Optical coherence metrology and tomography with improved registration
Methods and apparatus are provided for optical coherence metrology or tomography across an extended area of an eye with improved registration. At least two optical coherence tomograms are acquired, with each tomogram containing data from regions of an anterior surface of the eye that are at least partially overlapping, and data from one or more deeper structures such as the retina or the anterior or posterior lens surfaces. The tomograms are then processed to register the data from the overlapping portions of the anterior surface regions, thereby registering the data from the deeper structures. In certain embodiments the reference arm of the apparatus comprises a compound reflector having at least two axially separated reflective surfaces for applying differential delays to different portions of the reference beam. The depth of field of the apparatus is thereby extended to enable measurement of eye length. In certain embodiments eye length measurements at a number of angles of incidence provide information on total eye shape.
1. A method for performing optical coherence metrology across an extended area of an eye, said method comprising the steps of:
(i) acquiring, within a single frame of a two-dimensional sensor array, a first optical coherence tomogram of said eye, said first optical coherence tomogram containing data from a first region of an anterior surface of said eye, and data from a third region of said eye;
(ii) acquiring, within a single frame of said two-dimensional sensor array, a second optical coherence tomogram of said eye, said second optical coherence tomogram containing data from a second region of said anterior surface that is at least partially overlapping with said first region, and data from a fourth region of said eye; and
(iii) processing the first and second optical coherence tomograms to register the overlapping portions of the first and second regions of said anterior surface, thereby registering the data from the third and fourth regions of said eye,
wherein said method further comprises the step of imposing a predetermined optical path length difference on first and second laterally spaced portions of a reference beam or a sample beam when acquiring at least one of the first and second optical coherence tomograms.
2. The method according to claim 1 , wherein at least one of the first and second regions of said anterior surface includes a portion of the anterior sclera.
3. The method according to claim 1 , wherein at least one of the first and second regions of said anterior surface includes a portion of the limbus.
4. The method according to claim 1 , wherein each of the first and second optical coherence tomograms is acquired within a time period of 2 milliseconds or less.
5. The method according to claim 1 , wherein each of the first and second optical coherence tomograms contains data from a plurality of discrete points within the respective region of said anterior surface.
6. The method according to claim 1 , wherein said predetermined optical path length difference is imposed on first and second laterally spaced portions of a reference beam by a compound reflector having first and second axially separated reflective surfaces for reflecting the first and second laterally spaced portions of said reference beam.
7. The method according to claim 6 , wherein said compound reflector is selected such that said predetermined optical path length difference compensates for the axial depth of the eye.
8. An apparatus for performing optical coherence metrology across an extended area of an eye, said apparatus comprising:
an interferometer for acquiring, each within a single frame of a two-dimensional sensor array, first and second optical coherence tomograms of an eye, said first optical coherence tomogram containing data from a first region of an anterior surface of said eye and data from a third region of said eye, and said second optical coherence tomogram containing data from a second region of said anterior surface and data from a fourth region of said eye, wherein said first and second regions are at least partially overlapping; and
a computer coupled to a memory storing instructions that when executed configure the computer to process the first and second optical coherence tomograms to register the overlapping portions of the first and second regions of said anterior surface, thereby registering the data from the third and fourth regions of said eye,
wherein said interferometer includes a multi-length delay element for imposing a predetermined optical path length difference on first and second laterally spaced portions of a reference beam or a sample beam when acquiring at least one of the first and second optical coherence tomograms.
9. The apparatus according to claim 8 , wherein said interferometer is configured such that, in use, at least one of the first and second regions of said anterior surface includes a portion of the anterior sclera.
10. The apparatus according to claim 9 , wherein said interferometer is configured such that, in use, at least one of the first and second regions of said anterior surface includes a portion of the limbus.
11. The apparatus according to claim 8 , wherein said interferometer is configured such that, in use, each of the third and fourth regions of said eye comprises a region of the retina.
12. The apparatus according to claim 8 , wherein said apparatus is configured such that each of the first and second optical coherence tomograms can be acquired within a time period of 2 milliseconds or less.
13. The apparatus according to claim 8 , wherein said interferometer comprises a spatial sampling element for providing an array of beamlets, such that, in use, each of the first and second optical coherence tomograms contains data from a plurality of discrete points within the respective region of said anterior surface.
14. The apparatus according to claim 13 , wherein said spatial sampling element comprises a two-dimensional lenslet array.
15. The apparatus according to claim 13 , further comprising a structured aperturing partition for suppressing crosstalk between beamlets returning from said eye.
16. The apparatus according to claim 15 , wherein said structured aperturing partition comprises a first member having a plurality of apertures for passing on-axis beamlets returning from said eye.
17. The apparatus according to claim 16 , wherein said structured aperturing partition comprises a second member extending parallel to the propagation direction of said on-axis beamlets for suppressing the passage of off-axis light.
18. The apparatus according to claim 13 , wherein said interferometer and said spatial sampling element are configured such that, in use, each of the third and fourth regions of said eye comprises a plurality of discrete points on the retina.
19. The apparatus according to claim 8 , wherein said multi-length delay element is configured to impose said predetermined optical path length difference on first and second laterally spaced portions of a reference beam.
20. The apparatus according to claim 19 , wherein said multi-length delay element comprises a compound reflector having first and second axially separated reflective surfaces for reflecting the first and second laterally spaced portions of said reference beam.
21. The apparatus according to claim 20 , wherein said compound reflector is selected such that said predetermined optical path length difference compensates for the axial depth of the eye.
22. An apparatus for performing optical coherence metrology across an extended area of an eye, said apparatus comprising:
an interferometer for acquiring first and second optical coherence tomograms of an eye, said first optical coherence tomogram containing data from a first region of an anterior surface of said eye and data from a third region of said eye, and said second optical coherence tomogram containing data from a second region of said anterior surface and data from a fourth region of said eye, wherein said first and second regions are at least partially overlapping;
a computer coupled to a memory storing instructions that when executed configure the computer to process the first and second optical coherence tomograms to register the overlapping portions of the first and second regions of said anterior surface, thereby registering the data from the third and fourth regions of said eye; and
a multi-length delay element for applying a predetermined optical path length difference to first and second laterally spaced portions of a reference beam or a sample beam when acquiring at least one of the first and second optical coherence tomograms, said multi-length delay element being selected such that said predetermined optical path length difference compensates for the axial depth of said eye.