We demonstrate a high-speed, image-based tracking scanning laser ophthalmoscope (TSLO) that can provide high fidelity structural images, real-time eye tracking and targeted stimulus delivery. The system was designed for diffraction-limited performance over an 8° field of view (FOV) and operates with a flexible field of view of 1°–5.5°. Stabilized videos of the retina were generated showing an amplitude of motion after stabilization of 0.2 arcmin or less across all frequencies. In addition, the imaging laser can be modulated to place a stimulus on a targeted retinal location. We show a stimulus placement accuracy with a standard deviation less than 1 arcmin. With a smaller field size of 2°, individual cone photoreceptors were clearly visible at eccentricities outside of the fovea.

Fixational eye movements remain a major cause of artifacts in optical coherence tomography (OCT) images despite the increases in acquisition speeds. One approach to eliminate the eye motion is to stabilize the ophthalmic imaging system in real-time. This paper describes and quantifies the performance of a tracking OCT system, which combines a phase-stabilized optical frequency domain imaging (OFDI) system and an eye tracking scanning laser ophthalmoscope (TSLO). We show that active eye tracking minimizes artifacts caused by eye drift and micro saccades. The remaining tracking lock failures caused by blinks and large saccades generate a trigger signal which signals the OCT system to rescan corrupted B-scans. Residual motion artifacts in the OCT B-scans are reduced to 0.32 minutes of arc (~1.6 µm) in an in vivo human eye enabling acquisition of high quality images from the optic nerve head and lamina cribrosa pore structure.

In phase-resolved OCT angiography blood flow is detected from phase changes in between A-scans that are obtained from the same location. In ophthalmology, this technique is vulnerable to eye motion. We address this problem by combining inter-B-scan phase-resolved OCT angiography with real-time eye tracking. A tracking scanning laser ophthalmoscope (TSLO) at 840 nm provided eye tracking functionality and was combined with a phase-stabilized optical frequency domain imaging (OFDI) system at 1040 nm. Real-time eye tracking corrected eye drift and prevented discontinuity artifacts from (micro)saccadic eye motion in OCT angiograms. This improved the OCT spot stability on the retina and consequently reduced the phase-noise, thereby enabling the detection of slower blood flows by extending the inter-B-scan time interval. In addition, eye tracking enabled the easy compounding of multiple data sets from the fovea of a healthy volunteer to create high-quality eye motion artifact-free angiograms. High-quality images are presented of two distinct layers of vasculature in the retina and the dense vasculature of the choroid. Additionally we present, for the first time, a phase-resolved OCT angiogram of the mesh-like network of the choriocapillaris containing typical pore openings.

The development of high magnification retinal imaging has brought with it the ability to track eye motion with a precision of less than an arc minute. Previously these systems have provided only monocular records. Here we describe a modification to the Tracking Scanning Laser Ophthalmoscope (Sheehy et al. 2012) that splits the optical path in a way that slows the left and right retinas to be scanned almost simultaneously by a single system. A mirror placed at a retinal conjugate point redirects half of each horizontal scan line to the fellow eye. The collected video is a split image with left and right retinas appearing side by side in each frame. Analysis of the retinal motion in the recorded video provides an eye movement trace with very high temporal and spatial resolution. Results are presented from scans of subjects with normal ocular motility that fixated steadily on a green laser dot. The retinas were scanned at 4 degrees eccentricity with a 2 degree square field. Eye position was extracted offline from recorded videos with an FFT based image analysis program written in Matlab. The noise level of the tracking was estimated to range from 0.25 to 0.5 arc minutes SD for three subjects. In the binocular recordings, the left eye / right eye difference was 1 to 2 arc minutes SD for vertical motion and 10 to 15 arc minutes SD for horizontal motion, in agreement with published values from other tracking techniques.

Background: Objective tools for prognosis and disease progression monitoring in multiple sclerosis (MS) are lacking. The visuomotor system could be used to track motor dysfunction at the micron scale through the monitoring of fixational microsaccades. Aims: The aim of this study was to evaluate whether microsaccades are correlated with standard MS disability metrics and to assess whether these methods play a predictive role in MS disability. Method: We used a custom-built retinal eye tracker, the tracking scanning laser ophthalmoscope (TSLO), to record fixation in 111 participants with MS and 100 unaffected controls. Results: In MS participants, a greater number of microsaccades showed significant association with higher Expanded Disability Status Scale score (EDSS, p < 0.001), nine-hole peg test (non-dominant: p = 0.006), Symbol Digit Modalities Test (SMDT, p = 0.014), and Functional Systems Scores (FSS) including brainstem ( p = 0.005), cerebellar ( p = 0.011), and pyramidal ( p = 0.009). Both brainstem FSS and patient-reported fatigue showed significant associations with microsaccade number, amplitude, and peak acceleration. Participants with MS showed a statistically different average number ( p = 0.020), peak vertical acceleration ( p = 0.003), and vertical amplitude ( p < 0.001) versus controls. Logistic regression models for MS disability were created using TSLO microsaccade metrics and paraclinical tests with ⩾80% accuracy. Conclusion: Microsaccades provide objective measurements of MS disability level and disease worsening.

Abstract:We demonstrate a system that combines a tracking scanning laser ophthalmoscope (TSLO) and an adaptive optics scanning laser ophthalmoscope (AOSLO) system resulting in both optical (hardware) and digital (software) eye-tracking capabilities. The hybrid system employs the TSLO for active eye-tracking at a rate up to 960 Hz for real-time stabilization of the AOSLO system. AOSLO videos with active eyetracking signals showed, at most, an amplitude of motion of 0.20 arcminutes for horizontal motion and 0.14 arcminutes for vertical motion. Subsequent real-time digital stabilization limited residual motion to an average of only 0.06 arcminutes (a 95% reduction). By correcting for high amplitude, low frequency drifts of the eye, the active TSLO eye-tracking system enabled the AOSLO system to capture high-resolution retinal images over a larger range of motion than previously possible with just the AOSLO imaging system alone.

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.

From the Section Editor: The JNO “Disease of the Year: Multiple Sclerosis” series concludes with a focus on cutting edge techniques used to qualitatively and quantitatively evaluate ocular motility abnormalities. In their article, “Methods to Assess Ocular Motor Dysfunction in Multiple Sclerosis,” Sheehy and colleagues expand on the earlier works published by Lee et al, and Nerrant et al, which provide an elegant overview of extra-ocular movement findings associated with brainstem disorders, and multiple sclerosis, respectively. The tools highlighted by Sheehy and colleagues add to our understanding of structure-function relationships in multiple sclerosis, and further expand the role of visual system models in multiple sclerosis research and clinical trials. In the series finale, “The International Multiple Sclerosis Visual System Consortium: Advancing Visual System Research in Multiple Sclerosis,” Balcer and colleagues chronicle the inception, development, and achievements of IMSVISUAL, a consortium created by clinicians and researchers committed to advancing the role of visual outcomes in the care of multiple sclerosis patients. The ingenuity and accomplishments of IMSVISUAL will serve to inspire other international collaborations, and further advance scientific discovery in the field of neuro-ophthalmology. Background: 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.