chiastopic fusion

Chiastopic fusion is the fusion of two laterally separated targets by converging, with the right eye fixating the left target and the left eye fixating the right target.¹ The visual axes cross in front of the targets. The name comes from the Greek letter chi, which resembles the letter X.²

In chiastopic fusion the patient converges in front of the cards and accommodates at about the plane of the cards.³ Orthopic fusion is the opposite arrangement. The patient diverges beyond the plane of accommodation, and the visual axes cross behind the targets.^2,3

Chiastopic fusion trains convergent, or base-out, fusional reserves without prisms, lenses or glasses.^2,3 The three cats card, the Aperture Rule, Eccentric Circles and Free Space Fusion Cards all use it for convergence therapy.^2,3 The Eccentric Circles and Free Space Fusion Cards also carry antisuppression cues and accommodative controls.³