Although I have yet to repair cataracts, from what I've read you should place some sort of spacers around the outer edge between the tube and the safety glass. Some people have used little pieces from a Popsicle stick. I guess this is to keep the original dimensions as there's no longer any bonding material in between.

Might also prevent any damage in case something should strike the safety glass like a errant ball tossed by a kid etc.

Anthony