A 55-year-old man complaining of recurring obscured vision in both eyes presented to our clinic during his second episode of Vogt–Koyanagi–Harada (VKH) disease [Fig. 1a]. At 2 months after recurrence, a “sunset glow” change of the fundus was observed [Fig. 1c]. Upon fundus autofluorescence (FAF) imaging taken 3 months after recurrence, short wavelength FAF (SW-FAF) images revealed normal background autofluorescence (AF) with multiple focal granular hyper-AF signals [Fig. 1e], while near infrared FAF (NI-FAF) images demonstrated decreased background AF with multiple focal granular hyper-AF signals [Fig. 1f]. Most of the hyper-AF lesions were similar between FAF images, except in the macular area. Numerous hypo-AF dots surrounded by a relatively hyper-AF halo were also observed on both FAF images, which suggested corresponding swollen retinal pigmented epithelium (RPE) cells resembling a target (target sign). On FAF images taken 5 months after recurrence, several previous hyper-AF signals on both images had become weak or had disappeared [Fig. 1h,i]. Composite fundus imaging with the ultra-wide-field Optomap® 200Dx system (Optos, Dunfermline, Scotland, UK) at 1 year after recurrence revealed a characteristic “sunset glow” fundus with a clearly visible array of choroidal vessels [Fig. 2a]. In green (523 nm) laser separation imaging, retinal and choroidal vessels, including vortex veins, were clearly observed [Fig. 2b]. The red (633 nm) separation view appeared to penetrate deeper and demonstrated zones of sclera, but the choroidal vessels were obscured [Fig. 2c].
The “sunset glow” appearance of the fundus, which reflects depigmentation occurring at the RPE or choroid level, is commonly seen in eyes with chronic VKH disease that has persisted for months. VKH disease is thought to be caused by autoimmune reactions against proteins related to stromal choroidal melanocytes. The initial inflammatory events occur in the choroidal stroma, and adjacent structures, such as the RPE and the retina, are secondarily involved. SW-FAF and NI-FAF originate from two different fluorophores (lipofuscin and melanin). Lipofuscin does not demonstrate properties of NI-FAF that are known to be associated with melanin in RPE and the choroid. Decreased background NI-FAF images of the eye may be due to the depigmented RPE and choroid. Regarding the correspondences of hyper-AF lesions between the 2 FAF images, it is not unusual that some fundus lesions may exhibit similar and dual AF patterns. The exact mechanism underlying dual AF behavior is not known, but melanolipofuscin, oxidized melanin, or other inflammatory remnant fluorophores are potential causes.
The Optomap® 200Dx imaging system is a scanning laser ophthalmoscope that uses dual frequency lasers (523 nm green laser and 633 nm red laser), and simultaneously obtains both green and red separation views. Unlike the longer red laser wavelength, green lasers cannot penetrate significantly deeper than the RPE. For this reason, in healthy normal eyes, observation of the choroidal vessels or nevus posterior to the RPE with the green separation view is not possible. The choroidal vessels are better visualized on the red separation view. However, if the RPE and choroid are depigmented during the convalescent and chronic stages of VKH, the green laser may penetrate the depigmented RPE to the choroid and capture the choroidal vessels. These changes also enhance the penetration of the red (633 nm) laser, resulting in severe blurring of the choroidal vessels due to increased reflectance from the inner sclera. Therefore, if choroidal vessels begin to appear in the green separation view after initial treatment, subclinical choroidal inflammation may persist, resulting in RPE and choroidal depigmentation.
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