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Results for “Visual Acuity”

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At least 19 recordsLinked to original sources
PubMed1979

An analysis of visual acuity, visual fields, and disk cupping in childhood glaucoma.

We analyzed the long-term functional results in 102 eyes of 59 patients with childhood glaucoma with specific reference to the pattern of optic nerve damage. Optic disk photography and quantitative perimetry were used to judge the degree of damage that had been sustained. There was a predilection for initial visual field damage in the arcuate area, followed by further arcuate and nasal field loss, similar to the pattern of visual field loss seen in adult glaucoma. In children, as in adults, neural tissue appeared to be lost preferentially at the vertical disk poles. The selective pattern of glaucomatous optic nerve damage seemed not to depend upon the age of the optic nerve structures. In contrast to adult eyes, the scleral canal in children apparently enlarges with high IOP. Thus, disk cup size increase in children could occur from neural tissue loss, from scleral canal enlargement, or from a combination of the two processes.

Adolescent↗
PubMed1977

Optic nerve hypoplasia with good visual acuity and visual field defects: a study of children of diabetic mothers.

Seventeen children, born of severely diabetic mothers, exhibited segmental optic nerve hypoplasia with normal visual acuity and altitudinal or sector field defects corresponding to the hypoplastic areas of the disc. This is the first group of patients with optic nerve hypoplasia in which a possible cause has been identified. Optic nerve hypoplasia is neither a rare abnormality usually associated with serious central nervous system defects, nor is it always accompanied by decreased visual acuity.

Abducens Nerve↗
PubMed1977

Visual acuity and behavior of monocularly deprived monkeys after retinal lesions.

One eyelid of each of three Macaca nemestrina monkeys was sutured shut at 3 weeks of age. One animal had the central 10 degrees of the open eye retina lesioned at 3 weeks of age (EL1), a second at 9 months of age (LL1), and the third had no lesion (MD1). After a reverse suture at 9 months of age, the deprived eye was tested for grating acuity, visual behavior, and visual field. EL1 tested positively on all behavioral tasks by 1 month and showed good visual ability to negotiate a playroom but never performed better than 20/1,250 on grating acuity. MD1 showed little visual behavior in the playroom but tested at 20/400 acuity. LL1 rapidly recovered all aspects of visual behavior and tested at 20/80 visual acuity. Perimetry shows that LL1 and EL1 respond mainly in the central portion of the deprived eye visual field but not to the periphery or the monocular segment. We conclude that removal of the open eye retina after the critical period allows much visual recovery by the deprived eye but that removal of the open eye retina within the critical period does not prevent many of the effects of monocular deprivation.

Animals↗
PubMed1978

Visual acuity and the developing visual system.

The objective measurement of visual acuity in infants is reviewed. Recent techniques have shown that visual acuity levels as early as four to six months after birth. This and other evidence indicates that the most sensitive period in the development of the visual system may be during the first six months of life. With this as a rationale, it is suggested that eye care practitioners consider eye examinations and correction of refractive errors during infancy as a means of prevention of future strabismus and amblyopia.

Child, Preschool↗
PubMed1979

[The drop of visual acuity with distance and visual fatigue (author's transl)].

Using a new apparatus which enables us to measure in a continual manner the visual acuity for any distance; we have found considerable changes in the acuity between 24 metres and 10 centimetres. A drop in the visual acuity was found at the near vision. From dioptric and non-dioptric factors, we have infered our interpretation, which touches the question of visual fatigue and near vision.

Accommodation, Ocular↗
PubMed1979

Micropsia and visual acuity in macular edema. A study of the neuro-retinal basis of visual acuity.

Relative micropsia was measured by a matching technique in patients with unilateral, benign, macular edema. Quantitative assessment of foveolar micropsia to be a sensitive indicator of receptor displacement in this disorder, and may be a useful tool both for diagnosing and for monitoring macular edema. Parallel measurements of grating acuity showed a close proportionality between acuity and micropsia parameters. This result validates a new quantitative theory for the neuro-retinal basis of visual acuity. The theory allows prediction of the proportion of working visual neurons in patients with impaired acuity due to diseases that produce a diffuse loss, or disconnection, of macular cones. Our results indicate that so-called normal visual acuity (1.0 or 20/20) requires no more than 44% of the normal quantity of fovelar, neuro-retinal channels.

