Abstract

A technique is described of using the video output of the scanning laser ophthalmoscope to monitor the positions of fundus features with respect to an input laser raster. The monitoring performance characteristics are discussed as well as tracking methods and possible applications in psychophysics and laser photocoagulation.

© 1987 Optical Society of America

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References

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  1. L. R. Young, D. Sheena, “Survey of Eye Movement Recording Methods,” Behav. Res. Methods Instrum. 7, 394 (1975).
    [CrossRef]
  2. R. H. Webb, G. W. Hughes, “Scanning Laser Ophthalmoscope,” IEEE Trans. Biomed. Eng. BE-28, 488 (1981).
    [CrossRef]
  3. R. H. Webb, G. W. Hughes, “Confocal Scanning Laser Ophthalmoscope,” Appl. Opt. 26, 1492 (1987).
    [CrossRef] [PubMed]

1987 (1)

1981 (1)

R. H. Webb, G. W. Hughes, “Scanning Laser Ophthalmoscope,” IEEE Trans. Biomed. Eng. BE-28, 488 (1981).
[CrossRef]

1975 (1)

L. R. Young, D. Sheena, “Survey of Eye Movement Recording Methods,” Behav. Res. Methods Instrum. 7, 394 (1975).
[CrossRef]

Hughes, G. W.

R. H. Webb, G. W. Hughes, “Confocal Scanning Laser Ophthalmoscope,” Appl. Opt. 26, 1492 (1987).
[CrossRef] [PubMed]

R. H. Webb, G. W. Hughes, “Scanning Laser Ophthalmoscope,” IEEE Trans. Biomed. Eng. BE-28, 488 (1981).
[CrossRef]

Sheena, D.

L. R. Young, D. Sheena, “Survey of Eye Movement Recording Methods,” Behav. Res. Methods Instrum. 7, 394 (1975).
[CrossRef]

Webb, R. H.

R. H. Webb, G. W. Hughes, “Confocal Scanning Laser Ophthalmoscope,” Appl. Opt. 26, 1492 (1987).
[CrossRef] [PubMed]

R. H. Webb, G. W. Hughes, “Scanning Laser Ophthalmoscope,” IEEE Trans. Biomed. Eng. BE-28, 488 (1981).
[CrossRef]

Young, L. R.

L. R. Young, D. Sheena, “Survey of Eye Movement Recording Methods,” Behav. Res. Methods Instrum. 7, 394 (1975).
[CrossRef]

Appl. Opt. (1)

Behav. Res. Methods Instrum. (1)

L. R. Young, D. Sheena, “Survey of Eye Movement Recording Methods,” Behav. Res. Methods Instrum. 7, 394 (1975).
[CrossRef]

IEEE Trans. Biomed. Eng. (1)

R. H. Webb, G. W. Hughes, “Scanning Laser Ophthalmoscope,” IEEE Trans. Biomed. Eng. BE-28, 488 (1981).
[CrossRef]

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Figures (2)

Fig. 1
Fig. 1

To obtain these fiducial crosses, a 6-bit frame-grabber was set to continual-grab mode with the SLO as its source; the grabbed images were analyzed in real time by a computer; and a fiducial cross was written into frame-grabber memory prior to output for display. The frame-grabber output, including cross, was videotaped and studied frame-by-frame. Error in eye-movement monitoring was investigated by measuring the amount of variation in the placement of the fiducial, which had been placed approximately over the left edge of the vessel. Since each frame consists of two successive images, it can be seen that in one photo the velocity of eye motion is almost zero, while in the other photo the velocity is ~180°/s. (The white optic disk is ~5° in diameter.) Note: The images seen here have been degraded by six reproductions into different media before printing—video to 6-bit digital to video to tape to video to CRT to film. Frame-by-frame analysis was done at the CRT stage, where it was judged that resolution of cross position vs vessel position by human inspection was possible to about one-fifth the width of the fiducial cross (13 min of arc). After reproduction to film, this resolution dropped to about one-third of the width of the vessel (~20 min of arc), probably because the film represents integration of about sixteen frames of paused VCR signal.

Fig. 2
Fig. 2

Two stages of the fundus tracking algorithm are illustrated here. First, pixels are sampled and thresholded in a grid pattern covering the optic disk. The centroid of the brightest pixels in the disk is calculated. In the second stage, at a fixed offset from this centroid, a vessel-recognizing template is swept horizontally in search of the vessel. A template-correlation value is calculated by adding the values of the six off-vessel positions and subtracting twice the values at the three on-vessel positions. The template position having the highest correlation value is the one selected.

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