Eye disease debate: where does MEWDS begin, and why it matters

A long-running dispute over where damage begins in a puzzling eye disease remains unresolved, according to a new narrative review published in Frontiers in Medicine on 27 October 2026. The condition, multiple evanescent white dot syndrome, or MEWDS, belongs to a loosely grouped family of inflammatory retinal disorders known as the white dot syndromes. For decades, ophthalmologists have argued about whether the disease starts in the choriocapillaris, the delicate capillary bed feeding the outer retina; in the photoreceptors themselves; or in the retinal pigment epithelium, the supporting cell layer sandwiched between the two. The review, led by Xiaohong Wang and Zhihua Cui of the First Hospital of Jilin University with colleagues from Changchun University of Traditional Chinese Medicine, systematically maps the evidence for each of these three competing hypotheses and concludes that none of the current imaging techniques can definitively settle the question.

The white dot syndromes are an umbrella term for a heterogeneous group of idiopathic inflammatory chorioretinopathies that also includes acute posterior multifocal placoid pigment epitheliopathy, or APMPPE; birdshot chorioretinopathy; multifocal choroiditis; punctate inner choroidopathy; and acute zonal occult outer retinopathy. These conditions share several clinical features: they predominantly affect young to middle-aged adults, often present with photopsias, scotomas, and decreased visual acuity, and are frequently preceded by a viral-like prodrome. Notably, they arise in patients who are otherwise healthy and without systemic autoimmune disease, which has made them particularly enigmatic from an immunological standpoint. MEWDS shows a striking predilection for young females, with approximately 80 percent of affected patients being women of reproductive age, and myopia has been increasingly recognized as a potential risk factor.

The strongest case for a primary choroidal origin rests on indocyanine green angiography, or ICGA. In MEWDS, ICGA consistently reveals hypofluorescent dark dots that are significantly more numerous and more widely distributed than the white dots visible on clinical examination or color fundus photography. Papasavvas and colleagues demonstrated that these dark dots often extend well into the mid-periphery, far beyond the posterior pole lesions visible clinically. The review argues that this discrepancy between the angiographic and clinically apparent extent of disease is perhaps the single most important piece of evidence supporting the choriocapillaritis model: if the disease were primarily confined to the photoreceptor layer, one would expect concordance between clinical and angiographic findings. Herbort and colleagues have further argued that the late-phase hypofluorescence represents true choriocapillaris non-perfusion rather than mere retinal pigment epithelium uptake dysfunction, a claim grounded in the biophysical behavior of the dye.

That biophysical argument deserves attention. Indocyanine green is a molecule of roughly 775 daltons that is approximately 98 percent protein-bound in the bloodstream, forming a complex of about 60 to 80 kilodaltons. Even this large complex extravasates through the fenestrated endothelium of the choriocapillaris under physiological conditions. Because the dye freely diffuses into the vascular bed, late-phase hypofluorescence on ICGA cannot be attributed to molecular size restriction; proponents of the choriocapillaritis hypothesis contend that persistent hypofluorescence instead reflects the continued absence of dye, which would indicate genuine non-perfusion. Independent observational work by Monferrer Adsuara and colleagues confirmed that choroidal vascular changes in MEWDS exceed the clinically apparent lesions, and even suggested that APMPPE represents the more severe end of the same pathophysiological spectrum involving larger choroidal vessels.

Yet optical coherence tomography angiography has introduced an apparent paradox. Several studies using this technique have reported seemingly preserved choriocapillaris flow in MEWDS eyes, which would appear to contradict the ICGA-based model. Defenders of the choriocapillaritis hypothesis counter that OCT angiography detects flowing blood cells and is critically dependent on flow velocity; the choriocapillaris, particularly at its terminal end-arteriole level, may operate at flow velocities below the detection threshold of current systems. A normal-appearing choriocapillaris on OCT angiography may therefore reflect a detection artifact rather than genuine preservation of blood flow. However, the evidence is not one-sided: Labattut and colleagues found that ICGA hypofluorescent areas extended beyond blue-light autofluorescence abnormalities and concluded that their findings were more consistent with primary retinal pigment epithelium dysfunction than with choriocapillary non-perfusion. Some swept-source, wider-field OCT angiography studies have also detected flow deficits in at least some MEWDS patients, suggesting that methodological differences between studies may account for part of the discrepancy.

The photoreceptoritis hypothesis, by contrast, places the primary injury in the ellipsoid zone, the band of densely packed mitochondria in photoreceptor inner segments. High-resolution spectral-domain OCT and en-face OCT have revealed that the characteristic white dots of MEWDS correspond to disruptions of this zone and, in severe cases, the external limiting membrane. Cicinelli and colleagues quantitatively demonstrated that photoreceptor reflectivity on OCT aligns with visual function across all tested retinal locations, following a nonlinear association with a centrifugal recovery pattern. Cahuzac and colleagues described a hyper-early stage of MEWDS in which OCT abnormalities were detectable before the appearance of clinically visible white dots, suggesting that photoreceptor damage may precede the inflammatory signs visible on funduscopy. The Multimodal Imaging in Uveitis Task Force Report 6, by Munk and colleagues, established evidence-based OCT criteria for MEWDS emphasizing hyperreflective lesions extending from the retinal pigment epithelium through the ellipsoid zone into the outer nuclear layer.

