The present invention is generally 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 relaying 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. For example, light may propagate directly through the holding tank portion when there is no surgical fluid, but may be directed away from a light detector when the portion of the holding tank is filled with surgical fluid. As the light may be controllably refracted using the interface between the transparent holding tank material and the surgical fluid, the propagation properties of the light may be more reliably predicted and controlled. While the sensor may not determine the actual liquid level within the holding tank, a plurality of individual liquid detectors may be sufficient to determine when it is appropriate to (for example) turn drain pumps on and off, when the holding tank is in danger of being overfilled, and the like. Other aspects of the invention may provide devices, systems, and methods for producing different types of fluidics cassette using a single cassette body type.
