Higher-order Aberrations Research Articles

A Novel Procedure for Treating Radial Keratotomy (RK) Induced Corneal Irregularity Utilizing Treatment of Epithelial Compensation of Higher-Order Aberrations and Topographic Guided Ablation-The CREATE Protocol.

To present the outcomes of a retrospective study of treatment of radial keratotomy-induced corneal irregularity with topographic guided ablation and a trans-epithelial approach based on epithelial compensation. Sixty eyes of 31 patients were treated for radial keratotomy-induced corneal irregularity utilizing a customized trans-epithelial topographic guided ablation photorefractive keratectomy (PRK) for treatment of corneal higher-order aberrations and lower-order astigmatism. Three-month results were analyzed via measurement of vision, refraction, residual higher-order aberrations (HOAs), residual lower-order and higher-order aberrations, as well as for loss or gains of lines of best corrected visual acuity. Higher-order aberrations (HOA) were reduced by 69%, with an 80% reduction of higher-order aberrations grouped with lower-order aberrations (Grouped). Most (95%) of eyes achieved 20/40 vision or better, 50% of eyes gained 1-9 lines of best corrected vision, and no eyes had loss of best corrected vision. Use of the CREATE protocol to treat RK-induced corneal irregularity resulted in a significant decrease in HOA, as well as a significant improvement in corrected distance visual acuity.

The Increase in Corneal Stiffness After Accelerated Corneal Cross-Linking in Progressive Keratoconus Using Different Methods of Epithelial Debridement.

The purpose of this study was to investigate corneal stiffening after epithelium-off accelerated corneal cross-linking (CXL; 9 mW/cm²) in progressive keratoconus (KC) with different methods of epithelial debridement. This was a retrospective, interventional, and non-randomized study. In group 1, the epithelium was removed using a hockey knife (N = 45). In group 2 (N = 39) and group 3 (N = 22), the epithelial thickness was measured by optical coherence tomography (OCT) and the epithelium was ablated by excimer laser, but, in group 3, stromal ablation was performed additionally to correct high order aberrations (HOAs). Corneal biomechanics (integrated invers radius [IIR], stress-strain index [SSI]) and corneal tomography (thinnest corneal thickness [TCT]) were assessed with Corvis ST and Pentacam prior to and 1 month after CXL. Corneal tomography did not differ among the groups preoperatively (P > 0.05). TCT decreased significantly in all groups after surgery (all P < 0.05). Nonetheless, corneal biomechanical stiffening was found in all three groups indicated by a decreased IIR and an increased SSI (all P < 0.05). For group 3, the HOA improved significantly (P < 0.001). Among the groups, there were no significant differences in changes of biomechanical parameters, but TCT was significantly reduced after laser ablation. Corneal stiffening after CXL is independent from epithelial removal. In particular, despite the removal of stromal tissue to correct HOA, a stiffening effect was achieved in keratoconic corneas, even it was less pronounced compared to mechanical epithelial removal. The reduction in HOA indicates a possible improvement in visual acuity. Cross-linking stiffens the keratoconus independent of epithelial debridement technique and may compensate minor stromal laser ablation.

Higher Order Aberrations in Patients with Unilateral Nasolacrimal Duct Obstruction.

To compare corneal higher order aberrations (HOAs) in patients with epiphora caused by unilateral primary acquired nasolacrimal duct obstruction (PANDO) and their fellow eyes. A total of 122 eyes of 61 patients with unilateral PANDO were included. Affected eyes were named as group 1 and contralateral eyes as group 2. The Munk score and fluorescein dye disappearance test (FDDT) were assessed. Corneal topographic and HOAs measurements were taken by Sirius topography. There were 47 female and 14 male patients. The mean keratometry was 43.84 ± 1.4 in group 1 and 43.96 ± 1.4 in group 2 (p = 0.73). The mean corneal topographic astigmatism was 0.81 ± 0.7 in group 1 and 0.78 ± 0.5 in group 2 (p = 0.57). The mean coma-like aberration was 0.19 ± 0.2 in group 1 and 0.10 ± 0.1 in group 2 (p = 0.03). The mean spherical-like aberration was 0.16 ± 0.1 in group 1 and 0.11 ± 0.1 in group 2 (p = 0.04). The mean total corneal HOA was 0.30 ± 0.5 in group 1 and 0.23 ± 0.2 in group 2 (p = 0.04). The mean Munk score was 3.47 ± 1.0 in group 1. There was a positive correlation between the Munk score and both coma-like aberration (r = 0.53, p = 0.003) and total corneal HOAs (r = 0.44, p = 0.010). The mean FDDT grade was 2.60 ± 0.1 in group 1. A positive correlation was observed between the FDDT grade and both coma-like aberration (r = 0.48, p = 0.001) and total corneal HOAs (r = 0.33, p = 0.001). Epiphora in patients with PANDO can affect corneal HOAs. As patients' symptoms and tear pooling were increased as corneal HOA levels increased.

