v5 integrin is the sole integrin receptor at the apical surface of the retinal pigment epithelium (RPE) facing photoreceptor cells in the retina. There, it promotes RPE phagocytic signaling to the tyrosine kinase MerTK once a day in response to circadian photoreceptor disk shedding. Here, we identify a novel role for v5 integrin in permanent RPE-photoreceptor adhesion that is independent of v5 receptor function in retinal phagocytosis. To compare retinal adhesion of wild-type and 5 integrin^-/- mice we mechanically separated RPE and neural retina and quantified RPE protein and pigment retention with the neural retina. Lack of v5 integrin with normal expression of other RPE integrins greatly weakened retinal adhesion in young mice and accelerated its age-dependent decline. Unexpectedly, strength of wild-type retinal adhesion varied with a diurnal rhythm that peaked 3.5 hours after light onset, after completion of phagocytosis when integrin signaling to MerTK is minimal. Permanent v5 receptor deficiency attenuated the diurnal peak of retinal adhesion in 5 integrin^-/- mice. These results identify v5 integrin as the first RPE receptor that contributes to retinal adhesion, a vital mechanism for long-term photoreceptor function and viability. Furthermore, they indicate that v5 receptors at the same, apical plasma membrane domain of RPE cells fulfill two separate functions that are synchronized by different diurnal rhythms.