Changes In Wavefront Aberrations Research Articles

Combined simultaneous photorefractive keratectomy and collagen cross-linking in keratoconus suspect patients

To evaluate the safety and efficacy of combined simultaneous photorefractive keratectomy (PRK) with collagen cross-linking (CXL) in keratoconus suspects (KCS). This was a retrospective, non-randomized study of KCS patients who underwent combined simultaneous PRK with CXL. The efficacy, safety, refractive outcomes, and corneal wavefront aberration changes were assessed after the surgery and compared with existing preoperative data. Fifty-six eyes of 28 patients, including 20 females (71.4%), with a mean age of 30.92±4.09 years, were enrolled. The mean follow-up was 19.46±8.48 months (range: 7-35). At the conclusion of the study, mean uncorrected distance visual acuity LogMAR improved from 0.89±0.44 preoperatively to 0.04±0.09 postoperatively (P<0.001). In addition, a statistically significant corneal flattening was observed postoperatively, with a decrease in manifest refraction. A statistically significant increase was found in higher-order aberrations (P<0.001), horizontal coma (P<0.001), and spherical aberration (P<0.001) compared with preoperatively. Postoperatively, 41% exhibited refractive astigmatism of 0.50 diopter (D) or less; 83.8% showed 1.00 D or less. The results of our study indicate that combined simultaneous PRK with CXL can be a safe and effective method for treating refractive instability in KCS patients.

Changes of high order aberrations after photorefractive keratectomy (PRK) and FemtoLASIK

Purpose: a comparative study of corneal and total wavefront aberration changes after traditional PRK and FemtoLASIK.Material and methods. Corneal and total wavefront aberrations were studied on OPD-Scan III aberrometer (Nidek) in 63 patients (126 eyes) with moderate and high myopia before and after FemtoLASIK (Ziemer + Nidek-Quest, Japan) (44 patients, 88 eyes) and PRK (Nidek-Quest, Japan) (19 patients, 38 eyes). Spherical aberration (SA) was considered as the sum Z4 + Z8 + Z12.Results. The corneal asphericity coefficient Q changed to positive values after both types of intervention. Corneal RMS HOA increased in both Femto and PRK groups. Corneal Tilt 1 increased after FemtoLASIK and moved to negative values after PRK, corneal tilt 2 moved to negative values after Femto and to positive values after PRK. The vertical trefoil showed no significant change in the Femto group and dropped in the PRK group. The vertical and horizontal coma (coma 7, coma 8) changed synchronously. Corneal SA increased after Femtolasic, and became negative after PRK. The total aberrations showed a lesser change and the changes were not synchronized with the corneal ones: in particular, the RMS HOA fell from 0.28 ± 0.05 to 0.19 ± 0.05 in the Femto group, while the corneal RMS increased significantly. In the PRK group, the corneal RMS HOA showed some increase, but it was much less than corneal RMS: from 0.25 ± 0.07 to 0.62 ± 0.02 μm. The total SA increased from 0.11±0.03 to 0.27±0.02 in the Femto group and showed an insignificant drop from 0.09±0.03 to 0.03 ± 0.01, while remaining positive in the PRK group.Conclusions. The changes of the wavefront after FemtoLASIK and PRK are both significant and different. The revealed differences in the changes of corneal aberrations correspond to different profiles of the anterior surface of the cornea formed after FemtoLASIC and PRK. The internal optics of the eye partially compensates the corneal aberrations induced by excimer laser surgery.

Near Vision Tasks and Optical Quality of the Eye.

PurposeTo study the effect of near-vision reading task on optical quality of the eye when performed on a computer monitor and on printed paper, and to identify which of the two results in greater changes.MethodsTwo groups of subjects performed a 30-min reading task in two different conditions: on a computer monitor and on printed paper. Ocular, corneal, and internal wavefront aberrations (Zernike coefficients up to 6 order), root-mean-square of low- and high-order aberrations, spherical equivalent, vectoral components of ocular astigmatism (J45 and J0), and the compensation factor between internal and corneal aberrations were measured before and after the tasks. Their changes were analyzed in each group and between groups.ResultsStatistically significant changes in wavefront aberrations and in root mean square of low- and high-order aberrations were observed in both groups which was significantly greater when the task was performed on printed paper. Partial loss of compensation mechanism and variation in spherical equivalent in a negative direction occurred after both reading tasks; however, it was statistically significant only with printed paper reading task. The vectoral components of ocular astigmatism did not show statistically significant changes in either groups.ConclusionNear-vision reading tasks can change the optical quality of the eye, especially when the task is performed on printed paper.