Corneal Epithelial Remodeling Following Cylinder Correction With SMILE or FS-LASIK: A Contralateral Comparative Study.

To compare the corneal epithelial remodeling in eyes with high astigmatism that had small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK). Seventy-four patients with myopic astigmatism of greater than -2.00 diopters (D) and little binocular difference in spherical equivalent were included in this contralateral comparative study. All patients received SMILE in one eye and FS-LASIK in the other eye randomly. The corneal epithelial remodeling pattern was mapped using the latest RTVue spectral-domain optical coherence tomographer (Optovue) by region. Satisfactory refractive correction was achieved in all enrolled eyes with either SMILE or FS-LASIK. The corneal epithelium gradually thickened following surgical cylinder correction, distributing mainly along the flat medium. The corneal epithelium proliferation is milder centrally but more pronounced in the mid-peripheral area after SMILE, compared with FS-LASIK. The flat-steep difference in corneal epithelial thickness (CET) is evident in the mid-peripheral and peripheral areas, which is more obvious in SMILE. Residual cylinder was positively correlated with CET in eyes that had FS-LASIK, but not SMILE. More importantly, these epithelial changes were positively correlated with the ablation depth and higher order aberrations following surgical refractive correction. The postoperative CET map varied between SMILE and FS-LASIK. In eyes with high astigmatism, SMILE surgery is followed by milder and more stable corneal epithelial thickening. Moreover, the corneal epithelium is sensitive to stromal ablation and corneal remodeling is crucial to the postoperative visual quality. This study rigorously distinguished the CET difference between SMILE and FS-LASIK in astigmatic eyes and shed light on subsequent research. [J Refract Surg. 2024;40(10);e728-e741.].

A 6-Month Follow-Up Comparative Study of Single-Step Transepithelial Photorefractive Keratectomy (Trans-PRK) Using the StreamLight Software with and without Epithelial Thickness Customization.

To compare corneal aberrometry, densitometry, and refractive outcomes of single-step Transepithelial Photorefractive Keratectomy (Trans-PRK) with and without epithelial thickness customization. This was a prospective, interventional, randomized controlled study. Patients undergoing Trans-PRK using the WaveLight EX500 laser with StreamLight software (Alcon Laboratories, Forth Worth, TX, USA) were randomly assigned to control (55µm standard epithelial thickness) or customized (thinnest point of epithelial thickness for each patient) groups. MS-39 (CSO, Italy) anterior segment optical coherence tomography was used to measure the epithelial thickness. Inclusion criteria were spherical equivalent <6 diopters (D), astigmatism <4D, and CDVA 20/25 or better. The assessments were at baseline and 6 months post-op: visual acuity, refraction, aberrometry, and corneal densitometry. 108 eyes were enrolled, [control group (n=56) and customized group (n=52)]. Mean epithelial ablation thickness in the customized group was 54.81±3.56µm (p=0.470 vs control group). Both groups experienced significant postoperative increases in higher-order aberrations (HOA) and spherical aberrations, with no significant intergroup differences. Mean HOA RMS (µm) of the frontal cornea and total cornea increased by 0.27, and 0.29, respectively, in the control group, and 0.26 and 0.28, respectively, in the customized group (p<0.001 for all). Mean change in spherical aberrations in the frontal cornea and total cornea was 0.23µm (p<0.001) and 0.25µm (p<0.001), in the control group, and 0.19µm (p<0.001) and 0.20µm (p<0.001), in the customized group. Mean corneal densitometry in anterior cornea decreased by 0.63GSU (p=0.021) and 1.18GSU (p<0.001) in the control and customized groups. In the posterior cornea, it increased by 1.67GSU (p=0.004) and 0.38GSU (p=0.006). No significant differences in refractive and aberrometry outcomes between control and customized Trans-PRK groups, with corneal densitometry changes not affecting visual acuity.

