![]() ![]() The optical system of the day gecko shows no signs of distinct concentric zones and is thereby monofocal.ĭuring the evolution of the diurnal lizards, their eyes have lost the typical vertebrate duplex retina with both rods and cones and are instead left only with different types of single and double cones (Röll, 2000 Underwood, 1970 Walls, 1942). We compare the optical system of the helmet gecko to that of the diurnal day gecko, Phelsuma madagascariensis grandis. This is of the same magnitude as needed to focus light of the wavelength range to which gecko photoreceptors are most sensitive. The intraspecific variation is large but in most of the individuals studied the zones differed by 15 diopters. Using photorefractometry and an adapted laboratory Hartmann–Shack wavefront sensor of high resolution, we also show that the optical system of the helmet gecko has distinct concentric zones of different refractive powers, a so-called multifocal optical system. The optics and the large cones of the gecko are important reasons why they can use color vision at low light intensities. The sensitivity of the helmet gecko eye has been calculated to be 350 times higher than human cone vision at the color vision threshold. The nocturnal helmet gecko, Tarentola chazaliae, discriminates colors in dim moonlight when humans are color blind. ![]()
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