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Hendrik Jungnickel, Constanze Czok, Daniel Weigel, Armin Kiessling, Richard Kowarschik, Michael Gebhardt; Determination of Just-Noticeable Values of Coma and Trefoil Induced by Adaptive Optics. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2806.
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Coma and trefoil are - in addition to spherical aberration - the most prevalent higher order aberrations in healthy human eyes. The aim of the study was to determine the just-noticeable values of vertical coma and trefoil and whether full correction of these aberrations leads to the best subjective visual impression.
In 10 eyes of 10 subjects lower and higher order aberrations up to the 6th order were corrected by an adaptive optics system (deformable mirror MIRAO 52-e, Imagine Eyes). Pupil size was limited to 5 mm by a pinhole. 10 steps of vertical coma (C3-1, from -0.252 to 0.252 µm) and 10 steps of trefoil (C3-3, from -0.315 to 0.315 µm) were generated in randomized sequences. Subjects observed a non-directional black-and-white test pattern and decided in a one-after-another comparison whether the full correction or the correction with the induced aberration provided the better visual impression. 20 comparisons were made for each aberration step. Just-noticeable values of coma and trefoil were determined by means of the fitted psychometric functions (difference of the values for 75 % and 50 % detection probability).
Just-noticeable values showed a large interindividual spread and ranged from 0.028 µm to 0.138 µm (vertical coma) and 0.039 µm to 0.152 µm (trefoil) respectively. In 65 % of the cases the visual impression with slight induced aberration was better than full correction. Optimal amounts of trefoil showed a tendency to the habitual values of this coefficient.
Vertical coma affects the visual impression more than trefoil with the same value. Differential thresholds seem to be impacted by various factors. As one factor the neural adaption to the aberrations of the eye is conceivable. Although the optical image on retina is nearly optimal the full correction is subjectively rated worse.
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