Crosslinked All-Femtosecond Laser-Cut Corneal Allogenic Intracorneal Ring Segments (AFXL CAIRSs): Pilot Ex Vivo Study and Report of First Two Cases Performed in Italy.

Objectives: This pilot ex vivo study and first clinical experience in Italy evaluate the impact of using pre-implantation crosslinking on all-femtosecond laser-cut corneal allogenic intracorneal ring segments (AFXL CAIRSs). Methods: Six human donor eye-bank corneas were used for this preclinical ex vivo human study. Three donor (D) corneas were used for AFXL CAIRSs. First, they were prepared with an IntraLase™ femtosecond laser (Johnson & Johnson, New Brunswick, NJ, USA). The allogenic tissue rings were crosslinked before implantation with Riboflavin-UV-A accelerated crosslinking protocol (ACXL) with a 0.1% HPMC Riboflavin isotonic solution (Vibex Rapid, Glaukos-Avedro, Burlington, MA, USA) and a new KXL UV-A emitter (Glaukos-Avedro, USA). Three corneas were used as recipients (Rs) of the AFXL CAIRSs. After completing the ex vivo phase, IRB approval and signing a specific informed consent, the first two Italian patients were treated. A single ACXL CAIRS was implanted in a 51-year-old male with 53.53 D K steep, 363 μm minimum corneal thickness (MCT) and a double ACXL CAIRS was implanted in a 46-year-old male patient with 58.30 D K steep, 443 μm MCT. The longest follow-up was at three months. Results: Crosslinking of the segments enhanced tissue stiffness and grip, facilitating manipulation and CAIRS insertion into the recipient tunnels, and the yellowish color of the crosslinked segments improved visibility. The segment's thickness and volume remained unaltered during the follow-up. Both patients improved UDVA and BSCVA. K steep and High-Order Aberrations (HOAs) were reduced and MCT increased. Conclusions: Pre-implantation ACXL facilitated CAIRS insertion preserving dimensions and volume during the follow-up, rendering this important step a promising candidate in method standardization. Functional data and MCT improved significantly without adverse events.

A Closed-Form Analytical Conversion between Zernike and Gatinel–Malet Basis Polynomials to Present Relevant Aberrations in Ophthalmology and Refractive Surgery

The Zernike representation of wavefronts interlinks low- and high-order aberrations, which may result in imprecise clinical estimates. Recently, the Gatinel–Malet wavefront representation has been introduced to resolve this problem by deriving a new, unlinked basis originating from Zernike polynomials. This new basis preserves the classical low and high aberration subgroups’ structure, as well as the orthogonality within each subgroup, but not the orthogonality between low and high aberrations. This feature has led to conversions relying on separate wavefront reconstructions for each subgroup, which may increase the associated numerical errors. This study proposes a robust, minimised-error (lossless) analytical approach for conversion between the Zernike and Gatinel–Malet spaces. This method analytically reformulates the conversion as a nonhomogeneous system of linear equations and computationally solves it using matrix factorisation and decomposition techniques with high-level accuracy. This work fundamentally demonstrates the lossless expression of complex wavefronts in a format that is more clinically interpretable, with potential applications in various areas of ophthalmology, such as refractive surgery.

