It's been shown and stated many times that as the MS powers are wrung out the user's eyesight shrivels correspondingly to the point where it renders the person completely blind. But, does it also entails the lost of the mangenkyo's abilities ? (if so, when was it ever thrown out ?) the very nature of the sharingan in relation to the physical structures that endorse it gives rise to some new ideas
It might seem counter-intuitive to question this as we had customarily weld eye function univocally with vision. Setting aside any sight-enhancing abilities the sharingan grants its user and as operationally connected as they might be (as to set one's eyes on the target) they have been suggested to be individual functions.
The independence has been shown several times, of note by the time Sasuke fought Danzo. From the word go his vision was blearing out while his powers were not, contrariwise they were shaping up, showing improvement from the battle he just cut out, implying that anywhere this power plies on is not the same withering one that mainstays his vision, yet clearly pouring through the same structure [his eyes].Or Itachi having his retinas allegoricaly grayed out when losing his eyesight, being also Framing from Tobirama's comments on the Uchiha's doujutsu within the diencephalic framework of vision, that grapples with the erstwhile notion where was the eyeball wherefrom all these powers stem from. Opens the room for the vision lost to be best explained by a defect that nests in the ocular bulb itself, and sheds light on the solution to this gradual lost being the mechanical replacement of such ...Which by corollary would derive that those abilities, still and all quiescent, dwell within the eyeless user as just was Madara, who was able to use Susano in this very condition. Howbeit this idea squares off with Sasuke getting his visual accuity back by trading off his dying out eyeballs for a pair of another nonfunctioning eyes, passing over that while the problem resides physiologically within the eyeballs it's possible to be topographically located in some other stead, a biological or metaphysical structure defined as critical for eyeball functioning and which failure exclusively forks over that set of eyes, denoting that vision and justu are shored up by complex functions, that relay on many anatomical modules, some playing compulsory roles for a given trait while other have just auxiliary actions. The eyeballs in this regard play a tricky role on this model. In view of Kakashi bearing these abilities solely by getting hold on an eyeball I deem the idea that they, the eyes, are sufficient cause and still, not a necessary condition for these powers to be had [in potentiality/actuality]; case in point Sasuke, that preserved his mangekyo abilities even after replacing his former, original, eyes ( his unique Susano token and enton manipulation, the later not posessed by Itachi, the first one owing to each one a characteristic pattern in like manner not receiving the assets Itachi had within the limits of the same techniques i.e Yata mirror and the sword of Kusanagi )
Notice that while originally each eye was said to endow the user with a particular jutsu, for Sasuke and Itachi, it seems to not hold true for Sishui and Obito (that while being used differently, it's apparently the same technique [Kamui]).These divertions took place in settings where the eyes were roped off from one another to different users. Perhaps due to the dissociation from their native occupancies that support, as do other nearby linking, related functions and development. This all may extrapolate to higher order stages of the Sharingan phylogenetics, when the rinnegan was not availed to the same extent by only possessing the eyeball, like Nagato did, in constrast to what Madara showed himself capable of.