The corneal biomechanical changes after SMILE and LASIK refractive surgery were compared based on finite element analysis

The three-dimensional (3D) finite element model of human eye was established, and the intraocular pressure (IOP) was loaded to simulate refractive surgery. The biomechanical properties of human cornea after SMILE and LASIK surgery were studied from the stress, strain and induced wavefront aberration. Our results showed that SMILE had less impact on the biomechanics, having less stress and strain changes than LASIK. However, the stress and strain of the cornea increased with the increase of the diopter and were concentrated in the central region. We also investigated the changes in wavefront aberrations of the cornea after surgery, and the results indicated that the defocus and vertical commotion were significantly affected by SMILE and LASIK surgery, while the remaining aberrations were approximately unchanged. In conclusion, both SMILE and LASIK sergury procedures changed the postoperative corneal biomechanics, but SMILE had less impact on the biomechanics of corneal.

Corneal Densitometry After Small Incision Lenticule Extraction (SMILE) and Femtosecond Laser-Assisted LASIK (FS-LASIK): 5-Year Prospective Comparative Study.

Purpose: To investigate long-term changes in corneal densitometry (CD) following small incision lenticule extraction (SMILE) vs. femtosecond laser-assisted LASIK (FS-LASIK) in patients with myopia or myopic astigmatism.Methods: Prospective analysis was performed in 66 eyes of 38 patients (13 males) who underwent SMILE and 54 eyes of 29 patients (5 males) who underwent FS-LASIK. In all patients, an ocular examination was performed preoperatively, and at 6–12 months and 5 years postoperatively. CD was obtained with the Pentacam Scheimpflug imaging system at the 0–2-mm, 2–6-mm, and 6–10-mm zones of the cornea at depth of anterior 120 μm, midcornea, and posterior 60 μm. Correlation analysis was performed between postoperative change in CD and other variables such as age, type of surgery, central corneal thickness, spherical equivalent, lenticule thickness/ablation depth, and changes in wavefront aberrations.Results: At postoperative 6–12 months, a significant reduction at several corneal zones in the FS-LASIK cohort (P < 0.05) was observed. In the SMILE cohort, no significant change in CD relative to baseline was observed. However, at 5 years postoperatively, in both groups, a significant decrease in CD was observed in three zones of three layers (all P < 0.001). The change in CD was similar between groups at postoperative 6–12 months, but at 5 years the magnitude of change was significantly smaller in SMILE than FS-LASIK in the anterior and central layers (all P < 0.05).Conclusion: CD with the Scheimpflug imaging system showed a significant decrease at 5 years after SMILE or FS-LASIK, and the change was significantly less pronounced after SMILE.

Individualized Characterization of the Distribution of Collagen Fibril Dispersion Using Optical Aberrations of the Cornea for Biomechanical Models

PurposeThe spatial distribution of collagen fibril dispersion has a significant impact on both corneal biomechanical and optical behaviors. The goal of this study was to demonstrate a novel method to characterize collagen fibril dispersion using intraocular pressure (IOP)-induced changes in corneal optical aberrations for individualized finite-element (FE) modeling.MethodsThe method was tested through both numerical simulations and ex vivo experiments. Inflation tests were simulated in FE models with three assumed patterns of collagen fibril dispersion and experimentally on three rhesus monkey corneas. Geometry, matrix stiffness, and the IOP-induced changes in wavefront aberrations were measured, and the collagen fibril dispersion was characterized. An individualized corneal model with customized collagen fibril dispersion was developed, and the estimated optical aberrations were compared with the measured data.ResultsFor the theoretical investigations, three assumed distributions of fibril dispersion were all successfully characterized. The estimated optical aberrations closely matched the measured data, with average root-mean-square (RMS) differences of 0.29, 0.24, and 0.10 µm for the three patterns, respectively. The overall features of the IOP-induced changes in optical aberrations were estimated for two ex vivo monkey corneas, with average RMS differences of 0.57 and 0.43 µm. Characterization of the fibril dispersion in the third cornea might have been affected by corneal hydration, resulting in an increased RMS difference, 0.8 µm.ConclusionsA more advanced corneal model with individualized distribution of collagen fibril dispersion can be developed and used to improve our ability to understand both biomechanical and optical behaviors of the cornea.

