Remember Kakashi hasn’t had use of his Mangekyo Sharingan for the entire time he’s had it available, due to his poor stamina and chakra. However, he is truly losing eyesight, this is confirmed by Kakashi himself. Why Obito’s right eye is not yet blind even with all his use of his Mangekyo, is unknown.Is it possible that Obito fused his eyes with Sharingan he collected from the massacre to restore his vision? Since most of those eyes most likely did not unlock the Mangekyou Sharingan it wouldn’t have upgraded Obito’s eyes to the Eternal Mangekyou Sharingan. Or am I getting my understanding of Sharingan fusion mixed up?
When you make an Eternal Mangekyo Sharingan, you are removing your previous set of Mangekyo Sharingan and adding the spare pair instead. The eyes then morph into a version of both yours and the spare’s Mangekyo design, but they are still the spare set. For example, the eyes in Madara’s head are Izuna’s, and the eyes currently in Sasuke’s head are Itachi’s. The Sharingan also can’t act as a spare, it has to be a Mangekyo Sharingan of some kind.
The Sharingan Obito collected from the Uchiha Massacre are meant to act as replacements for his normal Sharingan left eye should he need to use it for Izanagi.
Obito’s Mangekyo Sharingan’s irregular vision is most likely caused by Hashirama’s cells present in his body. We are already aware that Hashirama’s cells have positive affect on Mangekyo eyes, as Danzo used it to increase the frequency he could use Kotoamatsukami through Shisui’s Mangekyo Sharingan.
that is the general theory on the situation, but it isn’t confirmed.