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Biomedical subjects

A Remole

Publications and source records attributed to A Remole.

At least 37 records · Page 2Linked to original sources
PubMed1986

Field of vergence limits.

The binocular visual field is the combined visual field obtained when the eyes are fixating a given point without head movements. The binocular field of fixation is the area within which central bifixation is possible by moving the eyes but not the head. This study introduces a new concept of the binocular field, namely, the vergence limit field, defined as the binocular field of fixation that allows for a specified amount of vergence eye movements at its limits. A newly developed instrument and technique were used to measure this field for a number of normal subjects.

Accommodation, Ocular↗
PubMed1986

Objective measurement of binocular fixation misalignment.

The amount of deviation from central fixation during binocular fusion of a vertical border was compared with conventional fixation disparity measured at the same time, forced convergence serving as the independent variable. Fixation eccentricity was measured objectively by monitoring a scleral blood vessel with a video camera and by analyzing the movement, greatly magnified, on a video screen. Fixation disparity was measured conventionally by interocular nonius alignment of vertically dissociated line segments. The results agree well with previous comparisons of these responses, in which the fixation eccentricity was measured by using a technique based on the effect of retinal stimulus location on border enhancement. As in the previous experiment, the fixation misalignment was found to be many times larger than the corresponding disparity for most forced convergence values. The large discrepancy between actual fixation misalignment and fixation disparity has thus been documented objectively as well as subjectively.

Convergence, Ocular↗
PubMed1985

Flicker haloes observed with subjective borders.

Subjective borders are known to behave quite similarly to real borders when the stimulus presents fragments of visually meaningful forms. There is less information on whether this also applies to unfamiliar stimulus elements. Thus, if a dark/bright stimulus border is presented intermittently at certain frequencies below flicker fusion, the bright border enhancement band increases greatly in width and takes on a textured appearance, resembling a halo streaming from the border. The percept is spontaneous and unlike anything experienced in real life. Preliminary observations showed that the effect occurs also at subjective borders. The extent of the halo from the border was measured for various flicker frequencies and compared with similar measurements obtained with real borders. It was found that the extent varies with frequency in an identical manner for real and virtual borders. Also, the halo was judged equal in qualitative appearance for both kinds of border. The striking similarity between virtual and real effects in this respect is best explained in terms of physiological border perception processes, possibly instigated by a cognitive mechanism.

Adult↗
PubMed1985

Fixation disparity vs. binocular fixation misalignment.

Conventional fixation disparity was compared with the corresponding foveal fixation misalignment measured by a recently developed method based on the effect of retinal eccentricity on the width of the border enhancement band. Unlike procedures using binocular nonius alignment, the method is not subject to adaptive changes in perceived direction. Forced convergence and divergence stimulation served as the independent variable. It was found that conventional fixation disparity represents only a small, constant fraction of the misalignment through the greater portion of the vergence range. However, when the misalignment is restricted to a small, central portion of the foveola, this relation changes drastically, and the fixation disparity can then be much larger than the fixation misalignment. During perfect fixation alignment of the foveal centers, there is always a significant amount of fixation disparity present. It is suggested that the large differences between fixation disparity and fixation misalignment are due to a fundamental, perceptual mechanism that is always at work during binocular vision, changing the relation between retinal location and perceived visual direction.

Convergence, Ocular↗
PubMed1985

Retinal image quality during oblique gaze through spectacle lenses: plastic vs. glass.

The optical performance of standard plastic and glass spectacle lenses was compared at increasing angles of oblique gaze up to 40 degrees on either side of the optic axis of the lenses. For this purpose, the border enhancement method was used, a method which is suitable for monitoring small order changes in the retinal image. It was found that the enhancement band width increases with obliquity of gaze in all cases, signifying a deterioration in the retinal image. A glass lens will exaggerate this deterioration to some extent, whereas a plastic lens will exaggerate it to the greatest extent. It is shown that the relatively poorer performance of plastic is due to a relatively larger amount of narrow-angle scattering than is produced by glass.

