Another good and easy exercise is to look at your thumb. Keep it about 3 inches from your nose and look at a spot about 20-30 feet away. Look back and forth.
The other one is to look at your thumb with your arm outstretched and bring it in close to your eyes then out again. Do it back and forth a few times.
Very good. Especially with most of us in cities and never focusing more than 2 blocks distance for most of our lives. Especially in childhood.
My g’mother (born in 1888 - Norway) was big on self care. First thing in the morning was our tablespoon of cod-liver oil.
When out of urban areas focus on the horizon then back to something close - back and forth. I do the moon and the branch or a tree in my backyard every night that’s clear.
I like your thumb exercise. Makes perfect sense and very handy. ;-)