**2. Primary stromal choroiditis with additional independent retinitis: birdshot retinochoroiditis (BRC)**

It is also known as vitiliginous chorioretinitis [5], and it is a bilateral, asymmetric, and progressive disease without known systemic involvement first described in 1980 by Ryan and Maumenee [6] that predominates in Caucasian women past the fourth decade of life and presents a strong association with HLA-A29 (90–95%) [7]. Because of this strong association, the disease should be better called HLA-A29 BRC [3]. Early symptoms include floaters, decreased vision, and photopsias, and later, it can present with nyctalopia, decreased color vision, and diminished contrast sensitivity. All these complaints may be related to vitritis, macular or optic disk edema and/or outer retina atrophy, or other complications. Multimodal imaging shows a dual and independent retinal and choroidal inflammation in BRC.

Fundus photography is useful in documenting retinal vasculitis of large veins, papillitis, and the classic depigmented ovoid spots that are more prominent inferonasal to the optic disk (**Figure 1**) and radiate to the equator. These choroidal spots typically indicate stromal scars and may never appear if the disease is treated early [3].

FAF exhibits hypoautofluorescent spots if RPE atrophy occurs more numerous than clinically and sometimes is not uniformly correspondent with the birdshot choroidal lesions suggesting a dual independent RPE damage by inner retina and choroid. A placoid macular hypoautofluorescence which correlates with poor visual outcome may also be seen [8].

## **Figure 1.**

*This patient presents mild vitritis, birdshot choroidal depigmented spots. (a) FAF shows optic nerve leakage and phlebitis in both eyes. Petaloid macular leakage is seen in late phase in the left eye. There is also "quenching" of the dye in the right eye. (b) Optical coherence tomography (OCT) in the left eye demonstrates ERM and CME. (c) In advanced stage, there is choroidal thinning in both eyes on OCT. (d) ERM: Epiretinal membrane; CME: Cystoid macular edema.*

## *Multimodal Imaging of White Dot Syndromes DOI: http://dx.doi.org/10.5772/intechopen.106467*

FFA shows optic nerve hyperfluorescence, vascular leakage (predominantly phlebitis), and macular leakage (**Figure 1**) [9]. Moreover, circulation times are called to be "delayed" in the venous circulation but in fact is a pseudo-delay or "quenching" of the dye due to diffuse capillary leakage of fluorescein into the surrounding tissue so that there is not enough dye to normally mark the veins (**Figure 1**) [10]. Active choroidal inflammatory lesions are not generally visible until they affect the overlying RPE appearing hypofluorescent in early phases with subtle late staining [11].

ICGA shows more numerous choroidal lesions and even before than clinical examination or FFA. They are seen as multiple hypofluorescent round spots in the early and mid-phases becoming isofluorescent in the late angiographic phase if active, probably, partial thickness granulomas, indicating non-penetration of the dye only at the site of inflammatory choroidal infiltrates. If the lesions remain hypofluorescent in late phase, it may be due to full thickness lesions or that the lesions have become atrophic [12, 13]. Also, there may be seen fuzzy vessels in active disease showing choroidal vasculitis during the intermediate and late phases [11–13].

OCT may show cystoid macular edema (CME), secondary epiretinal membrane (ERM) (**Figure 1**), loss of ellipsoid zone (EZ) with RPE degeneration beneath the areas of photoreceptor involvement, as well as other complications, such as macular atrophy, optic atrophy, and rarely, choroidal neovascularization (CNV). Enhanceddepth OCT imaging may be useful to evaluate choroidal thickening early in the disease and thinning in advanced disease (**Figure 1**).

En-face OCT-A has identified areas of flow void in the Haller layer corresponding to those hypofluorescent spots on ICGA with initial sparing of the choriocapillaris, thereby supporting the primary involvement of choroidal stroma in the disease with secondary involvement of choriocapillaris and the RPE [14]. It also demonstrates retinal capillary density reduction at the deep retinal capillary plexus level, which may indicate that ischemia, in addition to inflammation, may play a role in the development of retinal neovascularization (NV), retinal thinning, and reduction of visual function [15]. Other changes in both the superficial and deep capillary plexus that may explain the common finding of CME in BRC have been documented such as capillary dilatations and loops, telangiectatic vessels, increased intercapillary space, and decreased capillary density without a change in the size of the foveal avascular zone (FAZ) [16–18], and alternatively, it has been found a larger area of FAZ [19].
