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Results for “Visual Acuity”

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PubMed1982

Nitrous oxide influences pattern EP estimate of visual acuity.

The effect of nitrous oxide (N2O) inhalation on the pattern EP with the onset and disappearance of checkerboard patterns was studied in four healthy volunteers. Checkerboards with checks ranging from 2 to 55 min of arc were presented to subjects sedated at various levels. Under the highest level introduced, 60% N2O, fixation of the pattern was still adequate. The major consistent changes in the pattern onset EP under N2O inhalation are (a) preferential attenuation of the response to small checks and (b) an increase of the response amplitude to large checks. The change in the amplitude versus check-size curve under N2O inhalation restricts the assessment of visual acuity on the basis of the pattern EP. In patients sedated with N2O, EP methods can be used only as a gross indicant of visual acuity.

Administration, Intranasal↗

PubMed2003

The effect of observation time and contrast on visual acuity.

BACKGROUND: Field studies of the duration of fixation during daytime driving find that it is about 0.2 seconds on average. Thus, the time available to read traffic signs is often limited. There are other circumstances where time to read alphanumeric messages is limited. Data relating time of observation are needed for purposes of ergonomic design as the data available in the literature are limited and uncertain. METHOD: Visual acuity was measured using Landolt rings in negative contrast, which were presented on a computer screen with a background luminance of 32 cd/m(2) for durations that varied between two and 0.02 seconds at three different contrasts. RESULTS: Visual acuity depends on the log of the light dose reduced by a factor that may be related to absorption of the light by the eye media. For young observers, it was found that: VA = 0.57 (log C.t) + 1.705, where C is the contrast and is expressed as DL/L, where DL is the difference between target and background luminances in cd/m(2) and t is the observation time in seconds. CONCLUSION: This formula or the functions fitted to the data obtained can be used to calculate the increase in target size needed to allow for short observation times.

Adult↗

PubMed1984

Visual acuity and chart luminance.

It is desirable to standardize the conditions under which visual acuity is measured because of its importance in determining whether subjects meet occupational vision standards and as an indicator of the extent or stability of pathological conditions. The chart luminance is one parameter which needs to be standardized, and the effect of the luminance level upon acuity measurement is a critical factor in this determination. These data are measured for a subject population using Landolt rings and British letters. Over a "normal" photopic range of 40 to 600 cd/m2 the relation between the logarithm of the minimum angle of resolution (log MAR)) and log L (luminance) can be approximated by a straight line. A doubling of the luminance level within this range improves the acuity measurement by approximately one letter on a five-letter row. Landolt ring acuities are less affected by luminance than letter acuities. The application of these results to establishing a standardized luminance level and tolerance range is discussed.

Adult↗

PubMed1992

Visual acuity in low birth weight (1500-2500 g) neonates.

Binocular grating acuity was tested in 138 low birth weight (LBW) neonates (birth weights ranging from 1500 to 2500 g) by means of the prototype version of the Acuity Card Procedure. No surrounding screen was used. Mean visual acuity of 107 neonates successfully assessed at mean corrected ages of -1.9 weeks (+/- 1.9 weeks) amounted to 0.58 cycles/degree (S.D. 0.71 octaves). Success rate was 77.5%. Mean postnatal age was 2.3 weeks (+/- 1.6 weeks). Acuity values of various subgroups ranged between 0.68 cycles/degree (S.D. 1.3 octaves) in low-risk, small for gestational age (SGA) preterms (n = 7), to 0.56 cycles/degree (S.D. 0.7 octaves) in SGA fullterms (n = 34), independent whether at low-or at high-risk. These differences were not significant, although with multiple regression analysis with adjustment for corrected age of testing, mean acuity of low-risk preterms was slightly better than of low-risk fullterms (P = 0.055). No significant change of acuity over corrected age could be demonstrated, except for a slight progress (r = 0.57; P less than 0.05) in the subgroup of 13 low-risk fullterms. The high variability of acuity values in neonates and the slow acuity development at term age hamper assessment of differences between various subgroups of neonates.

