Posterior Corneal Elevation Research Articles

Two-year follow-up of posterior corneal elevation after small incision lenticule extraction for moderate myopia

Purpose To assess the changes in the posterior corneal elevation two years after small incision lenticule extraction (SMILE) in patients with moderate myopia. Methods Total 35 patients (70 eyes) who underwent SMILE operation were included in this study. Posterior corneal elevation (PCE), the average posterior central elevation change (ΔPCE) were assessed by Pentacam images at 6 months and 2 years after surgery (January 2022–December 2023). Uncorrected and best corrected distance visual acuities (UCDVA and BCDVA), and manifest refraction spherical equivalent (MRSE) were evaluated. These data were compared to the preoperative ones. Results The safety and efficacy indices were 1.00±0.03 and 0.95±0.08, respectively. All the eyes were within ±1.00 D 2 years after surgery. In the sixth postoperative month, the mean PCE was 2.61±2.88 and the mean ΔPCE was 0.68±3.45. After 2 years of surgery, the mean PCE was 1.98±2.72, and the mean ΔPCE was 0.02±1.17. Thirty-five (50%) eyes showed +ve ΔPCE (foreword posterior corneal surface protrusion) at 6 months of surgery, 30 (85.7%) of them showed decreased positivity (posterior surface moved posteriorly), while five (14.3%) eyes of them remained stable 2 years after surgery. Conclusion SMILE procedure resulted in changes in the PCE. However, these changes remained stable and within the normal range for 2 years after surgery. SMILE can be considered as a safe procedure for moderate myopia for 2 years of observation.

Optimizing keratoconus treatment with AI‐driven lenticule matching using pentacam indices

Aims/Purpose: The aim of this study is to develop an advanced artificial intelligence (AI) methodology to optimize the matching of donor and recipient lenticules for the treatment of keratoconus. This approach leverages Pentacam indices related to corneal thickness and topography to minimize the preparatory modifications required for stromal lenticule implantation.Methods: We will construct a comprehensive database of donor and recipient lenticules by systematically collecting Pentacam‐derived indices, including central corneal thickness (CCT), anterior and posterior corneal elevation, and corneal curvature, at preoperative, intraoperative, and postoperative stages. Using these datasets, an AI algorithm capable of identifying the most compatible lenticule pairs will be trained and validated. The algorithm's performance will be assessed based on its accuracy in predicting optimal matches and the practical effectiveness of the process.Results: As this project is in its preliminary phase, no results are currently available. However, we hypothesize that the AI‐assisted matching system will significantly enhance the compatibility of donor and recipient lenticules. Expected outcomes include increased postoperative central corneal thickness, improved corrected distance visual acuity (CDVA), and reduced corneal irregularity.Conclusions: This study aims to validate the potential of AI‐assisted matching of donor and recipient lenticules using Pentacam indices as a transformative approach in the treatment of keratoconus. By refining the customization process, we anticipate improvements in surgical efficiency and patient outcomes.

Characteristics of corneal aberration in patients with bilateral keratoconus and unilateral corneal Vogt's striae.

To assess the corneal high-order aberration (HOA) and its correlation with corneal morphological parameters in patients with bilateral keratoconus (KCN) and unilateral Vogt's striae. A total of 168 eyes of 84 patients with KCN, whose corneas had definite signs of unilateral Vogt's striae, were enrolled. Corneal HOA and morphological parameters were measured using Pentacam HR. The corneal morphological parameters between KCN eyes with and without Vogt's striae were evidently different (P<0.001). The 3rd coma 90°, 4th spherical aberration, 5th coma 90°, root-mean-square (RMS) (total), and RMS (HOA) in the front, back surfaces and total cornea in KCN eyes with Vogt's striae were significantly higher than those in KCN eyes without Vogt's striae (P<0.001). In KCN eyes with Vogt's striae, the 3rd coma 90° and 4th spherical aberration in the front surface and total cornea were negatively correlated with flat keratometry value (K1), steep keratometry value (K2), mean keratometry value (Km), maximum keratometry value (Kmax), anterior corneal elevation (ACE), and posterior corneal elevation (PCE; P<0.05). The 3rd coma 90°, 4th spherical aberration in back surface and RMS (total), RMS (HOA) in the front, back surfaces, total cornea were positively correlated with K1, K2, Km, Kmax, ACE, and PCE (P<0.05). Corneal HOA especially vertical coma and spherical aberration may increase when Vogt's striae appeared in KCN eyes. The scale of increase is significantly related with changes in corneal shapes.

