American journal of optometry and physiological optics最新文献

Control systems analysis is proposed as a method for understanding the pathophysiology of oculomotor imbalance, thereby permitting better differential diagnosis and more specific treatment. Clinical cases of nonstrabismic divergent deviations, with an emphasis on convergence insufficiency (CI) are presented and explained using conventional optometric diagnostic concepts and fixation disparity (FD) curves with control systems analysis as the central, unifying concept.

The advantages and the problems associated with use of alternating vision and simultaneous vision bifocal contact lenses are analyzed. The changes in pupil diameter associated with changes in illumination and in the distance of the task make the selection of the best bifocal design complex.

On the eye a contact lens is bathed in tear fluid, which increases its resistance to oxygen flux. For rigid gas-permeable lenses, this effect should be small during open-eye wear because a large amount of oxygen is provided by air-saturated tears that are pumped under the lens. However, under closed-eye conditions this study suggests substantial decrease in overall lens system oxygen transmissibility when lens transmissibility itself is greater than 20 x 10(-9) cm ml O2/s ml mm Hg and when the average thickness of the tear layer is greater than about 20 micron.

Patients with vertical heterophoria and a reduced ability to adapt to an induced vertical prism are appropriate patients for a vertical prismatic correction. A clinical method is presented for identifying those patients with a reduced ability to adapt to an induced vertical prism.

A single, masked controlled clinical trial showed that vision therapy improved both the accuracy and repeatability of stereophotogrammetric performance on the profiling task with experienced, visually normal observers. The average fixation disparity measured under working conditions decreased and stereoscopic acuity as measured with a Howard-Dolman apparatus increased. The data suggest that vision therapy is most helpful for those profiling situations in which disparity stimuli are plentiful and stereopsis is the dominant depth cue.

A method is described by which very small eye movements may be photographed over a wide angle, using the optical-lever technique. The method is applied to photographing eye movements for the experiment of J. Mueller. The fixating eye makes "irrelevant" movements that are not observable under direct observation or with less sensitive recording methods. The eye-movement records were measured, and the velocity and acceleration of accommodative vergence were determined for two amplitudes.

Snellen chart visual acuity is thought to change very little up to age 60 years. However, any changes in contrast in the retinal and/or neural image with age may only be detected in low contrast and low luminance testing conditions. Only under these conditions does contrast significantly influence visual acuity measurements. In this pilot experiment we show that low contrast visual acuity is considerably worse (two lines of Snellen acuity) for an older group (N = 8, mean age 57) than for a younger group (N = 9, mean age 24.6) in spite of the fact that each subject was referred to the study with 6/6 (20/20) or better acuity. At conventional contrast and luminance levels there is no significant difference between the two groups. The results also suggest that a simple measurement of contrast sensitivity for a small spot of light may allow a contrast correction factor to account for both age and luminance level differences in the contrast vs. acuity function.

Opacities in the cornea, crystalline lens, and vitreous may make conventional measurements of retinal/visual function of little value. Here, we present two psychophysical hyperacuity tests that are designed to detect and quantify retinal distortions even in the presence of substantial opacities. One test makes use of a two-dot vernier display in which directional bias as well as vernier acuity can be estimated. The second test is a multi-dot hyperacuity bisection task, which resembles a simplified Amsler grid test. By varying the spatial parameters of these stimuli, metamorphopsia may be quantified. The method is applicable both in clear and occluded ocular media.

Voluntary and reflex accommodation were measured monocularly in five normal subjects using a dynamic infrared optometer. Comparison of the peak velocity/amplitude relation (i.e., "main sequence") showed complete overlapping of the response distributions, suggesting similarity of motoneuronal controller signals for voluntary and reflex accommodation. Voluntary accommodation may represent a preprogrammed maneuver used in a variety of real-life predictable situations to optimize performance. Clinically, it may represent an important component in the training of accommodation dynamics.