COMPARISON O F P H O T O G R A P H I C T E C H N I Q U E S AND FILMS USED IN STEREOPHOTOGRAMMETRY O F T H E O P T I C DISK M A R I J A N E A. K R O H N , M.A.,
J O H N L. K E L T N E R ,
M.D.,
AND C H R I S A. J O H N S O N , P H . D. Davis,
Previous studies indicate that photogrammetric analysis of stereophotographs can provide measurements of the optic disk, which are useful in studying glauco ma and other optic disk defects. 1 - 4 The precision of stereophotogrammetry de pends on reproducible stereophotography, reliable photogrammetry, and film that does not introduce additional errors. Other investigators have compared meth ods of stereophotography, photogramme try, and film, and have reported that si multaneous stereophotography 3 , 5 with Kodak Photomicrography film 6 gave the most consistent results. We did a more extensive comparison of simultaneous and consecutive stereophotography by using a larger number of subjects and providing a statistical analysis. We also compared Kodak Photomicrography film and Kodachrome 25 because previous comparisons had not been evaluated quantitatively. S U B J E C T S AND M E T H O D S
For comparison between simultaneous and consecutive stereophotography, we chose eight eyes from five patients; five eyes had enlarged optic cups from glaucomatous damage, two eyes had medium sized normal cups, and one eye had a small normal cup. In the film comparison, we photographed six eyes from four pa-
From the Department of Ophthalmology, Uni versity of California, School of Medicine, Davis, California. This study was supported by National Eye Institute Research Grant No. EY-01841 (Dr. Keltner). Reprint requests to Marijane A. Krohn, M.A., Department of Ophthalmology, University of Cali fornia, School of Medicine, Davis, CA 95616.
California
tients; three eyes had optic cups damaged by glaucoma and three eyes had medium sized normal cups. All the photographs were taken by the same photographer, and all the photographs for each patient were taken on one day. Each eye was photographed six to eight times by each method and the three clearest photo graphs were chosen. We used the Donaldson stereoscopic fundus camera (simultaneous stereopho tography) with a 2.87-mm stereoscopic base and the lowest magnification setting, and the Zeiss Fundus Flash II (consecu tive stereophotography) with the Allen stereoscopic separator set at 2.5 mm stere oscopic base. By using the Zeiss camera and Allen separator, we carefully avoided adjusting the horizontal position of the camera between the stereoscopic pairs of photographs, to insure a stereoscopic base of 2.5 mm. The photographs on the Donaldson and the Zeiss cameras were recorded on Kodachrome 25 film. The photographs taken to compare Kodak Photomicrography film with Koda chrome 25 film were done on the Donald son stereoscopic fundus camera with the settings previously mentioned. A photogrammetric engineer analyzed the six stereoscopic pairs of photographs for each eye without names or dates disguised, on a Wild A-10 photogramme tric plotting instrument (magnification = X6.55, stereoscopic base = 200 mm). Digital x, y, and z coordinates were estab lished for 400 to 700 data points on each disk and transferred to punch cards for computer processing. A computer algo rithm determined the optic cup volume, area, and depth for each stereoscopic pair
AMERICAN JOURNAL O F OPHTHALMOLOGY 88:859-863, 1979
859
860
AMERICAN JOURNAL OF OPHTHALMOLOGY
on six pairs for each eye. Depth sensitivi ty of this procedure was 0.01 mm. Optic cup volume, area, and depth measure ments were determined by defining the top of the optic cup as the lowest point on the rim of the cup orifice. Thorough de scriptions of the basis and rationale un derlying this photogrammetric procedure have been reported previously. 2 ' 7 RESULTS
