**3.3 Outer retinal tubulation (ORT)**

ORT is a degenerative process of outer retinal reorganization located primarily in eyes where the macula is disrupted and RPE is absent. ORTs are ovoid or circular hyporeflective lesions surrounded by a hyperreflective ring always located in the ONL in eyes with advanced outer retinal diseases (**Figure 5**) [36]. It has been described in numerous retinal disorders showing macular atrophy involving RPE, such as AMD [36], mitochondrial diseases [37], and retinal dystrophies [38]. They have also been reported in cases of macular neovascularization including AMD, choroidal nevus, pseudoxanthoma elasticum [39], multifocal choroiditis with uveitis and CNMV, choroideremia [36], and enhanced S-cone syndrome [40]. Histologic studies showed interconnecting tubes of surviving cone photoreceptors interleaved with and contained by processes of Müller cells [41]. Histologically, the hyperreflective border of ORS seen in SD-OCT images corresponds with the presence of both an EML delimiting the lumen and mitochondria migrating from the inner segments to the cell bodies of degenerating cone photoreceptor. The main histologic characteristics of ORTs are [41]:


There are different shapes of ORTs: open, closed, forming, and branching. A branching or pseudodendritic pattern is observed mainly in macular neovascularization, whereas a single tube is more frequent in the border of geographic atrophy [42]. Regarding the etiology of these tubulations, it has been hypothesized to be related to the different shapes of the ELM descent (flat, curved, and reflected). As the RPE begins to atrophy, the ELM descent changes from flat to curved, then reflected to scrolled, and finally, an area of ORT may appear. In this process, Müller cells expand and fill the spaces created by the loss of photoreceptors, as they are the only structure persisting in end-stage of ORT. The presence of a scrolled ELM descent may represent a predictive factor for progression toward ORT. It has been reported that in cases of neovascularization, the progression to ORT experienced a shorter period between

**71**

**Figure 6.**

**Figure 5.**

**3.4 Dome-shaped macula**

*SD-OCT showing a dome-shaped macula.*

*New Landmarks, Signs, and Findings in Optical Coherence Tomography*

the steps of flat and curved ELM than eyes only with atrophic [42]. ORTs have a significant prognostic value since their presence suggests a poor visual acuity. They should be differentiated from intraretinal or subretinal fluid cysts located at the outer retinal layers. Intraretinal fluid cysts in cystoid macular edema (CME) have the arrangement as a petaloid manner, while ORTs are randomly arranged at the macula. Pseudocysts are usually distinguished from ORTs because they are located in the inner nuclear layer. Retinal tubulations are always located at the level of the ONL [3]. ORTs are circular hyporeflective lesions surrounded by a hyperreflective ring. This hyperreflective border is absent in cysts. Likewise, ORTs may contain a few focal hyperreflective spots in contrast to the completely hyporeflective cystoid lesions. The recognition of ORT may avoid unnecessary treatment because it is more refractory to anti-VEGF treatment compared to the cysts. Because outer tubulations tend to change slowly over time, it is unlikely to be associated with an active exudative or inflammatory process. For that reason, they do not require treatment [3, 42]. ORT can also be differentiated from rosettes described in retinoblastoma by their large size, tubular structure, and degenerative instead of developmental nature. In retinitis pigmentosa, there are also rosettes which are distinguished from ORTs by their location outside the macula and absence of degeneration of the underlying RPE [42].

Dome-shaped macula (DSM) is an inward protrusion of the macula as visualized by OCT (**Figure 6**). Different patterns have been described by OCT: a horizontal or vertical oval-shaped dome and a round dome [43]. DSM was first reported in myopic eyes with posterior staphyloma, but more recently has also been described

*DOI: http://dx.doi.org/10.5772/intechopen.84242*

*Outer external tabulation in atrophic age-macular degeneration.*

*New Landmarks, Signs, and Findings in Optical Coherence Tomography DOI: http://dx.doi.org/10.5772/intechopen.84242*

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

possible retinal toxicity due to HCQ toxicity.

**3.3 Outer retinal tubulation (ORT)**

**Figure 4.**

*once daily for 8 years.*

1.location at the level of ONL

2.presence of an ELM surrounding all or part of the lumen

4.disruption or absence of the underlying RPE

3.presence of enclosing radially oriented photoreceptors pointing to the lumen

There are different shapes of ORTs: open, closed, forming, and branching. A branching or pseudodendritic pattern is observed mainly in macular neovascularization, whereas a single tube is more frequent in the border of geographic atrophy [42]. Regarding the etiology of these tubulations, it has been hypothesized to be related to the different shapes of the ELM descent (flat, curved, and reflected). As the RPE begins to atrophy, the ELM descent changes from flat to curved, then reflected to scrolled, and finally, an area of ORT may appear. In this process, Müller cells expand and fill the spaces created by the loss of photoreceptors, as they are the only structure persisting in end-stage of ORT. The presence of a scrolled ELM descent may represent a predictive factor for progression toward ORT. It has been reported that in cases of neovascularization, the progression to ORT experienced a shorter period between

retinopathy. Nevertheless, its visualization on SD-OCT images should alert us to

*SD-OCT revealed the "flying saucer" sign in a woman treated with oral chloroquine at a dosage of 3 mg/kg* 

ORT is a degenerative process of outer retinal reorganization located primarily in eyes where the macula is disrupted and RPE is absent. ORTs are ovoid or circular hyporeflective lesions surrounded by a hyperreflective ring always located in the ONL in eyes with advanced outer retinal diseases (**Figure 5**) [36]. It has been described in numerous retinal disorders showing macular atrophy involving RPE, such as AMD [36], mitochondrial diseases [37], and retinal dystrophies [38]. They have also been reported in cases of macular neovascularization including AMD, choroidal nevus, pseudoxanthoma elasticum [39], multifocal choroiditis with uveitis and CNMV, choroideremia [36], and enhanced S-cone syndrome [40]. Histologic studies showed interconnecting tubes of surviving cone photoreceptors interleaved with and contained by processes of Müller cells [41]. Histologically, the hyperreflective border of ORS seen in SD-OCT images corresponds with the presence of both an EML delimiting the lumen and mitochondria migrating from the inner segments to the cell bodies of degenerating cone photoreceptor. The main histologic characteristics of ORTs are [41]:

**70**

**Figure 5.** *Outer external tabulation in atrophic age-macular degeneration.*

the steps of flat and curved ELM than eyes only with atrophic [42]. ORTs have a significant prognostic value since their presence suggests a poor visual acuity. They should be differentiated from intraretinal or subretinal fluid cysts located at the outer retinal layers. Intraretinal fluid cysts in cystoid macular edema (CME) have the arrangement as a petaloid manner, while ORTs are randomly arranged at the macula. Pseudocysts are usually distinguished from ORTs because they are located in the inner nuclear layer. Retinal tubulations are always located at the level of the ONL [3]. ORTs are circular hyporeflective lesions surrounded by a hyperreflective ring. This hyperreflective border is absent in cysts. Likewise, ORTs may contain a few focal hyperreflective spots in contrast to the completely hyporeflective cystoid lesions. The recognition of ORT may avoid unnecessary treatment because it is more refractory to anti-VEGF treatment compared to the cysts. Because outer tubulations tend to change slowly over time, it is unlikely to be associated with an active exudative or inflammatory process. For that reason, they do not require treatment [3, 42]. ORT can also be differentiated from rosettes described in retinoblastoma by their large size, tubular structure, and degenerative instead of developmental nature. In retinitis pigmentosa, there are also rosettes which are distinguished from ORTs by their location outside the macula and absence of degeneration of the underlying RPE [42].
