High Order Aberration Correction in a Post-Column Energy Filter

Aim. To present the results of intrastromal femtokeratoplasty (ISFKP) with implantation of corneal segments in the correction of higher order aberrations (HOA) in patients with I–II stage keratoconus. Materials and methods. The study included 15 patients (14 male and 1 female), a total of 17 eyes, with initial (I–II) stages of keratoconus. The patients underwent IFKP with implantation of corneal ring segments. A comprehensive assessment of the anterior segment of the eye was performed before and after surgery: measured indices of best corrected visual acuity (BCVA), total level of higher-order corneal aberrations (total HOA), level of comatic aberration (coma), level of trefoil aberration, level of spherical aberration, and percentage of HOA influence on wavefront. Results. The data obtained in average observation period of 18.5 months after surgery showed a characteristic increase in BCVA in each case (by 0.29±0.09 on average), as well as a decrease in overall HOA by 0.69±0.4 D, a decrease in coma by 0.74±0.4 D, and in spherical aberration by 0.07±0.12 D (p < 0.05). Also, the level of reduction of trefoil aberration and the percentage of AVP in the general wave front were revealed, however, these changes in were not significant (P>0.05). Conclusion. ISFKPwith implantation of corneal ring segments has proven to be an effective method for correcting high order aberrations, which determines an increase in BCVA in patients with keratoconus stages I–II. Keywords: keratoconus; higher order aberrations; corneal segments; refractive surgery.

For vision correction, the key is to help patients achieve good visual performance. In most cases, this means good visual acuity and good contrast sensitivity. The ocular aberrations can be considered as a combination of the spherocylindrical aberrations and irregular aberrations. In wavefront optics terminology, they are called low-order and high-order aberrations, respectively. In general, the degradation of visual performance due to the low-order aberrations is much higher than that due to the high-order aberrations. Traditional vision correction thus focuses on the correction of low-order aberrations. However, to achieve a better standard of vision, it is not enough just to correct low-order aberrations. For example, professional shooting athletes and fighter pilots may seek supervision to enhance their performance. The correction of higher order aberrations, however, is not limited to these small groups. The average person may seek enhanced vision to provide a reserve for ageing vision or to eliminate night-vision problems, such as halos, glares, etc.

We propose an automatic high-order aberration correction method for digital holographic microscopy based on orthonormal polynomial fitting over an irregular-shaped aperture. The corner detection technique is used to detect the specimen-free area for orthonormal polynomials over an irregular-shaped aperture. The high-order aberration correction method is completely automatic and requires only a single hologram. Experiments showed that in aberration correction, both lower-order phase curvatures and high-order aberrations could be corrected without requiring extra devices. Numerical simulations show that the proposed method provides more accurate high-order aberration correction than aberration correction methods based on least squares fitting with standard polynomials. Experimental results demonstrate the feasibility of using the proposed method for analyzing human macrophage cells.

We have constructed a new version of retinal imaging system with chromatic aberration concerned and the correlated optical design presented in this article is based on the adaptive optics fundus camera modality. In our system, three typical wavelengths of 550nm, 650nm and 480nm were selected. Longitude chromatic aberration (LCA) was traded off to a minimum using ZEMAX program. The whole setup was actually evaluated on human subjects and retinal imaging was performed at continuous frame rates up to 20 Hz. Raw videos at parafovea locations were collected, and cone mosaics as well as retinal vasculature were clearly observed in one single clip. In addition, comparisons under different illumination conditions were also made to confirm our design. Image contrast and the Strehl ratio were effectively increased after dynamic correction of high order aberrations. This system is expected to bring new applications in functional imaging of human retina.

A compact mode-locked Ti:sapphire laser, emitting a broad spectrum of 277 nm bandwidth, centered at 790 nm, was used to measure the dependence of the aberrations of the human eye with wavelength in the near infrared region. The aberrations were systematically measured with a Hartmann-Shack wave-front sensor at the following wavelengths: 700, 730, 750, 780, 800, 850, 870 and 900 nm, in four normal subjects. During the measurements, the wavelengths were selected by using 10 nm band-pass filters. We found that monochromatic high order aberrations, beyond defocus, were nearly constant across 700 to 900 nm wavelength in the four subjects. The average chromatic difference in defocus was 0.4 diopters in the considered wavelength band. The predictions of a simple water-eye model were compared with the experimental results in the near infrared. These results have potential applications in those situations where defocus or higher order aberration correction in the near infrared is required. This is the case of many imaging techniques: scanning laser ophthalmoscope, flood illumination fundus camera, or optical coherence tomography.