The state and dynamics of the wavefront of the eye in children with different refractions engaged in regular sport activities (badminton)

The paper isaimedat comparing the level of aberrations, structure of the wavefront, and its response to cycloplegia in children with different refractions before they started practicing badminton regularly and after a year’s duration of this practice.Material and methods.40 children (80 eyes) with refractive errors from +6.63 to -6.75 D (average -1.28 ± 2.28 D) aged 7 to 11 years (average 9.24 ± 1.06 years) were examined before the practice, 6 months after practice start (38 children, 72 eyes) and after 1 year of badminton playing (27 children, 54 eyes). All patients underwent wavefront aberrometry before and after cycloplegia on an OPD-Scan III (Nidek) aberrometer. We analyzed Zernike coefficients up to the 12th order inclusive: vertical and horizontal slope (tilt 1, tilt 2), vertical and horizontal trefoil (trefoil 6, trefoil 9), vertical and horizontal coma (coma 7, coma 8), spherical aberration (SA), mean square deviation from the ideal wavefront (RMS).Results.SA in myopia was found to be negative, in hyperopia positive; tilt 1, tilt 2, trefoil 9, coma 7 in myopia were significantly higher, and coma 8 significantly lower than in hyperopia. The slope of the wavefront (tilt 1, tilt 2) in cycloplegia falls significantly in hyperopic eyes and does not change in myopic ones. The latter fact points to insufficient tension of Zinn ligaments in the myopic eye. Regular badminton practice results in significant changes in wavefront aberrations, indicating a strengthening of the ligaments of the lens and the normalization of the ciliary muscle tone.Conclusions.The structure of the wavefront in children with different refractions shows significant differences. Badminton helps strengthen the ligaments of the lens.

Topography-guided transepithelial photorefractive keratectomy to correct irregular refractive errors after radial keratotomy

To evaluate the efficacy and safety of topography-guided transepithelial photorefractive keratectomy (PRK) in a group of patients with post-radial keratotomy (RK) showing irregular corneas. Feiz University Hospital, Isfahan, Iran. Prospective case series. Consecutive patients who had irregular astigmatism after RK with stable refraction and topography for at least 1year were recruited. All eyes had excimer laser topography-guided single-step transepithelial PRK. The efficacy, safety, predictability, and corneal wavefront aberration changes were assessed 6months after the surgery. Vector analysis was performed using the Alpins method to evaluate the astigmatic treatment. Twenty-two patients (22 eyes) were enrolled. The patients' ages ranged from 37 to 61years (45.77years±4.9 [SD]); there were 12 men (54.54%) and 10 women (45.46%). Uncorrected distance visual acuity significantly improved after 6months of treatment (0.45±0.19 logarithm of the minimum angle of resolution [logMAR] preoperatively and 0.25±0.19 logMAR after 6months) (P<.001). Moreover, the corrected distance visual acuity significantly improved at the end of the study (0.14±0.13 logMAR preoperatively and 0.09±0.11 logMAR after 6months) (P=.01). Furthermore, the aberrometric values were significantly reduced at the 6-month visit (P<.001). The mean of the surgically induced astigmatism was 2.15±1.44 diopters. No significant complication was observed. Topography-guided single-step transepithelial PRK is a safe and effective method for treating the irregular refractive errors in post-RK patients.

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.

Wavefront aberration changes caused by a gradient of increasing accommodation stimuli.

The aim of this study was to investigate the wavefront aberration changes in human eyes caused by a gradient of increasing accommodation stimuli. This is a prospective, single-site study. Healthy volunteers (n=22) aged 18-28 years whose refraction states were emmetropia or mild myopia, with astigmatism <1 diopter (D), were included in this study. After dilating the right pupil with 0.5% phenylephrine drops, the wavefront aberration of the right eye was measured continuously either without or with 1, 2, 3, 4, 5, or 6D accommodation stimuli (WFA1000B psychophysical aberrometer). The root mean square (RMS) values of the total wavefront aberrations, higher-order aberrations, and 35 individual Zernike aberrations under different accommodation stimuli were calculated and compared. The average induced accommodations using 1, 2, 3, 4, 5, or 6D accommodation stimuli were 0.848, 1.626, 2.375, 3.249, 4.181, or 5.085 D, respectively. The RMS of total wavefront aberrations, as well as higher-order aberrations, showed no significant effects with 1-3 D accommodation stimuli, but increased significantly under 4, 5, and 6 D accommodation stimuli compared with relaxed accommodation. Zernike coefficients of significantly decreased with increasing levels of accommodation. Higher-order wavefront aberrations in human eyes changed with increased accommodation. These results are consistent with Schachar's accommodation theory.

