Aberrations Of Eye Research Articles

Initial Outcomes with Customized Myopic LASIK, Guided by Automated Ray Tracing Optimization: A Novel Technique.

PurposeSafety and efficacy of a novel automated ray tracing optimization in customization of excimer ablation in myopic LASIK.MethodsIn a consecutive case series, 25 patients (50 eyes) undergoing femtosecond-laser-assisted myopic LASIK were evaluated. The novel, artificial-intelligence platform initially calculates the ablation profile based on a model eye for each case, based on interferometry axial length data. Low- and high-order aberration calculation is performed by raytracing based on wavefront and Scheimpflug tomography measurements, all from a single diagnostic device. Visual acuity, refractive error, keratometry, topography, high-order aberrations and contrast sensitivity were evaluated, over six months follow-up.ResultsChange from pre- to 6 months post-operative: mean refractive error improved from −5.06 ± 2.54 diopters (D) (range −8.0 to −0.50 D) to −0.11 ± 0.09 D (range −0.25 to + 0.25); refractive astigmatism from −1.07 ± 0.91 D (range −4.25 to 0 D) to −0.15 ± 0.04 D (range −0.25 to 0); and topographic astigmatism from −1.65 ± 0.85 D to −0.26 ± 0.11 D (range −0.60 to 0). About 65% of eyes gained one line of vision and 38% 2 lines. Pre- to post-operative high-order aberration average: RMSh changed from 0.25 um to 0.35 um. Contrast sensitivity improved post-operatively.ConclusionWe report safe and effective preliminary outcomes with a novel excimer laser customization by ray tracing optimization, for myopic LASIK treatments, employing several independent up-till-now diagnostics and a customized eye model reference for each case. It bears the potential advantage through total eye aberration data and ray tracing refraction calculation to offer improved and more predictable visual outcomes.

Eyes of Aniso-Axial Length Individuals Share Generally Similar Corneal Biometrics with Normal Eyes in Cataract Population.

Aims To determine the characteristics of corneal biometrics in eyes from aniso-axial length cataract patients compared with eyes from non-aniso-axial length individuals. Methods This is a retrospective case series. Cataract patients with preoperative binocular measurements were recruited. A binocular axial difference of ≥1 mm was considered to indicate aniso-axial length. The anterior segmental biometrics were measured using Pentacam HR (Oculus, Wetzlar, Germany) and IOLMaster 500 (Carl Zeiss Meditec, Jena, Germany). Comparisons of biometrics were made among 4 eye conditions: the longer eyes from aniso-axial length patients, the shorter eyes from aniso-axial length patients, the longer eyes from non-aniso-axial length patients, and the shorter eyes from non-aniso-axial length patients. The aniso-axial length eyes were also stratified into 8 subgroups with axial length (AL) increments of 1 mm, and the biometrics of the subgroups were compared. Results There was smaller anterior corneal astigmatism in the shorter aniso-axial length group than those in the longer aniso-axial length group (1.01 ± 0.70 D vs 1.12 ± 0.76 D, P=0.031). The longer aniso-axial length eyes had greater anterior corneal steep curvature (44.13 ± 1.69 D vs 43.87 ± 1.69 D, P=0.009) and anterior corneal astigmatism (1.12 ± 0.76 D vs 1.02 ± 0.69 D, P=0.023) compared with longer non-aniso-axial length subjects. Other corneal biometrics were similar between the aniso-axial length eyes and the non-aniso-axial length eyes. In the longer aniso-axial length group, the posterior corneal aberrations of eyes in the ≥5 mm subgroups were greater than those in the <5 mm subgroups (0.879 ± 0.183 μm vs 0.768 ± 0.178 μm for total aberrations, P < 0.001; 0.228 ± 0.086 μm vs 0.196 ± 0.043 μm for high-order aberrations, P=0.036; 0.847 ± 0.173 μm vs 0.741 ± 0.179 μm for low-order aberrations, P=0.001). Conclusion Eyes of aniso-axial length individuals share generally similar corneal biometrics with normal eyes in cataract population. Anterior corneal astigmatism of the longer eyes from the aniso-axial length cataract patients was higher than that of the longer eyes from the non-aniso-axial length individuals. Total posterior corneal aberrations of the longer aniso-axial length eyes increased when the binocular axial difference was over 5 mm.

