our lab does a lot of EM work on mouse eyes. i have embedded mouse eyes as old as 7.5 months for EM. we almost always remove the lens. it is possible to embed the lens but it is difficult to do. if you wish to continue keeping the eyes intact i suggest you go to JB4 with long and i do mean long infiltration times. my work is primarily the cornea and with old mice i infiltrate slowly over a period of a week before hardening.
good luck
john