Determination of ocular dominance

After looking at this thread: http://boards.straightdope.com/sdmb/showthread.php?t=621265 and looking at these tests: http://en.wikipedia.org/wiki/Ocular_dominance#Determination_of_ocular_dominance

I seem to have a problem with the tests. Take the The Porta test. When I hold my thumb out and focus on the distant object, I see my thumb as doubled. When I focus on my thumb I see the distant object as doubled.

So how do I tell which eye is dominant?

Am I missing something basic in these tests?

Try this instead.

Quickly point at something small across the room with your outstretched arm & fingertip. The tip of a lamp, the corner of a picture, whatever.

Now without moving your arm, close each eye in turn. Odds are you’ll find that seen with one eye, your fingertip points exactly at the target. Seen with the other eye, the fingertip points someplace off to the side of the target.

The eye which sees the finger and target in alignment is the dominant eye.

If your eyes are nearly evenly dominant, you’ll find that one eye sees the finger left of the target and the other sees it right of the target. But for most folks, one eye is dead on and the other is not.

The whole point of doing the pointing quickly is to ensure that only the automatic parts of your brain & muscles are involved. If you take time to carefully line them up, you’ll see the two-targets-or-two-fingers effect & get stumped.

I just tried this. With one eye I see my finger to the left of the object, with the other it is to the right. So I guess my eyes are pretty even then.

Question. When most people do the tests I linked to, I gather they do not have the problem I have? Can they focus on there outstretched thumb and still keep the distant object in focus?

What’s fun is, that can change. Seven or so years ago, I was strongly left eye dominant. Then my left eye went to relative shit because of pellucid marginal degeneration. It still works, but it’s much blurrier than my right, even with glasses. My right eye consequently is now dominant.

The blinking thing is the easiest way.