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At least 577 records · Page 32Linked to original sources
PubMed1997

A reduced motion aftereffect in strabismic amblyopia.

The motion aftereffect was measured using both static and dynamic test stimuli in a group of normal observers and a group of strabismic amblyopes. Amblyopes exhibited a reduced direct aftereffect for both static and dynamic stimuli and only two of the eight amblyopes exhibited any measurable interocular transfer for either test stimulus. It is hard to explain these results in terms of either the known spatial (contrast sensitivity and positional sensitivity) or motion deficits previously reported in amblyopia. These results suggest a primary motion deficit in amblyopia affecting both the static and dynamic motion aftereffects.

Adaptation, Ocular↗
PubMed1995

Spectacle lenses alter eye growth and the refractive status of young monkeys.

The influence of visual experience on ocular development in higher primates is not well understood. To investigate the possible role of defocus in regulating ocular growth, spectacle lenses were used to optically simulate refractive anomalies in young monkeys (for example, myopia or nearsightedness). Both positive and negative lenses produced compensating ocular growth that reduced the lens-induced refractive errors and, at least for low lens powers, minimized any refractive-error differences between the two eyes. These results indicate that the developing primate visual system can detect the presence of refractive anomalies and alter each eye's growth to eliminate these refractive errors. Moreover, these results support the hypothesis that spectacle lenses can alter eye development in young children.

Accommodation, Ocular↗
PubMed2005

Accuracy of GDx variable corneal compensation polarization measurements in normal human eyes: effect of accommodation, cycloplegia, focus, pupil size, and eye selection on reproducibility.

PURPOSE: To evaluate the reproducibility of variable corneal compensation (VCC) and the effect of accommodation, cycloplegia, eye selection, focus, and pupil size on this measurement of polarization. METHODS: Using a GDx scanning laser polarimeter, multiple measurements of the VCC were obtained from each eye of 33 healthy, young adults under differing conditions. Pupil size and refraction were independently measured with a pupillometer and an autorefractometer. The effects of eye, instrument focus, pupil diameter, cycloplegia, and accommodation were statistically assessed. RESULTS: The reproducibility of a single retardation measurement and its axis, as determined by the standard deviations (SD) of repeated measurements, is +/-1.58 nm and 2.10 degrees , respectively. There is a difference in retardation between right and left eyes, of 5.26+/-9 nm, P=0.002. Increasing pupil size increases retardation. Cycloplegia or defocusing decreases retardation, and pharmacologically induced accommodation has no effect on retardation. CONCLUSIONS: The retardation and its axis are highly reproducible measurements when the pupil is of physiologic size and the GDx is properly focused. There is a consistent difference in VCC retardation between the paired right and left eyes. This difference may reflect equipment-induced measurement artefact and/or an anatomic asymmetry between the paired eyes of the subjects studied. Clinicians should be cautious when comparing interocular VCC measurements between paired right and left eyes and using data pooled from both eyes for age-adjusted, normalized standards.

Accommodation, Ocular↗
PubMed1987

The recovery of structure from motion: no evidence for a special link with the convergent disparity mechanism.

Convergent and divergent stereo mechanisms were compared in their ability to recover structure from motion. Contrary to a recent result reported by Richards and Lieberman, no difference in their performance was found; both mechanisms appeared equally capable of supporting the perception of good structure from motion. Possible reasons for the disparate results are discussed.

Attention↗
PubMed1994

Convergence responses to monocularly viewed objects: implications for distance perception.

In four experiments the role of dark vergence and the implied distance from the familiar-size and suggested-size cues to distance on the convergence response was investigated. A nonius-alignment technique was used to measure the convergence response in total darkness (dark vergence) and the fusion-free convergence response to monocularly viewed objects presented at a distance of 75 cm under otherwise reduced stimulus conditions. Observers also estimated the size and distance of the objects. The results indicated a significant association between individuals' dark-vergence distances and the convergence distances to the objects. Furthermore, the convergence response was influenced by the implied distance from the familiar-size cue but not by the implied distance from size suggestions. Both the familiar-size and the suggested-size cues influenced reports of distance. The implications of these findings for distance perception are discussed with particular reference to the familiar-size cue to distance.

Adult↗
PubMed1984

Reading performance and eye-movements through Varilux 2 and ST-25 lenses.

Reading rate, reading comprehension, and photoelectrically recorded eye movements while reading through Varilux 2 and ST-25 lenses were compared for seven subjects who were predominantly myopic, who ranged from 25 to 60 years of age, and who wore adds of 1.00 to 2.25 D. Tests were done at near (40 cm) and intermediate (57 cm) distances before and after a month of adaptation to the lenses using paragraphs that subtended less than 14 deg. A three-way analysis of variance indicated no significant differences in performance between the two types of lenses.

