Suboptimal eye movements for seeing fine details.

Human eyes are never stable, even during attempts of maintaining gaze on a visual target. Considering transient response characteristics of retinal ganglion cells, a certain amount of motion of the eyes is required to efficiently encode information and to prevent neural adaptation. However, excessive motion of the eyes leads to insufficient exposure to the stimuli, which creates blur and reduces visual acuity. Normal miniature eye movements fall in between these extremes, but it is unclear if they are optimally tuned for seeing fine spatial details. We used a state-of-the-art retinal imaging technique with eye tracking to address this question. We sought to determine the optimal gain (stimulus/eye motion ratio) that corresponds to maximum performance in an orientation-discrimination task performed at the fovea. We found that miniature eye movements are tuned but may not be optimal for seeing fine spatial details

Methods to Assess Ocular Motor Dysfunction in Multiple Sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system causing the immune-mediated demyelination of the brain, optic nerve, and spinal cord and resulting in ultimate axonal loss and permanent neurological disability. Ocular motor dysfunction is commonly observed in MS but can be frequently overlooked or underappreciated by nonspecialists. Therefore, detailed and quantitative assessment of eye movement function has significant potential for optimization of patient care, especially for clinicians interested in treating visual symptoms or tracking disease progression. METHODS:: A brief history of eye tracking technology followed by a contextualized review of the methods that can be used to assess ocular motor dysfunction in MS-including a discussion of each method's strengths and limitations. We discuss the rationale for interest in this area and describe new tools capable of tracking eye movements as a possible means of monitoring disease. RESULTS/CONCLUSIONS:: This overview should inform clinicians working with patients with MS of how ocular motor deficits can best be assessed and monitored in this population. It also provides a rationale for interest in this field with insights regarding which techniques should be used for studying which classes of eye movements and related dysfunction in the disease

Visualization 2: Active eye-tracking for an adaptive optics scanning laser ophthalmoscope

Originally published in Biomedical Optics Express on 01 July 2015 (boe-6-7-2412

Imaging of optic nerve head pore structure with motion corrected deeply penetrating OCT using tracking SLO

Purpose To remove the eye motion and stabilize the optical frequency domain imaging (OFDI) system for obtaining high quality images of the optic nerve head (ONH) and the pore structure of the lamina cribrosa. Methods An optical coherence tomography (OCT) instrument was combined with an active eye tracking system to compensate for eye motion in OCT imaging. The OCT system was a phase-stabilized deeply penetrating OFDI system operating at center wavelength of 1040 nm and the eye tracker was an 840 nm scanning laser ophthalmoscope (SLO). Retinal tracking was performed using real-time analysis of the distortions within SLO frames. OFDI had axial resolution of 4.8 µm (6.5 µm in air) and the theoretical spot-size on the retina was 13.7 µm. Eye motion was reported at a rate of 960 Hz and motion signals were inverted to correction signals and used to keep the OCT scanning grid locked on the same retinal area throughout the measurement. In the case of a tracking lock failure (e.g. blink or large saccade), the tracker signaled the OFDI system to rescan corrupted B-scans immediately stepping back 10 B-scans and holding the position until signal was valid again. The achieved tracking bandwidth was 32 Hz due to an internal time lag of the hardware. The ONH of a healthy volunteer was imaged over an area of 2.7 × 2.7 mm (8.8°) using 700 A-scans/B-scan. To visualize the benefit of the tracking, each acquired B-scan in a volume dataset (total of 700 B-scans) was integrated over depth to create an enface image of the ONH. Results The ONH was successfully imaged with negligible artifacts from eye motion (Fig. 1). On the left side, the whole dataset is seen including the duplicate corrupted B-scans. The corrupted B-scans were then removed in post-processing, thus leaving the undistorted duplicates untouched. The measured residual motion in the OCT B-scans was 0.32 arcmin (~1.6 µm) in a human eye. Four volumes from the same location were registered together to visualize the lamina cribrosa throughout the different depth slices of the eye (Fig. 2). The pore structure was clearly visible up to 430 um from the bottom of the ONH cup. Conclusions It is possible to obtain high quality OCT images from ONH and lamina cribrosa by compensating the eye motion during the measurements

Media 2: High-speed, image-based eye tracking with a scanning laser ophthalmoscope

Originally published in Biomedical Optics Express on 01 October 2012 (boe-3-10-2611

Media 1: High-speed, image-based eye tracking with a scanning laser ophthalmoscope

Originally published in Biomedical Optics Express on 01 October 2012 (boe-3-10-2611

Fixational eye movements following concussion

The purpose of this study was to evaluate fixational eye movements (FEMs) with high spatial and temporal resolution following concussion, where oculomotor symptoms and impairments are common. Concussion diagnosis was determined using current consensus guidelines. A retinal eye-tracking device, the tracking scanning laser ophthalmoscope (TSLO), was used to measure FEMs in adolescents and young adults following a concussion and in an unaffected control population. FEMs were quantified in two fixational paradigms: (1) when fixating on the center, or (2) when fixating on the corner of the TSLO imaging raster. Fixational saccade amplitude in recent concussion patients (≤ 21 days) was significantly greater, on average, in the concussion group (mean = 1.03°; SD = 0.36°) compared with the controls (mean = 0.82°; SD = 0.31°), when fixating on the center of the imaging raster (t = 2.87, df = 82, p = 0.005). These fixational saccades followed the main sequence and therefore also had greater peak velocity (t = 2.86, df = 82, p = 0.006) and peak acceleration (t = 2.80, df = 82, p = 0.006). These metrics significantly differentiated concussed from controls (AUC = 0.67-0.68, minimum p = 0.005). No group differences were seen for the drift metrics in either task or for any of the FEMs metrics in the corner-of-raster fixation task. Fixational saccade amplitudes were significantly different in the concussion group, but only when fixating on the center of the raster. This task specificity suggests that task optimization may improve differentiation and warrants further study. FEMs measured in the acute-to-subacute period of concussion recovery may provide a quick (\u3c3 \u3eminutes), objective, sensitive, and accurate ocular dysfunction assessment. Future work should assess the impact of age, mechanism of injury, and post-concussion recovery on FEM alterations following concussion

Media 2: Real-time eye motion compensation for OCT imaging with tracking SLO

Originally published in Biomedical Optics Express on 01 November 2012 (boe-3-11-2950

Media 1: Real-time eye motion compensation for OCT imaging with tracking SLO

Originally published in Biomedical Optics Express on 01 November 2012 (boe-3-11-2950