He had trouble focusing on the target of his anger.

He opened his eyes, with some momentary trouble focusing them.

Now that she mentioned it, I was having a bit of trouble focusing.

Tired means you lack energy, have trouble focusing, and feel "out of it" all the time.

For some reason, he had trouble focusing on the leader.

You may have trouble focusing your eyes for several hours after the test.

The air between them seemed to dance, and my eyes had trouble focusing.

I had a little trouble focusing, but finally managed it.

He had no trouble focusing on their conversation while keeping watch.

I've had a lot of trouble focusing on the entire run.