What is the reason why you can't see a point in the triangle with one eye closed?

Distinguish the dominant eye, in addition to going to a hospital or a regular optical shop for optometry, you can use a simple method at home or in the office.

First, choose a target object, which can be a small cup or a pen, and cross your hands into a triangle. Through this triangle, you can see the pre-selected target object. Cover one eye respectively, and look through this triangular area with one eye to see if you can see the target object. If you can see, this eye is the main eye, and if you can't see, it is the auxiliary eye.