 mm with an artificial pupil. Similar by luminance detection, visual acuity was also determined by the product of background luminance and exposure time. From theses findings, we concluded that Bloch-Bunsen-Roscoe law was statisfied.

Adult↗

PubMed1990

Predicting visual acuity from detection thresholds.

Visual performance based exclusively on high luminance and high contrast letter acuity measures often fails to predict individual performance at low contrast and low luminance. Here we measured visual acuity over a wide range of contrasts and luminances (low mesopic to photopic) for 17 young normal observers. Acuity vs. contrast functions appear to fit a single template which can be displaced laterally along the log contrast axis. The magnitude of this lateral displacement for different luminances was well predicted by the contrast threshold difference for a 4 min arc spot. The acuity vs. contrast template, taken from the mean of all 17 subjects, was used in conjunction with individual spot contrast threshold measures to predict an individual's visual acuity over a wide range of luminance and contrast levels. The accuracy of the visual acuity predictions from this simple procedure closely approximates test-retest accuracy for both positive (projected Landolt rings) and negative contrast (Bailey-Lovie charts).

Adult↗

PubMed2005

Standard measures of visual acuity do not predict drivers' recognition performance under day or night conditions.

PURPOSE: This study investigated whether visual acuity or contrast sensitivity, measured under a range of luminance conditions, could predict drivers' recognition performance under real-world day and night road conditions. METHODS: Twenty-four participants, comprising three age groups (younger, mean = 21.5 years; middle-aged, mean = 46.6 years; and older, mean = 71.9 years), drove around a 1.8-km closed road circuit under day and nighttime conditions. At night, headlight intensity was varied over 1.5 log-units by ND filters mounted on the headlights. Participants drove around the circuit under five light conditions (daytime and four at night) and were asked to report relevant targets, including road signs, large low-contrast road obstacles, and pedestrians who wore retroreflective markings on either the torso or the limb joints (creating "biological motion"). Real-world recognition performance was measured as percent correct recognition and, in the case of low-contrast road obstacles, avoided. Clinical vision tests included high-contrast visual acuity and Pelli-Robson letter contrast sensitivity measured at four luminance levels. RESULTS: Real-world recognition performance of all age groups was significantly degraded under low light conditions, and this impairment was greater for the older participants. These changes in drivers' recognition performance were more strongly predicted by contrast sensitivity than visual acuity measured under standard photopic conditions. Interestingly, contrast sensitivity was highly correlated with visual acuity measured under low-luminance conditions. Further analyses showed that recognition performance while driving is better predicted by combinations of two tests: either 1) photopic visual acuity and photopic contrast sensitivity, or 2) photopic and mesopic visual acuity. CONCLUSIONS: These findings confirm that visibility is seriously degraded during night driving and that the problem is greater for older drivers. These changes in real-world recognition performance were better predicted by a standard test of contrast sensitivity than by visual acuity. Still better predictions can be obtained by the use of two vision tests. The implications of these findings for driver licensing standards are discussed.

Adult↗

PubMedDate not supplied

A modified letter matching chart for testing young children's visual acuity.

A new chart for testing children's visual acuity was designed. It was based on the matching principle and showed rows of the four letters H, O, T, and V at a distance of 3 m. A geometric progression of leter size was used. In order to disclose the crowding phenomenon, the distance between letters was equal to the letter width in each line. Fifty children's testability and visual acuity was studied with this chart and an E chart. It was found that the children performed better when the letter matching chart was used and that the letter matching visual acuity values were higher in about 2/3 of the eyes. The more interesting matching game and the closer viewing distance are possible causes of these differences.

Age Factors↗

PubMed1990

[Ocutrast--a new procedure for measuring mesopic visual acuity and glare sensitivity].