Analysis of third and fourth corneal high-order aberrations before and after small incision lenticule extraction (SMILE) in myopic and myopic astigmatic eyes using ray tracing aberrometry

BackgroundAim is to analyze alterations in third and fourth corneal higher-order aberrations using a ray tracing aberrometer (iTrace) induced by SMILE (small incision lenticule extraction) refractive surgery on Algerian patients; and also to investigate how corneal aberrations vary with spherical equivalent (SE), corneal central thickness (CCT), and age. Design Prospective, non-randomized case series that were carried out at the Chiali Smile Center, Algiers, Algeria.ParticipantsA total of 219 eyes from 110 myopic patients, with and without astigmatism, successfully concluded the ultimate follow-up. Participants exhibited an average age of 32.48 years, with preoperative mean corneal high-order aberrations (CHOA) measuring 0.005 ± 0.036 μm.MethodsA tracking trend analysis of high-order aberrations (HOAs) was conducted on the three groups of patients, assessing total corneal high-order aberrations after SMILE over periods of two, six, and twelve months.ResultsA substantial increase in total corneal high-order aberrations following SMILE, with a P value < 0.05. Conversely, there was a noteworthy and significant decrease in vertical trefoil for all groups (P value = 0.000). Interestingly, the corneal higher-order aberrations were more pronounced after two months compared to the six and twelve-month intervals. Spherical aberration demonstrated a significant increase with the extent of preoperative myopia and preoperative spherical equivalent both before and after SMILE surgery (P < 0.05), particularly in cases of high myopia. Moreover, there were significant reductions in preoperative and postoperative vertical coma (P = 0.047, P = 0.004, respectively) corresponding to the degree of preoperative myopia, with a more substantial decrease in vertical coma observed in cases of low myopia.ConclusionIn the post-SMILE period, a notable increase in vertical coma and spherical aberrations was observed, accompanied by a significant decrease in vertical trefoil across all eyes. These aberration changes were identified to be closely associated with the spherical equivalent.

Can AI Predict the Magnitude and Direction of Ortho-K Contact Lens Decentration to Limit Induced HOAs and Astigmatism?

Background: The aim is to investigate induced higher-order aberrations (HOA)s and astigmatism as a result of non-toric ortho-k lens decentration and utilise artificial intelligence (AI) to predict its magnitude and direction. Methods: Medmont E300 Video topographer was used to scan 249 corneas before and after ortho-k wear. Custom-built MATLAB codes extracted topography data and determined lens decentration from the boundary and midpoint of the central flattened treatment zone (TZ). An evaluation was carried out by conducting Zernike polynomial fittings via a computer-coded digital signal processing procedure. Finally, an AI-based machine learning neural network algorithm was developed to predict the direction and magnitude of TZ decentration. Results: Analysis of the first 21 Zernike polynomial coefficients indicate that the four low-order and four higher-order aberration terms were changed significantly by ortho-k wear. While baseline astigmatism was not correlated with lens decentration (R = 0.09), post-ortho-k astigmatism was moderately correlated with decentration (R = 0.38) and the difference in astigmatism (R = 0.3). Decentration was classified into three groups: ≤0.50 mm, reduced astigmatism by -0.9 ± 1 D; 0.5~1 mm, increased astigmatism by 0.8 ± 0.1 D; >1 mm, increased astigmatism by 2.7 ± 1.6 D and over 50% of lenses were decentred >0.5 mm. For lenses decentred >1 mm, 29.8% of right and 42.7% of left lenses decentred temporal-inferiorly and 13.7% of right and 9.4% of left lenses decentred temporal-superiorly. AI-based prediction successfully identified the decentration direction with accuracies of 70.2% for right and 71.8% for left lenses and predicted the magnitude of decentration with root-mean-square (RMS) of 0.31 mm and 0.25 mm for right and left eyes, respectively. Conclusions: Ortho-k lens decentration is common when fitting non-toric ortho-k lenses, resulting in induced HOAs and astigmatism, with the magnitude being related to the amount of decentration. AI-based algorithms can effectively predict decentration, potentially allowing for better control over ortho-k fitting and, thus, preferred clinical outcomes.

Objective quantification of posterior capsule opacification using swept-source anterior segment optical coherence tomography.

