Correction Of Higher-order Aberrations Research Articles

Интрастромальная фемтокератопластика с имплантацией роговичных сегментов в коррекции аберраций высшего порядка у пациентов с кератоконусом

Aim. To evaluate the potential of femtosecond laser assisted intrastromal keratoplasty (FLAIK) with implantation of corneal ring segments in the correction of higher order aberrations in patients with stage I–II keratoconus. Material and methods. 15 patients (14 men and 1 woman) were examined and treated surgically, in total of 17 eyes, with stage I and II keratoconus (according to the classification of Izmailova S.B., 2014). All patients underwent FLAIK with implantation of corneal ring segments. Results. The change in the estimated parameters at an average follow-up period of 4.7 months showed that after FLAIK with implantation of corneal ring segments, best corrected visual acuity increased statistically significantly (p < 0.05) in all cases and increased by an average of 0.29 ± 0.09. In addition, there was a statistically significant (p < 0.05) decrease in the total level of higher order aberrations by 1.5 times (by 0.69 ± 0.4 D), a decrease in the level of coma aberration by 1.7 times (by 0.74 ± 0.4 D), a decrease in the level of spherical aberration by 1.6 times (by 0.07 ± 0.12 D). Conclusions. FLAIK with implantation of corneal ring segments is an effective method for correcting higher-order aberrations in patients with keratoconus of stage I–II. FLAIK with keratoconus with implantation of corneal ring segments makes it possible to achieve a significant increase in BCVA in patients with stage I–II keratoconus. Key words: keratoconus, higher order aberrations, corneal segments, refractive surgery

High-resolution cryo-EM performance comparison of two latest-generation cryo electron microscopes on the human ribosome

Recent technological advances in cryo electron microscopy (cryo-EM) have led to new opportunities in the structural biology field. Here we benchmark the performance of two 300 kV latest-generation cryo electron microscopes, Titan Krios G4 from Thermofisher Scientific and CRYO ARM 300 from Jeol, with regards to achieving high resolution single particle reconstructions on a real case sample. We compare potentially limiting factors such as drift rates, astigmatism & coma aberrations and performance during image processing and show that both microscopes, while comprising rather different technical setups & parameter settings and equipped with different types of energy filters & cameras, achieve a resolution of around 2 Å on the human ribosome, a non-symmetric object which constitutes a key drug target. Astigmatism correction, CTF refinement and correction of higher order aberrations through refinement in separate optics groups helped to account for astigmatism/coma caused by beam tilting during multi-spot and multi-hole acquisition in neighbouring holes without stage movement. The obtained maps resolve Mg2+ ions, water molecules, inhibitors and side-chains including chemical modifications. The fact that both instruments can resolve such detailed features will greatly facilitate understanding molecular mechanisms of various targets and helps in cryo-EM structure based drug design. The methods and analysis tools used here will be useful also to characterize existing instruments and optimize data acquisition settings and are applicable broadly to other drug targets in structural biology.

Apparatus and its principle for thermal aberration compensation.

Thermal aberrations caused by absorption of laser beams degrade the image quality of exposure tools during the working process. Many compensators, such as lens movement or lens deformation, are used to compensate for low-order thermal aberrations of optical systems. In this paper, an apparatus with higher-order aberration correction capability is presented. The main principle of the apparatus is to actively heat and cool the lens near the pupil to generate a desired temperature profile to compensate for thermal aberrations. We first introduce the basic concept of the apparatus. Then we establish an analytical model to describe the lens temperature of the apparatus based on its working principle and demonstrate its compensation capability. Finally, an algorithm for dynamic thermal aberrations compensation is proposed to overcome the time lag effects of a thermally controlled lens.

Global tip-tilt and high-order aberration correction with plenoptic wavefront sensors in closed-loop AO systems.

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.

Perceptual impact of astigmatism induction in presbyopes

We investigated the effect of induced astigmatism on subjective best focus and on visual acuity in 28 subjects of different ages (pre-presbyopic and presbyopic) and with different refractive profiles (emmetropes and astigmats). Measurements were performed using a custom-developed Adaptive Optics system, which allowed correction of high order aberrations and induction of astigmatism (0.5, 1, 1.5 and 2.0 D; axis: 180°, 45° and 22.5°). Upon induction of astigmatism, best focus shifted towards negative values in pre-presbyopic emmetropic eyes (by −0.14 D for 0.5 D and by −0.33 D for 2.0 D), while it shifted towards positive values in presbyopes, both in emmetropic presbyopes (by +0.04 D for 0.50 D and by +0.16 D for 2.0 D) and in astigmatic presbyopes (by +0.23 D for 0.50 D and by +0.40 D for 2.0 D). Also, visual acuity was most sensitive to astigmatism induction in pre-presbyopic emmetropes and least sensitive in presbyopes, particularly when high order aberrations were corrected: visual acuity ratio with/without astigmatism was: 0.74/0.85/0.98 (for astigmatism induced at 180°) and 0.68/0.73/0.86 at 45°, for pre-presbyopic emmetropes/presbyopic emmetropes/presbyopic astigmats. These findings may be connected to long term exposure to astigmatism in astigmats and corrected presbyopes.

