Over the last 25 years I had a very informal exposure to Zen starting with some martial arts training. Some of that training was implicit by an expert instructor during sparing to drill staying focused and not worrying about what just happened. Missing a block for a punch or kick, that was now in the past, was now not important. And obviously closing your eyes to focus during sparing would be a very bad idea.

A couple of years ago I read (actually listened about 5 times) to the Power of Now by Eckhart Tolle and arrived at the conclusion having my eyes closed was not necessary. Tolle talks about thoughts of the past being frequently based in remorse and thoughts of the future frequently being based in anxiety. My personal conclusion was that observing nature and my environment could provide some distraction from those thoughts.

With some work I have developed the mental discipline to generally keep my thoughts focused in the now. When I find my mind wandering to the past or worrying about the future I try to observe a bird in a tree or the interesting shape of the tree. Just about anything, including my own tinnitus (ringing in the ears), can refocus my thinking.

So now my everyday living is sprinkled with bits of meditation. And sometimes I sit quietly with my eyes closed.

Both work for me.