To objectively quantify posterior capsule opacification (PCO) using swept-source anterior segment optical coherence tomography (SS-ASOCT) in pseudophakic eyes. Zhongshan Ophthalmic Center, Guangzhou, China. Prospective cross-sectional study. One hundred and eighty eyes with PCO (37 multifocal intraocular lenses [MfIOLs] and 143 monofocal intraocular lenses [MoIOLs]) were enrolled. The PCO Irregular Degree (PID), defined to evaluate the surface irregularity of PCO, the average and maximum thickness of PCO (AT-PCO, MT-PCO) were applied to quantify PCO based on SS-ASOCT (CASIA2) images. Corrected distance visual acuity (CDVA), high order aberrations (HOAs), modulation transfer function (MTF) and Strehl ratio were recorded. The associations between SS-ASOCT parameters and visual function parameters were assessed by Spearman's correlation analysis. PID, AT-PCO and MT-PCO showed significant correlations with CDVA, Strehl ratio and HOAs (CDVA: r = 0.702, 0.741, 0.736; Strehl ratio: r = -0.746, -0.719, -0.740; HOAs: r = 0.762, 0.734, 0.752). The correlations of these three parameters with Strehl ratio and HOAs were significantly higher than those of clinical PCO grading with Strehl ratio and HOAs (all P < 0.05). Particularly, PID demonstrated notable correlations with Strehl ratio and HOAs. In addition, patients with MfIOLs presented worse Strehl ratio and HOAs than those with MoIOLs after matching age, PID, AT-PCO and MT-PCO. This study provides a novel method for objectively quantifying PCO using successive cross-sectional SS-ASOCT images. AT-PCO, MT-PCO and PID are presented as new indicators to document PCO severity, with PID offering a unique perspective by considering the irregularity aspect of PCO.

Study of corneal and retinal thicknesses at five years after FS-LASIK and SMILE for myopia

BackgroundThis study aimed to observe corneal and retinal thicknesses at 5 years after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) for myopia, investigate the effect of epithelial remodeling on refractive status and visual quality, and compare retinal thicknesses among fundus tessellation grades.MethodsPatients who received FS-LASIK or SMILE 5 years before were enrolled in this cross-sectional study. After 1:1 propensity score matching, each surgical group obtained 177 patients (177 eyes). Examinations including visual acuity, refraction, corneal and retinal thicknesses, corneal higher-order aberrations (HOAs), and fundus photography were performed in this visit at 5 years after surgery. The Quality of Vision (QoV) questionnaire was used to assess visual symptoms and overall satisfaction. Corneal and retinal thicknesses between groups were compared, contributing factors were analyzed, and correlations with postoperative refractive status, HOAs, QoV scores and overall satisfaction were evaluated.ResultsThe discrepancy of epithelial thickness between central and pericentral zones in FS-LASIK group was larger than that in SMILE group, which was negatively correlated with postoperative spherical equivalent (SE), positively correlated with spherical aberration (all P < 0.05), but not correlated with QoV scores and overall satisfaction (all P > 0.05) in both surgical groups. There was no statistical difference in stromal thickness and total corneal thickness (all P > 0.05). Most annuluses of epithelial and stromal thicknesse were linearly related to preoperative SE (all P < 0.05). The macular thickness, ganglion cell complex thickness, and retinal nerve fiber layer thickness exhibited comparable values between two surgical groups and four fundus tessellation grades, with no significant association observed with postoperative SE (all P > 0.05).ConclusionThe tendency that epithelial thickness in central zone was thicker than peripheral zone was more obvious at 5 years after FS-LASIK compared to SMILE. This uneven distribution of epithelial thickness might play a role in myopic regression and the changes in HOAs, especially in patients with high myopia, but it had little effect on patients’ subjective visual quality and satisfaction. Retinal thicknesses were not affected by these two surgical methods, and they did not appear to be the clinical indicators for myopic regression or fundus tessellation progression.

Design method of zoom systems based on high-order structural aberration coefficients

Design method of zoom systems based on high-order structural aberration coefficients

Scheimpflug Tomographic Indices for Classifying Normal, Down Syndrome and Clinical Keratoconus in Pediatric Patients.

