The Byakugan (白眼, Byakugan? literally "White Eye," English manga "Evil Eye") is an eye technique (瞳術, dōjutsu?) that naturally occurs in members of the Hyuga clan. Byakugan possessors are characterized by their lavender, pupil-less eyes. When the Byakugan is activated, their pupils somewhat appear and the veins near their temples bulge. Possessors of the Byakugan are also capable of using the Gentle Fist style of combat.
A person with the Byakugan has a nearly 360 degree field of vision, except for a small blind spot at the back of the neck above the third thoracic vertebra. Byakugan users can detect anything around them within a small radius, the greater the users skill with the Byakugan, the larger the radius is, which makes them close-range combat experts. The Byakugan also gives the user the ability to see through basically any matter over extremely long distances. A small degree of telescopic vision is also present, as a Byakugan user can focus on a single object at any point within their range of vision. The degree of focus seems to be dependent on the skill of the user. The Byakugan's insight capacity makes it useful for searching, tracking, and identifying targets.
Protection of the Byakugan ability is very important to the Hyuga clan, and has led to the development of an elaborate family hierarchy. Members of the lesser branch house are branded with a cursed seal on their forehead at a young age. Whenever a branch house member dies, the cursed seal will seal the Byakugan ability so that enemies will not be able to discover its secrets.
IGN ranked Byakugan in the 3rd spot of the Top Ten Naruto Techniques, mentioning the applications for this kind of technique in everyday use are infinite in number.
The Sharingan (写輪眼, Sharingan? literally "Copy Wheel Eye," English manga "Mirror Wheel Eye") is an eye technique (瞳術, dōjutsu?) that naturally occurs in a select few members of the Uchiha clan. The Sharingan is thought to be descended from the Byakugan, but grants the user different abilities and a different insight. The Sharingan does not automatically appear from birth in a user; instead, it will usually appear when the user is in a life-threatening situation, where the power of the Sharingan could save them. After this first appearance, the user can then call up the Sharingan any time they wish. The power of the Sharingan is judged through the number of tomoe in the eye, with a maximum of three in each. The characters who currently possess the Sharingan include Sasuke Uchiha, Itachi Uchiha, Kakashi Hatake, and Tobi.
The Sharingan's first and most well known ability is to memorize any technique that it witnesses. It can memorize any standard form of jutsu with perfect accuracy, allowing the user to use the techniques as his own. In order to reproduce copied jutsu, however, one must have the necessary skill or ability to perform them. A prime example is Rock Lee's Strong Fist taijutsu. While Sasuke was able to copy some of Lee's moves, they put a much more significant strain on him since he hasn't had the same training as Lee has.
The Sharingan's second ability is granting the user incredible clarity of perception, allowing them to track fast-moving objects with ease and even predict the subsequent movements of those objects. The ability to track and predict movement is largely based on individual skill, as unskilled users have much more trouble tracking fast-moving objects. A fully-evolved Sharingan can track even the quickest opponents, though, like the first ability, it doesn't necessarily mean the user has the ability to react to it. This perception is also great enough to see through genjutsu and to observe the movement and flow of chakra, but not to the same extent or clarity as the Byakugan. It also gives color to chakra. Additionally, the Sharingan grants the user exceptional analytical powers, allowing them to instinctively pick up on various visual clues with little difficulty. For example, Sasuke was able to reproduce answers on another person's test by watching their pencil movements during the Chunin Exam.
The Sharingan's third capability is a unique brand of hypnosis that involves suggesting actions and thoughts to the opponent. When used in conjunction with the aforementioned aspects of the Sharingan, this allows the user to perfectly mimic every move their opponent makes, even before they do, making it appear as if the user can see the future. It also allows for other forms of hypnotism, such as putting an opponent to sleep, replaying memories to someone else, or creating various illusions to fool an opponent.
It is possible to transplant Sharingan eyes from one person to another, as occurred with Kakashi and his deceased comrade Obito Uchiha. However, transplanted eyes do not work as well in a non-Uchiha body; Kakashi's eye is always active, causing him great strain when he uses it and forcing him to recuperate for extended periods of time after a battle. Kakashi keeps it covered when not using it to avoid this side effect in his everyday activities. Uchiha clan members are not burdened with this weakness; while activation of the Sharingan does consume chakra, the drain is so small as to be almost insignificant. Itachi in particular seems to have no trouble keeping his Sharingan activated near-constantly.
The Mangekyo Sharingan (万華鏡写輪眼, Mangekyō Sharingan?, literally "Kaleidoscope Copy Wheel Eye") is a heightened form of Sharingan. It was first awakened by Madara Uchiha, who was able to use it to gain control over the Nine-Tailed Demon Fox. Over the generations other Uchiha came to possess their own Mangekyo Sharingan, though Madara, Itachi Uchiha, and Kakashi Hatake are the only characters to possess it in the current Naruto storyline. Unlike the standard Sharingan, the Mangekyo Sharingan differs between users, changing the form of the Sharingan's tomoe seal when activated. Those who possess a Mangekyo Sharingan suffer from ever-deteriorating eyesight, a process that becomes faster through repeated usage and culminates in blindness. Only by taking the eyes of a sibling can one's eyesight be permanently restored, combining the appearances of the two Mangekyo Sharingan and granting them immense strength in the process.
Itachi tells his brother, Sasuke Uchiha, that the Mangekyo Sharingan can be gained by killing one's closest friend. Though Itachi and many other Uchiha have done this to obtain their versions, Kakashi is unlikely to have done the same; Kakashi states at the start of the series that all of his friends are dead, and it is not until the gap in time between Part I and II that he develops his own. What Kakashi did to obtain his own Mangekyo Sharingan remains unknown