Photoreceptor inner and outer segment layer thickness in multiple evanescent white dot syndrome

Purpose: To evaluate the photoreceptor inner and outer segment layer thickness in eyes with MEWDS. Design: Prospective, non-comparative, observational case series. The follow-up duration was 4 months. Methods: Four women were diagnosed with unilateral MEWDS. The ages of the patients were 25, 24, 35, and 40 years. The retinal microstructure was assessed by spectral-domain optical coherence tomography (SD-OCT). The thickness of the photoreceptor inner (IS) and outer (OS) segments and sum of them (IS + OS) at the fovea were analyzed. Results: The visual acuity was reduced in three of four eyes at the acute phase. SD-OCT showed that the border of IS and OS (IS/OS) line and the cone outer segment tips (COST) line in the macula area were not detected in all four eyes. The IS + OS thickness was 50.3 ± 5.6 μm and that of the healthy fellow eyes was 73.5 ± 7.0 μm (n = 4 eyes). The thickness of the IS was 27.8 ± 2.6 μm and that of the OS was 45.8 ± 7.3 μm. In all eyes, there was a spontaneous improvement of the visual acuity. SD-OCT showed a recovery of only the IS/OS line in the macular area, but the COST line was not visible in three cases. The mean IS + OS thickness increased to 56.0 ± 7.9 μm (n = 4), IS = 26.0 ± 2.0 μm (n = 3), and OS = 30.1 ± 8.7 μm (n = 3) in the early recovery phase, and to 64.8 ± 9.3 μm (n = 4), IS = 28.5 ± 1.7 μm (n = 4), and OS = 36.3 ± 7.9 μm (n = 4) in the late recovery phase. The mean inner and outer segment thickness remained unchanged in the fellow eyes. Conclusion: Eyes with MEWDS have changes in the photoreceptor microstructures. The change in the IS + OS thickness during the natural recovery course might be due to an increase in the OS length.