A human who becomes the owner of a Death Note can, in exchange for half of his or her remaining life, acquire the power of the Shinigami Eyes, which will enable him or her to see a human’s name and remaining life span when looking at them.
If you have traded for the Shinigami Eyes, you will lose that power as well as the memories of the Death Note once you lose ownership of the note. Moreover, the half of your life you traded away will not be restored.
An individual with Shinigami Eyes can see the name and lifespan of another human by looking at that person’s face. By gaining ownership of a Death Note, an individual not only gains the ability to kill but also cannot be killed by a Death Note. From this point on, a person with a Death Note cannot see the life span of other Death Note owners, including himor herself.
In order to see the names and life spans of humans using the power of the Shinigami Eyes, the owner must be able to see more than half of that person’s face. When looking from top to bottom, he must be able to see at least from the head to the nose. If he looks at only the eyes and under, he will not be able to see the person’s name and lifespan. Also, even though some parts of the face for example the eyes, nose or mouth are hidden, if he can basically see the whole face he will be able to see the person’s name and lifespan.
It is still not clear how much exposure is needed to see a name and life span (more research needs to be done). If the above conditions are met, names and life spans can be seen using photos and digital images, no matter how old they are. But this is sometimes affected by the resolution and size of the image. Also, names and life spans cannot be seen using drawings, however realistic they may be.
Those with Shinigami Eyes will have eyesight of over 3.6 in the human measurement, regardless of their original eyesight.
If you have traded for the Shinigami Eyes, you will see a person’s primary life span in the human world.
The names you will see with the Shinigami Eyes are the names needed to kill that person. You will be able to see a name even if it isn’t officially registered anywhere.
Humans who have traded for Shinigami Eyes cannot see the names or life spans of humans who have already passed away (by looking at photos of them, for example).
The use of the Death Note in the human world sometimes affects other humans’ lives or shortens their original life spans, even if their names are not actually written in the notebook itself. In these cases, no matter the cause, the Shinigami sees only the original lifespan and not the shortened lifespan.
No matter what medical or scientific method is employed, it is impossible for humans to distinguish whether or not a human has Shinigami Eyes. Even Shinigami cannot distinguish this fact, except for the very Shinigami that traded his or her eye power with that human.