Changes in posterior corneal elevation after small incision lenticule extraction for different myopic diopters.

AIM: To study the changes and effect factors of posterior corneal surface after small incision lenticule extraction (SMILE) with different myopic diopters. METHODS: Ninety eyes of 90 patients who underwent SMILE were included in this retrospective study. Patients were allocated into three groups based on the preoperative spherical equivalent (SE): low myopia (SE≥-3.00 D), moderate myopia (-3.00 D>SE>-6.00 D) and high myopia (SE≤-6.00 D). Posterior corneal surfaces were measured by a Scheimpflug camera preoperatively and different postoperative times (1wk, 1, 3, 6mo, and 1y). Posterior mean elevation (PME) at 25 predetermined points of 3 concentric circles (2-, 4-, and 6-mm diameter) above the best fit sphere was analyzed. RESULTS: All surgeries were completed uneventfully and no ectasia was found through the observation. The difference of myopia group was significant at the 2-mm ring at 1 and 3mo postoperatively (1mo: P=0.017; 3mo: P=0.018). The effect of time on ΔPME was statistically significant (2-mm ring: P=0.001; 4-mm ring: P<0.001; 6-mm ring: P<0.001). The effect of different corneal locations on ΔPME was significant except 1wk postoperatively (1mo: P=0.000; 3mo: P=0.000; 6mo: P=0.001; 1y: P=0.001). Posterior corneal stability was linearly correlated with SE, central corneal thickness, ablation depth, residual bed thickness, percent ablation depth and percent stromal bed thickness. CONCLUSION: The posterior corneal surface changes dynamically after SMILE. No protrusion is observed on the posterior corneal surface in patients with different degrees of myopia within one year after surgery. SMILE has good stability, accuracy, safety and predictability.

Comparison of different corneal residual bed thickness after small incision lenticule extraction (SMILE).

PURPOSE: To evaluate the corneal biological parameters stability between the different corneal residual bed thickness (RBT) after Small Incision Lenticule Extraction (SMILE). METHODS: In this prospective clinical trial, 127 eyes of 64 patients underwent SMILE. According to the corneal RBT, the patients were divided into the 250-270 µm, 270-290 µm and 290-310 µm groups. Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) and Scheimpflug camera (Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany) measurements were performed preoperatively, 1 day, 1week, 1month and 3 months after surgery. RESULTS: The keratometer values among the three groups were no significant differences in postoperative periods (each P > 0.05), except the corneal thickness values (each P < 0.05). In the 250-270 µm and 270-290 µm groups, the keratometer and corneal thickness values were decreased at postoperative 1 week and increased at 1 and 3 months. The 290-310 µm group significantly higher posterior maximum elevation (PME) than the 250-270 µm group at 1 and 3 months (P = 0.022, 0.022, respectively), and higher preoperative thinnest point (PTE) at 1 week and 1 month (P = 0.013, 0.035, respectively). The PME of the 290-310 µm group was higher than the 270-290 µm group at 3 months (P = 0.045), and higher PTE at 1 week and 3 months (P = 0.022, 0.02, respectively). In all three groups, the maximal deformation amplitude (DA) was significantly higher at 1 and 3 months compared to postoperative 1 day and 1 week, and the IOP was decreased at 1 month then recovered at 3 months (each P < 0.05).The DA of the 250-270 µm group was significantly higher than the 290-310 µm group at postoperative 1 week, 1 and 3 months (P = 0.001, 0.01, 0.02, respectively). The change of the posterior corneal elevation and biomechanical parameters values were no significant differences among the three groups in postoperative periods (each P > 0.05). CONCLUSIONS: The range of 250-310 µm RBT was safe and stable at the early postoperative of SMILE. The RBT may be positively correlated with the posterior corneal elevation.

Posterior corneal elevation changes during 12 month of overnight orthokeratology.

Aims: the aim of this study to investigate the elevation changes in posterior corneal surface after 12 months of orthokeratology (ortho-k) treatment. Methods: In 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. Results: The 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). Conclusion: Although 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.

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).

BACKGROUND: To 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. METHODS: In 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. RESULTS: All 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). CONCLUSIONS: Posterior 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.

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

Purpose: This 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. Methods: This 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). Results: The 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). Conclusion: SMILE is predictable, effective, and safe in correcting myopic anisometropia. The postoperative changes in HOAs are characteristic.

