why does vision using the fovea have high visual acuity, but low sensitivity to light compared with vision using other parts of the retina.

the connections within the retina explain this. there is a different density and distribution of different types of cells in the retina - the fovea, in the centre of the eye, has a high density of cone cells (photoreceptors), but a lower density of rods, compared to the periphery. Cones are specialised for visual acuity, whereas rods are more sensitive to light - one photon of light is sufficient to activate a rod cell. therefore, the distribution of the photoreceptors explain the difference in sensitivity and acuity in different parts of the eye