A Diplopia Dilemma
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SURVEY OF OPHTHALMOLOGY
VOLUME 51 NUMBER 1 JANUARY–FEBRUARY 2006
CLINICAL CHALLENGES PETER SAVINO AND HELEN DANESH-MEYER, EDITORS
A Diplopia Dilemma Mark Saunders, FRANZCO,1 Celeste Guinane, BAS,1 Martin MacFarlane, FRACS,2 Ken Tarr, FRANZCO,2 M. Tariq Bhatti, MD,3,4,5 and David W. Pincus, MD, PhD5 Departments of 1Ophthalmology and 2Neurosurgery, Christchurch Hospital, Christchurch, New Zealand; Departments of 3Ophthalmology, 4Neurology, and 5Neurological Surgery, University of Florida College of Medicine, Gainesville, Florida USA
(In keeping with the format of a clinical pathologic conference, the abstract and key words appear at the end of the article.) [A video presentation that helps illustrate the concepts discussed in this paper has been created. Please log on to Survey of Ophthalmology’s Web page (www.Elsevier.com/locate/survophthal) to view the video.] either eye was covered. It was not gaze-dependent. Both reading and driving were difficult. At times he would fall when he walked down stairs but he rarely had any problem when he walked up stairs. He had difficulty fixing from near to far and back again. The diplopia had not varied from the onset. Headaches when present were of a fleeting nature that lasted up to 10 minutes, occurring sporadically every 1 or 2 days. There was occasional postural vertigo and unsteadiness. The patient was otherwise healthy and on no medications. The corrected visual acuity was 20/20 OU. Binocular vision was present including stereopsis to 60 seconds of arc. His current glasses had an appropriate prescription and incorporated 3 prism diopters (PD) of base-out prism. The visual fields were normal. The ocular media were clear. The fundi were normal with pink healthy optic disks. There were no focal neurological signs or abnormal long track signs.
Case Report. A 38-year-old healthy man awoke one morning with diplopia. He had seen an optometrist who prescribed new spectacles, which did not help. The patient has subsequently seen an ophthalmologist and a neurologist. The neurologist made a diagnosis of a presumed right fourth nerve palsy. Magnetic resonance imaging (MRI) showed a slightly irregular lesion in the tectum of the midbrain with marginal patchy gadolinium enhancement. There was mild compression and stenosis of the aqueduct and mild ventricular enlargement (Fig. 1). This did not change over a 5-month period. No treatment was undertaken. A repeat MRI scan 5 months later confirmed that there was no change in the size of the lesion. The diplopia had not changed over the 5-month period. He was then referred to a neuro-ophthalmologist because of the persistent diplopia. The patient had difficulty explaining the features of his diplopia. The double vision disappeared if
68 Ó 2006 by Elsevier Inc. All rights reserved.
0039-6257/06/$--see front matter doi:10.1016/j.survophthal.2005.11.004
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DIPLOPIA DILEMMA
Fig. 1.
Saggital MRI showing tectal lesion (*).
The range of ocular movement was normal. Cover test demonstrated 2 PD of right hyperphoria in primary position, which increased slightly on right and down gaze. A Bielschowski head tilt test was negative for a fourth nerve palsy. The nine positions of gaze are shown in Fig. 2. How do you explain the presenting symptom of diplopia? What further office examinations would you perform given the site of the lesion?
Comments Comments by M. Tariq Bhatti, MD, and David W. Pincus MD, PhD We are presented with a previously healthy man with a 5-month history of a poorly characterized complaint of binocular double vision and a myriad of other symptoms presumably due to a right fourth
Fig. 2.
cranial nerve palsy. A detailed history obtained from a patient with binocular double vision can provide valuable assistance to the examiner in formulating an initial list of possible diagnoses. Double vision that is dependent upon head or eye positioning, distance or near viewing, as well as symptoms precipitated by environmental conditions, can suggest a particular ocular motility problem. If a patient does not spontaneously offer such details, it is important to inquire specifically about them during the interview phase of the examination or demonstrate these features during the physical examination. In this particular case it appears, based on the initial examination findings, that not all of the patient’s symptoms can be readily attributed to the double vision. Certainly, patients with double vision may complain of difficulty reading or driving, but these problems are often corrected with monocular occlusion or prism therapy. In addition, the patient’s difficulties with alternating between near and distance fixation, and walking down stairs may be indicative of more than just a primary position misalignment of the eyes, but a dysfunction of the ‘‘dynamic’’ aspects of eye movement. We are told the neuro-ophthalmologic examination is essentially normal aside from a slight vertical misalignment of the eyes. The range of ocular movement is noted to be normal with a 2-PD right hyperphoria in primary gaze. An important piece of information provided is the finding of a negative Bielschowski head tilt test. The result of the threestep test indicates the pattern of the vertical misalignment is not consistent with a fourth cranial nerve palsy, but more likely a skew deviation, which is a supranuclear ocular motility disorder resulting
Composite of eye movements.
