A study has shown improved eyesight in children whose mothers consumed cannabis while they were pregnant.

The research, partly conducted by the University of Waterloo, looked at 145 children from the U.S. and New Zealand, most of which were exposed to narcotic substances like methamphetamines, alcohol, tobacco or cannabis while in the womb.

“They were assessed at birth, at six months and at two years,” said University of Waterloo department of optometry and vision science associate professor Ben Thompson.

When the children were reassessed at four-and-a-half, Thompson said researchers found those children exposed to cannabis showed an enhanced ability to track moving objects compared to children who had not.

Despite the findings, Thompson said no narcotic substances should be consumed during pregnancy.

“These two drugs changed the way these babies’ brains were developing,” said Thompson. “They had four-and-a-half years for their brains to normalize but they still had these noticeable differences.”

“Outside vision, it’s well understood that cannabis exposure has a negative impact on development.”