146
D. Cabrera DeBuc et al.
Previously, the mean overall cpRNFL thickness was found to correlate significantly with functional parameters such as EDSS score and contrast sensitivity
[127–129]. However, the thickness of the GCL+IPL in the macula as reported by
Tatrai et al. [13] was found to correlate better with these functional parameters, which
might thus be a better marker of axonal damage [130]. Tatrai et al. [13] results showed
good correlation between the EDSS score and the mean overall cpRNFL thickness
and the thickness of the GCL+IPL and the GCC in the macula. However, the ROC
(Receiver operating characteristic) analysis revealed that the value most capable of
determining the presence of neuronal damage was the weighted mean thickness of
the GCC having an AUC (Area under curve) value of 0.892 with a cutoff value of
104 µm having the highest sensitivity and specificity. The thickness of the RNFL and
GCL+IPL separately showed lower AUCs than the GCC which could be explained
with the better reproducibility of the GCC due to the high contrast between the IPL
and INL layers. Although Tatrai et al. results showed that the weighted mean GCC
thickness may provide a sensitive tool for the assessment of axonal degeneration,
care should be taken when interpreting its value as numerous neurodegenerative disorders, such as glaucoma [19, 131–134]. Alzheimer’s disease [29, 30] or Parkinson’s
disease [24–26] may also lead to ganglion cell death. The use of regional values
could help the differential diagnosis between various forms of neurodegeneration,
as glaucoma could presumably lead to an infero-superior pattern of GCC loss in the
macula, while according to Tatrai et al. [13] results MS is rather leading to a horizontal loss of the GCC most probably due to the loss of the papillo-macular nerve
bundle. However, further research is warranted to justify the above hypothesis.
Tatrai et al. [13] results imply that mainly the ganglion cells are affected in MS
and changes can be already present in eyes without previous history of ON which
could be the result of axonal loss due to the disease process of MS or mild ON
events not accompanied by pain. Using OCT image segmentation, Tatrai et al. could
also show in vivo that the neuronal damage affects the ganglion cells and not the
outer retina, while episodes of ON are resulting in a further pronounced loss of
the retinal ganglion cells. Furthermore, their measurements obtained with a custombuilt software were shown to be more sensitive compared to standard measurements
extracted by the Stratus OCT device (e.g. cpRNFL, total macular volume) and showed
a stronger correlation with physical disability measured by the EDSS. This implies
the potential clinical usefulness of the quantification of the macular GCC thickness
by OCT image segmentation, which could also facilitate the cost-effective follow-up
of neuronal damage due to MS.
6.3.2.2 Optical Properties Measurements
Although thickness differences may discern regions with signs of retinal disease from
normal regions, differences in texture descriptors of normal and abnormal retinal
tissue may also provide additional information of disease development. In fact, the
appropriateness of texture to classify tissues in OCT images has been shown in
previous studies [135]. By analyzing the spatial arrangement of color or intensities
D. Cabrera DeBuc et al.
Previously, the mean overall cpRNFL thickness was found to correlate significantly with functional parameters such as EDSS score and contrast sensitivity
[127–129]. However, the thickness of the GCL+IPL in the macula as reported by
Tatrai et al. [13] was found to correlate better with these functional parameters, which
might thus be a better marker of axonal damage [130]. Tatrai et al. [13] results showed
good correlation between the EDSS score and the mean overall cpRNFL thickness
and the thickness of the GCL+IPL and the GCC in the macula. However, the ROC
(Receiver operating characteristic) analysis revealed that the value most capable of
determining the presence of neuronal damage was the weighted mean thickness of
the GCC having an AUC (Area under curve) value of 0.892 with a cutoff value of
104 µm having the highest sensitivity and specificity. The thickness of the RNFL and
GCL+IPL separately showed lower AUCs than the GCC which could be explained
with the better reproducibility of the GCC due to the high contrast between the IPL
and INL layers. Although Tatrai et al. results showed that the weighted mean GCC
thickness may provide a sensitive tool for the assessment of axonal degeneration,
care should be taken when interpreting its value as numerous neurodegenerative disorders, such as glaucoma [19, 131–134]. Alzheimer’s disease [29, 30] or Parkinson’s
disease [24–26] may also lead to ganglion cell death. The use of regional values
could help the differential diagnosis between various forms of neurodegeneration,
as glaucoma could presumably lead to an infero-superior pattern of GCC loss in the
macula, while according to Tatrai et al. [13] results MS is rather leading to a horizontal loss of the GCC most probably due to the loss of the papillo-macular nerve
bundle. However, further research is warranted to justify the above hypothesis.
Tatrai et al. [13] results imply that mainly the ganglion cells are affected in MS
and changes can be already present in eyes without previous history of ON which
could be the result of axonal loss due to the disease process of MS or mild ON
events not accompanied by pain. Using OCT image segmentation, Tatrai et al. could
also show in vivo that the neuronal damage affects the ganglion cells and not the
outer retina, while episodes of ON are resulting in a further pronounced loss of
the retinal ganglion cells. Furthermore, their measurements obtained with a custombuilt software were shown to be more sensitive compared to standard measurements
extracted by the Stratus OCT device (e.g. cpRNFL, total macular volume) and showed
a stronger correlation with physical disability measured by the EDSS. This implies
the potential clinical usefulness of the quantification of the macular GCC thickness
by OCT image segmentation, which could also facilitate the cost-effective follow-up
of neuronal damage due to MS.
6.3.2.2 Optical Properties Measurements
Although thickness differences may discern regions with signs of retinal disease from
normal regions, differences in texture descriptors of normal and abnormal retinal
tissue may also provide additional information of disease development. In fact, the
appropriateness of texture to classify tissues in OCT images has been shown in
previous studies [135]. By analyzing the spatial arrangement of color or intensities