Subjective depth of field in presence of 4th-order and 6th-order Zernike spherical aberration using adaptive optics technology

PURPOSE: To study the impact on the subjective depth of field of 4th-order spherical aberration and its combination with 6th-order spherical aberration and analyze the accuracy of image-quality metrics in predicting the impact. SETTING: Laboratoire Aime Cotton, Centre National de la Recherche Scientifique, Universite Paris-Sud, Orsay, France. DESIGN: Case series. METHODS: Subjective depth of field was defined as the range of defocus at which the target (3 high-contrast letters at 20/50) was perceived acceptable. Depth of field was measured using 0.18 diopter (D) steps in young subjects with the addition of the following spherical aberration values: +/- 0.3 mu m and +/- 0.6 mu m 4th-order spherical aberration with 3.0 mm and 6.0 mm pupils and +/- 0.3 mu m 4th-order spherical aberration with +/- 0.1 mu m 6th-order spherical aberration for 6.0 mm pupils. RESULTS: The addition of 0.3 and +/- 0.6 mu m 4th-order spherical aberration increased depth of field by 30% and 45%, respectively. The combination of 4th-order spherical aberration and 6th-order spherical aberration of opposite signs increased depth of field more than 4th-order spherical aberration alone (ie, 63%), while the combination of 4th-order spherical aberration and 6th-order spherical aberration of the same signs did not (ie, 24%). Whereas the midpoint of the depth of field could be predicted by image-quality metrics, none was found a good predictor of objectionable depth of field. CONCLUSION: Subjective depth of field increased when 4th-order spherical aberration and 6th-order spherical aberration of opposite signs were added but could not be predicted with image-quality metrics.