Optic ataxia: a specific disruption in visuomotor mechanisms. I. Different aspects of the deficit in reaching for objects

Visually directed arm movements have been studied by film recordings in 10 patients with optic ataxia resulting from unilateral lesions of the parietal region, in 3 cases on the right and in 7 on the left. Half of the patients also underwent visuospatial perceptive tests. The results indicate the following. (1) Optic ataxia is a specific visuomotor disorder, independent of visual space misperception. (2) The proximal and the distal components of the movements are equally affected as shown in reaching and hand orientation tasks. (3) The percentages of spatial and orientation errors quantified, respectively, in these two situations show a different distribution across the different hand-field combinations according to the side of the lesion: whereas the right-damaged patients show a deficit essentially related to a field effect, the left-damaged patients show in addition to the latter an impairment related to a hand effect. These findings suggest that the 2 types of visuomotor mechanisms responsible for the proximal and distal components of visually-directed arm movements are controlled by the parietal cortex and that there should exist a hemisphere asymmetry in the functional organization of these mechanisms. (4) Reconstruction of the lesions drawn from CT scans in 8 of the patients shows a salient and constant involvement of the posterior parietal cortex, always including the intraparietal sulcus and either the superior part of the inferior parietal lobule or more often various parts of the superior parietal lobule. The weak co-occurrence of optic ataxia and hemispatial neglect, and their different lesion sites, indicate a double dissociation between these two symptoms.

An 'automatic pilot' for the hand in human posterior parietal cortex: toward reinterpreting optic ataxia

We designed a protocol distinguishing between automatic and intentional motor reactions to changes in target location triggered at movement onset. In response to target jumps, but not to a similar change cued by a color switch, normal subjects often could not avoid automatically correcting fast aiming movements. This suggests that an 'automatic pilot' relying on spatial vision drives fast corrective arm movements that can escape intentional control. In a patient with a bilateral posterior parietal cortex (PPC) lesion, motor corrections could only be slow and deliberate. We propose that 'on-line' control is the most specific function of the PPC and that optic ataxia could result from a disruption of automatic hand guidance.

Cerebellar ataxia with anti-glutamic acid decarboxylase antibodies: study of 14 patients

BACKGROUND

Antibodies to glutamic acid decarboxylase (GAD-Ab) are described in patients with insulin-dependent (type 1) diabetes mellitus (IDDM), in stiff-man syndrome, and, recently, in a few patients with cerebellar ataxia.

OBJECTIVES

To show a link between GAD-Ab and some patients with cerebellar ataxia and to clarify their clinical and immunologic profiles.

METHODS

Serum samples were selected from 9000 samples of 4 laboratories. The selection criterion was an immunohistochemical pattern compatible with GAD-Ab that was confirmed by radioimmunoassay. We identified 22 patients with stiff-man syndrome and 14 with cerebellar ataxia and GAD-Ab.

RESULTS

Thirteen of the 14 patients with cerebellar ataxia and GAD-Ab were women, and 11 had late-onset IDDM. Patients did not have clinical or radiologic evidence of brainstem involvement. Ten patients had oligoclonal IgG bands in the cerebrospinal fluid, and intrathecal GAD-Ab synthesis was observed in 5 of the 6 patients studied. The level of GAD-Ab of these patients was similar to those with stiff-man syndrome and significantly higher than those with IDDM or with polyendocrine autoimmunity (P<.001). However, the GAD-Ab levels of 6 of the 9 patients with polyendocrine autoimmunity overlapped with those of patients with cerebellar ataxia.

CONCLUSIONS

These results suggest a link between high level of GAD-Ab and some cases of cerebellar ataxia, particularly women with IDDM. If high serum levels of GAD-Ab are detected, the cerebrospinal fluid should be evaluated for the presence of oligoclonal IgG bands and intrathecal synthesis of GAD-Ab to further prove an autoimmune origin of the syndrome.

Grasping the past. delay can improve visuomotor performance

"Optic ataxia" is caused by damage to the human posterior parietal cortex (PPC). It disrupts all components of a visually guided prehension movement, not only the transport of the hand toward an object's location, but also the in-flight finger movements pretailored to the metric properties of the object. Like previous cases, our patient (I.G.) was quite unable to open her handgrip appropriately when directly reaching out to pick up objects of different sizes. When first tested, she failed to do this even when she had previewed the target object 5 s earlier. Yet despite this deficit in "real" grasping, we found, counterintuitively, that I.G. showed good grip scaling when "pantomiming" a grasp for an object seen earlier but no longer present. We then found that, after practice, I.G. became able to scale her handgrip when grasping a real target object that she had previewed earlier. By interposing catch trials in which a different object was covertly substituted for the original object during the delay between preview and grasp, we found that I.G. was now using memorized visual information to calibrate her real grasping movements. These results provide new evidence that "off-line" visuomotor guidance can be provided by networks independent of the PPC.

