This transient disorder typically presents in young adults with photopsia and manifests fundoscopically as multiple small, white dots in the posterior pole. Acute presentations demonstrate disruption of the photoreceptor ellipsoid zone (EZ) and interdigitation zone (IZ) (Fig. 25.4a, b) (de Bats et al. 2014; Kanis and van Norren 2006). The disruption may either be diffuse or multifocal. This may be associated with choroidal thickening on enhanced depth imaging OCT (EDI-OCT) and small round hyper-reflective points in other layers such as the ganglion cell layer (de Bats et al. 2014). During follow-up, reconstitution of the EZ occurs gradually over several weeks to months (Li and Kishi 2009) (Fig. 25.5). In some cases, this occurs with an intermediary appearance of small dome-shaped hyper-reflective material that eventually flattens (Amin 2006; Hashimoto and Kishi 2015). En face OCT at the level of the ellipsoid zone may display large patchy areas of hyporeflection corresponding to the diffuse areas of EZ attenuation (de Bats et al. 2014).

Patients with this acute posterior multifocal placoid pigment epitheliopathy (APMPPE) present with multiple, deep, creamy-white plaques of ½ to 1 disc diameter in size in the posterior pole. Unilateral presentation may also occur. The creamy plaques may be represented on OCT as outer retinal hyper-reflective material with sparing of the middle and inner retina (Scheufele et al. 2005; Souka et al. 2006) (Fig. 25.6). Marked anterior displacement of the neurosensory retina and retinal pigment epithelium (RPE) due to choroidal inflammation may occur (Lim et al. 2006). Areas of turbid subretinal fluid with overlying hyper-reflective material on the RPE (Birnbaum et al. 2010; Lee et al. 2011) and large intra-retinal cysts (Montero et al. 2011) are also described in the acute phase (Fig. 25.7). Serous detachments may be so significant as to mimic Vogt-Koyanagi-Harada disease (Wickremasignhe and Lim 2010). The fluid may become loculated by dividing intra-retinal septa (Lee et al. 2011).

In the convalescent phase, there is rapid resolution of the intra-retinal and subretinal fluid (Birnbaum et al. 2010). This occurs in conjunction with disruption or loss of the IZ, EZ, ELM and outer nuclear layer (ONL). As further repair occurs, there is a variable restoration of outer retinal and RPE elements (Lee et al. 2011) with some cases displaying persistent thinning of the ONL, EZ attenuation and RPE atrophy (Scheufele et al. 2005) (Fig. 25.8).

Relentless placoid chorioretinopathy (RPC) also known as ampiginous choroiditis is a related but distinct entity to APMPPE. Whilst initial presentation may be similar, patients with ampiginous choroiditis have prolonged clinical course marred with multiple recurrences. In the acute stages, OCT over the placoid lesions can show pigment epithelial detachment associated with hyper-reflectivity of the ganglion cell layer and the inner and the outer nuclear layers (Amer and Florescu 2008) (Fig. 25.9). In the resolution phase, OCT over the placoid scar shows RPE atrophy with associated window defect. However, in contrast to serpiginous chorioretinopathy, retinal and choroidal thickness in RPC is preserved (Dolz-Marco et al. 2014) (Fig. 25.10).

Birdshot chorioretinopathy (BCR) is a typically progressive posterior uveitis characterized by vitritis, small non-pigmented yellow-white spots predominantly of the nasal fundus and vasculitis and complicated by cystoid macular oedema (CMO). Macular oedema is a common vision-threatening complication of BCR. As described in a previous section, the oedema may be cystoid, diffuse, subretinal fluid or related to epiretinal membrane (Monnet et al. 2007). Classic birdshot lesions can be subtly appreciated as increased transmission of OCT signal to the sclera through the RPE and choroid (Keane et al. 2013) (Fig. 25.11a). Vitritis may be seen as hyper-reflective foci in the lucent background of the vitreous cavity (Fig. 25.11b). Patients with BCR may have suprachoroidal fluid on EDI-OCT (enhanced depth imaging OCT), and there is evidence that the amount of fluid may correlate with photopsias (Birnbaum et al. 2014). Other features include EZ loss, RPE disruption, possible choroidal thinning and outer retinal hyper-reflective lesions or ‘clumps’ (Keane et al. 2013). Such changes may occur outside the macula and require extra-macular scanning to be detected.

This disorder is typically characterized by a progressive and recurrent inflammation extending from the optic disc in a centrifugal manner. The active edge of inflammation is a creamy-white colour in the deep layers. The old lesions are seen as atrophic with variable pigment change. It may be complicated by choroidal neovascularization (CNV). Active lesions appear as hyper-reflectivities only in the outer retina (van Velthoven et al. 2006), disruption of the EZ and RPE (Arantes et al. 2011) (Fig. 25.12) or cystic macular oedema (Punjabi et al. 2008). En face OCT represents the new inflammation as hyper-reflectivity in the outer retina adjacent to the previous inflammation (van Velthoven et al. 2006). Atrophic, chronic lesions are characterized by subsistence of the retina due to loss of outer retinal elements such as the ONL, EZ and RPE (Arantes et al. 2011). Increased transmission through to the choroid is a secondary consequence. Lesions complicated by CNV will display OCT evidence of CNV (Punjabi et al. 2008) depending on the duration of the neovascularization and the involvement of the retina in the primary pathology.

Fundus autofluorescence is a useful adjunctive modality for identifying new lesions as hyper-autofluorescent and chronic lesions as hypo-autofluorescence or absent autofluorescence (Arantes et al. 2011).

