Changes In Spherical Aberration Research Articles

Comparison of early visual outcomes after low-energy SMILE, high-energy SMILE, and LASIK for myopia and myopic astigmatism in the United States.

To compare uncorrected distance visual acuities (UDVAs) and induced higher-order aberrations (HOAs) in the early postoperative period between low-energy (LE) small-incision lenticule extraction (SMILE), high-energy (HE) SMILE, and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) procedures. University based refractive surgery center. Retrospective cohort study. Records of patients who underwent SMILE or FS-LASIK were retrospectively reviewed. SMILE patients were separated into 2 groups: HE settings (125 nJ, 3.0 μm spot spacing) and LE settings (125-130 nJ, 4.5 μm spot spacing). UDVA was measured at postoperative day (POD) 1. Corneal HOAs and UDVA were measured at postoperative month (POM) 1. Induced spherical aberration, vertical coma, horizontal coma, total coma, and total HOAs were calculated. The study included 147 eyes of 106 patients, 49 in each group. For SMILE patients, the difference in mean UDVA at POD1 was highly statistically significant in favor of the LE group (-0.003 vs 0.141, P < .0001). No significant difference in mean UDVA at POD1 was noted between the LE group and FS-LASIK group (-0.003 vs -0.011, P = .498). Induced change in spherical aberration was less in LE SMILE than that in FS-LASIK (0.136 vs 0.186 μm, P = .02) at POM1. No significant differences in POM1 mean UDVA (-0.033 vs -0.036) or induced change in all other HOAs were noted between LE SMILE and FS-LASIK. LE settings were associated with significantly improved POD1 UDVA. POD1 and POM1 UDVA were comparable with those of FS-LASIK. Spherical aberration induction was less with LE SMILE than that with FS-LASIK, whereas all other induced HOAs were comparable with FS-LASIK.

The influence of orthokeratology compression factor on ocular higher‐order aberrations

BackgroundTo investigate the influence of compression factor upon changes in ocular higher‐order aberrations (HOAs) in young myopic children undergoing orthokeratology treatment.MethodsSubjects aged between six and < 11-years, with low myopia (0.50–4.00 D inclusive), low astigmatism (≤ 1.25 D), and anisometropia (≤ 1.00 D), were randomly assigned to wear orthokeratology lenses of different compression factors in each eye (one eye 0.75 D and the fellow eye 1.75 D). HOAs were measured weekly over one month of lens wear. Wavefront analysis was conducted over a 5‐mm pupil using a sixth order Zernike polynomial expansion. Linear mixed models were used to examine the individual Zernike co‐efficients and specific root‐mean‐square (RMS) error (spherical, comatic, total HOAs) metrics and their changes between the two eyes during the study period.ResultsTwenty‐eight myopic (mean manifest spherical equivalent refraction: −2.10 ± 0.58 D) children (median [range] age: 9.3 [7.8–11.0] years) were analysed. Significant interocular differences in HOAs at baseline were observed for Z6−6 and Z6−4 only (both p < 0.05). During the lens wear period, eyes fitted with the increased compression factor showed greater changes in primary spherical aberration (Z40, p = 0.04) and RMS values for spherical and total HOAs (both p < 0.01). Considering data from both eyes together, after adjusting for the paired nature of the data, some other Zernike terms (Z31 and Z60, both p < 0.01) and the RMS value of comatic aberrations (p < 0.001) significantly increased after one month of orthokeratology treatment. The increase in primary spherical aberration (Z40) was positively correlated with the reduction in spherical equivalent refractive error, but only in eyes fitted with the increased compression factor (r = 0.69, p < 0.001).ConclusionsIncreasing the orthokeratology compression factor by 1.00 D significantly altered some HOAs, particularly spherical aberration. Given the association between positive spherical aberration and eye growth in children, further research investigating the influence of orthokeratology compression factor on axial eye growth is warranted.