Humans↗
PubMed1978

Fresnel prisms and their effects on visual acuity and binocularity.

1. The visual acuity with the Fresnel membrane prism is significantly less than that with the conventional prism of the same power for all prism powers from 12 delta through 30 delata at distance and from 15 delta through 30 delta at near. 2. The difference in the visual acuity between base up and base down, and between base in and base out, is not significantly different for either the Fresnel membrane prism or for the conventional prism. 3. For both Fresnel membrane prism and the conventional prism, the visual acuity when looking straight ahead. 4. Using Fresnel membrane prisms of the same power from different lots, the visual acuity varied significantly. The 30 delta prism caused the widest range in visual acuity. 5. When normal subjects are fitted with the higher powers of the Fresnel membrane prism, fusion and stereopsis are disrupted to such an extent that the use of this device to restore or to improve binocular vision in cases with large-angle deviations is seriously questioned. 6. Moreover, the disruption of fusion and stereopsis is abrupt and severe and does not parallel the decrease in visual acuity. The severely reduced ability to maintain fusion may be related to the optical aberrations, which, in turn, may be due to the molding process and the polyvinyl chloride molding material. 7. Through the flexibility of the membrane prism is a definite advantage, because of its proclivity to reduce visual acuity and increase aberrations its prescription for adults often must be limited to only one eye. 8. For the same reasons in the young child with binocular vision problems, the membrane prism presently available should be prescribed over both eyes only in powers less than 20 delta. When the membrane prism is to be used as a partial occluder (over one eye only), any power can be used. 9. The new Fresnel "hard" prism reduces visual acuity minimally and rarely disrupts binocularity, thus increasing the potential for prismotherapy to establish binocularity. This prism is currently available only for use as a trial set. Since the cosmetic appearance of the Fresnel "hard" prism is similar to that of the Fresnel membrane prism and it is easier to maintain, it would be the prism of choice (over all other types) for bilateral prescriptions in the young patient with emmetropia. The manufacturer is urged to make these prisms available to fit a special round adjustable frame, such as that developed in Europe for use with the wafer prism.

Adolescent↗
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↗
PubMed1977

Spatial frequency and light-spread descriptions of visual acuity and hyperacuity.

Resolution (visual acuity) and differential spatial localization (hyperacuity) targets were selected to allow rigorous psychophysical measurements as well as ready expression of both their spatial frequency spectrum and their retinal image light distribution. Thresholds were about 1 arc min for acuity and 4-6 arc sec for hyperacuity. As is consistent with the reciprocal relationship between the space and spatial frequency domains, the small locally restricted spatial differences between just distinguishable patterns are represented in the frequency domain by equally small differences, which are distributed over the entire spatial frequency spectrum. While they occur in many test situations, phase variations of spatial frequency components are not necessary for achieving optimum acuity and hyperacuity.

Female↗
PubMed1977

Maturation of evoked potentials and visual preference in 6-45-day-old infants: effects of check size, visual acuity, and refractive error.

Visual evoked potentials (VEPs) and the percentage time fixated (PTF) were investigated in response to checkerboard light flashes in 10 human infaed as a function of the size of check in the evoking stimulus (diffuse light, 11, 22, 45, 90 and 180 min of arc), the refractive lens strength the checkerboards were viewed through (-6 to +6 diopters), and the age of the infants (6-26 or 27-45 days). Check size significantly influenced VEP amplitude in infants as young as 6 days. The 11' checks evoked greater responses that diffuse light suggesting a visual acuity of better than 20/220. Only the 27--45-day-olds behaviorally discriminated the checks, PTF indicating an acuity of 20/120. Evoked potential refraction with spherical lention between VEP amplitude and check size measured from different VEP components at different ages indicated the function contained two modes or components. The first mode was inverted "U-shaped" and was obtained in response to check sizes less than 45'. It was primarily due to changes in amplitude of the early VEP components (less than 210 msec after the evoking stimulus) and was poorly correlated with the behavioral PTF measure. It was proposed that this mode reflected subcortical activity. The second mode was a linear increase in amplitude as check size was increased from 45' to 180'. It was primarily due to changes in the amplitude of late VEP components (240--400 msec after the evoking stimulus) and was highly correlated with the percentage time the infants fixated the various check sizes. It was proposed that this mode reflected cortical activity. Age selectively influenced the late VEP components and the PTF behavioral measure, these measures being influenced by check size only in the 27--45-day-old infants. This change in responsivity of late VEP components and the transition from passive to more active and discriminating visual preference, suggest the onset of increased cortical function between 28 and 45 days of age.