Design of a human eye retinal camera optical system with dual-wavelength coaxial astigmatism correction

In order to better improve vision, an accurate measurement of the aberrations in the human eye has important experimental and clinical significance. An adaptive fundus camera that uses a double-column lens to correct human astigmatism is designed. In the illumination system, ring light generated by a pair of axicon lenses is used to illuminate the human eye, abandoning the traditional illumination method. In the target adjustment system, a simple real image is set, the plane mirror group and the double cylinder lens are adjusted, and the defocus and astigmatism of the human eye are corrected, so that the residual aberration of the human eye is controlled within the correction range of the adaptive imaging system. In the adaptive imaging system, a Shack–Hartmann wavefront sensor is used as a wavefront detector, and a liquid crystal spatial light modulator is used as a wavefront corrector to correct the high-order aberrations of the human eye. The lighting system and imaging system operate in different bands. The simulation results show that the illumination light path avoids the strongly reflected light of the cornea and can uniformly illuminate the human eye. The design of the adaptive imaging system achieves the diffraction limit, and the astigmatism is corrected by a cylindrical lens in the imaging system. Additional aberrations are generated, and the plane mirror is adjusted to adjust the optical path to accommodate human eyes with different diopters.

Optical Aberrations of Guinea Pig Eyes.

PurposeThe guinea pig is widely used in studies of refractive error development and myopia which often involve experimental optical manipulations. The study described here investigated the optical quality of the guinea pig eye, for which there are limited data, despite its fundamental importance to understanding visually guided eye growth.MethodsThe ocular aberrations of eight adolescent New Zealand pigmented guinea pigs (6–11 weeks old) were measured after cycloplegia using a custom-built Shack–Hartmann aberrometer and fit with a Zernike polynomial function to the 10th order (65 terms). The optical quality of their eyes was assessed in terms of individual Zernike coefficients, and data were further analyzed to derive root-mean-square (RMS) wavefront errors, modulation transfer functions (MTFs), point spread functions (PSFs), Strehl ratios, and depth of focus. A 4-mm pupil was used in all computations. The derived data are compared with equivalent data from normal young adult human eyes.ResultsThe guinea pigs exhibited low hyperopia and a small amount of positive spherical aberration, with other aberration terms decreasing with increasing order. Their average depth of focus, estimated from through-focus modulation, was 3.75 diopters. The RMS wavefront error of the guinea pig eye was found to be larger than that of the human eye for the same pupil size, reflecting a higher degree of aberrations, although the PSF (area) on the retina was smaller and sharper due to its shorter focal length. The radial average best-focus MTF derived for the guinea pig eye showed good performance at very low spatial frequencies, with a steeper decline with increasing frequency than for the human eye, dropping below 0.3 at 9 cpd. When converted to linear units (cycles/mm), the guinea pig eye had a higher spatial frequency cutoff and a slight contrast advantage for low spatial frequencies compared to the human eye.ConclusionsThe optical quality of the guinea pig eye is far superior to their reported behavioral visual acuity. This implies a neuroanatomical limit to their vision, which contrasts with the close match of optical and neural limits to spatial resolution in human eyes. The significance for eye growth regulation of the relative optical advantages exhibited by guinea pig eyes, when optical quality is expressed in linear rather than angular retinal units, warrants further consideration.

Corneal higher-order aberrations in phlyctenular keratitis.