The effects of higher-order ocular aberrations on functional visual performance were assessed for seven young healthy subjects, as a function of light level. Contrast acuity thresholds were measured for a functional vision test with and without correction of higher-order aberrations and at a number of different pupil sizes in three of the subjects investigated. A visual simulator incorporating an adaptive optics (AO) system was used for this purpose. The results show that when light level is decreased, the drop in neural contrast sensitivity limits the impact that increased optical degradations have on vision. The expected AO benefit for functional vision is given for scotopic, mesopic and photopic regimes.

Minimization of the emittance growth of multi-charge particle beams in the charge stripping section of RAON

The plenoptic wavefront sensor (PlWFS) has been proposed as being suitable for operating on extended objects in adaptive optics (AO) systems. We propose a new self-referencing method that uses the cell image of PlWFS as a correlation reference and enables the simultaneous measurement of high-order aberrations and tilt. Simulations have been performed for different operating conditions to verify the feasibility of the proposed method. These show that using the cell image results in better AO performance compared to existing reference generation techniques and allows stable wavefront tilt control with a small residual variance.

Correction and manipulation of peripheral refractive errors are indispensable for people with central vision loss and in optical interventions for myopia control. This study investigates further enhancements of peripheral vision by compensating for monochromatic higher-order aberrations (with an adaptive optics system) and chromatic aberrations (with a narrowband green filter, 550 nm) in the 20° nasal visual field. Both high-contrast detection cutoff and contrast sensitivity improved with optical correction. This improvement was most evident for gratings oriented perpendicular to the meridian due to asymmetric optical errors. When the natural monochromatic higher-order aberrations are large, resolution of 10% contrast oblique gratings can also be improved with correction of these errors. Though peripheral vision is mainly limited by refractive errors and neural factors, higher-order aberration correction beyond conventional refractive errors can still improve peripheral vision under certain circumstances.

Based on a binocular adaptive optics visual simulator, we investigated the effect of higher-order aberration correction on the temporal integration property of stereopsis. Stereo threshold for line stimuli, viewed in 550nm monochromatic light, was measured as a function of exposure duration, with higher-order aberrations uncorrected, binocularly corrected or monocularly corrected. Under all optical conditions, stereo threshold decreased with increasing exposure duration until a steady-state threshold was reached. The critical duration was determined by a quadratic summation model and the high goodness of fit suggested this model was reasonable. For normal subjects, the slope for stereo threshold versus exposure duration was about -0.5 on logarithmic coordinates, and the critical duration was about 200 ms. Both the slope and the critical duration were independent of the optical condition of the eye, showing no significant effect of higher-order aberration correction on the temporal integration property of stereopsis.

We use adaptive optics (AO) to study whether neural adaptation influences the amount of higher order aberration correction that produces the best subjective image quality. Three subjects performed two tasks, method of adjustment and matching, while viewing a monochromatic stimulus through the Rochester AO system. In both tasks, after correcting the subject's lower order aberrations with trial lenses, AO was used to modify the subject's higher order aberrations, multiplying it by a scaling factor between 1 and -1. In the adjustment task, subjects adjusted the scaling factor to find the best subjective image quality. In the matching task, subjects viewed the same stimulus sequentially blurred either by defocus or a scaled version of their own wave aberration, adjusting the defocus to match the blur corresponding to different scaled versions of their aberrations. Results from both tasks are consistent with a small amount of neural adaptation because the best subjective image quality occurred when some higher order aberrations were left uncorrected for all three subjects. Neural adaptation slightly modifies the best aberration correction, although this effect averaged only approximately 12% of complete adaptation. These results may have practical consequences for customized vision correction.

