Kent P. Pflibsen, François C. Delori, Oleg Pomerantzeff, and Michail M. Pankratov, "Fundus reflectometry for photocoagulation dosimetry," Appl. Opt. 28, 1084-1096 (1989)
A dosimetry technique has been developed which utilizes three-wavelength fundus reflectometry, a quantitative model of fundus reflectance, and a model of thermal tissue damage to control photocoagulation lesion size. The fundus reflectance model uses Lambert-Beer’s law exponential attenuators to describe the ocular media, retinal pigment epithelium (RPE), and choriocapillaris transmission characteristics while the choroid is described as a Kubelka-Munklike homogeneous scatterer/absorber. Three reflecting layers are included in the model at the retinal inner limiting membrane, Bruch’s membrane, and the sclera. Measured lesion size variability contained components which resulted from variations in choroidal blood and melanin and RPE melanin concentration. Photocoagulation dosimetry was found to reduce the photocoagulation lesion size coefficient of variation for red light from 45% to 10% for the control and dosimetry cases, respectively. Similar improvement was noted for yellow photocoagulation light.
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Ratio of the highest red reflectance to the lowest yellow reflectance measure in the initial data set (four rabbits).
Ratio of reflectance without sclera divided by reflectance with sclera. (Light) indicates a lightly pigmented rabbit and (Dark) a darkly pigmented one.
Ratio of yellow reflectance with the laser beam off of a large choroidal vessel to the yellow reflectance with the beam on the vessel.
Data taken from Bakker, Doc. Ophthalmol. 38, 271 (1974).
See text for explanation of symbols.
Obtained from fitting fundus reflectance model to reflectance measurements.
Scale factor to bring fundus model and transmission microdensitometry melanin scales into agreement.
Table III
Thermal Model Verification Data, Fixed RPE Absorbancea
Measured reflectance
Estimated absorbance
Measured lesion size (μm) and variation (%)
Achm (cm−1)
Achb (cm−1)
ARPE (cm−1)
Red
Yellow
Green
Red
Yellow
0.46
0.31
0.32
5
19
300
—
120 (31)
0.46
0.21
0.22
5
51
300
—
145 (18)
0.36
0.27
0.27
20
19
300
77 (29)
134 (16)
0.36
0.19
0.19
20
51
300
—
149 (7)
0.25
0.21
0.24
50
19
300
101 (13)
153 (14)
0.25
0.15
0.17
50
51
300
—
165 (11)
0.11
0.11
0.16
150
19
300
150 (10)
180 (5)
0.11
0.09
0.12
150
51
300
—
180 (9)
Measured reflectances are used to estimate Achm and Achb, while ARPE is held constant. The histologically measured lesion sizes are shown along with their coefficients of variation.
Table IV
Thermal Model Verification Data, Adjustable RPE Absorbance
Measured reflectance
Estimated absorbance
Measured lesion size (μm) and variation (%)
Achm (cm−1)
Achb (cm−1)
ARPE (cm−1)
Red
Yellow
Green
Red
Yellow
0.48
0.34
0.34
5
19
100
—
80(18)
0.48
0.24
0.23
5
51
100
—
112(11)
0.38
0.30
0.31
20
19
100
51 (19)
112(7)
0.38
0.21
0.22
20
51
100
—
125(6)
0.26
023
0.27
50
19
100
89 (10)
149(8)
0.26
0.17
0.20
50
51
100
—
167(9)
0.11
0.12
0.18
150
19
100
154(8)
171(NA)
0.11
0.10
0.14
150
51
100
—
175(11)
0.45
0.29
0.30
5
19
300
—
136(10)
0.45
0.20
0.21
5
51
300
—
155(7)
0.36
0.27
0.27
20
19
300
83(11)
143(7)
0.36
0.19
0.19
20
51
300
—
162(7)
0.25
0.21
0.24
50
19
300
101(9)
155(5)
0.25
0.15
0.17
50
51
300
—
163(11)
0.11
0.11
0.16
150
19
300
146(15)
184(29)
0.11
0.09
0.12
150
51
300
—
190(NA)
0.43
0.28
0.26
5
19
500
—
139(17)
0.43
0.19
0.18
5
51
500
—
166(8)
0.34
0.24
0.24
20
19
500
99(27)
156(11)
0.34
0.17
0.17
20
51
500
—
168(11)
0.23
0.19
0.21
50
19
500
118(11)
155(10)
Measured reflectances are used to estimate Achm and Achb, while ARPE is adjusted using microdensitometry data. The histologically measured lesion sizes are shown along with their coefficients of variation.
