Ocular myasthenia gravis saccades as a measure of extraocular muscle function

Sui H Wong; Matthew James Bancroft; Vijay K Tailor; Mohamed Abbas; Akila Sekar; Claire Noble; Maria Theodorou; Diego Kaski

doi:10.3389/fopht.2022.938088

Ocular myasthenia gravis saccades as a measure of extraocular muscle function

Front Ophthalmol (Lausanne). 2022 Oct 12:2:938088. doi: 10.3389/fopht.2022.938088. eCollection 2022.

Authors

Sui H Wong^{1

2}, Matthew James Bancroft², Vijay K Tailor^{1

3}, Mohamed Abbas¹, Akila Sekar², Claire Noble¹, Maria Theodorou¹, Diego Kaski²

Affiliations

¹ Moorfields Eye Hospital, London, United Kingdom.
² Department of Clinical and Movement Neurosciences, University College London, London, United Kingdom.
³ Department of Experimental Psychology, University College London, London, United Kingdom.

Abstract

Background: It is important to understand the pathophysiology of ocular myasthenia gravis (OMG) to improve treatment.

Aim: To use modern video-oculography to characterise saccadic eye movements in patients with OMG, including anti-AChR, anti-MuSK, anti-LRP4, and seronegative OMG.

Methods: In total, 21 patients with OMG and five age-matched healthy control subjects underwent video-oculography. Participants performed a sequence of horizontal saccades (3 minutes each) at ±5°, ± 10°, and ±20°, followed by 3 minutes of saccades directed at randomly presented targets at ±5°, ± 10°, and ±15°. We recorded the direction, amplitude, duration, peak, and average velocity of each saccade for each task for each participant.

Results: Saccadic amplitude, duration, and average velocity were all lower in OMG patients than in control subjects (p < 0.021). Saccadic amplitude and velocity decreased over time, but this decrease was similar in OMG patients and control subjects. Fixation drift and ocular disparity tended to be greater in OMG patients than in control subjects. Saccadic intrusions occurred more frequently in OMG patients than in control subjects (p < 0.001). No significant effects of time or group by time on fixation drift or ocular disparity were found.

Discussion: Saccadic velocities in OMG patients differed from those in normal control subjects, which suggests that OMG affects fast-twitch fibres, although fast-twitch fibres were still able to generate "twitch" or "quiver" movements in the presence of even severe ophthalmoplegia. Slow-twitch muscle fibres involved in gaze holding were also affected, accounting for increased fixation drift following saccades. Our objective finding of increased fixation drift and a larger number of saccadic intrusions mirror our anecdotal experience of patients with OMG who report significant diplopia despite minimal ophthalmoplegia on examination. Such microsaccades may be a surrogate for compensation of a gaze-holding deficit in MG.

Keywords: extraocular muscle; myasthenia gravis; ocular myasthenia gravis; saccades; video-oculography.