We present a study of binary mixtures of eye lens crystallin proteins. A coarse-grained model of aqueous alpha- and gamma-crystallin mixtures based on molecular dynamics simulations and SANS experiments is proposed. Thermodynamic perturbation theory is implemented to obtain the stability boundaries, or spinodal surface, of the binary mixture in the full parameter space. The stability of these high-concentration crystallin mixtures was found to depend on the alpha-gamma attraction in a manner that is both extremely sensitive and nonmonotonic; stronger or weaker attraction resulted in a spectacularly enhanced instability. The relevance of these mechanisms as possible sources of the alteration of the spatial distribution of the lens proteins encountered in cataract disease is discussed.