  The conformal infinity of a quaternionic-Kahler metric on a 4n-manifold with
boundary is a codimension 3-distribution on the boundary called quaternionic
contact. In dimensions 4n-1 greater than 7, a quaternionic contact structure is
always the conformal infinity of a quaternionic-Kahler metric. On the contrary,
in dimension 7, we prove a criterion for quaternionic contact structures to be
the conformal infinity of a quaternionic- Kahler metric. This allows us to find
the quaternionic-contact structures on the 7-sphere close to the conformal
infinity of the quaternionic hyperbolic metric and which are the boundaries of
complete quaternionic-Kahler metrics on the 8-ball. Finally, we construct a
25-parameter family of Sp(1)-invariant complete quaternionic-Kahler metrics on
the 8-ball together with the 25-parameter family of their boundaries.
