PURPOSE. Exposure to elevated ambient temperatures has been bmentioned as a risk factor for common eye diseases, primarily presbyopia and cataract. The aim of the present study was to examine the relationship among ambient, cornea, and body core temperature. METHODS. The relation between corneal temperature and ambient temperature was examined in 11 human volunteers. Furthermore, corneal temperature was measured using a thermal camera during elevation of body core temperature in three human volunteers and four rats. RESULTS. A linear relationship between corneal temperature and body temperature was found in the rat. For humans there was an initial linear increase in corneal temperature with increasing body temperature, but corneal temperature seemed to plateau at 36.5¡C to 37.0¡C despite a continued increase of body core temperature. A linear relationship between ambient and corneal temperature was found in humans but with a less steep slope than that between corneal and body core temperature. CONCLUSIONS. Corneal temperature is estimated to reach the maximum of 36.5¡C to 37.0¡C at ambient temperatures between 32.0¡C and 34.5¡C. If there is a causal relationship between elevated eye temperature, cataract, and presbyopia, the incidence of these eye diseases is predicted to increase with global warming. Importantly, the strong association between corneal temperature and body core temperature indicates that frequent infections could also be considered a risk factor for age-related lens disorders. © Association for Research in Vision and Ophthalmology.