A medical device fluid sensing system is provided. The system includes a transmitter array positioned in association with a fluid maintaining device, such as a reservoir in a cassette. Electrical circuitry is connected to the transmitter array and configured to cause the transmitter array to transmit light energy at a predetermined wavelength and producing a desired absorption coefficient based on expected conditions within the fluid maintaining device. The system also includes a receiver array configured to receive light energy transmitted through the fluid maintaining device and originating from the transmitter array, and a controller configured to determine fluid level in the fluid maintaining device based on conditions sensed by the receiver array. In one embodiment, three transmitters and three matching sensors are provided in a surgical cassette, and when optical energy having predetermined characteristics is provided to the transmitter array, the presence or absence of fluid is determined.
