*8.2.4 Ganglion cell complex*

*A Practical Guide to Clinical Application of OCT in Ophthalmology*

(lines) are centered at the optic disc.

*8.2.2 Three dimensional disc scan pattern*

to indicate an outside normal limits result.

*8.2.3 Diagnostic parameters*

create circumpapillary nerve fiber (NFL) map and 12 radial lines with 3.7 mm length, which are used to calculate the disc margin which forms the ONH scan. All B-scans

The three dimensional (3D) disc scan provides high definition OCT image both at horizontal and vertical direction for ONH. The 3D disc scan covers a default 5 mm × 5 mm square region and is adjustable. It contains 101 horizontal lines. The 3D disc scan contains a total of 51,813 A-scans and takes 2.2 s. The analysis includes B-scan fly through, 3D display, and en face summation of intensity in a retinal sub-layer or band. The 3D scan also creates a high definition OCT SLO projection as a baseline for registration of the ONH scan between multiple visits. Yellow indicates a borderline result. Thickness measures with a p-value less than 1% are colored red

The RNFL thickness profile is divided into 16 sectors and the sector averages are displayed outside of RNFL thickness map. Thickness measurement is compared with normative database with a probability value (p-value) between 5 and 95% shown as green color to indicate within normal limits. Thickness measures with a p-value less than 5% are colored yellow to indicate a borderline result and a p-value less than 1% are colored red to indicate thickness outside normal limits (**Figure 6**).

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**Figure 6.**

*RNFL thickness average analysis (Optovue A4 Version).*

The diagnosis of glaucoma was improved by concentrating on the ganglion cell complex rather than the entire retinal thickness. The ganglion cell complex is a three layered structure consisting of the nerve fiber, ganglion cell and inner plexiform layers (**Figure 7**).

It has been shown that glaucoma predominantly causes thinning of the GCC [14, 15]. The GCC scan consists of three-dimensional scans of the macular region that samples the macula with 14,928 A-scans over a 7-mm square area. The scan pattern consists of 1 horizontal line and 15 vertical lines at 0.5-mm intervals. The center of the GCC scan is shifted 0.75 mm temporally to improve sampling of the temporal periphery.

The GCC scan quantifies the thickness in all three retina layers affected by glaucoma thereby causing the ganglion cell layer to become thinner as glaucoma progresses. Since the macula contains 50% of all ganglion cells in the retina, GCC scan analysis is a robust method of assessing early ganglion cell loss in glaucoma.
