The present invention is directed to improved methods, devices, and systems for eye surgery. In some embodiments, the invention may provide new and/or improved devices, systems, and methods for detecting surgical fluids in a fluidics cassette, particularly cassettes which are used to couple an eye treatment probe to an eye treatment console. Rather than relying on internal reflection by a gas-liquid interface, the fluid detection techniques described herein may make use of the changes in propagation of light through a portion of the holding tank when the portion varies between empty and full. Other aspects of the invention may provide devices, systems, and methods for producing different types of fluidics cassette using a single cassette body type.