Impact of monovision on dynamic accommodation of early presbyopes

To examine the impact of monovision on dynamic changes in accommodation, pupil responses, spherical aberration and resultant image quality in early presbyopes. Refractive state, pupil size and spherical aberration levels were monitored in nine early presbyopes who exhibited some accommodation (40-50years, mean=42±2.37years) using a Shack-Hartmann aberrometer as a binocularly viewed stimulus stepped closer (from 2m to 40cm), or farther (from 40cm to 2m). Comparison data from two fully presbyopic (i.e. non-accommodating) subjects (ages 46 and 61years) and two young adults (ages 26 and 29years) were also collected. Each subject was fit with four different refractive strategies: (1) both eyes corrected for 2m, (2) both eyes corrected for 40cm, (3) monovision with the measured right eye corrected for 2m and, (4) monovision with the right eye corrected for 40cm. Monochromatic image quality was quantified using the AreaMTF metric. When fit with monovision, the largest number of early presbyopes produce an accommodative response dominated by the right eye correction (distance or near) as the stimulus is abruptly changed from the retinal conjugate plane of one eye to that of the other eye. However, the accommodative responses in some early presbyopes were always dominated by the distance corrected eye, the near corrected eye, or by convergence. When the stimulus approached, the near corrected eye experienced high image quality only if there was no accommodative response. However, reduced image quality was observed if an accommodative response was initiated. Neither accommodation nor pupil response latencies were longer with monovision corrections compared with bilateral distance corrections (p>0.05). In the early presbyopes, spherical aberration was reduced during near viewing, but primarily due to pupil miosis and not lens shape changes. As the stimulus was abruptly changed from the retinal conjugate plane of the distance corrected eye to that of the near corrected eye, most early presbyopes fit with monovision accommodated, which resulted in a decline, not an increase in image quality in the near corrected eye. These results reveal a non-optimal accommodative strategy in early presbyopes fit with monovision.

Wavefront properties of the anterior and posterior corneal surface after transepithelial photorefractive keratectomy in myopia.

The present study aimed to evaluate the changes of corneal higher-order aberrations (HOAs) after transepithelial photorefractive keratectomy (TransPRK) in patients with myopia. A total of 80 eyes of 80 patients with myopia with or without astigmatism were evaluated. Prior to and 1 year after the surgery, uncorrected and corrected distance visual acuity in logMAR were assessed. Wavefront aberrations on the anterior surface of the cornea, as well as the posterior and total cornea, were measured via Pentacam. The HOA of the anterior surface and total values of spherical and coma aberrations increased significantly (P<0.001). However, HOAs of the anterior surface, and posterior and total values of the trefoil were not significantly changed (P=0.442, 0.805 and 0.936, respectively). A significant correlation of the pre-operative mean spherical equivalent refraction (MSER), astigmatism and central corneal ablation depth (CCAD) with the changes in coma aberration (r=0.268, P=0.016; r=0.260, P=0.020; r=0.323, P=0.004, respectively) and HOA (r=0.554, P<0.001; r=0.312, P=0.005; r=0.583, P<0.001, respectively) of the anterior surface of the cornea was determined. Furthermore, a significant correlation of the pre-operative MSER and CCAD with the changes in spherical aberration of the anterior corneal surface (r=0.462, P<0.001; r=0.510, P<0.001, respectively) was obtained. In conclusion, TransPRK offers an effective option for improving visual function in patients with myopia. The anterior corneal HOA, as well as spherical and coma aberrations, were significantly increased post-operatively. The HOA of the posterior cornea was not significantly changed. The change in the trefoil aberration was significantly correlated with pre-operative astigmatism, but the pre- and post-operative values were not significantly different.

Changes in Spherical Aberration and Coma Aberration after Wearing Aspheric Soft Contact Lens in Young Myopes

Changes in Spherical Aberration and Coma Aberration after Wearing Aspheric Soft Contact Lens in Young Myopes

Patient-specific determination of change in ocular spherical aberration to improve near and intermediate visual acuity of presbyopic eyes.

The purpose was to determine the optimum negative spherical aberration induction required to improve near and intermediate visual acuity (VA) of presbyopic eyes. A total of 174 normal and diabetic (no retinopathy) presbyopic eyes (age ≥ 40 years) were measured with visual adaptive optics simulator (Voptica, Spain). First, baseline uncorrected VA and aberrations were measured. VA at 40 cm (near), 80 cm (intermediate) and distance was measured. Then, a negative spherical aberration (SA) was added to baseline ocular SA, and VA at all targets was reassessed after correction of distance refractive error. Clinically, baseline SA and root mean square of higher order aberrations were similar between the normal and diabetic presbyopic eyes. Baseline VA of the diabetic eyes at near and intermediate was better than the same of normal eyes (P = 0.001). After SA change, VA at near and intermediate of both normal and diabetic presbyopic eyes improved. However, fewer diabetic eyes needed higher SA change than normal eyes (P = 0.03). The corresponding trends with change in VA at near and intermediate were also similar between the normal and diabetic eyes. Patient-specific modulation of ocular SA to improve near and intermediate VA in a large cohort of eyes was successful in improving VA, sometimes even distance VA.

