**8. Cirrus OCT in clinical practice**

Average macular thickness is generated automatically with Cirrus-OCT. Each image had a 5 μm axial and 10 μm transverse resolutions in tissue and consisted of either 512 x 128 volume cube or 200 x 200 volume cube with a maximum scan velocity of 27,000 axial scans per sec‐ ond. Cirrus OCT presents high resolution raster scanning capabilities.

Figure 9a presents the HD 5 line raster of a normal retina: the highly reflective retinal layers are red, the layers with intermediate reflectivity are green and the low reflectivity is translat‐ ed intro blue color. The choriocapillaris under the RPE can also be seen. In figure 9b the macular thickness map and the 512 x 128 volume cube are illustrated.

Figure 10a: irregularities of the RPE band which is elevated by a moderately reflective struc‐ ture. Behind the RPE band: thick hyperreflective structure. Figure 10b: elevations of the RPE by hyperreflective structures.

Figure 11 illustrates the same patient as in figure 4, with Stratus OCT device. On figure 11a more details are shown, the RPE appears irregular, cysts in the neural retina with a hypore‐ flective content (fluid) are displayed, not visible on Stratus OCT. Figure 11b presents the macular thickness which is higher than with Stratus OCT. The difference comes from the different boundaries used by the algorihms of the two devices when measuring the macular thickness. The Cirrus OCT program measures the retinal thickness between the nerve fiber layer and the outer band of the RPE. The Stratus OCT program measures between the nerve fiber layer and the inner boundary of the RPE complex, though it has been reported that Stratus OCT has two outer reference lines: one at the junction between the inner/outer seg‐ ment of the photoreceptor cells and the other at the inner boundary of the RPE. In conse‐ quence, the Cirrus outer reference band is deeper than the first mentioned Stratus external band and is closer to the second mentioned one. The correlation of thickness measurements between the two devices is modest, the Cirrus OCT provides greater measurement depth.

Figure 12: irregularities and thinning of the RPE band especially in the right eye, fluid in the retina, increased macular thickness.

Figure 13: RPE band appears thinned and elevated by a moderately reflective tissue: fluid, CNV, increased central macular thickness. 3D macular cube

Figure 14: comparative aspects of the two eyes of the same patient: in the Right Eye the RPE band appears irregular and there is some fluid in the retina.

Figure 15: macular cube 200x200 shows increased central macular thickness, elevations of the RPE band, associated with increased vitreo-macular adhesion revealed by the 3D pre‐ sentation of the macular cube.

**Figure 9.** a: 5 line raster of a normal retina b: Normal macular thickness map

**Figure 8.** a and b: The same case depicted in figure 7, one year after Avastin injections

150 Age-Related Macular Degeneration - Etiology, Diagnosis and Management - A Glance at the Future

ond. Cirrus OCT presents high resolution raster scanning capabilities.

macular thickness map and the 512 x 128 volume cube are illustrated.

Average macular thickness is generated automatically with Cirrus-OCT. Each image had a 5 μm axial and 10 μm transverse resolutions in tissue and consisted of either 512 x 128 volume cube or 200 x 200 volume cube with a maximum scan velocity of 27,000 axial scans per sec‐

Figure 9a presents the HD 5 line raster of a normal retina: the highly reflective retinal layers are red, the layers with intermediate reflectivity are green and the low reflectivity is translat‐ ed intro blue color. The choriocapillaris under the RPE can also be seen. In figure 9b the

Figure 10a: irregularities of the RPE band which is elevated by a moderately reflective struc‐ ture. Behind the RPE band: thick hyperreflective structure. Figure 10b: elevations of the RPE

Figure 11 illustrates the same patient as in figure 4, with Stratus OCT device. On figure 11a more details are shown, the RPE appears irregular, cysts in the neural retina with a hypore‐ flective content (fluid) are displayed, not visible on Stratus OCT. Figure 11b presents the macular thickness which is higher than with Stratus OCT. The difference comes from the different boundaries used by the algorihms of the two devices when measuring the macular thickness. The Cirrus OCT program measures the retinal thickness between the nerve fiber layer and the outer band of the RPE. The Stratus OCT program measures between the nerve

**8. Cirrus OCT in clinical practice**

by hyperreflective structures.