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

BACKGROUND: To study the 5-year changes in the posterior corneal surface after small incision lenticule extraction (SMILE) for high myopia. METHODS: Eighty 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. RESULTS: All 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). CONCLUSIONS: SMILE causes no protrusion in posterior corneal surface for correction of high myopia at the follow-up visit of 5 years.

Predictive factors of posterior corneal shift after small incision lenticule extraction: a 5-year follow-up study.

PURPOSE: The aim of this study was to determine risk factors affecting changes in posterior corneal elevation (PCE) and predict the 5-year stability after small incision lenticule extraction (SMILE). METHODS: This retrospective, longitudinal study enrolled 161 patients post-SMILE. The PCE values were measured at the apex, thinnest, maximal and 24 other prespecified preoperative points and at 6 months, 1 year and 5 years postoperatively. RESULTS: Posterior corneas exhibited time-dependent, region-dependent and angle-dependent changes. For every dioptre increase in the absolute preoperative spherical equivalent (SE), 10-µm decrease in the central corneal thickness (CCT), 10-µm increase in the maximum lenticule thickness (MLT), 10-µm decrease in the residual bed thickness (RBT), 10% increase in the percentage ablation depth (PAD, MLT divided by CCT) and 10% decrease in the percentage stromal bed thickness (PSBT, RBT divided by CCT), PCE exhibited average forward displacements of 0.2-0.4, 0.2-0.7, 0.1-0.2, 0.1-0.3, 0.6-1.0 and 0.5-1.1 µm, respectively (p < 0.05). PSBT was the variable with the highest accuracy in predicting 5-year stability of posterior corneas (area under curve = 0.75). The cut-off values of SE, CCT, MLT, RBT, PAD and PSBT for increased PCE were -8.00 to -8.31 D, 481.0-498.5 µm, 139.5-144.5 µm, 255.5-263.5 µm, 26.9-28.3% and 48.9-52.6%, respectively. CONCLUSION: Eyes with thinner corneas, higher myopia requiring greater MLT and lower RBT exhibited greater predispositions towards posterior protrusion. The thresholds for preventing forward posterior corneal displacement were 26.9-28.3% for PAD and 48.9-52.6% for PSBT. Prediction of posterior corneal stability is useful for assessing surgical risks post-SMILE.

Three-Year Follow-Up of Posterior Corneal Elevation in Thin Corneas After Small Incision Lenticule Extraction.

PURPOSE: To evaluate the changes in posterior corneal elevation in thin corneas after small incision lenticule extraction (SMILE). METHODS: In this prospective study, 97 eyes of 97 patients undergoing SMILE were recruited. Eyes were categorized into the following groups based on the preoperative minimum central corneal thickness (CCT): group A (37 eyes, 480-499 µm), group B (30 eyes, 500-529 µm), and group C (30 eyes, 530-560 µm). The posterior corneal surface was measured with a Pentacam over a 3-year follow-up period. Changes in the posterior corneal elevation at the central point (PCE), thinnest point (PTE), and predetermined area were measured. RESULTS: No iatrogenic keratectasia was observed during the follow-up period. The mean changes in PCE, PTE, and the inferior area in group A were 1.14 ± 3.40 µm, -0.11 ± 3.20 µm, and -0.26 ± 1.23 µm, respectively (P ≥ 0.125). Although statistically significant change in the central-4 mm area was noted, the value was quite small (0.98 ± 1.67 µm) and was not higher than that in the other two groups (P = 0.003). For all three groups, the elevation remained stable or showed a backward change in the central annulus, while there was a small forward displacement in the 6-mm optical zone. In group A, changes in elevation values yielded negative statistical correlations with residual bed thickness and CCT (P ≤ 0.006) (except for the inferior area, the 4-mm and 6-mm optical zone). CONCLUSIONS: With a strict preoperative assessment, SMILE achieved good safety and efficacy in correcting myopia in thin corneas and enabled a stable posterior corneal surface over a 3-year follow-up period. SYNOPSIS: Careful preoperative assessment and suitable surgical design should be taken to ensure posterior corneal stability after SMILE in thin corneas.

Comparison of posterior corneal elevation in children with and without vernal keratoconjunctivitis using a new tomographer.

