Fig 1.
Compensation of the choriocapillaris signal.
A 10 μm thick slab between 31 and 41 μm under the RPE reference was segmented to extract an en-face image of the choriocapillaris from the structural OCT (A) and the angiogram (B). After being inverted and blurred (C), the structure image was multiplied with the angiogram (B) in order to compensate for signal loss under areas of RPE alterations (i.e. drusen). The resulting image (D) was then analyzed.
Fig 2.
The OCT fundus image (A) was used to assist manual delineation of the geographic atrophy (GA) region. The compensated choriocapillaris angiogram (B) was thresholded in order to obtain a binarized picture where the black pixels represent the signal voids in the choriocapillaris flow (C). The percentage of flow voids was calculated outside the atrophy (D), within two concentric 500 μm wide regions surrounding the GA (para-atrophy region (E) and peri-atrophy region (F).
Fig 3.
Flow chart diagram explaining the selection process of eligible eyes for the study.
Among the initial cohort of 57 subjects with geographic atrophy (GA) in at least one eye, only 23 (33 eyes) met all the inclusion criteria and were included in the analysis. OCT-A: Optical coherence tomography angiography; SSI: Signal Strength Index.
Fig 4.
Graphic representation of the correlations explored in the study.
Scatterplots showing the yearly geographic atrophy growth rate (yGR) after square root transformation and the percentage of flow voids outside the atrophy (FVOUT) (A) in the para-atrophy region (FV500) (B), and the difference between para- and peri-atrophy regions (ΔFV) (C). R: Pearson’s correlation coefficient; p value: two tailed p-value.
Table 1.
Univariable and multivariable generalized estimating equations analysis.
Fig 5.
Examples of eyes with geographic atrophy and different growth rate.
One eye from two patients with geographic atrophy (GA) are shown in the two rows of images. A and D are the optical coherence tomography (OCT) fundus photos at baseline while B and E were acquired after one year. The two patients show a very different yearly growth rate (0.07 and 0.73 for the first and second row respectively). The OCT angiogram at the level of the choriocapillaris (C and F) from the baseline visit for these two patients shows dramatically different flow impairment surrounding the lesion, with considerably greater flow voids in the latter case (41,2% versus 53% for the first and second row respectively).
Fig 6.
Eye with geographic atrophy demonstrating difference in flow voids between the para-atrophy region and more distant regions.
One eye from a patient with geographic atrophy (GA) is shown in the two images. The optical coherence tomography (OCT) fundus photo is on the left while the corresponding OCT angiogram at the level of the choriocapillaris (CC) is on the right. In the OCT angiogram, there is a clearly evident difference in flow voids between the region outside the GA and the para-atrophy region (38,23% vs 47,05% respectively).