Increased onset of vergence adaptation reduces excessive accommodation during the orthoptic treatment of convergence insufficiency

Abstract

This research tested the hypothesis that the successful treatment of convergence insufficiency (CI) with vision-training (VT) procedures, leads to an increased capacity of vergence adaptation (VAdapt) allowing a more rapid downward adjustment of the convergence accommodation cross-link. Nine subjects with CI were recruited from a clinical population, based upon reduced fusional vergence amplitudes, receded near point of convergence or symptomology. VAdapt and the resulting changes to convergence accommodation (CA) were measured at specific intervals over 15 min (pre-training). Separate clinical measures of the accommodative convergence cross link, horizontal fusion limits and near point of convergence were taken and a symptomology questionnaire completed. Subjects then participated in a VT program composed of 2.5h at home and 1h in-office weekly for 12-14 weeks. Clinical testing was done weekly. VAdapt and CA measures were retaken once clinical measures normalized for 2 weeks (mid-training) and then again when symptoms had cleared (post-training). VAdapt and CA responses as well as the clinical measures were taken on a control group showing normal clinical findings. Six subjects provided complete data sets. CI clinical findings reached normal levels between 4 and 7 weeks of training but symptoms, VAdapt, and CA output remained significantly different from the controls until 12-14 weeks. The hypothesis was retained. The reduced VAdapt and excessive CA found in CI were normalized through orthoptic treatment. This time course was underestimated by clinical findings but matched symptom amelioration.

Changes in stimulus and response AC/A ratio with vision therapy in Convergence Insufficiency

“…Poor vergence adaptation13, 18, 19 reduced ability of the system to make rapid changes to the decay of the convergence accommodation (CA) amplitudes,18, 19 unstable monocular preference 23 and asymmetry in eye movements, and convergence peak velocity 24 have been reported to be associated with CI. Vision therapy or orthoptic training program has been shown to improve the vergence adaptation, improve the decay of the convergence accommodation output, and eye movement parameters in CI 15, 19, 24.…”

“…Vision therapy or orthoptic training program has been shown to improve the vergence adaptation, improve the decay of the convergence accommodation output, and eye movement parameters in CI 15, 19, 24. Brautaset and Jennings 17 evaluated the effect of orthoptic treatments on the stimulus AC/A and CA/C ratio in six CI subjects and reported no change in the parameters after 12 weeks of home vision training.…”

“…It is hypothesized that conventional orthoptic therapy such as pencil push-up exercises alone may not improve the vergence adaptation as the stimulus to both accommodation and vergence are congruent in such training 18, 19. A structured in-office VT program where the therapy is designed in a way that the accommodation and vergence systems are incongruent may improve vergence adaptation and clinical vergence parameters 8, 9, 19.…”

“…Best corrected visual acuity better than 6/6, N6 and stereopsis >100 arc seconds were common criteria for both the cases and controls. The inclusion criteria for the control group included; BCVA better than 6/6, N6 (with appropriate refractive correction), normal accommodative and vergence parameters, 19 absence of any binocular vision anomaly, any ocular pathology, and/or any other exclusion criteria (Table 1). The controls were recruited from the student and staff population who were novice to the testing procedures as that of the cases.…”

“…Literature reporting near phoria changes with vision therapy is equivocal 14, 15, 16, 17. Recent studies have reported that vergence adaptation and concurrent decay of convergence output could be improved with a standard VT protocol 18, 19. If poor vergence adaptation is the underlying mechanism in CI, it would be logical to predict that the change in vergence adaptation would alter the cross link ratios of accommodative convergence to accommodation (AC/A) and convergence accommodation to convergence (CA/C).…”