Kligman, Brad E. MD; Baartman, Brandon J. MD; Dupps, William J. Jr MD, PhD Author Information

A new technology of deformable mirror will be presented. Based on magnetic actuators, these deformable mirrors feature record strokes (more than +/- 45μm of astigmatism and focus correction) with an optimized temporal behavior. Furthermore, the development has been made in order to have a large density of actuators within a small clear aperture (typically 52 actuators within a diameter of 9.0mm). We will present the key benefits of this technology for vision science: simultaneous correction of low and high order aberrations, AO-SLO image without artifacts due to the membrane vibration, optimized control, etc. Using recent papers published by Doble, Thibos and Miller, we show the performances that can be achieved by various configurations using statistical approach. The typical distribution of wavefront aberrations (both the low order aberration (LOA) and high order aberration (HOA)) have been computed and the correction applied by the mirror. We compare two configurations of deformable mirrors (52 and 97 actuators) and highlight the influence of the number of actuators on the fitting error, the photon noise error and the effective bandwidth of correction.

To verify whether there exists any difference in higher order aberrations after undergoing myopic LASIK (laser in situ keratomileusis) with conventional ablation and customized ablation in different eyes of the same patient. This was a prospective randomized study of 54 myopic eyes (27 patients) that underwent LASIK using the Nidek EC-5000 excimer laser system (Nidek, Gamagori, Japan). Topography-guided customized aspheric treatment zone (CATz) was used in the first eye of the patient (study group) and the other eye of the same patient was operated on with conventional ablation (control group). Higher order aberrations [root-mean-square (RMS) in the 5-mm zone] of both groups were observed with the Nidek OPD-Scan aberrometer before and 3 months after LASIK. Preoperative mean refractive error was similar between two eyes of the same patient (t=-0.577, P>0.05). Preoperatively, higher order aberrations (RMS in the 5-mm zone) in the CATz ablation and conventional groups were (0.3600+/-0.0341) microm and (0.2680+/-0.1421) microm, respectively. This difference was not statistically significant (t=1.292, P>0.05). Three months after LASIK, higher order aberrations (RMS in 5-mm zone) in the CATz ablation and conventional groups were (0.3627+/-0.1510) microm and (0.3991+/-0.1582) microm, respectively. No statistically significant difference was noted between pre- and postoperative higher order aberrations in the CATz group (t=-0.047, P>0.05). However, a statistically significant increase in higher order aberrations was observed after conventional ablation (t=-5.261, P<0.05). A statistically significant difference was noted in the increase of higher order aberrations after LASIK between groups (t=-2.050, P=0.045). LASIK with conventional ablation and topography-guided CATz ablation resulted in the same BSCVA (best spectacle-corrected visual acuity) 3 month after LASIK. Higher order aberrations were increased, but the increase of higher order aberrations after customized ablation treatment was less than that after conventional ablation.

Purpose: The aim of this study was to evaluate the distribution of wavefront aberrations in Indian children with refractive errors and to determine the correlation between the degree of refractive error and aberration. Materials and Methods: A prospective study was conducted on 216 eyes of 108 consecutive children attending the outpatient clinic. Based on refractive error, the children were allocated to five groups: “Emmetropic,” “hyperopic,” “simple astigmatism,” “compound astigmatism,” and “myopic” group. Lower order aberrations (LOAs) and higher order aberrations (HOAs) were analyzed within and between the groups. Results: Mean age of the children was 10.9 years. Of the total 216 eyes, 40 eyes had emmetropia, 52 had simple astigmatism, 54 had compound astigmatism, 43 had myopia, and 27 had hyperopia. In all the groups, increase in spherical equivalent was associated with increase in LOAs of defocus and astigmatism and the root mean square (RMS) of total HOAs. In comparison with the “emmetropic” group, all other groups showed a significant increase in LOAs (P < 0.001) and RMS of total HOAs (P < 0.001), with the “compound astigmatism” group showing higher values. Spherical aberrations were found to be associated with simple astigmatism, compound astigmatism (P = 0.008), and myopia (P = 0.041). Statistical analysis was done using analysis of variance applying Bonferroni correction factor and Pearson's correlation coefficient. Conclusions: Ametropic eyes are associated with HOAs. Indian children were found to have higher values of aberrations when compared to other races. Practitioners may need to factor this while treating children for refractive errors.