The study aimed to evaluate the precision of different Pentacam indices in diagnosing keratoconus (KC) in pediatric patients with and without Down Syndrome (DS) and determine suitable cutoff values. This prospective multicenter cross-sectional study evaluated 216 eyes of 131 patients aged 6-18 years (mean age 12.5 ± 3.2 years) using Pentacam. Patients were categorized into four groups: KC, forme fruste keratoconus (FK), DS, and control, excluding DS patients with topographic KC. Receiver operating characteristic curves were generated to determine the optimal cutoff points and compare the accuracy in identifying KC and FK in patients with and without DS. In DS patients, corneal morphology resembled KC features. The most effective indices for distinguishing KC in DS patients were the average pachymetric progression index (AUC = 0.961), higher-order aberration of the anterior cornea (AUC = 0.953), anterior elevation (AUC = 0.946), posterior elevation (AUC = 0.947), index of vertical asymmetry (AUC = 0.943), and Belin/Ambrosio enhanced ectasia total derivation value (AUC = 0.941). None of the indices showed good accuracy for distinguishing FK in DS patients. The thresholds of these indices differed significantly from non-DS patients. The results highlighted the need for DS-specific cutoff values to avoid false-positive or false-negative diagnoses in this population.

Computational approach for correcting defocus and suppressing speckle noise in line-field optical coherence tomography images.

The trade-off between transverse resolution and depth-of-focus (DOF) typical for optical coherence tomography (OCT) systems based on conventional optics, prevents "single-shot" acquisition of volumetric OCT images with sustained high transverse resolution over the entire imaging depth. Computational approaches for correcting defocus and higher order aberrations in OCT images developed in the past require highly stable phase data, which poses a significant technological challenge. Here, we present an alternative computational approach to sharpening OCT images and reducing speckle noise, based on intensity OCT data. The novel algorithm uses non-local priors to model correlated speckle noise within a maximum a posteriori framework to generate sharp and noise-free images. The performance of the algorithm was tested on images of plant tissue (cucumber) and in-vivo healthy human cornea, acquired with line-field spectral domain OCT (LF-SD-OCT) systems. The novel algorithm effectively suppressed speckle noise and sharpened or recovered morphological features in the OCT images for depths up to 13×DOF (depth-of-focus) relative to the focal plane.

Prospective Objective Analysis of Corneal Haze Following Customized Transepithelial PRK Without Mitomycin C Combined With Accelerated Corneal Cross-Linking Versus Corneal Cross-Linking Alone.

To compare haze and refractive outcomes in patients undergoing combined accelerated corneal cross-linking (A-CXL) and selective wavefront-guided transepithelial photorefractive keratectomy (WG-transPRK) without mitomycin C (MMC) versus those undergoing A-CXL. This prospective study analyzed 95 eyes (86 patients) with progressive keratoconus from October 2018 to October 2022. The first group underwent CXL combined with corneal or ocular WG-transPRK (CXL+PRK, n = 52), targeting higher order aberrations (HOAs). The second underwent CXL only (n = 43), both following the same accelerated CXL protocol without MMC on the SCHWIND Amaris laser platform (SCHWIND eye-tech-solutions). Baseline and postoperative evaluations (1, 3, 6, and 12 months) included uncorrected (UDVA) and corrected (CDVA) distance visual acuity, manifest refraction, tomography, corneal HOAs, and optical coherence tomography (OCT) scans. A patented machine learning algorithm objectively detected and quantified stromal haze on OCT scans in grayscale units. In both groups, anterior corneal haze reflectivity and subepithelial haze peaked at 3 months postoperatively, then progressively decreased at 6 and 12 months. Haze did not differ between groups at any time point. By 12 months, CDVA increased by 2.5 lines in the CXL+PRK group (P < .001) and by 0.7 lines in the CXL group (P = .10), and maximum keratometry decreased from 51.70 ± 5.10 to 47.90 ± 7.90 diopters (D) (CXL+PRK group) (P < .001) and from 51.20 ± 5.10 to 50.30 ± 4.60 D (CXL group) (P = .004). Corneal HOAs decreased in both groups but more in the CXL+PRK group. Combining CXL with WG-transPRK without MMC does not result in increased haze when compared to A-CXL alone. This combined approach achieves greater improvements in visual, topographic, and aberrometric parameters. [J Refract Surg. 2024;40(9):e583-e594.].

