The barrier is the EyeSeal, a disposable patient interface. The EyeSeal is filled with saline solution, and on the other side of the EyeSeal membrane the fluid pathway is completed by filling the instrument module with distilled water. See the instrument manual for the Insight 100 for directions on keeping the device clean. Each EyeSeal can be used for a single patient, since it is designed for use by either eye. EyeSeals should never be reused.