Background During the development of Huntington disease smooth pursuit may become impaired, decreasing the gain of the pursuit and releasing the saccadic intrusions. Although UHDRS includes the pursuit evaluation, it estimates the performance of this oculomotor function only qualitatively. Meanwhile its quantitative evaluation without eye movement recording equipment is practically impossible. It barely allows to notice large saccadic intrusions and it cannot detect reduction of the gain. Furthermore UHDRS motor score uses four point scale to assess the pursuit, rating it from “normal”, through “jerky”, “incomplete range” and “cannot pursue”. Such a subjective method strongly depends on examiner’s skill and experience.
Technique We designed the system that allows objective measurement of smooth pursuit parameters and its quantification. Additionally, the immobilisation of the head usually required in studying smooth pursuit is unnecessary. The sensor is placed on the subject’s head along with the laser servo projector mounted on forehead plate allowing for viewing the moving target on the wall. Eye movement measuring system uses infrared reflectometry, providing high temporal and spatial resolution (1kHz, 5 angular minutes). Such a device, along with accompanying custom-designed software, allows automatic detection of saccadic intrusions as small as 1 degree.
Conclusions The developed instrumentation demonstrated the capability for immediate and quantitative assessment of the smooth pursuit quality. Furthermore, it is characterised by easy application and minimal intrusiveness.
- smooth pursuit
- oculomotor function
- quantitative measurement
- eye movement recording equipment