Purpose: To assess the posterior corneal elevation (PCE) in children with vernal keratoconjunctivitis (VKC) and compare the same with that of age and gender-matched normal children. Methods: This was a case control study. We included 110 children attending the Pediatric ophthalmology outpatient department of a tertiary eye care center in South India between September 2019 and June 2020. Fifty-five children with VKC and 55 normal age and gender-matched children were examined by Sirius tomographer/topographer (CSO, Italy) to determine the PCE, thinnest corneal thickness (TCT), simulated K (Sim K), keratoconus front (KVf) and keratoconus vertex back (KVb). The parameters were compared between the two groups. Results: A total of 220 eyes of 110 children were examined. The mean age in both groups was 10.44 ± 3.28 years, each group included 44 males and 11 females. There was no statistically significant difference in TCT and Sim K between the two groups. The mean PCE was 18.8 ± 8.4 µm in VKC group and 11.7 ± 3.9 µm in control group (P < 0.001). Both KVf and KVb were significantly higher in VKC group when compared to the control group. Conclusion: Children with VKC have significantly higher PCE as measured by Sirius tomographer, and hence, all VKC children should be screened for development of KC and the Sirius tomographer may be an appropriate tool for the same.

Comparison of posterior corneal elevation after SMILE and FS-LASIK in correcting myopia over -9.0 diopters.

BACKGROUND: To compare the changes in posterior corneal elevation after small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) in correcting myopia over -9 diopters (D). METHODS: In this prospective comparative study, 82 eyes of 82 patients scheduled for refractive correction were recruited. Eyes were randomly assigned to the SMILE group (45 eyes, -10.43±0.92 D) or FS-LASIK group (37 eyes, -10.97±1.37 D). The posterior corneal surface was measured using a Scheimpflug camera (Pentacam, Oculus, Germany) preoperatively and at 1 day, 1 month, and 6 months after surgery. Posterior corneal elevation in the central point and central 4-mm area, and in various optical zones above the best-fit sphere, was analyzed. A P value of less than 0.05 was considered statistically significant. RESULTS: All surgeries were completed successfully. The safety index and efficacy index were 1.20 and 1.00, respectively, in the SMILE group, and was 1.10 and 0.90, respectively, in the FS-LASIK group. No significant difference existed in all analyzed data before and at 6 months after surgery in both the SMILE group and the FS-LASIK group. Changes in posterior corneal elevation after FS-LASIK were greater than after SMILE, with no statistical significance (P≥0.07). In the SMILE group, residual bed thickness was found to be moderately negatively correlated with changes in the elevation in the central area (P≤0.045); whereas it was positively correlated in the peripheral area (P=0.002). CONCLUSIONS: SMILE and FS-LASIK presented stable posterior corneal surface in correction of myopia over -9.0 D at the follow-up visit of 6 months.

Clinical research of changes in posterior corneal elevation after small incision lenticule extraction / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM:To assess the changes of posterior corneal elevation after small incision lenticule extraction(SMILE). <p>METHODS:A retrospective study was conducted on 120 patients(240 eyes)who underwent SMILE surgery with myopia. All patients were examined with the Pentacam of preoperation and 1d, 1wk, 1, 3, 6 and 12mo postoperatively, respectively. We analyze the change of the posterior corneal elevation of the apex, and the change of mean posterior corneal elevation in the circle of 2mm, and 6mm diameter.<p>RESULTS:Comparison among the three groups showed that the differences of apex and 2mm circle at a different time and between the groups were statistically significant(apex: <i>F</i>_time=30.09, <i>P</i>_time<0.01; <i>F</i>_group=7.29, <i>P</i>_group<0.01; 2mm circle: <i>F</i>_time=24.72, <i>P</i>_time<0.01; <i>F</i>_group=7.44, <i>P</i>_group=0.01), and there was no statistically significant difference in interaction time and groups(apex: <i>F</i>_time×group=1.65, <i>P</i>_time×group=0.15; 2mm circle: <i>F</i>_time×group=1.81, <i>P</i>_time×group=0.25). The difference of 6mm circle at different time points after the operation was statistically significant(<i>F</i>_time=18.34, <i>P</i>_time<0.01), while the difference in interaction time and groups was not statistically significant(<i>F</i>_group=2.21, <i>P</i>_group=0.12; <i>F</i>_time×group=1.34, <i>P</i>_time×group=0.25). In the low and moderate myopia groups, the changes of the apex, 2mm circle and 6mm circle in the posterior corneal elevation were statistically significant within 1mo after surgery(<i>P</i><0.05); In the high myopia group, there were statistically significant at the apex and 2mm circle within 3mo after surgery(<i>P</i><0.05); There was statistically significant after surgery at 6mm circle within 1mo(<i>P</i><0.05). In all cases, the difference of the posterior corneal elevation between 1wk and 1d was negative at the apex and 2mm circle, after that, the difference became positive and smaller. The reverse was true at the 6mm circle. <p>CONCLUSION:Among three groups after SMILE, the central posterior cornea was slightly backward, and the peripheral cornea was slightly forward, the changes were most obvious after 1wk and then returned gradually. It means the surgery was safe, stable, precise, and predictable.

