Medicare pays for procedure's medially necessary. You will be responsible for your deductible and copay. You doctor may recommend a specialist. Copays for specialist typically are a bit more then your general practitioner. Additionally medications prescribed may or may not be in your plans formulary. Check with your medical professionals to ensure what they prescribe will be covered.
Medicare not only covers the cost of surgery but also will pay for the cost of a lens implant.
The Crystalens is a "premium" lens and you may be required to pay an additional fee over and above the Medicare allowance.
Your doctor can advise you on your responsibility.