The geniculo-calcerine tract (known as the optic radiation) is a collection of axons carrying visual information from the lateral geniculate nucleus of the thalamus to the primary visual cortex (also called striate cortex).
Much of this tract can go straight to the occipital lobe; however, the fibres carrying information from the lower retina must loop around the lateral ventricle via Meyer's loop (passing into the temporal lobe) to get to the visual cortex.
For this reason, a lesion in the temporal lobe can cause a loss of vision to the superior quadrant, (the top half of what we see, for instance the sky).
