In this patient, there is a mild esotropia on neutral gaze as the left eye is slightly deviated medially. There is impaired left eye abduction resulting in diplopia when the patient is instructed to look towards the left.
Discussion of the sign
Abduction of the eye is controlled by the lateral rectus muscle, which is innervated by the ipsilateral sixth cranial nerve (abducens nerve). Common causes of an impaired eye abduction include disorders affecting the abducens nucleus located in the pons (e.g. due to a stroke or demyelinating disease) and also disorders affecting the abducens nerve. Sixth nerve palsies may be the consequence of microvascular neuropathies (e.g. due to hypertension, diabetes mellitus or vasculitis). Due to its long intracranial course, sixth nerve palsies also commonly occurs in patients with raised intra-cranial pressure as a “false-localising sign”. Sixth nerve palsies may also occur (usually in combination with other cranial nerve palsies) in patients with pathologies affecting the petrous apex or cavernous sinus.