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from disruption of the otolithic-ocular pathways within the brainstem.5 The vertical misalignment of a skew deviation may be comitant or incomitant and in some patients the hypertropia may alternate between eyes in right and left gazes (alternating skew deviation). There may be associated ocular torsion (incyclotorsion of the hypertropic eye) best detected by the double Maddox rod test or indirect funduscopy. The ocular misalignment of skew deviation is often constant, but periodic and paroxysmal forms have also been described.6 To determine what office examination test will be useful in determining this patient’s symptoms it is important to appreciate the concept that functionally, the ocular motor system can be divided into six systems:7 1. 2. 3. 4. 5. 6.
Vestibulo-ocular Fixation or gaze holding Optokinetic Vergence Smooth pursuit Saccadic
Each system operates relatively independently through a set of premotor neurons that project to the three ocular motor cranial nerves (third, fourth, and sixth cranial nerves) with the ultimate goal of establishing clear, stable, and single binocular vision. In order to coordinate the precise combined movement between the eyes there exist multiple parallel descending supranuclear pathways from the cerebral cortex, relaying through the basal ganglion, thalamus, superior colliculus, and cerebellum, ultimately synapsing onto the premotor and ocular motor cranial nuclei in the brainstem. Therefore,
any patient with a suspected ocular motility abnormality should undergo clinical assessment of each of these functional systems (Table 1). As in this particular case, it is not sufficient to measure the ocular misalignment and assess the symmetry and range of ocular movements. The dynamic quality, speed, and extent of eye motion during saccadic and smooth pursuit eye movements need to be evaluated.
Case Report (Continued) What additional clinical sign would you look for?
Comments (Continued) Comments by Drs. Bhatti and Pincus The patient demonstrates normal horizontal eye movements during both smooth pursuits and saccades. Upgaze and downgaze smooth pursuit movements are also normal, but in striking contrast there is dysfunction of vertical saccadic movements on attempted upgaze as manifested by decreased amplitude (hypometria) and decreased velocity of the eye movements. It is also noted that on attempted upward saccades there are small converging and retracting movements of the eyes, known as convergence-retraction nystagmus (the use of the term nystagmus for this condition is a misnomer because the eye movements are not a true form of nystagmus but rather a saccadic disorder). The findings of an upgaze saccadic palsy and convergence-retraction nystagmus may explain the patients’ difficulties with visually oriented tasks because objects of concern cannot be fixated and maintained on the fovea.
TABLE 1
Eye Movement Systems Eye Movement System
Function
Vestibulo-ocular (VOR)
Stabilize image during brief head rotations
Optokinetic (OKN)
Stabilize retinal image during sustained head rotation Maintain stable eye tracking or combined eye--head tracking of slowly moving object Maintain foveal fixation of object during movement of eyes in opposite direction
Smooth pursuit Vergence
Saccades Fixation
Rapid change of fixation to fovea of objects of interest Maintain image on fovea of stationary image
Clinical Assessment Doll’s eye maneuver Caloric testing Head rotation during Snellen visual acuity testing Large field stimulus Present slowly moving small target Optokinetic drum Near rule: measure near point of convergence and accommodation Prism bar: measure fusional amplitudes Present two objects separated by distance Optokinetic drum Observe eyes during fixation of stationary target
DIPLOPIA DILEMMA
The constellation of skew deviation, upgaze saccadic palsy and convergence-retraction nystagmus is indicative of the dorsal midbrain syndrome also known as pretectal or Parinaud syndrome.1 Other clinical findings that may be encountered with this syndrome include a downgaze preference (‘‘sun setting’’ sign in children), upper eyelid retraction (Collier sign), convergence or divergence insufficiency, convergence spasm, pseudoabducens palsy, and square wave jerks. In the majority of patients with the dorsal midbrain syndrome, the pupils will be in a mid-dilated position with lightnear dissociation (pupil response to near effort is stronger than the direct light reflex). In this patient, the pupillary light reflex should be evaluated and if found to be absent or sluggish then the pupillary response to near effort assessed.
Case Report (Continued) What are your differential diagnosis and your management plan for the diplopia?