Simultaneous compared with consecu tive stereophotography—The photogram metric measurements of optic cup vol ume, area, and depth were similar for three trials per eye on the Donaldson camera compared with three trials per eye on the Zeiss camera. Means, standard deviations, and percent errors (a/X • 100) for each eye are presented in Table 1. A mean percent error (CT/X • 1.00) for volume
NOVEMBER, 1979
among three trials on eight eyes showed 9.9% for the Donaldson camera and 12.0% for the Zeiss camera. Area and depth showed slightly greater differences in mean percent error between the two photographic methods (Table 2). A Stu dent's t-test for related measures compar ing volume (t = 2.2, df = 7, P > .05), area (t = 1.88, df = 7, P > .10), and depth (t = 0.51, df = 7, P > .20) showed no significant differences between the Donaldson and Zeiss camera photo graphs. The photogrammetric measure ments from photographs taken on the Zeiss camera (consecutive stereophotography) showed more variation than those measured from photographs by the Donaldson camera (simultaneous stereophotography); however, the difference in variation is hot statistically significant. Kodak Photomicrography compared
TABLE 1 M E A N , STANDARD DEVIATION AND PERCENT ERROR (CT/X ■ 100) FOR OPTIC CUP VOLUME, AREA, AND DEPTH OF INDIVIDUAL EYES USING THE DONALDSON AND ZEISS RETINAL FUNDUS CAMERAS
Zeiss Eye No. 1 2 3 4 5 6 7 8
Mean S.D. % error Mean S.D. % error Mean S.D. % error Mean S.D. % error Mean S.D. % error Mean S.D. % error Mean S.D. % error Mean S.D. % error
Donaldson
Volume
Area
Depth
Volume
Area
Depth
.056 .023 41 .152 .007 5 .293 .012 4 .399 .024 6 .379 .027 7 .572 .051 9 .330 .025 8 .549 .087 16
.428 .164 38 1.010 .075 7 1.452 .129 9 1.868 .046 2 1.463 .365 25 1.837 .206 11 1.281 .036 3 1.891 .206 11
.390 .060 15 .507 .049 10 .493 .035 7 .510 .017 3 .640 .056 9 .623 .090 15 .487 .045 9 .543 .031 6
.064 .016 25 .149 .010 7 .377 .040 11 .453 .024 5 .385 .036 9 .623 .078 13 .442 .026 6 .519 .015 3
.403 .023 6 .932 .143 15 1.808 .170 9 2.131 .204 10 1.498 .058 4 1.831 .156 9 1.479 .056 4 1.962 .029 1
.477 .116 24 .520 .040 8 .530 .036 7 .543 .045 8 .583 .031 5 .636 .046 7 .553 .023 4 .507 .015 3
VOL. 88, NO. 5
STEREOPHOTOGRAMMETRY OF THE OPTIC DISK
861
TABLE 2 MEAN AND RANGE OF PERCENT ERROR (
J O H N L. K E L T N E R ,
M.D.,
AND C H R I S A. J O H N S O N , P H . D. Davis,
Previous studies indicate that photogrammetric analysis of stereophotographs can provide measurements of the optic disk, which are useful in studying glauco ma and other optic disk defects. 1 - 4 The precision of stereophotogrammetry de pends on reproducible stereophotography, reliable photogrammetry, and film that does not introduce additional errors. Other investigators have compared meth ods of stereophotography, photogramme try, and film, and have reported that si multaneous stereophotography 3 , 5 with Kodak Photomicrography film 6 gave the most consistent results. We did a more extensive comparison of simultaneous and consecutive stereophotography by using a larger number of subjects and providing a statistical analysis. We also compared Kodak Photomicrography film and Kodachrome 25 because previous comparisons had not been evaluated quantitatively. S U B J E C T S AND M E T H O D S
For comparison between simultaneous and consecutive stereophotography, we chose eight eyes from five patients; five eyes had enlarged optic cups from glaucomatous damage, two eyes had medium sized normal cups, and one eye had a small normal cup. In the film comparison, we photographed six eyes from four pa-
From the Department of Ophthalmology, Uni versity of California, School of Medicine, Davis, California. This study was supported by National Eye Institute Research Grant No. EY-01841 (Dr. Keltner). Reprint requests to Marijane A. Krohn, M.A., Department of Ophthalmology, University of Cali fornia, School of Medicine, Davis, CA 95616.
