Automatically limit meta description to 160 characters

I stumbled across the documentation I was after.

For anyone looking for the same info here it is:
https://yoast.com/wordpress/plugins/seo/api/

To solve my issue I added the below in functions.php:

function yoast_trim_description( $str ) {
     return substr($str, 0, 160);
}
add_filter( 'wpseo_metadesc', 'yoast_trim_description' );

Marked resolved.