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Results for “Visual Acuity”

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PubMed1972

Visual acuity and contrast sensitivity in patients with cerebral lesions.

Spatial contrast sensitivity as a function of spatial frequency was measured in patients with cerebral lesions. In most of these patients visual acuity, as measured by the Snellen chart, was 20/30 or better, yet marked departures from normal contrast sensitivity were found. The greatest loss in contrast sensitivity occurred at high frequencies, but in one patient the loss was greatest in the midfrequency range. This finding lends support to the channel hypothesis of spatial contrast discrimination.

Adult↗

PubMed1993

Surgical complications and visual acuity results in 536 cases of plate haptic silicone lens implantation.

Implantation of a plate haptic intraocular lens was planned in 536 cases. This paper reports the uncorrected and corrected visual acuities and complications in 33 patients in whom there were surgical complications that prevented implantation of the plate haptic lens. Excluding five patients (15%) who had pre-existing pathology, 21 (75%) had uncorrected acuity of 20/40 or better and 27 (96%) had corrected acuity of 20/40 or better five to six weeks postoperatively. The plate haptic lens can only be used with capsulorhexis and an intact anterior capsular rim and posterior capsule. Two alternative backup lens styles--a loop lens for placement in the torn bag or the sulcus and an anterior chamber lens--have to be in the operating room for each surgery.

Cataract Extraction↗

PubMed1988

Assessment of malingerers' visual acuity by Lotmar's visometer test.

The authors, after having mentioned several methods to detect malingering, have attempted to demonstrate the reliability of Lotmar's visometer test in assessing the real visual acuity of ten malingerers (five of whom denied bilateral vision). The authors confirmed their data with several other subjective and objective methods that demonstrated the reliability of the visometer test.

Diagnosis, Differential↗

PubMed1986

The significance of minor defects of visual acuity in school children: implications for screening and treatment.

Information collected on the children of the 1970 Birth Cohort Study has been used to examine the educational performance of children who have minor defects of visual acuity. Results suggest that children with mild degrees of hypermetropia may experience difficulty learning to read but with exclusion of this group significant educational disability was not associated with minor visual defects. The significance of this finding is discussed in conjunction with information on prevalence of defects and current practice in screening and treating visual defects in school children. Some anomalies in current practice are identified.

Child↗

PubMed2005

The foveal photoreceptor layer and visual acuity loss in central serous chorioretinopathy.

PURPOSE: To describe changes of the foveal photoreceptor layer using optical coherence tomography (OCT) in central serous chorioretinopathy (CSC) and evaluate the correlation with visual acuity (VA) loss. DESIGN: Observational case series. METHODS: We studied 28 eyes with acute or chronic CSC using high-resolution OCT. The tomographic findings of the detached foveal photoreceptor layer were compared with VA. Sixteen eyes also were evaluated after foveal reattachment. RESULTS: The outer photoreceptor layer (OPL) in the detached fovea was preserved in 14 eyes, of which 13 had symptoms for <1 year and atrophic in 14 eyes with symptoms for >1 year. The preserved OPL had an even profile in 7 eyes and a granulated profile in 7 eyes. Mean VA was 0.19 logMAR with a preserved OPL and 0.72 logMAR with an atrophic OPL (P <.001). Cases seen after the detachment resolved included 6 eyes with preserved even OPL, 5 eyes with preserved granulated OPL, and 5 eyes with atrophic OPL. Mean final VA was 0.06 logMAR in eyes with preserved OPL and 0.90 logMAR in eyes with atrophic OPL (P <.001). The VA improved in 73% of eyes with preserved OPL and no eyes with atrophic OPL (P = .025). The VA recovered completely in 83% of eyes with preserved even OPL and no eyes with preserved granulated OPL (P = .015). CONCLUSION: High-resolution OCT demonstrates changes in the foveal photoreceptor layer in CSC that highly correlate with VA loss and may predict visual recovery after macular reattachment.

Acute Disease↗

PubMed2000

Prevalence of usual-corrected binocular distance visual acuity impairment in Hispanic and non-Hispanic adults.

