Video-Oculography for the Diagnosis of Ocular Myasthenia Gravis: A Review of Diagnostic Accuracy, Cost-Effectiveness, and Guidelines

Myasthenia gravis is an autoimmune disorder characterized by muscle weakness, as a result of neuromuscular transmission impairment; the fluctuating muscle weakness generally occurs in voluntary skeletal muscles, and varies in severity between patients. The prevalence is estimated to be 77.7 per million persons according to a meta-analysis of epidemiologic studies published between 1950 and 2017 worldwide. This makes myasthenia gravis the most common neuromuscular transmission disorder.Ocular myasthenia gravis occurs when the extrinsic ocular muscles are involved. Ocular muscle weakness can cause symptoms such as ptosis (dropping of the upper eyelid) or binocular diplopia (double vision). Ocular symptoms are common in those with myasthenia gravis. Some patients with myasthenia gravis have only ocular symptoms. However, for more than 80% of the those with ocular symptoms only at the onset of myasthenia gravis, weakness spreads to other muscle groups at some point. One retrospective cohort study has indicated that early intervention for ocular myasthenia gravis was associated with the decrease in the frequencies of ocular symptoms and the delay or potential prevention of the occurrence of generalized myasthenia gravis.The diagnosis of ocular myasthenia gravis is not an easy task when ptosis is the only ophthalmic symptom. A series of tests can be used to diagnose ocular myasthenia gravis, such as serum antibodies, the tensilon test, and electromyography (EMG). These exams are not always able to identify the patients with ocular myasthenia gravis. The detection of antibodies to muscle acetylcholine receptors or the muscle-specific receptor tyrosine kinase in the serum can be useful in identifying cases, but antibodies do not present in all patients, rendering the antibody test ineffective for some. The tensilon test has a sensitivity around 80% and uses edrophonium, a drug that blocks acetylcholinesterase and reverse muscle weakness temporarily. However, edrophonium can cause life-threatening side effects, such as hypotension and bradycardia. EMG uses repetitive nerve stimulations to detect decreasing amplitude with repetitive stimulation. Single-fibre EMG is used to detect variability between individual muscle fibres within a motor unit. By measuring the jitter of the muscle fibres, single-fibre EMG can determine whether acetylcholine release is within normal ranges and the neuromuscular transmission functions well. One major disadvantage of EMG is that it requires electrodes inserted in the target muscles. The invasive nature of this test can prevent patients from being examined.Recently, video-oculography, a non-invasive test that tracks eye movements using video cameras, has been used in medicine for a few indications. There is some evidence showing that eye-tracking technology, such as video-oculography, can be used for the diagnosis of ocular myasthenia gravis. With the potential to avoid side effects of invasive procedures and prevent generalized myasthenia gravis, there is a need to review the diagnostic accuracy and cost-effectiveness of video-oculography for the detection of ocular myasthenia gravis, as well as the clinical guidelines regarding the use of eye-movement analysis (video-oculography) for suspected myasthenia gravis.