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Melanie C. Campbell, Marsha Kisilak, Jennifer J. Hunter, Juan M. Bueno, Denise King, Elizabeth L. Irving; Optical aberrations of the eye and eye growth: Why aberrations may be important to understanding refractive error development. Journal of Vision 2002;2(10):111. doi: 10.1167/2.10.111.
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We and others have shown that the monochromatic aberrations of myopes differ from those of emmetropes. Other measurements suggest that optical aberrations are important to the relationships between eye size, depth of focus, visual acuity, defocus and emmetropization. For example, small eyes are more tolerant to both defocus and optical aberrations. Marcos and colleagues have shown a relationship between depth of focus and aberrations. Roorda and co-workers showed that the direction of defocus can be recognised from an individual's monochromatic aberrations.
Firstly, if tolerance to optical aberrations were related to eye size in a similar manner to a tolerance to defocus, optical aberrations as well as refractive error would be expected to emmetropize with eye growth. Our experiments on chick eyes have shown that, for a 1.6 mm pupil size, the optical aberrations of the eye reduce with eye growth as the chicks age. In the fellow, myopic eyes, fitted with −15 D goggles, the aberrations are significantly larger. This is the first evidence that aberrations reduce with growth in a process analogous to emmetropization.
Secondly, which monochromatic aberrations can provide a signal to the direction of defocus in emmetropic eyes? We have modelled the point spread functions (PSF's) of human emmetropic eyes as a function of defocus. Either small amounts of astigmatism or spherical aberration can provide signals to the direction of defocus. Analyses of the point spread functions of human emmetropic and myopic eyes, reconstructed from experimental Hartmann Shack measurements, confirm an asymmetry in the PSF's with the direction of defocus which may differ between emmetropic and some myopic eyes.
In conclusion, optical aberrations are under active control during eye growth in chicks, they differ between human myopes and emmetropes and they may provide an important signal to the direction of defocus of the eye
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