Measuring saccades in patients with Niemann-Pick type C: A comparison between video-oculography and a novel eye tracking test based on continuous psychophysics

A Grillini; L H Koens; G Lizaitiene; F Lange; F W Cornelissen; M A J Tijssen

doi:10.1016/j.prdoa.2022.100170

Measuring saccades in patients with Niemann-Pick type C: A comparison between video-oculography and a novel eye tracking test based on continuous psychophysics

Clin Park Relat Disord. 2022 Oct 26:7:100170. doi: 10.1016/j.prdoa.2022.100170. eCollection 2022.

Authors

A Grillini¹, L H Koens^{2

3}, G Lizaitiene⁴, F Lange⁵, F W Cornelissen¹, M A J Tijssen^{2

3}

Affiliations

¹ Laboratory of Experimental Ophthalmology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9700 RB Groningen, The Netherlands.
² Department of Neurology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9700 RB Groningen, The Netherlands.
³ Expertise Center Movement Disorders Groningen, University Medical Center Groningen, Groningen, Hanzeplein 1, 9700 RB Groningen, The Netherlands.
⁴ Faculty of Medicine, Vilnius University, M. K. Čiurlionio g. 21/27, LT-03101 Vilnius, Lithuania.
⁵ Department of Clinical Neurophysiology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9700 RB Groningen, The Netherlands.

Abstract

Introduction: Vertical supranuclear gaze palsy is a key feature of Niemann-Pick type C (NP-C) and is commonly quantified using video-oculography (VOG). VOG requires sitting still for long times and performing specific tasks, thus it can be challenging or impossible for patients severely affected by movement disorders or cognitive impairment. To overcome this limitation, we measure saccades of NP-C patients using a fast eye tracking test based on continuous psychophysics and compare it to VOG.

Methods: Saccades of six NP-C patients and six age-matched controls were assessed using VOG and Standardized Oculomotor and Neuro-ophthalmic Disorders Assessment (SONDA). In SONDA, participants continuously track a semi-randomly moving dot on a computer screen while their gaze is being tracked. For both assessments, saccades were quantified using four conventional measures: amplitude, gain, latency, and peak velocity. Furthermore, SONDA's continuous measures were quantified with several novel spatio-temporal properties.

Results: In the NP-C patients, both methods revealed reduced amplitude, gain, peak velocity, and increased latency of vertical saccades compared to horizontal saccades and compared to healthy controls. Effect sizes obtained with SONDA were overall larger than those for VOG. SONDA's spatio-temporal properties showed similar trends.

Conclusion: SONDA reveals a deterioration of vertical saccades in NP-C patients that is consistent with VOG. SONDA's measures based on continuous psychophysics are consistent with traditional saccadic parameters and can potentially provide complementary information. SONDA shows larger effect sizes than VOG, suggesting that it provides robust and clinically relevant outcomes with a more intuitive task and shorter testing time.

Keywords: Eye movement disorders; NP-C, Niemann-Pick type C; Niemann-Pick type C; SONDA; SONDA, Standardized Oculomotor and Neuro-ophthalmic Disorders Assessment; VOG; VOG, Video-oculography; VSGP, Vertical supranuclear gaze palsy; Vertical supranuclear gaze palsy.