Hi Alexandra,
Welcome to IIS. When you observe leave both eyes open, cover the eye you are not using with your hand, but leave it open.
This relaxes the muscles in both eyes so you wont get a headache or eyestrain through squinting with one eye shut for extended periods.
A good idea is to go to your local Chemist and get an eye patch, this will achieve the same thing but with both hands free, so long as you remember to still leave that eye open.
Regards
Trevor