All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
You do not have to scratch your eyelids to wash what is underneath those scales and crusts. Rather, it is sufficient for you to pour water on them because they are considered part of the external surface of the body; therefore, it is not necessary to remove them (for ritual purification). The scholars of Fiqh stated that it is not necessary to remove the scabs formed over wounds and the like, and such dandruff-like scales and crusts apparently fall into this category. The Shaafi‘i scholar Al-Isnawi mentioned that it is not obligatory to remove the dirt that originates from the body and that it is not considered a barrier preventing water from reaching the skin. Thus, the scales and crusts in reference are pardoned with greater reason, especially that removing them causes harm.
Allah knows best.