Change in convergence and accommodation after two weeks of eye exercises in typical young adults

Abstract

Background: Although eye exercises appear to help heterophoria, convergence insufficiency, and intermittent strabismus, results can be confounded by placebo, practice, and encouragement effects. This study assessed objective changes in vergence and accommodation responses in naive young adults after a 2-week period of eye exercises under controlled conditions to determine the extent to which treatment effects occur over other factors.

Methods: Asymptomatic young adults were randomly assigned to one of two no-treatment (control) groups or to one of six eye exercise groups: accommodation, vergence, both, convergence in excess of accommodation, accommodation in excess of convergence, and placebo. Subjects were tested and retested under identical conditions, except for the second control group, who were additionally encouraged. Objective accommodation and vergence were assessed to a range of targets moving in depth containing combinations of blur, disparity, and proximity/looming cues.

Results: A total of 156 subjects were included. Response gain improved more for less naturalistic targets where more improvement was possible. Convergence exercises improved vergence for near across all targets (P = 0.035). Mean accommodation changed similarly but nonsignificantly. No other treatment group differed significantly from the nonencouraged control group, whereas encouraging effort produced significantly increased vergence (P = 0.004) and accommodation (P = 0.005) gains in the second control group.

Conclusions: True treatment effects were small, significantly better only after vergence exercises to a nonaccommodative target, and rarely related to the response they were designed to improve. Exercising accommodation without convergence made no difference to accommodation to cues containing detail. Additional effort improved objective responses the most.

Fig 1

The remote haploscopic videorefractor. The two targets (brightly colored clown target or Gabor image were designed to maximize or minimize blur cues, respectively). A, motorized beam. B, target monitor, moving between fixation distances. C, upper concave mirror. D, lower concave mirror. E, “hot” mirror. F, image of subject's eye, where occlusion takes place. G, PlusoptiX S04 PowerRef II. H, headrest. J, black cloth screen, which can be raised to occlude the target when required.

Fig 2

Response gain changes. Change in mean response gain according to cue condition (shaded sections on x-axis) and exercise group (lower text on x-axis) within cue condition A gain of 1.0 indicates perfect performance for target demand. A, Vergence gain change. In all cases above, reduced gain is due to underperformance for near. B, Accommodation gain change. B, blur available; D, disparity available; P, proximity/looming available; O, minimal cue condition.

Fig 3

Mean improvement in gain across all cue conditions for the different treatment groups. Error bars denote standard error of the mean. An improvement in gain of 0.1 denotes approximately 0.3 D or 0.3 meter angles at 33 cm (approximately 2^Δ for an interpupillary distance of 6 cm). Asterisks denote significant differences from the nil (no treatment) group.

Fig 4

Change in responses at 33 cm after treatment. Convergence in meter angles (1 = approximately 6^Δ for average adults); accommodation in diopters. Stimulus: bpd, blur + proximal + disparity; bd, proximal removed; bp, disparity removed; dp, blur removed; b, blur only; d, disparity only; p, proximal only; o, none.