Coma Aberration Research Articles

Variation of coma aberration with prismatic soft contact lenses

Purpose: To analyze the variation in vertical coma and the rest of ocular aberrations before and after fitting prismatic soft contact lenses (PSCL).

Safety and satisfaction of myopic small-incision lenticule extraction combined with monovision

BackgroundTo investigate the safety and optical quality of small-incision lenticule extraction (SMILE) combined with monovision, and patient satisfaction with the procedure.MethodsThe present study assessed a non-random case series involving 60 eyes of 30 patients (mean age 45.53 ± 3.20 years [range 41 to 52 years]) treated bilaterally using the VisuMax 500 system (Carl Zeiss Meditec, Jena, Germany) between January and July 2016. The target refraction was plano for the distance eye, and between − 0.5 and − 1.75 diopters (D) for the near eye. Visual acuity, refraction errors, ocular aberrations, and satisfaction questionnaire scores were calculated 1 year after surgery.ResultsAll surgeries were uneventful, with a mean safety index of 1.03 and 1.04 in dominant and nondominant eyes, respectively. Binocular uncorrected distance visual acuity of all patients was ≥20/32, while binocular uncorrected near visual acuity was ≥20/40 1 year postoperatively. Higher-order aberration (0.45 ± 0.14, 0.51 ± 0.15 μm), spherical (0.18 ± 0.15, 0.21 ± 0.14 μm) and coma aberration (0.31 ± 0.16, 0.27 ± 0.17 μm) were identical between dominant and nondominant eyes after surgery. The overall satisfaction rate was 86.7% (26/30), with large contributions from age (OR = 1.76 95% CI: 1.03–2.53; P = 0.036). Binocular uncorrected distance visual acuity was related to preoperative spherical diopter (r = − 0.500; P = 0.005).ConclusionsMonovision appears to be a safe and effective option for myopia patients with presbyopia who are considering the SMILE procedure. Patients with younger age were more satisfied with the procedure.

Comparing corneal higher-order aberrations in corneal wavefront-guided transepithelial photorefractive keratectomy versus small-incision lenticule extraction

To evaluate the changes in corneal higher-order aberrations (HOAs) after corneal wavefront-guided transepithelial photorefractive keratectomy (PRK) and small-incision lenticule extraction (SMILE). Yonsei University College of Medicine and Eyereum Eye Clinic, South Korea. Retrospective case series. Medical records of patients having either corneal wavefront-guided transepithelial PRK or small-incision lenticule extraction were examined. The root-mean-square total HOAs,3rd-order coma aberration, and 4th-order spherical aberration were measured preoperatively and 6months postoperatively. Independent t tests and analysis of covariance were used to compare changes in corneal HOAs between the 2 groups. The study comprised 77 eyes having corneal wavefront-guided transepithelial PRK and 81 eyes having small-incision lenticule extraction. The total HOAs and spherical aberration increased after transepithelial PRK (all P<.001), whereas coma aberration was stable after transepithelial PRK. The total HOAs, spherical aberration, and coma aberration increased after small-incision lenticule extraction (P<.001 for total HOAs, spherical aberration; P=.004 for coma). At 6months postoperatively, total HOAs and spherical aberration were significantly larger in the transepithelial PRK group than in the small-incision lenticule extraction group. Coma aberration was larger in the small-incision lenticule extraction group than in the transepithelial PRK group. Spherical aberration induction was significantly smaller in the small-incision lenticule extraction group than in the transepithelial PRK group (P<.001), and coma aberration induction was larger in the small-incision lenticule extraction group than in the transepithelial PRK group (P=.011). Small-incision lenticule extraction demonstrated that the induction of total HOAs was comparable to corneal wavefront-guided transepithelial PRK, accompanied by smaller spherical aberration induction and larger coma aberration induction. During small-incision lenticule extraction, surgeons should aim to obtain optimum centration for smaller induction of corneal HOAs.

Effects of aberrations on effective point spread function in STED microscopy.

Like other imaging techniques, stimulated emission depletion (STED) microscopy suffers from aberrations. While their effects on depletion patterns have been explicitly investigated, the study on how aberrations affect the effective point spread function (PSF) in STED microscopy is still missing. For STED researchers, however, this study is beneficial, as it directly bridges image qualities and aberrations. In this paper, we quantitatively analyze the effects of primary aberrations, including astigmatism, coma, trefoil, and spherical aberration, in two-dimensional (2D) and three-dimensional (3D) STED microscopy, and further discuss the corresponding aberration tolerance. Specifically, attention is given to the modification of the shape, the size, and the peak intensity of the effective PSF in the presence of these aberrations.

