Board Thread:Naruto Discussions/@comment-1872728-20160329033053/@comment-24521038-20160429173449

I think straight tomoe refers to shape of the normal Sharingan's Tomoe. If you look at Sharingan users, unlike Sasuke's Sharingan others Sharingan's tomoe is curved. When Sharingan evolves to Mangekyou Sharingan, its abilities evolves too thus creates their movement to become more fluid than other non straight tomoe Sharingan users i think.