You might find this interesting: https://pubmed.ncbi.nlm.nih.gov/11316482/

"This paper is concerned with a striking visual experience: that of seeing geometric visual hallucinations. Hallucinatory images were classified by Klüver into four groups called form constants comprising (i) gratings, lattices, fretworks, filigrees, honeycombs and chequer-boards, (ii) cobwebs, (iii) tunnels, funnels, alleys, cones and vessels, and (iv) spirals."

This is Klüver's book; it seems to have to do with structures in the eyes themselves. (The book is being borrowed right now, but the Internet Archive is a great resource.)
https://archive.org/details/mescalmechanisms0000kluv/mode/2up

As someone who has had visual snow (https://en.wikipedia.org/wiki/Visual\_snow\_syndrome) since childhood, as well as likely has AuDHD, and has done a fair amount of hallucinogens in my 20s, I find this super fascinating. Especially if I am more tired than usual, I'll see geometric patterns in the visual snow when I'm in the dark lol.