A selective imaging of tinnitus

We selectively imaged the neural correlates of tinnitus, by contrasting a condition with no phantom auditory sensation with a condition during which tinnitus is present, using a rare form of tinnitus elicited by eye movements. Using positron emission tomography (PET), we demonstrate that phantom auditory sensation increases regional cerebral blood flow bilaterally in temporo-parietal association auditory areas but not in the primary auditory cortex. These results confirm that conscious perception does not necessarily require activation in primary areas and suggest that the perceptual qualities of tinnitus, e.g. intensity, frequency and spatial localization, are represented in temporo-parietal regions. Activation in these regions is compatible with cortical processing of ascending auditory messages generated at subcortical levels.

Processing of facial emotional expression: spatio-temporal data as assessed by scalp event-related potentials

Event-related potentials (ERPs) were recorded in 10 adult volunteers, who were asked to view pictures of faces with different emotional expressions, i.e. fear, happiness, disgust, surprise and neutral expression [Ekman, P. & Friesen, W.V. (1975). Pictures of Facial Affect. Consulting Psychologist Press, Palo Alto, CA]. ERPs were recorded during two different tasks with the same stimuli. Firstly, subjects were instructed to pay attention to the gender of the faces by counting males or females. Secondly, they had to focus on facial expressions by counting faces who looked surprised. The classical scalp 'face-related potentials', i.e. a vertex-positive potential and a bilateral temporal negativity, were recorded 150 ms after the stimulus onset. Significant differences were found, firstly between late-latency ERPs to emotional faces and to neutral faces, between 250 and 550 ms of latency and, secondly, among the ERPs to the different facial expressions between 550 and 750 ms of latency. These differences appeared only during the expression discrimination task, not during the gender discrimination task. Topographic maps of these differences showed a specific right temporal activity related to each emotional expression, some particularities being observed for each expression. This study provides new data concerning the spatio-temporal features of facial expression processing, particularly a late-latency activity related to specific attention to facial expressions.

High prevalence of CACNA1A truncations and broader clinical spectrum in episodic ataxia type 2

OBJECTIVE

To characterize the nature of CACNA1A mutations in episodic ataxia type 2 (EA2), to search for mutations in sporadic cases, and to delineate better the clinical spectrum.

BACKGROUND

EA2 is an autosomal dominant disorder characterized by recurrent acetazolamide-responsive attacks of cerebellar ataxia. The mutated gene, CACNA1A, located on chromosome 19, encodes the alpha1A subunit of a voltage-dependent calcium channel. So far, only three CACNA1A mutations have been identified-in two EA2 families and in one sporadic case. These three mutations disrupted the reading frame and led to truncated proteins. Interestingly, distinct types of CACNA1A mutations have been identified in familial hemiplegic migraine (missense mutations) and spinocerebellar ataxia type 6 (SCA-6) progressive cerebellar ataxia (expanded CAG repeats). However, except for SCA-6, these genotype-phenotype correlations relied on the analysis of very few families.

METHODS

To characterize CACNA1A mutations, eight familial and seven sporadic EA2 patients were selected. All 47 exons of CACNA1A were screened by a combination of single-strand conformer polymorphism and sequencing analysis. In addition, the length of the CAG repeat has been determined in all patients.

RESULTS

Seven new mutations were detected in four multiple case families and three sporadic cases. Six of them lead most likely to truncated or aberrant proteins. CAG repeat sizes were in the normal range.

CONCLUSION

These data clearly establish the specificity of EA2 mutations compared with SCA-6 and familial hemiplegic migraine. Detailed clinical analysis of the mutation carriers showed the highly variable penetrance and expression of this disorder: Several of the carriers did not show any clinical symptom; others displayed atypical or permanent neurologic symptoms (such as recurrent, transient diplopia or severe, permanent, and isolated cerebellar ataxia).

