1. Optical Instruments II Instruments for Imaging the Retina

2. 1. Fundus Camera Fundus camera optics are very similar to those of the indirect ophthalmoscope.

3. principle of indirect ophthalmoscope GTT 04 same principle for fundus camera

4. GTT 04

5. Practical Retinal Illumination System GTT 04

7. GTT 05

8. hole in 45 o mirror

9. camera or CCD Fundus camera

10. 2. Scanning Laser Ophthalmoscope (SLO) Uses much lower light levels than fundus camera – continuous viewing. Many wavelengths including IR—no mydriasis

11. Confocal Principle Red cell in thick sample imaged by lens Blue cell, nearer to surface, imaged at different point Pinhole in image plane passes all light from blue cell Pinhole blocks most of light from red cell Based on Webb, RH, Rep Prog Phys 59:427

12. Fast (35  S) horizontal line scan Slower vertical scan (17 mS) Video rate raster pattern SLO Raster Scan

13. laser AOM rotating faceted mirror—40,000 rpm vertical scan—60 Hz photo- detector video monitor laser-beam raster on retina pinhole

14. laser laser-beam raster on retina Video source (computer, camera) Acousto- Optic Modulator video monitor

16. SLO more light efficient than fundus camera iris pupilillumination exit pupil illumination exit pupil FUNDUS CAMERA SLO

17. SLO with Adaptive Optics (AO) Corrects laser beam aberrations caused by eye’s optics. Results in very high resolution images of retina.

18. AO SLO laser micromirror array X – Y scan beamsplitting mirror Hartmann- Shack wavefront sensor aberration signals

19. Hartmann-Shack Principle

22. AO turned on Human retina AO SLO A. Roorda UC Berkley

25. AO SLO optical sectioning (images in depth)

26. 3. Optical Coherence Tomography (OCT)

27. Coherence of Light Waves

28. Laser Beam Coherence Laser coherence length

29. Michelson Interferometer reference arm sample arm

30. Interference Fringes in Michelson Interferometer

31. low coherence lengthlong coherence length

32. Michelson Interferometer Optical Coherence Tomography electronics video monitor

33. sample video monitor electronics reference arm sample arm

34. Fringes form when reference mirror path length matches path length of a reflective piece in the tissue in the sample arm. Fringes only form when the path difference is within the coherence length of the light source. IN MICHELSON INTERFEROMETER

35. video monitor electronics A SCAN B SCAN

36. OCT using fiber optics electronics photodetector SLD sample reference

38. Time Domain OCT’s Axial (‘A’) scan comes from mirror movement in time. Resolution in both directions about 10  m. About 750 A scans/sec 1 – 2 sec for one complete image Eye movements a problem

39. Fourier Domain OCT (FDOCT) Reference mirror stationary Reflectance of tissue at each depth recorded simultaneously Two types: Swept Source (SSOCT) & Spectral Domain SDOCT) Called this because raw output of the OCT is the Fourier transform of the depth reflectance signal.

40. Swept-Source FDOCT swept laser fixed ref mirror inverse Fourier transform electronics 1/  (wavenumber) I Distance (  m)

41. FDOCT provides improved resolution and reduced image formation times compared to TDOCT TDOCT FDOCT  10  m < 3  m 750 16,000 1– 2sec 0.03 sec Axial & lateral resolution A-scans/sec Image formation time (512 A scans)

42. Drexler W et al. Nature 2001

44. J. Izatt

45. Bioptigen Inc. 1,000 A scans. 17 images/sec Fundus image from 3D data Volumetric 3D image (5.7 sec)