*8.2.3 Diagnostic parameters*

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 7.**

*Ganglion cell complex.*

*Role of Optical Coherence Tomography in the Evaluation and Management of Glaucoma*

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

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

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.

Ganglion cell layer results are displayed in terms of three maps (**Figure 8**). The thickness map is color coded in a manner that brighter colors (red and orange) represent thicker areas and cooler colors (blue and green) represent thinner areas.

In addition to the GCC thickness map, two other maps are also calculated and displayed on the analysis page for the GCC scan. A deviation map is calculated based on comparing the thickness map to the normative databases. The percent deviation is displayed with a color map where dark colors mean loss. Yellow and red are above average GCC (no loss). Blue is around 20% GCC loss and black is 50% loss or greater. The significance map is the GCC thickness map compared to the normal database at each single point, with probability values. Any point with thickness

Fovea has no ganglion cells and so is very thin (black spot).

*DOI: http://dx.doi.org/10.5772/intechopen.84202*

*8.2.4 Ganglion cell complex*

layers (**Figure 7**).

temporal periphery.

*8.2.4.1 Ganglion cell map displays*

**Figure 6.** *RNFL thickness average analysis (Optovue A4 Version).*

*Role of Optical Coherence Tomography in the Evaluation and Management of Glaucoma DOI: http://dx.doi.org/10.5772/intechopen.84202*