Age-Related Changes in Corneal Spherical Aberration

To analyze the age-related changes in corneal spherical aberration (CSA) and higher order aberrations (HOAs) and to develop a novel model to estimate the change in CSA with age. This was a cross-sectional study of the right eyes of 3,769 patients. Anterior corneal spherical aberration (ASA), posterior corneal spherical aberration (PSA), total corneal spherical aberration (TSA), and the root mean square of corneal HOAs were measured using a Scheimpflug tomographer. Smoothed fitting curves were plotted as a function of age and the average change in spherical aberration was calculated for different ages. The mean magnitude of ASA, PSA, TSA, and HOAs (6 and 4 mm) were 0.270 ± 0.111, -0.144 ± 0.031, 0.228 ± 0.120, 0.453 ± 0.194, and 0.141 ± 0.075 µm, respectively. All parameters showed a statistically significant non-linear change with age. The age after which the aberrations increased at a faster rate, namely the turning points of age, were 39 years for ASA, PSA, TSA, and 6-mm HOAs (95% confidence interval [CI]: 35 to 42, 36 to 41, 36 to 42, and 35 to 56 years, respectively) and 46 years for 4-mm HOAs (95% CI: 36 to 56 years). There were significant increases in increment rates after the turning points. The average change of TSA was -0.013 µm/10 years from 18 to 39 years and 0.057 µm/10 years after 39 years. There were statistically significant correlations between ASA and TSA (r = 0.976, P < .001) and PSA and TSA (r = 0.192, P < .001), but not between ASA and PSA (r = -0.003, P = .835). CSA and HOAs increased non-linearly with age and became more positive after 39 and 46 years of age, respectively. Based on the increment rates and turning points of age, a novel model is provided to help calculate the value required to compensate for the increasing CSA associated with the aging cornea. [J Refract Surg. 2018;34(11):760-767.].

Presbyopic Excimer Laser Ablation: A Review.

To provide an overview of the efficacy and safety of available presbyopic excimer laser ablation profiles. Literature review. Monovision with excimer laser traditionally applies near correction to the non-dominant eye. Different excimer laser presbyopic approaches include the increase in depth of focus, through the controlled change of spherical aberration or asphericity, or multifocal ablation patterns with central or peripheral near vision zones. The studies investigating different excimer laser ablation patterns applied in previously myopic eyes revealed high levels of efficacy with all ablation profiles (between 68% and 99% achieving binocular uncorrected distance visual acuity [UDVA] of 20/25 or better, and between 70% and 100% achieving uncorrected near visual acuity [UNVA] presenting J3 or better). In hypermetropic eyes, most of the studies revealed high levels of efficacy with different platforms (between 78% and 100% achieving binocular UDVA of 20/25 or better and between 70% and 100% achieving UNVA presenting J3 or better). Loss of two or more lines of corrected distance visual acuity varied between 0% and 10% in the myopic eyes and between 0% and 14% in the hyperopic eyes. There is evidence that excimer laser presbyopic strategies accomplish spectacle independence at reasonable levels. There are reliable and safe options for both myopic and hyperopic eyes with satisfactory outcomes regarding near and distance vision. [J Refract Surg. 2018;34(10):698-710.].

Two-dimensional simulation of eccentric photorefraction images for ametropes: factors influencing the measurement.

