The comic story behind this intriguing picture can be found here (in French - if you use Chrome, right-click for Google to translate it)
http://www.la-fontaine-ch-thierry.net/clunettes.htm
- essentially a pretty boy managed to get himself admitted to the convent as a nun, and got one of the young sisters pregnant. The angry prioress made all the nuns parade with minimal clothing, she put on her specs (les lunettes) to peer at their parts closely - with all these naked females around, suddenly the guilty one's sex shot into view in a way that knocked off the prioress's glasses!
Thomas Rowlandson illustrated the same scene, the print is in the V&A:
https://collections.vam.ac.uk/item/...jean-de-la-satirical-print-rowlandson-thomas/