Influence of Biometric and Corneal Tomographic Parameters on Normative Corneal Aberrations Measured by Root Mean Square.

Background/Objectives: To determine the impact of corneal and biometry parameters on the normative root mean square (RMS) values of corneal aberrations measured at a 6 mm diameter. Methods: The RMS values for corneal aberrations (anterior, posterior, and total) were measured along with corneal parameters using Scheimpflug tomography on 770 normal subjects. The biometric parameters were measured with an optical biometer. A multiple linear regression model was used to assess the effect of these parameters on the RMS values for corneal aberrations. Results: The mean RMS values for low-order (LOAs) and high-order 6 mm aberrations (HOAs) were 1.883 ± 0.797 µm and 0.484 ± 0.173 µm, respectively, and for the anterior and posterior cornea, the values were 0.775 ± 0.166 µm and 0.189 ± 0.036 µm, respectively. For the anterior cornea, the main predictors of the RMS LOAs (R2 = 69.8%) were anterior corneal astigmatism (ACA) and anterior corneal elevation (Ele F) on the apex (both p < 0.0001) and for the RMS HOAs (R2 = 33.3%) the main predictors were age, ACA, and Ele F on the thinnest point (all p < 0.0001). For the posterior cornea, considering only the posterior corneal variables, the main predictors of the RMS LOAs (R2 = 63.4%) were posterior corneal astigmatism and posterior corneal elevation (Ele B) on the thinnest point and apex (all p < 0.0001) and for the RMS HOAs (R2 = 46%) the main predictors were the mean posterior keratometry and Ele B on the thinnest point and apex (all p < 0.0001). Conclusions: Normative data of RMS values for corneal aberrations measured over 6 mm are influenced by age and several corneal parameters, which should be considered when evaluating the diagnostic ability of the RMS values.

Posterior corneal elevation after small incision lenticule extraction (SMILE) in eyes of different myopia severity

PurposeTo investigate the changes in posterior corneal elevation after small incision lenticule extraction (SMILE) surgery in eyes of different myopia severity. MethodsA total of 141 eyes of 86 patients were recruited and followed at 1 month, 3 months, 6 months, and 12 months after SMILE surgery. The eyes were divided into four groups according to the spherical equivalent (SE): low myopia (LM, −3.00 D≤SE<−0.50 D, 35 eyes), moderate myopia (MM, −6.00 D≤SE<−3.00 D, 54 eyes) and high myopia (HM, −10.00 D≤SE<−6.00 D, 52 eyes). Posterior corneal elevation was measured by Pentacam HR. Posterior corneal apex elevation (PCAE), posterior maximum elevation (PME), and posterior elevation at the thinnest point of the cornea (TPC) in the central 4-mm area were recorded and compared among different examination time points in the same group or among different groups at the same time point. ResultsUncorrected distance visual acuity (UDVA) at 12 months was 20/20 or better in 100.00 % of eyes in LM group, 100.00 % in MM group and 96.15 % in HM group (P > 0.05). There were significant reductions of post-operative PCAE compared to baseline in the LM group (P = 0.038) and HM group (P<0.001), and the reduction was marginally significant in the MM group (P = 0.076). No statistically significant changes in PME were observed after SMILE surgery in the three groups (all P > 0.05). TPC was significantly decreased after the surgery in the MM group (P = 0.022) and the HM group (P<0.001), and was marginally significantly decreased in the LM group (P = 0.063). There was no significant difference in PCAE and PME among the three groups at baseline or any postoperative timepoint (all P > 0.05). TPC was significantly different among the three groups at 3 months, 6 months and 12 months (all P < 0.05), but not at baseline (P = 0.066) or 1 month (P = 0.080). ConclusionIn the first year after SMILE surgery, PCAE was decreased in both LM and HM eyes, and TPC were decreased in MM and HM eyes, but PME was stable after the surgery.

Posterior corneal stability after small incision lenticule extraction with different optical zones.