OBJECTIVES: The purpose of this study was to perform comparative analyses of the population-based prevalence of usual-corrected binocular distance visual acuity impairment among Hispanics and non-Hispanics in the United States. METHODS: Data from the Hispanic Health and Nutrition Examination Survey (HHANES), 1982-1984, and the National Health and Nutrition Examination Augmentation Survey I (NHANES I-A), 1974-1975, were analyzed to investigate the epidemiology of usual-corrected binocular distance acuity in adults 25 to 74 years of age among Cuban-Americans (N=396), Mexican-Americans (N=1,381), Puerto Ricans (N=513), African-Americans (N=250), and non-Hispanic white Americans (N=2, 660). Binocular distance acuity was assessed using Sloan Letters or Landolt Rings with the participants wearing their corrective lenses, if any. RESULTS: Prevalences of 20/50 or worse usual-corrected binocular distance acuity were 3.5%, 4.6%, and 6.6% for Cuban-Americans, Mexican-Americans, and Puerto Ricans, respectively, in the HHANES; and 7.7% and 4.1% for African-Americans and non-Hispanic whites, respectively, in the NHANES I-A. Within the HHANES, after adjustment for gender and age, Puerto Rican adults were found to have a significantly higher prevalence of visual impairment (20/50 or worse) and were significantly less likely to become unimpaired with usual correction than Cuban-American adults. Within the NHANES I-A, African-Americans were found to have a higher prevalence of visual impairment (20/50 or worse) and were significantly less likely to become unimpaired with usual correction than non-Hispanic whites. Higher prevalences of visual impairment (20/50 or worse) were associated with increasing age for all ethnic groups. After controlling for age, odds of usual-corrected visual impairment (20/50 or worse) were significantly higher in women than in men for Cuban-Americans and Mexican-Americans (odds ratios: 4.5 and 2.6, respectively). CONCLUSIONS: The results from this study suggest that compared to other Hispanic groups and non-Hispanic whites, Puerto Rican and African-American adults may not be receiving similar eye care services and/or may have more severe eye diseases.

Adult↗

PubMed2005

[The relationship of magnification change and visual acuity after implanting phakic anterior chamber intraocular lens for extreme high myopia].

OBJECTIVE: To investigate the change of retinal image magnification and its relationship to post-operative best corrected visual acuity (BCVA) after implanting phakic anterior chamber intraocular lens for extreme high myopia. METHODS: 30 eyes in 23 patients with -15.13 to -29.00 Diopter (D) of myopia were implanted. The magnification change of retinal image was calculated with ZEMAX software. The relationship among myopic diopter, magnification change, BCVA, and post-operative BCVA improvement were analyzed. RESULTS: The post-operative BCVA improved by 1 or more lines in 28 of 30 eyes (93%) at 3 months. 2 eyes (7%) no change of BCVA. There was positive correlations between myopic diopter and magnification change (r = 0.996, P < 0.01), and magnification change and post-operative BCVA improvement (r = 0.42, P = 0.02). There was negative correlations between myopic diopter and pro-operative BCVA (r = -0.62, P < 0.01), and post-operative BCVA (r = -0.57, P < 0.01). CONCLUSION: Magnification change was one of reason for post-BCVA improvement. There is a positive correlation between Magnification change and post-BCVA improvement.

Adolescent↗

PubMed1998

Assessment of visual acuity and contrast sensitivity in the chick using an optokinetic nystagmus paradigm.

While the chick is one of the widely used animal models for eye growth studies very little is known about its visual spatial resolution performance. Using optokinetic nystagmus responses as an indicator of stimulus visibility, we estimated the visual acuity of young chicks to be between 6.0 and 7.7 cycles deg-1 at 2 and 4 days of age and slightly higher, between 7.7 and 8.6 cycle deg-1, at 8 days. Contrast sensitivity measured using the same experimental paradigm was greatest at around 1.2 cycle deg-1, for which the contrast threshold lay between 4% and 11%. Sensitivity became progressively poorer for frequencies both higher and lower than this. These data suggest that the visual performance of the chick is slightly poorer than that of the pigeon which has a similar eye size and exhibits similar foraging behaviour.

Animals↗

PubMed1999

Visual acuity tests using chart, line, and single optotype in healthy and amblyopic children.

PURPOSE: The purpose of this study was to evaluate the difference between full chart, single line, and single optotypes visual acuity (VA) test results in healthy and amblyopic children. METHODS: Thirty-five children with amblyopia (20 with strabismus and 15 with anisometropia) and 40 ophthalmologically normal age-matched children were examined. The mean age of the patients in the study and control groups did not differ significantly (P= .9). A commercial projector that projected tumbling-E randomly placed optotypes was used. The VA of the amblyopic eye of the patients in the study group and the right eye of the patients in the control group was examined first using a full chart of optotypes, then using a single line of optotypes, and finally with individual symbols. The procedure was repeated with the other eye. RESULTS: LogMAR VA improved when the full chart was substituted with a single line, and improved by a similar increment further with single optotypes, in both the study and control groups. VA improved significantly more in eyes with amblyopia than in control subjects. Results were not influenced by age. CONCLUSION: VA testing using a single line gives better, sometimes misleading results, than tests with a full chart because it reduces but does not eliminate the crowding effect. When using a device that can employ more than 1 mode, the exacttest mode should be specified and maintained throughout the follow-up.

