Just as the vast majority of us are either right or left handed, we also have a dominant eye. It may not seem obvious, but the brain constantly receives a separate and unique image from each eye. Dr. Lawrence D. Lampert, an optometrist in Boca Raton, Florida, specializing in sports vision, points out that the dominant eye processes information 14 to 21 milliseconds faster than the non-dominant eye. The brain uses this dominant image as the main frame of reference while the second image, being a hair late to the party, is relegated to providing depth perception.
Extend your arms forward holding the paper towel tube at eye level.
With both eyes open, look through the tube and focus on a small object 15 to 20 feet away. Focusing on a light switch works well.
Close your left eye. If the light switch is unchanged, you are right eye dominant. If the light switch jumps out of sight, you are left eye dominant.
To double check your finding, open both eyes and refocus on the light switch through the tube again. This time close your right eye (if you are right eye dominant this will be a bit harder). The results will be exactly reversed.