Scott N J Watamaniuk, Ph.D., a professor of psychology at Wright State University, received a four-year $500,000 grant to investigate how the brain coordinates the movements of the two eyes.
The research is a collaboration with Stephen Heinen, Ph.D., senior scientist at the Smith-Kettlewell Eye Research Institute in San Francisco and a Wright State alumnus.
Watamaniuk’s funding is part of a nearly $2 million grant awarded by the National Institute of Health’s National Eye Institute to Smith-Kettlewell.
The research has potential implications for those who have strabismus, a condition that results in misaligned eyes.
Watamaniuk said the prevailing theory proposed by Ewald Hering in 1868 says that the brain sends a single command that moves the eyes. From the ophthalmologist’s perspective, since it is believed that the brain controls eye movement simultaneously if one eye is moving correctly but the other is not, the signal from the brain is working and there must be something else wrong with the other eye.
Mild cases of strabismus are treated by putting a patch over the eye that is functioning correctly to tone up the muscles of the misaligned eye so that it works properly. For some patients this corrects the problem, but for others that slight deviation gets progressively worse over time. In more severe cases surgery is used as a corrective measure.
“Since the prevailing theory is that the signals from the brain to both eyes are the same, it is believed that muscles controlling the eye are imbalanced,” said Watamaniuk. “So, surgical treatment of strabismus involves snipping muscle fibers to weaken them. Unfortunately, while initially successful, in 40 percent of these operations the eye goes back to where it was within six to 12 months.”
The surgery is typically performed in children before the age of 6 to allow the visual part of the brain to develop properly. If the procedure is done too late, stereopsis, or depth perception, which allows a person to see the world in 3D, will not develop normally.
“There are about a million of these surgeries a year. So, that means for 400,000 of them, it won’t work,” Watamaniuk said.
Watamaniuk said this issue sparked a discussion with a pediatric ophthalmologist colleague of his from the Smith-Kettlewell Eye Research Institute, an independent, nonprofit research institute known for its research on vision, eye diseases and sensory rehabilitation engineering.
A competing theory to Hering’s was proposed in 1867 by Hermann von Helmholtz that the movement of each eye was controlled by the brain independently. If this is the case, strabismus would not necessarily be caused by a defect of the eye.
“Most people measure eye movements based on following an object on a screen, which doesn’t have any of the depth information,” said Watamaniuk. “Our experiment, which was published in 2021, had people follow a real object set up on a track that moved back and forth directly in line with the middle of the subject’s eyes and while the movement of both eyes was recorded.”
The same movement was then recorded while covering one eye with an infrared pass filter. Participants in the study could not see through the filter, but the eye trackers, which used infrared light, could still track the eyes and record what they were doing.
“When we did that, the covered eye did not move as it should. Or at least did not move as it had been moving, and certainly did not move the way that Hering’s theory said it should,” said Watamaniuk. “The covered eye was behind in time by up to two seconds. Its movements were not syncing. You cannot have one signal from the brain coming to both eyes and have a two-second delay.”
This information presents numerous questions that Watamaniuk hopes to answer through further research. If he is correct about disproving Hering’s theory, why does the surgery work in 60% of strabismus patients and what can be done for the others?
Watamaniuk said that for those patients for which surgery is successful, the problem of strabismus may occur in the brain stem where things happen somewhat reflexively. There are centers there that are responsible for controlling eye movements, but they do not get a lot of feedback from higher centers in the brain.
Another area of the brain that is responsible for eye movement is the prefrontal lobe, which is responsible for higher-level functions and will take in data from the way the eye functions.
“The brain stem doesn’t care if you have done something to the eye, like correcting alignment through surgery. It just executes the command,” said Watamaniuk. “The prefrontal lobe gets used to certain data. So, if it is used to feedback from the eye that says it works a certain way, it will try and ‘correct’ the eyes’ alignment after surgery. One question we are trying to answer is what type of diagnostics can we come up with to tell in which part of the brain the problem exists.”