Recent advances in the diagnosis of optic neuritis（ON）related to central nervous system（CNS）autoimmune inflammatory demyelinating disease owe to the discovery of unique biomarkers as autoantibodies against aquaporin（AQP）4 and anti-myelin oligodendrocyte glycoprotein（MOG）, together with the development of neuroimaging technic as the diagnostic tool for multiple sclerosis（MS）. Each of the ON in MS, anti-AQP4 antibody-positive neuromyelitis optica spectrum disorders（NMOSD）, and anti-MOG antibody-associated disease（MOGAD）show unique clinical features with crucial differences in treatment and prognosis. NMOSD is characterized by severe and recurrent ON（unilateral or bilateral）and myelitis spanning more than three vertebrate segments. Autoantibodies target CNS water channel AQP4 predominantly expressed on astrocytic foot processes that induce complement activation. Features favoring MOGAD include optic disc edema and bilateral and recurrent ON. They are usually steroid-responsive with good outcomes. MOGAD shows diverse clinical phenotypes depending on age at onset, as acute disseminated encephalomyelitis（ADEM）in children and myelitis/cerebral cortical disease in adults together with ON. Anti-AQP4 antibodies have been shown to be pathogenic in NMOSD; however, the pathogenicity of anti-MOG antibodies has not been investigated thoroughly. The treatment strategies for autoantibody-mediated ON are very different from those for MS. It is important to diagnose them properly with autoantibody detection and neuroimaging tests, and they need long-term follow-up care.
The following is a summary of points for the gentle and easy evaluation of abnormal eye movements.
Point 1: Understand the five categories of normal eye movement.
Eye movements are classified into four types of conjugate eye movements（saccades, pursuit, vestibulo-ocular reflex, and optokinetic nystagmus）and one type of disconjugate eye movement. The motor commands and control signals for the different types of eye movements are generated by different neural circuits in the oculomotor center.
Point 2: The oculomotor periphery consists of the nuclei of cranial nerves III, IV, and VI, and their axons and extra ocular muscles. It does not distinguish oculomotor signals for different types of eye movements and is named the final common pathway. The orbital soft tissue has viscoelasticity, and the eye position is maintained by sustained contraction of the extra ocular muscles, which antagonizes the elastic resistance of the orbit.
In mammals, extra ocular muscle planes are roughly coincided with semicircular canal planes.
Point 3: By understanding the mechanism of the oculomotor center and evaluating eye movement disorders by type and direction, it is possible to make a localized diagnosis.
Point 4: Convergence signals of disconjugate eye movements project directly from the mesencephalic reticular formation to the bilateral medial rectus subnuclei without passing through the abducens internuclear neuron. Therefore, diplopia caused by disorder in the disconjugate eye movement center does not show horizontal eye position or fixation eye dependence.
Point 5: Subjective head-free eye movements are gaze movements and involve eye-in head movements and head-in-space movements. Therefore, it is not uncommon for patients with diplopia or nystagmus to achieve a compensatory head position when looking forward.
In the case of thyroid-associated ophthalmoplegia, a patient with vertical diplopia may have a natural chin-up position when looking upward.
The horizontal component of vestibular eye movements is derived from the lateral semicircular canal, vestibular nucleus, and contralateral abducens nucleus pathway. The vestibular pathway moves the eyes away from the vestibular nucleus. Since this pathway is suppressed by the cerebellum, ipsilateral and contralateral eye deviations can occur in the central lesion. The torsional component is derived from the anterior and posterior semicircular canals, vestibular nucleus, and trochlear or oculomotor nucleus pathways. This vestibular pathway rotates the eyes in a direction opposite to the vestibular nucleus. Since the pathway is crossed, both ipsilateral and contralateral eye rotations can occur in the central lesion. The upward component is derived from the anterior semicircular canal, and the downward component is derived from the posterior semicircular canal; the posterior semicircular canal pathway is not suppressed by the cerebellum, unlike other semicircular canal pathways. Partial damage to the vertical eye-movement pathway causes upward or downward eye deviation.
In general, it is believed that voluntary eye movement systems such as the saccade system use horizontal and vertical two dimensional Cartesian coordinates. However, the vestibuloocular reflex system（VOR）, which has horizontal, vertical and torsional components, uses three dimensional（3D）semicircular canal coordinates. Unlike the well-known VOR three-neuron arc, the output pathways from the superior colliculus to ocular motoneurons, especially in the vertical saccade system, have not been determined thus far. Therefore, we analyzed the neural circuits from the superior colliculus to the ocular motoneurons using an intracellular technique, and found the upward and downward torsional saccade systems were similar to the anterior and posterior semicircular canal systems, respectively. Furthermore, similar to the anterior and posterior semicircular canal systems, the upward and downward torsional saccade systems are mutually inhibitory. These similarities between the saccade and VOR systems imply that the saccade system uses the same 3D semicircular canal coordinate as the VOR system. The excitatory commissural connections between the bilateral superior colliculi are most likely involved in generating pure vertical saccades by simultaneously activating bilateral symmetrical vertical systems to maintain Listing’s law.
Oculomotor adjustments of open eyes in darkness can be overlooked, but oculomotor symptoms can directly contribute to diagnosis and pathogenesis. Herein, I report four examples of successful consultation with neurologists who specialized in neuro-ophthalmology.
