**1. Introduction**

Traditionally, management of posterior segment inflammation secondary to uveitis relied on fundus fluorescein angiography (FFA) and indocyanine green angiography (ICG) for assessment of the pathological alteration of the inner- and outerblood-retina-barriers (BRB), disturbances in choroidal perfusion, and the structural sequelae of inflammation in the macular area and elsewhere in the retina and the choroid [1, 2]. These tests offered indirect biological clues to evaluate the quality of the retinal and choroidal circulations in terms of patterns of leakage and grades of perfusion; henceforth, determination of disease evolution through remissions and exacerbations, titration of posology and monitoring tissue response to therapy [3, 4].

#### **1.1 Limitations of conventional angiographic modalities**

Despite the invaluable input of these diagnostic tools, they had inherent limitations that posed major impediment to full exploration of the pathological events in the posterior segment secondary to different uveitides. Firstly, the profuse leakage of the sodium fluorescein molecule from the choriocapillaris, and the optical scattering of incident light by the retinal nerve fiber layer confined the utility of FFA mostly to single-layered evaluation of the pathological cascade of events developing at the level of superficial capillary plexus (SCP) and left the observer with vague deductions regarding the ongoing pathology in the deep capillary plexus (DCP), the choriocapillaris and the choroidal stroma [5–9]. Secondly, the inflammatory by-products of uveitides and the associated pathological features included intra-, sub-retinal and sub-retinal pigment epithelium (RPE) fluid and/or lipoproteinaceous deposits, sub-retinal and sub-RPE fibrosis, RPE thickening and pigment epithelial detachment (PED). These features shared common FFA leakage and ICG fluorescence properties among themselves and with choroidal neovascular membrane (CNV) that might complicate posterior segment inflammation, which made these entities virtually indistinguishable from each other and subsequently delayed diagnosis and prompt intervention for treating CNV. Thirdly, the longevity of uveitis disease process and its propensity to undulating course of remissions and exacerbations render repetitive dye-based FFA and ICG angiography impractical and even hazardous in routine clinical practice due to their invasive nature [3, 4, 10].

## **1.2 Swept-source optical coherence tomography (SS-OCT) and optical coherence tomography angiography (SS-OCTA) technology: novel imaging modality in uveitides**

The introduction of swept-source optical coherence tomography (SS-OCT) technology revolutionized imaging of ocular posterior segment in uveitides and circumvented several classical obstacles that long represented significant hindrance to correct diagnosis. Firstly, SS-OCT employed a long wavelength laser source (1050 nm) operating at an ultra-high scanning speed (100.000 A-scan/second). The tandem of ultra-high-speed image acquisition, laser beam collimation and reduced sensitivity roll-off feature helped defraying scattering of the scanning light as it traveled through the retina, with subsequent rendition of ultra-high-definition images of retinal layers quasi-in-vivo histological tissue dissection [11, 12]

Moreover, these features enhanced beam penetration in media opacities and poorly dilatable pupils, which are common features associated with uveitis and that pose significant impediment to interpretable images. New morphological changes in the vitreo-retinal interface, the retina, the choroidal layers, and changes in choroidal thickness secondary to uveitides were unveiled and employed as biomarkers for diagnosis of uveitis, detection of ensuing complications and monitoring disease progression and response to therapy. Secondly, superior axial resolution and greater depth of penetration of the incident beam in enhanced depth (EDI)- and SS-OCT imaging allowed simultaneous documentation of pathological changes in the vitreous, vitreo-retinal interface, retina, and choroid in a single frame amenable to scrutiny and exploration of the true magnitude of tissue involvement by the disease process [13–18].

Thirdly, SS-OCT incorporated a blood flow detection algorithm; OCTARA (Optical Coherence Tomography Angiography Ratio Analysis). This novel feature allowed evaluation of the retinal vascular plexuses and of the choriocapillaris that are frequently targeted in uveitides. The algorithm relies on decorrelation motion contrast between rapidly repeated SS-OCT B-scans to visualize blood flow in vivo without the need for contrast injection. This OCTA implement benefits from being

**87**

*Swept-Source Optical Coherence Tomography and Optical Coherence Tomography Angiography…*

merged with SS-OCT technology to generate separate en-face images of the retinal SCP, DCP, and the choriocapillaris. It is worthy of note that OCTARA algorithm generates OCTA images by registering B-scan repetition at each scan location then computing a ratio-based result between corresponding image pixels. This method preserves the integrity of the OCT spectrum and does not result in compromised axial resolution, an inherent disadvantage of other OCTA technologies [19–22]. OCTA excelled in delineating inflammatory CNV that could complicate posterior uveitis and determining its state whether active, quiescent, or recurrent based on the neovascular network morphological criteria [10, 23, 24]. Inflammatory CNV has long posed a diagnostic predicament in the past due to overlapping leakage and/or fluorescence patterns with non-neovascular inflammatory tissue on FFA and ICG, respectively. Likewise, CNV and non-neovascular inflammatory lesions frequently exhibit similar light backscattering properties that render them indistin-

