lepersquint?

"On the north side of the church, and outside it, is a projecting structure half underground. This is the anchorite's cell: on the level of the ground is a small aperture protected by a rusty iron grating without glass and without shutter; by this window everything must be handed into the occupant. If we look through the bars, we see that within there reigns a dim and terrible twilight, for no gleam of sunshine can penetrate this cold and gloomy den, and even on this bright and sunny morning the air is cold and damp like the air of a crypt. On the other side is a narrow slit in the wall, like the lepersquint, through which the anchorite can witness the Elevation of the Host; at the end of the cell a raised stone serves as an altar, a crucifix stands upon it, and before it the anchorite spends most of his time day and night, praying. The present occupant has been built up in this cell for many years; he subsists on what is brought to them. There is never any fear of his being starved or forgotten: he is well provided for, and the people offer them dainties which he will not touch, for he lives on bread and water: sick or well, he will never leave this cell till they find them lying dead on the floor and carry them out. And when the cell is empty there will be no difficulty in finding a successor to occupy his place and fulfill the same dreary austere life."

The Survey of London


"On the south side are the remaining parts of a leper's window, blocked up by a stone on which a rude outline of the Virgin is cameoed, through which the priest gave spiritual advice, the leper not being allowed to enter the church, and through this oblique aperture the leper might, to some extent, participate in the service and receive the Blessed Sacrament passed to them through the niche on a long forked stick. Others, excommunicate for any reason, and to be kept outside, might also use the lepersquint or Lychnoscope, for viewing, on the slant, the ' Elevation of the Host." There seems sufficient evidence to state that where a leper's window is found in a parish church that parish has sent a contingent of men to the Holy Land, the survivors of whom have had the ill-luck to introduce this loathsome disease into their native homes. 

–The Old Kingdom of Elmet:
York and the Ainsty District;
a descriptive sketch of the history,
antiquities, legendary lore,
picturesque features,
and rare architecture.