To assess the changes in the posterior corneal surface following small incision lenticule extraction (SMILE) with different optical zones. In this retrospective study, 106 eyes of 106 patients who underwent SMILE were recruited 3 years after the procedure. Eyes were divided into two groups according to the size of the surgical optical zone: group A (52 eyes, ≤6.2 mm) and group B (54 eyes, ≥6.5 mm). Posterior central elevation (PCE) and 12 other points at 45°, 135°, 225° and 315° with distances of 1 mm, 2 mm and 3 mm from the centre were recorded from Pentacam. No iatrogenic keratectasia was identified, and eyes in the two groups showed comparable visual results. The overall trend in posterior corneal elevation changes was consistent for both groups. PCE decreased significantly from 1.33 ± 2.32 to 0.75 ± 2.41 in group A (P = 0.024) and from 0.87 ± 2.61 to 0.06 ± 2.74 in group B (P = 0.003). All points in the central 2 mm region in both groups were reduced postoperatively. In the 4 mm and 6 mm corneal annulus, almost all points at 225°and 315° showed backward displacement, with the most prominent change occurring at 315° in the 6 mm annulus (P < 0.001), indicating no forward protrusion in the inferior area. No forward protrusion in the posterior corneal surface was observed 3 years after SMILE with different optical zones. Comprehensive preoperative measurements are essential for ensuring corneal stability and avoiding iatrogenic keratectasia.

Visual and refractive outcomes after SMILE versus FS-LASIK: a paired-eye study.

To compare visual acuity, refraction, Schirmer test, tear break-up time (TBUT), esthesiometry, optical quality, higher order aberrations and posterior corneal elevation measurements before and after small-incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK). Paired eye, randomized, cohort study. Follow-up was performed at days 1 and 7, and at months 1, 3, 6 and 12. Forty-two eyes were enrolled in the study. Over time, a difference in posterior corneal elevation was statistically significant (p < 0.01) with a greater change in patients treated with SMILE. There was no difference in corrected distance visual acuity and uncorrected distance visual acuity and cylinder between the two techniques; however, there was a statistical significant difference in spherical error and spherical equivalent (p < 0.01). There was no difference between the eyes with FS-LASIK and SMILE in the assessment regarding the TBUT, the Schirmer test and esthesiometry. SMILE showed more changes in the posterior elevation with a progressive backward shift throughout time during follow-up. SMILE and FS-LASIK provides similar results in myopic patients regarding visual acuity, refraction, Schirmer test, TBUT and esthesiometry.

Regional analysis of posterior corneal elevation after laser refractive surgeries for correction of myopia of different degrees.

To evaluate regional changes in the posterior corneal elevation after three laser refractive surgeries for correction of myopia of different degrees. Retrospective, comparative, and non-randomized study. Two hundred patients (200 eyes) who underwent laser epithelial keratoplasty (LASEK), femtosecond-assisted laser in-situ keratomileusis (FS-LASIK), and small-incision lenticule extraction (SMILE) were included in this study. According to preoperative spherical equivalent (SE), each surgical group was divided into two refractive subgroups: low-to-moderate myopia (LM group) and high myopia (H group). The posterior corneal elevation from Pentacam Scheimpflug tomography was analyzed preoperatively and at 1 month, 3 months, 6 months, and 12 months postoperatively. Three subregions of the posterior cornea were divided in this study as the central, paracentral, and peripheral regions. Generalized Estimating Equations (GEE). For all three surgical groups, similar changing trends were seen in the two refractive subgroups. H group presented a larger changing magnitude than the LM group in FS-LASIK over time ( P < 0.05), whereas no significant difference was noted in the two refractive subgroups of LASEK or SMILE ( P > 0.05). At 12 months postoperatively, the central posterior corneal elevation returned to the preoperative level in LASEK ( P > 0.05) but shifted forward significantly in FS-LASIK and SMILE ( P < 0.05). Different posterior corneal regions respond differently to corneal refractive surgeries. LASEK, FS-LASIK, and SMILE demonstrate different trends in the regional changes in posterior corneal elevation. The corneal shape seems more stable in LASEK than in FS-LASIK and SMILE.

Corneal Tomography in a Commercially Available Optical Coherence Tomography Device and Comparison With a Rotating Scheimpflug Camera.