Automatic high order aberrations correction for digital holographic microscopy based on orthonormal polynomials fitting over irregular shaped aperture

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.

Peripheral resolution and contrast sensitivity: effects of monochromatic and chromatic aberrations.

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.

Optimization-based real-time open-loop control of an optofluidic refractive phase modulator.

We present a novel open-loop control method for an electrostatically actuated optofluidic refractive phase modulator, and demonstrate its performance for high-order aberration correction. Contrary to conventional electrostatic deformable mirrors, an optofluidic modulator is capable of bidirectional (push-pull) actuation through hydro-mechanical coupling. Control methods based on matrix pseudo-inversion, the common approach used for deformable mirrors, thus perform sub-optimally for such a device. Instead, we formulate the task of finding driving voltages for a given desired wavefront shape as an optimization problem with inequality constraints that can be solved using an interior-point method in real time. We show that this optimization problem is a convex one and that its solution represents a global minimum in residual wavefront error. We use the new method to control both the refractive phase modulator and a conventional electrostatic deformable mirror, and experimentally demonstrate improved correction fidelity for both.

Effects of Illumination-Dependent Pupil Size on Higher Order Aberration

Purpose : We investigated the effect of illumination-dependent pupil size on higher order aberration. Methods : Thirty five patients (mean age, 22.5 ± 1.04 years) who had no ocular or systemic disease and had no other relevant surgical experience were selected, and we measured aberration. Due to the property of i.Profiler plus instrument, it is assumed that the pupil size ʻ3 mmʼ under photopic vision is similar to photopic vision environment and pupil size ʻmaximumʼ under semidark room is similar to mesopic vision environment. Correlation analysis between pupil size and equivalent defocus and equivalent blur circle was performed. Results : RMS values were 0.30±0.13 ㎛ and 0.38±0.15 ㎛ when the pupil size was divided into 3 mm and maximum. The equivalent defocus of total high order aberration was 0.28±0.14 D at the pupil size of 3 mm and 0.41±0.16 D at the maximum, which are significant differences(p=0.000). The difference of equivalent defocus of spherical aberration, coma aberration, and trefoil aberration was 0.07 D, 0.04 D, and 0.02 D at 3 mm and maximum, respectively, and there were significant differences in the spherical(p=0.000) and coma aberration(p=0.000)). There were significant positive correlations between equivalent defocus and equivalent blur circle(total higher order aberrations (R2=0.7045, p < 0.01), spherical aberration(R2=0.9376, p < 0.01), coma aberration(R2=0.8429, p < 0.01) and, trefoil aberration(R2=0.7824, p < 0.01)). Conclusions : The result of the aberration measurement is expressed as equivalent defocus, so that the degree of required correction can be expressed as diopter. Unless the correction of high order aberrations is considered, it is valuable to study the visual discomfort of high order aberrations as there would be a change in the corrected visual acuity.

The effect of soft contact lens thickness in visual function after intracorneal ring segments surgery.

To study the influence of soft contact lens (SCL) central thickness and material in keratoconus on visual function after intracorneal ring segment (ICRS) surgery. A pilot, experimental, prospective, cross-sectional and double-blind study was performed. Fourteen keratoconus patients with age range of 34.75±9.22years (7 males and 7 females) with ICRS implanted were involved in the study. Two different SCL materials [Hioxifilcon A (G-5X/p-GMA/HEMA) and Lucifilcon A (silicone-hydrogel)] with four different central thicknesses (0.1, 0.2, 0.3 and 0.4mm) were fitted in one eye per patient, selected randomly. High and low corrected distance visual acuity (CDVA) and contrast sensitivity (CS), corneal topography and corneal and total aberrometry were measured. Corneal spherical like, coma like and root mean square (RMS) decreased significantly for 0.3 and 0.4mm in both SCL materials (p<0.05). Total RMS decreased significantly for 0.4mm with both SCL materials (p<0.05). High and low CDVA improved for 0.4mm of thickness for both materials (p<0.05). Statistically increasing were found in all thicknesses studied for CS in both materials (p<0.05). A central thickness of the SCL equal or superior to 0.4mm seems to decrease the ocular high order aberration (HOA) and to improve the visual function in keratoconus patients implanted with ICRS. However, the modulus of rigidity of the SCL would not influence the HOA correction.