To characterize tomographic patterns and quantify corneal higher-order aberrations (HOAs) in eyes with corneal scar due to phlyctenular keratitis. Retrospective consecutive case series. This study included 51 eyes of 38 patients (24 women; 14 men) with corneal scar due to phlyctenular keratitis. HOAs of the total cornea, and of the anterior and posterior surfaces were measured using anterior segment optical coherence tomography (AS-OCT). Corneal tomographic patterns were classified into five types: increased regular astigmatism, ectasia, asymmetric, flattening and minimal change patterns. The correlation between corneal HOAs and visual acuity was evaluated. Mean months from onset was 50.7 ± 74.7 and mean number of recurrences 2.1 ± 1.1 (1-5). Mean logarithm of the minimal angle of resolution (logMAR) was 0.19 ± 0.31. AS-OCT showed ectasia pattern in 16 eyes (31.4%), asymmetric pattern in 12 eyes (23.5%), increased regular astigmatism pattern in 9 eyes (17.6%), flattening pattern in 3 eyes (5.9%) and minimal change pattern in 11 eyes (21.6%). HOAs of the total cornea were 0.57 ± 0.44μm and 1.16 ± 0.77μm within a 4-mm and 6-mm diameter, significantly larger than in normal controls (P < 0.0001). LogMAR visual acuity was significantly correlated with corneal HOAs (4-mm: r = 0.558, P < 0.0001, 6-mm: r = 0.566, P < 0.0001), central corneal thickness (r = - 0.349, P = 0.016), and corneal astigmatism (r = 0.414, P = 0.004), but not with average keratometric value (r = - 0.092, P = 0.537). The most common tomographic pattern was ectasia, followed by a asymmetric pattern in eyes with phlyctenular keratitis. Corneal HOAs were associated with decreased visual acuity in phlyctenular keratitis patients.

Wavefront coding with Jacobi-Fourier phase masks for retinal imaging.

Wavefront coding is a technique that combines optical phase elements and digital signal processing in order to increase the effective depth of focus of optical systems. The success of wavefront coding lies in the design of a suitable phase mask placed at the system's aperture. This element allows for image formation invariant under the effects of different second-order optical aberrations. In optical systems limited by temporally or spatially varying high-order aberrations, the use of wavefront coding has not been fully demonstrated. Here we propose the choice of Jacobi-Fourier shaped phase masks to produce sharp and clear retinal images of living eyes. To demonstrate the potential use of the technique, we analyze the performance of the Jacobi-Fourier phase masks through experimental simulations to alleviate aberrations for different eye aberrations. We will show that the best mask choice is robust to noise while keeping acceptable resolution and reducing image artefacts.

Impact of asteroid hyalosis on internal higher-order aberrations in eyes with cataract accompanied by acoustic shadows on swept-source optical coherence tomography examination.

Increased internal higher-order aberrations (HOAs) have been reported in eyes with asteroid hyalosis, which is usually asymptomatic. This report describes 2 patients with cataract and concurrent asteroid hyalosis. In the first case, internal HOAs were within the normal range, and swept-source optical coherence tomography (SS-OCT) did not show acoustic shadows. After cataract surgery, visual acuity improved and internal HOAs remained within normal limits. However, in the second case, SS-OCT revealed multiple acoustic shadows, presumably due to asteroid hyalosis, and internal HOAs increased in both eyes. After combined vitrectomy and cataract surgery, visual acuity and the internal HOA values improved in both eyes, and acoustic shadows disappeared on SS-OCT. Phacovitrectomy should be considered if the cause of visual impairment is cataract and asteroid hyalosis. Objective assessment of internal HOAs by a wavefront sensor and checking for acoustic shadows on SS-OCT might be useful in detecting this combination of ophthalmic conditions.

Profiles of intraocular higher-order aberrations in healthy phakic eyes: prospective cross-sectional study.

Ocular wavefront aberration is a crucial optical factor affecting retinal imaging. Internal aberrations contributed to compensation mechanism of ocular aberration. However, previous studies mainly focused on total and corneal higher order aberrations, and little is known about the profile of internal HOA (IHOA) in healthy subjects. Participants with healthy crystalline lenses were prospective enrolled. The root mean square (RMS) of IHOAs for a pupil diameter of 4 mm were measured with an iTrace aberrometer. Lenticular parameters were measured with a swept source anterior segment optical coherence tomography (AS-OCT). Regression analyses were used to determine factors associated with logarithmic IHOAs. Sixty-six Chinese participants (132 eyes) ranging from 5 to 59 years were analyzed. Logarithmic IHOA was positively associated with axial length (AL) (coefficient =0.101, P=0.016), and negatively associated with ocular refraction (coefficient =-0.032, P=0.023). Logarithmic internal coma increased by 0.161/mm (P=0.016) as AL became longer and decreased by 0.081/diopter (P<0.001) as ocular refraction became hyperopic. Lens tilt (coefficient =-0.121, P=0.037), decentration (coefficient= 3.027, P=0.003), and radius of anterior lens surface curvature (RAL) (coefficient= 0.096, P=0.026) were associated with logarithmic internal trefoil. lens tilt was also associated with logarithmic internal spherical aberration (coefficient =-0.195, P=0.018) and second astigmatism (coefficient =-0.132, P=0.030). Binocularly, the extent of coma, trefoil was different, while that of spherical aberration, secondary astigmatism was consistent. The vectors of the same type of IHOAs were nearly paralleled. IHOAs are mainly affected by ocular refraction, RAL, lens tilt and decentration. Intraocular differences and directions of higher-order aberrations follow certain rules, and their effects on visual function warrant further study.