Measurements of glare sensitivity and mesopic visual acuity are becoming increasingly important for clinical use. They can help to trace indications for cataract operation at an early stage or for YAG laser capsulotomy in cases of mild capsular fibrosis. Up to now, there are no standardized methods for monocular and binocular measurements. A new instrument named Ocutrast has been developed. A study of 100 healthy subjects aged up to 60 years was carried out. Under a field luminance of 1.0 cd/m2 and a contrast of 1:23, visual acuity was measured without and with glare. Standardized conditions were guaranteed. The mean values were lower at higher age, but were not reduced under glare. Additionally two groups of patients (n = 50) were examined. In cataract eyes and in pseudophakic eyes a one line reduction of mesopic visual acuity under glare was found. The conclusion is: a two line reduction of mesopic visual acuity between measurements without and with glare can be regarded to be out of range. Under clinical aspects, this method can contribute to the indication to cataract operation or to YAG laser capsulotomy in pseudophakic eyes.

Adaptation, Ocular↗

PubMed2006

Visual performance of aspherical and spherical intraocular lenses: intraindividual comparison of visual acuity, contrast sensitivity, and higher-order aberrations.

PURPOSE: To intraindividually compare visual performance in terms of photopic high-contrast visual acuity (HCVA), mesopic HCVA, mesopic low-contrast visual acuity (LCVA), and contrast sensitivity (CS) in patients after implantation of either an aspherical or a spherical intraocular lens (IOL). SETTING: Department of Ophthalmology, Johann Wolfgang Goethe-University, Frankfurt am Main, Germany. METHODS: Forty eyes of 20 patients were randomized to implantation of an aspherical IOL (Tecnis Z9000, AMO) in 1 eye and a spherical IOL (Sensar AR40e, AMO) in the other eye. Three to 4 months postoperatively, photopic HCVA (270 cd/m(2)) was measured with the observer-independent Frankfurt-Freiburg Contrast and Acuity Test System (FF-CATS) and high-mesopic HCVA and LCVA (8 cd/m(2)) were measured with Early Treatment Diabetic Retinopathy Study charts. CS was assessed with the FF-CATS under photopic (167 cd/m(2)), high-mesopic (1.67 cd/m(2)), and low-mesopic (0.167 cd/m(2)) luminance conditions with and without glare. For each individual eye, higher-order wavefront aberrations were reconstructed for a physiological mesopic pupil diameter. Intraindividual differences (Delta(i)) in visual acuity, contrast sensitivity, and higher-order aberrations (HOAs) were calculated, and the influence of age and Delta(i) HOA on Delta(i) contrast sensitivity (logCS) under high-mesopic conditions was investigated using multiple regression analysis. RESULTS: There were no statistically significant differences between the Tecnis IOL and the Sensar IOL in visual acuity measurements or contrast sensitivity measurements. For physiological mesopic pupil diameter, primary spherical aberration (Z(4)(0)) was significantly lower in the Tecnis group (P<.001). For all parameters studied except Z(4)(0), the Delta(i) values were distributed around zero. Multiple regression analysis showed only a partial influence of Delta(i) Z(4)(0) on Delta(i) logCS (adjusted R(2) = 0.49) but did not show any influence of age, coma-like aberration, or residual HOA. CONCLUSIONS: Although Z(4)(0) was significantly lower in the eyes with the aspherical IOL, no statistically significant differences were found between aspherical and spherical IOLs in LCVA, HCVA, and contrast sensitivity. Statistical analysis of intraindividual contrast sensitivity differences showed that in most patients, this Z(4)(0) difference was too low to have an effect on contrast sensitivity.

Aged↗

PubMed1999

Impact of cataract surgery on visual acuity and subjective functional outcomes: a population-based study in Sweden.

