What is the ruling on removing the niqab when experiencing pain in the eyes and head, especially after LASIK surgery and the doctor's advice to remove it, and the husband's conviction regarding this, while adhering to the شرعي (Shari'i) dress?

Covering the face is obligatory for a Muslim woman. If you are able to cover your face without harm, then do so. If the niqab causes harm or if harm is feared from it, then there is no blame in uncovering it, because "hardship is removed by Islamic law" and "difficulty brings ease." This is based on the Almighty's saying: "And He has not placed upon you in the religion any difficulty" and His saying: "Allah intends for you ease and does not intend for you hardship." You should remain in your home and not go out except for a necessity.