Relationship Between Decentration and Induced Corneal Higher-Order Aberrations Following Small-Incision Lenticule Extraction Procedure.

To investigate the amount of lenticule decentration following small-incision lenticule extraction (SMILE) by using the Keratron Scout tangential topography difference map, and the relationship between the magnitudes of total decentration and induced corneal higher-order aberrations (HOAs). This retrospective observational case series study analyzed decentration values obtained from the Keratron Scout tangential topography difference map of 360 eyes (360 patients) that underwent SMILE. Root mean square total HOAs, third order coma aberration, fourth order spherical aberration, as well as individual coefficients for vertical and horizontal coma were measured preoperatively and 3-months postoperatively. Simple linear regression analysis and piecewise regression models were used to determine the relationship between the magnitudes of total decentration and induced corneal HOAs. The mean total decentration distance from the corneal vertex was 0.36 ± 0.22 mm (range, 0.02-1.27 mm). There were significant differences in total HOAs, coma, vertical and horizontal comas, and spherical aberration between preoperative and 3-month postoperative assessments. Significant relationships between the magnitudes of total decentration and induced corneal HOAs were noted. Subgroup analysis according to the degree of total decentration (group I, total decentered displacement ≤0.335 mm; and group II, total decentered displacement >0.335 mm) revealed that induced changes in total HOAs, coma, vertical coma, and spherical aberration were significantly larger in group II than in group I. A minimal degree of decentration was closely related to a smaller induction of corneal HOAs. Efforts to optimize centration are critical for achieving better surgical outcomes in SMILE.

Effect of a contact lens on mouse retinal in vivo imaging: Effective focal length changes and monochromatic aberrations

For in vivo mouse retinal imaging, especially with Adaptive Optics instruments, application of a contact lens is desirable, as it allows maintenance of cornea hydration and helps to prevent cataract formation during lengthy imaging sessions. However, since the refractive elements of the eye (cornea and lens) serve as the objective for most in vivo retinal imaging systems, the use of a contact lens, even with 0 Dpt. refractive power, can alter the system's optical properties. In this investigation we examined the effective focal length change and the aberrations that arise from use of a contact lens. First, focal length changes were simulated with a Zemax mouse eye model. Then ocular aberrations with and without a 0 Dpt. contact lens were measured with a Shack-Hartmann wavefront sensor (SHWS) in a customized AO-SLO system. Total RMS wavefront errors were measured for two groups of mice (14-month, and 2.5-month-old), decomposed into 66 Zernike aberration terms, and compared. These data revealed that vertical coma and spherical aberrations were increased with use of a contact lens in our system. Based on the ocular wavefront data we evaluated the effect of the contact lens on the imaging system performance as a function of the pupil size. Both RMS error and Strehl ratios were quantified for the two groups of mice, with and without contact lenses, and for different input beam sizes. These results provide information for determining optimum pupil size for retinal imaging without adaptive optics, and raise critical issues for design of mouse optical imaging systems that incorporate contact lenses.

A heuristic approach for actuator layout designs in deformable mirror devices based on current value optimization

Deformable mirrors are vital components in fundus imaging modality incorporating adaptive optics systems. The application of precisely controlled electric currents to multiple electrodes located under the mirror surface deform its shape so that optical aberrations caused by a patient’s eye can be nullified. The higher number of actuators used, the more accurately the mirror surface can be transformed to a target shape. However, deformable mirror manufacturability limitations demand that the number of electromagnetic actuators be minimized, so there is a pressing need for an efficient method to determine the layout of a minimum number of actuators that will deliver desired aberration correction performance. In this paper, we present an actuator layout design method based on the degree to which each actuator contributes to mirror shaped adjustment, calculated according to the amount of electric current supplied to individual actuators. This method minimizes the number of actuators while preventing the error between a target mirror shape and the actual deformed mirror shape from exceeding a certain limit. To assess the aberration correction performance for each actuator layout, we also provide a method for optimizing the electric currents supplied to an array of actuators that will correctly adjust the mirror surface to target Zernike modes, corresponding to defocus, astigmatism, coma and trefoil aberrations, given the imposition of upper and lower limits upon the currents supplied to the actuators.

