To know which of your eyes is dominant, you can perform simple tests at home, such as the thumb or hole-in-the-card test. The thumb test is relatively easy as it only requires your thumb. To do this test, you need to extend your arm in front of you and put your thumbs up in your line of sight. Then with both your eyes open, focus on a distant object and ensure that your thumb aligns with the thing. Lastly, close one eye at a time. Your dominant eye keeps your thumb directly aligned to the object while your other eye is closed. Another type of eye dominance test is called the hole-in-the-card test. You need a piece of paper or a card for this test. In the center of the card, cut a hole approximately 1.25 inches in diameter. Next, extend your arm and hold your card in front of you. Look through the hole to focus on a distant object, and then close one eye at length. Your dominant eye allows you to see the distant object through the hole in the paper.