An adapter couples a length of optical fiber to a hollow probe and to an optical coherence tomography instrument. The length of optical fiber may be greater than the length of the adapter itself. The optical fiber is fixed to an optical coupler at a proximal end of the adapter and may be maintained in a curved configuration by features located in an internal cavity of the adapter. An optical fiber advance mechanism be used to advance and/or retract the length of optical fiber to align it within the hollow probe.