To compare the outcomes of corneal tomography obtained with an anterior-to-posterior segment optical coherence tomography device (Revo, Optopol Technologies Sp. z o.o.) and a rotating Scheimpflug camera (Pentacam AXL, Oculus Optikgeräte, Wetzlar, Germany). In healthy subjects, agreement in stereometric parameters commonly used in cataract and refractive surgery was assessed. Comparison between the devices was performed using correlation coefficients, the Bland-Altman method, and a paired t test. Results of right eyes of 78 patients (47 women) aged 25.24±5.56 years were analyzed. The flat and steep anterior keratometry values were significantly higher for Revo than Pentacam (43.65±1.58 D vs. 42.99±1.47 D; P = 0.000, and 44.53±1.57 D vs. 43.82±1.49 D; P =0.000, respectively) and showed excellent correlation ( r =0.978 and 0.974, respectively). The results for maximal keratometry manifested a higher difference (45.89±1.69 D vs. 44.27±1.51 D for Revo and Pentacam, P =0.000) but were also strongly correlated ( r =0.871). Revo showed significantly lower corneal thickness values than Pentacam, both for apex pachymetry (535.54±32.45 vs. 550.74±31.55 μm; P =0.000) and for thinnest pachymetry (522.58±32.16 vs. 547.25±31.95 μm; P =0.000). The correlation coefficients for anterior and posterior corneal elevation at the thinnest point showed weak positive correlation ( r =0.179 and 0.185), while the correlation for corneal asphericity was moderate ( r =0.317). There was a significant difference between keratometric values obtained with Revo and the Pentacam AXL, although the measurements showed excellent correlation. Similar results were found for corneal thickness measurements, but not for corneal surface elevation and corneal asphericity.

Changes in the posterior corneal surface after femtosecond laser-assisted lenticule intrastromal keratoplasty (LIKE) performed into a pocket (SMI-LIKE) or under a flap (FS-LIKE)

BackgroundTo compare the changes in posterior corneal surface after small-incision lenticule intrastromal keratoplasty (SMI-LIKE) and femtosecond laser-assisted lenticule intrastromal keratoplasty (FS-LIKE) for hyperopia correction.MethodsIn this prospective comparative randomized study, 23 eyes with hyperopia were recruited. Eyes were categorized into two groups—SMI-LIKE group (11 eyes) and FS-LIKE group (12 eyes). Lenticules from myopia small incision lenticule extraction were implanted into a pocket (SMI-LIKE group) or at a depth of 100 µm under a flap (FS-LIKE group). Posterior corneal elevations in the center, mid-periphery, and periphery, as well as mean keratometry of the posterior corneal surface (Kmb) were measured using a Pentacam over a three-month follow-up.ResultsAll surgeries were completed successfully and no complications occurred. At one day postoperatively, there was a slight backward change with SMI-LIKE and a forward change with FS-LIKE in the central region of the posterior corneal elevation. Conversely, the peripheral area showed forward displacement in SMI-LIKE and an apparent backward change in FS-LIKE. The mid-peripheral regions manifested a backward change after the procedure throughout the entire follow-up in both groups. Kmb exhibited flattening at one month postoperatively and subsequently returned to its original level at three months after SMI-LIKE while in FS-LIKE, Kmb steepened after lenticule implantation with a significant change noted at one day postoperatively (P = 0.001).ConclusionsPosterior corneal surface after SMI-LIKE and FS-LIKE exhibited different change patterns in various corneal regions, with the most prominent change occurring at one day postoperatively during the three-month follow-up.Trial registration: Chinese Clinical Trial Registry: ChiCTR-ONC-16008300. Registered on Apr 18th, 2016. http://www.chictr.org.cn/edit.aspx?pid=14090&htm=4

Femtosecond laser-assisted minimally invasive lamellar keratoplasty for advanced keratoconus

Objective: To evaluate the initial safety and efficacy of femtosecond laser-assisted minimally invasive lamellar keratoplasty (FL-MILK) for advanced keratoconus. Methods: It was a case series study. Patients with advanced keratoconus who underwent FL-MILK between August 2017 and April 2020 at Shandong Eye Hospital were prospectively included. The femtosecond laser was used to create an intrastromal pocket in the recipient cornea and a lamellar cornea in the donor. The lamellar cornea was then gently inserted into the intrastromal pocket through the incision and flattened. Clinical measurements included best-corrected visual acuity, 3-mm anterior corneal mean keratometry, anterior and posterior central corneal elevation, central corneal thickness, corneal biomechanics, and endothelial cell density. The follow-up was conducted at 1 month, 12 months, and 24 months after the operation. Results: There were 33 patients (35 eyes) in the study. Twenty-six patients were male and 7 patients were female. The mean age was (20.34±5.24) years old. All patients completed 12 months of follow-up, and 25 patients (27 eyes) completed 24 months of follow-up. No epithelial ingrowth, infection, or allogeneic rejection was observed. Compared with the preoperative data, the anterior central corneal elevation significantly decreased (P<0.001), the mean keratometry significantly decreased (P<0.05), and the central corneal thickness significantly increased (P<0.001). The corneal biomechanical strength was significantly improved, with the deformation amplitude ratio at 2.0 mm decreasing from 1.39±0.14 preoperatively to 1.21±0.10 at 24 months postoperatively (P<0.001) and the stiffness parameter at the first applanation increasing from 41.49±11.47 preoperatively to 88.41±18.17 at 24 months postoperatively (P<0.001). There were no significant changes in the mean best-corrected visual acuity, posterior corneal elevation, mean spherical equivalent, and endothelial cell density (all P>0.05). Conclusions: FL-MILK may be a feasible option for advanced keratoconus. This procedure may provide a new resolution for keratoconus.