Comparison of long-term decentration and tilt in two types of multifocal intraocular lenses with OPD-Scan III aberrometer.

To compare the long-term decentration and tilt in two multifocal intraocular lenses (MfIOLs) with an OPD-Scan III aberrometer. Eighty cataract patients who underwent uneventful MfIOL implantation (42 with AcrySof® IQ ReSTOR® SN6AD1 and 38 with AMO Tecnis® ZMB00) were enrolled. At 1 year after surgery, a postoperative visual acuity evaluation included the measurement of uncorrected distance visual acuity, corrected distance visual acuity, distance-corrected near visual acuity, and distance-corrected intermediate visual acuity. OPD-Scan III aberrometer was used to collect the decentration, tilt, and high-order aberration (HOA) data. Significance was tested with Student's t test, Mann-Whitney U test, paired t test, and χ2 test RESULTS: The average intraocular tilt was lower in the SN6AD1 group than in the ZMB00 group, whereas the average decentration of the two groups did not differ significantly. The mean total ocular HOAs, ocular trefoil, total internal HOAs, and spherical aberrations were significantly lower in the SN6AD1 group than in the ZMB00 group. In both the SN6AD1 and ZMB00 groups, the intraocular tilt was directly proportional to the total ocular HOAs, coma, and spherical aberration. However, there was no significant correlation between decentration and any type of HOA in SN6AD1 group, whereas decentration correlated positively with total ocular HOAs, coma, and spherical aberration in ZMB00 group. Both MfIOLs significantly improve the visual acuity of the patients. However, tilt was lower in the SN6AD1 group than in the ZMB00 group 1 year after surgery, which provide fewer HOAs and better visual quality.

Comparison of ocular wavefront aberrations in subluxated lenses before and after lens extraction with intraocular lens implantation

To compare the change in ocular higher-order wavefront aberrations (HOAs), visual acuity, and modulation transfer function (MTF) after lens extraction with intraocular lens (IOL) implantation in patients with subluxated lenses. Iladevi Cataract & IOL Research Centre, Ahmedabad, India. Prospective case series. Eyes with subluxated lenses having lens extraction with IOL implantation were included. Capsular bag fixation with in-the-bag IOL implantation or sutured or sutureless scleral fixation of the IOL was performed. Aberrometry was performed preoperatively and 6months postoperatively. The following were compared: root-mean-square (RMS) value for total ocular HOAs, coma aberration, spherical aberration, MTF, and corrected distance visual acuity (CDVA). Of the 39 eyes with subluxated lenses, 26 eyes had Cionni ring fixation, 9 had sutured scleral fixation, and 4 had intrascleral fixation of the IOL. The mean preoperative and postoperative values, respectively, were as follows: RMS HOAs, 10.5μm±9.5 (SD) and 4.73±4.6μm(P<.001); coma aberration, 2.46±2.4μm and 0.11±0.1μm(P=.03); and spherical aberration, 0.37±0.9μm and 0.02±0.06μm(P=.02). The MTF improved significantly in all eyes (mean 0.05±0.02 preoperatively and 0.32±0.16 postoperatively) (P=.005). The CDVA was statistically significant improved 6months postoperatively. Lens extraction with IOL fixation in eyes with subluxated lenses significantly reduced ocular HOAs and improved the MTF.

Orbital-angular-momentum photons for optical communication in non-Kolmogorov atmospheric turbulence

We investigate the effects of non-Kolmogorov atmospheric turbulence on the transmission of orbital-angular-momentum single photons for different turbulence aberrations in optical communication, via the channel capacity. For non-Kolmogorov model, the characteristics of atmosphere turbulence may be determined by different cases, including the increasing altitude, the mutative index-of-refraction structure constant and the power-law exponent of non-Kolmogorov spectrum. It is found that the influences of low-order aberrations, including Z-tilt, defocus, astigmatism, and coma aberrations, are different and the turbulence Z-tilt aberration plays a more important role in the decay of the signal.

Nonrotationally symmetric aberrations of off-axis two-mirror astronomical telescopes induced by axial misalignments.

