Horus' eyes were a symbol of wisdom, immortality, and somehow they control physical and spiritual existence in our life.

-There is no death for those who see with Horus' eyes.

-The left eye symbolized the sun,
meant the spiritual powers, wisdom and metaphysics.

-As for the right one was the moon that symbolized every physical and tangible thing.

Both of the eyes worked together to keep cosmic balanced by transforming a human's physical energy of instincts and strength to serve his spiritual side..
Which could create a third dimension of the universe.

So the absence of one of Horus's eyes meant that some defect had occurred to the whole cosmic system!
which led to disruption of human consciousness and an imbalance the whole concept of life.