Eye-rolling robot may reveal clues about human health
Photo caption: Dr. Stephen L. Macknik, far right, with his research team. Front row: Olivya Caballero, Biomedical Engineer. Back row, l to r: Jordi Chanovas, PhD student; Manuel Ledo, Research Support Specialist; Daniel Cortes Rastrollo, Programmer Analyst; Ashwin Venkatakrishnan, Biomedical Engineer; Dr. Robert Alexander, Research Assistant Professor.
Your eyes are constantly moving—only you don’t know it. Even when you think you’re keeping them still, they’re actually jiggling around in tiny micromovements.
Vision scientists have identified and explained a number of these eye movements, but the smallest one, called tremor, is too fleeting and minuscule for current technology to record accurately. However, a new system being developed at SUNY Downstate will allow scientists to study tremor in depth and discover its mechanisms and function.
Eye movements are critical to our survival as a species. The only place you actually have 20/20 vision is right in the center—your thumbnail, if you’re holding your arm out in front of you. Everywhere else you’re legally blind.
To compensate for this disadvantage, we evolved to develop a group of muscles to move our eyes around (the ocular-motor system). The largest eye movement, known as saccade (French for ‘jump’), leaps from point to point as we scan our surroundings (for predators or prey, for example). Once we detect an object of interest (such as a potential mate) and focus our 20/20 vision on it, other movements, called fixational eye movements, take over.
But fixational eye movements presented a different evolutionary problem. Without fresh input, brain cells stop firing, and whatever we’re looking at starts to fade from view. In response, our brains developed microsaccades, a jiggling motion of the eye that constantly provides new information to our neurons as we’re gazing at one object.
Even between microsaccades our eyes are still moving, drifting around without our being aware of it. As they drift, they’re also making an infinitesimal motion, about the size of one photoreceptor cell. That motion is called tremor, and it’s far too slight to study with current eye-tracking systems.
Says vision scientist Stephen Macknik, who heads the Lab of Translational Neuroscience at SUNY Downstate, “Drift and tremor happen at the same time, but we don’t know how they contribute to our vision differently. Tremor might be contributing to how we see very, very small things, while drift might be moving the eye around so that tremor can do its job. They’re conflated in our experiments. We need to deconflate them, but we need tools to measure what’s happening.”
Macknik and Nicolas Brunet, who works in Macknik’s lab, are developing that tool—a video system that can zoom in on the eye with at least ten times or more resolution than previous systems. This will allow them to see minute motions that weren’t discernible before and view tremor and drift and microsaccades and saccades all in relationship to each other.
Macknik and Brunet received a Technology Accelerator Fund investment to advance their project. It will be used not on the video system itself but on building a revolutionary mechanism for testing the system’s accuracy when enhanced with proprietary improvements. Brunet is constructing a robot with a fake eye that mimics the movements of the human eye, down to 1/3600 of a thumbnail.
Says Brunet, “We are trying to determine how small and how often the movements we can make with the robots. The next step is to place a fake eye in the robot and move it around to see if we’re actually able to make those tiny little movements that represent tremor with a fake eye.” If the video system can record the robot’s infinitesimal eye movements, it will be good to go on human subjects.
Drift and tremor drive half of what we see, so the capacity to disentangle and objectively record them will break open an entire field of investigation for vision labs around the world. Beyond the basic research, the information it yields will have significant applications in the field of human health.
According to Macknik, a number of diseases affect the ocular-motor system, so better understanding of the system’s components can reveal all sorts of details about brain health. For instance, knowing what actually happens during drift and tremor could be important to helping ophthalmological patients with muscular dystrophy determine to what extent the disease is affecting their eye movements. A more discriminatory system could lead to better diagnoses of Parkinsonian disorders and progressive supranuclear palsy, which are often confused, leading to potentially awful end-of-life consequences.
The technology itself can be used to enhance people’s lives. For those like the late Stephen Hawking, whose neurodegenerative disease forced him to rely on an eye-tracking device to communicate, the team's system will greatly expand the resolution and capabilities of these types of eye tracking systems.
It could also boost public safety. For example, eye movements change when a person is aroused, fatigued, or mentally overworked. An improved mechanism for tracking eye movements could keep tired pilots out of the cockpit, stressed soldiers off the battlefield, and fatigued surgeons away from a scalpel.
Current video technology tracks the eye's pupil. As a biological feature, however, the pupil is wet and messy, with a high degree of “noise” and variability from person to person. A superior eye-tracking system that can objectively, precisely, and universally track eye movements would allow a doctor to verify if a patient with locked-in syndrome, for instance, is actually aware or just in a coma, a critical first step toward rehabilitation.
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