Increased blood flow might be the key factor.
Eating dark chocolate might improve your ability to see, at least in the short term, researchers have found.
In a recent study, "small enhancements in visual acuity and large-letter contrast sensitivity and a slightly larger improvement in small-letter contrast sensitivity" were noted after participants ate dark chocolate. That's compared with the results of the same participants after eating milk chocolate.
The testing took place two hours after the chocolate was consumed. Participants ate a 72% Cacao Dark Chocolate bar and a Crispy Rice Milk Chocolate bar, both from Trader Joe's, on separate occasions.
The researchers said the results might be due to increased blood flow after eating the dark chocolate, though they cautioned that "the duration of these effects and their influence in real-world performance await further testing."
"Several studies suggest that dark chocolate from favanol-rich cacao beans may enhance blood flow to central and peripheral nervous systems, improve cardiovascular function, and retard memory loss and other signs and symptoms of degenerative diseases, including Alzheimer and Parkinson diseases," they wrote.
The research, which involved 30 participants, was conducted at University of the Incarnate Word Rosenberg School of Optometry in San Antonio, TX. It was published in JAMA Ophthalmology.
In an analysis of the research, the United Kingdom's National Health Service noted that the study was limited by its small size. It also said the difference in results after consumption of dark chocolate versus milk chocolate was small, "and the participants had better-than-normal vision after eating either bar."
"They were reading at 20 metres what a person of normal vision could read at 15 after the milk and 12 after the dark," NHS wrote. "But whether this would translate into any noticeable real-life long-term difference is up for debate."