Eccentric photorefraction and Purkinje image tracking are used to estimate refractive state and eye position simultaneously. Beyond vision screening, they provide insight into typical and atypical visual development. Systematic analysis of the effect of refractive error and spectacles on photorefraction data is needed to gauge the accuracy and precision of the technique. Simulation of two-dimensional, double-pass eccentric photorefraction was performed (Zemax). The inward pass included appropriate light sources, lenses and a single surface pupil plane eye model to create an extended retinal image that served as the source for the outward pass. Refractive state, as computed from the luminance gradient in the image of the pupil captured by the model's camera, was evaluated for a range of refractive errors (-15D to +15D), pupil sizes (3mm to 7mm) and two sets of higher-order monochromatic aberrations. Instrument calibration was simulated using -8D to +8D trial lenses at the spectacle plane for: (1) vertex distances from 3mm to 23mm, (2) uncorrected and corrected hyperopic refractive errors of +4D and +7D, and (3) uncorrected and corrected astigmatism of 4D at four different axes. Empirical calibration of a commercial photorefractor was also compared with a wavefront aberrometer for human eyes. The pupil luminance gradient varied linearly with refractive state for defocus less than approximately 4D (5mm pupil). For larger errors, the gradient magnitude saturated and then reduced, leading to under-estimation of refractive state. Additional inaccuracy (up to 1D for 8D of defocus) resulted from spectacle magnification in the pupil image, which would reduce precision insituations where vertex distance is variable. The empirical calibration revealed a constant offset between the two clinical instruments. Computational modelling demonstrates the principles and limitations of photorefraction to help users avoid potential measurement errors. Factors that could cause clinically significant errors in photorefraction estimates include high refractive error, vertex distance and magnification effects of a spectacle lens, increased higher-order monochromatic aberrations, and changes in primary spherical aberration with accommodation. The impact of these errors increases with increasing defocus.

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.

Predicted accommodative response from image quality in young eyes fitted with different dual-focus designs.

To investigate the separated and combined influences of inner zone (IZ) diameter and effective add power of dual-focus contact lenses (CL) in the image quality at distance and near viewing, in a functional accommodating model eye. Computational wave-optics methods were used to define zonal bifocal pupil functions, representing the optic zones of nine dual-focus centre-distance CLs. The dual-focus pupil functions were defined having IZ diameters of 2.10 mm, 3.36 mm and 4.00 mm, with add powers of 1.5 D, 2.0 D and 2.5 D (dioptres), for each design, that resulted in a ratio of 64%/36% between the distance and treatment zone areas, bounded by a 6 mm entrance pupil. A through-focus routine was implemented in MATLAB to simulate the changes in image quality, calculated from the Visual Strehl ratio, as the eye with the dual-focus accommodates, from 0 to -3.00 D target vergences. Accommodative responses were defined as the changes in the defocus coefficient, combined with a change in fourth and sixth order spherical aberration, which produced a peak in image quality at each target vergence. Distance viewing image quality was marginally affected by IZ diameter but not by add power. Near image quality obtained when focussing the image formed by the near optics was only higher by a small amount compared to the other two IZ diameters. The mean ± standard deviation values obtained with the three adds were 0.28 ± 0.02, 0.23 ± 0.02 and 0.22 ± 0.02, for the small, medium and larger IZ diameters, respectively. On the other hand, near image quality predicted by focussing the image formed by the distance optics was considerably lower relatively to the other two IZ diameters. The mean ± standard deviation values obtained with the three adds were 0.15 ± 0.01, 0.38 ± 0.00 and 0.54 ± 0.01, for the small, medium and larger IZ diameters, respectively. During near viewing through dual-focus CLs, image quality depends on the diameter of the most inner zone of the CL, while add power only affects the range of clear focus when focussing the image formed by the CL near optics. When only image quality gain is taken into consideration, medium and large IZ diameters designs are most likely to promote normal accommodative responses driven by the CL distance optics, while a smaller IZ diameter design is most likely to promote a reduced accommodative response driven by the dual-focus CL near optics.

Evaluation of Clinical Outcomes after LASIK for the Correction of Myopia Using the Advanced Customvue Excimer Laser Platform

-Purpose: To evaluate early visual, refractive and aberrometric outcomes after wave front-guided LASIK for the correction of low to moderate myopia and myopic astigmat is musing the excimer laser platform Advanced Custom Vue. Methods: A prospective, non-comparative study in 100 myopic eyes of 50 patients evaluating LASIK results over a period of 3 months. Main outcome variables included visual acuity, refraction, total higher-order aberrations (HOAs), spherical aberration (SA) and coma-like aberration. The surgery was performed using the VISX STAR S4 (Johnson and Johnson Vision) excimer laser and a wave front-guided ablation designed according to the iDesign aberrometer data (Johnson and Johnson Vision). Results: Mean preoperative sphere decreased from -4.07 ± 1.78 D to 0.32 ± 0.30 D at 3 months after surgery. Mean preoperative cylinder was reduced from -1.09 ± 0.88 D to -0.26 ± 0.28 D after the complete follow-up. Postoperative uncorrected distance visual acuity (UDVA) was 0.00 logMAR (20/20) or better in 100% of eyes, and 65.3% of eyes reached an UDVA of -0.20 logMAR (20/12.5) or better (p < 0.05). For a 6-mm pupil, the root mean square (RMS) for total ocular HOAs increased with surgery by 0.03 μm (p = 0.050), whereas the coma-like RMS increased by 0.05 μm (p < 0.001). The change in spherical aberration was +0.08 μm (p < 0.001). Conclusion: Wavefront-guided LASIK using the new generation excimer laser platform Advanced Custom Vue is safe and effective for treating myopia and myopic astigmatism, minimizing the postoperative level of HOAs.

