  The visual perception of the natural night sky in many places of the world is
strongly disturbed by anthropogenic light. Part of this artificial light is
scattered in the atmosphere and propagates towards the observer, adding to the
natural brightness and producing a light polluted sky. However, atmospheric
scattering is not the only mechanism contributing to increase the visual
skyglow. The rich and diverse biological media forming the human eye also
scatter light very efficiently and contribute, in some cases to a big extent,
to the total sky brightness detected by the retinal photoreceptors. In this
paper we quantify this effect and assess its relevance when the eye pupil is
illuminated by light sources within the visual field. Our results show that
intraocular scattering constitutes a significant part of the perceived sky
brightness at short distances from streetlights. These results provide
quantitative support to the everyday experience that substantial gains in
naked-eye star limiting magnitudes can be achieved by blocking the direct light
from the lamps that reaches the eye pupil. Urban lighting designs that reduce
the illuminance over the eye pupil and locate the sources at large angles with
respect to the visual axis are expected to help decreasing the artificial
intraocular skyglow.
