Alternating Sursumduction presents the most fascinating and challenging problems that orthoptists encounter. When it is the only disorder, it is no obstacle to binocular vision; it is evident on dissociation only, disappearing when both eyes are uncovered. But it commonly occurs together with other motor anomalies, the most usual being latent nystagmus and the A phenomenon (Lang 1968). Signs of alternating Sursumduction (=ASD) and the other anomalies present may be marked or very slight, often affecting one eye more than the other. The picture may be further complicated by refractive error and temperament.