The information outage probability of a shot-noise limited direct detection multiple-input multiple-output (MIMO) optical channel subject to block fading is considered. Information is transmitted over this channel by modulating the intensity of a number of optical signals, one corresponding to each transmit aperture, and individual photon arrivals are observed at multiple receive photodetector apertures. The transmitted signals undergo multiplicative fading, and the fading occurs in coherence intervals of fixed duration in each of which the channel fade matrix remains constant. The channel fade matrix varies across successive coherence intervals in an independent and identically distributed fashion. The transmitter and the receiver are assumed to have perfect channel state information (CSI). The main contributions are a formulation of the outage probability problem as an optimization problem and an exact characterization of the optimal solution for the special case of the MIMO Poisson fading channel with two transmit apertures.