Gwen’s doctor discovers that gwen has reduced visual acuity. gwen’s doctor performs a procedure called , which detects the eye’s refractive error using an instrument called the .

 Refraction

                Phoropter

Explanation:

Refraction (refractive power): As light enters the eye, the lens helps focus light rays so that they come to a focus on the retina. This action is called refraction.

An instrument called a phoropter detects the eye’s error of refraction.