Comments (Continued) Comments by Drs. Bhatti and Pincus Before we discuss the differential diagnosis of the dorsal midbrain syndrome and the management options for this patient, it may be instructive to discuss in some detail one of the cardinal features of the dorsal midbrain syndrome, the vertical gaze palsy and the neural control of vertical eye movements (Fig. 3). The current understanding of the complex anatomical, physiologic, pathologic, and behavioral aspects of human eye movements is incomplete and much of our knowledge is based on experimental primate studies, clinical observation with radiologic, and occasionally postmortem, correlation and more recently functional neuroimaging techniques.6 Vertical saccadic and torsional eye movements are generated by premotor nuclei located within the rostral midbrain (mesencephalon) that relay signals to the third and fourth cranial nuclei. In addition, the pathways for vertical smooth pursuit and vertical vestibular generated eye movements ultimately synapse onto the third and fourth cranial nuclei. Therefore, a variety of supranuclear vertical eye movement disorders may be encountered from lesions in the midbrain including upgaze palsy, downgaze palsy, or combination of both, double elevator palsy, vertical one-and-one- half syndrome, and skew deviation.4 There appears to be three main structures within the rostral midbrain tegmentum
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Fig. 3. Diagram of vertical eye movement pathways. riMLF 5 rostral interstitial nucleus of the medial longitudinal fasciculus; INC 5 interstitial nucleus of Cajal; PC 5 posterior commissure; MLF 5 medial longitudinal fasciculus; SR 5 superior rectus muscle; IR 5 inferior rectus muscle; IO 5 inferior oblique muscle; SO 5 superior oblique muscle.
critical in the generation and maintenance of supraversion (upgaze) and infraversion (downgaze) (Fig. 4): Rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) Interstitial nucleus of Cajal (INC) Posterior commissure (PC)
Fig. 4. Saggital view of brainstem illustrating the relative position of the important structures for vertical eye movements.
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We will briefly discuss the role of each structure separately. The riMLF is considered the neural substrate for vertical saccades. It contains excitatory and inhibitory burst cells for upward and downward saccadic eye movements. The primary projection of these cells is to the elevators (superior rectus and inferior oblique muscles) and depressors (inferior rectus and superior oblique muscles) of the eyes. The riMLF projects ipsilaterally to the subnuclei of the inferior rectus and fourth nuclei and bilaterally to the superior and inferior oblique subnuclei. Clinically, lesions of the riMLF result in either a downward saccadic palsy or a combined upward and downward saccadic palsy. In addition, unilateral lesions lead to a contralateral ocular rotation and torsional nystagmus of both eyes.2 The INC is the primary neural integrator for vertical gaze-holding and contributes to eye-head coordination. As a neural integrator, the INC integrates velocity-coded signals into position-coded signals of all eye movements to overcome the natural elastic properties of the orbital tissues by delivering impulses to the yoke extraocular muscles for constant contraction during eccentric fixation.6 Unilateral lesions of the INC can result in the ocular tilt reaction (manifested by contralateral head tilt, ipsilateral hypertropia with intorsion, and contralateral hypotropia with extorsion) and ipsilesional torsional nystgmus. Bilateral lesions can result in a vertical gaze palsy with sparing of vertical saccadic eye movements and upbeat nystagmus. The PC is comprised of a group of nuclei as well as axons from the INC projecting to the contralateral INC, third nerve nuclear complex, and fourth nuclei. In addition, the PC contains fibers from the nucleus of the PC projecting to the contralateral riMLF and INC that are important for vertical upward eye movements. An insult to the PC can result in impaired vertical eye movements, in particular upward saccades, and other manifestations of the dorsal midbrain syndrome (see above). Additional structures and cells involved in vertical eye movements include the medial longitudinal fasciculus (for vertical gaze holding, vertical vestibular, and vertical smooth pursuit eye movements), periaqueductal grey matter, M-group cells, y-group cells of the inferior cerebellar peduncle, vestibular nucleus and the central mesencephalic reticular formation. Because some of these pathways are located in the pons and medulla, lesions in these areas can result in pathologic vertical eye movements. In addition, horizontal eye movement abnormalities have been described from lesions of the mesencephalic reticular formation within the midbrain.8
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There are a variety of voluntary and reflexive saccadic eye movements (Table 2). Saccadic eye movements can reach velocities of 600 /sec. The speed of the saccade is dependent on its amplitude, with larger amplitudes generating increasingly faster saccades. There is often a latency period of 200 msec prior to the development of the movement and once a saccade begins no changes can be made until the end of its determined position. However, visual information is continually being processed during the saccade and can be used to influence the timing, size and direction of the next saccade. Several cortical and subcortical regions are involved in the development of saccadic eye movements. These regions are interconnected to one another and form parallel descending pathways to the premotor nuclei for vertical eye movement. Some of the important structures and their functions are the following: Frontal eye fields: Contribute to the