The influence of the sampling dots on the analysis of the wave front aberration by using the covariance matrix method

The covariance matrix method is a simple method for solving the Zernike polynomial with the higher fitting precision. In this paper, it was used to analyze the several optical wave fronts of the fine polished aluminum disk surface captured by a Twyman-Green interferometer system. We had found that the PV (peak-to-valley) and rms (root-mean-square) values of the wave front aberration changes with changing the Zernike term and the expressions for the several optical wave fronts with the different sampling dots were wrong. By analyzing the relations among the condition number of the coefficients matrix, the Zernike term, and the number of the sampling dots, it was indicated that the number of the sampling dots had only reduced the fluctuation the PV and the rms value while the Zernike term increases, but did not change the case that the expressions for the wave front aberration were wrong when the Zernike term is larger than 14, especially when the number of the sampling dots is less. Such an analysis will be valuable in solving the Zernike polynomial for the wave front aberration analysis by using the covariance matrix method in optical testing.

Dynamic Changes in Ocular Zernike Aberrations and Tear Menisci Measured with a Wavefront Sensor and an Anterior Segment OCT

To measure dynamic change characteristics of spatial and temporal variations in the post-blink tear film of normal eyes. A wavefront sensor was used to measure dynamic changes in wavefront aberrations, up to the seventh order, for 10 seconds in a group of 33 normal young adults. Tear menisci were imaged with an anterior segment optical coherence tomography (AS-OCT) system and tear film break-up times (TFBUTs) were determined. Systematic changes in main axis astigmatism (R(2) = 0.933, P < 0.0001), vertical coma (R(2) = 0.935, P < 0.0001) and spherical aberrations (R(2) = 0.879, P = 0.0002) occurred during the 10-second post-blink period. Both lower tear meniscus height and area increased by 10 seconds compared with the initial levels (P < 0.0001 for each). The change of vertical coma had significant correlation with the increase of lower tear meniscus areas during the 10-second post-blink period (R(2) = 0.181, P = 0.014). Subjects with TFBUTs < 15 seconds had significantly increased main axis astigmatism, vertical coma, and spherical aberrations by 10 seconds. Subjects with longer TFBUTs did not have any significant wavefront aberrations during that period. Systematic changes in some Zernike aberrations after blinking are associated with the changes in tear menisci and TFBUT. There was a substantial individual variation in dynamic changes of Zernike aberrations, suggesting the necessity to explore individual differences in tear quality and tear performance. Dynamic wavefront measurement combined with anterior segment optical coherence tomography could provide a useful tool to understand spatial and temporal processes of the tear film in clinical practice.

Changes in wave-front aberrations after rigid gas permeable contact lens fitting in post—laser in situ keratomileusis patients with visual complaints

Objective: To evaluate the effect of rigid gas permeable (RGP) contact lenses in reducing wave-front aberrations in post-laser in situ keratomileusis (LASIK) myopic patients. Design: Cross-sectional study. Participants: Thirty patients with visual complaints after conventional LASIK procedure for correcting myopia. Methods: The 30 patients were fitted with RGP contact lenses. Wave-front measurements were taken before and after RGP contact lens wearing. Results: Compared with bare eye examinations, root mean-square values of higher-order aberrations (HOAs) significantly decreased with RGP contact lens use. Amongthese, spherical aberration decreased from 0.507 (SD 0.304) μm to 0.164 (SD 0.121) μm( t = 7.186, p < 0.001); coma decreased from 0.470 (SD 0.312) μm to 0.165 (SD 0.090) μm ( t = 5.566, p < 0.001); secondary coma decreased from 0.079 (SD 0.050) μm to 0.044 (SD 0.027) μm ( t = 4.118, p < 0.001); and total HOAs decreased from 0.782 (SD 0.449) μm to 0.307 (SD 0.140) μm ( t = 6.710, p < 0.001). Conclusions: Fitting RGP contact lenses effectively decreased HOAs induced by conventional myopic LASIK surgery. Possible reasons may be the elimination of irregularity and dissymmetry on the corneal anteriorsurface, relief of the aspherical extent of the central corneal surface, and enlargement of the effective optical zone.

Dynamic wavefront aberrations and visual acuity in normal and dry eyes

Purpose: The aim was to study the dynamic properties of wavefront aberrations and visual acuity in normal and dry eyes.Methods: Thirty dry‐eye patients and 27 normal subjects participated in this study. Multi‐file mode of a Hartmann‐Shack wavefront sensor was used to measure dynamic wavefront aberrations for a period of 45 seconds. Dynamic measurements of visual acuity (VA) were made for 150 seconds using a multi‐functional VA tester. Standard deviation of the measurements (RMS or VA) over the testing period was used to estimate instability of the dynamic wavefront aberration and VA.Results: For most subjects, both wavefront aberration and VA changed over time and the instability varied substantially among individuals. Blink‐dependent fluctuation in wavefront aberration or VA was observed for some dry‐eye subjects. On average, the dry‐eye group had greater instability than the normal group in either the higher order wavefront aberrations (t = 2.09, p = 0.03, for OD; t = 3.76, p = 0.001, for OS) or the VA (t = 2.09, p = 0.02, for OD; t = 204, p = 0.03, for OS). Instability of VA in the dry‐eye group was significantly correlated with blink rate (r = 0.28, p = 0.02).Conclusion: Dynamic changes in wavefront aberrations and VA are highly individual dependent, while the dry eye tends to be less stable than the normal eye. The results suggest that tear‐film fluctuation might play a role in determining dynamic wavefront aberration and VA, however, contributions from other factors should not be overlooked. For dry eye, dynamic change in VA depends on blink rate.

