London, Apr 19 : The popular antidepressant drug, Prozac, might soon have an unexpected new medical use - as a treatment for lazy eye syndrome, according to a new study in rats with impaired vision.
The study shows that daily doses of drug fluoxetine (Prozac) help rats' brains' visual centres to rewire themselves and correct the defect.
If the drug has a similar effect in humans, it could potentially help the roughly 1-5 percent of people thought to have amblyopia, or 'lazy eye'.
It is believed that fluoxetine and other selective serotonin re-uptake inhibitors (SSRIs) relieve depression by boosting the amount of the mood-related messenger molecule serotonin that is circulating among the brain's cells, reports Nature.
But the new research, led by Jose Fernando Maya Vetencourt of the Scuola Normale Superiore in Pisa, Italy, suggests that it can have other effects too.
The research team tested the theory that SSRIs increase the plasticity of the brain's nerve cells - their capacity to make and break connections with each another. It is this feature that underlies the mental wiring of processes such as accurate vision.
According to Ben Webb, a visual neuroscientist at the University of Nottingham, UK, the main cause of amblyopia is thought to be the problems with brain wiring.
If the eyes are not aligned properly, the developing brain can 'ditch' one as it struggles to make sense of the sensory information it is receiving. Over time, the neglected eye fails to forge a proper neural connection with the brain, and therefore delivers poor vision for life.
It is treatable if caught early, Webb says, "ideally as early as you can test a child - say, 18 months".
Children with lazy eye typically spend a few hours a day wearing an eyepatch over the normal eye to encourage the brain to engage with the affected eye, although this treatment is rarely continued beyond about the age of 9, when the visual cortex is generally thought to be fully developed.
The fluoxetine given to the rats in the study seems to have encouraged the visual cortex to return to a juvenile state, allowing the brains to make these corrections even in adulthood.
Some neuroscientists had suspected that fluoxetine might increase brain plasticity because some users show enhanced neuron development in certain brain areas.
Maya Vetencourt and his colleagues tested the idea on rats that had had one eye sewn shut during their early life. They then swapped the animals' eyes, and gave some of the rats a daily dose of fluoxetine for four weeks.
The adult animals' vision recovered fully, says Maya Vetencourt.
The rats not only showed full activity in their visual neurons, they also behaved as if they were fully-sighted.
The study is published in Science 1.