20 Macular Degeneration

**Figure 12.** Increased macular thickness, RPE irregularities, fluid in the retina due to AMD

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**Figure 13.** RPE band appears thinned and elevated by a moderately reflective tissue: fluid, CNV, increased central

macular thickness. 3D macular cube

**Figure 10.** a: Irregularities of the RPE b and b: Elevations of the RPE band

**Figure 11.** The same patient as in figure 4 a and b

**Figure 10.** a: Irregularities of the RPE b and b: Elevations of the RPE band

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**Figure 12.** Increased macular thickness, RPE irregularities, fluid in the retina due to AMD

(a) (b)

152 Age-Related Macular Degeneration - Etiology, Diagnosis and Management - A Glance at the Future

**Figure 10.** a: Irregularities of the RPE b and b: Elevations of the RPE band

20 Macular Degeneration

**Figure 10.** a: Irregularities of the RPE b and b: Elevations of the RPE band

**Figure 11.** The same patient as in figure 4 a and b

)

**Figure 13.** RPE band appears thinned and elevated by a moderately reflective tissue: fluid, CNV, increased central macular thickness. 3D macular cube

**9. Future directions**

**9.2. Swept source OCT**

ers and lesions components is possible [16].

**9.1. Limits of the current OCT examination techniques**

by the restricted numerical aperture of the optical system [16].

A significant progress for neovascular AMD imaging was the development of FD-OCT tech‐ nologies. They use a central wavelength of 800-850 nm, a stationary reference arm, a high speed spectrometer and a charged-coupled device (CCD) line-scan camera. The mechanical scanning is not needed in order to detect light echoes simultaneously. As consequence, the aquisition speed increases to 25,000-52,000 A-scan/second. The axial resolution is of 3-7 μm, significantly improving the signal-to-noise ratio and the detection of individual retinal lay‐

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Despite the significant advantages previously mentioned, there are some limitations of SD-OCT: motion and segmentation artifacts, interinstrument comparability [11,12]. Despite the significant progress in retinal imaging offered by the current OCT techniques, TD-OCT and SD-OCT have shortcomings originating in the limitation of resolution, both axial and lateral. The absorbtion of infrared radiation by the anterior segment structures and ocular media limits the image resolution. The axial resolution is limited by the image scattering by the oc‐ ular structures (so-called speckle noise) and the lateral resolution limitation is determined

SS-OCT is another form of FD-OCT that uses a light source with the wavelength of ap‐ proximately 1,050 nm. A short cavity-swept laser replaces the superluminiscent diode la‐ ser. The emission has different frequencies that can be rapidly tuned over a broad bandwidth [11, 28]. A high speed complementary metal oxide semiconductor camera (CMOS) and two parallel photodetectors are used in order to obtain scan rates of 100,000-400,000 A-scan/second, with the axial resolution of 5.3 μm over a 4-mm imaging range.(trebuie modificat) [29]. Advantages: images to the level of individual photorecep‐ tors are obtained, particularly when coupled with adaptive optics. With SS-OCT the socalled fringe washout (signals at the edges of the B-scan) is reduced as compared to SD-OCT; the sensitivity is better with imaging depth; the image range is longer: approximately 7.5 mm, which allows the evaluaiton of the anterior segment without the use of complex imaging techniques that might generate errors [9]; the efficiency of detec‐ tion is higher; the dual balanced detection can be performed. The above mentioned ad‐ vantages considerably decrease the patient-induced errors by movements and breathing and permit the better penetration in case of ocular media opacities [30]. Limits: even with best patient cooperation, images are still subject to artifacts. Therefore, various algo‐ rithms have been imagined in order to improve the resolution by eliminating these arti‐ facts [30]. The potential application of OCT in the sub-RPE space and choroid is limited by its shallow penetration: approximately 1-3 mm. The degree of choroidal penetration is determined by several factors: the proportion of scattered photons, the absorbtion spec‐ trum of water, the scatter by the ocular media, the absorbtion by melanin [10]. Photon

**Figure 14.** Comparative aspects of the two eyes of the same patient: in the Right Eye the RPE band appears irregular and there is some fluid in the retina.

**Figure 15.** Macular cube 200x200 shows increased central macular thickness, elevations of the RPE band, associated with increased vitreo-macular adhesion revealed by the 3D presentation of the macular cube
