Eye size is fundamental to vision in that increasing size improves photon capture, leading to the enhanced ability to detect light. Due to the high metabolic cost of maintaining eyes, considerable size variation is observed among animals and can serve as an indicator of the importance of vision. In the deep sea, constraints on energy resources and ambient light place strong selection pressure on eyes, providing a unique opportunity for studying the ecological correlates of eye size evolution. Here, we examined eye size across 454 specimens of 15 species of Sergestidae shrimps, in order to test hypotheses about the relationship of eye size to light organ morphology, vertical migration behavior, and depth. Examining eye-to-body size scaling over growth, we found significant variation in allometric slopes between species, suggesting varying degrees of eye investment for a given body size that align to differences in phylogeny and ecology. To correct for phylogeny, we used a phylogenetic generalized least squares approach to determine the ecological correlates of average eye size between species. We found that eye size (corrected for body size) is at least predicted by interspecific differences in light organ morphology, suggesting that investment in eye size may be driven by differences in bioluminescence signaling. Overall, our study provides new insights into eye size evolution, helping to disentangle the phylogenetic, morphological, and ecological constraints that underlie vision in the deep sea.