Gestational Exposure to Marijuana Smoke May Impact Eye Function

Mothers who smoke marijuana during pregnancy could be damaging the structure of their unborn babies’ retinas, the part of the eye that converts light into neural signals, according to a new study from the University of Sao Paulo Medical School.

In an address at the 2017 annual meeting of the Association for Research in Vision and Ophthalmology (ARVO) in Baltimore, MD, Paulo Zantut, MD, PhD, showed for the first time that gestational exposure to marijuana smoke in animals affects the development of the eye, and that these alterations seem to progress with age even after exposure has stopped.

Because of this, Zantut suggested that human babies exposed to marijuana in the womb may require clinical care earlier in life than the non-exposed population.

“In our study, we included 20 pregnant mice that were exposed daily for 5 minutes to either marijuana smoke or filtered air. After birth, 5 puppies from each group had their retinas examined to determine retinal thickness, [which was] determined by a non-invasive imaging test,” Zantut said, adding that thin retinas are a known marker of poor visual function.

Data showed that on average, the outer retinas of puppies prenatally exposed to marijuana were 12% thinner. 3 months after birth, the outer retina of the puppies whose mothers were exposed to marijuana smoke during pregnancy was 11% thinner. After one year, that number increased to 20% thinner.

Results were significant for inner retinas as well. 3 months after birth, the inner retina was 8% thinner on average.

“Our results show that the thinning of the entire retina continues after birth, despite cessation of exposure to marijuana smoke,” Zantut said.

This is particularly concerning because 13% of pregnant women use marijuana to reduce pregnancy symptoms like lack of appetite and nausea, Zantut said, citing statistics from the National Institutes of Health. Moreover, the use of marijuana during pregnancy increases the odds of an infant being underweight by 77%.

Marijuana “effects the development and maturation of the brain of infants, causing memory impairment, increased risk for hyperactivity, impulsivity and impaired attention,” Zantut said. “Children whose mothers used marijuana during pregnancy have increased odds of using marijuana themselves later in life.”

The retina is an extension of the central nervous system. It transfers light energy in the eye into electrical signals that are conducted to the brain through the optic nerve, Zantut said. Thin retinas are a known marker of poor visual function.