The photoreceptoritis position faces its own limitations, which the review spells out candidly. No biopsy or autopsy study of acute MEWDS has confirmed primary photoreceptor inflammation, so the entire argument rests on imaging inference rather than tissue-level proof. Ellipsoid zone disruption is also not specific to primary photoreceptor injury: it can result from ischemic injury secondary to choriocapillaris non-perfusion, from retinal pigment epithelium dysfunction affecting outer segment renewal, or from inflammatory cytokine-mediated damage. In retinal arterial occlusive diseases, for example, ellipsoid zone disruption is a well-recognized consequence of inner retinal ischemia transmitted to the outer retina. Some patients also demonstrate recovery of ellipsoid zone integrity on OCT but incomplete recovery of visual function, a dissociation that challenges the notion that photoreceptor damage is the sole determinant of clinical outcome.

The third hypothesis, primary retinal pigment epithelium dysfunction, draws on fundus autofluorescence imaging, which detects lipofuscin within these cells as a marker of metabolic activity. In MEWDS, autofluorescence consistently shows hyperautofluorescent spots corresponding to the visible white dots, often extending beyond the funduscopically apparent lesions, and abnormalities can be detected in areas where the ellipsoid zone appears intact on OCT. Parmann and colleagues noted that certain autofluorescence patterns suggest intrinsic retinal pigment epithelium metabolic activation rather than secondary changes. This hypothesis also gains conceptual support from the epithelium’s established immunoregulatory role: the cells constitutively express Fas ligand, which induces apoptosis of infiltrating Fas-expressing T cells, and secrete transforming growth factor-beta 2 and alpha-melanocyte stimulating hormone, which suppress local immune activation and promote regulatory T cell differentiation. If these mechanisms fail, immune privilege at the outer retinal interface could break down, permitting the inflammatory cascade observed in the disease. The main counterargument is biophysical: because the dye-protein complex freely extravasates through the fenestrated endothelium, late-phase hypofluorescence is more parsimoniously explained by the absence of dye within the vascular bed than by impaired uptake by dysfunctional epithelial cells.

Beyond the anatomical debate, the review synthesizes converging mechanistic lines that have matured since 2023. A viral-like prodrome precedes ocular symptoms in approximately 50 percent of MEWDS cases, and the COVID-19 pandemic provided an unprecedented natural experiment: multiple case reports and systematic analyses have documented MEWDS onset following SARS-CoV-2 infection and, notably, following COVID-19 vaccination. Zeng and colleagues identified a consistent temporal relationship between vaccination and MEWDS onset, with most cases occurring within one to two weeks of immunization, and Ramirez Marquez and colleagues documented contralateral recurrences following booster vaccination. MEWDS has also been reported after human papillomavirus vaccination, suggesting that immune activation rather than direct viral invasion may be the relevant mechanism. These observations support a molecular mimicry framework in which viral antigens or vaccine-induced immune responses trigger cross-reactivity between antiviral immunity and self-antigens at the outer retina-choriocapillaris interface. Anti-retinal autoantibodies add a further layer, though the review cautions that this evidence derives principally from acute zonal occult outer retinopathy and autoimmune retinopathy cohorts rather than prospectively characterized MEWDS series, and the antibodies may be a consequence of retinal injury rather than a cause.

Elsewhere in the white dot syndrome family, the mechanisms have converged far more clearly. Birdshot chorioretinopathy exhibits one of the strongest gene-disease associations in ophthalmology, with HLA-A29 present in more than 95 percent of cases, an interleukin-17-mediated immune response, and diffuse choroidal stromal infiltration originating in the deep choroid; Gelfman and colleagues identified a critical ERAP1-HLA-A29 gene-gene interaction modulating risk. APMPPE and serpiginous choroiditis show convincing evidence of primary choriocapillaris ischemia, with ICGA-demonstrated vascular occlusion and, in APMPPE, a documented coxsackievirus association. Multifocal choroiditis and punctate inner choroidopathy are characterized by breaches in Bruch’s membrane with inflammatory communication between the choroid and retina. Reflecting this diversity, the MUV Task Force Report 11, published in 2026, explicitly deconstructs the white dot syndrome concept and assigns each entity to a distinct anatomical group, placing MEWDS in a photoreceptor/retinal pigment epithelium group without evidence of primary choroidal vascular occlusion. The review’s authors emphasize that this assignment is an imaging-based consensus rather than a histopathological verdict, since virtually all mechanistic claims in the field rest on inference rather than tissue proof. Their conclusion is that the umbrella term should be retired in favor of disease-specific, mechanism-driven nomenclature, while the MEWDS primary-site debate awaits prospective longitudinal imaging studies, standardized autoantibody testing, and larger multi-ancestry genetic cohorts to be resolved.

Subject of Research: Immunopathogenesis and anatomical site of disease initiation in multiple evanescent white dot syndrome and related white dot syndromes

Article Title: Immunopathogenesis of MEWDS and the white dot syndromes: anatomical specificity and mechanistic heterogeneity

Article References: Wang, X., Li, Z., Kong, W., Yin, T., & Cui, Z. (2026). Immunopathogenesis of MEWDS and the white dot syndromes: anatomical specificity and mechanistic heterogeneity. Frontiers in Medicine, 13, 1979898. https://doi.org/10.3389/fmed.2026.1979898

Image Credits: AI Generated

DOI: 10.3389/fmed.2026.1979898

Keywords: MEWDS, white dot syndromes, choriocapillaris, photoreceptors, retinal pigment epithelium, ICGA, OCT angiography, HLA-A29, viral triggers, molecular mimicry, MUV Task Force, multimodal imaging