It may be too obscure for this crowd [adjusts sci-fi hipster hat*], but my first thought was the Opener cult in M John Harrison’s The Centauri Device, whose adherents install windows in their bodies so that God can see into their innermost beings.
“Your eyes are the windows to your soul. Well, that, and your transparent nanocrystalline yttria-stabilized-zirconia skull implants.”
– Hallmark, Valentines Day 2017