Apparent Defective Abduction Without Diplopia.

Sixth nerve palsies present with horizontal diplopia and typically have a neurological or neurovascular aetiology. They can be confirmed by clinically evaluating the velocity of the abducting saccade, which is slowed. Three cases are presented in which the patients had apparent defective abduction of one eye, resulting from not only neurological causes but also orbital causes. Clinicians should have a high index of suspicion in patients with defective abduction without diplopia and should include apparent defective abduction without diplopia (ADAD) in the list of potential differential diagnoses, considering not only neurological involvement but also orbital involvement.