MEWDS is an uncommon entity first described in 1984 by Jampol et al. as a unilateral visual acuity loss notable for white dots of the “the retinal pigment epithelium (RPE) or deep retina and a granularity of the fovea.”[4] MEWDS is unilateral. It causes visual loss and occurs predominantly in young women. Thus, it might be confused with optic neuritis, especially when patients presented with ocular pain, disc swelling, and RAPD.[5]
The exact pathogenesis is unknown. Several past and present publications have classified MEWDS in the sub-group of primary inflammatory choriocapillaropathies.[6, 7] Recent studies have reported that the photoreceptor layer is damaged in MEWDS and photoreceptor loss is at the origin of the typical hyper-autofluorescent areas seen on blue light fundus autofluorescence (BL-FAF), characterizing MEWDS. However, this layer is only damaged secondarily due to choriocapillaritis.[8]
An infectious etiology is thought to be involved in the pathogenesis of MEWDS since there is a viral prodrome.[9] The proposed mechanism is that MEWDS is triggered by an autoimmune response following infection with viruses similar to what has been noted in acute zonal occult outer retinopathy (AZOOR) complex disorders.[10] Another hypothesis is that inflammation and autoimmune diseases are discrete entities. Their presentation is based on interaction of genetics, immune system pathways, and environmental triggers (e.g., viral infection, immunization, stress, female sex).[11] This patient also had symptoms related to upper respiratory infection one month prior to her visual symptom.
Several clinical elements are helpful in the diagnosis, including a flu-like viral episode preceding symptoms (photopsias and subjective scotomas), fundal yellow-white dots, granularity of the fovea, mild vitreous cells, mild disc edema, very variable decrease of visual acuity, and visual field impairment that can both be very severe depending on the degree of severity of choriocapillaris non perfusion. [1, 12, 13] Multimodal imaging has contributed significantly to an easier diagnosis. Visual field testing might reveal an enlarged blind spot. Fluorescein angiography shows early wreath-like discreet hyperfluorescence with late staining in the involved area. Indocyanine green angiography (ICGA) reveals hypocyanescent spots that are usually more numerous than white spots noted on examination, indicating choriocapillaris hypo or non-perfusion. SS-OCT of MEWDS shows disruption mainly of the ellipsoid zone (EZ-photoreceptor outer segments) and interdigitation zone (IZ) complex throughout the posterior pole. Posterior vitreous cells might also be visible on OCT imaging. The combination of ICGA, blue light fundus autofluorescence (BL-FAF), and SD-OCT represents an extremely forceful triad complementing clinical findings in the diagnosis of MEWDS.[14] Although ICG was not tested in this patient, en face OCT revealed hyporeflective spots corresponding to white dots noted on fundus examination.
Optic neuritis and MEDWS can be differentiated by the lack of ocular pain aggravated by eye movement in MEWDS compared to optic neuritis, more loss of color vision or contrast sensitivity than visual acuity in optic neuritis, and RAPD evident in optic neuritis (some vestigial but uncommon in MEWDS). Patients with optic neuritis complain of blurry vision and impaired color vision, whereas patients with MEWDS complain of central/paracentral scotoma.[2] Our patient presented with ocular pain aggravated by eye movement. Her disc swelling was prominent. However, white dots were faint and RAPD was observed, which was mistaken for optic neuritis. Her color vision was normal. MRI did not show any abnormalities. FA showed perivascular leak and hyperfluorescent spots, which did not support optic neuritis. We reached the final diagnosis based on en face OCT, BL-FAF, and SS-OCT findings.