The truth of Ninja -Ninja Encyclopedia-

Metsubushi

Ninja makes Enemy Blind with Metsubushi

Needless to say, in a battle, if a man lost his sight, his fighting strength would be gone as he may be completely blind. For that reason, in almost all modern martial arts the any attack on the eyes of opponents is strictly prohibited. This is only the case in martial arts which have certain rules though. In the case of a ninja such regulations certainly did not apply, far from it, if anything, attacks on the eyes could be very effective for them. The fights that ninjas encountered were all fraught with danger and the threat of death so it is quite natural that ninja invented a tool which could make their enemy blind.
"Metsubushi (–Ś’ׂµ) " was a weapon with a length of less than 100mm and a weight of around 100g. Its shape was like a round whistle. On both ends of a metsubushi, a blowing hole and an outlet were attached. Inside the weapon, various items were jammed such as iron powder, sand, red pepper, and chemicals. As a Ninja breathed into the metsubushi, the contents spout out from the outlet to the face of the target. Even if a ninja could not see his enemy completely, making the enemy blind would certainly be advantageous. After that, the ninja could do anything they wanted like killing the enemy or escaping.
As the contents were all stimulants, metsubushi affected not only the eyes, but also the nose of the target. At any rate, a ninja could deprive the enemy of their combat efficiency as long as a slight amount of the substance of the metsubushi went on the enemyfs face.
There was also another type of metsubushi that was made from paper and eggshells. Ninjas put stimulants into the broken eggshell and further wrap it with paper. This then worked as a simple tear bomb that ninjas would throw at the face of their enemy.
As ninjas had strong and powerful fingers, they also had the ability to break the eyeballs of the enemy. Blinding the enemy was a very effective assault for the ninja as it is was so powerful.