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At least 1,099 records · Page 61Linked to original sources
PubMed1980

Stereopsis and fixation disparity following prolonged monocular occlusion.

The effects of 12 days of continuous monocular occlusion on the stereoscopic acuity and the magnitude of the fixation disparity associated with a given amount of prism-forced vergence were investigated in six adult subjects with normal binocular vision. After the period of occlusion, all six subjects were able to perceive stereopsis, although four of the six subjects demonstrated a slight but reversible elevation in stereothresholds. The general shape of the fixation disparity curve for a given individual was not altered by occlusion, but changes in the magnitude of the fixation disparity were observed for some subjects.

Adult↗
PubMed1982

Contrast sensitivity as a function of exposure duration in the amblyopic visual system.

The spatiotemporal differences between the normal and amblyopic visual systems were investigated by measuring contrast sensitivity as a function of exposure duration for specific spatial frequencies of a sine-wave grating. At threshold, normal subjects had contrast-time reciprocity curves with slopes of approximately 0.7, indicating less than perfect temporal summation. The integration time (critical duration) varied as a function of spatial frequency with longer integration times for higher spatial frequencies (in agreement with previous studies). Amblyopic subjects had integration times and reciprocity slopes that were similar to the normals for low spatial frequencies; however, at high spatial frequencies there were significant differences. These results show that an amblyopic eye may either lack sustained neurons or alternately have sustained neurons with abnormal response characteristics.

Amblyopia↗
PubMed1983

Effects of defocus on monkey (Macaca nemestrina) contrast sensitivity: behavioral measurements and predictions.

An observer's contrast sensitivity function (CSF) can be affected by degradation of either the optical or neural components of the visual system. In a continuing effort in this laboratory to separate these two components in infant and mature monkeys, we have measured behavioral CSF's with the retinal image defocused by as much as 6 D. With increased defocus, sensitivity decreases much more rapidly at high spatial frequencies than at low frequencies. Furthermore, we find that calculations of retinal image contrast, based upon available optical parameters of the monkey eye, underestimate the amount of optical defocus which still allows pattern detection by our monkeys at high spatial frequencies. Several possible explanations for this apparent conflict are discussed, including optical aberrations present in the primate eye, and the "spurious resolution" of defocused sinusoidal gratings.

Animals↗
PubMed1983

Contrast sensitivity in albinotic patients.

Vertical and horizontal grating contrast sensitivity functions (CSF) were measured on eight albinotic patients. Several of these patients also had CSF measurements performed through their telescopic aids. For all the patients, the horizontal grating CSF was more sensitive than the vertical grafting CSF. Although there are many pathological problems that could result in this sensitivity difference (high astigmatism, neural modification, etc.), we propose that in this case, the nystagmoid eye movements are the main causative factor. Through the telescopic aid, the CSF resolution acuity and peak sensitivity increased. The increase in resolution was somewhat less than would be predicted based on magnification. The increase in sensitivity is believed to be the result of stimulation of more sensitive peripheral retina. This increase in sensitivity is an added benefit to these patients corrected with low vision aids.

Albinism↗
PubMed1984

Large-sample norms for contrast sensitivity.

A portable microprocessor-controlled instrument automatically measured the static and dynamic contrast sensitivity functions (CSF's) of 265 observers for a normal population at the Dayton Air Fair and Air Force Museum. Repeat measures for six observers taken 6 months later show small, nonsystematic differences from original measurements. Median values of contrast sensitivity as well as regions encompassing 75 of 90% of our sample are shown.

Adult↗
PubMed1984

An anticipated threshold technique for measuring contrast sensitivity.

A new psychophysical procedure for assessing contrast sensitivity rapidly and reliably is reported. The technique consists of increasing the contrast of a conventional sine wave grating according to the parameters set in a computer implemented algorithm. During the first half of a trial, the contrast increases quickly to a point just below an expected threshold, and in the second stage the contrast increases slowly until a threshold is reached. Details and advantages of the algorithm are presented as well as a comparison of data generated by this and other techniques.

Computers↗
PubMed1985

Effect of restricted viewing time on mid-match points for normal observers on the Moreland and Pickford Nicolson anomaloscopes.

Restricted viewing time has previously been shown to produce a tritan classification for color normal observers on the City University Colour Vision Test (CUCVT). The present investigation, which uses the Moreland anomaloscope, studies the effect of restricted viewing time on mid-match point (MMP). It shows that a color normal observer requires more green in a match under these conditions. A study of the Rayleigh equation using the Pickford Nicolson anomaloscope shows that restricted viewing time does not affect the MMP for this metameric match for color normal observers.

Adult↗
PubMed1986

Vision and refractive status among grade 1 children of the Province of New Brunswick.

A public health program instituted and funded by the Government of the Province of New Brunswick and operated by the Provincial Optometric Association screened 10,464 grade 1 children using a modified clinical technique (MCT). This paper reports the prevalence of refractive and sensory-motor anomalies in large samples of this child population, all of whom were 6 years of age.

Child↗
PubMed1986

Population norms for edge contrast sensitivity.

The contrast sensitivity (CS) for a single edge appears to be a reliable indicator of the peak of the contrast sensitivity function (CSF). We propose that for general clinical practice and in the functional assessment of patients with low vision, the simple measurement of edge CS provides an adequate indicator of the peak of the CSF. We conducted a trial in which edge CS was measured in a routine clinic setting.