In unobscured off-axis astronomical telescopes with an offset pupil, the effects of axial misalignments are very different from those in on-axis ones. Specifically, a series of nonrotationally symmetric aberrations with characteristic field dependence will be induced by axial misalignments. This paper takes off-axis two-mirror astronomical telescopes as an example to discuss the field characteristics of several important nonrotationally symmetric aberrations (including astigmatism, coma, and trefoil aberration) induced by axial misalignments in off-axis astronomical telescopes. The expressions of these aberrations are derived under some approximations. The accuracy of the proposed expressions is demonstrated. The specific field characteristics of these aberrations are presented and explicated. It is shown that the effects of axial misalignments bear strong similarities to the effects of the lateral misalignments in the symmetry plane of the off-axis system. On the other hand, the inherent relationships between astigmatism and coma induced by axial misalignments are further revealed, which are different from those induced by lateral misalignments. This fact presents the possibility of separating the effects of axial misalignments and lateral misalignments. Most of this work can be extended to other off-axis astronomical telescopes with more freedom.

Dynamic changes in higher-order aberrations after correction of lower-order aberrations with adaptive optics in myopic and emmetropic eyes.

This study investigated the instantaneous changes of higher-order aberrations (HOAs) following lower-order aberrations (LOAs) correction with a closed-loop adaptive optics (AO) system in myopic and emmetropic eyes. Data were analyzed using generalized additive mixed models. Time-related changes in HOAs were modeled with two-piecewise linear regressions and were compared between myopic and emmetropic eyes. Both vertical coma and spherical aberrations shifted to the positive direction immediately after LOA correction. The fluctuations of the above values were significantly faster in myopic than in emmetropic eyes. Understanding these changes in HOAs following LOA correction may help in achieving better visual outcomes.

Development of a real-time wave field reconstruction TEM system (II): correction of coma aberration and 3-fold astigmatism, and real-time correction of 2-fold astigmatism.

In this study, a function for the correction of coma aberration, 3-fold astigmatism and real-time correction of 2-fold astigmatism was newly incorporated into a recently developed real-time wave field reconstruction TEM system. The aberration correction function was developed by modifying the image-processing software previously designed for auto focus tracking, as described in the first article of this series. Using the newly developed system, the coma aberration and 3-fold astigmatism were corrected using the aberration coefficients obtained experimentally before the processing was carried out. In this study, these aberration coefficients were estimated from an apparent 2-fold astigmatism induced under tilted-illumination conditions. In contrast, 2-fold astigmatism could be measured and corrected in real time from the reconstructed wave field. Here, the measurement precision for 2-fold astigmatism was found to be ±0.4 nm and ±2°. All of these aberration corrections, as well as auto focus tracking, were performed at a video frame rate of 1/30 s. Thus, the proposed novel system is promising for quantitative and reliable in situ observations, particularly in environmental TEM applications.

A homogeneous focusing system for diode lasers and its applications in metal surface modification

High power diode lasers are applied in many different areas, including surface modification, welding and cutting. It is an important technical trend in laser processing of metals in the future. This paper aims to analyze the impact of the shape and homogeneity of the focal spot of the diode laser on surface modification. A focusing system using the triplet lenses for a direct output diode laser which can be used to eliminate coma aberrations is studied. A rectangular stripe with an aspect ratio from 8:1 to 25:1 is obtained, in which the power is homogeneously distributed along the fast axis, the power is 1117.6 W and the peak power intensity is 1.1587 × 106 W/cm2. This paper also presents a homogeneous focusing system by use of a Fresnel lens, in which the incident beam size is 40 × 40 mm2, the focal length is 380 mm, and the dimension of the obtained focal spot is 2 × 10 mm2. When the divergence angle of the incident light is in the range of 12.5–20 mrad and the pitch is 1 mm, the obtained homogeneity in the focal spot is the optimum (about 95.22%). Experimental results show that the measured focal spot size is 2.04 × 10.39 mm2. This research presents a novel design of homogeneous focusing systems for high power diode lasers.