generation of voluntary saccades Parietal eye fields: Influence programming of saccades to visual targets and shifts of visual attention Basal ganglion: Inhibit reflexive saccades during fixation and assist in voluntary saccades Thalamus: Contribute to the programming of saccades Superior colliculus: Involved in visually driven reflexive saccades Cerebellum: Influence the latency and amplitude of saccades In contrast to saccades, smooth pursuit eye movements travel at speeds no faster than 30 /sec with a latency period of 100 msec. Their movement depends on small central moving targets. The size, location, and dynamic properties of the target are carried by the afferent visual system via the magnocellular and parvocellular pathways to cortical structures. The generation of smooth pursuit movement relies on the processing of the visual target by the primary visual (striate) cortex and extrastriate cortical regions within the temporalparietal-occipital junction. Additional areas involved in smooth pursuit eye movements include the frontal eye fields and cerebellum. Descending vertical smooth pursuit pathways are relayed to the pons (y-group cells) reaching the midbrain through the medial longitudinal fasciculus. As mentioned above, there are several clinical findings that characterize the dorsal midbrain syndrome, not all of which may be present in a single patient. As the name suggests, the syndrome occurs from an insult to the structures within the rostral dorsal midbrain, including the tectal plate
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DIPLOPIA DILEMMA TABLE 2
Classification of Saccades Classification Volitional saccades Predictive, anticipatory Memory-guided Antisaccades To command Reflexive saccades Express saccades Spontaneous saccades Quick phases
Definition Elective saccades made as part of purposeful behavior Saccades generated in anticipation of or in search of the appearance of a target at a particular location Saccades generated to a location in which a target has been previously present Saccades generated in the opposite direction to the sudden appearance of a target (after being instructed to do so) Saccades generated on cue Saccades generated to novel stimuli (visual, auditory or tactile) that unexpectedly occur within the environment Very short latency saccades that can be elicited when the novel stimulation is presented after the fixation stimulus has disappeared (gap stimulus) Seemingly random saccades that occur when the subject is not required to perform any particular behavioral task Quick phases of nystagmus generated during vestibular or optokinetic stimulation or as automatic resetting movements in the presence of spontaneous drift of the yes
Reprinted from Leigh and Zee6 with permission of Oxford University Press, Inc.
(roof of the midbrain). Although all vertical eye movements (upgaze, downgaze, reflexive, and voluntary) can be affected in the dorsal midbrain syndrome, an upgaze saccadic palsy is most frequent due to interruption of the fibers of the PC.9 The dorsal midbrain syndrome can occur from a variety of causes with the most common being midbrain cerebrovascular accidents, tumors involving the pineal gland or tectal plate and hydrocephalus. In this case the MRI demonstrates a posterior third ventricular-pineal region mass, which may be directly compressing the PC. Alternatively, tumors in this region may cause indirect pressure on the PC resulting from tumor obstruction of the aqueduct of Sylvius leading to hydrocephalus. At this stage we would suggest performing an endoscopic third ventriculostomy (ETV) with endoscopic or stereotatic biopsy. Alternatively, ETV could be performed and the biopsy postponed until serum and cerebrospinal fluid markers for beta-HCG and alphafetoprotein are measured.
Case Report (Continued) Three months later the patient was readmitted semi-acutely with raised intracranial pressure confirmed by intracranial pressure monitoring. A right frontal burr hole and an endoscopic third ventriculostomy performed. Two slight protuberances were noted on the upper posterior aspect of the third ventricle, these were slightly pink in color and presumably represented the tumor in the upper part of the tectum. To avoid bleeding the lesion was not biopsied. A third ventriculostomy hole was created in the floor of the third ventricle through
into the interpeduncular cistern and enlarged to 6--8 mm in diameter. CSF was taken for cytology. There were no abnormal cells and no malignant cells. The tumor markers of alphafeta protein and HCG were negative. Six days postoperatively a follow-up MRI showed reduction in the size of the lateral ventricles. The midline CSF flow study indicated a patent third ventriculostomy endoscopic hole. A follow-up MRI scan performed 3 months later showed an unequivocal enlargement of the tumor with complete obliteration of the aqueduct. The tumor extended from the level of the upper part of the inferior colliculi to occupy the posterior end of the third ventricle. It measured 2.75 cm in maximum length and 1.5 cm in vertical height. There was no change in the clinical findings. A decision to proceed with conventional radiotherapy was undertaken. Six months later a follow-up MRI scan showed a very good appearance compared to the earlier studies. There was almost complete disappearance of the tectal plate mass. There was no abnormal enhancement. The CSF flow studies indicated that there was still no flow down the aqueduct and the third ventriculostomy was widely patent. The rapid response of the tectal plate tumor to radiotherapy would strongly suggest that the tumor was a germinoma. Germinomas are extremely sensitive to radiotherapy and are usually cured by this treatment. The patient continues to need to patch one eye because of the lack of vertical saccades and the ocular instability due to convergence-retraction.
