As early as 1967, Gass reported the presence of cloudy white exudate surrounding PED in patients with CSC with accompanying evidence of angiographic leakage (Gass 1967). Subsequent studies found that fibrin is present from 19 to 62 % of eyes with CSC (Ooto et al. 2010; Shinojima et al. 2010; Kim et al. 2012; Nair et al. 2012). The presence of fibrin indicates serous exudate, rich in protein, pigment granules, or homogeneous hyaline-like masses (Gass 1967). Fibrin appears as a hyper-reflective lump in the subretinal space on SD-OCT (Fig. 18.2), often overlying small PED, corresponding to leakage sites on FA (Kim et al. 2012). En face OCT scanning often shows a break in the PED associated with fibrin indicating active leakage from these PEDs. Shinjojima and colleagues visualized fibrin-like substance beneath the RPE in 62 % of eyes and suggested that plasma components, including fibrinogen, might be released from choriocapillaris and form fibrin beneath RPE, which leak into the subretinal space through defects in the RPE (Shinojima et al. 2010). Smooth protrusions of the RPE are also associated with fibrin in eyes with CSC.

In eyes with acute CSC, characteristic focal dipping or sagging of the posterior retina (Fujimoto et al. 2008; Song et al. 2012; Nair et al. 2012; Kim et al. 2012) could be seen accompanying fibrin over the leakage site in up to 38 % of eyes at a mean of 8 days after disease onset (Song et al. 2012) (Fig. 18.3). Song et al. suggested that this might be a result of a focal residual attachment of the retina with reactive exudation that persisted until the detachment of neurosensory retina from the RPE was complete. Therefore, focal dipping or sagging of the posterior retina associated with fibrin may be an early indicator of acute CSC. Subretinal fibrinous exudates were observed in around 24 % of eyes with early chronic CSC in their study that persisted into the late chronic stage.

Gass in 1973 first described a series of five cases of bullous exudative retinal detachment as an unusual manifestation of CSC (Gass 1973). This rare presentation is thought to be an exaggerated form of typical CSC. Clinically, there is bullous retinal detachment with shifting subretinal fluid. There are large, single, or multiple-leaking PEDs which are often hidden under cloudy subretinal exudation (Sahu et al. 2000). FA reveals multiple foci of intense RPE leakage communicating with the detached subretinal space (Fig. 18.4). It is thought that proteins and fibrinogen escape into the subretinal space through these intensive leakage sites leading to the presence of a thick subretinal exudate which subsequently seals the leakage site (Fig. 18.5). Fibrin may also stimulate the fibrosis leading to formation of subretinal fibrotic membrane (Hooymans 1998; Schatz et al. 1995).

On SD-OCT scans, bullous neurosensory retinal detachments and large PEDs could be visualized. Spontaneous RPE rip appearing as a defect in the RPE with a rolled edge has also been reported (Lee et al. 2013) (Fig. 18.6). Due to the bullous appearance, bullous CSC might be mistaken with other diseases such as rhegmatogenous retinal detachment, idiopathic uveal effusion syndrome, multifocal choroiditis, Vogt-Koyanagi-Harada disease, choroidal metastasis, or lymphoma (Gass and Little 1995). Bullous CSC can be idiopathic in healthy individuals or can occur following high-dose corticosteroid therapy, organ transplantation, and hemodialysis or in pregnant women. Although most cases of bullous retinal detachment in CSC resolve either spontaneously, with discontinuation of steroid, following delivery or after laser photocoagulation, the visual outcome is usually variable. One series reported visual deterioration in all bullous CSC patients with 50 % having a final vision of 20/200 or worse, while others reported a good outcome with 80 to 100 % achieving vision of 20/40 or better (Fawzi et al. 2006; Gass 1973, 1991, 1992; Gass and Little 1995; Sahuet al. 2000).