Posterior corneal elevation changes during 12 month of overnight orthokeratology

Aimsthe aim of this study to investigate the elevation changes in posterior corneal surface after 12 months of orthokeratology (ortho-k) treatment. MethodsIn this retrospective chart review, medical records of 37 Chinese children who wore ortho-k lenses over 12 months were reviewed. The data of only right eye were analyzed. Variables including the flat and steep keratometry of anterior and posterior corneal principal meridians, central corneal thickness (CCT), posterior thinnest elevation of cornea (PTE), posterior central elevation of cornea (PCE) and posterior mean elevation of cornea (PME) were measured by Pentacam. Variables including anterior chamber depth (ACD), lens thickness (CLT) and ocular axis length (AL) were measured by optical biometry. All variables differences between baseline and 12 months after ortho-k treatment were assessed by statistical analyses. ResultsThe average age of all subjects was 10.70 ± 1.75 years (range 8–15 years old). The baseline spherical equivalent (SE) was −3.26 ± 1.52 D (−0.50D to −5.00D). Both flat and steep keratometry of anterior corneal surface and CCT were significantly decreased after 12 month follow up during ortho-k treatment (both P < 0.000). Both flat and steep keratometry of posterior corneal surface were not significantly different after 12 month follow up compared with that of baseline (P = 0.426, 0.134 respectively). PCE, PTE and PME were not significantly changed over 12 months of ortho-k treatment (P = 0.051, 0.952 and 0.197 respectively). The ACD was significantly decreased in 12 month follow up during ortho-k treatment (P = 0.001). The CLT and the AL were significantly increased during this period (both P < 0.000). ConclusionAlthough the anterior corneal surface was significantly changed by ortho-k lens, the posterior corneal surface did not show any changes during 12 months follow up. Simultaneously, The ACD, CLT and AL were significantly changed during this period.

Correlation between the ablation ratio and posterior corneal stability after small incision lenticule extraction for high myopia

PurposeThe aim of this study is to investigate changes in posterior corneal elevation and their correlations with the ablation ratio 3 years after small incision lenticule extraction (SMILE) for high myopia.MethodsEighty eyes underwent SMILE were enrolled in this study. Eyes were classified into two groups based on the ablation ratio (AR, lenticule thickness from SMILE machine/thinnest corneal thickness): group A (< 25%, 40 eyes) and group B (≥ 25%, 40 eyes). Pentacam was used to measure the posterior corneal elevation at the central point, thinnest point, and posterior maximum elevation (PME) and the mean posterior elevation in the central 2-mm area (MPE-2 mm), 4-mm area, and 6-mm area at the 3-year follow-up.ResultsMore than 85% of the eyes had an AR of less than 27%, and no cases of iatrogenic keratectasia developed. In both groups, for central region, posterior elevation decreased implying backward displacement; for peripheral region, it increased indicating forward trend. There was no significant difference in changes in all determined parameters between the two groups (P ≥ 0.07). Moreover, no significant correlation was noted between AR and posterior elevation changes. In group A, decreasing changes in PME (r = − 0.42, P = 0.01) and MPE-2 mm (r = 0.40, P = 0.01) demonstrated negative correlations with residual bed thickness.ConclusionRegion-dependent changes were demonstrated in the eyes that underwent SMILE. The central area showed a subtly declining posterior elevation, and the peripheral area showed a slightly increasing elevation. The limited ablation ratio had no impact on the changes in posterior corneal elevation.