Birth Weight↗

PubMed2000

Dynamic visual acuity during linear acceleration along the inter-aural axis.

We investigated visual-vestibular interactions during linear acceleration along the inter-aural axis. Eighteen healthy volunteers and two patients with central neurological diseases were subjected to transaural linear acceleration in the direction of gravity force (frequency: 0.5-1.5 Hz; amplitude: 5 cm). During linear acceleration, eye movements were recorded under three test conditions: eyes closed (EC), while staring at an imaginary target (IT) and during the testing of dynamic visual acuity (DVA). As parameters of evaluation we used the amplitude of horizontal eye movements, phase shift and the decrease of DVA threshold (DVAT). Under all test conditions, eye amplitude increased with rising stimulus frequency and exceeded, especially in the higher frequency range, a hypothetically calculated eye amplitude for smooth pursuit. The combination of a visual and vestibular input (DVA and IT) led to a better compensation (lower phase shift) than under vestibular stimulation alone (EC). Eye movements during low-frequency stimulation depended more on the visual system while responses in the higher frequency range were mainly triggered by the otolith organ. At 1.5 Hz the compensatory function of the visual-vestibular system was limited (rising phase shift) and DVAT decreased even in a significant number of healthy subjects. Patients with diseases of the central nervous system showed a higher phase shift and thus a stronger decrease of DVAT (two levels) already at a stimulus frequency of 1.25 Hz.

Acceleration↗

PubMed1996

Infant peripheral vision: the development of monocular visual acuity in the first 3 months of postnatal life.

Quantitative data on the early morphological development of the human retina show that the peripheral region is relatively more mature than the central region. These results have stimulated researchers to compare the development of visual functions in the central and peripheral regions of the visual field. Here, we used preferential looking to evaluate 1-, 2- and 3-month-old infants' central and peripheral (10 degrees and 30 degrees) monocular visual acuity. There were three findings: (i) both central and peripheral acuities were poor at 1 month, improved over the age range tested, but were still about 3 octaves worse than adults' acuity; (ii) at all ages monocular acuity decreased with increasing eccentricity; (iii) 2- and 3-month-olds showed higher acuity for gratings in the temporal than in the nasal visual field at 30 degrees. The implications of these results for issues in visual development are discussed.

Adult↗

PubMed1980

An ultrasonographic study of diabetic vitreo-retinal disease with low visual acuity.

Ninety-three diabetics (168 eyes) with opaque ocular media and low visual acuity (range amaurosis to 0.1) were examined by ultrasonography (A- and B-scan) using a Coleman Ophthalmoscan 100. Dense vitreous membranes were found in 112 (67%) eyes, 100 (60%) of which showed posterior membranes. Preretinal or prepapillary proliferations (extraretinal stalks) were demonstrated in 71 (42%) eyes. Fifty-four (32%) eyes had retinal detachments (40 localized, 14 total). These were present in 10 (50%) of the 20 amaurotic eyes. The ultrasonic accuracy was checked in 49 eyes at vitrectomy. It was 78% for retinal detachments and 67% for prepapillary and preretinal proliferations. The stalks circumscribed within 2 mm or less were the hardest to detect. Ultrasonography thus aids to predict the prognosis after vitrectomy. The visual prognosis appears to be much more optimistic in eyes with vitreous membranes and prepapillary proliferations than in those with vitreous membranes associated with preretinal proliferations.

Diabetic Retinopathy↗

PubMed1989

Speed of visual acuity for vertical eye-movements with a change of accommodation.

Speed of visual acuity was measured for Landolt-C targets presented above and below the line of sight as the targets were moved from 2.4 m to 0.6 m from the observer. Target recognition was faster for a downward than an upward eye movement. There was no difference in response times for the up and down eye-movements when the fixation and target distances were the same.

Accommodation, Ocular↗

PubMed1990

Comparison of Snellen and interferometer visual acuity in an aging noncataractous population.

