A medical device comprises a transmitter array positioned in association with a fluid maintaining device； electrical circuitry connected to the transmitter array and configured to cause the transmitter array to transmit light energy at a predetermined wavelength； a receiver array configured to receive light energy transmitted through the fluid maintaining device and originating from the transmitter array, wherein the receiver array is configured to determine an absorption coefficient based on conditions within the fluid maintaining device； and a controller configured to determine fluid level in the fluid maintaining device based on conditions sensed by the receiver array.
