I suggest that you take care of your eye first and let it fully heal before applying anything else. Since you used extensions, your lashes were damaged, and they need time to grow back on their own, even if it takes a while. It’s important not to try adding anything to “help” them right now, at least not in the first few days until everything is okay again.
Castor oil is great, but it can also cause irritation or even inflammation if you don’t use it properly. You should never apply it directly to the lash line because it’s too close to the waterline. If you decide to use it, put a tiny amount on a cotton swab and apply it only to the lashes. It’s best to do this at night, and then wash the area well in the morning. If you notice any irritation, stop using it immediately. Try to find the purest castor oil possible, most of the ones sold today aren’t truly pure.
But again, focus on your eye issue first. Let your lashes recover naturally. They will look weak and thin at first because of the extensions, and the initial growth always comes in like that. Once they settle and start growing stronger, then you can begin your journey to improve them.
I won’t give any magic work for it because I’ve never done anything like that, but since lashes are made of keratin (a protein), increasing your intake of omega-3, protein, vitamins A, C, and E, and biotin can help. These all occur naturally: omega-3 in fish, protein in eggs, vitamins in fruits and vegetables, and biotin in nuts. Do some research on this and you'll find a lot of information.
Avoid mascara, especially waterproof ones, and keep your lashes as clean as possible. Small habits make a big difference.
And remember: castor oil doesn’t make lashes grow, but it prevents falling and breaking. Hair growth, body hair... is largely dependent on genetics; it's not something you can't change, but keep it in mind.