The interrelated effects of body size and choroid rete development on the ocular partial pressure of oxygen (PO2) of the mainly temperate Atlantic cod, Gadus morhua, and the exclusively polar Greenland cod, G. ogac, were investigated using micro-optode O2 sensors. Due to a difference in geographical distribution, it is hypothesized that G. ogac will possess features favouring visual-metabolic processes in a cold, dark environment. The relative size of the eye was identical between species and exhibited negative body-size scaling. The oxygen-secreting retia of both gadid species are extremely well developed and, although variable, recordings of ocular PO2 were consistently and often greatly in excess of atmospheric pressures (27.7–138.3kPa). The choroid rete was slightly more developed in G. ogac, but ocular PO2 was not significantly different between the two species. Choroid rete development scaled isometrically with body size in both species and may explain why differences in body size did not account for any of the variation in ocular PO2 measures. The hypothesis that polar-fish species exhibit marked visual-metabolic adaptations as a result of their cold, dark environment is not wholly supported by the current data.