Amblyopia—or “lazy eye”—arises early in life when one eye provides poorer visual input than the other. As the brain adapts, neural circuitry shifts toward the stronger eye, causing the weaker eye to fall further behind. While patching and other treatments can be effective in infancy and early childhood, they typically fail later in life, after neural connections have matured.

But new research from neuroscientists at The Picower Institute for Learning and Memory at MIT suggests that recovery may still be possible in adulthood. In a study published in Cell Reports, scientists demonstrated that temporarily and reversibly anesthetizing the retina of the amblyopic eye for just 2 days can restore normal visual responses in adult mice.

The findings offer an important refinement to previous work from the lab of Picower Professor Mark Bear, which showed in 2021 that anesthetizing the non-amblyopic eye could strengthen the amblyopic one—similar in spirit to traditional childhood patching. That earlier approach has since been replicated in multiple adult species. Now, evidence suggests that directly treating the amblyopic eye itself may also work, while eliminating the need to disrupt vision in the stronger eye.

“If it does, it’s a pretty substantial step forward because it would be reassuring to know that vision in the good eye would not have to be interrupted by treatment,” Prof. Bear said in a article posted on the Picower Institute website. “The amblyopic eye, which is not doing much, could be inactivated and ‘brought back to life’ instead.” He emphasized, however, that the strategy must still be validated in additional species—and ultimately in people—before moving toward clinical use.

The study’s lead author is former graduate student Madison Echavarri-Leet, whose doctoral research focused on uncovering the mechanism that makes such recovery possible.

For decades, Prof. Bear’s lab has investigated how neural circuits in the visual system adapt to changes in sensory experience. Earlier studies—including a 2016 collaboration with Dalhousie University—found that temporary retinal anesthesia could help reverse amblyopia in animal models. Yet the biological mechanism behind the recovery remained unclear.

Clues surfaced from an overlooked 2008 experiment in the lateral geniculate nucleus (LGN), the brain region that relays retinal signals to the visual cortex. The team had observed that when input from one retina was blocked, LGN neurons began firing rhythmic, synchronous “bursts” of electrical activity—patterns similar to those seen during early brain development, when synaptic connections are first being formed.

In the new study, Ms. Leet and colleagues tested whether these bursts were critical to therapeutic recovery. Using the anesthetic compound tetrodotoxin (TTX), they found that retinal inactivation triggered bursting not only in LGN neurons connected to the treated eye but also in those associated with the untreated eye. Further experiments revealed that this bursting relied on a specific T-type calcium channel. When the team genetically eliminated these channels in mice, the burst activity disappeared—and with it, the treatment’s restorative effect. Amblyopic mice no longer showed visual improvement when their non-amblyopic eye was anesthetized.

This result demonstrated that the bursts are necessary for recovery.

Reviving the Amblyopic Eye Directly

Given that bursting occurs regardless of which retina is silenced, the researchers asked: Could anesthetizing only the amblyopic eye be enough to re-balance visual signaling?

To answer this, they administered TTX to the amblyopic eye of adult mice, temporarily shutting down retinal activity for 48 hours. A week later, measurements in the visual cortex showed that signals from the two eyes were far more balanced in treated animals compared to controls. In other words, the amblyopic eye’s influence in the brain had been restored to parity with the stronger eye.

The results point toward a potentially transformative treatment strategy—one that may avoid interrupting vision in the unimpaired eye.

“We are cautiously optimistic that these findings may lead to a new treatment approach for human amblyopia, particularly given the discovery that silencing the amblyopic eye is effective,” the authors wrote.

While the findings mark a promising advance, Prof. Bear stresses that further testing is essential, particularly in species with visual systems that more closely resemble those of humans. If replicated, the approach could provide a long-sought pathway for treating amblyopia beyond early childhood, when neural plasticity has traditionally been thought to wane.

The work was supported by the National Institutes of Health, the Swiss National Science Foundation, the Severin Hacker Vision Research Fund, and the Freedom Together Foundation.