Measurement of the peripheral aberrations of human eyes: A comprehensive review

It has been nearly 50 years since the first glimpse of the relationship between myopia and peripheral refractive errors. According to experiments on both animals and humans, the eyes with hyperopic peripheral vision appear to be at higher risk of developing myopia than those with myopic peripheral refractive errors. Despite the first measurement of peripheral refraction being achieved by a modified manual optometer, the concept of emmetropization triggered a rapidly increasing number of studies on peripheral aberrations. Not only the horizontal off-axis aberrations but also the meridional aberrations at different angles are measured by researchers during the development of peripheral aberrations measuring techniques. According to the differences among the working principles, a variety of techniques have been adopted for performing such measurements. The methods developed to realize the high-performance measurement involve the subject cooperating actively by rotating the head or eyes, the rotation of the whole optical path, and the combination of measurements of many light paths. This paper provides a review of the peripheral aberrations measuring techniques and their current status. This article also highlights the development trend of the measuring techniques of peripheral aberrations and practical applications of peripheral aberration measurements, such as the control of the accommodation, the measuring time, and the dynamic range problem of the wavefront sensor. Although wavefront sensing peripheral measurement is widely recognized for its capability to reveal both lower-order aberrations and higher-order aberrations, the efficiency of an autorefractometer is incomparable. The current study reveals that the most widely used peripheral aberration measurement methods are the use of an open field autorefractometer and Hartman-shack wavefront sensor-based techniques.

Redefining vision assessment.

This review outlines ophthalmic diagnostic systems, which objectively evaluates the human visual system and its potential beyond that of Snellen acuity. Advances in ophthalmic diagnostic systems have allowed for a deeper understanding of the optical principles of the human eye and have created the opportunity to evolve our current standards of vision assessment beyond Snellen acuity charts. Definitive comparative and validation trials will continue to be necessary in order for these advanced diagnostics to gain more widespread acceptance in the specialty, in addition to providing the guidance on the specific indications and utilities. Advancements in wavefront analysis, light scatter measurements, and adaptive optics technologies can provide greater insight into an individual optical system's potential and irregularities. Modalities that test for anterior corneal surface and whole eye aberrations, light scatter and contrast sensitivity can be an excellent educational tool for our patients to help them better understand their visual dysfunction and can prove useful for medical or surgical decision-making.

Comparison of wavefront aberrations in eyes with multifocal and monofocal iols before and after Nd:YAG laser capsulotomy for posterior capsule opacification.

The aim of this study was to compare wavefront aberrations before and after Nd:YAG capsulotomy in multifocal intraocular lens (MfIOL) and monofocal (MoIOL) pseudophakic eyes with posterior capsule opacification (PCO). Wavefront aberrations were measured using a ARK-10000 topographer before and after Nd:YAG capsulotomy in eyes that underwent MfIOL or MoIOL implantation and developed PCO. Total and higher-order aberrations (HOAs) values were evaluated as root mean square (RMS). The study included 64 eyes with MfIOLs (64 patients) and 72 with MoIOLs (72 patients) that developed PCO. Total RMS values before and 1month after Nd:YAG capsulotomy were 0.863 ± 0.27 and 0.504 ± 0.24 in the MFIOL group and 0.862 ± 0.31 and 0.466 ± 0.26 in the MoIOL group, respectively. Total RMS values did not differ significantly between the groups before (p = 0.914) or 1month after Nd:YAG laser capsulotomy (p = 0.357), but decreased significantly after Nd:YAG capsulotomy compared to baseline in both the MfIOL (p = 0.027) and MoIOL (p = 0.012) groups. HOA values before and 1month after Nd:YAG capsulotomy were 0.546 ± 0.23 and 0.364 ± 0.19 in the MfIOL group and 0.500 ± 0.21 and 0.346 ± 0.18 in the MoIOL group, respectively. HOA values did not differ significantly before (p = 0.828) or after Nd:YAG capsulotomy (p = 0.111), while both groups showed significant reduction in HOAs after Nd:YAG capsulotomy (MfIOL: p = 0.021, MoIOL: p = 0.027). Nd:YAG capsulotomy reduces total and HOAs to the same extent in eyes with both MfIOLs and MoIOLs, with no significant impact of the IOL design.