PURPOSE: First, to determine the effects of cataract surgery on subjectively experienced visual function and visual acuity in a defined population, at a specific frequency of surgery. Secondly, to validate questionnaire data regarding the visual function of cataract patients. METHODS: A prospective population-based investigation of the subjective visual functional and visual acuity outcomes of cataract surgery over a 1 year time interval at one institution was conducted. All operated cases (n = 459) were grouped into three levels of visual impairment, according to the preoperative visual acuities of their better eyes. Subjective reading, TV watching, distance estimation and ability to orientate in unfamiliar surroundings, before and after surgery, were assessed using self-administered questionnaires. The subjective outcomes were related to the subjects' post-operative visual acuities. The statistical evaluations comprised analyses of variance, Yates'-corrected chi-squared tests, weighted kappa and correlation statistics. RESULTS: The pre-operative subjective visual disabilities of the patients were significantly correlated with the pre-operative visual acuities of the patients' better eyes. There was an improvement in subjective reading ability, distance estimation and ability to orientate in unfamiliar surroundings for most patients at all three pre-operative visual acuity levels. After surgery there was a stronger correlation between the subjective functional improvement and the increase in visual acuity for the operated eye than for the better eye. CONCLUSIONS: An incidence of cataract surgery of 3.3 per 1000 population for the year the present study was conducted seems not to be an over-utilisation of resources. Irrespective of the visual acuity level before cataract surgery, the vast majority of patients gain better subjective visual function and better acuity after surgery. It is possible to gain valid information from cataract surgery patients using a short questionnaire.

Activities of Daily Living↗

PubMed2001

Influence of sex, visual acuity, and systemic disease on delayed presentation for cataract surgery in Austria.

PURPOSE: To determine the influence of sex, age, preoperative visual acuity, and systemic disease on the delay in presentation for first-eye cataract surgery. SETTING: University Eye Clinic, Vienna, Austria. METHODS: This retrospective study comprised 200 consecutive patients with age-related cataract who were referred to the Ophthalmology Department of the University of Vienna and who had cataract surgery in the first eye. Patients with additional intraocular procedures or with other ocular comorbidity were excluded. Age, sex, preoperative best corrected Snellen visual acuity in both eyes, ocular and systemic comorbidity, and the duration of preoperative visual deterioration were recorded. The patients were divided into groups depending on systemic comorbidity. The severity of disease was categorized as no therapy necessary or nonexistent, nonsevere, or severe. RESULTS: The mean age of women and men was 74.9 years and 70.7 years, respectively, and the mean preoperative visual acuity, 0.31 and 0.24. The duration of preoperative visual deterioration was 8.6 months and 12.2 months, respectively. All differences were statistically significant (P <.05). The visual acuity in the better eye was not significantly different between men and women. Neither the presence nor the type of systemic disease influenced preoperative visual acuity or the duration of preoperative visual deterioration. CONCLUSIONS: Although the visual acuity in the better eye was not different between men and women, men had cataract surgery after a longer duration of visual deterioration and with a worse visual acuity. More public information about cataract surgery is required to keep visual deterioration secondary to cataract to a minimum.

Adult↗

PubMed1983

Subjective and objective ocular disturbances in reattached retina after surgery for retinal detachment, with special reference to visual acuity and metamorphopsia.

A questionnaire about postoperative complaints was given to patients after surgery for retinal detachment. Their visual acuity and visual field problems were analyzed. Only one third of all the patients felt postoperative improvement. Blurred vision and metamorphopsia after operation were complained of in one third of all the patients. Blurred vision was apt to be complained of in patients with macular detachment before operation. About 77% of patients with blurred vision had a visual acuity of less than 0.5. Metamorphopsia was frequently complained of in patients treated with the segmental buckling procedure.

Adolescent↗

PubMed1993

Measurement of central and peripheral dynamic visual acuity thresholds during ocular pursuit of a moving target.

