Spatial scaling of the binocular capture effect.

Purpose: Binocular "capture" occurs when the perceived visual direction of a monocular stimulus is displaced in the direction of the cyclopean visual direction of nearby binocular targets. This effect increases with the vertical separation of broadband monocular stimuli. The present study investigated whether the "capture" effect exhibits a systematic relationship with the spatial frequency composition of monocular lines and vertical separation.

Stereopsis from a performance perspective.

Purpose: A patient can demonstrate a poor stereoscopic test or task performance for reasons inherent within the test/task itself for reasons dependent on normal physiology common to all human subjects, and also for reasons that are outside of normal physiology and are unique or idiosyncratic to a particular person's visual system. This article reviews the literature for the first two reasons, but emphasizes the pathophysiology involved in the idiosyncratic and abnormal reasons.

Results: Using control systems analysis, it is shown that deficits in stereoscopic performance can be explained by reference to the quantitative aspect of stereoscopic threshold and qualitative aspects such as speed of response, reliability-robustness, and strength of percept.

Effects of heterophoria on stereopsis.

The effects of horizontal heterophoria on Howard-Dolman stereopsis scores were investigated in a population of 1765 stereophotogrammetrists with no obvious impediment to binocular vision as determined in a vision screening. Exophoria over the 1 to 7 delta range showed no systematic and statistically valid effect on stereopsis but esophoria did show an effect. In a related population of 1339 stereophotogrammetrists, subjects with as little as 1 delta (+/- 0.

Interpretation of divergent oculomotor imbalance through control system analysis.

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.

Effect of vision therapy on stereophotogrammetric profiling--a controlled clinical trial.

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.

Convergence insufficiency, fixation disparity, and control systems analysis.

The diagnosis and management of convergence insufficiency (CI) is discussed through a control systems model of the combined accommodation and disparity vergence mechanisms. The emphasis is put on drawing definite clinical implications such that CI can be understood as a logical continuum from its etiology, through symptoms, signs, and finally through its treatment.

Fusion lock diameter and the forced vergence fixation disparity curve.

The effect of the diameter of the fusion lock on the forced vergence fixation disparity (FD) curve was investigated because of ambiguity in the results of previous investigations. Data gathered from 20 asymptomatic subjects with normal binocularity showed that the fusion lock diameter had no noticeable effect on the shape of the curve. Further investigations using symptomatic subjects showing large FDs or steep forced vergence FD curves showed that fusion lock diameter did have an effect on the curves of these subjects.

Effect of orthoptic procedures on stereoscopic acuities.

Ten stereophotogrammetry students and three graduate photogrammetrists were given 7 weeks of nonspecific orthoptic exercises. The visual systems of these 13 experimental subjects were matched to those of 13 control subjects chosen from the students and staff of the Ferris State College of Optometry. Stereoscopic acuities were determined before and after the training period on both groups using a Wild Stereoplotter, a Howard-Dolman apparatus, and the Keystone Multi-Stereo Test.

The relation between night myopia and accommodative convergence.

Accommodation and convergence normally bear a tight relation to each other. To the extent that night myopia is due to an actual change in lens convexity, accommodation in night myopia should be accompanied by a commensurate change in convergence. This prediction was shown to be false because of variability in the convergence mechanism.

Population study of fixation disparity, heterophoria, and vergence.

Data on phorias, vergences, and fixation disparities were gathered for distant and near viewing conditions from a nonclinical, young adult population. Normative values were computed from the data for analysis and comparison. Our study revealed slightly less exophoria at far and near than Morgan's study, together with large base-out vergence readings.