From the Guidelines
Internuclear ophthalmoplegia (INO) is a specific gaze disorder that requires immediate referral to a neurologist for comprehensive evaluation and management of the underlying condition, which is typically multiple sclerosis in younger patients and stroke or vascular disease in older patients. The diagnosis of INO is primarily clinical, based on the characteristic eye movement abnormalities during horizontal gaze testing, including impaired adduction of the affected eye and nystagmus in the abducting eye. Neuroimaging, particularly MRI, is essential to identify the underlying cause, as it can help detect damage to the medial longitudinal fasciculus (MLF), a nerve tract in the brainstem that coordinates eye movements between the sixth and third cranial nerve nuclei 1.
The management of INO focuses on addressing the underlying condition, with no specific treatment for INO itself. For multiple sclerosis-related INO, immunomodulatory therapies may be prescribed, while stroke-related INO requires appropriate vascular risk factor management 1. The prognosis varies depending on the cause, with some cases resolving spontaneously while others persist.
In terms of diagnostic evaluation, a complete ophthalmic examination with emphasis on the sensorimotor evaluation and completion of the three-step test and consideration of the upright-supine test is necessary 1. Additionally, careful checking for other neuro-ophthalmic signs and symptoms, such as Horner’s syndrome, cranial nerve palsy, and nystagmus, is crucial. Fundus examination to check for papilledema or optic atrophy and visual field testing may also provide additional information on the etiology.
Initial treatment with prism may be helpful to manage diplopia while waiting for possible recovery, and botox, prism, or strabismus surgery may be considered for cases that do not resolve 1. The goals of surgery should be customized for the individual patient, who may be bothered to different degrees by diplopia, head tilt, and perceived tilting of the visual vertical.
It is essential to consider referral to a neurologist or neuro-ophthalmologist if the INO is not isolated or is associated with other neurological signs and symptoms, as neuroimaging and further evaluation may be necessary 1. Small vertical fusional amplitudes in a case of isolated INO, absent a history of trauma, may indicate an acquired cause and should be evaluated with neuroimaging. The ophthalmologist should discuss the findings, explain the disorder, provide diagnosis, and discuss management options with the patient and, as appropriate, with a neuro-ophthalmologist, neurologist, or other specialist, as indicated 1.
From the Research
Diagnosis of Internuclear Ophthalmoplegia (INO)
- Internuclear ophthalmoplegia (INO) is a sign of exquisite localizing value, often due to either multiple sclerosis or infarction 2.
- The differential diagnosis of INO should be tripartite: multiple sclerosis, stroke, and other causes 2.
- INO is clinically characterized by total or partial failure to adduct one eye in lateral gaze and a monocular nystagmus of the abducting eye 3.
- The method of choice for diagnostic imaging of MLF lesion in patients with INO is magnetic resonance imaging (MRI) 3, 4, 5.
Causes of Internuclear Ophthalmoplegia (INO)
- The most common causes of INO are multiple sclerosis and brainstem infarction 2, 3, 4.
- Other causes include head trauma, brainstem and fourth ventricular tumors, Arnold-Chiari malformation, infection, hydrocephalus, and lupus erythematosus 3.
- Unusual causes of INO include trauma, tentorial herniation, infection, tumor, iatrogenic injury, hemorrhage, vasculitis, and miscellaneous 2.
Treatment and Management of Internuclear Ophthalmoplegia (INO)
- There is no specific treatment mentioned in the provided studies, but the diagnosis and management of the underlying cause are crucial 2, 3, 4, 6, 5.
- A validated standardized infrared oculography protocol (DEMoNS) can be used for quantifying prosaccades in patients with MS and healthy controls, which can help in diagnosing INO 6.
- The versional dysconjugacy index (VDI) can be calculated to describe the ratio between the abducting and adducting eye, which can help in diagnosing INO 6.