Previously, visual acuity thresholds for eccentric retinal points have been documented for targets that oscillate while the observer fixates a central point. This research describes the situation where the observer tracks a moving target in constant linear motion, thereby involving the pursuit and saccadic eye movements. The increase of visual acuity thresholds with target motion (0 to 70 degrees/s) was evaluated as a function of retinal eccentricity. Nine retinal points were evaluated, (central, 5 degrees and 10 degrees nasal, 5 degrees and 10 degrees temporal, 5 degrees and 10 degrees superior, and 5 degrees and 10 degrees inferior to the fovea). Eight normal subjects viewed computer-generated randomly oriented E's monocularly through a horizontally rotating mirror. A computer automatically calculated the minimal angle of resolution (MAR) threshold values. Result indicated that the change in visual acuity thresholds was dependent upon retinal location. The thresholds for central and peripheral eccentricities plotted as a function of angular velocity were linear but the slope of the linear function was much reduced for peripherally viewed targets compared to centrally viewed targets. Although both peripheral and central visual acuity thresholds may increase with increasing target velocity due to velocity mismatch errors and saccadic suppression and/or omission, the reduction in slope for peripherally viewed targets may be due to differential temporal summation, retinal smear, and/or separate retinogeniculate pathway processing.

Adolescent↗

PubMed1995

Visual acuity vs letter contrast sensitivity in retinitis pigmentosa.

This study examined the quantitative relationship between foveal visual acuity and contrast sensitivity for large-letter optotypes in a group of patients with retinitis pigmentosa (RP), in order to assess more completely the extent of foveal vision loss in this group of hereditary retinal dystrophies. High-contrast visual acuity and large-letter contrast sensitivity were measured with a computer-based testing system and with commercially available letter charts (Lighthouse Distance Visual Acuity Test; Pelli-Robson Contrast Sensitivity Chart). Findings from 20 patients with typical RP or Usher syndrome were compared with those from 15 age-similar control subjects with normal vision. On both the computer-based test and the chart tests, the patients with RP showed approximately equal reductions in visual acuity and large-letter contrast sensitivity. However, intersubject controls was greater for contrast sensitivity than for visual acuity on both test protocols. As a result, the patients with RP required a greater reduction in contrast sensitivity than in acuity to exceed the normal range, indicating that visual acuity was the more sensitive index of the loss of foveal visual function.

Adult↗

PubMed1996

Factors influencing visual acuity after photocoagulation for subfoveal choroidal neovascularization of exudative age-related macular degeneration.

PURPOSE: To evaluate factors influencing visual acuity after laser photocoagulation for subfoveal choroidal neovascularization of exudative age-related macular degeneration. METHODS: Subfoveal choroidal neovascular membranes were photocoagulated. Factors favoring a visual acuity of 20/200 or better were analyzed using Fisher's exact probability test or chi-square test on 28 eyes in which visual acuity was 20/200 or better, and 23 eyes with a visual acuity below 20/200 at the most recent follow-up examination. RESULTS: Factors predicting a postoperative visual acuity of 20/200 or better were (1) distance between one lateral margin of the neovascular membrane and the center of the foveal avascular zone was one-third disc diameter or less, and (2) pretreatment retinal sensitivity at the fixation point was 10 dB or more. CONCLUSION: Good indications for photocoagulation treatment of subfoveal choroidal neovascular membrane were a neovascular membrane margin near the center of the foveal avascular zone and relatively good retinal sensitivity at the fixation point adjacent to the scotoma. These factors predict a visual acuity of 20/200 or better after treatment.

Aged↗

PubMed2003

The visual acuity and refractive state of the American kestrel (Falco sparverius).

The pattern electroretinogram (PERG) was used to measure the visual acuity and refractive state of nine American kestrels (Falco sparverius). Visual acuity was determined from psychometric functions of PERG amplitude vs. spatial frequency. Refractive state was measured by finding the trial lens that resulted in the highest acuity. All nine kestrels were found to be emmetropic. Their median visual acuity was 29 c/deg. The PERG, however, underestimates behaviorally determined visual acuity by approximately 37%. When adjusted for this underestimation, the median kestrel acuity was 46 c/deg. The visual acuity of American kestrels is compared to reports in the literature of 17 other species of birds.

