as ‧ tig ‧ ma ‧ tis ‧ m /əˈstɪɡmətɪz ə m/ BrE AmE noun [uncountable]
[ Date: 1800-1900 ; Origin: ↑ a- 2 + Greek stigma 'mark, point' ; because there is no point at which light focuses ]
difficulty in seeing clearly that is caused by a change in the inner shape of the eye