In first case, the patient had multiple sclerosis with ophthalmalgia and characteristic oculomotor symptoms and trigeminal paralysis. The patient was diagnosed with pontine lesions near the trigeminal root entry zone of trigeminal paralysis based on the characteristic ocular symptoms such as upbeat nystagmus. In the other case, the patient’s chief complaint of chronic dizziness was associated with opsoclonus. Both opsoclonus and autoantibodies to glutamate receptor δ2 contributed to the diagnosis of autoimmune encephalitis/encephalopathy. In the other two cases, the oculomotor examination results of the patient with Wernicke's encephalopathy associated with primary position upbeat nystagmus and of the patient with Lambert–Eaton myasthenic syndrome associated with downbeat nystagmus and gaze-evoked nystagmus affected the treatment decisions of other departments. Neuro-ophthalmological examination requires effective cooperation with other departments, and for many cases, consultation with specialists in neuro-ophthalmology is required.
We investigated subjective symptoms, ophthalmic findings, accommodation power, and accommodation tension/relaxation time in 28 cases of intracranial hypotension syndrome. TriIRIS and ARK-1were performed in cases without visual acuity or field disturbance.
Ophthalmic symptoms included ocular pain（74.1％）, out-of-focus（60.7％）, monocular diplopia（42.9％）, binocular diplopia（35.7％）, visual acuity disturbance（28.5％）, photophobia（25.0％）, and visual field defects（7.1％）.
No abnormalities were observed in the eyes of patients with visual acuity disturbances. Afferent visual field defects were found in half of the cases with visual field disturbances. The accommodation power were lower than the average age in 75％ cases. The visual symptoms improved in all cases after infusion therapy, and 2/3 cases showed improved gaze tracking and decreased blinks during convergence in TriIRIS. However, none of the cases displayed any changes in the ARK-1test. Improvement in the visual appearance after infusion therapy for intracranial hypotension syndrome might be because of enhancement in the function of the convergence reflex.
In cases of late or end-stage glaucoma, it is often easy to overlook changes to the optical nerve and vision field due to an already low visual function and pale discs. In this case, new lesions of neurosarcoidosis were successfully diagnosed in a patient with late stage glaucoma, using Magnetic Resonance Imaging（MRI）.
A 48-year-old man presented with a sudden decrease in visual acuity in the right eye that had manifested three days prior to his visit. The patient was also being treated for skin sarcoidosis, and 10 years earlier, he was diagnosed with secondary glaucoma with iritis. There was no change to the pale discs. However, compared to his last visit, the patient exhibited a decrease in visual acuity（from 1.7 logMAR to counting finger）and critical fusion frequency of flicker（CFF: from 17 Hz to 0 Hz）in the right eye. Therefore, we decided to perform a contrast-enhanced MRI to check for optic neuritis. In addition to swelling, the MRI revealed multiple nodules along the meninges in the pons, Sylvian fissure, and midbrain. This was consistent with neuritis in both eyes, the abnormality was diagnosed as neurosarcoidosis.
The patient underwent a three-day course of pulse steroid therapy. We were unable to record any measured improvement in VA or CFF. The Goldmann visual field test revealed increased sensitivity in both eyes and improvement to the degree of visual field（VF）in the left eye.
If unusual and sudden changes occur in patients with late glaucoma, MRI scans could be effective in diagnosing other abnormalities present in the optic nerves or the brain.
In his 40s, a male subject presented a case of traumatic chiasmal syndrome（TCS）with hemifield slide phenomenon and complaints of diplopia and photophobia. The patient was diagnosed with bitemporal hemianopia caused by a skull base fracture sustained from blunt frontal region trauma. Four years after the onset, the patient visited our clinic due to experiencing photophobia and diplopia while driving. The visual acuity was 0.6 OD and 1.2 OS. Static and dynamic visual field examination revealed bitemporal hemianopia. Magnetic resonance imaging showed no abnormalities in the pituitary body. Spasms of the anterior communicating artery were considered to cause ischemia of the optic chiasm, resulting in bitemporal hemianopia. As there was exophoria at near position and the absence of significant limitation in ocular motility, we presumed that diplopia was the consequence of a hemifield slide phenomenon caused by fusion deficiency that resulted from bitemporal hemianopia. Moreover, photophobia could have resulted from damage to the suprachiasmatic nucleus. Fusion training and the use of light-shielding glasses improved the symptoms of diplopia and photophobia.
A 9-year-old girl was referred to our hospital with a complaint of decreased visual acuity in the right eye and orbital pain. At the initial visit, her visual acuity was 0.8 in the right eye. On examination, we could not confirm a relative afferent pupillary defect owing to excessive blinking. Dilated fundoscopic examination revealed optic disc swelling in the right eye with a normal-appearing disc in the left eye. Goldmann perimetry revealed expansion of Marriott’s blind spot to the macular region. Fluorescein angiography revealed hyperfluorescence of the right optic disc; however, brain magnetic resonance imaging did not reveal any abnormalities. Steroid pulse therapy was administered based on a high index of clinical suspicion for optic neuritis. Despite complete recovery of the visual field, her visual acuity and optic disc swelling remained unchanged. We suspected buried optic disc drusen（ODD）based on ultrasonographic findings of a bright echo pattern. Follow-up Goldmann perimetry revealed a spiral pattern, suggesting non-organic visual dysfunction. We report a rare case of unilateral buried ODD. The diagnosis of buried ODD is challenging, particularly in unilateral cases, because this condition mimics optic edema. Non-organic visual dysfunction should be considered in the differential diagnosis even in cases of organic disorders.