Screaming Begins Again Lizard Glowing Eyes
March 2009
Volume 9, Issue 3
Figure 1
(a) Two day geckos, Phelsuma madagascariensis grandis, and (b) eight nocturnal helmet geckos, Tarentola chazaliae, were used in our study. Scale bars, 1 cm. (c) The photorefractometry method was used to qualitatively determine the optical system of the gecko eye. (d) In order to perform quantitative measurements, we developed an adapted Hartmann–Shack wavefront sensor (for details, see text).
Figure 2
Examples of wavefronts and the corresponding local refractive power maps for the ideal cases of (a) pure defocus and (b) spherical aberration. (c) The measured spot pattern from two helmet geckos; NG6 (left half) and NG5 (right half), where NG6 turned out to differ from all the other geckos by having extreme transitions between zones of different refractive power. (d) The measured spot pattern from the two day geckos, where the left and right halves are consisting of DG1 and DG2, respectively. Between spots, it is approximately 40 μm.
Figure 3
The pupil area and standard deviation of three nocturnal helmet geckos in different light intensities. The three pictures within the graph show the pupil sizes at certain light intensities, given in candela per square meter below each picture.
Figure 4
(a) Horizontally sectioned helmet gecko eye. Assuming a well-focused eye and using Gullstrand's model, calculation yields a post nodal distance of 3.6 mm for this specimen and a mean value of 3.5 mm ± 0.1 mm for all three helmet geckos examined. Radii of the cornea as well as the anterior and posterior lens surfaces are shown as r 1, r 2, and r 3, respectively. Scale bars, 1 mm. (b) Transmission electron micrograph image of cones in the retina of the helmet gecko with inner (I) and outer (O) segments, where the outer segments measure 30–40 μm in length and approximately 10 μm in width. Scale bar, 10 μm.
Figure 5
Results of the two optical methods used in this study. Photorefractometric pictures (left column) of (a) one day gecko and (b–e) four helmet geckos. Scale bar, 1 mm. In the helmet gecko pictures, the broken lines indicate the concentric zones with distinct refractive power transitions suggesting multifocality. DG1 (a) shows no such concentric zones, which suggests a monofocal optical system. The wavefront graphs (middle column) show the change in optical path lengths for light passing through different parts of the pupil (scale, micrometer). The maps of local refractive powers (right column) show how the refractive power changes over the pupil (scale, diopter). The black dots indicate the determined optical center. Two evident differences between the species are that in the (a) day geckos the refractive power decreases monotonically toward the outer parts of the pupil, while the refractive power in the (b–e) helmet geckos are increasing, and not in a monotonic manner. Blue color indicates low refractive power in the region and red color indicates high refractive power. Values at the axes indicate pupil sizes (in millimeters). See text for further explanation.
Figure 6
Radial profiles of the distribution of the refractive power over the pupil of diurnal (red) and nocturnal geckos (black). The change in refractive power is given relative to the center of the pupil (set to zero diopters). The dots and the error bars show the average values and the standard deviations of three measurements in the left eyes. See text for further explanation.
Figure 7
Photorefractometric image (left) of the eye of NG6 with the light-adapted pupil indicated by white lines and dots. The light-adapted (middle) and dark-adapted (right) pupils of the eyes of NG6 are shown for comparison.
Table 1
The optical sensitivity, S w , in dim light was calculated using Equation 1. The mean values and standard deviations for the three helmet geckos are shown. The eye of the helmet gecko is 350 times more light-sensitive than that of humans at intensities when each of them discriminate colors. When assuming a cone diameter of 10 μm, the nocturnal Tokay gecko (Gekko gecko) has an S w value of the same magnitude as the helmet gecko.
© 2009 ARVO
Source: https://jov.arvojournals.org/article.aspx?articleid=2193495
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