7 Quantitative Analysis of Retinal Layers’ Optical Intensities …
183
In 2006, it was first reported that the retinal thickness was increased in the acute
phase of CRAO, and was subsequently reduced at follow-up of several months. However, the observed extent of retinal edema did not correlate with the visual prognosis
[34]. Later, with the introduction of spectral domain OCT with higher resolution, it
was found that the thickness of inner retina decreased in chronic phase of CRAO
but there was no similar change in the outer retina [35]. Recently, it was reported
that in the acute phase of branch retinal artery occlusion (BRAO), the thicknesses
were markedly increased in the inner layers including the retinal nerve fiber layer
(RNFL)/ganglion cell layer (GCL), inner plexiform layer (IPL) and inner nuclear
layer (INL)/outer plexiform layer (OPL), and mildly increased in the outer nuclear
layer (ONL). In the chronic phase, reduction of thickness was noted with an observed
loss of differentiation between the IPL and INL/OPL. In contrast, no thickness change
of the photoreceptor/retinal pigment epithelium (RPE) layer was observed in either
the acute or chronic phase [36].
Besides change of the retinal thickness, it was also observed that the reflectivity
increased in the inner retina and correspondingly decreased in the outer retina in
the acute phase of CRAO. In the chronic phase, the increased reflectivity of the
inner retinal layers were reduced and the decreased reflectivity in the outer retina
layer recovered [37, 38]. However, the observed reflectivity changes have not been
assessed quantitatively in any of the previous studies.
7.5.2 Subjects and Data Acquisition
In this study [27], forty eyes of 40 patients diagnosed as CRAO who received 3D-OCT
examination within one week of onset were included. Since most CRAO patients are
elderly, we included 33 eyes of 33 subjects aged >=65 years old without any retinal
disorder or high myopia were included as controls. All the study subjects received
comprehensive ophthalmic examinations including fundus photography and spectral
domain 3D-OCT examination.
Spectral domain OCT examination was performed using Topcon 3D OCT-1000
(Topcon Corporation, Tokyo, Japan). Macula was scanned using standard 6 × 6 mm
protocol, in which 3D acquisition consisted of 64 B-scan slices. Fundus photographs
were obtained from each subject at the same time. The OCT image size was 512 ×
64 × 480 voxel. Image quality index was provided by the on-board OCT software.
The raw images were exported from the OCT scanner for analysis.
7.5.3 Image Analysis
The same automatic segmentation method was used to obtain the retinal layers from
the OCT image volumes. The following layers were obtained between the surfaces,
vitreous, NFL, GCL, IPL, INL, OPL, ONL + Henle’s fiber layer (HFL), photoreceptor
183
In 2006, it was first reported that the retinal thickness was increased in the acute
phase of CRAO, and was subsequently reduced at follow-up of several months. However, the observed extent of retinal edema did not correlate with the visual prognosis
[34]. Later, with the introduction of spectral domain OCT with higher resolution, it
was found that the thickness of inner retina decreased in chronic phase of CRAO
but there was no similar change in the outer retina [35]. Recently, it was reported
that in the acute phase of branch retinal artery occlusion (BRAO), the thicknesses
were markedly increased in the inner layers including the retinal nerve fiber layer
(RNFL)/ganglion cell layer (GCL), inner plexiform layer (IPL) and inner nuclear
layer (INL)/outer plexiform layer (OPL), and mildly increased in the outer nuclear
layer (ONL). In the chronic phase, reduction of thickness was noted with an observed
loss of differentiation between the IPL and INL/OPL. In contrast, no thickness change
of the photoreceptor/retinal pigment epithelium (RPE) layer was observed in either
the acute or chronic phase [36].
Besides change of the retinal thickness, it was also observed that the reflectivity
increased in the inner retina and correspondingly decreased in the outer retina in
the acute phase of CRAO. In the chronic phase, the increased reflectivity of the
inner retinal layers were reduced and the decreased reflectivity in the outer retina
layer recovered [37, 38]. However, the observed reflectivity changes have not been
assessed quantitatively in any of the previous studies.
7.5.2 Subjects and Data Acquisition
In this study [27], forty eyes of 40 patients diagnosed as CRAO who received 3D-OCT
examination within one week of onset were included. Since most CRAO patients are
elderly, we included 33 eyes of 33 subjects aged >=65 years old without any retinal
disorder or high myopia were included as controls. All the study subjects received
comprehensive ophthalmic examinations including fundus photography and spectral
domain 3D-OCT examination.
Spectral domain OCT examination was performed using Topcon 3D OCT-1000
(Topcon Corporation, Tokyo, Japan). Macula was scanned using standard 6 × 6 mm
protocol, in which 3D acquisition consisted of 64 B-scan slices. Fundus photographs
were obtained from each subject at the same time. The OCT image size was 512 ×
64 × 480 voxel. Image quality index was provided by the on-board OCT software.
The raw images were exported from the OCT scanner for analysis.
7.5.3 Image Analysis
The same automatic segmentation method was used to obtain the retinal layers from
the OCT image volumes. The following layers were obtained between the surfaces,
vitreous, NFL, GCL, IPL, INL, OPL, ONL + Henle’s fiber layer (HFL), photoreceptor