The Influence of Decentration on Higher-Order Aberrations in Artisan Aphakic Intraocular Lens Implantation Eyes.

Purpose To characterize the influence of decentration on higher-order aberrations of Artisan aphakic intraocular lens implantation eyes. Setting. Department of Ophthalmology and Vision Science, Eye and ENT Hospital of Fudan University, Shanghai, China. Design Retrospective case series. Methods Twenty-three eyes of 18 patients were retrospectively examined. Location of the IOL was imaged using a slit-lamp, and decentration (the distance from the center of a pupil to the geometric center of the IOL) was measured using the AutoCAD 2007 software. Ocular and internal higher-order aberrations were measured using the wavefront analyzer KR-1W (Topcon) and their correlation with decentration were analyzed. Coma, spherical, 3rd-, 4th-order, trefoil, tetrafoil aberrations, ocular, and internal higher-order aberrations were calculated for a 4.0 mm pupil diameter. Results The mean age of patients was 33.6 ± 21.4 years (ranging from 7 to 72 years). The mean follow-up period was 28.2 ± 10.5 months (ranging from 12 to 52 months). The mean postoperative best-corrected visual acuity (BCVA) was 0.19 ± 0.19 logMAR (range −0.18–0.52). The mean decentration was 0.57 ± 0.28 mm (range 0.15–1.21 mm). There was no correlation between Artisan IOL decentration and ocular higher-order aberrations, internal higher-order aberrations, coma, spherical, 3rd-, 4th-order, trefoil, and tetrafoil aberrations, respectively. There was a positive correlation between Artisan IOL decentration and 2nd-astig aberrations when 2nd-astig aberrations were less than 0.1. Conclusions The position of Artisan IOLs showed slight decentration and the amounts of decentration were not large enough to influence higher-order aberrations.

Repeatability of OCT Anterior Surface and Bowman's Layer Curvature and Aberrations in Normal and Keratoconic Eyes.

To study the repeatability of anterior surface and Bowman's layer curvature in normal and keratoconic eyes using optical coherence tomography (OCT). In this study, 96 normal and 96 keratoconic eyes underwent corneal imaging using Pentacam (Oculus Optikgeräte, Wetzlar, Germany) and OCT (Triton, Topcon Corporation, Tokyo, Japan). The elevation data from segmented air-epithelium (A-E) and epithelium-Bowman's layer (E-B) interfaces in OCT scans were used to quantify curvature and aberrations. The wavefront aberrations were evaluated with the ray tracing method and 6th order Zernike polynomials. The intraclass correlation coefficient (ICC), within-subject standard deviation (Sw), and coefficient of variation (CoV) were used to assess repeatability. For curvatures, the Sw was less than 0.25 diopters (D) for the normal and keratoconic eyes. The Sw was highest for root mean square of lower order aberrations (0.14 µm) in keratoconic eyes. The CoV for curvatures was well below 0.5% for both groups. For some aberrations irrespective of groups, the CoV was greater because some individual aberrations (mean of three successive measurements) tended to be smaller in magnitude and even a small Sw resulted in a high CoV. For all variables, the ICC ranged between 0.80 and 0.99 for both the OCT and Pentacam measurements. Most variables were similar between the A-E and E-B interfaces (P > .05) for both groups. However, both differed significantly from all Pentacam variables (P < .05) in normal and keratoconic eyes. The repeatability of OCT curvatures and aberrations compared well with the Pentacam indices for normal and keratoconic eyes. [J Refract Surg. 2020;36(4):247-252.].

VioBio lab adaptive optics: technology and applications by women vision scientists.

