Corneal topography measurement and alignment of corneal surgical procedures
Methods and apparatus are configures to measure an eye without contacting the eye with a patient interface, and these measurements are used to determine alignment and placement of the incisions when the patient interface contacts the eye. The pre-contact locations of one or more structures of the eye can be used to determine corresponding post-contact locations of the one or more optical structures of the eye when the patient interface has contacted the eye, such that the laser incisions are placed at locations that promote normal vision of the eye. The incisions are positioned in relation to the pre-contact optical structures of the eye, such as an astigmatic treatment axis, nodal points of the eye, and visual axis of the eye.
1. An apparatus for treating an eye, the eye having a cornea and a lens, the lens having an anterior surface and a posterior surface, the apparatus comprising:
a tomography system for measuring a tomography of the eye; and
a processor comprising a tangible medium configured to:
determine a curvature of the cornea, a curvature of an anterior lens surface, and a curvature of a posterior lens surface of the eye based on the measured tomography of the eye;
determine an optical axis of the eye in response to one or more of the curvature of the cornea, the curvature of the anterior lens surface, and the curvature of the posterior lens surface;
determine an anterior optical node of the eye in response to the curvature of the cornea, the curvature of the anterior lens surface, and the curvature of the posterior lens surface, wherein the anterior optical node is located along the optical axis; and
determine a posterior optical node of the eye in response to the curvature of the cornea, the curvature of the anterior lens surface, the curvature of the posterior lens surface, and one or more indices of refraction of the lens of the eye, wherein the posterior optical node is located along the optical axis, and wherein the anterior and posterior optical nodes have a property that a ray aimed at one of the anterior and posterior optical nodes is refracted by the eye such that it appears to have come from the other one of the anterior and posterior optical nodes and with the same angle with respect to the optical axis.
2. The apparatus of claim 1 , wherein the processor comprises instructions to determine a center of curvature of the cornea, a center of curvature of the anterior lens surface and a center of curvature of the posterior lens surface based respectively on the curvature of the cornea, the curvature of the anterior lens surface, and the curvature of the posterior lens surface, and to determine a position and an orientation of the optical axis by minimizing distances of the optical axis from the center of curvature of the cornea, the center of curvature of the anterior lens surface and the center of curvature of the posterior lens surface.
3. The apparatus of claim 2 , wherein the optical axis extends through the center of curvature of the cornea, the center of curvature of the anterior lens surface and the center of curvature of the posterior lens surface.
4. The apparatus of claim 1 , wherein the processor further comprises instructions to determine a visual axis of the eye when the patient views a fixation target, the visual axis extending away from an optical axis of the eye, and wherein the processor comprises instructions to determine a position and an orientation of the visual axis and the optical axis in relation to locations of tissue structures of the eye prior to coupling a patient interface to the eye.
5. The apparatus of claim 4 , wherein the tissue structure of eye comprises one or more of an iris of the eye, blood vessels of the eye, a limbus of the eye, or a corneal thickness profile of the eye and wherein the processor further comprises instructions to measure the location of the tissue structure of the eye without the eye contacting the patient interface and to determine and display the visual axis and the optical axis to a user without the eye contacting the patient interface in response to the location of the tissue structure without the eye contacting the patient interface.
6. The apparatus of claim 4 , wherein the processor further comprises instructions to determine the visual axis of the eye and the optical axis of the eye in response to the locations of the tissue structures of the eye with the eye coupled to the patient interface.
7. The apparatus of claim 6 , wherein the tissue structure of eye comprises one or more of an iris of the eye, blood vessels of the eye, a limbus of the eye, or a corneal thickness profile of the eye, and wherein the processor further comprises instructions to measure the location of the tissue structure of the eye with the eye coupled to the patient interface and to determine and display the visual axis and the optical axis to a user with the eye coupled to the patient interface in response to the location of the tissue structure with the eye coupled to the patient interface.
8. The apparatus of claim 1 , wherein the tomography of the eye is measured prior to contacting the eye with a patient interface, and wherein the apparatus further comprises a second tomography system for measuring a second tomography of the eye when the eye has contacted the patient interface, the first tomography system being physically separated from the second tomography system.
9. The apparatus of claim 1 , wherein the processor further comprises instructions to display one or more of a visual axis of the eye, an optical axis of the eye, a line of sight of the eye, a pupillary axis of the eye, a vertex of the cornea, a first Purkinje image of the eye, or cyclo torsional axis of the eye in response to measurements of the eye with the eye contacting the patient interface.
10. The apparatus of claim 1 , wherein the processor further comprises instructions to display one or more of a visual axis of the eye, an optical axis of the eye, a line of sight of the eye, a pupillary axis of the eye, a vertex of the cornea, a first Purkinje image of the eye, or a cyclo torsional axis of the eye with the eye contacting the patient interface in response to first measurements of the eye without the eye contacting the patient interface and second measurements of the eye with the eye contacting the patient interface.