Impact of ablation ratio on 5-year postoperative posterior corneal stability after refractive surgery: SMILE and FS-LASIK.

BACKGROUND: To investigate the impact of the ablation ratio on 5-year postoperative posterior corneal stability in myopic eyes after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery. METHODS: A prospective, nonrandomized, cohort study: 80 eyes of 43 patients underwent SMILE surgery and 63 eyes of 32 patients underwent FS-LASIK surgery at the EYE & ENT Hospital, Fudan University. Ablation ratio was defined as lenticule thickness (SMILE cases) or ablation depth (FS-LASIK cases) divided by central corneal thickness (CCT). Posterior corneal elevation changes were recorded as posterior central elevation (PCE), posterior corneal surface at thinnest point (PTE) and posterior corneal mean elevation (PME). Patients were followed up at 6-month and 5-year interval to investigate the impact of the ablation ratio on posterior corneal elevation after SMILE and FS-LASIK surgery. RESULTS: PCE dropped at the 6-month follow-up for both SMILE (decreased by -1.11 ± 2.93 µm, P < 0.05) and FS-LASIK groups (decreased by -0.46 ± 3.72 µm, P < 0.05). PTE also dropped in SMILE (reduced by -2.04 ± 3.02 µm, P < 0.05) and FS-LASIK group (reduced by -1.28 ± 4.21 µm, P < 0.05) at the 6-month follow-up. Stable PCE (elevation change: SMILE -0.28 ± 4.03 µm; FS-LASIK 0.79 ± 4.13 µm, P > 0.05) and PTE (elevation change: SMILE -0.08 ± 4.28 µm; FS-LASIK 1.42 ± 3.85 µm, P > 0.05) for both groups were recorded at the 5-year follow-up compared to the 6-month visit. Ablation ratio was strongly correlated with 5-year postoperative PCE (ß = 2.68 ± 1.05, P < 0.01) and PTE (ß = 2.35 ± 1.17, P < 0.05). Cut-off value for 5-year postoperative raised PCE and PTE was 27.3 and 27.1%, respectively. CONCLUSIONS: Ablation ratio was strongly correlated with postoperative posterior corneal elevation in a 5-year follow-up in both SMILE and FS-LASIK groups. PCE and PTE underwent slight backward displacement 6-month postoperatively and remain stable at the 5-year follow-up. Threshold of the ablation ratio for resisting forward displacement of posterior corneal surface was 27.3 and 27.1% for SMILE and FS-LASIK groups, respectively.

Changes of anterior segment structure after sub-bowman keratomileusis / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM: To observe the effect of sub-bowman keratomileusis(SBK)on the posterior corneal curvature, posterior corneal elevation and anterior chamber parameters.<p>METHODS: Prospective self controlled study. Totally 49 patients(97 eyes)with myopia who had planned for SBK were included in this study, mean posterior corneal curvature, central posterior corneal elevation(PCE), anterior chamber volume(ACV), central and peripheral anterior chamber depth(ACD)were measured by Oculyzer before and 1wk, 1y, 3y after surgery. Repeated measure analysis of variance was adopted for data analysis.<p>RESULTS: There were no significant differences in mean posterior corneal curvature at any time point postoperatively compared with that preoperatively(<i>P</i>>0.05). However, central PCE, ACV and central ACD at 1wk, 1y and 3y postoperatively were all decreased(<i>P</i><0.01). Except for the anterior peripheral ACD at 3y after SBK, other peripheral ACD at any time point postoperatively were all decreased(<i>P</i><0.05).<p>CONCLUSION: The posterior corneal curvature remained stable after SBK, while the central PCE shifted slightly backward and the entire anterior chamber became shallow.