Using standard clinical procedures we have compared visual acuity (VA) estimates made with a hand-held white light interferometer to those obtained with a Snellen acuity chart. Fifty noncataractous patients with a mean age of 45 years (SD = 18) were tested. Snellen and interferometric acuity measures were obtained with and without refractive correction. On average, aided Snellen VA's were better (decimal acuity = 0.98) than the unaided interferometric VA's (decimal acuity = 0.67). Although we found a statistically significant p less than 0.01) correlation between unaided interferometric and aided Snellen VA's, the correlation was poor (r = 0.36). This poor correlation may account for the often observed failure to estimate postoperative aided Snellen VA with preoperative interferometric VA in cataract patients.

Adolescent↗

PubMed1999

Retinal structure and visual acuity in a polyprotodont marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata).

The visual system of the fat-tailed dunnart (Sminthopsis crassicaudata), a small polyprotodont marsupial, has been examined both anatomically and behaviourally. The ganglion cell layer was examined in cresyl-violet stained wholemounts and found to contain a mean of 81,400 ganglion cells (SD +/- 3,360); the identification of ganglion cells was supported by a correspondence to optic axon counts. Ganglion cells were distributed as a mid-temporally situated area centralis, embedded in a pronounced visual streak. Localised implants of horseradish peroxidase into retinal wholemounts revealed both A-type and B-type horizontal cells. Sections of the outer retina showed it to be rod-dominated, with a rod-to-cone ratio of 40:1 at the area centralis; cones were found to contain oil droplets but double cones were not a prominent feature. The retinal pigment epithelium consisted of squamous cells. Visual acuity, estimated from counts of peak ganglion cell density (8,300/mm2, SD +/- 1,180) and measurements of posterior nodal distance (2.9 mm), was found to be 2.30 cycles per degree. The value was close to that of 2.36 cycles per degree estimated by behavioural tests using a Mitchell jumping stand; values were similar at low, intermediate and high light levels. Our findings are discussed in relation to the lifestyle of the dunnart.

Animals↗

PubMed2005

Microdot test of foveal function. A comparison with visual acuity at high and low contrast.

PURPOSE: To define normal values across age from novel computerized tests of foveal vision and to compare the findings with visual acuity (VA) at high and low contrast. SUBJECTS AND METHODS: Sixty-one healthy volunteers, aged 22-87, with subjectively normal vision participated in the study. The right eye from each subject was tested with Snellen letter VA at high contrast, at 10% contrast using the Tri-VA test and with the Rarebit Microdot Fovea Test (RMFT), in addition to biomicroscopy and fundus examination. RESULTS: The median letter VA was 0.77 minimum angle of resolution (MAR; range 0.63-1.54) with a significant decline in letter VA with increasing age (r = 0.7, p < 0.001). The median Tri-VA resolution threshold at 10% contrast was 1.8 MAR (range 0.9-4.1) and a significant age effect (r = 0.7) was observed, most pronounced above 65 years. The median RMFT hit rate was 100% (range 97-100) in the age group below 65 years and 87.5% (range 34-98) in subjects older than 65 years. CONCLUSION: The study shows a decline in foveal function with age with all three methods, reflecting the loss of neural detectors with increasing age. The hit rate to microdot stimuli appears to be a sensitive measure, which can be used for fine-graded evaluation of foveal function.

Adult↗

PubMed1995

Endophthalmitis after penetrating trauma. Risk factors and visual acuity outcomes.