The inner segment/outer segment (IS/OS) junction of the photoreceptors, also known as the ellipsoid zone (EZ), shows up as a hyper-reflective line on OCT scans and has been found to be closely related to visual acuity. In normal individuals, the IS/OS line is continuous at the macula, while the IS/OS line is disrupted in various disease states. In CSC, the IS/OS line is usually not visible in eyes with serous retinal detachment but becomes visible again in the majority of eyes after resolution of the subretinal fluid (Kim et al. 2012). This indicates a disruption of the normal photoreceptor assembly during the serous macular detachment, which normalizes with phagocytosis of photoreceptor shed discs by the RPE upon reattachment.

During the acute phase of CSC, there is elongation of the photoreceptor OS, which is seen on SD-OCT as a thickened and smooth posterior surface of the detached retina (Ooto et al. 2011; Song et al. 2012). After several months, the posterior surface of the detached retina takes on a granulated or partially thinned appearance, and hyper-reflective dots begin to appear intraretinal or on the posterior retinal surface, reflecting accumulation of shed OS (Fujimoto et al. 2008; Kim et al. 2012; Ojima et al. 2007) (Fig. 18.7). In the late phase of CSC, the posterior surface of the retina is usually thinned due to long-standing shedding and disintegration of the photoreceptors. A chronic sustained serous retinal detachment results in the disruption of the outer photoreceptor layer, and atrophy of the RPE ensues.

SD-OCT findings of IS/OS line discontinuity, longer length of IS/OS disruption, thinning of the outer nuclear layer, disruption in external limiting membrane integrity, presence of hyper-reflective dots, and RPE hypertrophy have all been shown to be associated with poor final visual acuity in eyes with resolved CSC (Matsumoto et al. 2009; Ozdemir and Erol 2013; Yalcinbayir et al. 2014) (Fig. 18.8). Therefore, periodic imaging with SD-OCT in eyes with CSC is useful in assessing the visual prognosis of these patients.

Yellowish deposits forming a reticulated leopard spot pattern have been reported in eyes with chronic neurosensory detachment caused by CSC (Iida et al. 2002). These deposits can be found within the areas of neurosensory detachment and increase in size and amount with increasing duration of symptoms (Wang et al. 2005). SD-OCT imaging of these yellowish drusen-like granular deposits correlated well with the hyper-reflective deposits found on the posterior surface of the neurosensory retina as well as in the subretinal cavity (Fig. 18.9). It has been suggested that these deposits are composed of fragments of photoreceptor OS that accumulate when they were unable to be phagocytosed by RPE due to presence of neurosensory detachment, especially when the detachment is prolonged for over 4 months (Pryds and Larsen 2013). Other possible explanations for these deposits include plasma proteins extruded from the choriocapillaris, inflammatory debris, and lipid exudate originating from occult choroidal neovascularization secondary to CSC (Wang et al. 2005). Eyes with foveal subretinal deposit on presentation usually do not recover to the full functional and structural status compared with the asymptomatic fellow eyes even after complete resolution of the neurosensory retinal detachment following treatment with photodynamic therapy. This seems to indicate that the subretinal deposits are associated with irreversible foveal damage in CSC (Pryds and Larsen 2013).

While the time-domain OCT allows visualization of the IS/OS junction with a resolution of up to 10 μm, the SD-OCT has an axial resolution of up to 1 μm, which enables visualization the external limiting membrane (ELM), in addition to showing the IS/OS line more clearly. The outer nuclear layer (ONL) represents the cell bodies of the cone photoreceptors. The outer limit of the ONL is the ELM, while at the central fovea, the inner boundary of the ONL almost abuts the internal limiting membrane (ILM). Matsumoto and colleagues defined the distance between the ILM and ELM at the fovea as the ONL thickness and evaluated this in patients with CSC (Matsumoto et al. 2009). Eyes were classified into two groups according to BCVA. Eyes with BCVA poorer than 20/20 were found to have significantly thinner ONL compared with those with BCVA better than 20/20, which in turn was significantly thinner than the ONL of normal controls. It was hypothesized that in serous retinal detachment, the retinal insults begin in the photoreceptor OS, where the disruption of the physiological phagocytosis of the OS by RPE cells leads to elongation of the OS, which eventually leads to apoptosis of photoreceptor cell bodies and thinning of the ONL. The thinning of central foveal thickness has been replicated in other studies (Kim et al. 2012; Ooto et al. 2010). The ONL reflects photoreceptor volume and was found to be a more sensitive indicator of visual outcome than IS/OS junction disruption (Ooto et al. 2010).