Comparison of Visual Quality and Subjective Ocular Symptoms with Comfilcon A Silicone Hydrogel Contact Lens Wearing Times

Purpose: To compare the visual quality and subjective ocular symptoms with Comfilcon A silicone hydrogel contact lens wearing times. Methods: Twenty seven subjects (24.30 ± 2.96 years, 14 females, 13 males) took part in this study. Subjects were fitted with silicone hydrogel contact lenses providing best-corrected visual acuity. Best-corrected visual acuity (VA) at two contrast levels (100% and 10%) and best-corrected contrast sensitivity (CS) for four spatial frequencies (3, 6, 12 and 18 cycles/degree) were measured under photopic and mesopic conditions. Corneal higher-order aberrations (HOAs) were measured with 4-mm and 6-mm pupils using Wavefront Analyzer. Subjects were asked to complete the questionnaire for subjective ocular symptoms related contact lens. All measurements and questionnaires were performed after wearing silicone hydrogel lenses for 2 hours and 9 hours in a day. Results: Regarding visual quality under photopic and mesopic conditions, there was no statistically significant difference between 2 hours and 9 hours wear in high contrast, low contrast VA and CS. We also did not find out any significant changes in corneal HOAs, including third-order, fourth-order, coma, and spherical aberration for both 4-mm and 6-mm pupils between the two wearing times. Among the relative frequency items of subjective ocular symptoms related contact lens, there were statistically differences between 2 hours and 9 hours wear in discomfort, dryness, and closing eyes (p=0.031, p=0.001, and p=0.031, respectively). Conclusion: It can be identified that Comfilcon A silicone hydrogel contact lenses showed no change in the optical quality and visual quality of the eye for more than 9 hours wear. However, uncomfortable ocular symptoms and dryness increased as much as wearing time of the silicone hydrogel contact lens was longer. Thus, guidance of contact lens care to reduce those symptoms is considered necessary.

Crystalline lens paradoxes revisited: significance of age-related restructuring of the GRIN.

The accommodating volume-constant age-dependent optical (AVOCADO) model of the crystalline lens is used to explore the age-related changes in ocular power and spherical aberration. The additional parameter m in the GRIN lens model allows decoupling of the axial and radial GRIN profiles, and is used to stabilise the age-related change in ocular power. Data for age-related changes in ocular geometry and lens parameter P in the axial GRIN profile were taken from published experimental data. In our age-dependent eye model, the ocular refractive power shows behaviour similar to the previously unexplained "lens paradox". Furthermore, ocular spherical aberration agrees with the data average, in contrast to the proposed "spherical aberration paradox". The additional flexibility afforded by parameter m, which controls the ratio of the axial and radial GRIN profile exponents, has allowed us to study the restructuring of the lens GRIN medium with age, resulting in a new interpretation of the origin of the power and spherical aberration paradoxes. Our findings also contradict the conceptual idea that the ageing eye is similar to the accommodating eye.

Spherical Soft Contact Lens Designs and Peripheral Defocus in Myopic Eyes.