The control column lesions were made with constant laser parameters and the dosimetry column lesions were made using prephotocoagulation and postphotocoagulation reflectometry in the upper rows to estimate RPE and choroidal absorbance and with only prephotocoagulation reflectometry in the lower two rows to estimate choroidal absorbance.
This reduction in lesion variability was not found to be statistically significant.
Tables (5)
Table I
Comparison of Experimental Reflectances with Each of the Proposed Fundus Reflectance Models
Ratio of the highest red reflectance to the lowest yellow reflectance measure in the initial data set (four rabbits).
Ratio of reflectance without sclera divided by reflectance with sclera. (Light) indicates a lightly pigmented rabbit and (Dark) a darkly pigmented one.
Ratio of yellow reflectance with the laser beam off of a large choroidal vessel to the yellow reflectance with the beam on the vessel.
Data taken from Bakker, Doc. Ophthalmol. 38, 271 (1974).
See text for explanation of symbols.
Obtained from fitting fundus reflectance model to reflectance measurements.
Scale factor to bring fundus model and transmission microdensitometry melanin scales into agreement.
Table III
Thermal Model Verification Data, Fixed RPE Absorbancea
Measured reflectance
Estimated absorbance
Measured lesion size (μm) and variation (%)
Achm (cm−1)
Achb (cm−1)
ARPE (cm−1)
Red
Yellow
Green
Red
Yellow
0.46
0.31
0.32
5
19
300
—
120 (31)
0.46
0.21
0.22
5
51
300
—
145 (18)
0.36
0.27
0.27
20
19
300
77 (29)
134 (16)
0.36
0.19
0.19
20
51
300
—
149 (7)
0.25
0.21
0.24
50
19
300
101 (13)
153 (14)
0.25
0.15
0.17
50
51
300
—
165 (11)
0.11
0.11
0.16
150
19
300
150 (10)
180 (5)
0.11
0.09
0.12
150
51
300
—
180 (9)
Measured reflectances are used to estimate Achm and Achb, while ARPE is held constant. The histologically measured lesion sizes are shown along with their coefficients of variation.
Table IV
Thermal Model Verification Data, Adjustable RPE Absorbance
Measured reflectance
Estimated absorbance
Measured lesion size (μm) and variation (%)
Achm (cm−1)
Achb (cm−1)
ARPE (cm−1)
Red
Yellow
Green
Red
Yellow
0.48
0.34
0.34
5
19
100
—
80(18)
0.48
0.24
0.23
5
51
100
—
112(11)
0.38
0.30
0.31
20
19
100
51 (19)
112(7)
0.38
0.21
0.22
20
51
100
—
125(6)
0.26
023
0.27
50
19
100
89 (10)
149(8)
0.26
0.17
0.20
50
51
100
—
167(9)
0.11
0.12
0.18
150
19
100
154(8)
171(NA)
0.11
0.10
0.14
150
51
100
—
175(11)
0.45
0.29
0.30
5
19
300
—
136(10)
0.45
0.20
0.21
5
51
300
—
155(7)
0.36
0.27
0.27
20
19
300
83(11)
143(7)
0.36
0.19
0.19
20
51
300
—
162(7)
0.25
0.21
0.24
50
19
300
101(9)
155(5)
0.25
0.15
0.17
50
51
300
—
163(11)
0.11
0.11
0.16
150
19
300
146(15)
184(29)
0.11
0.09
0.12
150
51
300
—
190(NA)
0.43
0.28
0.26
5
19
500
—
139(17)
0.43
0.19
0.18
5
51
500
—
166(8)
0.34
0.24
0.24
20
19
500
99(27)
156(11)
0.34
0.17
0.17
20
51
500
—
168(11)
0.23
0.19
0.21
50
19
500
118(11)
155(10)
Measured reflectances are used to estimate Achm and Achb, while ARPE is adjusted using microdensitometry data. The histologically measured lesion sizes are shown along with their coefficients of variation.
The control column lesions were made with constant laser parameters and the dosimetry column lesions were made using prephotocoagulation and postphotocoagulation reflectometry in the upper rows to estimate RPE and choroidal absorbance and with only prephotocoagulation reflectometry in the lower two rows to estimate choroidal absorbance.
This reduction in lesion variability was not found to be statistically significant.