Fusional vergence

Abstract: Studies of the linear vestibulo-ocular reflex (LVOR) suggest that eye movement responses to linear head motion are rudimentary. This may be due to inadequate control of target distance (D). As D approaches infinity, eye movements are not required to maintain retinal image stability during linear head displacements, but must become increasingly large as D shortens. The LVOR in the presence of visual targets (VLVOR) was tested by recording human vertical eye and head movements during self-generated vertical linear oscillation (averaging 2.7 Hz at peak excursion of 3.2 cm) while subjects alternately fixated targets at D = 36, 142, and 424 cm. Response sensitivity rose from 0.10 deg/cm (5.8 deg/s/g) for D = 424 cm to 0.65 deg/cm (37.5 deg/s/g) for D = 36 cm. Results employing optical manipulations, including spherical lenses to modify accommodation and accommodative convergence, and prisms to modify fusional vergence without altering accommodation, imply that the state of vergence is the most important variable underlying the effect. Trials in darkness (LVOR) and with head-fixed targets (visual suppression of the LVOR) suggest that, while visual following and perhaps "mental set" influences results, the major proportion of the VLVOR response is driven by vestibular (presumably otolith) inputs.

Abstract: Purpose. The purpose of this article is to compare vision therapy/orthoptics, pencil pushups, and placebo vision therapy/orthoptics as treatments for symptomatic convergence insufficiency in adults 19 to 30 years of age. Methods. In a randomized, multicenter clinical trial, 46 adults 19 to 30 years of age with symptomatic convergence insufficiency were randomly assigned to receive 12 weeks of office-based vision therapy/orthoptics, office-based placebo vision therapy/orthoptics, or home-based pencil pushups. The primary outcome measure was the symptom score on the Convergence Insufficiency Symptom Survey. Secondary outcome measures were the near point of convergence and positive fusional vergence at near. Results. Only patients in the vision therapy/orthoptics group demonstrated statistically and clinically significant changes in the near point of convergence (12.8 cm to 5.3 cm, p 0.002) and positive fusional vergence at near (11.3 to 29.7 ,p 0.001). Patients in all three treatment arms demonstrated statistically significant improvement in symptoms with 42% in office-based vision therapy/orthoptics, 31% in office-based placebo vision therapy/orthoptics, and 20% in home-based pencil pushups achieving a score <21 (our predetermined criteria for elimination of symptoms) at the 12-week visit. Discussion. In this study, vision therapy/orthoptics was the only treatment that produced clinically significant improvements in the near point of convergence and positive fusional vergence. However, over half of the patients in this group (58%) were still symptomatic at the end of treatment, although their symptoms were significantly reduced. All three groups demon- strated statistically significant changes in symptoms with 42% in office-based vision therapy/orthoptics, 31% in office-based placebo vision therapy/orthoptics, and 20% in home-based pencil push-ups meeting our criteria for elimination of symptoms. (Optom Vis Sci 2005;82:E583-E595)

Abstract: When binocular fixation is shifted between two targets which require change in vergence as well as an equivalent or greater alteration in the mean visual direction, the observed eye motions do not--as asserted by Yarbus (1957) and widely accepted today--consist of slow symmetrical change in vergence, upon which a conjugate (binocularly balanced) saccade is additively superimposed. In all tested target configurations, an unexpectedly large fraction of the total change in vergence occurred during the saccades; observed values ranged from about 40% in certain tasks, to essentially 100% when large version (4 degrees) was combined with small vergence change (less than 1 degree). In these latter situations, binocular congruence can be restored within about 50 ms by appropriately unbalanced saccades, rather than about 500 ms, as expected if slow fusional vergence movement were required. When larger vergence changes are demanded, additivity between vergence movement and conjugate saccade is also violated in that the rate of vergence change during the saccades is several-fold larger than the rate before the saccade or during subsequent completion of the required change in vergence. Furthermore, the residual fusional vergence movement observed in these tests was usually strongly asymmetrical, and often almost entirely monocular. Vertical saccades are nearly as effective as horizontal saccades in mediating a large fraction of an intended change in vergence. In saccades, which contributed strongly to (or fully mediated) an intended vergence change, target-specific binocular differences in saccadic excursion of as much as 40-50% were observed; hence, these eye movements are not fully yoked, as the term 'conjugate' implies. Instead, the eyes behave in such situations as though visual information from each eye is processed separately prior to the saccade, in order to generate the neural signals which control open-loop saccadic movement of the eye.

Abstract: Introduction It is an imposing accomplishment of the visuomotor innervating system to continue deftly repositioning a pair of retinas so that single binocular vision is enjoyed while the eyes are scanning a distant scene. Yet, still more impressive is the ability to instantaneously shift the eyes from the distant scene to a wrist watch, identify the time, and immediately refixate the distant panorama. This feat of a swift, precise, coordinated change in the optics and alignment of the eyes which provides the finest detail of the near visual pattern to be sharply and singly seen is made possible by the near vision complex. The simultaneous application of many distinct phenomena during fixation at near makes up the near vision complex, the most important being (1) accommodation, (2) accommodative convergence, (3) fusional vergence, (4) fixation movement (version), and (5) pupillary constriction. This paper deals only with the first three components of