Partial remission of hemiplegia and somatoparaphrenia through vestibular stimulation in a case of unilateral neglect

In a case of long lasting severe neglect resulting from a large right parieto-temporo-occipital infarct, vestibular stimulation produced a temporary reduction of the motor deficit and disappearance of the somatoparaphrenic delusion, in addition to the already reported improvement of extrapersonal and personal neglect and anosognosia. These data open new perspectives in the understanding of the neglect syndrome and of functional involvement of the parietal lobe in space representation.

Visually guided reaching: bilateral posterior parietal lesions cause a switch from fast visuomotor to slow cognitive control

The visually guided reaching of two patients with bilateral optic ataxia was explored in two experiments. In Experiment 1 simple delayed pointing was compared with immediate pointing. In the immediate pointing task both variable and constant errors increased with target eccentricity. In contrast to the performance of control subjects and contrary to their own beliefs, the patients both showed improved accuracy in the delay condition. This improvement was manifest as a reduction in both pointing variability and in the constant angular error towards the point of fixation. Both angular errors and their improvement with the delay were proportional to target eccentricity. Experiment 2 used a task in which the target was pre-viewed 5s prior to its re-exposure for pointing ('delayed real pointing'). On some trials a conflict was introduced between the present and previous visual information by changing the target's location during the delay. In contrast to control subjects, who ignored the pre-viewed location and aimed directly at the current target, both patients with optic ataxia initiated their movements towards the previously viewed target location. Evidently they relied on off-line information in preference to on-line visual information. In addition, the patients often failed to detect the changes in target location. One of the patients sometimes even guessed incorrectly that the target had changed its location, and her movement trajectory was then more affected by her false belief than by the target's actual location. These findings confirm that posterior parietal lesions severely disrupt direct visuomotor transformations, and suggest that the residual performance is mediated indirectly by expectations or beliefs about target position.

Optic ataxia errors depend on remapped, not viewed, target location

Optic ataxia is a disorder associated with posterior parietal lobe lesions, in which visually guided reaching errors typically occur for peripheral targets. It has been assumed that these errors are related to a faulty sensorimotor transformation of inputs from the 'ataxic visual field'. However, we show here that the errors observed in the contralesional field in optic ataxia depend on a dynamic gaze-centered internal representation of reach space.

Preserved prism adaptation in bilateral optic ataxia: strategic versus adaptive reaction to prisms

To date the anatomical substrate(s) of prism adaptation remain(s) particularly debated, with two main candidates emerging from the literature: the posterior parietal cortex (PPC) and the cerebellum. The functional processes involved in the acquisition of the adaptive aftereffects also remain largely unknown. The main result shown here is that a patient with a bilateral optic ataxia can adapt to an optical deviation, which allows us to make a step forward on these two issues. First, it demonstrates that the corresponding part of the PPC is not a necessary substrate for prism adaptation. Second, since this patient exhibits deficit for fast visuo-motor guidance, it provides direct evidence for a dissociation between on-line visuo-motor control and visuo-motor plasticity. Since the intermanual transfer rate of adaptation is larger in this patient than in control subjects, the PPC may still have an influence on adaptation under normal conditions. We propose a model of the relative contribution of the PPC and the cerebellum during prism exposure, associating these two structures with the two interacting behavioural components of prism adaptation described by previous psychophysical experiments: the strategic component would be linked to the PPC and the adaptive component to the cerebellum. In this model, the strategic component enters in conflict with the development and the generalisation of the adaptive aftereffects. This idea is compatible with the fact that a lesion of the PPC increases the transfer rate and the generalisation of the adaptation, as is also observed in unilateral neglect.

Saccadic eye movements in schizophrenic patients

The nature of saccadic abnormalities in schizophrenia was investigated in three different paradigms: (1) the visually guided saccade; (2) the antisaccade; and (3) the remembered saccade paradigm. Subjects comprised 14 schizophrenic patients and 14 normal volunteers. Deficits in the schizophrenic group were observed in the antisaccade and remembered saccade tasks, both of which were characterized by increased latency and reduced gain. Moreover, in the antisaccade task, schizophrenic patients showed an increased number of errors compared with control subjects. Saccadic abnormalities in the patients were correlated with impaired performance on the Wisconsin Card Sorting Test. These data suggest that schizophrenic patients have difficulty in inhibiting reflexive saccades and in producing voluntary saccades. The implications of these findings for a prefrontal cortex dysfunction involved in oculomotor control in schizophrenia are discussed.

