Deuteranomalia: This is caused by reduced sensitivity to green light. Deutan color vision deficiencies are by far the most common forms of color blindness. This subtype of red-green color blindness is found in about 6% of the male population,
mostly in its mild form deuteranomaly.
Protanopia: Caused by a reduced sensitivity to red light due to either defective or a lack of long
-wavelength cones (red cones). Some scientists estimate that being a protan is associated with a risk of a road accident equivalent to having a blood alcohol level of between 0.05 and 0.08 per cent.
Tritanopia: People affected by tritan color blindness confuse blue with green and yellow with violet. This is due to a defective short-wavelength cone (blue cone). Whilst
Protanopia and Deuteranomalia are significantly more common in men, tritanopia affects both sexes in equal amounts.
Monochromacy: Only around 0.00003% of the world’s population suffers from total color blindness, where everything is seen in black and white.
Dark Spot and Jovian ‘Galaxy’ - This enhanced-color image of a mysterious dark spot on Jupiter seems to reveal a Jovian “galaxy” of swirling storms. Juno acquired this JunoCam image on Feb. 2, 2017, at an altitude of 9,000 miles (14,500 kilometers) above the giant planet’s cloud tops. This publicly selected target was simply titled “Dark Spot.” In ground-based images it was difficult to tell that it is a dark storm. Citizen scientist Roman Tkachenko enhanced the color to bring out the rich detail in the storm and surrounding clouds. Just south of the dark storm is a bright, oval-shaped storm with high, bright, white clouds, reminiscent of a swirling galaxy. As a final touch, he rotated the image 90 degrees, turning the picture into a work of art.
Cephalopod eyes are fascinating. Just like us vertebrates they have camera-type eyes, a hollow liquid-filled chamber with an opening, the iris, and a lens through which light enters and is projected onto the photosensitive surface, the retina. Despite their similarities, vertebrate and cephalopod camera-type eyes have different origins and evolved independently. There are some striking differences that highlight this:
Unlike us, the photoreceptor cells of cephalopods point outwards towards the source of the light rather than inwards. This not only means the we have “inverted” retinas, it also means that cephalopods don’t have a blind spot because the nerve fibers that transmit the visual impulses from the retina to the brain collect and exit the eye behind the retina rather than in front of it. The developmental origins of the eye tissues are also different. For instance, in vertebrates the complex layers of the retina develop from nerve tissue, while the lens develops from skin tissue. In cephalopods both tissues develop from progenitor skin cells.
Cephalopods have excellent vision, and use complex visual cues to communicate with each other, camouflage themselves, and send signals to their environment. To do this they use highly adaptible pigment-filled cells in their skin called chromatophores. The capricorn night octopus (Callistoctopus alpheus) in the photo looks blue, but if it would open all its chromatophores it would turn deep red with bright white polka dots.
Photo credit: David Liittschwager, National Geographic.