Permissibility of closing the eyes during Salaah

Asalamualykum respected mufti…jazakallah for your efforts in answering all my questions it has been a great help..may Allah reward you tremendously and praise be to Allah who has made it possible and granted mufti the ability to undertake this task and made mufti sahebs service a means of us gaining knowledge…
1)is it permissible to close the eyes in salaah for concentration