Spectral-domain Optical Coherence Tomography Imaging of Age-related Macular Degeneration
Figure 4: 78-year-old Man with Geographic Atrophy A
B
C
D
E
F
Area: 14.52 mm²
Area: 14.59 mm²
A: Colour fundus images; B: Fundus autofluorescence (FAF) images. Observe the difficulty in identifying the entire lesion in the colour images compared with the FAF images; C: Horizontal B-scan of the macula with increased choroidal light penetration in areas where the retinal pigment epithelium (RPE) is absent. The white arrow shows the transition between the areas where the RPE is present and absent; D: B-scan with red lines representing the sub-RPE layers used to compose the enhanced optical coherence tomography (OCT) fundus image; E: OCT fundus image; F: Enhanced OCT fundus image. The boundaries of the lesion were manually outlined.
Figure 5: Right Eye of a 76-year-old Woman with Wet Age-related Macular Degeneration AB CD E
Volume: 0.225 mm3 FG H I J
Volume: 0.171 mm3
A: Colour fundus images; B: Horizontal B-scan showing a pigment epithelial detachment (PED) and the presence of subretinal fluid; C: Retinal thickness map with areas of increased retinal thickness (red and yellow); D: Retinal pigment epithelium (RPE) segmentation map with a PED; E: RPE elevation map with quantisation of the PED volume; F–J: Post-treatment images following the use of an intravitreal vascular endothelial growth factor (VEGF) inhibitor. The subretinal fluid on the B-scan (G) decreases, and the retinal thickness map (H) shows a corresponding decrease in thickness. The PED decreases as observed qualitatively on the RPE segmentation map (I) and the PED volume decreases as observed quantitatively on the RPE elevation map (J).
provide different information, none has been shown to be superior to another.
SD-OCT was shown to be a useful tool for imaging and measuring GA.8,9,28
A wide spectrum of morphological alterations can be observed when evaluating eyes with GA using high-definition B-scans. The loss of the RPE and photoreceptors is easily observed in these B-scans. Bearelly et al. reported that photoreceptor loss occurred most frequently in a bridging fashion across the margin of GA.28
GA is currently imaged using SD-OCT by using the OFI, which represents a virtual fundus image resulting from the en face
EUROPEAN OPHTHALMIC REVIEW
summation of the reflected light from each A-scan. This en face OFI identifies GA as a bright area, due to the increased penetration of light into the choroid where atrophy has occurred in the macula. The absence of the RPE and choriocapillaris are responsible for this increased penetration of light associated with GA.8,9
The OFI was
shown to correlate well with the GA seen on clinical examination, colour fundus imaging and autofluorescence imaging.10,28,29
More recently, a newer algorithm developed by Carl Zeiss Meditec, Inc., provides an enhanced OFI, which is the summation of the reflected light from beneath the RPE. In addition, this new algorithm automatically measures the area of GA. A study comparing the measurements of GA area with the OFI and the enhanced OFI
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