Mangekyo Sharingan Issues
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.
Well, the first thing to mention is that the Eyes become a Jutsu in itself, in Uchiha's case, called the Sharingan. Thus, obtaining the already awakened Eyes, equal to obtaining the (Dou)Jutsu (whether the user is capable of using it is another thing).
The moment that a special chakra created in the brain enters the eyes, the eyes are mutated and transformed, thus becoming a jutsu, in the same way as a normal tag becomes an Explosive Tag. At that point, the (dou)jutsu (Sharingan) can be activated by simply sending chakra to it, thus anyone with chakra can technically use the Sharingan (after it was Awakened = Mutated = Eye turned into a jutsu). The jutsu is already prepared to use after the Eyes are awakened. From the looks of it, the (dou)jutsu itself is not a Kekkei Genkai, but rather that special chakra in the brain that creates the jutsu is (the thing that mutates/transforms/alter the normal eyes into a doujutsu).
As to each jutsu appearing in each MS eye, well the moment MS awakens (is mutated from Sharingan to MS, form Doujutsu to another Doujtsu) at least one additional jutsu appears in the eyes, seemingly max up to 3. So far, from the ones we know beside Madara's and Izuna's (not much is mentioned about them), each eye had a special jutsu. It's also worth mentioning that other jutsu that can be casted through normal or Sharingan eyes, can still be casted through MS, they even become more potent.
Usually, when it comes down to strictly Ninjutsu-type-Eyes, one jutsu is being simply a casting-type (Amaterasu, Kakashi's Kamui), while the other one is of manipulating-type (Kagutsuchi, Obito's Kamui). It's worth mentioning that while the first one is strictly limited to what the Eye sees, the other one seemingly can work without seeing it's target (like Obito using it without looking at his body, or like Sasuke can manipulate flames without looking at them as well). The casting-type eye usually posses more raw fire power, but the flexibility of the manipulating-type often gives better advantages. It's also worth mentioning that in Sasuke's and Obito's case, the Left Eye is the casting-type, while their Right Eye is the manipulating-type (the casting/manipulating-types refer to their foremost function, but both are able to separately cast the jutsu, though that manipulating one doesn't hold as much raw power as the casting one).
Seeing as we have only one (known) type of Genjutsu-type-Eyes, it's hard hard to say if there is some kind of trend here or not. From the looks of it, the jutsus in Shisui's eyes were different, though both were considered to be powerful genjutsu (to the point that they even had a cool downs, in Kotoamatsukami's case it was a decade). Kotoamatsukami is the stronger (ultimate one, so this means there were other) one and is cast from the Left Eye and needs the eye to see it's target (specifically eye to eye contact). One the other hand the Right Eye posses a weaker Genjutsu, but instead one doesn't need to see the target, since Danzou was able to manipulate Mifune even while his eye was completely covered. In this case, it can be said that again the casting-type is the left one and it needs to see the target, while the right one is the manipulating-type and doesn't need to see the target.
Another special example, the Hybrid-type-Eyes of Itachi (Nin-Gen version). This is the only known case in which each of the eyes posses a completely different ability, of different types at that. Both of his jutsu require to see the target (in Tsukuyomi's case it even needs a direct eye to eye contact). The Tsukuyomi is in his Left Eye and Amaterasu in the Right Eye. While Tsukuyomi might be somewhat considered to be a manipulating-type to some extend (especially within the illusionary dimension), Amaterasu would have been considered the casting-type (though both of the jutsu are technically casting-type). This would mean that Itachi's Sharingan was reversed compared to everyone's (known) else.
Also, Madara himself mentioned a new trend/part of the MS. Specifically he mentioned that Sasuke's MS is the the Straight-Swirl type. If we take into consideration the above, then that would mean Itachi is so far the only one (known) who possessed the Reverse-Swirl type. Of course there is currently no way to make sure what it really means...
Some MS are also able to awaken the Susanoo, which is seemingly might awaken after the jutsu in each eye is mastered. Very rare and also considered the pinnacle of the Uchiha power. It's power rivals the power of the Bijuu.
Well, when Sasuke's vision truly became terrible, the large Susano'o he was creating against Kakashi suddenly fizzled out. Granted, Sasuke was weakened at the time. I still think we're meant to take from this that blindness=loss of eye techniques.