Optical Instruments.ppt
- 1. GTT/98 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. 74.1 153.6 20 D Pupil Conjugate Plane Gullstrand Retinal Illumination Light introduced in pupil conjugate plane In focus in pupil plane Mpupil conjugate = 153.6 74.1 = 2.1 M pupil conjugate = 1 2.1 = 0.48 GTT 04
- 5. Pupil conjugate plane Lamp Aperture 45 mirror Practical Retinal Illumination System GTT 04
- 7. GTT 05
- 8. hole in 45o mirror
- 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 mS) 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 pupil illumination 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
- 22. AO turned on Human retina AO SLO A. Roorda UC Berkley
- 25. A. Roorda UC Berkley AO SLO optical sectioning (images in depth)
- 26. 3. Optical Coherence Tomography (OCT)
- 27. coherent incoherent partially coherent Coherence of Light Waves
- 29. fixed mirror movable mirror laser negative lens screen interference fringes beam-splitting prism L 1 L 1 L 2 Michelson Interferometer reference arm sample arm
- 30. screen plane waves from fixed mirror plane waves from movable mirror Interference Fringes in Michelson Interferometer
- 31. low coherence length long coherence length
- 32. movable mirror laser negative lens fixed mirror Michelson Interferometer Optical Coherence Tomography photodetector electronics video monitor
- 33. lateral (X) scanning mirror negative lens axial (Z-axis) scan photodetector 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. lateral (X) scanning mirror negative lens axial (Z-axis) scan photodetector video monitor electronics A SCAN B SCAN
- 36. OCT using fiber optics electronics photodetector SLD sample reference
- 37. GTT/98
- 38. Time Domain OCT’s Axial (‘A’) scan comes from mirror movement in time. Resolution in both directions about 10 mm. 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 (mm)
- 41. FDOCT provides improved resolution and reduced image formation times compared to TDOCT TDOCT FDOCT ~ 10 mm < 3 mm 750 16,000 1 – 2 sec 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)