What is a dominant eye?
Just as most people favor one hand, most favor one eye. Your dominant eye is the one your brain trusts slightly more for lining things up. Roughly two-thirds of people are right-eye dominant. It doesn't always match your writing hand, and it says nothing about which eye sees better.
Why knowing your dominant eye helps
Shooters and archers aim with their dominant eye, so cross-dominance (for example right-handed and left-eye dominant) changes how you should stand or aim. Photographers usually look through the viewfinder with it. Eye doctors use it when fitting monovision contact lenses or planning cataract and laser surgery.
How the test works
This is a version of the classic Miles test. Stand back from the screen, stretch out your arms and make a small triangle with your thumbs and index fingers. Frame the target with both eyes open, then close one eye. The eye that keeps the target inside the triangle is your dominant eye.