  The experiment of Etano et al which demonstrated the quantum Zeno effect
(QZE) in an optical experiment was explained by Frerichs and Schenzle without
invoking the wave function collapse. In this report it is proposed that the
collapse does occur, and it can be explained by the `environment induced
decoherence' theory. The environment here consists of the completely quantized
field vacuum modes. The spontaneous emission life time of the atom sets a
fundamental limit on the requirement of `continuous measurements' for QZE. This
limit turns out to be related to the time-energy uncertainty relation discussed
by Ghirardi et al.
