Aberrometer with a dynamically adjustable video fixation target

An instrument for dynamically measuring one or more optical parameters of a subject's eye, the instrument comprising:

• (a) a primary optical path, pointing towards the subject's eye, having a Z-axis that is coincident with the primary optical path;
• (b) a dynamically-adjustable video fixation target, aligned along the primary optical path and having a first Z-axis position, which is configured to compensate for astigmatism and defocus of the subject's eye;
• (c) a wavefront sensor, aligned along the primary optical path, which is configured to dynamically measure wavefront aberrations of the subject's eye;
• (d) a movable Badal stage, which is movable along the primary optical path;
• and
• (e) a movable electromechanical stage, which is mounted to the movable Badal stage, having a second Z-axis position;
• (f) a pair of independently-rotatable, cylindrical lenses aligned along the primary optical path, which have equal and opposite power;
• and
• (g) an electromechanical adjustment means for independently rotating at least one of the pair of independently-rotatable, cylindrical lenses;
• wherein the wavefront sensor is attached to the movable Badal stage;
• wherein the dynamically-adjustable video fixation target is moveably attached to the movable electromechanical stage;
• and
• wherein the movable electromechanical stage is configured to move the dynamically-adjustable video fixation target along the primary optical path independently from any motion of the movable Badal stage along the primary optical path.