Question

practice it
structure in the eye that focuses light rays on the retina
sensors
mirrors
viewfinders
lens
filters

Explanation:

The lens in the eye refracts (bends) light rays to focus them on the retina. Sensors detect light but don't focus it. Mirrors aren't part of the eye's light - focusing mechanism. Viewfinders are not in the eye. Filters don't focus light on the retina.

Answer:

lens