The lens case is NOT in his jacket! It's in his pants. Sensei even highlighted it for you, so you wouldn't miss it:
http://www.mangago.me/read-manga/saezuru_tori_wa_habatakanai/mf/manga/saezuru_tori_wa_habatakanai/c017/pg-17/
The jacket--or rather, Doumeki covering Yashiro with the jacket represents something entirely different and that's why we see Yashiro staring at it.
It was not a question sense of the word, it was just (a hopping question ) in order to be a reason for Yashiro to discovers Doumeki's feelings towards him, I just wish for this to happen ( It will be beautiful some how ) .....
In other words > ( What do you think if Yashiro ............)
What if Yashiro see the contact lenses in Doumeki jacket?