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White Dot Syndromes

Philipp K. Roberts, MD; Lee Jampol, MD; and Amani A. Fawzi, MD

White spot syndromes (WSS) are a group of inflammatory diseases characterized by the appearance of white or yellow-white lesions in the retina, the retinal pigment epithelium (RPE), the choroid, or a combination of these layers. WSS are rare and their etiology remains largely unknown. It has been suggested that genetically predisposed individuals may develop these diseases, often after an environmental event (viral infection, vaccination, etc).^1,2 Symptoms may include photopsias, visual field defects, and loss of visual acuity that ranges from mild and temporary, to severe and permanent.

There are many WSS and subforms, and for a comprehensive review of WSS the reader is directed to the recent literature.¹ In view of the limited data and emerging knowledge regarding the imaging of these entities using optical coherence tomography angiography (OCTA), this chapter will focus on birdshot chorioretinopathy (BCR), serpiginous choroiditis (SC), multifocal choroiditis (MFC)/punctate inner choroidopathy (PIC), and acute zonal occult outer retinopathy (AZOOR).

OCTA, as the newest addition to our armamentarium of imaging modalities in posterior uveitis, has enormous potential. The fast and noninvasive mode of image acquisition has provided a tremendous advantage over dye-based fundus angiography, particularly in uveitis patients, who often suffer from associated systemic inflammatory disease. The ability to monitor these patients with OCTA will greatly improve the diagnosis and management of these entities and their associated sequelae, especially secondary choroidal neovascularization (CNV).

BIRDSHOT CHORIORETINOPATHY

BCR, first described in 1980 by Ryan and Maumenee,³ is a chronic bilateral disease, commonly affecting young to middle-aged, otherwise healthy patients.¹ Symptoms typically include floaters, nyctalopia, photopsias, decreased color vision, and blurred vision.¹ Deep yellowish-white lesions, symmetrically radiating from the optic disc toward the periphery in a shotgun-like pattern, are the hallmark of this disease. Retinal vasculitis and arteriolar narrowing occur. The pathologic mechanism underlying BCR is not fully understood, but immune-related inflammatory processes seem likely, given the strong association with human leukocyte antigen-A29 serotype, and the histopathologic findings of multiple lymphocytic accumulations in the choroid, in close proximity to retinal vessels as well as in the optic nerve head.⁴ These findings support the notion of ocular inflammatory processes, simultaneously involving different levels of the ocular vasculature.

Imaging findings include hypo-autofluorescent lesions on fundus autofluorescence (FAF), which can be more numerous than the lesions seen clinically. In contrast to fluorescein angiography (FA), on which the birdshot lesions are usually not seen, indocyanine green angiography (ICGA) typically reveals many more birdshot lesions than can be observed clinically.5

OCTA was recently used in a series of 4 patients with BCR and revealed changes of the retinal vasculature as well as “flow void” choriocapillaris at the birdshot lesions.⁶ Retinal vascular changes were found in all patients including abnormally tortuous retinal vessels, capillary loops, focal dilations, and an increased intercapillary space in the retinal capillary network. While aforementioned abnormalities in the retinal capillary network were also found in one of our patients imaged with the RTVue XR Avanti spectral domain OCT device (Optovue Inc), a healthy-appearing “honeycomb” pattern was observed in the choriocapillaris vasculature in the macula beneath healthy-appearing RPE (Figure 28-1). It is plausible that while the retinal vessels seem to be affected in the macula even at early stages, choroidal inflammatory foci appear to be more prominent outside the arcades, colocalizing with the birdshot lesions, and may spare the macula until later in the disease. This could potentially explain why cystoid macular edema (CME) is such a common finding in BCR patients, while CNV occurs only rarely and fits well the hypothesis that BCR is an inflammatory disease affecting the retina and the choroid independently and nonsynchronously.⁷ Deep choroidal inflammatory foci, however, which are characteristic for BCR, might be missed with current OCTA devices because of the limited penetration depth in ocular tissue.⁴ For a more profound understanding of choroidal pathology, we believe that technical improvements such as swept source OCT (SS-OCT) operating at longer wavelengths may be critical.

SERPIGINOUS CHOROIDITIS

SC is a rare choroidal and outer retinal inflammatory disease of unknown etiology that typically affects young to middle-aged patients. Often patients are asymptomatic until the fovea is affected and generally both eyes are involved, but asynchronously and asymmetrically. SC is characterized by geographic yellow-gray placoid lesions of the outer retina, RPE, choriocapillaris, and deep choroidal vessels.¹ The lesions may start in the peripapillary area and radiate in a centrifugal fashion with finger-like projections. A macular variant is also seen. As the lesions become inactive, extensive RPE and choriocapillaris atrophy occurs with subretinal fibrosis and pigment accumulations in the chronic stage of the disease. Recurrences are common, which is why it is important to monitor these patients for appearance of active lesions that often develop near old lesions.

For evaluating and staging of disease activity, FAF has been shown to be an excellent tool.⁸ While active lesions show hyper-autofluorescence on FAF, they become increasingly hypo-autofluorescent as they heal. On FA, active lesions show early hypo-fluorescence with variable late hyper-fluorescence and staining, whereas old lesions show window defects due to RPE atrophy with increased late fluorescence at the lesion borders, representing dye leakage from damaged choriocapillary vessels. Leakage on FA also occurs in cases with CNV development secondary to SC, which is a common event in this disease. ICGA shows early and late hypo-fluorescence and has proven useful in the evaluation of SC, revealing more extensive lesions than can be appreciated clinically or by FA.¹ The hypo-fluorescence on ICGA is believed to be caused by either delayed choroidal perfusion or nonperfusion and perhaps blockage by the overlying lesion.⁹ On conventional OCT, SC lesions typically show disruption or opacification of outer retinal layers, RPE with secondary “choroidal illumination,” and only minimal irregularities of inner retinal layers. Exudative retinal detachment or CME may be present.1

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