Knowing what the brain is seeing in three dimensions: A novel, noninvasive, sensitive, accurate, and low-noise technique for measuring ocular torsion

Abstract

Torsional eye movements are rotations of the eye around the line of sight. Measuring torsion is essential to understanding how the brain controls eye position and how it creates a veridical perception of object orientation in three dimensions. Torsion is also important for diagnosis of many vestibular, neurological, and ophthalmological disorders. Currently, there are multiple devices and methods that produce reliable measurements of horizontal and vertical eye movements. Measuring torsion, however, noninvasively and reliably has been a longstanding challenge, with previous methods lacking real-time capabilities or suffering from intrusive artifacts. We propose a novel method for measuring eye movements in three dimensions using modern computer vision software (OpenCV) and concepts of iris recognition. To measure torsion, we use template matching of the entire iris and automatically account for occlusion of the iris and pupil by the eyelids. The current setup operates binocularly at 100 Hz with noise <0.1° and is accurate within 20° of gaze to the left, to the right, and up and 10° of gaze down. This new method can be widely applicable and fill a gap in many scientific and clinical disciplines.

Upright Perception and Ocular Torsion Change Independently during Head Tilt

“…(A) Example of eye image obtained from the cameras with the overlay of automatically detected eyelids and pupil (top) and the iris pattern extracted and optimized to calculate torsion (bottom). For more details see Otero-Millan et al (2015). (B) Subjective visual vertical (SVV) paradigm.…”

“…This system uses two cameras (Firefly MV, PointGrey Research Inc., Richmond, BC, Canada) mounted on goggles to capture infrared images of each eye. To measure and track torsional eye position, we used a method developed by our group (Figure 1A) that operates binocularly in real time at 100 Hz and with a noise level less than 0.1° (Otero-Millan et al, 2015). …”

“…We used a modified SVV paradigm to track changes in upright perception over time. While it is technically challenging to measure torsional eye position, we have developed a novel video method that allows tracking ocular torsion in real time (Otero-Millan et al, 2015). First, we examined the correlation between changes in SVV and ocular torsion during head tilt and their corresponding aftereffects when the head was brought back to upright position.…”

The video ocular counter-roll (vOCR): a clinical test to detect loss of otolith-ocular function

“…This method operates in real time at 100 Hz with a noise level less than 0.1°. Further technical details about this method have been published previously [9]. Participants sat upright in dim light fixing on a red dot (diameter = 0.33°) on a CRT monitor (1280 px by 1024 px) 135 cm away.…”

“…However, OCR measurement using VOG has not been previously reported as a clinical test for vestibular loss. Here we used a VOG method that can track torsional eye position in real time to measure static OCR (vOCR) [9]. We measured vOCR in patients with known vestibular loss and in healthy controls to determine whether it can detect loss of otolith-ocular function.…”