Methods and systems for determining change in eye position between successive eye measurements

An instrument for making measurements of an eye, comprising:

• a light source configured to produce range-finding light having a linear shape;
• a split-prism rangefinder configured to receive returned range-finding light that has been reflected by the eye to determine a distance of the eye;
• an optical system including at least one beamsplitter configured to direct the range-finding light from the light source toward the eye and to direct reflected range-finding light from the eye toward the split-prism rangefinder;
• an optical coherence tomographer (OCT) device configured to measure structures of the eye;
• a processor coupled to the split-prism rangefinder and the OCT device, wherein the processor is programed to:
• control the OCT device to make a first OCT measurement of the eye at a first time;
• control the split-prism rangefinder to capture a first range-finding light image of the reflected range-finding light from the eye during the first OCT measurement;
• control the OCT device to change a reference path in the OCT device;
• control the OCT device to make a second OCT measurement of the eye at a second time subsequent to the first time;
• control the split-prism rangefinder to capture a second range-finding light image of the reflected range-finding light from the eye during the second OCT measurement;
• determine a movement of the eye between the first time and the second time based on the first and second range-finding light images captured by the split-prism rangefinder;
• and
• combine the first and second OCT measurements while compensating for the movement of eye between the first time and the second time.