Wavefront-Customized Soft Contact Lenses for High-Order Aberration Correction in Normal Eyes

Wavefront-Customized Soft Contact Lenses for High-Order Aberration Correction in Normal Eyes

Visual Performance and Optical Quality of Standardized Asymmetric Soft Contact Lenses in Patients With Keratoconus.

To evaluate the visual performance and optical quality of a standardized asymmetric soft contact lens (SCL) used for correction of higher-order aberrations (HOAs) in eyes with keratoconus. We included 30 eyes (26 patients) with keratoconus (average K: 45.7 ± 2.3 diopters [D]). The patients were subjected to corneal tomography, aberrometry, measurements of manifest refraction and visual acuity (VA), and visual analog scale (VAS) assessments. The study lenses were made using a molding method and consisted of six standardized types, in which an asymmetric power distribution of approximately 2 to 12 D (2-D step) was used to correct HOAs. The lens type suitable for each eye was selected based on the corneal tomography and aberrometry data. The on-eye performance of the lens was evaluated using aberrometry (4-mm pupil), over refraction, VA, and VAS. The standardized asymmetric SCL improved the best spectacle-corrected VA from -0.07 ± 0.09 to -0.11 ± 0.08 logMAR (P < 0.05) and the mean VAS score from 66.2 ± 21.8 to 75.4 ± 20.5 (P < 0.05). Vertical coma decreased significantly (-0.50 ± 0.36 μm without SCL; -0.36 ± 0.34 μm with SCL; P < 0.01). In subgroup analysis, subjects in the high VAS group (score ≥ 75) accounted for 70% of all subjects, and this was the group in which the vertical coma decreased significantly from the level without the lens. A standardized asymmetric SCL can reduce HOAs and improve vision quality when compared with spectacles in patients with keratoconus who wear rigid gas-permeable lenses.

Training to improve contrast sensitivity in amblyopia: correction of high-order aberrations

Perceptual learning is considered a potential treatment for amblyopia even in adult patients who have progressed beyond the critical period of visual development because adult amblyopes retain sufficient visual plasticity. When perceptual learning is performed with the correction of high-order aberrations (HOAs), a greater degree of neural plasticity is present in normal adults and those with highly aberrated keratoconic eyes. Because amblyopic eyes show more severe HOAs than normal eyes, it is interesting to study the effects of HOA-corrected visual perceptual learning in amblyopia. In the present study, we trained twenty-six older child and adult anisometropic amblyopes while their HOAs were corrected using a real-time closed-loop adaptive optics perceptual learning system (AOPL). We found that adaptive optics (AO) correction improved the modulation transfer functions (MTFs) and contrast sensitivity functions (CSFs) of older children and adults with anisometropic amblyopia. When perceptual learning was performed with AO correction of the ocular HOAs, the improvements in visual function were not only demonstrated in the condition with AO correction but were also maintained in the condition without AO correction. Additionally, the learning effect with AO correction was transferred to the untrained visual acuity and fellow eyes in the condition without AO correction.

Effect of scanning beam size on the lateral resolution of mouse retinal imaging with SLO.

Scanning laser ophthalmoscopy (SLO) employs the eye's optics as a microscope objective for retinal imaging in vivo. The mouse retina has become an increasingly important object for investigation of ocular disease and physiology with optogenetic probes. SLO imaging of the mouse eye, in principle, can achieve submicron lateral resolution thanks to a numerical aperture (NA) of ∼0.5, about 2.5 times larger than that of the human eye. In the absence of adaptive optics, however, natural ocular aberrations limit the available optical resolution. The use of a contact lens, in principle, can correct many aberrations, permitting the use of a wider scanning beam and, thus, achieving greater resolution then would otherwise be possible. In this Letter, using an SLO equipped with a rigid contact lens, we report the effect of scanning beam size on the lateral resolution of mouse retinal imaging. Theory predicts that the maximum beam size full width at half-maximum (FWHM) that can be used without any deteriorating effects of aberrations is ∼0.6 mm. However, increasing the beam size up to the diameter of the dilated pupil is predicted to improve lateral resolution, though not to the diffraction limit. To test these predictions, the dendrites of a retinal ganglion cell expressing YFP were imaged, and transverse scans were analyzed to quantify the SLO system resolution. The results confirmed that lateral resolution increases with the beam size as predicted. With a 1.3mm scanning beam and no high-order aberration correction, the lateral resolution is ∼1.15 μm, superior to that achievable by most human AO-SLO systems. Advantages of this approach include stabilization of the mouse eye and simplified optical design.