Comparing the Postoperative Outcomes of Intrastromal Corneal Ring Segments in Three Different Topographic Patterns of Eccentric Keratoconus.

To compare the postoperative outcomes following implantation of KERATACx ring segments (Imperial Medical Technologies Europe GmbH) in patients having eccentric keratoconus with three different topographic patterns. This retrospective cohort study was conducted at Maadi Eye Subspeciality Center, Cairo, Egypt. The study included patients with keratoconus who had implantation of KERATACx ring segments. Three groups were segregated based on topographic keratoconus patterns using the Sirius CSO Topographer (CSO Italia): type I ectasia where the cone coincides with the corneal flat axis, type II ectasia in which the cone coincides with neither the steep nor the flat axis and lies between the two axes, and type II ectasia for cones coinciding with the corneal steep axis. The visual and topographic outcomes were compared preoperatively and postoperatively for the three enrolled groups. This study enrolled 92 eyes of 92 patients and had a mean ± standard deviation follow-up of 16.9 ± 9.2 months. The patients' medical records revealed that night vision complaints and halos around the light were experienced the most by the type III ectasia group (31.25%). For the type III ectasia group, four topographic indices and one visual parameter did not show statistically significant differences between the preoperative and postoperative data (inferior-superior difference at 2- and 4-mm diameter, coma aberration, higher order aberrations, and uncorrected distance visual acuity), contrary to the type I and II ectasia groups, which showed significant improvements in all evaluated parameters. The type III morphological pattern of ectasia is the least likely to benefit from KERATACx ring segments implantation. [J Refract Surg. 2024;40(9):e625-e634.].

Repeatability of a Combined Adaptive Optics Visual Simulator and Hartman-Shack Aberrometer in Pseudophakic Eyes With and Without Previous Corneal Refractive Surgery.

To evaluate the intrasession repeatability of wavefront aberrations obtained by a combined adaptive optics visual simulator and Hartman-Shack aberrometer in pseudophakic eyes with and without previous corneal refractive surgery. Three consecutive measurements were performed in one eye of each individual. Total ocular aberrations were recorded up to the 5th Zernike order for a 4.5-mm pupil. Repeatability was assessed by calculating the within-subject standard deviation (Sw), the repeatability limit (R), and the intraclass correlation coefficient (ICC). Vector analysis was performed to assess astigmatism variability between scans. The study enrolled 32 normal individuals and 24 individuals with a history of refractive surgery. In normal and eyes that had previous refractive surgery, respectively, the Sw values were 0.155 and 0.176 diopters (D) for sphere and 0.184 and 0.265 D for cylinder. The Sw values for all 3rd order terms ranged from 0.037 to 0.047 µm in normal eyes and 0.044 to 0.063 µm in eyes that had previous refractive surgery. The Sw for primary spherical aberration was 0.020 µm in normal eyes and 0.026 µm in eyes that had previous refractive surgery. ICC values for measurements of astigmatism yielded larger variability (ICC = 0.751 and 0.879). However, both groups demonstrated excellent repeatability (ICC > 0.9) for root mean square higher order aberrations (RMS-HOA) and total RMS values. In pseudophakic eyes, the adaptive optics Hartmann-Shack device demonstrated acceptable repeatability for measurement of sphere and 3rd and 4th order HOAs with higher variability for astigmatism measurements, especially in eyes with a prior history of corneal refractive surgery. [J Refract Surg. 2024;40(9):e645-e653.].

High hyperopic LASIK with reduction of corneal prolateness to control-induced spherical aberration.

