Refraction determines the lens power you need to compensate for any refractive error (nearsightedness, farsightedness or astigmatism). Using an instrument called a phoropter, your optometrist places a series of lenses in front of your eyes. He or she then measures how these lenses focus light using a handheld lighted instrument called a retinoscope. Your doctor may choose to use an instrument that automatically evaluates the focusing power of the eye. The lens power is then refined based your input on the lenses that give you the clearest vision.

This testing can be done without eye drops to determine how the eyes respond under normal seeing conditions. However, an optometrist will use eye drops with patients who can’t respond verbally or when some of the eyes’ focusing power may be hidden. The drops temporarily keep the eyes from changing focus during testing.