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Concluding Comments Comments by Drs. Bhatti and Pincus With recent advances in instrumentation, fiberoptic technology, and endoscopic technique, ETV has evolved into an excellent option in the management of patients with hydrocephalus due to third ventricular outflow obstruction. ETV creates an opening in the floor of the third ventricle, proximal to site of obstruction, to allow cerebrospinal fluid to enter the basal cistern system and absorption through normal cerebrospinal fluid pathways. The technical details of ETV are not pertinent to this discussion, but it should be noted that the complication rate is less than 5% with adverse events including arterial hemorrhage due to basilar artery injury, third cranial nerve palsy, meningitis, hemiparesis, delayed closure of the fistula, and hypothalamic dysfunction.3 ETV is not performed by all neurosurgeons and traditional cerebrospinal fluid shunting procedures remain an alternative option. At the University of Florida, patients do not undergo radiation therapy of pineal region lesions without a tissue diagnosis. We believe—due to the high degree of safety and accuracy of stereotactic or endoscopic biopsy, and the potential for lesions to benefit from chemotherapy with or without surgery in addition to radiotherapy—biopsy is appropriate in most cases.
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References 1. Baloh RW, Furman JM, Yee RD: Dorsal midbrain syndrome: clinical and oculographic findings. Neurology 35:54--60, 1985 2. Buttner U, Buttner-Ennever JA, Rambold H, Helmchen C: The contribution of midbrain circuits in the control of gaze. Ann NY Acad Sci 956:99--110, 2002 3. Cohen AR: Endoscopic neurosurgery, in Wilkins RH and Rengachary SS (eds): Neurosurgery. Vol 1. New York, McGraw-Hill, 1996, ed 2, pp 539-46 4. Hommel M, Bogousslavsky J: The spectrum of vertical gaze palsy following unilateral brainstem stroke. Neurology 41: 1229--34, 1991 5. Keane JR: Ocular skew deviation. Analysis of 100 cases. Arch Neurol 32:185--90, 1975 6. Leigh RJ, Zee DS: The neurology of eye movements, in The Contemporary Neurology Series. Oxford, Oxford University Press, 1999, ed 3 7. Sharpe JA: Neural control of ocular motor systems, in Miller NR and Newman NJ (eds): Walsh & Hoyt’s Clinical NeuroOphthalmology, Vol 1. Baltimore, Williams & Wilkins, 1998, ed 5, pp 1101-67 8. Zackon DH, Sharpe JA: Midbrain paresis of horizontal gaze. Ann Neurol 16:495--504, 1984 9. Zee DS: Supranuclear and internuclear ocular motor disorders, in Miller NR and Newman NJ (eds): Walsh & Hoyt’s Clinical Neuro-Ophthalmololgy, Vol 1. Baltimore, Williams & Wilkins, 1998, ed 5, pp 1283-349 The authors reported no proprietary or commercial interest in any product mentioned or concept discussed in this article. Drs. Bhatti and Pincus gratefully acknowledge the assistance of David Peace, MS, Medical Illustrator, University of Florida Brain Institute, Department of Neurological Surgery. We also wish to express appreciation for the editorial assistance of Mabel Wilson. This mansucript was supported by an unrestricted departmental grant from Research to Prevent Blindness, Inc., New York, NY. Reprint address: M. Tariq Bhatti, MD, College of Medicine, University of Florida, Department of Ophthalmology, PO Box 100284, Gainesville, FL 32610-0284.
Abstract. A 38-year-old man experienced double vision with pupillary abnormalities and convergence retraction nystagmus. A mass, which responded to radiation therapy, was seen as the cause of his dorsal midbrain syndrome. The neural control of vertical eye movements is reviewed and the management of a third ventricular-pineal region mass discussed. (Surv Ophthalmol 51:68--74, 2006. Ó 2006 Elsevier Inc. All rights reserved.) Key words. convergence retraction nystagmus diplopia dorsal midbrain syndrome deviation third ventricular tumor vertical eye movement control
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