2003 Yale study A 2003 study by Brian DeBroff and Patricia Pahk tested whether black eye grease actually had anti-glare properties. The subjects of the study were divided into three groups: wearers of eye black, wearers of anti-glare stickers, and wearers of
petroleum jelly. The subjects' vision was tested using an
eye chart while being exposed to natural sunlight. The study concluded that eye black reduced glare of the sun and improved
contrast sensitivity, whereas commercial anti-glare stickers and petroleum jelly (the control substance) were found to be ineffective. However, the study was subject to unavoidable
demand bias, wherein the test subjects could have unconsciously changed their responses during testing based on the fact that they knew which substance they were wearing. Also, the petroleum jelly could have introduced glare that would not occur on natural skin and the study did not test a control condition of natural skin.
Learning bias is also a factor in the results due to chart repetition. which improved on DeBroff's methodology, found eye black to reduce glare from the sun in women and in those whose eye-color was not blue. The study also tested males and blue-eyed subjects. However, the results were not statistically significant due to a too-small sample size of those test subjects. Some testing was also performed indoors under artificial lighting when inclement weather prohibited outdoor testing. However, those results showed little difference and were not statistically significant. The Powers study was not a
double-blind study because those in contact with the test subjects knew which substance was applied. Also, the eye tests were performed at a distance of only .
MythBusters test On an episode of
MythBusters,
Adam Savage and
Jamie Hyneman tested whether eye black reduces glare. They determined that, while eye black does not eliminate glare, it does improve an athlete's ability to differentiate between light and dark, enhancing a player's ability to track moving objects in a sunny environment. ==Messages in eye black==