Board Thread:Boruto Discussions/@comment-33545035-20191020164526/@comment-4080775-20191027120331

@Halcyonite I don't think he could see "Nano-sized" insects in that fight, and even Obito (Tobi at the time) said it was "Tiny Bombs on the microscopic level". Then Sasuke says "Bombs invisible to the naked eye. But my Sharingan can see the color of chakra." And that's from the manga.

Even when Obito was looking at that Torune's nano-scale insects, he didn't perceive them on that scale directly in the up-close area of the finger. Obito is very knowledgable on various jutsu and literally could have heard that Torune used Nano-scale insects, without ever having to actually view them on such a small level. And we know the Sharingan can't see within a target's body like the Byakugan can.

An concerning Jigen changing sizes. Every time he changed size to go small, Sasuke would immediately lose sight of him, before picking him back up a little later, so he didn't constantly see him nor keep track of him every time.