Previously thought to be separate entities, it has been proffered that punctate inner choroidopathy (PIC) is indistinguishable from multifocal choroiditis (MFC) (Spaide et al. 2013). Both manifest multifocal white-yellow deep infiltrates that may become punched-out scars but had previously been separated by the presence of visible inflammatory cells, lesion size or refractive correction. For the purposes of this section, they will be considered together. Active lesions of MFC may appear as dome-shaped sub-RPE deposits, dehiscence of the RPE, subretinal infiltration and/or loss of the EZ (Channa et al. 2012; Spaide et al. 2013; Vance et al. 2011a). The choroid appears largely uninvolved on multimodal imaging including EDI-OCT (Spaide et al. 2013) but may have increased transmission defects from RPE disruption (Vance et al. 2011a, b). Vitreal cells may be visible in the scans. Chronic lesions may show variable presence of the normal outer retinal lamellae or persistent elevation or the absence of the RPE (Channa et al. 2012; Spaide et al. 2013). CNV can complicate MFC and it may be difficult to distinguish it from a new acute MFC lesion. CNV may be associated with subretinal heterogeneous material and round hyporeflective structures suggestive of a vascular lumen (Spaide et al. 2013) (Fig. 25.13).

Prior to OCT and infrared imaging, this condition was clinically detected as subtle, lobular macular red-brown retinal lesions in patients presenting with paracentral scotomas.

There are two subtypes of OCT appearance of acute macular neuroretinopathy (AMN):

It has been postulated that these two patterns represent capillary ischaemia from interruption of the superficial (inner) retinal capillary plexus or deep (outer) retinal capillary plexus (Yu et al. 2014).

The definition of AZOOR is variable. This section refers to otherwise well patients with an initial presentation of photopsia or diminished night vision, well-defined scotoma or enlarged blind spot without any visible fundus abnormality or features consistent with alternative diagnoses.

OCT in the acute phase shows diffuse loss of ellipsoid zone and interdigitation zone in the involved area as determined by ERG, visual field or autofluorescence (Li and Kishi 2007; Mrejen et al. 2014). Treatment with local or systemic immune suppression has been shown to promote at least partial reconstitution of these lamellae in areas with intact outer nuclear layers (Spaide et al. 2008).

In the chronic phase, patients develop a trizonal appearance with normal OCT outside the area of AZOOR, subretinal material in active areas and atrophy of photoreceptors, RPE and choroid in the chronic areas (Mrejen et al. 2014). Other studies with EDI-OCT report that choroidal thickness is unaffected but confirm the attenuation of the ellipsoid zone and reduced or absent outer nuclear layer (Fujiwara et al. 2010). Epiretinal membrane is common (Fujiwara et al. 2010).

Sarcoidosis is a multisystem, idiopathic, non-caseating granulomatous disease. It may affect the anterior segment, retina, optic nerve or choroid. On OCT imaging, retinal and optic nerve head granulomas appear as inner retinal, hyper-reflective nodules protruding into the vitreous (Goldberg et al. 2015). The surrounding tissue is disturbed; there is reduced signal transmission to outer retinal structures, and there may be subretinal fluid (Goldberg et al. 2015). Lesions regress but may not ever completely dissolve (Goldberg et al. 2015). Choroidal granulomas may be identified on EDI-OCT as homogenous lesions that may be isoreflective or hyporeflective relative to the surrounding choroid (Invernizzi et al. 2015; Rostaqui et al. 2014). The overlying choriocapillaris is compressed (Modi et al. 2013). The lesions may be round or lobulated and only half will have well-defined margins (Invernizzi et al. 2015).

Given their clinical, ophthalmological, histopathological and imaging similarities, these two conditions shall be discussed together in the context of OCT appearance. Choroidal thickening, an undulating RPE and serous retinal detachments characterize the acute phase (Figs. 25.16 and 25.17) (Fong et al. 2011; Ishihara et al. 2009). Wavy, hyper-reflective lines traversing and bridging the entirety of the subretinal fluid pockets can be seen (Tsjuikawa et al. 2005). These may represent fibrinous septa (de Smet and Rao 2005) and are responsible for the loculation of fluid compartments seen on fluorescein fundus angiography (FFA) (Yamaguchi et al. 2007). The EZ may be thickened and irregular (Gupta et al. 2009). Hyper-reflective dots, potentially representing small vessels of the choriocapillaris that are present in normal EDI-OCT, have been shown to be less numerous in the acute stage of disease (Fong et al. 2011). Single-layer RPE analysis demonstrates small elevations that correspond to areas of punctate hyperfluorescence on FFA, and troughs in the RPE correspond to hypofluorescent lines on FFA (Gupta et al. 2009). Within a week of steroid therapy, serous retinal detachment starts to resolve (Fig. 25.18), and by 1 month, 75 % of detachments are completely resolved (Ishihara et al. 2009). EZ integrity is reconstituted more gradually and may take 3 months (Ishihara et al. 2009). In the convalescent phase, there is marked, rapid reduction in the choroidal thickness to normal levels after initiation of steroid therapy within 3–14 days (Maruko et al. 2011). In chronic cases of VKH, the choroid is likely to be thinner than control eyes (da Silva et al. 2013). It may be possible to use EDI-OCT measurements of choroidal thickness to gauge treatment response or disease recurrence. Dalen-Fuchs nodules that are seen with both conditions have previously been characterized histologically into three types (Reynard et al. 1985). Type 1 consists of focal hyperplasia and aggregation of RPE cells. Type 2 consists of epithelioid cells and lymphocytes covered by intact dome of RPE. Type 3 consists of degeneration of RPE and release of disorganized Dalen-Fuchs nodule into the subretinal space. With SD-OCT, it is possible to distinguish between the types; however the clinical significance of the different types remains unclear (Figs. 25.19 and 25.20).