Measurement and prediction of subjective gradations of images in presence of monochromatic aberrations.

The three objectives of this study were (i) to explore the effect of various levels of aberrations on subjective vision by scoring images, (ii) to compare subjective scores obtained with real optics and simulated images and (iii) to test the ability of image quality metrics to predict these scores. In a first experiment, 14 subjects evaluated the quality of images degraded by 0.05, 0.1, 0.2, 0.4 and 0.8µm of defocus, astigmatism, trefoil, coma, spherical aberration (SA4) and secondary spherical aberration (SA6) by putting a mark on a 5-items continuous grading scale. The desired aberration was introduced either by a deformable mirror or by displaying a simulated image. In the second experiment, 5 of the previous subjects evaluated the quality of through-focus images in presence of SA4, SA6 and combinations of SA4 and SA6. Both experiments were performed with an artificial pupil of 6mm diameter. The addition of increasing amounts of aberrations reduced the subjective grading of the targets, with SA6, SA4 and defocus being the most degrading aberrations. The correlation between the results obtained with the AO device and with simulated images gave a r(2) of 0.95. Combinations of 0.4µm of SA4 and 0.2µm of SA6 of opposite signs induced a bimodal through-focus image score curve. We were able to anticipate the subjective gradation of subject's vision thanks to image quality metrics (r(2)=0.92). Image quality score shows similar results as that obtained by objective image quality metrics, which provides a useful tool for optical designers and practitioners.

Effect of coma and spherical aberration on depth-of-focus measured using adaptive optics and computationally blurred images.

PURPOSE: To compare the effect of primary spherical aberration and vertical coma on depth of focus measured with 2 methods. SETTING: Laboratoire Aimé Cotton, Centre National de la Recherche Scientifique, and Université Paris-Sud, Orsay, France. DESIGN: Evaluation of technology. METHODS: The subjective depth of focus, defined as the interval of vision for which the target was still perceived acceptable, was evaluated using 2 methods. In the first method, the subject changed the defocus term by reshaping the mirror, which also corrected the subject's aberrations and induced a certain value of coma or primary spherical aberration. In the second procedure, the subject changed the displayed images, which were calculated for various defocuses and with the desired aberration using a numerical eye model. Depth of focus was measured using a 0.18 diopter (D) step in 4 nonpresbyopic subjects corrected for the entire eye aberrations with a 6.0 mm and 3.0 mm pupil and with the addition of 0.3 µm and 0.6 µm of positive primary spherical aberration or vertical coma. RESULTS: There was good concordance between the depth of focus measured with both methods (differences within 1/3 D, r(2) = 0.88). Image-quality metrics failed to predict the subjective depth of focus (r(2) < 0.41). CONCLUSION: These data confirm that defocus in the retinal image can be generated by optical or computational methods and that both can be used to assess the effect of higher-order aberrations on depth of focus. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Optimizing the subjective depth-of-focus with combinations of fourth- and sixth-order spherical aberration.

We optimize the subjective depth of focus (DoF) with combinations of spherical aberration (SA4) and secondary spherical aberration (SA6) in various levels. Subjective DoF was defined as the visual interval for which three 20/50 high-contrast letters was perceived acceptable (objectionable blur limits). We used an adaptive optics system to dynamically correct the observer's aberrations and control their accommodation. DoF was measured with a 0.18-D step on three non-presbyopic subjects. The target seen by the subjects was modified to include 25 combinations of SA4 and SA6 (i.e. 0, ± 0.15 and ± 0.30 µm) for 3, 4.5 and 6mm of pupil diameter. We found a mean DoF of 1.97D with a 3mm pupil size, which decreased by 28% with a 4.5mm pupil and by 34% with a 6mm pupil. For 6mm pupil we found an increase of subjective DoF of 45% and 64% with the addition of 0.3 and 0.6 µm of SA4, and of 52% and 117% with the addition of 0.15 and 0.3 µm of SA6. The largest DoF measured (4.78D) increased 3.6 times that of the naked eye and was found for a combination of opposite signs of SA4 and SA6 of 0.6 and 0.3 µm respectively. Reducing the pupil size minimized the effect of aberrations on subjective DoF. Combination of SA4 and SA6 of opposite sign could increase DoF more than three times for pupils larger than 4.5mm. Subjective DoF is well predicted by measuring the induced variation of vergence arising in the pupil size.

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 Aimé Cotton, Centre National de la Recherche Scientifique, Université 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 µm and ±0.6 µm 4th-order spherical aberration with 3.0 mm and 6.0 mm pupils and ±0.3 µm 4th-order spherical aberration with ±0.1 µm 6th-order spherical aberration for 6.0 mm pupils. RESULTS: The addition of ±0.3 and ±0.6 µm 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.

Through-focus visual performance measurements and predictions with multifocal contact lenses.

We measured high-contrast visual acuity (VA) and 12c/deg contrast sensitivity (CS) through-focus functions (TFF) of four eyes of four cyclopleged subjects in three conditions: naked eye, with a center-distance and center-near Proclear(R) multifocal addition 2D contact lens. In all conditions, an adaptive optics system statically compensated the astigmatism of the subject's eye alone. Multifocal contact lenses enlarged the width of the curve of through-focus visual performance but reduced the peak performance. We investigated the ability of image quality metrics based on wave-aberration measurements to predict VA and CS TFF. CS(12) metric through-focus and measured through-focus contrast sensitivities were well correlated (r(2)=0.74). Even if visual acuity metrics were often poorer than measured ones, the shapes of the measured through-focus curves and rMTFa(5-15) through-focus were quite comparable (r(2)=0.67).

Effect of monochromatic induced aberrations on visual performance measured by adaptive optics technology.

PURPOSE: The two objectives were 1) to measure visual acuity (VA) and contrast sensitivity (CS) losses induced by various amounts of individual Zernike aberrations, and 2) to examine the accuracy of image quality metrics in predicting these visual performance losses. METHODS: Monocular 10 cycles/degree (cpd) and 25 cpd CS and high- and low-contrast VA were measured when introducing individual Zernike aberrations in four patients dynamically corrected using a CRX1 adaptive optics system (Imagine Eyes) and a 5.5-mm pupil. Seven levels (0, +/- 0.1, +/- 0.3, and +/- 0.9 microm) of astigmatism, spherical aberration, coma, and trefoil and four levels of defocus were induced. Several image quality metrics based on the radially averaged modulation transfer function (rMTF) and optical transfer function (rOTF) calculations were computed to attempt to predict the losses in VA and CS. RESULTS: Modes near the center and at the top of the Zernike pyramid decreased VA significantly more than modes near the edge or at the bottom of the pyramid. The measured CS losses were reasonably correlated to the rMTF calculated at 10 cpd (R2 = 0.87) and 25 cpd (R2 = 0.75). The high-contrast VA degradations were also reasonably predicted (R2 = 0.85) by the intersection between the rMTF and the neural contrast threshold function. The low-contrast VA losses were also well predicted (R2 = 0.88) by three rMTF-based metrics. CONCLUSIONS: Image quality metrics based on wavefront aberration measurements were able to predict the impact of individual Zernike aberrations on CS and VA.