Every 40 seconds, someone in the United States experiences a stroke, according to the U.S. Centers for Disease Control and Prevention. A vast majority of strokes (some 87%) are ischemic, meaning they block blood flow to the brain. When an ischemic stroke occurs in the brain’s occipital lobe, which processes visual information, this can result in vision loss in part of the visual field. In the most severe cases, patients suffer from homonymous hemianopia (HH), in which the same half of the visual field is totally lost in both eyes, while the other half is maintained.
Gislin Dagnelie, Ph.D., a professor of ophthalmology and the associate director of the Lions Vision Research and Rehabilitation Center at the Wilmer Eye Institute, learned from his colleagues in the Low Vision Clinic that much remains unknown about how patients deal with HH, and that outcomes vary widely. This past summer, he received a grant from Research to Prevent Blindness (RPB) and the Lions Clubs International Foundation (LCIF) —two organizations that have provided decades-long support to Wilmer — to investigate why some people with HH can develop ways to adapt to their vision loss by using effective scanning strategies, while others suffer long- term, disabling consequences. With scanning, individuals willfully direct their gaze into the blind side of the visual field to detect things they can’t see by looking straight ahead. But not everyone with HH learns to scan effectively.
Limitations caused by HH can be severe, Dagnelie explains, resulting in a patient’s inability to see, for example, items on the right side of a room or the entire left side of a loved one’s face. Difficulties with reading and scanning the visual environment typically ensue and can cause people to experience collisions with people or objects, drastically affecting an individual’s personal and professional life.
“HH presents a form of low vision that is tricky to pin down,” Dagnelie says. “When patients have macular degeneration or glaucoma, low vision specialists often prescribe magnifiers and other devices to help with blurry vision, but with HH, the missing visual field cannot be restored, and helping the patient compensate for the defect is often by trial and error, involving occupational therapy (OT) to train individuals in techniques like scanning.” The outcomes, he says, are inconsistent. Some patients learn to compensate largely on their own or with minimal help from a therapist, and others spend significant time in OT, only to keep struggling.
Since HH occurs instantaneously with an occipital stroke, Dagnelie and his team, including Liancheng Yang, the senior system manager, Chris Bradley, Ph.D., a research associate, and Arathy Kartha, Ph.D., a postdoctoral fellow, hope to recruit participants to the RPB- and LCIF-funded study as soon as possible after they experience a stroke. To help with recruitment, his team will use Epic, the electronic medical records system at Johns Hopkins Medicine and the Wilmer Eye Institute.
“We’ve created a way for certain diagnoses and keywords entered in Epic to trigger an alert to the doctor about this research,” Dagnelie explains. For instance, when a neurologist or neuro- ophthalmologist enters a diagnosis of HH in a patient’s record, a flag will pop up in real time alerting the clinician, who can then tell the patient about the research opportunity.
Only a dozen or so participants will take part in this first phase of the study because, as Dagnelie says, “we need to look carefully at what happens in a few patients, so we know what changes to look for in a larger number.” That larger number, in the second part of the study, will be about 100 subjects.
Participants will wear a video headset designed specifically for Dagnelie and his team’s investigation. The headset will display a video with various stimuli and scenes, which participants will attempt to look at and identify when prompted. Meanwhile, a tracker within the headset will document each participant’s eye movements, allowing Dagnelie and his team to quantify and analyze how individuals with HH use their eyes and, for example, how long it takes to notice new stimuli. Using the eye tracker also enables the team to establish a control group, given that some people with normal vision will be recruited, and their vision will be artificially restricted by blanking out everything to the right or left of where they look. This way, the team can study how a person responds to the experience of sudden HH, without the added anxiety of having just suffered a stroke.
“Our hunch is that an individual’s response to HH, and whether they can compensate, depends in large part on their eye movements,” Dagnelie shares. “There is a lot of variability in how people look at the world, and we want to find out: What is the natural way people respond to HH? How do their eyes move and respond to the environment, and how does that contribute to how they adapt?”
The study’s second phase will look at therapeutic approaches to HH, based on lessons learned in the earlier phase about eye movement, with a goal of creating more nuanced and specific treatment guidelines for a broad range of patients.
“Therapy right now is hit and miss,” Dagnelie says. “We hope our work will lead to a more systematic approach to HH, so that when patients come in, the clinician can measure eye movement with the headset and use that information to determine what type of therapy may be most effective to help them overcome their problems. Receiving this grant from RPB and LCIF has been a game changer for our research.”