Question

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

Explanation:

The lens in the eye refracts (bends) light rays to focus them on the retina. Sensors detect light but don't focus it. Viewfinders are not part of the eye's anatomy. Filters block certain wavelengths, not focus light. Mirrors reflect light, which isn't the eye's mechanism.

Answer:

lens