Amblyopia↗

PubMedDate not supplied

Visual acuity, binocular vision, and ocular muscle balance in VLBW children.

Thirty-four very low birth weight (VLBW) 6-year olds and 31 normal birth weight (NBW) 6-year olds were assessed for visual acuity, binocular vision, and ocular muscle balance. Significantly more of the children in the VLBW group failed the tests of binocular vision and ocular muscle balance. Failure in tests of binocular vision was associated with higher numbers of days on mechanical ventilation and higher number of days in the intensive care nursery during the first months of life.

Child↗

PubMed2004

Reliability and validity of the Melbourne Edge Test and High/Low Contrast Visual Acuity chart.

PURPOSE: The purposes of the study were to investigate the test-retest reliability and the validity of new versions of the Melbourne Edge Test (MET) and the High/Low Contrast Visual Acuity (H/LCVA) chart and to investigate the agreement between the original and new versions. METHODS: The MET original photographic version, MET new light box version, H/LCVA Chart original photographic version, H/LCVA Chart new printed version, and the Pelli-Robson chart were administered twice to one eye of 22 subjects with low vision and 20 soft contact lenses wearers. RESULTS: For the low vision group, the test-retest 95% limits of agreement were +/- 5.2 dB for the MET new light box version and +/- 0.39 logarithm of the minimum angle of resolution (logMAR) for the LCVA component of the H/LCVA new printed version. For the soft contact lens group, the test-retest 95% limits of agreement were +/- 2.1 dB for the MET new light box version and +/- 0.26 logMAR for the LCVA component of the H/LCVA new printed version. Moderate to high correlations were obtained between contrast sensitivity tests, thus providing evidence of validity. Scores obtained for the new test versions were significantly higher than the original versions (p < 0.01). CONCLUSIONS: Of all the tests administered, the MET original photographic version and the Pelli-Robson Chart had the highest test-retest reliability for the low vision group. For the soft contact lens group, the H/LCVA original version (low contrast letters, 18% Weber) and the Pelli-Robson Chart had the highest reliability.

Adolescent↗

PubMed1981

New standards procedures for measuring visual acuity.

Portions of the Committee on Vision Working Group 39 report relevant to optometry practice are reproduced here along with supplementary comments. The report presents standards for test conditions, procedures, and criteria that will enable different examiners to obtain the same results when measuring visual acuity. The Landolt C ring is recommended as the primary standard optotype; other optotypes may be used if they are shown to yield comparable results. Adoption of metric measurements is suggested for both distance and near acuity.

Humans↗

PubMed2001

Correlation between pupillary size and intraocular lens decentration and visual acuity of a zonal-progressive multifocal lens and a monofocal lens.

OBJECTIVE: To see whether there is a correlation between pupillary area or intraocular lens (IOL) decentration and tilt and the visual acuity (VA) at all distances for eyes with a zonal-progressive multifocal IOL or a monofocal IOL. DESIGN: Comparative, nonrandomized, interventional study. PARTICIPANTS: Fifty-five eyes of 55 patients undergoing five-zone refractive multifocal IOL implantation and 55 eyes of 55 age-matched patients undergoing monofocal IOL implantation. INTERVENTION: All eyes underwent phacoemulsification and IOL implantation. MAIN OUTCOME MEASURES: The VAs from far to near distances were examined using an all-distance vision tester at 1 month after surgery. The pupillary area was also measured using an infrared pupillometer, and the degrees of IOL decentration and tilt were measured using a Scheimpflug videophotography system. Univariate associations between VA and the pupillary area and IOL decentration or tilt were evaluated statistically. RESULTS: The mean intermediate VAs and contrast sensitivities at all spatial frequencies in the multifocal IOL group were worse than those in the monofocal IOL group, whereas near VA was better in the multifocal group. In the multifocal group, smaller pupillary area was associated significantly with worse near logarithm of the minimum angle of resolution (LogMAR) VA (r = 0.636), but not with far or intermediate VAs. When pupil diameter was 4.5 mm or greater, near mean VA reached 20/63. A greater degree of IOL decentration was associated significantly with worse far and intermediate LogMAR VAs (r = 0.460 at 5.0 m and 0.527 at 1.0 m) but not with near VA. When decentration was 0.9 mm or greater, distance mean VA did not reach 20/32. However, the correlation between tilt and VA was not statistically significant. In the monofocal group, no significant correlation was found between pupillary area, IOL decentration, or tilt and the VA. CONCLUSIONS: Smaller pupil size is correlated significantly with worse near VA, whereas greater decentration is correlated with worse distance and intermediate VA in eyes with refractive multifocal IOLs. Specifically, a pupil diameter of less than 4.5 mm cannot provide useful near VA, and decentration of 0.9 mm is the maximum allowable limit for adequate distance VA. However, pupil size and IOL decentration do not influence VA in eyes with monofocal IOLs.