Adaptation, Ocular↗
PubMed1992

Current perspective on microfluctuations of accommodation.

The collaboration of Fergus Campbell, Gerald Westheimer and John Robson in the 1950s produced insight into the nature of accommodation microfluctuations and instigated work which has led to the current view that the nominally steady-state accommodation response exhibits temporal variations which can be characterized by two dominant regions of activity: a low-frequency component (LFC less than 0.6 Hz) and a high-frequency component (HFC greater than or equal to 1.0 less than or equal to 2.3 Hz). A functional role has been attributed to these microfluctuations as they offer a means by which a directional cue could be derived from an even-error stimulus. However, there is no consensus regarding the respective contribution made by each of the dominant components in the accommodation control process. Using a newly-designed measurement and recording system we have conducted a series of experiments to investigate the nature and aetiology of the microfluctuations. The incidence and magnitude of microfluctuations in LFCs and HFCs for central and peripheral lens zones were investigated while five young emmetropic subjects viewed a near target. The form of the power spectra of the fluctuations was found to be similar for central and peripheral zones although an overall reduction in magnitude was observed in the periphery. The HFCs are thus a consistent feature of microfluctuations in central zones and not, as previously suggested, merely a spurious feature of peripheral zones. A significant between-subject variation in the location of HFCs was found and led us to consider the relationship between HFCs and other physiological systems which provide intraocular rhythmic variation.(ABSTRACT TRUNCATED AT 250 WORDS)

Accommodation, Ocular↗
PubMed2005

Focus cues affect perceived depth.

Depth information from focus cues--accommodation and the gradient of retinal blur--is typically incorrect in three-dimensional (3-D) displays because the light comes from a planar display surface. If the visual system incorporates information from focus cues into its calculation of 3-D scene parameters, this could cause distortions in perceived depth even when the 2-D retinal images are geometrically correct. In Experiment 1 we measured the direct contribution of focus cues to perceived slant by varying independently the physical slant of the display surface and the slant of a simulated surface specified by binocular disparity (binocular viewing) or perspective/texture (monocular viewing). In the binocular condition, slant estimates were unaffected by display slant. In the monocular condition, display slant had a systematic effect on slant estimates. Estimates were consistent with a weighted average of slant from focus cues and slant from disparity/texture, where the cue weights are determined by the reliability of each cue. In Experiment 2, we examined whether focus cues also have an indirect effect on perceived slant via the distance estimate used in disparity scaling. We varied independently the simulated distance and the focal distance to a disparity-defined 3-D stimulus. Perceived slant was systematically affected by changes in focal distance. Accordingly, depth constancy (with respect to simulated distance) was significantly reduced when focal distance was held constant compared to when it varied appropriately with the simulated distance to the stimulus. The results of both experiments show that focus cues can contribute to estimates of 3-D scene parameters. Inappropriate focus cues in typical 3-D displays may therefore contribute to distortions in perceived space.

Accommodation, Ocular↗
PubMed1989

Visual accommodation and target detection in the vicinity of a window post.

The visual environment of a driver in a car or a pilot in an airplane has intervening objects from the vehicle such as A-pillar posts between the windscreen and the doors in the car or cockpit pillars in the airplane. The presence of such objects can bias the observer's visual accommodation response because of the Mandelbaum effect (e.g., Owens, 1979). When subjects were allowed to focus toward a distance by looking through a large aperture in an intervening post, the detection (monocular) of a briefly presented distant target was found to be significantly better than when no aperture was present. When the size of the aperture was decreased from 2.3 to 1.15 deg diameter, target detection performance was significantly decreased and remained constant as further reduction of foveal cues was made. Although the detection results were generally in agreement with the visual accommodation results, detection accuracy changed significantly only with marked changes in accommodation. In addition to an accommodation bias, interference to target detection was also observed for those targets occurring at a laterally proximal position to the intervening object.

Accommodation, Ocular↗
PubMed1986

Adaptive gain control of saccadic eye movements.

Properties of gain adaptivity in the saccadic system were studied. Subjects had to track a target which moved in single or double steps. The first target step which elicited the primary saccade had an amplitude in the range of 8-16 deg. The primary saccade triggered a further target displacement of 4 deg either in the same or--in different experimental sessions--in the opposite direction of the first target step. These consistent intrasaccadic target displacements lead to adaptive changes of saccadic amplitudes. The experimental data show that the saccadic system adapts to the stimulus sequence in a simple, parametric manner, namely by changing its gain. Consequently, it is assumed that a single gain element determines saccade sizes for all target eccentricities. Further, it is shown that adaptation has different time courses for gain increase and decrease, and its performance is close to completeness. The results are discussed with respect to the undershooting behaviour of goal-directed saccades and the functional demands to the saccadic system.

Adaptation, Ocular↗