Correction of Ametropia in Patients with Posterior Elevation of the Cornea

Purpose: to evaluate the effectiveness of ametropia correction in patients with posterior corneal elevation but without signs of subclinical keratoconus, based on postoperative results of transepithelial photorefractive keratectomy (Trans PRK).Patients and methods. A retrospective comparative study was conducted to analyze the results of surface ablation, which was performed using transepithelial photorefractive keratectomy in 18 patients with posterior corneal elevation (36 eyes). The control group included 18 patients with eyes without these changes (36 eyes). Both groups were comparable in age, gender and refraction. Demographic data, pre- and postoperative refraction, NCOSIS and ICOSIS, maximum ablation, I/S ratio index, central corneal thickness, anterior and posterior keratometry, Biaocci-Versachi index for anterior and posterior surfaces, RMS (mk/mm2) in standard deviation, the highest elevation point of the posterior surface of the cornea — KVB (microns), index of asymmetry of tangential curvature of anterior and posterior were determined and analyzed in all patients the surfaces are SIF (D) and SIB(D), which determines the vertical asymmetry in the upper and lower hemispheres of the cornea.Results. Observations of the dynamics of these parameters were carried out for 12 months after surgery for patients of both groups, and showed that the conclusion of Trans PRK in patients with posterior corneal elevation leads to similar refractive results compared with normal eyes. The safety and effectiveness indicators for both groups were also comparable. Significant differences in the speed of vision restoration between the groups were revealed, which is manifested by significant differences in visual acuity indicators within 1 month after surgery, but by 1 year the differences are leveled. It was determined that the effectiveness of astigmatism correction in the group with posterior elevation was significantly lower. The refractive results in the elevation group were good. During the observation, there was no pronounced dynamics of the indicators of elevation of the posterior surface of the cornea.Conclusion: the method of transepithelial photorefractive keratectomy can be recommended for the treatment of ametropia in patients with posterior corneal elevation, but without signs of subclinical keratoconus, however, the development of additional nomograms is required in order to increase the predictability of laser vision correction in patients of this category.

Corneal densitometry in bilateral keratoconus patients with unilateral corneal Vogt's striae: a contralateral eye study.

To investigate corneal densitometry and correlations with corneal morphological parameters in patients with bilateral keratoconus (KC) with unilateral Vogt's striae. This prospective contralateral study enrolled 112 patients (224 eyes) with evident KC characteristics (corneal topography with asymmetric bow-tie pattern, inferior steepening), and at least one KC sign (conical protrusion of the cornea at the apex, corneal stromal thinning, Fleischer ring, Vogt's striae) on slit-lamp examination. Corneal densitometry and morphological parameters were measured using Pentacam HR. The mean age was 23.93 ± 6.81years. Fifty-two (23.22%), 111 (49.55%), and 61 (27.23%) eyes were in mild, moderate, and severe groups, respectively. Corneal densitometry values of the anterior 0-2mm and 2-6mm, intermediate 0-2mm and 2-6mm, posterior 2-6mm, and total cornea 2-6mm were significantly higher in eyes with Vogt's striae (P < 0.05), whereas those of the anterior 6-10mm, posterior 0-2mm, and total cornea 6-10mm were significantly lower in eyes with Vogt's striae (P < 0.05). Anterior 0-2mm and total cornea 2-6mm corneal densitometry values were positively correlated with anterior K1 (A-K1), K2 (A-K2), Km (A-Km), Kmax (A-Kmax), anterior corneal elevation, and posterior corneal elevation (P < 0.05), and negatively correlated with central corneal thickness and thinnest corneal thickness in eyes with Vogt's striae (P < 0.05). A-K2, A-Km, and A-Kmax were significantly correlated with the densitometry values of the anterior 0-2mm and intermediate 0-2mm in eyes without Vogt's striae (P < 0.05). Vogt's striae mainly occur on the anterior and intermediate layers during KC progression.

Two-year stability of posterior corneal surface after transepithelial photorefractive keratectomy with a residual stromal thickness less than 350μm.