California
tients; three eyes had optic cups damaged by glaucoma and three eyes had medium sized normal cups. All the photographs were taken by the same photographer, and all the photographs for each patient were taken on one day. Each eye was photographed six to eight times by each method and the three clearest photo graphs were chosen. We used the Donaldson stereoscopic fundus camera (simultaneous stereopho tography) with a 2.87-mm stereoscopic base and the lowest magnification setting, and the Zeiss Fundus Flash II (consecu tive stereophotography) with the Allen stereoscopic separator set at 2.5 mm stere oscopic base. By using the Zeiss camera and Allen separator, we carefully avoided adjusting the horizontal position of the camera between the stereoscopic pairs of photographs, to insure a stereoscopic base of 2.5 mm. The photographs on the Donaldson and the Zeiss cameras were recorded on Kodachrome 25 film. The photographs taken to compare Kodak Photomicrography film with Koda chrome 25 film were done on the Donald son stereoscopic fundus camera with the settings previously mentioned. A photogrammetric engineer analyzed the six stereoscopic pairs of photographs for each eye without names or dates disguised, on a Wild A-10 photogramme tric plotting instrument (magnification = X6.55, stereoscopic base = 200 mm). Digital x, y, and z coordinates were estab lished for 400 to 700 data points on each disk and transferred to punch cards for computer processing. A computer algo rithm determined the optic cup volume, area, and depth for each stereoscopic pair
AMERICAN JOURNAL O F OPHTHALMOLOGY 88:859-863, 1979
859
860
AMERICAN JOURNAL OF OPHTHALMOLOGY
on six pairs for each eye. Depth sensitivi ty of this procedure was 0.01 mm. Optic cup volume, area, and depth measure ments were determined by defining the top of the optic cup as the lowest point on the rim of the cup orifice. Thorough de scriptions of the basis and rationale un derlying this photogrammetric procedure have been reported previously. 2 ' 7 RESULTS
Simultaneous compared with consecu tive stereophotography—The photogram metric measurements of optic cup vol ume, area, and depth were similar for three trials per eye on the Donaldson camera compared with three trials per eye on the Zeiss camera. Means, standard deviations, and percent errors (a/X • 100) for each eye are presented in Table 1. A mean percent error (CT/X • 1.00) for volume
NOVEMBER, 1979
among three trials on eight eyes showed 9.9% for the Donaldson camera and 12.0% for the Zeiss camera. Area and depth showed slightly greater differences in mean percent error between the two photographic methods (Table 2). A Stu dent's t-test for related measures compar ing volume (t = 2.2, df = 7, P > .05), area (t = 1.88, df = 7, P > .10), and depth (t = 0.51, df = 7, P > .20) showed no significant differences between the Donaldson and Zeiss camera photo graphs. The photogrammetric measure ments from photographs taken on the Zeiss camera (consecutive stereophotography) showed more variation than those measured from photographs by the Donaldson camera (simultaneous stereophotography); however, the difference in variation is hot statistically significant. Kodak Photomicrography compared
TABLE 1 M E A N , STANDARD DEVIATION AND PERCENT ERROR (CT/X ■ 100) FOR OPTIC CUP VOLUME, AREA, AND DEPTH OF INDIVIDUAL EYES USING THE DONALDSON AND ZEISS RETINAL FUNDUS CAMERAS
Zeiss Eye No. 1 2 3 4 5 6 7 8
Mean S.D. % error Mean S.D. % error Mean S.D. % error Mean S.D. % error Mean S.D. % error Mean S.D. % error Mean S.D. % error Mean S.D. % error
Donaldson
Volume
Area
Depth
Volume
Area
Depth
.056 .023 41 .152 .007 5 .293 .012 4 .399 .024 6 .379 .027 7 .572 .051 9 .330 .025 8 .549 .087 16
.428 .164 38 1.010 .075 7 1.452 .129 9 1.868 .046 2 1.463 .365 25 1.837 .206 11 1.281 .036 3 1.891 .206 11
.390 .060 15 .507 .049 10 .493 .035 7 .510 .017 3 .640 .056 9 .623 .090 15 .487 .045 9 .543 .031 6
.064 .016 25 .149 .010 7 .377 .040 11 .453 .024 5 .385 .036 9 .623 .078 13 .442 .026 6 .519 .015 3
.403 .023 6 .932 .143 15 1.808 .170 9 2.131 .204 10 1.498 .058 4 1.831 .156 9 1.479 .056 4 1.962 .029 1
.477 .116 24 .520 .040 8 .530 .036 7 .543 .045 8 .583 .031 5 .636 .046 7 .553 .023 4 .507 .015 3
VOL. 88, NO. 5
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TABLE 2 MEAN AND RANGE OF PERCENT ERROR (