PURPOSE: To identify clinical characteristics that were associated with an increased incidence of endophthalmitis in eyes with penetrating ocular trauma. METHODS: In part 1, a retrospective analysis was performed on 258 consecutive patients with penetrating ocular trauma presenting to the Bascom Palmer Eye Institute between October 1987 and January 1991. In part 2 of the study, 28 consecutive patients with culture-proven endophthalmitis were identified from the Clinical Microbiology Registry from April 1987 through September 1987 and February 1991 through August 1993. Clinical variables were evaluated in each part for association with an increased risk of endophthalmitis. RESULTS: In part 1 of the study, endophthalmitis developed in 13 (5%) of the 258 patients. Endophthalmitis did not occur in eyes that had blunt injury. In those eyes with a lacerating injury, there was an increased relative risk of infection in eyes with disruption of the crystalline lens. This risk factor was found statistically significant by univariate and multivariate analysis. In part 2 of the study, lens disruption was present in 24 (86%) of 28 patients with culture-proven endophthalmitis. Of the 41 patients with infection from part I and part II, 22 (54%) achieved visual acuity of 20/ 400 or greater. Endophthalmitis caused by coagulase-negative staphylococci had the best visual outcome, with 7 (64%) of 11 patients obtaining visual acuity of 20/ 400 or greater. CONCLUSION: Lens disruption in eyes with penetrating trauma is a significant risk factor for the development of endophthalmitis. The prognosis for useful vision in eyes with posttraumatic endophthalmitis is best when infection is caused by less virulent organisms.

Anti-Bacterial Agents↗

PubMed2002

Retrospective, longitudinal, and cross sectional study of visual acuity impairment in choroideraemia.

BACKGROUND/AIMS: Few studies have reported on the change in visual acuity (VA) in patients with choroideraemia. In order to determine the degree and rate of VA impairment associated with this disease, the central VA was analysed in a large group of patients with choroideraemia. METHODS: The authors completed a retrospective, cross sectional review of 115 patients with choroideraemia from three tertiary care centres. A longitudinal analysis was performed on 45 of these patients who met the inclusion criteria of at least three visits over a minimum period of 4.5 years. Multiple linear regression analysis was used to explore the 5 year rate of VA change while controlling for initial VA and initial age. Multiple logistic regression was also used to investigate VA impairment. RESULTS: In the cross sectional group (n = 115), 84% (87/103) of patients under the age of 60 had a VA of 20/40 or better while 33% (4/12) of patients 60 years of age or older had a VA of 20/200 or worse at their most recent visit. The majority of the patients (93%) in the longitudinal subgroup of 45 patients had a VA of 20/30 or better at their initial visit. The mean 5 year rate of VA change was 0.09 logMAR equivalent (approximately one line on the Lighthouse chart). CONCLUSION: In this cohort of patients with choroideraemia, there was typically a slow rate of VA loss and the prognosis for central VA retention was, as a group, favourable until the seventh decade.

Adolescent↗

PubMed2006

Relation between increased anaerobic glycolysis and visual acuity in long-standing type 2 diabetes mellitus without retinopathy.

In long-standing diabetes mellitus, blood flow to essential organs including the retina is reduced owing to macrovascular and/or microvascular changes. Poor glycolytic pathway of glucose metabolism owing to tissue hypoxia caused by ischemia at capillary bed of essential organs produces excessive lactic acid and less of adenosine triphosphate, which lead to poor cellular function. The purpose of the study was to evaluate the relationship between increased anaerobic glycolysis and visual acuity in type 2 diabetes mellitus without retinopathy. Fifty patients of type 2 diabetes mellitus of 10-12 years duration, without retinopathy, constituted the study group. The controls were 50 age-matched healthy persons without diabetes mellitus. Blood lactate level and best-corrected visual acuity (BCVA) were measured in both the groups. The mean blood lactate level was 1.05 mM/l in the control group and 2.32 mM/l in the study group. BCVA of 20/20 (log MAR 0) was seen in 48 (96%) patients of the control group and in 27 (54%) patients of the study group. BCVA of 20/30 (log MAR 0.2) was seen in 23 (46%) patients in the study group and 2 (4%) in the control group. Association of higher blood lactate level with decreased BCVA in the study group was statistically significant (P< 0.001).

Anaerobic Threshold↗

PubMed1980

Correlations between intraocular pressure, visual field and visual acuity, based on 11 years of observations of treated chronic glaucomas.

