Biomedical Optics & Medical Imaging
Light propagation explains our inverted retina
Erez N. Ribak and Amichai M. Labin
An engineering tool has shown that the retinal structure aids in improving our vision acuity.
18 October 2010, SPIE Newsroom. DOI: 10.1117/2.1201009.003189
Our eyes are built like a digital camera: the lens comes in front, and the detector—the retina—at the back. Light is converted into electrical signals by photoreceptor cells (see Figure 1). The latter are divided between cones, which can discriminate colors, and rods, which are color blind but much more light-sensitive and which support night vision. But unlike cameras, the retina contains transparent layers of neurons in front of the photoreceptors. These neurons process the detected image and wire it to the brain, but since they are in front, they also distort the image. The key question is why this wiring is not done behind the detector cells. Photoreceptors are placed behind the neurons in all vertebrates, indicating that it is evolutionarily efficient.1 The inverted retina has mystified people since the structure and function of the eye were first exposed in the late 19th century.
While neurons run along the retina and across the light path, glial (Muller) cells intersect the retina in the light-propagation direction and across the neural layers. These cells are each attached to one cone and a few rods. They are also shaped like funnels, narrowing down towards the photoreceptors (see Figure 1). They were considered (among other functions) mechanical and metabolic supports for the neurons. Retinal glial cells can also transmit light, because their refractive index is higher than that of their neighborhood.2
Figure 1. Section through the retina. Except for the absorbing layers at the bottom (R), all parts are transparent, and colors are for demonstration purposes only. The retina is mostly composed of neuron layers (L) and their nuclei (N). Light arrives from the pupil (top) through the vitreous humor (V) and is captured in the funnels of the Muller cells (M), where it is concentrated down to the cones (C). The rest of the light is scattered into the narrower rod photoreceptors that surround the cones in the photoreceptor layer (P). The thickness of the retina, except for its very center, is one quarter to one half a millimeter.
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NOTA CAUSTICANTE DESTE BLOGGER:
Eu queria ver a cara de alguns cientistas da Nomenklatura científica, e da Galera dos meninos e meninas de Darwin, que desceram o cacete nos criacionistas e no Design Inteligente por causa da retina invertida do ser humano. Eles disseram, e não vão poder mais dizer, que nenhum engenheiro inteligente planejaria a retina invertida pelas razões blá blá blá e mais blá blá blá.
Agora esta dupla de cientistas com sua pesquisa mais detalhada demonstrou que existe sim finalidade -- TELEOLOGIA -- que Darwin, dizem ter eliminado da Biologia. NADA MAIS FALSO!!! A cada dia que passa, mais e mais complexidade se descobre nas formas bióticas que o paradigma darwiniano não tem competência heurística em explicar. Aliás, um paradigma em falência heurística desde 1859.
Estou rachando de rir dessa turma, sem dó e nem piedade.
