Simple Eye Exam Reveals How Much You Like Chocolate

You know when you give a child a candy bar, and they seem to get a little twinkle of joy in their eyes? Maybe that’s just a look of gratitude—or maybe it’s all the dopamine floating around their retinas. A new study shows it could be possible to use an eye test to observe the chemical response someone gets while chowing down on chocolate.

The brain reacts to certain stimuli (for example, eating chocolate) by releasing dopamine. A lesser-known dopamine release also happens in the eye, in response to light exposure. Those two sources of dopamine are thought to be unrelated, but researchers from Drexel University recently tested that with a simple study.

The Drexel team used electroretinography, or ERG, an electrode-based test that measures retinal response to light. When the study group was given a piece of chocolate brownie to snack on during the test, their retinal responses jumped. The responses were just as high, in fact, as when the participants were given a drug meant specifically to induce a dopamine response. Both the chocolate and drug responses were much greater than when the participants were given water as a control substance.

The findings suggest it may be possible to measure chemical responses to food through ERG testing, instead of through more invasive (and frequently more expensive), brain-based procedures.

Then again, this was a very small study; only nine people participated. The researchers admit it would take a larger study to validate the findings, let alone see how valuable they are for other research. Better figure this one out soon, though.

The study is published in the journal Obesity.