Medicare regulators gave Wills Eye Hospital a glimmer of hope that the facility could regain its designation as a hospital for reimbursement and treatment purposes, according to a letter Tuesday from Seema Verma, administrator for the Centers for Medicare and Medicaid Services.

Wills, despite its name, is not a hospital under Medicare. The Center City institution gave up that designation in July 2006 when it sold its inpatient business to Jefferson, operating instead as an ambulatory surgery center at Eighth and Walnut Streets.

Wills has been fighting to get that hospital certification back since 2013, when it completed a $6.5 million renovation that included a four-bed inpatient unit. But Medicare officials resisted, insisting that Wills is an ambulatory surgery center because it does not have enough inpatients.

Veema's letter said: "CMS is in the process of reviewing our hospital surveyor guidance to better clarify when a facility meets the statutory definition of a hospital. The surveyor clarification would focus on a hospital's capability and capacity to provide inpatient care."

Wills could reapply for Medicare certification as a hospital and, if it did, "would be surveyed under these new expectations once implemented," the letter said.

Members of Pennsylvania's Congressional delegation, including U.S. Sens. Bob Casey and Patrick Toomey and U.S. Rep. Patrick Meehan, have been advocating for Wills in Washington.

Wills Eye officials did not immediately respond to a request for comment.