To evaluate visual outcomes of high hyperopic laser in situ keratomileusis (LASIK), using corneal aspherization to control the induced spherical aberration. Fondation Ophtalmologique Adolphe de Rothschild, Paris, France. Prospective interventional case series. Prospective interventional study of consecutive high hyperopes (≥+3 diopters [D] of spherical equivalent [SE]) undergoing LASIK with the WaveLight FS200 femtosecond and EX500 excimer laser platform. An aspheric ablation profile (planned change in corneal asphericity ΔQ = +0.2) was delivered using the Custom-Q nomogram on an optical zone of ≥6.5 mm centered near the corneal vertex. Uncorrected corrected distance visual acuity (UDVA) and corrected distance visual acuity, as well as changes in SE, corneal asphericity (ΔQ), and higher-order aberrations, were analyzed preoperatively and on day 1, 1, 3, 6, and 12 months. 117 eyes of 63 patients (mean age of 30.1 ± 5.6 years) were included. Preoperatively and at 12 months postoperatively, the mean SE was 5.1 ± 1.1 D and 0.00 ± 0.7 D, respectively. 88% of eyes achieved 0 logMAR or better UDVA at 12 months. 1 month postoperatively, there was a statistically significant induction of positive spherical aberration decreasing progressively and significantly until the last visit (preop SA4 = 0.09 ± 0.11 μm, day 1 SA4 = 0.30 ± 0.32 μm, 12 months SA4 = 0.08 ± 0.21 μm, P = .056). 2 eyes needed enhancement at 12 months. LASIK for high levels of hyperopia showed good outcomes mainly due to aspheric-customized ablation profile with a change of ΔQ = +0.2 in corneal asphericity.

Comparison between 80-microns versus 100-microns flap femtosecond LASIK for correction of myopia and myopic astigmatism.

This study aimed to compare the safety, efficacy, and visual outcomes of 80-microns LASIK versus 100-microns LASIK in managing myopia and myopic astigmatism. The study was conducted at a tertiary care hospital in North India. This was a prospective contralateral eye study that included patients with myopia and myopic astigmatism seeking refractive correction. The eligibility criteria included normal corneal topography, an epithelial thickness less than 60 microns, a calculated percentage tissue ablation (with 100-microns flap) less than 40%, a calculated residual stromal bed thickness (with 100-microns flap) more than 300 microns, and willingness to participate and follow up. Patients with glaucoma, cataracts, other visually disabling ocular pathologies, and a history of past ocular surgery were excluded. All patients underwent LASIK with 80-microns LASIK in one eye and 100-microns LASIK in the other eye. The patients were followed up for 6 months, and the results were analyzed. The study included 216 eyes of 108 patients. The mean preoperative spherical equivalent in the 80-microns group and the 100-microns group was -3.53 ± 1.81 and -3.69 ± 1.32 diopters, respectively (P = 0.78). The mean 6 months decimal postoperative UCVA was 0.98 ± 0.13 in the 80-microns group and 0.97 ± 0.14 in the 100-microns group (P = 0.99). The postoperative change in the higher-order aberration profile was comparable in both groups (P = 0.78). The percentage tissue ablation was significantly lower in the 80-microns group (P = 0.002). The incidence of flap micro striae and OBL was higher in the 80-microns group, while neither of these had any visual implications. The study concluded that 80-microns LASIK is an efficacious and safe alternative to 100-micron LASIK, especially useful in patients with higher myopia.

Recent Advances in Refractive Surgery: An Overview.

Refractive surgery has experienced substantial advancements over the past few years, driven by innovative techniques and continuous technological progress aimed at enhancing visual outcomes and patient satisfaction. Refractive errors such as myopia, hyperopia, and astigmatism affect a significant portion of the global population, impacting quality of life and productivity. Recent advancements have been fueled by a deeper understanding of ocular biomechanics and visual optics, leading to more precise and effective treatments. Traditional methods such as LASIK and PRK have been refined, and new procedures like SMILE (Small Incision Lenticule Extraction) have been introduced, expanding the range of treatable refractive errors and improving safety and predictability. Customized treatments, such as wavefront-guided LASIK and topography-guided PRK, allow for individualized plans tailored to each patient's unique corneal characteristics, enhancing visual acuity and reducing higher-order aberrations. The use of femtosecond lasers in procedures like Femto-LASIK and femtosecond laser-assisted cataract surgery (FLACS) offers unparalleled precision, reducing surgical risks and improving outcomes. Implantable Collamer Lenses (ICLs) and corneal crosslinking (CXL) have emerged as effective options for specific patient groups. Advanced diagnostic tools like optical coherence tomography (OCT) and Scheimpflug imaging have improved surgical planning and complication management. As research and technology continue to evolve, these advancements promise even greater improvements in refractive surgery, addressing the visual needs of the global population.