I think this “sub-optimal” argument against a Designer is stupid, because designs are always trade-offs between different quality goals, but just to put this one to bed, here is Evolution News.
Now a new paper in Nature Communications, “Müller cells separate between wavelengths to improve day vision with minimal effect upon night vision,” has expanded upon this research, further showing the eye’s optimal design. According to the paper, Müller cells not only act as optical fibers to direct incoming light through the optic nerve, but are fine-tuned to specific wavelengths to ensure that light reaches the proper retinal cells. From the Abstract:
Vision starts with the absorption of light by the retinal photoreceptors — cones and rods. However, due to the ‘inverted’ structure of the retina, the incident light must propagate through reflecting and scattering cellular layers before reaching the photoreceptors. It has been recently suggested that Müller cells function as optical fibres in the retina, transferring light illuminating the retinal surface onto the cone photoreceptors. Here we show that Müller cells are wavelength-dependent wave-guides, concentrating the green-red part of the visible spectrum onto cones and allowing the blue-purple part to leak onto nearby rods. This phenomenon is observed in the isolated retina and explained by a computational model, for the guinea pig and the human parafoveal retina. Therefore, light propagation by Müller cells through the retina can be considered as an integral part of the first step in the visual process, increasing photon absorption by cones while minimally affecting rod-mediated vision.
(Amichai M. Labin, Shadi K. Safuri, Erez N. Ribak, and Ido Perlman, “Müller cells separate between wavelengths to improve day vision with minimal effect upon night vision,” Nature Communications, DOI: 10.1038/ncomms5319 (July 8, 2014).)
The paper presents Müller cells as a direct answer to the view that the vertebrate eye has a suboptimal wiring:
[T]he mammalian retina and the peripheral retina of humans and primates are organized in a seemingly reverse order with respect to the light path. This arrangement places the photoreceptors, responsible for light absorption, as the last cells in the path of light, rather than the first. Therefore, the incident light must propagate through five reflecting and scattering layers of cell bodies and neural processes before reaching the photoreceptors. This ‘inverted’ retinal structure is expected to cause blurring of the image and reduction in the photon flux reaching the photoreceptors, thus reducing their sensitivity. It has been recently reported that retinal Müller cells act as light guides serving to transfer light across the retina, from the vitreo-retinal border towards the photoreceptors.
Bookmark it because this is the kind of silly objection to design that they hear on the Discovery Channel, PBS, etc.