Methods and apparatus for optically recognizing tissue parameters during an energy-based tissue-sealing procedure involve grasping tissue with a tissue-sealing instrument, illuminating the grasped tissue or tissue adjacent to the grasped tissue with light, analyzing the light that is transmitted, scattered, or reflected by the tissue, and recognizing the tissue based on the result of analyzing the light. The wavelength of the light may be selected so that a vessel is sufficiently recognizable in tissue containing the vessel. A marker may also be introduced into fluid flowing in the vessel to increase the contrast between the vessel and tissue containing the vessel. Analyzing the light includes analyzing the spatial and spectral distribution of light. Analyzing the light may also include forming the light into an image of the illuminated tissue. The image of the illuminated tissue may be projected onto the eyes of a surgeon or sensed by a matrix of light detectors disposed on a jaw member of the tissue-sealing instrument and transmitted to a display.
