**10.1 Classification of outer retina and RPE atrophy**

GA usually is characterized by RPE atrophy and recently received the term RPE and outer retina atrophy (RORA). When there is a photoreceptor loss without RPE atrophy, the term proposed is outer retina atrophy (ORA). ORA also occurs in eyes after regression of reticular pseudodrusen. SD-OCT is characterized by thinning of the outer retina, including the ELM and the inner segment of the EZ band and decreased choroidal thickness. ORA increases the risk for progression to RORA or macular neovascularization [44].

#### **Figure 11.**

*cRORA. The green arrow in the red-free image, on the left, shows the location where the OCT B-scan, on the right, was taken. This scan demonstrates an area greater than 250μm in diameter with choroidal hypertransmission due to absence of the RPE layer and overlying outer retinal thinning and loss of photoreceptors.*

#### **Figure 12.**

*iRORA. OCT-B scan demonstrates choroidal heterogeneous hypertransmission (pink arrowhead), subsidence of the INL and OPL (green arrowhead) as well as RPE attenuation and overlying photoreceptor disruption (red arrowhead).*

Along several meetings, experts proposed a classification according to OCT findings and four terms were described: cRORA, complete RPE and outer retina atrophy; iRORA, incomplete RPE and outer retina atrophy; cORA, complete outer retinal atrophy and iORA, incomplete outer retinal atrophy (**Figures 11**–**14**) [46].

iRORA is defined on OCT by the following criteria: (1) a region of signal hypertransmission into the choroid, (2) a corresponding zone of attenuation or disruption of the RPE, with or without persistence of basal laminar deposits, and (3)

#### **Figure 13.**

*cORA. OCT-B scan demonstrates thinning of the outer retina with loss of visibility of the ELM, EZ, IZ (interdigitation zone) (red arrowhead). It is possible to note regressing reticular pseudodrusen (yellow arrowhead).*

#### **Figure 14.**

*iORA. OCT-B scan demonstrates thinning of the outer retina where intermittent areas of EZ and ELM can still be identified (arrowhead). It is also possible to note an uninjured RPE layer.*

### *OCT Biomarkers for AMD DOI: http://dx.doi.org/10.5772/intechopen.97752*

evidence of overlying photoreceptor degeneration (subsidence of the INL and OPL, presence of a hyporreflective wedge in the henle fiber layer (HFL), thinning of the outer nuclear layer (ONL), disruption of the external limiting membrane (ELM), or disintegration of the EZ), and when these criteria do not meet the definition of cRORA. A minimum size to determine that a lesion is iRORA was not proposed. iRORA progresses into cRORA over a variable period, from months to years. If each of the areas of RPE change and hypertransmission has a diameter of at least 250 μm on the OCT B-scan, in addition to evidence of photoreceptor loss, then they qualify as cRORA.

*En face* OCT allows to observe a hyperreflective contour that is the ELM descent. On FAF, this border is hyperautofluorescent. Studies have confirmed histologically that the descent ELM is an important biomarker for the development of a complete atrophy of the RPE and outer retina. Increase of ELM reflectivity also was found as possible biomarker for severe photoreceptor loss and gliosis [47–53].

Understanding AMD phenotype is very important to define prognosis and individualized forms of treatment and follow up. Biomarkers on OCT have been crucial for a better understanding of AMD.