Morphological alterations of the RPE invariably occur at the point of angiographic leakage on FA in CSC. They can be shown on both cross-sectional and en face SD-OCT scans as PED, RPE irregularities, RPE bulge or protrusions (defined as an absence of an optically clear space within the lesion in contrast with PED), RPE hyperplasia, and RPE micro-rip (Gupta et al. 2010a; Kim et al. 2012; Lehmann et al. 2013; Shinojima et al. 2010).

PEDs are found in nearly all eyes with acute CSC. They are shown to persist in chronic CSC and in quiescent eyes even after resolution of SRF (Fujimoto et al. 2008; Song et al. 2012). Serous PEDs in SD-OCT are characterized by separation of the RPE (shown as a hyper-reflective line) from the underlying Bruch’s membrane with an optically empty space in between. PEDs in acute CSC tend to be semicircular in shape with a smooth surface (Fig. 18.10), while those in chronic CSCs are usually low or flat with a dimpled or irregular surface (Song et al. 2012) (Fig. 18.11). It has been postulated that in CSC, the RPE overlying the hyperpermeable choroidal circulation is damaged from the exudation and becomes dysfunctional. The increased hydrostatic pressure from the choroidal circulation pushes the RPE forward and thereby creating a PED. A “micro-rip” or blowout of the RPE can occur if the damage is severe, resulting in a focal leak which shows up as a leakage spot on fluorescein angiography (Fujimoto et al. 2008). These RPE micro-rips could be seen morphologically on SD-OCT scans (Kim et al. 2012). Once the fluid egresses from the sub-RPE space to the subretinal space, the pressure equalizes which causes the collapse of the PED. As the walls of the PED collapse, the RPE micro-rip may seal or bundle up appearing as RPE irregularities or hyperplasia on OCT (Gupta et al. 2010a, b; Shinojima et al. 2010). Once the RPE seals, the subretinal fluid will usually absorb leading to spontaneous CSC resolution.

Abnormalities in the RPE can be seen not only in eyes with active CSC but also in asymptomatic fellow eyes. Gupta and colleagues demonstrated that RPE bumps and PED could be seen in 94 % and 12 % of asymptomatic fellow eyes of CSC patients, respectively (Gupta et al. 2010b). The study provided evidence that CSC is a bilateral disease with asymmetrical clinical features. The RPE bumps may be related to underlying hyperpermeable choroid together with impaired RPE function leading to pooling of fluid in the sub-RPE space and might represent a preclinical or subclinical state of the disease. Yalcinbayir and colleagues noted that RPE bumps and hypertrophy were correlated with poor visual acuity, and the presence of these abnormalities on OCT may provide an indirect evidence of earlier photoreceptor damage and worse visual outcome (Yalcinbayir et al. 2014).

PED in CSC can also be visualized using en face OCT. They appear as circular with smooth inner silhouette on coronal section and are characterized by a hypo-reflective area surrounded by a well-defined hyper-reflective margin. PEDs tend to be located within or at the edge of serous retinal detachment (Lehmann et al. 2013). With the en face SD-OCT, RPE hyperplasia can be seen as a hyper-reflective area overlying the RPE in 31 % of eyes with CSC (Lehmann et al. 2013). These areas of RPE hyperplasia are often located with small PEDs over the leakage points on FA. Under the RPE abnormalities, they noted choroidal cavitations, shown as multiple black hypo-reflective cystic lesions corresponding to abnormal choroidal dilatations on transverse EDI-OCT scans.

Choroidal neovascularization (CNV) can arise as a complication of CSC, as with any other lesions of the RPE or the Bruch’s membrane. It occurs more frequently in chronic retinal pigment epitheliopathy and has a reported incidence of 4 % (Chan et al. 2003). CNV may occur after a long period after resolution of the acute disease and might be confused with CNV associated with age-related macular degeneration (AMD) in older patients (Wang et al. 2005). CNV in long-standing CSC are more likely to be type 2 membranes (Chan et al. 2003), but associations with type 1 CNV and polypoidal choroidal vasculopathy (PCV) have also been reported (Fung et al. 2012). Patients who have received laser photocoagulation for CSC can also develop laser-induced CNV, with a reported incidence from 0.6 to 5 % (Matsunaga et al. 1995).