This study aimed to investigate the stability of posterior corneal surface 2years after transepithelial photorefractive keratectomy (TPRK) in patients with a residual stromal thickness less than 350μm. In total, 408 eyes of 212 patients (160 women, 52 men) who underwent TPRK were enrolled in this retrospective study. All surgeries were performed in the Amaris 750S excimer laser platform with smart pulse technology. The posterior corneal elevation, anterior chamber depth, Q value, and curvature were measured using Pentacam preoperatively and postoperatively. All patients were followed up for 2years. The relationship between percent tissue altered (PTA), age, and changes in posterior corneal surface was analyzed. The mean preoperative spherical equivalent was - 6.80 ± 1.18 D (range: - 9.00 to - 2.63 D). The mean residual stromal thickness was 336.46 ± 7.25μm (range: 310-348μm). The mean PTA was 30.93 ± 2.03% (range: 24.29-35.28%). At 2years after surgery, the elevation of six points in the central area decreased by 1.91 ± 2.97μm, 2.98 ± 3.23μm, 1.17 ± 3.85μm, 1.70 ± 2.88μm, 1.36 ± 3.19μm, and 1.65 ± 3.18μm, compared with the preoperative value (P < 0.05). The elevation of three points in the peripheral area increased by 1.87 ± 6.34μm, 0.68 ± 6.00μm, and 0.95 ± 5.50μm (P < 0.05). There was no significant linear relationship between PTA, age, and changes in posterior corneal surface, anterior chamber depth, and K2 (all P > 0.05). Within 2years after TPRK, the posterior corneal surface remained stable in patients with a residual stromal thickness between 310 and 350μm. There was no sign of iatrogenic ectasia during the follow-up period.

Corneal morphological changes after small incision lenticule extraction for myopic anisometropia.

PurposeThis research aims to study the corneal morphological changes in adult patients with myopic anisometropia after small incision lenticule extraction (SMILE) and the safety, efficacy, and predictability of clinical outcomes.MethodsThis was a prospective cohort study. Patients with myopic anisometropia [refractive difference >2.0 diopters (D)] were included in this study who underwent SMILE at our hospital from September 2019 to March 2021. For the two eyes of each patient, the one with higher myopia was defined as group A, and the fellow eye was group B. The follow-up time points were set as 1 week, 1 month, 3 months, and 6 months after the surgery. The data collected were uncorrected and best-corrected distance visual acuity (UDVA and CDVA), spherical equivalent (SE), efficacy and safety indexes, posterior corneal elevation (PCE), anterior and posterior corneal radius of curvature in the 3 mm area at the center of the thinnest point of the cornea (ARC and PRC), and higher-order aberrations (HOAs).ResultsThe study included 36 patients (72 eyes), and the mean age was 25.2 ± 6.4 years. The preoperative SEs were −6.45 ± 1.25 D in group A and −3.76 ± 1.29 D in group B. Six months after surgery, the SEs in groups A and B were −0.09 ± 0.50 D and 0.07 ± 0.47 (P = 0.059), respectively. The efficacy indexes were 1.06 ± 0.16 in group A and 1.07 ± 0.14 in group B (P = 0.750). The safety indexes were 1.08 ± 0.14 in group A and 1.12 ± 0.15 in group B (P = 0.173). The PCE was significantly reduced at 6 months after surgery in pagebreak both groups (P < 0.05). The ARC was significantly higher than before the surgery (P < 0.05) in the two groups. The two groups showed significant increases in total HOAs, coma 90°, and spherical aberrations (P < 0.05).ConclusionSMILE is predictable, effective, and safe in correcting myopic anisometropia. The postoperative changes in HOAs are characteristic.

Changes in Corneal Morphology and Biomechanics in Cases of Small Incision Lenticule Extraction with Prophylactic Accelerated Collagen Cross-Linking.