It is worthy of note that OCTA does not provide information on vascular leakage, which is a crucial index of the integrity of the inner BRB in cases of vasculitis associated with uveitides. In cases of active vasculitis, OCTA could be even misleading as the leakage of plasma from a disrupted inner BRB into the extra-cellular compartment might slow-down the blood stream velocity well below the detection threshold of OCTA, which might be falsely interpreted by OCTA as reduced vessel

In the following case presentations, we present our experience with SS-OCT and SS-OCTA using the swept-source DRI OCT Triton machine version 10.11 (Topcon Corporation, Tokyo, Japan) and the OCTARA algorithm (Topcon Corporation, Tokyo, Japan), respectively, in imaging common non-infectious and infectious uveitides, with emphasis on the importance of multi-modal imaging approach in which different imaging modalities complement one another to reveal the true extent of

VKH is a multi-system disorder featuring ocular, auditory, integumentary, and neurological manifestations. Ocular involvement in VKH is in the form of bilateral granulomatous panuveitis that is notorious of profound drop of vision, hence the need for early aggressive treatment. Posterior segment involvement in the acute stage comprises diffuse choroiditis, optic disc hyperemia, multifocal serous retinal detachment or bullous exudative retinal detachment. As the chronic stage of the disease ensues, the patient develops ocular depigmentation in the form of chorio-

The primary target tissue in VKH is the choroidal stroma which endures dense infiltration with inflammatory cells and subsequent thickening due to engorgement of choroidal vessels and serous exudation. Eventually, the RPE dehisces giving way to the inflammatory infiltrates and serous fluid into the sub-retinal space. RPE folds develop due to displacement by the thickened choroid. The choriocapillaris undergoes ischemic changes especially in recurrent cases in the form of localized vascular loss. This could be explained by severe hypoperfusion secondary to inflammation or by pressure atrophy from inflammatory granulomas

retinal depigmented scars and retinal pigmentary disturbances [27, 28].

*DOI: http://dx.doi.org/10.5772/intechopen.84245*

density and capillary non-perfusion [3].

**2. Authors' case presentations**

the ongoing pathology.

**2.1 Non-infectious uveitides**

*2.1.1 Vogt-Koyanagi-Harada (VKH)*

guishable from each other on structural OCT [3, 4, 25, 26].

*Swept-Source Optical Coherence Tomography and Optical Coherence Tomography Angiography… DOI: http://dx.doi.org/10.5772/intechopen.84245*

merged with SS-OCT technology to generate separate en-face images of the retinal SCP, DCP, and the choriocapillaris. It is worthy of note that OCTARA algorithm generates OCTA images by registering B-scan repetition at each scan location then computing a ratio-based result between corresponding image pixels. This method preserves the integrity of the OCT spectrum and does not result in compromised axial resolution, an inherent disadvantage of other OCTA technologies [19–22].

OCTA excelled in delineating inflammatory CNV that could complicate posterior uveitis and determining its state whether active, quiescent, or recurrent based on the neovascular network morphological criteria [10, 23, 24]. Inflammatory CNV has long posed a diagnostic predicament in the past due to overlapping leakage and/or fluorescence patterns with non-neovascular inflammatory tissue on FFA and ICG, respectively. Likewise, CNV and non-neovascular inflammatory lesions frequently exhibit similar light backscattering properties that render them indistinguishable from each other on structural OCT [3, 4, 25, 26].

It is worthy of note that OCTA does not provide information on vascular leakage, which is a crucial index of the integrity of the inner BRB in cases of vasculitis associated with uveitides. In cases of active vasculitis, OCTA could be even misleading as the leakage of plasma from a disrupted inner BRB into the extra-cellular compartment might slow-down the blood stream velocity well below the detection threshold of OCTA, which might be falsely interpreted by OCTA as reduced vessel density and capillary non-perfusion [3].

### **2. Authors' case presentations**

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

**1.1 Limitations of conventional angiographic modalities**

Despite the invaluable input of these diagnostic tools, they had inherent limitations that posed major impediment to full exploration of the pathological events in the posterior segment secondary to different uveitides. Firstly, the profuse leakage of the sodium fluorescein molecule from the choriocapillaris, and the optical scattering of incident light by the retinal nerve fiber layer confined the utility of FFA mostly to single-layered evaluation of the pathological cascade of events developing at the level of superficial capillary plexus (SCP) and left the observer with vague deductions regarding the ongoing pathology in the deep capillary plexus (DCP), the choriocapillaris and the choroidal stroma [5–9]. Secondly, the inflammatory by-products of uveitides and the associated pathological features included intra-, sub-retinal and sub-retinal pigment epithelium (RPE) fluid and/or lipoproteinaceous deposits, sub-retinal and sub-RPE fibrosis, RPE thickening and pigment epithelial detachment (PED). These features shared common FFA leakage and ICG fluorescence properties among themselves and with choroidal neovascular membrane (CNV) that might complicate posterior segment inflammation, which made these entities virtually indistinguishable from each other and subsequently delayed diagnosis and prompt intervention for treating CNV. Thirdly, the longevity of uveitis disease process and its propensity to undulating course of remissions and exacerbations render repetitive dye-based FFA and ICG angiography impractical and even hazardous in routine clinical practice due to their invasive nature [3, 4, 10].

