Retinal response to cannabis use

Denise A. Valenti, OD, FAAO, shares key highlights from her presentation, "Marijuana and Driving: Your Retina and Brain," which she presented during the American Optometric Association (AOA) Optometry's Meeting in Chicago.

This transcript has been lightly edited for clarity:

Hi, I'm Dr. Denise Valenti. I'm the CEO and owner of IMMAD (Impairment Measurement Marijuana and Driving). I actually have decades of experience as a clinical optometrist. I actually initially specialized in aging, gerontology, low vision, and driving.

My residency, I had opportunity to work with Dr. Randy Jose. When we were researching — what was novel at the time — optic telescopes, bioptic telescopes for driving. As the years evolved as a clinician, I had opportunity to be consultant with General Motors on aging and safety issues.

My clinical experience changed as I switched into research. Initially, my research activity involved looking at retina structure and function of Alzheimer's disease and Parkinson's. We began concentrating on retina and cannabis in 2012. Our initial interest had been in working with, again, retinas structural function in treatments for Alzheimer's using cannabis, because we still believe it's pretty promising. However, there's a large body of research by some prominent optometrists that they did while they were at Berkeley in the 70s. But these papers are excellent quality and superior to most of the research now and that they were placebo, double blind, dose-controlled studies.

What they found was dysfunction in the retina with recent acute cannabis use. That prompted us to pivot a little bit because we realized some of the same work we had been doing with Parkinson's — looking at the retina, using frequency doubling technology — could help identify impairment to drive with marijuana. So as a result of all that work, I have a large body of information and knowledge that is very important to clinicians, optometrists whose primary care provider are in an excellent position to help educate their patients on responsible cannabis use.

Now, when I say responsible, we've learned that the visual system is harmed with adolescent use, and that does contribute to driving impairment. Adolescent use results in reductions in brain volume of those very regions — the frontal orbital cortex — that process vision, particularly contrast and motion, which again has consequences for driving.

Related: Marijuana and driving: Hitting a pothole

The lecture also talked a little bit about how the retinal response to cannabis use involves a depletion of dopamine for the retina, [and] we know that from Parkinson's disease. Well, when you have a depletion of dopamine, you cannot see as well. And again, this is of implications for the driving.

For primary care clinicians, though, we do now know that chronic heavy use of marijuana — even when you are not using cannabis — can result in dysfunctions in the retina. Again, that's very important for optometrists to know this because as they see these patients in day-to-day care, if they're not asking about recreational use, they may be chasing changes in the retina that are truly explainable, and may not be significant disease.

I was excited to present this lecture and it was a very engaging audience and wanting this information. I do hope they learned enough to take back to put it into practice. And if they have questions, they're more than welcome to call me or email and I can provide what information I do have or put them in the right direction. I want to thank the AOA for inviting me.