Changes of Higher-order Aberrations According to the Increase of refractive Errors

To identify the relationship between spherical refractive errors and HoAs and the relationship between cylindrical refractive errors and HOAs, the HOAs within 6mm zone were measured. The refractive errors and HOAs were measured by KR-9000PW (Topcon Corp., Japan), a wavefront aberrometer using Hartmann-Shack method, and the aberrations within the 6mm range of pupil diameter were measured. The Zernike coefficients from 3rd to 4th expressions were analyzed. All HOAs such as trefoil aberration, coma aberration, tetrafoil aberration, 2nd astigmatism, and spherical aberration that were analyzed showed a significant correlation with cylindrical refractive error. on the other hand, only spherical aberration had a correlation with the spherical refractive error in the comparison between HoAs and spherical refractive error, and the remaining aberrations had no significant correlation. In the comparison with Zernike coefficients, Z40, Z42, and Z44 had a significant correlation with the Spherical refractive error and cylindrical refractive error, while Z31 had a significant correlation only with the spherical refractive error. The other coefficients had no significant correlation with both spherical refractive error and cylindrical refractive error. Since HOAs have very small values compared to refractive error and the values change greatly in each measurement, it is considered necessary to measure HoAs more precisely to identify the correlations among each other.

Studying the changes of ocular wavefront aberrations after neodymium

Aimof the study The aim of this study is to evaluate the changes of wavefront aberrations after performing neodymium : yttrium aluminum garnet (Nd : YAG) laser posterior capsulotomy for the management of posterior capsular opacifications. Patients and methods This study is a prospective study that was performed on 100 eyes of 87 patients with posterior capsule opacification following phacoemulsification, in the period from March 2017 to October 2017. A complete ophthalmic examination and optical wavefront imaging were performed to every patient. Patients underwent posterior capsulotomy using Nd : YAG laser with a follow-up period of 6 months. Results There were no significant changes in postoperative refraction at P value more than 0.05 still the best-corrected visual acuity showed a clinically significant at P value less than 0.05. The intraocular pressure was statistically significantly increased on the first postoperative day (P&lt;0.05) but not in other postoperative visits. Regarding higher order aberrations there was a statistically significant improvement in total third-order aberrations (P&lt;0.05), coma aberration (P&lt;0.05), total fourth-order aberrations (P&lt;0.05), spherical aberration (P&lt;0.05), and total higher order aberrations (P&lt;0.05) while quadrafoil and fifth-order aberrations showed no statistically significant changes. Conclusion Nd : YAG laser posterior capsulotomy causes a significantly decrease in wavefront aberrations in patients with posterior capsule opacification.

Numerical analysis of wavefront aberration correction using multielectrode electrowetting-based devices.

We present numerical simulations of multielectrode electrowetting devices used in a novel optical design to correct wavefront aberration. Our optical system consists of two multielectrode devices, preceded by a single fixed lens. The multielectrode elements function as adaptive optical devices that can be used to correct aberrations inherent in many imaging setups, biological samples, and the atmosphere. We are able to accurately simulate the liquid-liquid interface shape using computational fluid dynamics. Ray tracing analysis of these surfaces shows clear evidence of aberration correction. To demonstrate the strength of our design, we studied three different input aberrations mixtures that include astigmatism, coma, trefoil, and additional higher order aberration terms, with amplitudes as large as one wave at 633 nm.

Visual rehabilitation in moderate keratoconus: combined corneal wavefront-guided transepithelial photorefractive keratectomy and high-fluence accelerated corneal collagen cross-linking after intracorneal ring segment implantation

BackgroundTo investigate the effects of combined corneal wavefront-guided transepithelial photorefractive keratectomy (tPRK) and accelerated corneal collagen cross-linking (CXL) after intracorneal ring segment (ICRS) implantation in patients with moderate keratoconus.MethodsMedical records of 23 eyes of 23 patients undergoing combined tPRK and CXL after ICRS implantation were retrospectively analyzed. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction spherical equivalent (MRSE), corneal indices based on Scheimpflug tomography, higher-order aberrations (HOAs), and corneal biomechanical properties were evaluated before and after ICRS implantation, and at 1, 3, and 6 months after combined tPRK and CXL.ResultsThere were significant improvements in final logMAR UDVA and logMAR CDVA, and reductions in sphere, MRSE, and all corneal indices from baseline. Significant improvements in logMAR UDVA and reductions in sphere, MRSE, maximal keratometry, keratometry at the apex, mean keratometry, and keratoconus index were noted after ICRS implantation. After tPRK and CXL, significant improvements in logMAR UDVA and logMAR CDVA, and reductions in cylinder and all corneal indices were observed. There were significant improvements in final root mean square HOAs and coma aberrations from baseline, but no changes from baseline after ICRS implantation. Significant reductions in final radius and deformation amplitude from baseline were noted.ConclusionsCombined tPRK and accelerated CXL after ICRS implantation in moderate keratoconus appears to be a safe and effective treatment, providing an improvement in visual acuity, corneal indices, and HOAs.Trial registrationretrospectively registered (identification no. NCT03355430). Date registered: 28/11/2017.