Age Factors↗
PubMed1977

Relation of visual acuity to illumination, contrast, and distance in the partially sighted.

Visual acuity (minimum target size for threshold visibility) was measured as a function of luminance, contrast, and distance in experiments using 16 partially sighted persons. The results indicate large individual differences in dependence of visual acuity on both luminance and contrast. Visual acuity often failed to change systematically with variations in the testing distance; the effects of contrast and luminence on visual acuity also frequently failed to show any systematic dependence on viewing distance. The relation of acuity in the partially sighted to medical diagnosis is discussed along with some practical implications.

Albinism↗
PubMed1978

Screening for impaired visual acuity in middle age in general practice.

Screening for impaired distant visual acuity was one component of a controlled trial of multiphasic screening in middle age carried out in two general practices. The prevalence of impaired visual acuity (6/18 or worse in the better eye) at the initial screening in 1967 was 9.6% overall, ranging from 5.9% in people aged 40-49 years to 16.3% in those aged over 60. The question "Do you have difficulty seeing distant objects?" had a low sensitivity and high specificity, rendering it unsatisfactory for use in mass population screening for visual impairment. The prevalences of impaired visual acuity in the screening and control groups at the survey in 1972 showed no significant differences in any age group. Mass screening for defects of visual acuity in the course of a multiphasic examination is thus unlikely to reduce the prevalence of impaired distant visual acuity in the community.

Adult↗
PubMed1977

Visual acuity and contrast sensitivity in multiple sclerosis--hidden visual loss: an auxiliary diagnostic test.

In 48 patients with multiple sclerosis sine-wave gratings were used to test visual sensitivity for coarse, medium, and fine detail rather than measuring visual acuity for fine detail only, as in conventional clinical tests. In 20/48 patients the test revealed a visual defect of neural origin, qualitatively different from that caused by refractive error. In 11 of these 20 patients, visual sensitivity to detail of medium coarseness was markedly degraded, even though sensitivity to both coarse and fine detail was unimpaired. In 3 of these 20 patients visual sensitivity to coarse detail was selectively degraded. These visual defects could not be detected by the Snellen test, yet the patient might experience visual problems in everyday life and also experience distorted visual perception. Possible neural bases for these visual impairments are discussed. Since 8 of the 14 patients with selective loss showed no clinical evidence of visual involvement, the test can aid the earlier diagnosis of multiple sclerosis.

Adolescent↗
PubMed1978

Fading and feedback in the modification of visual acuity.

Two experiments assessing the modification of visual acuity by fading plus feedback procedures are presented. The training procedure involved a gradual increase of the distance myopic subjects could accurately discriminate letters requiring a minimum of 20/20 vision at approximately 23 feet. In Experiment I experimental and matched control groups of mildly to moderately myopic subjects were compared on repeated Ortho-rater examinations of visual acuity. The experimental group showed a significant improvement relative to the control group who received no training. Multiple-baseline across-stimuli designs were used in Experiment II to evaluate training effects for another group of subjects with moderate to severe myopia. Two measures of acuity were obtained. Accuracy of discrimination of letters at various preselected distances was determined each session while Ortho-rater examinations were given periodically throughout training. Changes in discrimination accuracy over sessions appeared to be related to fading for three of the four subjects, and Ortho-rater acuity changes were observed for each subject. Some short-term maintenance of improved vision was evident on both acuity measures.

Accommodation, Ocular↗
PubMed1978

Visual acuity in hard and soft contact lens wearers: a comparison.

Visual acuity measurements with spectacles, with hard contact lenses and with hard contact lenses plus overrefraction were made on 75 eyes. Similar data was taken on 75 eyes wearing soft contact lenses. In each case, some eyes showed a decrease in visual acuity with contact lenses but the soft lenses wearers showed a greater percentage of eyes with visual acuity decrease.

Contact Lenses↗