We present an approximate analytical method for the evaluation of packet loss probability in synchronous optical packet-switched networks which operate under limited deflection routing with the contention resolution method based on priorities. Packets are lost because they experience too many deflections and stay prohibitively long in the network. The presented results are those for the network in the torus topology of a two-dimensional grid, which operates at a steady state with the uniform load u, u ∊ {0, 1}. To our knowledge, this is the only article to present such an analysis for networks with nodes of the 4 × 4 type. For the network composed of 100 nodes, we predict the packet loss probability as low as 10^-9, while our simulator provided results on the order of 10^-6. We verify our analysis by simulation, when possible.