Peripheral retinal defocus has been implicated in myopia progression. The effect of commercially available spherical soft contact lenses (SCLs) on peripheral defocus of adult myopic eyes was investigated. Twenty-five young adults with spherical equivalent (SE) refractions between -0.50D and -6.00D were enrolled. Cycloplegic autorefraction (right eye) was measured centrally and ±20°, ±30°, and ±40° from the line of sight along the horizontal meridian using an autorefractor. Four commercially available spherical SCLs (Biofinity, Acuvue2, PureVision2, and Air Optix Night & Day Aqua) were evaluated. SE defocus (M) was used to calculate relative peripheral defocus (RPD) while wearing each SCL and relative peripheral refraction of the uncorrected eye. Spherical aberration (SA) changes caused by each SCL were measured along the line of sight by aberrometry. Peripheral defocus was analyzed using repeated-measures analyses of variance (RM-ANOVA). The association between changes in axial SA and the change in peripheral defocus was evaluated using linear mixed models. The mean age (±SD) and central SE refractive error were 24.0 ± 1.3 years and -3.45 ± 1.42D, respectively. PureVision2 did not change RPD (P = .33). Significant myopic shifts on the temporal retina were found with three lenses: Acuvue 2 (-0.29D at 30°; -0.80D at 40°; both P ≤ .01), Biofinity (-1.21 D at 40°; P = .02), and Air Optix Night & Day Aqua (-0.23D at 20°, -0.48D at 30°, and -1.50D at 40°; all P < .004). All SCLs caused a negative change in SA. SCLs inducing less negative (more positive) SA changes were associated with a less hyperopic change in RPD. Spherical SCL design can influence the peripheral defocus profile experienced by a myopic eye. Several, but not all, SCLs reduced peripheral hyperopia. Differences in how SCL types influence peripheral defocus may have implications for myopia progression.

Accommodation and pupil behaviour of binocularly viewing early presbyopes.

To study accommodation behaviour of early presbyopes with the full suite of accommodative stimuli, and to monitor changes in spherical aberration, pupil size and image quality that accompany the accommodative response. Using a high resolution Shack-Hartmann aberrometer, we measured refractive state as a binocularly viewed 0.30 logMAR (6/12 or 20/40) letter E was moved from 2m to 20cm and simultaneously monitored pupil diameter and spherical aberration for 19 subjects (mean age: 42±7.18years). Refractive state was defined using three standard criteria: minRMS, paraxial, and optimum image quality using the Visual Strehl ratio metric (VSOTF). Because of changes in spherical aberration, accommodative gain measured with the paraxial criterion is generally greater (on average by 34%) than the minRMS gain in early presbyopes. The slope of stimulus/response curve is relatively stable up to age 41 and then declines progressively in spite of a full binocular set of accommodative cues. Reduced accommodative gain appears once accommodative amplitude has dropped to below 3D, and gain drops to <0.5 as amplitude drops to 1.5D. This decline happens at different ages in different presbyopes. Prior to the early 40s, changes in accommodation are restricted to a reduction in amplitude, but during the 40s the continued loss of accommodative amplitude is accompanied by a concurrent drop in accommodative gain. Therefore, reduced near image quality in early presbyopes is caused by lower accommodative amplitudes and gains, which may explain the apparent acceleration in symptoms and near add prescriptions during the mid to late 40s.

Corneal Spherical Aberration and Corneal Asphericity after Small Incision Lenticule Extraction and Femtosecond Laser-Assisted LASIK.

Purpose To investigate corneal spherical aberration and corneal asphericity after small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK). Methods This study enrolled 70 patients having SMILE and 64 subjects receiving FS-LASIK. The preoperative spherical equivalent (SE) was −5.83 ± 1.23 diopters (D) and −6.20 ± 1.52 D, respectively. The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), SE, corneal spherical aberration, and asphericity over the 6.0 mm cornea were evaluated preoperatively and postoperatively. Results At 6 months, the UDVA, CDVA, and SE were −0.12 ± 0.11, −0.05 ± 0.05, and −0.16 ± 0.19 D in SMILE and −0.10 ± 0.06, −0.03 ± 0.06, and −0.08 ± 0.25 D in FS-LASIK. There was no difference between groups in the postoperative UDVA, CDVA, or SE (P > 0.05). SMILE showed lower inductions of spherical aberration along the anterior surface and the total cornea and less increases in corneal asphericity of the anterior surface postoperatively than FS-LASIK (P < 0.01). There were significant correlations between the changes in spherical aberration and corneal asphericity (P < 0.001). Conclusions SMILE and FS-LASIK exhibited excellent visual results and refractive outcomes. SMILE induced less increase in corneal spherical aberration and better preserved the corneal asphericity of the anterior corneal surface than FS-LASIK. Corneal asphericity changes contributed to the corneal spherical aberration changes following SMILE and FS-LASIK.

Minimum change in spherical aberration that can be perceived.

