It's hyperbolic language to express the difference between the first time He came (He came to the Jews [Jn. 1.11; Mt. 15.24]) and the second time He will come—for the whole world to see (Rev. 1.7). It speaks of universality of revelation; no race or people is excluded. It will be a physical coming, but people will also discern His coming spiritually. Even those who reject Him will "see" in the sense that they know about it and will understand.

"...even those who pierced him” refers not only to the Jews and Romans, but to all who reject Him—those who in any era have identified themselves as opponents of Jesus. He will be recognized by friends and enemies, religious groups, and all ethnicities. These are again statements of universality.

How will every eye see Christ when he is coming with the clouds?

Behold, he is coming with the clouds, and every eye will see him, even those who pierced him, and all tribes of the earth will wail on account of him. Even so. Amen.

Revelation 1:7 ESV

Those who pierced him are all dead. The tribes of the earth must be people who are alive on the earth and are upset at Jesus return. They are wailing.

So how can the dead Jewish and Romans who pierced Jesus suddenly be alive on the earth when he is coming with the clouds?

What about blind people?

Every eye will see him.