Positional eye movement assessment is an important but perhaps under-utilised component of the eye movement assessment, helping not only in the diagnosis of BPPV, but also a range of central neurological disorders such as Chiari malformation, multiple sclerosis, and multiple system atrophy . Correct identification of positional eye movements can be complicated by extraneous eye and eyelid movements that may occur during the examination. Whilst this may be true of other neuro-ophthalmological assessments , in the context of a positional nystagmus, that may be brief, involve complex (sometimes disconjugate) eye oscillations, and may be transient, the ability to differentiate organic (vestibular or cerebellar) eye movements from functional eye/eyelid movements becomes more pertinent.
Convergence spasm remains the only functional positional eye movement that has been reported in the neurological literature [6, 7]. Given the frequency of convergence spasm across outpatient neurology, it is perhaps not surprising that it also appears to be the most commonly observed functional positional eye movement [8, 9]. It can be distinguished from organic causes of ocular esodeviation (most notably sixth nerve palsies) when the convergence is accompanied by pupillary constriction , particularly if it occurs with suggestion (case 1, Video 1). The first patient described in this report (case 1) had a background of positional downbeat nystagmus , most likely accounting for the persistent symptoms of dizziness and associated visual disturbance with head movement. The positional convergence spasm appeared to be asymptomatic, although if occurring whilst supine may have explained the visual blurring when reading in bed.
In the second case, the patient developed persistent blinking and blepharospasm-like eyelid movements, present only during the positional provocation manoeuvre, and not present during the ‘casual’ examination, again indicative of a functional disorder  or a secondary reaction to the provocation manoeuvre. Of note, the frequent blinking induced a recurrent Bell’s phenomenon (upward deviation of the globe occurring during eyelid closure), that could be confused for upbeat nystagmus, or indeed oculogyric crises . The latter however, is typically accompanied by pain, precipitated by use of neuroleptics, and would not be expected to occur exclusively during a positional manoeuvre . Case 2 was diagnosed with PPPD and vestibular migraine, a recognized trigger for PPPD , and his symptoms improved with cognitive behavioural therapy for PPPD, and upon repeat examination 4 months after finishing treatment the excessive blinking, and positional vertigo, had disappeared. The temporal relationship between the treatment and resolution of clinical signs suggests that the positional symptoms were either related to PPPD, or more likely associated with vestibular migraine , that was now less active.
In cases 3 and 4 we observed horizontal saccadic oscillations mimicking ocular flutter, that are distinguished from this by their brief duration and their modulation by distraction . Moreover, our patient manifest saccadic oscillations only during positional testing—a feature that is not observed in organic flutter. Our patient (case 3) had undergone detailed brain imaging, positron emission tomography and cerebrospinal fluid assessment in relation to his previous lymphoma, but such investigations can be held in abeyance where a thorough examination of the eye movements is suggestive of a functional cause. The symptom of the patient in case 3 fulfilled the criteria for vestibular migraine, and he was offered treatment with Flunarizine. He declined treatment and both symptoms and the positional eye movements persisted at follow-up 6 months later. Whilst in case 3 the positional manoeuvre did not reveal additional organic eye movements, the saccadic oscillations observed in case 4 were accompanied by brief crescendo-decrescendo torsional nystagmus, typical for posterior canal BPPV. We propose that the ensuing saccadic oscillations were a reaction to the BPPV-related positional vertigo, or perhaps an involuntary attempt at suppressing the positional symptoms.
A co-association of organic and functional symptoms or signs is common in neurological disorders . The presence of functional positional eye/eyelid movements with organic nystagmus and vertigo suggests these functional movements may represent an attempt to suppress the underlying nystagmus (and thus reduce the intensity of accompanying vertigo) or be an expression of the discomfort experienced during the manoeuvre, as in the case of functional eye blinking. The latter highlights the importance of adequate explanation and reassurance prior to performing a positional manoeuvre, particularly in individuals susceptible to anxiety. In all cases presented, the functional eye movements were largely asymptomatic and resolved either spontaneously (case 1), or with treatment of the underlying precipitant (cases 2, 4), without the need for specific interventions. Finally, a careful eye movement assessment in patients presenting with vertigo or imbalance necessitates a positional manoeuvre to correctly identify vestibular disorders, and associated functional signs, thus allowing appropriate treatment and avoiding unnecessary investigations.