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Frank Thorn, Sondra J. Thorn, Ji-Chang He, Richard Held, Jane Gwiazda; How do optical aberrations and defocus affect retinal images?. Journal of Vision 2002;2(7):185. doi: 10.1167/2.7.185.
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Purpose: Retinal image blurring results primarily from defocus and ocular optical aberrations and is far more complex than Gaussian blur. We have measured the aberrations of 316 children and young adults in Boston and Beijing. The effects of aberrations on the retinal images of some of these children have been simulated (Thorn et al, 2000). We now extend this work by demonstrating how the effects of wavefront aberrations and different amounts of defocus combine to degrade the retinal image of different types of stimuli.
Methods: Wavefront aberrations were measured using a ray-tracing wavefront sensor. Aberration profiles were described by the first 7 orders of a Zernike polynomial function from which an MTF and point-spread function were calculated. This point-spread function was used to create retinal image simulations for the 40 children examined in Boston (ages 11 to 16 years).
Results: When eyes are in focus, the appearances of simulated retinal images vary from having a slight haziness to image smearing and multiple ghost images. Defocus degrades retinal image quality in the less aberrant eyes as a function of the amount of defocus with plus power inducing a different pattern of degradation than minus power. Highly aberrant eyes show less incremental degradation of the retinal image with defocus although the image's appearance may change markedly. These effects are more noticeable with text than with natural scenes.
Conclusions: Optical aberrations and defocus alter retinal images in complex ways and their effects vary markedly from person to person for different types of stimuli. When creating models of the neural mechanisms underlying vision, researchers must be aware that the stimulus patterns they present to subjects are not the same as those projected onto their retinas and differ from person to person. Thus their models should take the effects of realistic optical degradations into account.
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