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Wide-field retinal hemodynamic imaging with the tracking scanning laser ophthalmoscope

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Real time, high-speed image stabilization with a retinal tracking scanning laser ophthalmoscope (TSLO) enables new approaches to established diagnostics. Large frequency range (DC to 19 kHz), wide-field (40-deg) stabilized Doppler flowmetry imaging was demonstrated in initial human subject tests. The fundus imaging method is a quasi-confocal line-scanning laser ophthalmoscope (LSLO). The retinal tracking system uses a confocal reflectometer with a closed loop optical servo system to lock onto features in the ocular fundus and automatically re-lock after blinks. By performing a slow scan with the laser line imager, frequency-resolved retinal perfusion and vascular flow images were obtained free of eye motion artifacts. Normal adult subjects and patients were tested with and without mydriasis to characterize flow imaging performance.

©2004 Optical Society of America

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Figures (8)

Fig. 1.
Fig. 1. (2.3 MB) Video and x-y eye positions during automatic re-lock after blinks. Slewing is caused by tracking biases that move the tracking mirrors when lock is lost at high servo gain
Fig. 2.
Fig. 2. Diagram illustrating the slow scan technique for SDF (a) and for the HRF (b). The order of the BTC scan sequence is numbered on the diagram. The scan equation is shown below the diagram for each type. After Fourier transformation, the data cube is displayed as a video where individual frames are created by binning individual frequencies with a moving window.
Fig. 3.
Fig. 3. (2.0 MB) Reconstructed image and blood flow video for a healthy 24 year old subject.
Fig. 4.
Fig. 4. (2.2 MB) Reconstructed image and blood flow video for normal subject with light pigmentation.
Fig. 5.
Fig. 5. (3.0 MB) Reconstructed image and blood flow video for patient with central serous chorioretinopathy (indicated by blue arrows).
Fig. 6.
Fig. 6. Laminar Poiseuille flow measured in a major nasal retinal artery (indicated by yellow box) from a high-frequency, high-magnification scan. The FWHM vessel edges (circles) are plotted and fit to a parabolic curve. The frequency of flow in the vessel is indicated up to the measured resolution limit of the imaging system. The maximum detectable frequency in that vessel is also indicated (diamond, error bars indicate range of bin). Estimated peak velocity was 4.6±0.4 cm/s.
Fig. 7.
Fig. 7. (2.3 MB) Reconstructed image and blood flow video for macular degeneration patient showing reduced perfusion in the macula.
Fig. 8.
Fig. 8. False color composite blood flow images for second normal subject (a,d) and both patients (b,c,e,f). Upper row (a-c) shows images created with individually normalized frequencies bins and lower row shows images created when the composite image was normalized to the power in each bin. Red: f < 400 Hz, Green: f = 400 – 1000 Hz, Blue: f ~ 1000 Hz.

Equations (1)

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u p = f p λ n sin θ B


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