Purpose To study the corneal morphology and biomechanics in cases of small incision lenticule extraction with prophylactic accelerated collagen cross-linking (SMILE Xtra). Methods This study was a retrospective study. 28 eyes of 14 patients with moderate-high risk of postoperative ectasia according to the Randleman scoring system underwent SMILE Xtra procedure. Outcome data were recorded including uncorrected distance visual acuity (UDVA), manifest refraction spherical equivalent (MRSE), surface regularity index (SRI), surface asymmetry index (SAI), simulated keratometry (SimK), posterior axial curvature (PAC), anterior and posterior corneal elevations (ACE and PCE), central corneal thickness (CCT), corneal resistance factor (CRF), corneal hysteresis (CH), and cornea-compensated intraocular pressure (IOPcc). The follow-up period was 12 months. Results There were 28, 26, 22, 12, and 10 eyes enrolled at postoperative 1st day and 1st, 3rd, 6th, and 12th months, respectively. The UDVA improved from 1.27 ± 0.18 logMAR preoperatively to -0.06 ± 0.04 logMAR postoperatively (P < 0.05). The MRSE improved from -5.05 ± 1.15 D preoperatively to -0.14 ± 0.30 D postoperatively (P < 0.05). SAI, SimK, PAC, PCE, and CCT all changed significantly at 1st month postoperatively (P < 0.05) and stabilized during the remainder of the follow-up (P > 0.05). There was no significant change in SRI or ACE before and after surgery (P > 0.05). CRF, CH, and IOPcc all decreased significantly at 1st month postoperatively (P < 0.05) and remained stable afterwards (P > 0.05). Conclusions The changes in the corneal morphology and biomechanics remained stable after SMILE Xtra, and there was no sign of postoperative ectasia or refractive regression. Combined with the improvement of visual and refractive results, SMILE Xtra may be a promising method for corneal refractive surgeries in patients at risk.

Three-year clinical outcomes and posterior corneal elevation change after small-incision lenticule extraction in suspicious corneas.

To determine the long-term clinical outcomes and change in posterior corneal elevation after small-incision lenticule extraction (SMILE) in eyes with suspicious tomographic features. Hospital clinic. Retrospective, case-controlled, observational. This study included 43 patients with suspicious corneas (group A), defined by corneal morphology and a final D score from a Scheimpflug camera (Pentacam), and 43 patients with normal corneal topography (group B). Refraction, visual acuity, and posterior corneal elevation over a 6-mm central diameter, including posterior central elevation (PCE), posterior elevation at the thinnest point (PTE), and posterior maximal elevation (PME), were measured preoperatively and at 6 months, 12 months, and 36 months postoperatively. The preoperative spherical equivalent was -5.51 ± 1.33 D in group A (n = 43) and -5.41 ± 1.19 D in group B (n = 43). Postoperative uncorrected distance visual acuity was 20/20 or better in 39 (91%) of 43 eyes in group A and 41 (95%) of 43 eyes in group B ( P = .160); all eyes in both groups remained stable or had gained corrected distance visual acuity. The mean change in PCE, PTE, and PME at 3 years was -1.22 ± 2.65 μm, -1.21 ± 2.70 μm, and -1.00 ± 5.09 μmin group A and -1.76 ± 3.25 μm, -1.60 ± 3.33 μm, and -1.56 ± 5.01 μm in group B, respectively, indicating a tendency for backward displacement of the posterior surface, whereas the between-group difference was not statistically significant ( P = .154, P = .547, and P = .319, respectively). Refraction, visual outcomes, and posterior corneal shift seem comparable between corneas with normal and suspicious tomographic features three years after SMILE. More long-term studies are warranted to corroborate the findings of this study.

Five-year stability of posterior corneal surface after small incision lenticule extraction for high myopia

BackgroundTo study the 5-year changes in the posterior corneal surface after small incision lenticule extraction (SMILE) for high myopia.MethodsEighty eyes received SMILE was included in this prospective study. They were allocated into two groups based on the spherical equivalent: high myopia (40eyes, -7.49 ± 0.70D) and moderate myopia (40eyes, -4.43 ± 0.87D). Certain points of posterior corneal elevation (the central point (PCE), thinnest point (PTE), maximal point (PME), and in various corneal areas) were evaluated using a Scheimpflug camera (Pentacam; Oculus GmbH, Germany) preoperatively and at 6 months and 5 years after surgery.ResultsAll surgeries were completed uneventfully and no ectasia was developed throng the observation. The safety index and efficacy index were 1.14 and 1.03 in the high myopia group, and 1.16 and 1.06 in the moderate myopia group, respectively. Most of the calculated values in the high myopia group showed a slight increase at 6 months but decreased at 5 years. At 5 years postoperatively, the value of the PTE was significantly lower than at baseline in both groups (P ≤ 0.047); a statistical difference was also revealed in the PME in the moderate group with slight changes (10.15 ± 3.01 μm vs. 11.60 ± 4.33 μm, P = 0.002); no statistical significance was observed in other calculated values (P ≥ 0.067). Similarly, no significant linear correlation was noted between changes in all values and the residual bed thickness either (P ≥ 0.057).ConclusionsSMILE causes no protrusion in posterior corneal surface for correction of high myopia at the follow-up visit of 5 years.