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You are absolutely correct concerning the use of protective sunglasses for the two hours preceding photochemotherapy, in addition to the five hours after treatment. Although the peak blood levels of methoxsalen are at two hours, there is a substantial amount present during the two hours prior to this peak as well.
Roenigk HH. Photochemotherapy for Psoriasis-Reply. Arch Dermatol. 1978;114(8):1243. doi:10.1001/archderm.1978.01640200091038