Adaptive Optics allows measurement and manipulation of the optical aberrations of the eye. We review two Adaptive Optics set-ups implemented at the Visual Optics and Biophotonics Laboratory, and present examples of their use in better understanding of the role of optical aberrations on visual perception, in normal and treated eyes. Two systems (AOI and AOII) are described that measure ocular aberrations with a Hartmann-Shack wavefront sensor, which operates in closed-loop with an electromagnetic deformable mirror, and visual stimuli are projected in a visual display for psychophysical measurements. AOI operates in infrared radiation (IR) light. AOII is provided with a supercontiniuum laser source (IR and visible wavelengths), additional elements for simulation (spatial light modulator, temporal multiplexing with optotunable lenses, phase plates, cuvette for intraocular lenses-IOLs), and a double-pass retinal camera. We review several studies undertaken with these AO systems, including the evaluation of the visual benefits of AO correction, vision with simulated multifocal IOLs (MIOLs), optical aberrations in pseudophakic eyes, chromatic aberrations and their visual impact, and neural adaptation to ocular aberrations. Monochromatic and chromatic aberrations have been measured in normal and treated eyes. AO systems have allowed understanding the visual benefit of correcting aberrations in normal eyes and the adaptation of the visual system to the eye's native aberrations. Ocular corrections such as intraocular and contact lenses modify the wave aberrations. AO systems allow simulating vision with these corrections before they are implanted/fitted in the eye, or even before they are manufactured, revealing great potential for industry and the clinical practice. This review paper is part of a special issue of Ophthalmic & Physiological Optics on women in visual optics, and is co-authored by all women scientists of the research team.

Wavefront aberrations in children with different types of amblyopia

Purpose. To quantify and characterize higher-order aberrations in eyes of children with amblyopia caused by different etiology factors; to evaluate the relationship between the wavefront profile and the effectiveness of the amblyopia treatment. Material and methods. This study involved 26 children (52 eyes) from 3 to 9 years old (average age 6.2±3 years) with different types of amblyopia: unilateral amblyopia due to impaired binocular vision and anisometropia, as well as unilateral or bilateral amblyopia caused by hyperopia. Patients were divided into four groups depending on the effectiveness of pleoptic treatment: 14 children (24 eyes) – with positive treatment results, 8 children (12 eyes) – with refractory amblyopia, 4 pre-treatment newly diagnosed patients (6 eyes) without previous history of optical correction, and 10 non-amblyopic contralateral eyes (control group). All patients had central fixation and didn`t have any severe systemic diseases. Higher-order aberrations were measured with iTrace Visual Function Analyzer (Tracey Technologies, Houston, TX) after instillation of 1% cyclopentolate eyedrops. Results and discussion. Wavefront profiles were significantly different in the studied groups. Total spherical aberrations and astigmatism were significantly higher in group with refractory amblyopia (-0.53±1.19 and 2.25±1.07, p=0.02) compared with all the other groups: the group of patients before pleoptic treatment (-0.17±0.23 and 1.79±1.47), group treated with high efficiency (-0.31±0.81 and 1.04±0.13) and with control group (-0.13±0.17 and 1.38±0.11). Total coma-like aberrations didn`t show statistically significant differences in all studied groups (р=0.06). The level of corneal higher-order aberrations (total, coma, spherical) in all three amblyopic groups was higher than in the control group without amblyopia. Conclusion. We revealed statistically significant differences in the wavefront profiles in children with amblyopia of various etiologies in comparison with the control group, including higher-order aberrations. The data obtained indicate that an amblyopic eye with hyperopia has higher level of spherical aberrations and astigmatism due to higher level of internal HOAs, particularly spherical aberrations and astigmatism, which is typical for patients with unsuccessful treatment. Therefore, that type of aberrations is likely to be the main cause of refractory amblyopia.