Eyeglasses↗
PubMed1984

Binocular fixation misalignment measured by border enhancement: a simplified technique.

In a previous study, a new method of monitoring binocular fixation performance was presented. The method is based upon the effect of fixation eccentricity on border enhancement: that is, the width of the enhancement band increases consistently with increasing distance of the border stimulation from the foveal center. Unlike the conventional methods of measuring fixation disparity, the procedure is essentially independent of interocular nonius alignment. However, there are some difficulties inherent in the interpretation of measurements of binocularly presented border stimulation, for it is not always clear whether the enhancement band is perceived monocularly or as a binocular average. In this study, we show how this problem can be eliminated by removing a section of the border presented to one eye, the other eye seeing a monocularly presented border segment. A secondary result of the study is a confirmation that convergence-associated accommodation does not significantly influence the enhancement measurements provided an optimum size artificial pupil is used.

Accommodation, Ocular↗
PubMed1983

Border enhancement as a function of binocular fixation performance.

Traditionally, fixation disparity is measured by interocular vertical alignment of unfusable monocular targets. The disparity generally increases with forced ocular vergences, producing characteristic individual functions. This study explores a new method of monitoring binocular fixation performance; the method is based on the effect of the distance of the border stimulus from the foveal center on the lateral spread of border enhancement. That is, as this distance increases, the enhancement spread increases. It is found that, as increasing ocular vergence is applied, the enhancement also increases, in a manner resembling conventional fixation disparity measurements. However, some dissimilarities between the border enhancement functions and the conventional functions suggest that the directional values used as a basis for the latter undergo modifications.

Accommodation, Ocular↗
PubMed1983

An instrument for mapping corneal light-scattering characteristics.

A simple inexpensive apparatus for measuring the forward light-scattering properties of excised corneas is described. The apparatus generates a light scatter profile to indicate the angular dependence of the intensity of scattered light over a 140 degree angle within a time of 9 s. The potential clinical use of light scatter measurements in the detection of corneal disease and other uses for this apparatus are discussed.

Animals↗
PubMed1983

A new eikonometer: the multimeridional apparent frontoparallel plane.

A new method for diagnosing and measuring aniseikonia is described. It is based on apparent frontoparallel plane (AFPP) settings when rod stimuli are presented in 45 and 135 degrees meridians as well as in the vertical meridian. The oblique presentation of the stimulus introduces a new approach to the study of aniseikonia. To explain the results obtained, new theoretical concepts have been presented. Clinically, the method is distinguished by its ease of application to nearly all patients with functional binocular vision.

Aniseikonia↗
PubMed1982

Spatial frequency thresholds versus border enhancement: sensitivity to retinal defocus.

Two psychophysical methods for monitoring retinal defocus are compared. One methods, spatial frequency thresholds with sine wave grids, is well known. The second methods is relatively new: it uses the effect of defocus on the width of the perceptually enhanced region of brightness or darkness generated next to a luminance edge. Both methods produce characteristic functions as the retinal image is thrown out of focus. However, spatial frequency thresholds appear relatively unchanged until a certain level of defocus has been introduced, whereas border enhancement spread is affected even by very small deviations from focus. It is suggested that variations in the frequency threshold are dampened in the near-focus range by aberrations and by the nonlinear relation between contrast and defocus, but chiefly by the resolution limit of the retina and visual pathways. However, it is found that the apparent lack of response to small deviations from focus is due to a drastic compression rather than absence of threshold changes. If responses through this region are shown on a greatly expanded scale in relation to the rest of the function. fluctuations appear that often match those generated by border enhancement.

Differential Threshold↗
PubMed1982

A new method of measuring vergence limits: the rotatory grid technique.

