Abstract
Abstract: :
Purpose: Our aim was to measure the higher-order optical aberrations of eyes in chickens during the first week of life. Methods: Optical aberrations of newly hatched chicks (Shaver cockerels) were measured 1, 4, and 7 days after hatching with a Shack-Hartmann aberrometer (COAS, by Wavefront Sciences, Albuquerque, NM). Zernike aberration coefficients through the 4th order were normalized by pupil area to express all results in the common metric of equivalent defocus, in units of diopters. Real-time monitoring of the pupil, the retinal point-spread function, and the wavefront aberration enabled us to take repeated measurements under normal physiological conditions without the need for anesthesia, cycloplegia, lid retractors, or tear supplements. Results: Total RMS error of the higher-order Zernike terms exceeded Marechal's criterion for diffraction-limited optics (< wavelength/14) for 81% of eyes on Day 1, for 98% of eyes on Day 4, and for 100% of eyes on Day 7. However, when normalized by pupil area (which increased with age), the equivalent defocus of all the Zernike modes declined slightly with age. Aberration magnitude declined exponentially with Zernike order, just as for human adult eyes (Bradley, et. al. ARVO 2001), but was from 6 to 10 times larger than for human eyes. For any given Zernike mode, the distribution of aberration coefficients was randomly distributed around zero but the magnitude of these aberrations was typically much larger than for human eyes. The only systematic deviation of the population mean from zero was for astigmatism axis 90/180 (i.e second order, frequency +2), which was slightly positive (i.e against-the-rule). Unlike adult human eyes, there was no tendency for spherical aberration to be positive or larger in magnitude relative to other fourth-order aberrations. The mean magnitude of every higher-order mode was less than the mean magnitude of astigmatism (0.5D). Conclusion: We conclude that the optical quality of the developing chick eye is significantly worse than for human adult eyes. Nevertheless, the absolute magnitude of higher order aberrations in the chick eye are small compared to astigmatism. This result, plus the absence of systematic bias towards positive or negative values of individual Zernike modes, suggests that image quality under conditions of myopic or hyperopic rearing would be dominated by defocus.
Keywords: 519 physiological optics • 543 refractive error development • 481 myopia