Aging↗
PubMed1987

Changes in contrast sensitivity during the first six months of soft lens wear.

Changes in the contrast sensitivity function (CSF) and corneal thickness of six subjects were monitored during the first 6 months of soft lens wear. Contrast sensitivity suffered a temporary reduction during the first two weeks of wear, subsequently recovering rapidly to normal baseline levels. Corneal thickness increased by 4.9% on the first day of wear, thereafter gradually returning to, but never attaining, prefitting levels. No evidence was found to support complaints of poor vision by long-term soft lens patients. The etiology of the contrast decrements revealed in the early (or adaptation) stages of soft lens wear is discussed.

Adolescent↗
PubMed1988

Effect of hydrogel lens wear on contrast sensitivity.

Conflicting reports on the adequacy of the visual performance provided by hydrogel contact lenses continue to appear in the literature. We conducted a study to determine the effect on visual performance, as assessed by contrast sensitivity measurements, of (1) lens wear of optimally fitting 38% water content lenses and (2) altered lens parameters, including fitting characteristics, of 38% and 67% water content lenses. During normal wear of lenses, neither the lenses themselves nor any contact lens-induced corneal changes produced measurable visual losses. The visual performance was also independent of lens fit or lens thickness over the ranges used here. The higher water content lenses provided marginally poorer visual performance.

Contact Lenses, Hydrophilic↗
PubMed1989

Peripheral visual acuity with monovision and other contact lens corrections for presbyopia.

We have conducted two experiments to investigate the effect of monovision and other contact lens corrections for presbyopia upon peripheral visual acuity. In the first study, we measured binocular peripheral visual acuity using Landolt rings with seven subjects wearing a monovision correction. The Landolt rings were presented at eccentricities of 10, 20, 40, and 70 degrees on each side of the subject, with near additions of +1.50 D, +2.50 D, and no addition. We found no significant effect of monovision correction on peripheral visual acuity. In the second experiment we measured the peripheral visual acuity of 11 presbyopic subjects wearing distance contact lenses with lookover spectacles, soft progressive bifocal contact lenses, soft concentric bifocal contact lenses, monovision contact lenses, modified monovision contact lenses, and hard bifocal contact lenses using Koenig bar targets. There were no significant differences in peripheral visual acuity between any of the contact lens corrections for presbyopia.

Adolescent↗
PubMed1989

Effect of defocus on visual acuity as measured by source and observer methods.

The relation between refractive error and visual acuity has been measured by two very different methods. In one called "source methods," emmetropes or corrected ametropes view defocused stimuli presented on projection screens or photographs. In the type called "observer methods," focused stimuli are presented to the observers who are either uncorrected ametropes or emmetropes defocused by lenses placed (usually), in the spectacle plane. The study reported in this paper demonstrates for the first time that these two methods of defocusing retinal images and their effects on visual acuity can be correlated. Results show that the source method of producing defocus could be used interchangeably with the observer method in investigating the rates of change of visual acuity with defocus for young normal observers. The angular diameter of the defocused image of a point, the blur disc diameter in object space, allows the two methods to be compared. Although the results show that the two methods are highly correlated, they show that the source method gives a statistically but not clinically significant lower acuity. The results of both methods are used to derive an equation linking refractive error, visual acuity, and pupil diameter.

Accommodation, Ocular↗
PubMed1989

Central and peripheral sensitivity to temporally modulated stimuli presented to the sighting and nonsighting eyes.

Thirty-two visually normal observers showed reduced sensitivity to uniform field flicker in the fovea of the nonsighting eye relative to the sighting eye. The two eyes showed equal sensitivity to flicker in the peripheral retina. This result with visually normal observers is analogous to that found in observers with functional amblyopia. It is also consistent with the hypothesis that amblyopic and normal suppressive processes share a common mechanism.

Contrast Sensitivity↗
PubMed1989

Accommodation to size and blur changing in counterphase.

We explored the influence of changing size and blur on accommodation by presenting the two stimuli sinusoidally in counterphase. The frequency response of the accommodative system (0.05 to 1 Hz) was determined using a high-speed infrared optometer while the subject viewed the target in a Badal optometer. Blur was provided by moving the target dioptrically toward and away from the subject, and size of the target was altered by a variable aperture. Both stimuli were varied sinusoidally at the same frequency, but in counterphase. We find that both size and blur can have an influence on accommodation: blur is particularly powerful at low temporal frequencies, whereas size becomes effective at moderate and high temporal frequencies.

Accommodation, Ocular↗
PubMed1989

Binocular vision without visual stress.

The use of changes in fixation disparity, the associated phoria, and the dissociated phoria in assessing the degree of visual stress requires that we know the effect of vision under close working conditions (40 cm) on these parameters. The authors have previously reported that reading under the stress of abnormally low illumination, or at too close a working distance (20 cm), increases fixation disparity and associated phoria and is associated with symptoms and visual discomfort. The current study shows that reading at photopic levels of illumination and at a working distance of 40 cm does not change the magnitudes of fixation disparity and associated phoria. Reading under these conditions is not accompanied by an onset of symptoms or visual discomfort. This result indicates that changes in fixation disparity and associated phoria are a product of visual stress and are not produced by reading itself.

Adolescent↗