Vector analysis of astigmatic changes and optical quality outcomes after wavefront-guided laser in situ keratomileusis using a high-resolution aberrometer

To assess the ocular optical quality results as well as theastigmatic changes after wavefront-guided laser insitu keratomileusis (LASIK) in eyes with myopic astigmatism. Instituto Clínico-Quirúrgico Oftalmológico, Bilbao, Vizcaya, Spain. Prospective case series. Thirty-three eyes having wavefront-guided LASIK with the Star S4IR excimer laser combined with the iDesign system were enrolled in the study. Changes in visual acuity, refraction, higher-order aberrations, and ocular scattering index (OSI) were evaluated during a 3-month follow-up. The Alpins method was used to analyze the astigmatic changes. A significant reduction was observed in refraction (P<.001), with significant improvement in uncorrected (UDVA) and corrected (CDVA) distance visual acuities (P<.001). All eyes had a spherical equivalent within ±0.50 diopter (D) and UDVA of 20/25 or better at 90days after surgery. A total of 27.3% of eyes gained lines of CDVA. No significant changes were observed in primary coma and spherical aberration (P≥.551). Likewise, no significant changes were observed in OSI (P=.361), with a mean 90-day postoperative value of 0.66±0.58 (SD). A significant change to negative values of the magnitude of error (P=.007) and a significant decrease in the correction index (P=.004) were observed during the follow-up, with mean 90-day postoperative values of -0.24±0.28 D and 0.86±0.17 D, respectively. Wavefront-guided LASIK using a high-resolution aberrometer provided safe and efficacious correction of myopic astigmatism, with preservation of the ocular optical quality.

Topographic characteristics after Descemet's membrane endothelial keratoplasty and Descemet's stripping automated endothelial keratoplasty.

PurposeTo investigate the topographic characteristics of the posterior corneal surface after Descemet’s endothelial membrane keratoplasty (DMEK) and Descemet’s stripping automated endothelial keratoplasty (DSAEK) and their effects on postoperative visual acuity.MethodsNineteen eyes of 19 patients after DMEK, 23 eyes of 23 patients after DSAEK, and 18 eyes of 18 control subjects were retrospectively analyzed. Best spectacle-corrected visual acuity (BSCVA), aberration factors (higher-order aberrations [HOAs], spherical aberrations [SAs], and coma aberrations [Comas] at 6.0 mm) were evaluated preoperatively and at 1, 3, and 6 months postoperatively. The posterior refractive pattern of the topography map was classified into 5 grades (0–5) (posterior color grade) using anterior segment optical coherence tomography. Correlations between BSCVA and some factors (abbreviation factors, posterior color grade) were analyzed.ResultsBSCVA was significantly better after DMEK than after DSAEK (P < 0.001). Posterior HOAs, SAs, and Comas after each type of endothelial keratoplasty were significantly greater compared to control (P < 0.01). Posterior HOAs, total/anterior/posterior SAs, and posterior color grade were significantly lower in the DMEK group than in the DSAEK group at 3 months (P < 0.024 [posterior HOAs], P = 0.047 [total SA], P < 0.001 [anterior SAs], P = 0.021 [posterior SAs], and P < 0.001 [posterior color grade]) and 6 months postoperatively (P = 0.034 [posterior HOAs], P < 0.001 [total SAs], P < 0.001 [anterior SAs], P = 0.013 [posterior SAs], and P = 0.004 [posterior color grade]). BSCVA was significantly correlated with HOAs, SAs, and posterior color grade (P < 0.001 for all except anterior HOAs [P = 0.004]).ConclusionsHigh posterior color grades were associated with larger aberration factors and had a negative effect on visual function after endothelial keratoplasty. Rapid improvement of visual function after DMEK may be attributed to less change at the posterior surface.