Temporal integration property of stereopsis after higher-order aberration correction

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.

Lateral resolution enhancement using programmable phase modulator in optical coherence tomography.

Adaptive optics plays an important role in the correction of high-order aberrations to enhance lateral resolution. An OCT system coupled with a programmable phase modulator is designed to verify lateral resolution improvement. The Hamamatsu high-resolution, non-pixelized, optically addressed light modulator (PAL-SLM) PPM X7550 series is used to correct aberrations, utilizing a simple method based on phase information from OCT images. The advantages of this method are its high simplicity and low cost. A raster scanning technique is adopted to scan samples covered with scattering suspension. Metal lines covered with scattering suspension are imaged, and a respective correction is applied to remove the aberration. Results demonstrate an improvement in lateral resolution on metal grid samples.

Effects of higher-order aberration correction on stereopsis at different viewing durations.

To better understand how the eye's optics affects stereopsis, we measured stereoacuity before and after higher-order aberration (HOA) correction with a binocular adaptive optics visual simulator. The HOAs were corrected either binocularly or monocularly in the better eye (the eye with better contrast sensitivity). A two-line stereo pattern served as the visual stimulus. Stereo thresholds at different viewing durations were obtained with the psychophysical method of constant stimuli. Binocular HOA correction led to significant improvement in stereoacuity. However, better eye HOA correction could bring either a bad degradation or a slight improvement in stereoacuity. As viewing duration increased, the stereo benefit approached the level of 1.0 for both binocular and better eye correction, suggesting that long viewing durations might weaken the effects of the eye's optical quality on stereopsis.

Extremely high-power CO2 laser beam correction.

This paper presents the results of high-power CO2 laser-aberration correction and jitter stabilization. A bimorph deformable mirror and two tip-tilt piezo correctors were used as executive elements. Two types of wavefront sensors, one Hartmann to measure higher-order aberrations (defocus, astigmatism etc.) based on an uncooled microbolometer long-wave infrared camera and the other a tip-tilt one based on the technology of obliquely sputtered, thin chromium films on Si substrates, were applied to measure wavefront aberrations. We discuss both positive and negative attributes of suggested wavefront sensors. The adaptive system is allowed to reduce aberrations of incoming laser radiation by seven times peak-to-valley and to stabilize the jitter of incoming beams up to 25 μrad at a speed of 100 Hz. The adaptive system frequency range for high-order aberration correction was 50 Hz.

Improvement of Optics, Mechanics and the Usability of a Mechanical Eye Model for Vision Quality Evaluation of IOLs.

Cataract surgeries are one of the most frequent medical interventions with more than 11 million surgeries per year. During the surgery the clouded human lens is extracted and an artificial lens - the intraocular lens (IOL) - is implanted into the affected eye. Nowadays IOLs with different optical properties such as monofocal, bifocal or multifocal lenses are used for implantation. The postoperative lens position is influenced by healing processes resulting into shifts and tilts of the IOL that finally affect the refractive outcome. New IOL designs allow also the correction of high order aberrations and presbyopia. To fulfil the requirements of more sophisticated IOLs a closer investigation of the positioning sensitivity is necessary. A mechanical eye model was implemented for testing different types of IOLs under physiological conditions. New measurement setups are presented to get more detailed information about optical quality criteria such as the modulation transfer function (MTF), point spread function (PSF) and Strehl ratio. Additionally image quality is evaluated by the determination of the Zernike coefficients and the patients’ physiological impression of vision.

Binocular visual performance with aberration correction as a function of light level.

The extent to which monocular visual performance of subjects with normal amounts of ocular aberrations can be improved with adaptive optics (AO) depends on both the pupil diameter and the luminance for visual testing. Here, the benefit of correction of higher order aberrations for binocular visual performance was assessed over a range of luminances for natural light-adapted pupil sizes with a binocular AO visual simulator. Results show that binocular aberration correction benefits for visual acuity and contrast sensitivity increase with decreasing luminances. Also, the advantage of binocular over monocular viewing increases when visual acuity becomes worse. The findings suggest that binocular summation mitigates poor visual performance under low luminance conditions.