The exact hypothesis of secondary CNV in CSC is unclear. It is hypothesized that in normal eyes, the Bruch’s membrane acts as a barrier against CNV formation (Fung et al. 2012). In cases of CSC, chronic RPE decompensation or splitting of the RPE/Bruch’s membrane complex in serous PEDs together with ischemic changes of the choriocapillaris may be factors leading to CNV development (Chan et al. 2003; Levine et al. 1989).

CNV in CSC typically has classic features of a well-delineated membrane in the early phase with intense leakage in the late phase on FA (Cooper and Thomas 2000). OCT shows a subretinal membrane associated with subretinal fluid (Fig. 18.12). Intravitreal anti-vascular endothelial growth factor (anti-VEGF) therapy such as bevacizumab and ranibizumab has been investigated and appeared to be a useful treatment modality, with OCT resolution or reduction of the subretinal fluid and shrinkage of the CNV membrane (Konstantinidis et al. 2010; Montero et al. 2011; Nomura et al. 2012) (Fig. 18.13).

In both acute and chronic CSC, RPE hyperplasia that corresponds to focal leak on FA could be seen and can act as a guide to localize treatment area. Choroidal cavitation, defined as multiple, black hypo-reflective cystic lesions, could be seen in en face OCT at a layer just beneath the choriocapillaris, situated in areas of abnormal RPE. This could represent ischemic choroidal areas around focal hyper-fluorescent spot observed on FA (Lehmann et al. 2013).

Focal choroidal excavation (FCE) is a localized trough within the submacular choroid, along the RPE/Bruch’s membrane complex line seen on SD-OCT scans. On fundus examination, FCE appears as mild pigmentary mottling or a small yellowish spot, which can only be confirmed with OCT imaging. It can be classified as conforming, if the photoreceptor tips are attached to the apical surface of the RPE (Fig. 18.15), or nonconforming if the photoreceptor tips and the RPE are separated (Fig. 18.16). Eyes with nonconforming type are generally more visually symptomatic as patients may develop metamorphopsia or blurred vision. FCE can also be classified in terms of its location: foveal if the foveal center is within the choroidal excavation or extrafoveal if the foveal center is not within the excavation.

While FCE was first reported in normal eyes, it is more commonly found in association with other macular diseases such as PCV and CNV (Lee and Lee 2014). In a small case series, FCE was found to be present in around 8 % of eyes with CSC, especially in myopic eyes (Ellabban et al. 2013). It is unclear whether FCE is a congenital or acquired condition, but FCE tends to remain unchanged over time. There are close topographic associations between FCE and CNV/PCV. It has been suggested that anatomic alterations or relative choroidal ischemia at the excavation site due to focal thinning could predispose FCE eyes to develop CNV at the excavated area (Lee and Lee 2014). FCE is often found to be within or next to leakage points seen in FA (Ellabban et al. 2013; Suzuki et al. 2014). Choroidal vascular hyperpermeability was found in nearly all eyes around the FCE or in a wide area outside the FCE (Luk et al. 2015). It remains unknown whether FCE plays a pathogenic role in the development of CSC.

En face SD-OCT imaging at the level beneath the FCE has shown unusual choroidal tissue devoid of normal large choroidal vessels bridging between the bottom of the excavation and the outer choroidal boundary (Ellabban et al. 2013). In some eyes, the outer boundary of the choroid seemed to be pulled inward, showing the underlying suprachoroidal space. This suggests a focal scarring process might be involved resulting in focal retraction of the RPE with FCE formation. This finding is supported by later studies where this hyper-reflective band was found in 54 % of eyes with FCE (Lee et al. 2014). This hyper-reflective layer was found to be associated with decreased choroidal thickness which further supports the theory that there is scarring and contraction of choroidal tissue in the development of FCE.