Adult↗

PubMed1993

Magnification and visual acuity in refractive surgery.

In comparisons of retinal image size within the same eye before and after refractive surgery, a change in the plane of correction from the spectacle to the cornea induces a change in retinal magnification. Comparing retinal image size between eyes of different individuals, a change in the plane of correction as well as the type of ametropia (axial or refractive) interacts to change the retinal magnification. Consequently, comparing acuity before and after refractive surgery without considering the effects of retinal magnification can be misleading. Magnification effects can be large, accounting for a visual acuity increase of 1 line or more. Here we model the magnification induced by refractive surgery in various reference eyes and discuss implications in the context of current clinical trials.

Humans↗

PubMed1986

Contralateral decreased visual acuity and extraocular muscle palsies following retrobulbar anesthesia.

Numerous complications resulting from retrobulbar injections in the injected eye and orbit have been reported. A rare complication of retrobulbar anesthesia is the occurrence of decreased visual acuity and extraocular muscle palsies in the contralateral eye. We report three cases of contralateral dysfunction of cranial nerves II and III, following retrobulbar anesthesia. None of the patients suffered permanent sequelae. Several methods of decreasing the probability of such an occurrence are discussed.

Aged↗

PubMed1994

Implications for dynamic visual acuity with changes in aged and sex.

Using a Landolt ring with a gap of 40' of arc which moved at a decreasing velocity until the gap was discriminated, we measured the dynamic visual acuity of 826 subjects, males and females ages 5 to 92 years, and found rapid development between the ages of 5 and 15 years. This experiment showed that dynamic discrimination peaked at age 15 and then declined at a constant rate from age 20 on. The discrimination of male subjects was superior to that of female subjects at most ages, but a significant sex difference was observed only at age 5. We speculate that males may have better discrimination than females but variability is substantial.

Acceleration↗

PubMed1988

A novel high-frequency visual acuity chart.

A high-frequency eye test chart using letters or figures of alternating black and white stripes (or dots) on a grey background was developed. Any cross-section of the letters has a Fourier transform with a zero frequency component equal to the luminance of the grey background. When the letters are out of focus, their image on the retina fades rapidly into the grey background, rendering them invisible rather than merely blurred as in a standard chart. The chart was calibrated by simulating refractive errors with defocusing lenses applied to a photographic camera and to subjects' eyes. No constant ratio was found between the size of the Snellen letters and the size of the high-frequency letters for equal visibility. The new chart requires letters for 20/200 acuity to be only 3.6 times larger than those for 20/20 vision. Results confirm the arbitrary nature of the Snellen fraction and warn about the accuracy of visual acuity determined by using charts of different letter types, calibrated by Snellen's system.

Equipment Design↗

PubMed1987

Pupil response as an objective measure of visual acuity.

Pupillary responses to brief presentations of sinusoidal grating patterns were measured. The results show that the amplitude of the pupillary responses varies systematically with grating spatial frequency. Gratings of spatial frequencies in the range 1-5 c deg-1 elicited the maximum percentage change in pupil area, with higher and lower spatial frequency gratings producing smaller responses. The bandpass nature of the pupil response function was compared to contrast sensitivity functions obtained under the same viewing conditions. The effects of defocus and eccentric fixation on both contrast sensitivity and pupil response functions were qualitatively similar. Grating acuities calculated from contrast sensitivity data correlated well with similar data extracted from pupil response functions. The results suggest that automated pupillometry can provide an attractive means for objective measurement of visual acuity.

Fixation, Ocular↗