I am currently making payments on a ~4k loan that was paid directly to the doctor for laser eye surgery.
Can I deduct the 4k loan as a health expense? Or the payments I am making on the loan? Or nothing at all?
You deduct expenses when you incur them (when you pay the hospital, for example). Medical expenses are deducted on Schedule A, subject to 7.5% AGI threshold. Financed or not - doesn't matter. The medical expense is deductible (if it is medically necessary), the loan interest is not.