A display system configured to project light to an eye (302, 304, 1000) of a user to display virtual image content in a vision field of said user, said eye having a cornea, an iris, a pupil, a lens, a retina, and an optical axis extending through said lens, pupil, and cornea, said display system comprising: a frame configured to be supported on a head of the user; a head-mounted display disposed on the frame, said display configured to project light into said user's eye to display virtual image content to the user's vision field at different amounts of at least one of divergence and collimation and thus the displayed virtual image content appears to originate from different depths at different periods of time; one or more eye tracking cameras (462, 324) configured to image the user's eye; and processing electronics (260, 270) in communication with the display and the one or more eye tracking cameras, the processing electronics configured to obtain an estimate of a center of rotation of said eye based on images of said eye obtained with said one or more eye tracking cameras, wherein said processing electronics are configured to: determine an array of positions based on a plurality of spatial locations on an image of the user's eye obtained with said one or more eye tracking cameras, wherein said array of positions corresponds to at least a portion of an ellipse; determine a plurality of linear paths (1912A-D) extending from a location on a first side of said array of positions through said array of positions to a second opposite side of said array of positions; and determine a circular region (1906, 1908) based on a gaze which corresponds to the user looking at virtual image content on the display system based on said plurality of linear paths, said circular region having a radius, R. a frame configured to be supported on a head of the user; a head-mounted display disposed on the frame, said display configured to project light into said user's eye to display virtual image content to the user's vision field at different amounts of at least one of divergence and collimation and thus the displayed virtual image content appears to originate from different depths at different periods of time; one or more eye tracking cameras (462, 324) configured to image the user's eye; and processing electronics (260, 270) in communication with the display and the one or more eye tracking cameras, the processing electronics configured to obtain an estimate of a center of rotation of said eye based on images of said eye obtained with said one or more eye tracking cameras, wherein said processing electronics are configured to: determine an array of positions based on a plurality of spatial locations on an image of the user's eye obtained with said one or more eye tracking cameras, wherein said array of positions corresponds to at least a portion of an ellipse; determine a plurality of linear paths (1912A-D) extending from a location on a first side of said array of positions through said array of positions to a second opposite side of said array of positions; and determine a circular region (1906, 1908) based on a gaze which corresponds to the user looking at virtual image content on the display system based on said plurality of linear paths, said circular region having a radius, R. determine an array of positions based on a plurality of spatial locations on an image of the user's eye obtained with said one or more eye tracking cameras, wherein said array of positions corresponds to at least a portion of an ellipse; determine a plurality of linear paths (1912A-D) extending from a location on a first side of said array of positions through said array of positions to a second opposite side of said array of positions; and determine a circular region (1906, 1908) based on a gaze which corresponds to the user looking at virtual image content on the display system based on said plurality of linear paths, said circular region having a radius, R.