Influence of Age on Ocular Wavefront Aberration Changes With Accommodation

To perform a quantitative analysis of high order wavefront aberrations of the entire optical system of the eye that accompanies accommodation demands in the healthy and emmetropic eye. Fifty-six healthy emmetropic eyes of 30 patients were separated into three groups according to age: group 1, 20 to 29 years; group 2, 30 to 39 years; and group 3, 40 to 49 years. Using iTrace ray-tracing technology, pupil diameter, objective refraction, and wavefront aberrations at accommodation demands of 0 to 4.00 diopters (D) in five 1.00-D increments were determined. In analyzing higher order aberrations in the central 4-mm diameter zone of the pupil, Zernike polynomials were used to study the changes associated with accommodation in the magnitude of total higher order aberrations, third order aberrations (coma-like aberrations), fourth order aberrations (spherical-like aberrations), and the spherical aberration component (C4(0)) of the fourth order aberrations. Pupil diameter decreased significantly (P < .05) with accommodation demand in each group. Total higher order aberrations in group 1 increased significantly (P < .05). No significant change was seen in third order aberrations in any group, but fourth order aberrations increased significantly (P < .05) in group 1. Spherical aberration (C4(0)) showed phase shifts from positive to negative in all groups, but the shift in group 3 was minimal, remaining positive even for a 4.00-D accommodation demand. Among higher order aberrations accompanying accommodation demands, spherical aberration (C4(0)) in particular showed characteristic changes; however, these changes showed age-related disparities. The changes were probably due to the effects of reduction in accommodation resulting from age-related changes in the crystalline lens.

Changes in Wavefront Aberration With Pharmaceutical Dilating Agents

Finding the best way to capture the wavefronts of small pupils for refractive surgery has become a more pressing issue as the general population ages. This study explores whether pharmaceutical dilation impacts wavefront measurement and pupil centroid. Baseline measurements were performed on 32 eyes using the VISX WaveScan Wavefront system. Pupils were dark adapted. One drop of 0.05% tropicamide was placed in each eye, and wavefront measurements were conducted at 10, 20, and 30 minutes. One drop each of 0.5% tropicamide and 2.5% phenylephrine were administered after the measurements. Wavefronts were captured again 30 minutes after the last eye drop. All patients returned for repeated procedures. Wavefront analysis was performed using the same pupillary area as the smallest capture from the same visit. Pupil center shift was taken into account. Mean patient age was 40 +/- 12 years (range: 20 to 59 years). Mean dark-adapted pupil was 6.40 +/- 1.17 mm. Pupil centers shifted randomly after pharmacological dilation compared to the dark-adapted condition. Pupil centers of 45% of the population shifted by > or = 0.2 mm. Repeatability coefficients were established for the wavefront measurements. After controlling for pupil diameter and pupil center, total high order aberrations root-mean-square (RMS) had changed significantly in 18% of the population. The diluted tropicamide formula, which caused less dilation effect, also induced less high order aberration RMS change. Pharmaceutical dilation agents cause random shifts of the pupil centroid from the dark-adapted pupil condition and could induce changes in wavefront measurements. Caution is required when resorting to dilation to obtain a wavefront measurement of smaller pupils.

Effects of the Seidel aberrations on visual target discrimination.

The effects of Seidel aberrations (primary defocus, spherical aberration, astigmatism, and coma) were simulated on four images using a digital image-processing system. The tolerances of the human visual system to different levels and combinations of the aberration types were determined by a forced-choice discrimination technique. The resulting threshold levels, expressed in units of wavelength, specify the changes in wave-front aberration that can be detected with some defined probability and represent just-noticeable differences (JND's) in image quality. The results are related to the corresponding Strehl intensity ratios and to the equivalent modulation transfer functions. The ultimate aim of the work is to link wave-front distortion to human visual discrimination, in order that meaningful methods of assessing visual image quality may be devised. The present investigation lays the foundations for further work, which, inter alia, will determine the effects of some higher-order aberrations.