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Optical Instruments II

Optical Instruments II. Instruments for Imaging the Retina. 1. Fundus Camera. Fundus camera optics are very similar to those of the indirect ophthalmoscope. principle of indirect ophthalmoscope. same principle for fundus camera. GTT 04. GTT 04. Practical Retinal Illumination System.

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Optical Instruments II

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  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 same principle for fundus camera GTT 04

  4. GTT 04

  5. Practical Retinal Illumination System GTT 04

  6. GTT 05

  7. hole in 45o mirror

  8. Fundus camera camera or CCD

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

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

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

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

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

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

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

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

  17. Hartmann-Shack Principle

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

  19. AO SLO optical sectioning (images in depth) A. Roorda UC Berkley

  20. 3. Optical Coherence Tomography (OCT)

  21. Coherence of Light Waves

  22. Laser Beam Coherence Laser coherence length

  23. Michelson Interferometer reference arm sample arm

  24. Interference Fringes in Michelson Interferometer

  25. low coherence length long coherence length

  26. video monitor electronics Michelson Interferometer Optical Coherence Tomography

  27. reference arm sample arm video monitor sample electronics

  28. IN MICHELSON INTERFEROMETER 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.

  29. A SCAN B SCAN video monitor electronics

  30. OCT using fiber optics electronics sample reference SLD photodetector

  31. 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 Time Domain OCT’s

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

  33. Swept-Source FDOCT fixed ref mirror swept l laser electronics inverse Fourier transform I 1/l (wavenumber) Distance (mm)

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

  35. Drexler W et al. Nature 2001

  36. J. Izatt

  37. 1,000 A scans. 17 images/sec Volumetric 3D image (5.7 sec) Fundus image from 3D data Bioptigen Inc.

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