Intermittent diplopia: a practical guide

Intermittent binocular diplopia is challenging to assess, as symptoms may be absent during examination yet its possible causes range from benign decompensation to serious disease. We outline a practical method to evaluate intermittent diplopia, focusing on four key steps: (1) confirming binocular diplopia, (2) assessing monocular ductions to detect paretic or restrictive deficits, (3) determining comitance (whether the angle of strabismus is equal in all directions of gaze) to distinguish fusional from neurological or orbital causes and (4) evaluating fatigability to identify ocular myasthenia. We emphasise clinical scenarios requiring targeted testing, including giant cell arteritis and malignancy and discuss when orthoptic or ophthalmic referral is more appropriate than extensive neurological investigation. We also describe recognisable neurological entities such as ocular neuromyotonia and superior oblique myokymia. We aim to provide clinicians with an efficient method to assess intermittent diplopia, avoid unnecessary investigations and ensure that important pathology is not missed.