Using special prisms or lenses in the phoropter, the eye care practitioner will test the way the eyes aim when relaxed and the ability to point and hold the eyes on a target. This quantifies the phoria finding described under the cover test section.
A patient's depth perception—called stereopsis—may also be tested. A common test for this is known as the stereo fly test. The patient wears a pair of poloraid spectacles and looks at special photos, one of which is a picture of a fly. If the patient has depth perception the fly will appear to stand off the page. Other photos are used to quantify the degree of stereopsis.