Animals↗

PubMed1996

[Objective determination of visual acuity. Improvement of an infrared nystagmography method and comparison with pattern visual evoked potentials].

BACKGROUND: The purpose of this study was to optimize a new nystagmographical method of objective assessment of visual acuity and compare it to an electrophysiological method. METHODS: In the nystagmographical method motionless brake marks were superimposed on a moving grating pattern, causing suppression of optokinetic nystagmus (OKN). The smallest brake mark that interrupted the OKN was taken as an objective measure for visual acuity (VA). In the electrophysiological method rapid sequences of high-contrast checkerboard patterns of different spatial frequency were presented in a pattern on-off mode in a foveal field. The VEP response function was extrapolated to 0 microV. The objective values of 94 healthy eyes with artificially reduced vision (VA 0.05-2.0) and 314 eyes with pathological reduction of VA due to different etiologies were compared. RESULTS. The selectivity of the nystagmographical method could be improved. With the exception of strabismic amblyopia, the results were closely correlated with the VA. The least VA could be estimated in steps of 0.06, 0.1, 0.2, 0.5 and 0.8. CONCLUSIONS: The new nystagmographical method yields useful information about the least VA if strabismic amblyopia is excluded.

Adolescent↗

PubMed1988

Low-contrast visual acuity cards in pediatric ophthalmology.

The usual high-contrast visual acuity chart is well known as the best indicator of central visual function. It has the limitation of only testing the high frequency, high-contrast sensitive cells in the visual system. Some conditions demonstrate a normal response on the standard visual acuity test, but abnormal results when testing visual fields or contrast-sensitivity function (CSF). A variety of diseases fall into this category (multiple sclerosis, diabetes mellitis, glaucoma, CNS tumors in the visual system, etc). The testing of CSF permits us not only to vary the size of the target (spatial frequency), but also to determine the contrast of the target first visible to the patient. Due to the time necessary to conduct the test and the important challenge of obtaining consistent subjective responses, contrast-sensitivity testing in children has been difficult. Recently, Regan has developed low-contrast visual acuity cards similar in format to those used in the Sheridan Gardiner test. Although they do not require literacy, correct responses can be immediately verified and the test can be carried out within a short period of time. These cards allow testing well within the child's limited attention span. In the future it may be possible to use this method of testing to detect CSF defects in amblyopia similar to those previously reported by Hess and others and to see how these defects are affected by standard treatment.

Age Factors↗

PubMed1986

Retinal visual acuity with pattern VEP normal subjects and reproducibility.

Retinal visual acuity was determined using an objective method by means of VEP. Sixty subjects with subjective visual acuity ranging from 20/25 to 20/12 were measured with a computer-controlled laser interferometer, using interference fringes modulated in counterphase as pattern-reversal stimulus. Steady-state VEPs taken at different spatial frequencies were evaluated by Fourier analysis and linear regression. Objective retinal acuity was calculated as the intersection between the linear regression line and the linear scaled spatial frequency axis. In 68% of all cases, the difference between objective and subjective visual acuity was less than +/- 5.1 cycles per degree (c/d) (+/- 15.4% referred to subjective acuity); in 86%, the difference was less than +/- 7.7 c/d (+/- 23.1%).

Evoked Potentials, Visual↗

PubMed2001

Assessment of visual acuity in relation to central nervous system activation in children with mental retardation.

Assessment of visual acuity was combined with observations of behavioral state indicating CNS activation in 24 individuals with mental retardation. Visual acuity was assessed by presentations of Teller Acuity Cards on two occasions. Behavioral state was classified along a scale with four categories during visual acuity testing. Results showed good test-retest reliability for the Teller Acuity Cards. Six participants had different behavioral state scores on the two test occasions, but displayed similar visual acuity on both tests. No participant rated as "drowsy" displayed responses on the acuity test. Results indicate that forced-choice preferential-looking technique can be used to test visual acuity in this population unless the participant is drowsy.

Adolescent↗