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Optical Coherence Tomography Angiography in Choroiditis, Retinitis, and Vasculitis

Andre Romano, MD; Rubens Belfort Jr, MD, PhD; and Daniela Ferrara, MD, PhD

Optical coherence tomography (OCT) redefined the diagnosis and management of various diseases of the vitreous, retina, and choroid. In the assessment of chorioretinal inflammatory conditions, the importance of OCT has been extensively recognized.¹ Uveitis may account for up to 10% of visual loss in adults, and it often relies on ancillary tests for efficient management.^1,2

In posterior uveitis, OCT is valuable for many reasons, including measurement of central choroidal thickness, monitoring the course of macular edema, and in supporting early diagnosis of secondary choroidal neovascularization (CNV).

Macular edema is the primary cause of vision loss in uveitis, affecting up to 40% of all cases and up to 70% of cases with intermediate uveitis.^3,4 It can present on OCT as diffuse, cystoid, or serous retinal detachment.^1,5

Abnormalities of the vitreoretinal interface, such as vitreomacular traction and epiretinal membrane, can occur in approximately half of eyes with uveitis and contribute to macular edema and secondary visual impairment. OCT is extremely valuable in identifying such abnormalities.^3,5

Visual acuity (VA) and visual prognosis in chorioretinal inflammation are strictly correlated to the integrity of the retinal layers, especially in the outer neurosensory retina and retinal pigment epithelium (RPE).

Although its visualization is considered important, the role of the choroid on OCT remains challenging because of image degradation caused by dense pigmentation and light scatter from the choroidal vascular network.

Recent technological advances on spectral domain (SD) and swept source (SS) OCT significantly improved the image of the choroid, with specific techniques and improved software or imaging algorithms that can overcome motion artifacts and reduce speckle noise.⁶

OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IN CHORIORETINAL INFLAMMATIONS

OCT angiography (OCTA) offers a precise, rapidly performing imaging modality that does not require the use of any dye. OCTA provides both structural and blood flow information.⁷ Both the retinal and the choroidal microvasculature can be visualized using OCTA. One of the greatest advantages of this technology is that examination of en face images at multiple depth levels and cross-sectional images through the region of pathology makes it very attractive for inflammatory diseases because it may affect different layers of the retina.

The system used in this chapter is the XR Avanti OCT (Optovue Inc) that uses the split-spectrum amplitude-decorrelation angiography algorithm to produce angio-OCT.

Multifocal choroiditis (MFC) and punctate inner choroidopathy (PIC) are idiopathic posterior uveitis, and are considered to be part of the same disease spectrum of the white dot syndromes because of genetic and clinical similarities. Both conditions are characterized by bilateral and multiple small chorioretinal lesions, and can also evolve with peripapillary atrophy and secondary CNV.8,9

PIC is a relatively uncommon inflammatory multifocal disorder, usually bilateral, that affects predominantly young myopic women.¹⁰ Its pathophysiology is not completely understood, but it is suggested that it affects the inner choroid and RPE.¹¹

The clinical differentiation between the 2 entities may be challenging, although typical cases may have distinct manifestations. MFC presents with marked signs of intraocular inflammation, which resolves leaving densely pigmented lesions that may extend to the midperiphery of the fundus.

En face OCT and cross-sectional horizontal scans through the fovea in MFC shows focal changes at multiple levels including the RPE and ellipsoid zone, but also at the inner retina.

OCTA depicts decreased capillary density at the level of both the superficial and deep capillary plexus in the corresponding location. The architecture of the vascular network is regular and is not affected at this stage (Figure 29-1).

SD-OCT demonstrates that the majority of the lesions, regardless of clinical activity, present with involvement of the RPE, overlying an apparently intact Bruch’s membrane. Nevertheless, SD-OCT does not permit a detailed study about the extent of choroidal involvement, as well as details about in vivo histopathology.¹²

OCTA recently became an alternative to provide the opportunity to study the inner and outer retinal vascular plexus, without dye injection. En face OCT selects specific retina layers through a previously established algorithm.

PIC may present with recurrent inflammatory activity when associated with CNV; however, B-scan full-depth imaging (FDI) OCT shows inflammatory cells in the vitreous above the premacular bursa, and discrete RPE elevation in clinically inactive lesions (Figures 29-2 and 29-3).

Architecture of superficial and deep capillary plexus in OCTA remained apparently unaffected; however, careful examination of the choriocapillaris revealed focal capillary dropout that corresponds to the chorioretinal lesions seen on color fundus retinography and the focal RPE splits seen on cross-sectional OCT (Figure 29-4).

Typically, small vessels at the choriocapillaris present a slow flow; therefore, decorrelation signal is lower in the OCT angiogram. Conversely, in the presented case of PIC, the flow may be even slower with focal areas of dropout or atrophy of the vascular structure, or a reduced or impaired flow showing in the OCT angiogram.

Therefore we believe the ability to combine information from FDI-OCT and angio-OCT to detect subclinical disease activity makes this technology fundamental in the management of this entity.

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