When equally spaced, vertical, straight lines are rotated about a horizontal axis perpendicular to the plane of the grid, the horizontal separation between the lines increases with the angle of rotation. With the grid presented binocularly, the increase in horizontal separation between the lines can be used to measure the vergence limits of subjects. Results obtained by this method were compared with those obtained by Risley prisms and by a haploscope. The new method has advantages over the traditional methods: it is not affected by the aberrations and distortions generated by prisms and it presents a more natural stimulus situation than the tubular haploscope.

Accommodation, Ocular↗
PubMed1981

Application of the aniseikonic ellipse to prisms.

The aniseikonic ellipse is derived from the meridional magnification effects of the two eyes on a circular object and represents the aniseikonic ratio in all meridians. It facilitates the analysis and prediction of aniseikonic space distortions. This study shows how the concept can be applied not only to lens magnification but also to the distortion and nonuniform magnification produced by prisms. Since prism images of a circle are asymmetrical, the corresponding aniseikonic "ellipse" is also asymmetrical. Moreover, its dimensions will vary with the nonuniform magnification across the prism. However, for small portions of the prism field it can be used conventionally as for lenses. In addition, the nonlinear binocular distortions occurring over larger portions of the field can be derived from the aggregate effect of representative aniseikonic ellipses in the various portions of the prism.

Aniseikonia↗
PubMed1981

Effect of saline solution immersion on corneal scattering characteristics.

The scattering characteristics of the cornea were measured during immersion in various saline concentrations. Initially, scattering was monitored subjectively by spatial frequency thresholds and contrast thresholds on sine wave grids, and by the border enhancement method. Although all three methods responded to corneal scattering changes produced during immersion, the latter method proved to be the most sensitive. The border enhancement method was subsequently applied during immersion of the cornea in various hypotonic and hypertonic saline solutions. Scattering changes were recorded during an immersion period of 1 hr followed by a recovery period of 1/2 hr. As expected, the scattering increased with hypotonicity. However, certain features of the time characteristics of the scattering changes suggest that the effect of the immersion fluid is modified by the tear flow.

Cornea↗
PubMed1980

Contrast thresholds versus border enhancement: effect of scattered light.

Contrast thresholds with sine wave grids, spatial frequency thresholds and border enhancement spread were measured while the amount of scattering in the retinal image was varied. Narrow-angle scattering similar to that produced by the cornea and crystalline lens was generated by specially designed filters. The purpose was to assess the effectivity of these widely different responses as measures of small order scattering effects. As noted by other investigators, spatial frequency thresholds proved insensitive to small amounts of scattering. On the other hand, contrast thresholds for high frequency targets and border enhancement spread both showed significant changes with small amounts of scattering. Of these two criteria, border enhancement proved to be the more consistent scattering index.

Humans↗
PubMed1980

Heine's principle in vergence stimulation.

When left and right pairs of vertical parallel lines are presented stereoscopically with some disparity, they fuse so that they are perceived as a single pair of lines separated in depth. Heine showed that when such line pairs are rotated about the lines of sight in the same direction and by equal amounts from the vertical, their perceived separation in depth increases, an effect which results from the increase on horizontal disparity. This report describes how certain aspects of Heine's principle can be adapted to manipulate vergence stimulation. The technique can be implemented with very simple equipment. Possible applications of this method in binocular vision management are suggested.

Accommodation, Ocular↗
PubMed1980

Flicker-induced asymmetries in border enhancement and the distinction between brightness and darkness systems.

Border enhancement is observed in a flickering bright-dark field. It is found that both the dark and the bright portions of the enhanced region increase in extent from the border during certain flicker frequencies, but not symmetrically about the border. This asymmetry is described by plotting the ratio of the dark and bright enhanced regions against stimulus frequency. The ratio fluctuates with frequency, the amplitude of the fluctuations being greatest at low frequencies. The foveal region stimulated by the border has some effect on the ratio functions. They cannot be mimicked by ratios obtained from enhancement responses to low and high luminances on either the dark or bright side of the border. It is suggested that these flicker-induced asymmetries are best understood in the context of separate neural systems for the perception of darkness and brightness.

Fovea Centralis↗