Optic ataxia is not only 'optic': impaired spatial integration of proprioceptive information

Optic ataxia is considered to be a specific visuo-manual guidance deficit, which combines pointing errors due to the use of the contralesional hand ("hand effect") and to the presentation of the visual target in the contralesional field ("field effect"). The nature of the hand effect has not been identified. The field effect is acknowledged as an impaired spatial integration of visual target location. However, spatial integration of proprioceptive information from the arm has never been experimentally tested in these patients. Here, we specifically investigated the capacity of two patients with unilateral optic ataxia in tasks requiring different levels of proprioceptive integration from primary information processing to proprioceptivo-motor integration. In a first experiment -proprioceptive pointing with the ipsilesional hand toward the index finger of the contralesional hand- revealed a large mislocalisation of the ataxic hand accounting for the hand effect. In a second experiment -proprioceptive pointing with the ataxic arm toward the finger of the ipsilesional hand- revealed reaching errors for non-visual targets, i.e. optic ataxia is not specific to 'optic' targets. Altogether, the present results call for a redefinition of this neurological condition in the framework of parietal functions.

CSF biomarkers in posterior cortical atrophy

OBJECTIVE

To describe CSF biomarker profiles in posterior cortical atrophy (PCA), which induces high-order visual deficits often associated with Alzheimer disease (AD) pathology, and relate these findings to clinical and neuropsychological assessment.

METHODS

This prospective observational study included 22 patients with PCA who underwent CSF biomarker analysis of total tau (t-tau), phosphorylated tau on amino acid 181 (p-tau181), and amyloid β (Aβ(42)). At group level, the CSF profiles of patients with PCA were compared to those of patients with typical AD and patients with other dementia (OD). Individually, the clinical presentation of patients with PCA was correlated to their CSF profile to assess the predictability of clinical features for diagnosis of underlying AD pathology.

RESULTS

At group level, the PCA biomarker profile was not different from that of the AD group, but very different from that of the OD group (p < 0.001). More than 90% of patients with PCA had CSF profiles consistent with AD. All patients with PCA with either isolated higher-order visual deficit (n = 8) or visual deficit associated with memory impairment (n = 11) had CSF profiles consistent with AD. Only one of the 3 patients with PCA with asymmetric motor signs fulfilled biological CSF criteria for AD.

CONCLUSIONS

PCA syndrome is usually associated with CSF biomarkers suggestive of AD, as shown by previous neuropathologic studies. This does not apply in case of motor signs suggesting associated corticobasal syndrome. CSF biomarkers help to discriminate AD from non-AD processes associated with this condition.

Magnetic resonance imaging in familial paroxysmal ataxia

A magnetic resonance imaging study was performed in three symptomatic members of two families with a diagnosis of acetazolamide-responsive familial paroxysmal ataxia. A selective atrophy of the cerebellar vermis, mostly of the anterior part, was demonstrated in the three cases. The first ample documentation of a neuroanatomical abnormality in this condition was achieved in this study.

Pointing errors in immediate and delayed conditions in unilateral optic ataxia

The present paper provides an analysis of the pointing errors of a patient with unilateral optic ataxia (O.K.) following right hemispheric damage, revealing the type of errors related tothe use of the contralesional hand and/or to the reaching of targets located in the contralesional visual field. In addition, comparison between immediate and delayed pantomime pointing allow testing of whether pointing deficits of this patient are specific to real-time visuo-motor control and, subsequently, whether delay could improve his pointing performance. The results show different patterns in the four hand-field combinations. The following conclusion can be drawn from the results of the delayed condition. In the case of patient O. K., the delay reduced the pointing variability for both hands in the left visual field but not in the right visual field. However, the pointing biases did not improve accordingly. As in healthy subjects, target locations tended to be coded in memory with a bias directed toward the fixation point. These results are discussed and contrasted with respect to those previously obtained in the literature in patients with bilateral optic ataxia.

Buspirone, a 5-hydroxytryptamine1A agonist, is active in cerebellar ataxia. Results of a double-blind drug placebo study in patients with cerebellar cortical atrophy

OBJECTIVE

To establish the antiataxic effect of buspirone hydrochloride, a serotonergic 5-hydroxytryptamine1A (5-HT1A) agonist, in a homogenous group of patients characterized by the same well-defined single condition, cerebellar cortical atrophy.

SETTING

University ataxia research center.

METHODS

Double-blind randomized study of buspirone vs placebo during a 4-month period.

