1 Clinical Applications of Retinal Optical Coherence Tomography
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1.3.2 Macular Ganglion Cell Thickness
The ganglion cell layer appears as a relatively hyporeflective layer between the
RNFL and inner plexiform layer on OCT. It is the thickest at the macular region.
However, it is difficult to segment ganglion cell layers based on reflectivity. Therefore,
it was measured with other layer(s) together. In Zeiss Cirrus OCT, the Ganglion Cell
Analysis consists of ganglion cell layer and inner plexiform layer. In Optovue OCT,
the Ganglion cell complex include RNFL, GCL and IPL. Topcon OCT provides
macular RNFL, GCL+IPL, and NFL+GCL+IPL thickness measurements. The scan
region is divided into various sectors. The macular ganglion cell thickness map
is displayed using similar color scale which are compared to normal database. In
glaucoma patients, the ganglion cell thickness is reduced [9] (Fig. 1.13).
1.3.3 Optic Nerve Head Morphology
The morphology of optic nerve head is an important parameter for analyses of the
amount of optic nerve damage using biomicroscope. In OCT, the borders of optic
disc and optic cup can be automatically segmented in a similar way to the evaluations
performed by ophthalmologists. The border of optic disc is defined as the termination
of Bruch’s membranes. The software can then calculate the disc area, cup area, rim
area, average cup to disc ratio, vertical cup to disc ratio. These parameters are then
compared to a normative database [10]. In patient with glaucoma, the optic cup/disc
ratio is increased and the neuro-retinal rim thickness is reduced (Fig. 1.12).
1.4 Retinal Vascular Diseases
Retinal vascular diseases include retinal artery occlusion, retinal vein occlusion,
retinal vasculitis, diabetic retinopathy, and others.
1.4.1 Retinal Artery Occlusion
Retinal artery occlusion is the sudden blockage of retinal blood supply. It can be further classified into central retinal artery occlusion and branch retinal artery occlusion.
On fundus photography, retinal artery occlusion is characterized by whitening and
opacity of retina, which is transparent in physiological condition. The fovea lacks
inner retinal tissue and therefore, cannot be affected by the retinal artery occlusion.
The fovea remains red but surrounded by the white opacity retina, which is known
as “cherry red spot” (Fig. 1.14). On OCT, retinal thickness increases at acute stages
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1.3.2 Macular Ganglion Cell Thickness
The ganglion cell layer appears as a relatively hyporeflective layer between the
RNFL and inner plexiform layer on OCT. It is the thickest at the macular region.
However, it is difficult to segment ganglion cell layers based on reflectivity. Therefore,
it was measured with other layer(s) together. In Zeiss Cirrus OCT, the Ganglion Cell
Analysis consists of ganglion cell layer and inner plexiform layer. In Optovue OCT,
the Ganglion cell complex include RNFL, GCL and IPL. Topcon OCT provides
macular RNFL, GCL+IPL, and NFL+GCL+IPL thickness measurements. The scan
region is divided into various sectors. The macular ganglion cell thickness map
is displayed using similar color scale which are compared to normal database. In
glaucoma patients, the ganglion cell thickness is reduced [9] (Fig. 1.13).
1.3.3 Optic Nerve Head Morphology
The morphology of optic nerve head is an important parameter for analyses of the
amount of optic nerve damage using biomicroscope. In OCT, the borders of optic
disc and optic cup can be automatically segmented in a similar way to the evaluations
performed by ophthalmologists. The border of optic disc is defined as the termination
of Bruch’s membranes. The software can then calculate the disc area, cup area, rim
area, average cup to disc ratio, vertical cup to disc ratio. These parameters are then
compared to a normative database [10]. In patient with glaucoma, the optic cup/disc
ratio is increased and the neuro-retinal rim thickness is reduced (Fig. 1.12).
1.4 Retinal Vascular Diseases
Retinal vascular diseases include retinal artery occlusion, retinal vein occlusion,
retinal vasculitis, diabetic retinopathy, and others.
1.4.1 Retinal Artery Occlusion
Retinal artery occlusion is the sudden blockage of retinal blood supply. It can be further classified into central retinal artery occlusion and branch retinal artery occlusion.
On fundus photography, retinal artery occlusion is characterized by whitening and
opacity of retina, which is transparent in physiological condition. The fovea lacks
inner retinal tissue and therefore, cannot be affected by the retinal artery occlusion.
The fovea remains red but surrounded by the white opacity retina, which is known
as “cherry red spot” (Fig. 1.14). On OCT, retinal thickness increases at acute stages