As with all aspects of the neurological examination, important clues come from a thorough and appropriate history. In relation to eye movement disorders the patients may be complaining of double vision, in which case they should be asked whether it is constant or intermittent; does it occur, or is it maximal, in certain directions of gaze; what is the relationship of one image with the other; and have they tried covering one eye and did that relieve the symptom? A less frequently reported symptom is oscillopsia, an illusion of movement of stationary objects, when enquiries need to be made whether the movement is horizontal or vertical, and does it become maximally apparent in certain positions of gaze, as for example in downbeat nystagmus when the oscillopsia is maximal on down gaze. Nystagmus will not be described here and has been covered in a previous article in Practical Neurology .1 The first part of any examination is observation and again this may provide clues to the diagnosis. Look out for abnormal head postures, turns or tilts, the latter typically occurring in an isolated trochlear nerve palsy; abnormal patterns of eye–head coordination, such as the head thrusts seen in ocular motor apraxia; abnormalities of the eyelids such as ptosis in an oculomotor palsy and myasthenia gravis, or retraction as is seen in thyroid ophthalmopathy and progressive supranuclear palsy. We are now ready to examine the eye movements, hopefully with the benefit of some clues to the diagnosis already obtained from the history and simple observation of the patient. ### Ocular misalignment First ask the patient to look at a distant object and observe any obvious ocular misalignment or abnormal, spontaneous eye movements. If one eye is deviated inward relative to the other this is referred to as an esotropia , whereas if there is …