PATIENTS

Nineteen patients met the inclusion criteria; all completed the study. Of these 19 patients, 9 were treated with placebo and 10 were treated with the drug.

MAIN OUTCOME MEASURES

A semiquantitative scale for kinetic and static ("postural") cerebellar functions; quantitative clinical measurements measuring time in standard tests that evaluated stance, speech, writing, and drawing; and posturographic analysis of the sway path and sway area of the center-of-foot pressure. The primary end point was improvement of the posttherapeutic change of one of the semiquantitative ataxic scores. The secondary end points were modification of the changes of quantitative measures--clinical or posturographic.

RESULTS

In intention-to-treat analysis, a significant improvement of the primary end point, ie, the posttherapeutic change of the ataxic kinetic score, was shown. Among secondary end points, the maximum time of standing with feet together also was significantly improved.

CONCLUSIONS

Buspirone is active in cerebellar ataxia of patients with cerebellar atrophy. These results confirm the data suggested by open-label studies with buspirone. However, the effect is partial and not clinically major. These pharmacological results might be due to serotonergic mechanisms and confirm a possible link between cerebellar ataxia and the metabolism of serotonin.

Anatomy of optic nerve radiations as assessed by static perimetry and MRI after tailored temporal lobectomy

AIMS

To determine the course of optic nerve radiations in the temporal lobe, especially their retinotopic organisation and the anterior limit of the Meyer's loop.

METHODS

18 adult patients who had undergone a tailored temporal lobectomy for epilepsy were included in this study between 1994 and 1998. The rostrocaudal extent of the lateral temporal lobe resection assessed intraoperatively by the surgeon and by postoperative MRI was compared with the postoperative visual fields determined by automated static perimetry (ASP).

RESULTS

15 patients (83%) presented a postoperative visual field deficit (VFD) confined to the superior homonymous field contralateral to the side of the resection. All degrees from a minimal upper field loss to a complete quadrantanopia were observed. The VFDs were somewhat stereotyped, predominating along the vertical meridian. The smallest anteroposterior resection resulting in a VFD was limited to 20 mm from the tip of the temporal lobe. A relation was observed between the extent of the lateral resection in front of the second and third convolutions and the occurrence and extent of postoperative VFDs. No patient reported persisting subjective visual impairment.

CONCLUSION

The high frequency of postoperative VFDs appears to be due to the greater sensitivity of ASP. The characteristics of the stereotyped VFDs allow new conclusions about the course and retinotopy of optic nerve radiations. The anterior limit of Meyer's loop is likely to be located more rostrally than previously believed.

Vertigo and upside down vision due to an infarct in the territory of the medial branch of the posterior inferior cerebellar artery caused by dissection of a vertebral artery

A 48 year old woman developed an acute vestibular syndrome associated with upside down vision a few hours after minor cervical trauma. Magnetic resonance imaging showed an ischaemic lesion in the territory of the medial branch of the posterior inferior cerebellar artery. An arteriogram showed a dissection of the left extracranial vertebral artery.

Up-regulation of hippocampal serotonin metabolism in mild cognitive impairment

OBJECTIVE

Recent studies have suggested modifications of serotonin cerebral metabolism and of 5-HT(1A) receptors density in Alzheimer disease (AD). This study aims at exploring hippocampus 5-HT(1A) receptor density in patients at the amnesic mild cognitive impairment (aMCI) and mild AD dementia stages.

METHODS

With use of PET with a selective 5-HT(1A) antagonist, 2'-methoxyphenyl-(N-2'-pyridinyl)-p-[(18)F]fluoro-benzamidoethylpiperazine ([(18)F]MPPF), the hippocampus 5-HT(1A) binding potential (BP) was quantified in 10 patients with mild AD, in 11 patients with aMCI, and in 21 aged paired control subjects. To take into account hippocampal atrophy, a partial volume correction was applied to the [(18)F]MPPF data, leading to the calculation of a corrected BP (BP(c)). Comparison of hippocampus BP over populations was performed using Kruskal-Wallis rank analysis.

RESULTS

Hippocampus serotonergic receptor binding distinguishes patients from controls and patients with aMCI from patients with AD. In aMCI patients, the mean hippocampus BP(c) was 59% higher than the controls' (p < 0.005), and it was conversely 35% lower in patients with mild AD (p < 0.01). The difference in BP(c) values between patients with aMCI and mild AD was large, resulting in a p value of <0.0005. These differences were not related to hippocampus atrophy.

