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, sallallaahu 'alayhi wa sallam, is His slave and Messenger.
The basic ruling regarding removing eyebrow hair is prohibition, as plucking is strongly warned against in religious texts. However, it is permissible in two cases:
First: If removal is necessary for medical treatment.
Second: If the eyebrow hair exceeds the natural limit—being excessive in a way that is harmful or disfiguring—so that it reaches the point of distortion, then it is permissible to remove enough to restore the eyebrow to its normal appearance. The amount that may be removed is limited to what is necessary to correct the deformity and return the eyebrows to their natural state.
The general principle among jurists is that what is permissible for necessity or need is measured according to the need; it is not left to people’s whims or preferences, but should be limited to the extent needed.
Allah knows best.