  The optical design of the Multi Conjugate Adaptive Optics Relay for the
Extremely Large Telescope experienced many modifications since Phase A
conclusion in late 2009. These modifications were due to the evolution of the
telescope design, the more and more accurate results of the performance
simulations and the variations of the opto-mechanical interfaces with both the
telescope and the client instruments. Besides, in light of the optics
manufacturing assessment feed-backs, the optical design underwent to a global
simplification respect to the former versions. Integration, alignment,
accessibility and maintenance issues took also a crucial role in the design
tuning during the last phases of its evolution. This paper intends to describe
the most important steps in the evolution of the optical design, whose
rationale has always been to have a feasible and robust instrument, fulfilling
all the requirements and interfaces. Among the wide exploration of possible
solutions, all the presented designs are compliant with the high-level
scientific requirements, concerning the maximum residual wavefront error and
the geometrical distortion at the exit ports. The outcome of this decennial
work is the design chosen as baseline at the kick-off of the Phase B in 2016
and subsequently slightly modified, after requests and inputs from alignment
and maintenance side.
