Up/down anisotropies of vertical saccades in healthy children depending on the mode and the depth of execution

Oculomotor Impairments in Children After Posterior Fossa Tumors Treatment

Posterior fossa tumors (PFT) are the most common pediatric brain tumors, and the study of the somatic and cognitive status of PFT survivors still remains a critical problem. Since cerebellar damage can affect eye movement centers located in the vermis and hemispheres, such patients suffer from disturbances in visual perception, visual-spatial functions, reading, etc. Our investigation aimed at describing oculomotor impairments in PFT survivors linked to core oculomotor functions assessed through eye tracking method: gaze holding, reflexive saccades, and organization of voluntary saccades and their dependency on age at tumor diagnosis. Also, we investigated the relationship between oculomotor functions and ataxia measured with International Cooperative Ataxia Rating Scale (ICARS). A total of 110 children (patients and age-matched healthy controls, aged 9-17 years old) participated in the study. We found that the earlier the child had a tumor, the more impaired gaze holding (p = 0.0031) and fewer isometric saccades (p = 0.035) were observed at the time of examination. The above-mentioned functions in healthy controls improved with age. Visual scanning was also impaired compared to controls but was not related to age at diagnosis. A positive correlation between ICARS scores and number of hypermetric saccades (r = 0.309, p = 0.039), but no correlation with the number of hypometric saccades (r = - 0.008, p = 0.956). Furthermore, number of hypometric saccades did not differ between patients and controls (p = 0.238). Thus, primarily hypermetric saccades can be considered a prominent oculomotor symptom of cerebellar tumors. Our study provides basis for new methods of PFT diagnosis and rehabilitation procedure evaluation, both playing essential roles in modern pediatric neurooncology.

Measuring vergence and fixation disparity in 3D space

As the eyes continuously move in 3D space, they rarely converge at the exact depth of the plane even when fixating a 2D image or computer screen. Rather, the lines of gaze measured by eye movement recordings show some misalignment so-called fixation disparity. Fixation disparity occurs in front of or behind the plane, and the eyes may also be lagged vertically. For those reasons, vision research requires mathematical tools to calculate where exactly the lines of gaze cross the stimulus plane. Seminal research on vergence eye movements targeting stimuli lying on isovergence curves has been content with simple computation of the difference between the two eye rotation angles. Recently, the need of new calculations has emerged with the increasing use of eye-trackers providing the eye coordinates on a computer screen. Previous studies have made this attempt but with restrictions. We introduce here a complete calculation of fixation disparity in 3D space allowing vision researchers to study the precision of gaze regardless of the stimulus location in 3D space and of whether the eyes lag horizontally and/or vertically.