An ophthalmic endo-illumination system (206) includes a light source that produces a light beam (305), a fiber port that receives an optical fiber (310), a condenser (302) that couples at least a portion of the light beam into the optical fiber received at the fiber port, and a beam splitter (304) disposed between the fiber port and the condenser. The beam splitter is configured to receive the light beam from the condenser and split the light beam into a first beam (312) which is coupled to the optical fiber and a second beam (314) which is coupled to a monitoring fiber (306). An optical sensor (308) is provided to detect an amount of the second beam output from the monitoring fiber. The coupling efficiency of the first beam coupled into the optical fiber may be determined based on the amount of the second beam output from the monitoring fiber.
