Fill 0% on the layers.
Blending Options-Gradient Overlay

Create Futuristic EyeBall in Photoshop CS

Gradient?s parameters:

Create Futuristic EyeBall in Photoshop CS

Draw one more circle with the same instrument used
before.

Create Futuristic EyeBall in Photoshop CS

Blending Options-Gradient Overlay

Create Futuristic EyeBall in Photoshop CS

Gradient?s parameters:

Create Futuristic EyeBall in Photoshop CS