It is important to know the visual sensitivity to optical blur from both a basic science perspective and a practical point of view. Of particular interest is the sensitivity to blur induced by spherical aberration because it is being used to increase depth of focus as a component of a presbyopic solution. Using a flicker detection-based procedure implemented on an adaptive optics visual simulator, we measured the spherical aberration thresholds that produce just-noticeable differences in perceived image quality. The thresholds were measured for positive and negative values of spherical aberration, for best focus and + 0.5 D and + 1.0 D of defocus. At best focus, the SA thresholds were 0.20 ± 0.01 µm and -0.17 ± 0.03 µm for positive and negative spherical aberration respectively (referred to a 6-mm pupil). These experimental values may be useful in setting spherical aberration permissible levels in different ophthalmic techniques.

Photorefractive keratectomy combined with corneal wavefront–guided and hyperaspheric ablation profiles to correct myopia

To evaluate the effects of photorefractive keratectomy (PRK) combined with corneal wavefront-guided ablation profiles and hyperaspheric ablation profiles on changes in higher-order aberrations (HOAs). Yonsei University College of Medicine and Eyereum Clinic, Seoul, South Korea. Comparative observational case series. Medical records of patients who had corneal wavefront-guided hyperaspheric PRK, corneal wavefront-guided mild-aspheric PRK, or non-corneal wavefront-guided mild-aspheric PRK were analyzed. The logMAR uncorrected distance visual acuity (UDVA), manifest refraction spherical equivalent (MRSE), and changes in corneal aberrations (root-mean-square [RMS] HOAs, spherical aberration, coma) were evaluated 1, 3, and 6months postoperatively. The records of 61 patients (96 eyes) were reviewed. There was no statistically significant difference in logMAR UDVA or MRSE between the 3 groups at any timepoint. Corneal RMS HOAs were significantly smaller in the corneal wavefront-guided hyperaspheric group and the corneal wavefront-guided mild-aspheric group than in the noncorneal wavefront-guided mild-aspheric group at each timepoint. Corneal spherical aberration was significantly smaller for corneal wavefront-guided hyperaspheric PRK than for noncorneal wavefront-guided mild-aspheric PRK 6months postoperatively. Changes in corneal spherical aberration (preoperatively and 6months postoperatively) in corneal wavefront-guided hyperaspheric PRK were significantly smaller than in corneal wavefront-guided mild-aspheric PRK (P=.046). Corneal coma was significantly smaller with corneal wavefront-guided hyperaspheric PRK and corneal wavefront-guided mild-aspheric PRK than with noncorneal wavefront-guided mild-aspheric PRK 3months and 6months postoperatively. Corneal wavefront-guided hyperaspheric PRK induced less corneal spherical aberration 6months postoperatively than corneal wavefront-guided mild-aspheric PRK and noncorneal wavefront-guided mild-aspheric PRK. None of the authors has a financial or proprietary interest in any material or method mentioned.

Optimal incision sites to reduce corneal aberration variations after small incision phacoemulsification cataract surgery.

To analyze the effect of steep meridian small incision phacoemulsification cataract surgery on anterior, posterior and total corneal wavefront aberration. Steep meridian small incision phacoemulsification cataract surgery was performed in age-related cataract patients which were divided into three groups according to the incision site: 12 o'clock, 9 o'clock and between 9 and 12 o'clock (BENT) incision groups. The preoperative and 3-month postoperative root mean square (RMS) values of anterior, posterior and total corneal wavefront aberration including coma, spherical aberration, and total higher-order aberrations (HOAs), were measured by Pentacam scheimpflug imaging. The mean preoperative and postoperative corneal wavefront aberrations were documented. Total corneal aberration and total lower-order aberrations decreased significantly in three groups after operation. RMS value of total HOAs decreased significantly postoperatively in the 12 o'clock incision group (P<0.001). Corneal spherical aberration was statistically significantly lower after steep meridian small incision phacoemulsification cataract surgery in BENT incision group (P<0.05) and Pearson correlation analysis indicated that spherical aberration changes had no significant relationship with total astigmatism changes in all three corneal incision location. Corneal incision of phacoemulsification cataract surgery can affect corneal wavefront aberration. The 12 o'clock corneal incision eliminated more HOAs and the spherical aberrations decreased in BENT incision group obviously when we selected steep meridian small incision. Cataract lens replacement using wavefront-corrected intraocular lens combined with optimized corneal incision site would improve ocular aberration results.