**1.2 Swept-source optical coherence tomography (SS-OCT) and optical** 

images of retinal layers quasi-in-vivo histological tissue dissection [11, 12] Moreover, these features enhanced beam penetration in media opacities and poorly dilatable pupils, which are common features associated with uveitis and that pose significant impediment to interpretable images. New morphological changes in the vitreo-retinal interface, the retina, the choroidal layers, and changes in choroidal thickness secondary to uveitides were unveiled and employed as biomarkers for diagnosis of uveitis, detection of ensuing complications and monitoring disease progression and response to therapy. Secondly, superior axial resolution and greater depth of penetration of the incident beam in enhanced depth (EDI)- and SS-OCT imaging allowed simultaneous documentation of pathological changes in the vitreous, vitreo-retinal interface, retina, and choroid in a single frame amenable to scrutiny and exploration of the true magnitude of tissue involvement by the disease process [13–18]. Thirdly, SS-OCT incorporated a blood flow detection algorithm; OCTARA (Optical Coherence Tomography Angiography Ratio Analysis). This novel feature allowed evaluation of the retinal vascular plexuses and of the choriocapillaris that are frequently targeted in uveitides. The algorithm relies on decorrelation motion contrast between rapidly repeated SS-OCT B-scans to visualize blood flow in vivo without the need for contrast injection. This OCTA implement benefits from being

**modality in uveitides**

**coherence tomography angiography (SS-OCTA) technology: novel imaging** 

The introduction of swept-source optical coherence tomography (SS-OCT) technology revolutionized imaging of ocular posterior segment in uveitides and circumvented several classical obstacles that long represented significant hindrance to correct diagnosis. Firstly, SS-OCT employed a long wavelength laser source (1050 nm) operating at an ultra-high scanning speed (100.000 A-scan/second). The tandem of ultra-high-speed image acquisition, laser beam collimation and reduced sensitivity roll-off feature helped defraying scattering of the scanning light as it traveled through the retina, with subsequent rendition of ultra-high-definition

**86**

In the following case presentations, we present our experience with SS-OCT and SS-OCTA using the swept-source DRI OCT Triton machine version 10.11 (Topcon Corporation, Tokyo, Japan) and the OCTARA algorithm (Topcon Corporation, Tokyo, Japan), respectively, in imaging common non-infectious and infectious uveitides, with emphasis on the importance of multi-modal imaging approach in which different imaging modalities complement one another to reveal the true extent of the ongoing pathology.

#### **2.1 Non-infectious uveitides**

#### *2.1.1 Vogt-Koyanagi-Harada (VKH)*

VKH is a multi-system disorder featuring ocular, auditory, integumentary, and neurological manifestations. Ocular involvement in VKH is in the form of bilateral granulomatous panuveitis that is notorious of profound drop of vision, hence the need for early aggressive treatment. Posterior segment involvement in the acute stage comprises diffuse choroiditis, optic disc hyperemia, multifocal serous retinal detachment or bullous exudative retinal detachment. As the chronic stage of the disease ensues, the patient develops ocular depigmentation in the form of chorioretinal depigmented scars and retinal pigmentary disturbances [27, 28].

The primary target tissue in VKH is the choroidal stroma which endures dense infiltration with inflammatory cells and subsequent thickening due to engorgement of choroidal vessels and serous exudation. Eventually, the RPE dehisces giving way to the inflammatory infiltrates and serous fluid into the sub-retinal space. RPE folds develop due to displacement by the thickened choroid. The choriocapillaris undergoes ischemic changes especially in recurrent cases in the form of localized vascular loss. This could be explained by severe hypoperfusion secondary to inflammation or by pressure atrophy from inflammatory granulomas [29, 30]. These areas of choriocapillaris loss appear on OCTA examination as sharply demarcated flow-voids that might recover after resolution of inflammation [31, 32]. Recurrent attacks of inflammation with subsequent breaching of the RPE-Bruch's complex could trigger CNV formation. In that context OCTA helps differentiating CNV from inflammatory tissue by demonstrating the hyperintense signal characteristic of CNV formation in the outer retina slab [3, 4].
