Axial length measurement monitor
An OCT axial length measurement device is configured to measure an area of the retina within a range from about 0.05 mm to about 2.0 mm. The area can be measured with a scanned measurement beam or plurality of substantially fixed measurement beams. The OCT measurement device may comprise a plurality of reference optical path lengths, in which a first optical path length corresponds to a first position of a cornea, and a second optical path length corresponds to a second position of the retina, in which the axial length is determined based on a difference between the first position and the second position. An axial length map can be generated to determine alignment of the eye with the measurement device and improve accuracy and repeatability of the measurements. In some embodiments, the OCT measurement device comprises a swept source vertical cavity surface emitting laser (“VCSEL”).
1. A method of measuring a change in a refractive error of an eye, the method comprising:
measuring a first axial length of the eye between a zone of a retina and a zone of a cornea with a first plurality of A-scans at a first time to determine a first axial length of the eye, the zone of the retina comprising a maximum distance across within a range from about 0.05 mm to about 2 mm; and
measuring a second axial length of the eye between the zone of the retina and the zone of the cornea at a second time with a second plurality of A-scans to determine the second axial length of the eye at the second time;
wherein the change in the refractive error corresponds to a difference between the first axial length and the second axial length,
wherein each of the first plurality of A-scans and the second plurality of A-scans simultaneously measures a distance of the zone of the cornea and a distance of the zone of the retina with an OCT measurement beam.
2. The method of claim 1 , wherein the first maximum distance across is within a range from about 0.1 mm to about 1.5 mm.
3. The method of claim 1 , wherein each of the first plurality of A-scans and the second plurality of A-scans is measured with a scanning OCT measurement beam.
4. The method of claim 3 , wherein the scanning OCT measurement beam moves along a first trajectory to measure the first plurality of A-scans and a second trajectory to measure the second plurality of A-scans.
5. The method of claim 1 , wherein the first plurality of A-scans is measured with a first plurality of fixed measurement beams and the second plurality of A-scans is measured with a second plurality of fixed measurement beams.
6. The method of claim 5 , wherein the first plurality of fixed measurement beams arranged to generate the first plurality of A-scans and the second plurality of fixed measurement beams is arranged to generate the second plurality of A-scans.
7. The method of claim 1 , wherein the first plurality of A-scans measures a first plurality of corneal locations distributed on a first corneal zone and the second plurality of A-scans measures a second plurality of corneal locations distributed on a second corneal zone and wherein the first axial length corresponds to a difference between a first plurality of retinal locations and the first plurality of corneal locations and the second axial length corresponds to a difference between a second plurality of retinal locations and the second plurality of corneal locations.
8. The method of claim 7 , wherein a first plurality of axial lengths is determined and a second plurality of axial lengths is determined, the first plurality of axial lengths corresponding to first differences between each of the first plurality of corneal locations and a corresponding first retinal location, the second plurality of axial lengths corresponding to second differences between each of the second plurality of corneal locations and a corresponding second retinal location.
9. The method of claim 7 , wherein the first corneal zone substantially overlaps with the second corneal zone.
10. The method of claim 1 , wherein the maximum distance across comprises a diameter.
11. The method of claim 7 , wherein one or more of the first corneal zone or the second corneal zone comprises an annulus.
12. The method of claim 7 , wherein the first corneal zone or the second corneal zone comprises an area.
13. The method of claim 1 , wherein the first axial length comprises a first axial length map and the second axial length comprises a second axial length map and wherein the change in a refractive error corresponds to a difference between the first axial length map and the second axial length map.
14. A system to measure the change in a refractive error of an eye, the system comprising a processor configured with instructions to implement the method of claim 1 .
15. The system of claim 14 , further comprising:
a swept light source to generate an OCT beam and vary a wavelength of the OCT beam; and
an interferometer coupled to the swept light source, the interferometer comprising a measurement optical path and a reference optical path, the reference optical path comprising a first reference path to measure the distance of the zone of the cornea and a second reference path to measure the distance of the zone of the retina.
16. The system of claim 15 , further comprising a detector coupled to the interferometer to receive a first interference signal and a second interference signal, the first interference signal resulting from light from the first reference path interfering with light from the measurement optical path, the second interference signal resulting from light from the second reference path interfering with light from the measurement optical path.