This application describes apparatuses and techniques for identifying and marking a position corresponding to the intersection of a patients line of sight with the anterior surface of the human cornea to aid centration of an ocular implant. The apparatus can include a first optical subsystem configured to project a first light through an aperture and along an instrument axis such that the patient will observe an annulus around a disc when the patients visual axis is substantially collinear with the instrument axis and the patient will not observe the annulus when the visual axis is not substantially collinear with the instrument axis. The apparatus may also include a second optical subsystem configured to project a second light along the instrument axis such that the second light appears to a clinician to be an annulus around the first light.