Effects of the LASIK flap thickness on corneal biomechanical behavior: a finite element analysis

BackgroundIt is well known that the biomechanical properties change after LASIK refractive surgery. One reason is the impact of flap creation on the residual stroma. The results have revealed that the change is closely related with the flap thickness in several studies. However, the quantitative relationships between the distributions of displacement and stress on the corneal surface and flap thickness have not been studied. The aim of the study was to quantify evaluate the biomechanical change caused by the LASIK flap.MethodsBy building a finite element model of the cornea, the displacement, the stress and the strain on the corneal surface were analyzed.ResultsThe results showed that the corneal flap could obviously cause the deformation of the anterior corneal surface. For example, the displacement of the corneal vertex achieved 15 μm more than that without corneal flap, when the thickness of corneal flap was 120 μm thick. This displacement was enough to cause the change of aberrations in the human eyes. In the central part of the cornea, the stress on the anterior corneal surface increased with flap thickness. But the change in the stress on the posterior corneal surface was significantly less than that on the anterior surface. In addition, the stress in the central part of the anterior corneal surface increased significantly as the intra-ocular pressure (IOP) increase. Furthermore the increase of IOP had a clearly less effect on stress distribution at the edge of the cornea. Distributions of strain on the corneal surface were similar to those of stress.ConclusionsThe changes in the biomechanical properties of cornea after refractive surgery should not be ignored.

Analytical solution of a personalized intraocular lens design for the correction of spherical aberration and coma of a pseudophakic eye.

This manuscript reports on a closed-form solution determining the personalized required shape of a new intraocular lens able to remove spherical aberration and coma of a pseudophakic eye. The proposed analytical method, within the framework of the Seidel theory of third-order optical aberrations, considers corneal conicities, fourth-order aspheric surface of the intraocular optics, pupil-shift effect and ocular kappa angle.

Wavefront sensing, novel lower degree/higher degree polynomial decomposition and its recent clinical applications: A review.

We are in the midst of a shift towards using novel polynomials to decompose wavefront aberrations in a more ophthalmologically relevant way. Zernike polynomials have useful mathematical properties but fail to provide clinically relevant wavefront interpretation and predictions. We compared the distribution of the eye's aberrations and demonstrate some clinical applications of this using case studies comparing the results produced by the Zernike decomposition and evaluating them against the lower degree/higher degree (LD/HD) polynomial decomposition basis which clearly dissociates the higher and lower aberrations. In addition, innovative applications validate the LD/HD polynomial basis. Absence of artificial reduction of some higher order aberrations coefficients lead to a more realistic analysis. Here we summarize how wavefront analysis has evolved and demonstrate some of its new clinical applications.

Do Polymer Coatings Change the Aberrations of Conventional and Wavefront-guided Scleral Lenses?

The findings of this study indicate that patients could simultaneously be offered the individualized optical correction of wavefront-guided (WFG) lenses and the superior comfort afforded by polymer coatings. This could be helpful to patients with ectasia suffering ocular dryness or dependent on scleral lenses for lengthy periods of wear. Wavefront-guided scleral lenses target lower- and higher-order aberrations of individual eyes using submicrometer-level contours in the anterior lens surface. Hydrophilic polyethylene glycol (PEG) polymer coatings applied to lens surfaces improve comfort and wettability. This study aimed to quantify aberration changes (e.g., masking) when applying polymer coatings to WFG and conventional scleral lenses. Two control lenses (remained uncoated) and 14 experimental lenses (two repeated builds of seven aberration designs: one spherical, two coma, four full WFG [second- to fifth-order aberrations]) were manufactured, and aberrations were measured (mean of three) by two operators before and after coating. Root mean square (RMS) and visual image quality (logVSX) differences were calculated for 6-mm diameters. Median RMS aberration change due to coating was 0.012 μm (range, 0.008 to 0.057 μm). Maximum logVSX change due to coating was 0.073, predicting an approximately one letter change in acuity. Instrument sensitivity was 0.002 μm. Acute instrument and operator variabilities (standard deviations of individual [second- to fifth-order Zernikes] were all <0.027 μm). Longitudinal variability (control lenses) was low: all less than 0.017 μm. Although RMS of differences between repeated builds of all lenses was less than 0.25 D and not statistically significant, relatively, manufacture constituted the major variability, and RMS difference between repeated builds was at least four times greater than the effect of coating (median, 0.167 μm; range, 0.088 to 0.312 μm). Application of polymer coatings caused measurable changes in aberrations of WFG and conventional scleral lenses; however, these were clinically and statistically insignificant and within variability of repeated lens manufacture. In their current states, WFG lenses and polymer coatings could be used simultaneously.

Corrigendum: A review of higher order aberrations of the human eye

Corrigendum: A review of higher order aberrations of the human eye