A muḥrim wearing eyeglasses

Answer (and Allah grants success): The author of al-Bayān al-Shāfī transmits from Imām al-Qāsim ibn Ibrāhīm—peace be upon him—and Imām Abū Ṭālib—peace be upon him—that it is permissible for a muḥrim to bind his forehead with a cloth back to his nape. What has been authenticated for the madhhab is that he should not bind it; and if he does, a fidyah is due upon him, because he has covered part of the head.
I say: there is no disagreement that covering the head during iḥrām is not allowed, nor covering any part of it. The first view is built on the notion that what the band covers is not of the head, while the second view is built on the notion that what the band covers of the nape and sides enters into the concept of “head.”
Know that the term head applies to what is mounted above the neck; hence the ḥadīth, “Protect the head and what it contains,” meaning guarding the tongue, hearing, and sight from falling into the unlawful and falsehood. It is said, “A man’s head was cut off,” intending what we have mentioned.
The term “head” is also used for the places of hair growth, or the hair that grows on the head—one says, “He shaved his head” or “trimmed it.” This latter sense is what is intended in the chapter on iḥrām.
Accordingly, there is nothing upon the wearer of eyeglasses, for the eyes are not part of what is meant by “head” in this chapter, and the temples through which the arms of the glasses pass are of the face according to the people of the madhhab. The temple is what lies between the eye and the ear; and the ears, as it appears to me in this chapter, are not of the head—evidenced by His saying, Exalted is He, “with your heads shaved and [your hair] shortened” [al-Fatḥ: 27]. The ears are not a place for shaving or trimming. On this basis, no part of the glasses rests upon the [legally relevant] head.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.1