Question: Nevada Subscriber Answer: Medicare covers glaucoma screenings for high-risk patients, but the doctor isn't sure the patient will meet Medicare's description of "high risk." When your office performs a service -- even a non-covered procedure like certain glaucoma screenings -- you deserve payment for it. If you don't want to get caught absorbing the cost of services that a patient requests or the ophthalmologist recommends, and you know Medicare will not reimburse for a given service, you'd better use modifier GA and reach for an advance beneficiary notice. Properly used, the modifier/ABN combination allows you to collect payment for the ophthalmologist's effort directly from the patient. The proper time to have the patient sign an ABN is before the ophthalmologist performs the service or procedure that you don't think the patient's carrier will reimburse. In some circumstances, you may not know for certain if Medicare will cover the service. When in doubt, protect yourself and request that the patient sign an ABN. Rule: When Medicare sees the GA modifier and does deny payment for the service, it will send an explanation of benefits to the patient confirming that he is responsible for payment. If you fail to append the modifier, Medicare may not inform the patient of his responsibility.