Optical instrument alignment system

An ophthalmic apparatus, comprising:

• an optical instrument having a first set of optics configured to receive light from the eye of a patient along a first optical axis defined by the first set of optics;
• and
• a system for positioning the optical instrument with respect to a desired position relative to the eye in an x-y-z three-dimensional coordinate system, the desired position comprising x, y, and z coordinates, the positioning system comprising a photodetector and being calibrated to define a reference location on the photodetector, the reference location on the photodetector being determined based at least in part on the corneal curvature of the eye and on the desired position relative to the eye, the apparatus being configured such that a spatial relationship between at least one optical indicia and the reference location on the photodetector varies as the apparatus is moved relative to the eye to provide positioning information for positioning the instrument with respect to the desired position, the optical indicia comprising light from at least one light source arranged about the first optical axis and reflected from the eye to the photodetector along a second optical axis, different from the first, the light source being positioned such that the light from the light source reflects to the photodetector from a location offset from the corneal apex when the optical instrument is located at the desired position relative to the eye.