The bloodline has two stages, the first is active at birth. Kunshagan Eye (First) and Tentousama Kunshagan Eye (Second). The difference is when it reaches Tentousama, you gain more powerful jutsus and immortality like Madara has. Everything else is the same. The drawback to gaining the immortality is the wielder can no longer use comatosis stare. If they do attempt to, they will go blind permanently. Goodside about that, is the person they use it on, will die. But again, the user is permanently blind and as such, loses some of his most powerful bloodline jutsus.
Luckily, the Tentousama Kunshagan Eye is not so easy to gain. You must be the age of 20 and take a life that effects you dramatically. It doesn't have to be someone close, but normally, it is since the death has to cause a sense of dramatical damage. Then, within 24 hours of the death, the user must kill themselves. When they awake, they are healed, but if they attempted to kill themselves by cutting or anything physical, the mark or scar never fades from their skin. A reminder of their attempt and a permanent reminder of their sorrow and lose.