The ANTARES telescope Cherenkov light detection is based on 885 optical modules operated in the sea water at a depth greater than 2000 m and a constant temperature of 13.3°C, which have been immersed between 2006 and 2008. After 8 to 10 years of operation, a large fraction of the optical modules is still operational. More details about ANTARES can be found here.
The optical module consists of a pressure resistant glass sphere housing a photomultiplier and its active base providing the high-voltage, slow-control access and the readout of the signal (Anode, 12th and 14th Dyode). The glass sphere has a 17 inch diameter and is qualified up to 700 bar.