does '5 yearly check-ups' mean I will have to have my eyes tested five times a year in order to have a valid EASA Class 1 medical?
Fear not, intrepid young aviator ! No, it doesn't mean that at all !
Perhaps a simple hyphen would have made it clearer ( "5-yearly check-ups" ).
It's easier to say that you would need to have your eyes and vision checked EVERY FIVE YEARS ! Hope that sounds better !