In a retrospective study of 114 patients under treatment for chronic glaucoma (81 without and 33 with visual field defect) over an 11-year period of observation, a highly significant correlation between intraocular pressure and progression of visual field defects could be demonstrated. This correlation could be shown for the visual field outer boundary in 81 eyes with ocular hypertension and for typical visual field defects in 33 eyes with chronic glaucoma. The relationship was, however, only significant when both the standard deviation of the annual intraocular pressure and the influence of cataract development upon visual acuity were considered. Quantitative analysis of the results of Goldmann perimetry was by planimetry and took into account only changes during the 11-year observation period.

Aged↗

PubMed1992

Visual acuity of low- and high-risk neonates and acuity development during the first year.

Binocular grating acuity of 65 neonates was measured using Teller acuity cards. At the time of testing, age corrected for prematurity ranged from -3 weeks to 2 weeks. On the basis of clinical data, serial ultrasound scans and EEG recording newborns were divided into 4 subgroups: fullterm low-risk (FLR, n = 22); preterm low-risk (PLR, n = 20); preterm medium-risk (PMR, n = 9) and preterm high-risk (PHR, n = 14). Mean visual acuity of PLR infants (0.86 cy/deg; S.D. 0.34 oct) was not significantly different from that of FLR newborns (0.80 cy/deg; S.D. 0.71 oct); the lower variability of the PLR infants might possibly be caused by their longer postnatal experience. Within the preterm groups, mean visual acuity of PLR newborns was found to be significantly higher than that of PMR (0.73 cy/deg; S.D. 0.26 oct) and PHR infants (0.73 cy/deg; S.D. 0.35 oct). This difference can not be explained by dissimilarities in postnatal or corrected age. Brain impairment, as documented by US scans and EEG recording could account for these findings. Longitudinal data are needed in order to substantiate these findings and correlate them with later neurological and neuro-imaging outcome. Preliminary results of an ongoing longitudinal study suggest acuity development of most, but not all, PHR infants, in whom a cystic-periventricular leukomalacia had been diagnosed, to be worse than that of low- and medium-risk infants.

Electroencephalography↗

PubMedDate not supplied

Visual acuity development in normal and abnormal preterm human infants.

The grating acuity of preterm infants was determined by measurements of the visual evoked potential (VEP) produced by phase alternation of sinusoidal luminance gratings. The development of visual acuity in healthy preterm infants appears to be accelerated when compared with full term infants of the same post-conceptual age. Cortical insults and the more advanced stages of retinopathy of prematurity may adversely affect acuity development as indexed by the VEP. Preterm twins also appear to have lower acuity than preterm monoparous infants.

Evoked Potentials, Visual↗

PubMed2002

Proximal versus distal cue utilization in spatial navigation: the role of visual acuity?

Proximal versus distal cue use in the Morris water maze is a widely accepted strategy for the dissociation of various problems affecting spatial navigation in rats such as aging, head trauma, lesions, and pharmacological or hormonal agents. Of the limited number of ontogenetic rat studies conducted, the majority have approached the problem of preweanling spatial navigation through a similar proximal-distal dissociation. An implicit assumption among all of these studies has been that the animal's visual system is sufficient to permit robust spatial navigation. We challenged this assumption and have addressed the role of visual acuity in spatial navigation in the preweanling Fischer 344-N rat by training animals to locate a visible (proximal) or hidden (distal) platform using double or null extramaze cues within the testing environment. All pups demonstrated improved performance across training, but animals presented with a visible platform, regardless of extramaze cues, simultaneously reached asymptotic performance levels; animals presented with a hidden platform, dependent upon location of extramaze cues, differentially reached asymptotic performance levels. Probe trial performance, defined by quadrant time and platform crossings, revealed that distal-double-cue pups demonstrated spatial navigational ability superior to that of the remaining groups. These results suggest that a pup's ability to spatially navigate a hidden platform is dependent on not only its response repertoire and task parameters, but also its visual acuity, as determined by the extramaze cue location within the testing environment. The standard hidden versus visible platform dissociation may not be a satisfactory strategy for the control of potential sensory deficits.

Aging↗