CONCLUSION

A compensatory mechanism illustrated by an up-regulation of serotonergic metabolism has been shown at the stage of amnesic mild cognitive impairment (aMCI) in contrast with a dramatic decrease at later stages of Alzheimer disease (AD). This difference of hippocampus serotonergic receptor labeling allows distinguishing of patients with aMCI from those with mild AD. Exploring 5-HT(1A) receptors with 2'-methoxyphenyl-(N-2'-pyridinyl)-p-(18)F-fluoro-benzamidoethylpiperazine PET seems to be of interest for better understanding pathophysiologic changes at early stages of AD.

Room tilt illusion. A central otolith dysfunction

BACKGROUND

We report a sudden 90 degrees room tilt illusion (RTI) following vestibular stimulation in 3 patients with persistent skew deviation caused by a brain stem lesion. Room tilt illusion is a transient tilt perception of the visual surrounding, on its side or even upside down, that is often reported with brain stem lesions. Although its pathophysiologic cause is not well known, the RTI suggests an impairment of otolith pathways, as reported in skew deviation.

METHODS

The 3 patients with brain stem lesions were reexamined as part of a follow-up of patients with signs of otolith dysfunction. A registration of vestibular function was performed with a rotatory chair, including earth-vertical axis rotation for canal stimulation and off-vertical axis rotation (OVAR) for otolith stimulation. Measurement of the subjective visual vertical (SVV) was also performed.

RESULTS

The otolith-ocular reflex registered by OVAR was impaired in the 3 patients with skew deviation and the SVV in 2 patients. After each direction of OVAR stimulation, the 3 patients reported an RTI as the room was illuminated.

CONCLUSIONS

The coexistence of otolith oculomotor (skew deviation and impaired otolith-ocular reflex) and perceptual (tilt of SVV and RTI) disorders suggests a common otolith dysfunction. However, an RTI occurred specifically after vestibular stimulation and when the room was illuminated. We thus suggest that RTI reflects a dynamic visuo-otolith mismatch.

Detection of mild papilloedema using spectral domain optical coherence tomography

OBJECTIVE

To propose a method of diagnosis of mild papilloedema (PO) using peripapillary total retinal (PTR) thickness measurement by spectral domain optical coherence tomography (OCT).

METHODS

24 eyes in 24 patients with PO caused by increased intracranial pressure and 22 eyes in 22 normal subjects were studied. OCT high-quality fundus images were analysed and graded by three masked observers using the Modified Frisén Scale. Eyes with PO were divided into two subgroups: those with mild PO (n=18) and those with moderate-severe PO (n=6). Two methods of measurements were evaluated and compared: retinal nerve fibre layer (RNFL) thickness measurements using standard optic disc cube 200 × 200 acquisition protocol and PTR thickness measurements using the 'macular' cube 512 × 128 acquisition protocol centred on the optic disc. Thickness values were calculated globally and for each quadrant (temporal, superior, nasal, inferior) and compared among the three groups (control, mild PO, moderate-severe PO). The main outcome measures were RNFL and PTR thickness.

RESULTS

Average RNFL and PTR thickness in the moderate-severe PO, mild PO and control groups were 299.3 ± 10.9, 112.4 ± 6.3, 96 ± 5.7 and 804.5 ± 17, 463.1 ± 9.8 and 332.4 ± 8.9 μm, respectively. Moderate-severe PO differed from mild PO and control groups using both RNLF thicknesses and PTR thicknesses measurements. Mild PO did not differ from controls using RNLF thickness measurement (p=0.17), but was statistically different using PTR thickness measurement (p<0.001).

CONCLUSION

PTR thickness measurement increases the sensitivity of detection of mild PO compared with conventional RNFL measurement. This new way of using OCT may be useful for clinicians to detect mild PO.

Idiopathic ocular neuromyotonia: a neurovascular compression syndrome?

Ocular neuromyotonia in the muscles innervated by the right oculomotor nerve was diagnosed in a patient without a history of radiation therapy. Electromyography of the levator palpebrae showed continuous motor unit activity. Brain MRI disclosed a close contact between the right third cranial nerve and a basilar artery dolichoectasia. The patient partly benefited from carbamazepine therapy. This unique finding suggests that neurovascular compression syndrome could be an hitherto unrecognised cause of ocular neuromyotonia.