Scanning ophthalmoscopes

1. A scanning ophthalmoscope for scanning the retina of an eye comprising:

a source of collimated light;

a first scanning element;

a second scanning element;

a scan compensation device;

wherein the first scanning element produces a one-dimensional collimated light scan in a first direction;

wherein the scan compensation device delivers the one-dimensional collimated light scan from the first scanning element onto the second scanning element in such a manner that the scan in the first direction appears to be provided from an apparent point source; and

wherein the second scanning element produces from the one-dimensional collimated light scan a two-dimensional collimated light scan by scanning in a second direction from the apparent point source;

wherein the scanning ophthalmoscope further comprises a scan transfer device, wherein the scan transfer device has two foci and the apparent point source is provided at a first focus of the scan transfer device and an eye is accommodated at a second focus of the scan transfer device, and wherein the scan transfer device transfers the two-dimensional collimated light scan from the apparent point source into the eye,

wherein the rotational axis of the second scanning element is substantially parallel to a line joining the two foci of the scan transfer device, and

wherein the line joining the two foci of the scan transfer device lies substantially on a plane defined by the one-dimensional collimated light scan produced by the scan compensation device.

2. A scanning ophthalmoscope according to claim 1 in which the rotational axis of the second scanning element is within approximately 5° of the line joining the two foci of the scan transfer device.

3. A scanning ophthalmoscope according to claim 2 in which the rotational axis of the second scanning element is within approximately 2° of the line joining the two foci of the scan transfer device.

4. A scanning ophthalmoscope according to claim 1 in which the rotational axis of the second scanning element and the line joining the two foci of the scan transfer device, has a degree of parallelism which depends on chosen eccentricities of one or more components of the scanning ophthalmoscope.

5. A scanning ophthalmoscope according to claim 1 in which the rotational axis of the second scanning element and the line joining the two foci of the scan transfer device, has a degree of parallelism determined by a user of the scanning ophthalmoscope, according to an acceptable level of shear in images of the retina produced by the ophthalmoscope.

6. A scanning ophthalmoscope according to claim 1 in which the line joining the two foci of the scan transfer device is within approximately 5° of the plane defined by the one-dimensional collimated light scan produced by the scan compensation device.

7. A scanning ophthalmoscope according to claim 6 in which the line joining the two foci of the scan transfer device is within approximately 2° of the plane defined by the one-dimensional collimated light scan produced by the scan compensation device.

8. A scanning ophthalmoscope according to claim 1 in which the line joining the two foci of the scan transfer device and the plane defined by the one-dimensional collimated light scan produced by the scan compensation device, has a degree of coincidence which depends on chosen eccentricities of one or more components of the scanning ophthalmoscope.

9. A scanning ophthalmoscope according to claim 1 in which the line joining the two foci of the scan transfer device and the plane defined by the one-dimensional collimated light scan produced by the scan compensation device, has a degree of coincidence determined by a user of the scanning ophthalmoscope, according to an acceptable level of shear in images of the retina produced by the ophthalmoscope.

10. A scanning ophthalmoscope according to claim 1 in which the scan compensation device comprises an elliptical mirror.

11. A scanning ophthalmoscope according to claim 10 in which the scan compensation device comprises an aspherical mirror.

12. A scanning ophthalmoscope according to claim 11 in which the scan compensation device comprises an ellipsoidal mirror.

13. A scanning ophthalmoscope according to claim 1 in which the scan compensation device comprises a pair of parabola mirrors.

14. A scanning ophthalmoscope according to claim 1 in which the scan compensation device comprises a pair of paraboloidal mirrors.

15. A scanning ophthalmoscope according to claim 1 in which the scan transfer device comprises an elliptical mirror.

16. A scanning ophthalmoscope according to claim 15 in which the scan transfer device comprises an aspherical mirror.

17. A scanning ophthalmoscope according to claim 16 in which the scan transfer device comprises an ellipsoidal mirror.

18. A scanning ophthalmoscope according to claim 1 in which the scan transfer device comprises a pair of parabola mirrors.

19. A scanning ophthalmoscope according to claim 1 in which the scan transfer device comprises a pair of paraboloidal mirrors.

20. A scanning ophthalmoscope according to claim 1 in which the scan compensation device comprises two foci, a first focus coincident with a center from which said one-dimensional scan is produced at said first scanning element, and a second focus coincident with said apparent point source.

21. A scanning ophthalmoscope according to claim 20 in which said second focus of the scan compensation device is coincident with said first focus of the scan transfer device.

22. A scanning ophthalmoscope according to claim 1 in which the first scanning element comprises a rotating mechanism.

23. A scanning ophthalmoscope according to claim 22 in which the first scanning element comprises a rotating polygon mirror.

24. A scanning ophthalmoscope according to claim 1 in which the second scanning element comprises an oscillating mechanism.

25. A scanning ophthalmoscope according to claim 24 in which the second scanning element comprises an oscillating plane mirror.

26. A scanning ophthalmoscope according to claim 1 in which the source of collimated light comprises a laser light source.

27. A scanning ophthalmoscope according to claim 1 which is able to produce up to 150 degree scans of the retina of the eye, measured at the pupillary point of the eye.

28. A scanning ophthalmoscope according to claim 27 which is able to produce 120 degree scans of the retina of the eye, measured at the pupillary point of the eye.

29. A method of scanning the retina of an eye comprising the steps of:

providing a source of collimated light, a first scanning element, a second scanning element and a scan compensation device;

using the source of collimated light to produce a one-dimensional collimated light scan in a first direction; using the scan compensation device to deliver the one-dimensional collimated light scan from the first scanning element onto the second scanning element in such a manner that the scan in the first direction appears to be provided from an apparent point source;

using the second scanning element to produce a two-dimensional collimated light scan from the one-dimensional collimated light scan by scanning in a second direction from the apparent point source;

providing a scan transfer device having two foci; positioning the second scanning element such that its rotational axis is substantially parallel to a line joining the two foci of the scan transfer device;

providing the apparent point source at a first focus of the scan transfer device and accommodating the eye at the second focus of the scan transfer device;

using the scan transfer device to transfer the two-dimensional collimated light scan from the apparent point source to the eye;

wherein the line joining the two foci of the scan transfer device lies substantially on a plane defined by the one-dimensional collimated light scan produced by the scan compensation device.