Purchase this article with an account.
G. O. Sipe, J. R. Dearworth, Jr., J. F. Blaum, D. H. McDougal; Spectral Sensitivity of the Photointrinsic Iris in the Turtle. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5038.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The pupil in the turtle remains partially responsive to light after denervation of the eye (Dearworth et al., 2006; ARVO abstract). Our purpose in this study was to define the spectral sensitivity underlying this response.
After red-eared sliders (Trachemys scripta elegans) were euthanized, eyes were removed from orbits. Eyes were then hemisected, and the anterior segments were placed into a perfusion chamber, bubbled with 95%O2/5%CO2. Pupil area was tracked by an infrared camera using the ViewPoint EyeTracker® (Arrington Research, Inc.). Anterior segments were subjected to 10 min of light and then 40 min of dark. Measure of pupilloconstriction was determined by taking the difference of the pupil area measured at 40 min in the dark from the area measured at 10 min in the light. Five wavelengths generated using narrow band pass filters (Edmund Industrial Optic) with full width at half maximum of 10nm were tested each at five different intensities over a 4 logarithmic range.
Pupilloconstrictions were greatest at the highest irradiances for each wavelength: 11.64% ± 7.18 (SEM) at 410nm (n=4), 12.84% ± 3.22 at 430nm (n=4), 13.30% ± 2.88 at 480nm (n=8), 13.08% ± 3.12 at 520nm (n=6), and 20.83% ± 3.29 at 640nm (n=5). For each wavelength, data plots of pupilloconstriction versus irradiance were curve fit by Hill equations, Pmax [IB/(IB + CB)], where Pmax is maximal pupilloconstriction, I is irradiance, and B is a constant to derive an irradiance threshold value, C. Irradiance threshold values in log quanta/cm2/sec1 were 12.76 for 410nm derived with fit (R2= 0.96), 12.66 for 430nm (R2= 0.98), 12.40 for 480nm (R2= 0.79), 12.36 for 520nm (R2=0.99), and highest at 13.74 for 640nm (R2=0.90). Relative sensitivity was determined from the log reciprocals of these thresholds and plotted as a function of wavelength for comparison to various nomograms of visual pigments. Goodness-of-fit to nomograms was expressed as the profile-fitting error (PFE), the ratio between the sum of squared residuals and sum of squared observed responses. The spectra of data fit best (PFE=1.2%) porphyropsin from rod photoreceptors of turtle with max=518nm.
In addition to being regulated by retinal feedback via parasympathetic nervous pathways, the iris musculature in the red-eared slider turtle is photointrinsically responsive. Our results also suggest that the pigment underlying the mechanism is vitamin A2 based.
This PDF is available to Subscribers Only