Early changes in posterior corneal elevation and related factors after femtosecond laser assisted LASIK and SBK / 中华实验眼科杂志

Objective To compare the early change of posterior corneal elevation with femtosecond laser assisted laser in situ keratomileusis (FS-LASIK) and sub-Bowman keratomileusis (SBK) by Oculyzer and analyze the related factors after FS-LASIK.Methods A longitudinal observational study was designed.Ninety-one eyes of 46 patients with myopia or myopic astigmatism in the First Affiliated Hospital of Anhui Medical University from January to April in 2016 were divided into FS-LASIK group (53 eyes of 27 patients),SBK group (38 eyes of 19 patients)according to the patients' wishes and each part of corneal elevation change values were explored after FS-LASIK and SBK surgeries.The posterior corneal elevation was measured at twenty-seven measuring points along the central,paracentral,midperipheral and peripheral zone (vertex and 1,2 and 3 mm radius) using Oculyzer preoperatively,l day,7 days and 1 month postoperatively,respectively.Written informed consent was obtained from each patient before the surgery.Results In the FS-LASIK group,the posterior corneal elevation difference values in the central zone were (-0.924± 1.859),(-1.151 ± 1.586) and (-0.940 ± 1.994) μm 1 day,7 days and 1 month postoperatively,respectively.In the periphery zone,the elevation difference values were (1.046 ± 1.667),(1.172 ± 1.566) and (1.023±1.622)μm.In the paracentral and midperipheral zone,the cornea displayed slightly backward or forward shift.In SBK group,the posterior corneal elevation difference values of the ve,ex were (-0.684 ± 1.454),(-1.053 ±1.723) and (-0.553 ± 1.572) μm 1 day,7 days and 1 month after operation,respectively.In the paracentral and midperipheral zone displayed the same trend with FS-LASIK group,and in the periphery,the values were (1.207 ±1.317),(1.327 ± 1.529) and (1.208 ± 1.415) μm.There were no statistically significant differences in posterior corneal elevation between the two surgery modes among the three time points (all at P ＞ O.05).At 1 month postoperatively,only two independent variables,which were spherical equivalent (SE) and ablation depth (AD)entered the regression in the central and paracentral zones.Independent variables,such as central thinnest corneal thickness (TCT),SE,AD,residual bed thickness (RBT) and the ratio of AD and TCT (AD/TCT) did not enter the regression in other two areas.Conclusions The posterior corneal elevation in the central 6 mm area shows tiny change in the early stage and the variation is larger 7 days after operation in the two groups,but it does not result in keratectasia.With the increase of SE and AD,the posterior corneal elevation is more likely to be affected.

Accelerated corneal collagen cross-linking in pediatric keratoconus: One year study.

PURPOSE: To evaluate the safety and effectiveness of accelerated corneal collagen crosslinking (CXL) in pediatric keratoconus. DESIGN: Prospective non-randomized observational study. METHODS: 33 eyes of 25 children with keratoconus were included. The corneal epithelium was mechanically removed. Next, riboflavin/hydroxypropyl methylcellulose solution) was applied for 10 min. Accelerated CXL (10 mW/cm2 for 9 min), was accomplished. Visual acuity, slit lamp examination, refraction, keratometry readings, pachymetry, anterior and posterior elevations, average progression indices, and Q values were recorded. The follow-up visits were scheduled on one day, 3 days, 7 days, one month and then on 3, 6, 12 months after the procedure. RESULTS: It was statistically significant improvement of the mean UAVA, AVA, and the mean corneal astigmatism (P < .0001). The mean corneal thickness showed a significant reduction. The preoperative mean K max reading was reduced from 49.12 ± 3.7 D preoperatively to 47.9 ± 3.7 D at 12 months. The mean max anterior elevation, average progression index and Q value showed statistically significant improvement. No significant impact on posterior elevation was recorded. Serious complications were not encountered in this study. CONCLUSION: Accelerated CXL shows a stabilization and beneficial clinical outcomes in pediatric keratoconus. It seems an effective and safe procedure in this age group. Effects of accelerated CXL on the posterior corneal surface will need further evaluation.

Comparison of the change in posterior corneal elevation and corneal biomechanical parameters after small incision lenticule extraction and femtosecond laser-assisted LASIK for high myopia correction.

PURPOSE: To compare posterior corneal elevation (PCE) changes and corneal biomechanical changes post fematosecond laser-assisted laser in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) procedures using the Pentacam system and the Ocular Response Analyzer (ORA). DESIGN: Retrospective observational case series study. METHOD: 106 patients with bilateral myopia who underwent either FS-LASIK (56 patients) or SMILE (50 patients) were reviewed, only the right eye was used in the analysis. Inclusion criteria include a spherical equivalent of -6.00DS and completion of 12 months follow up. The main outcome evaluated was change in PCE at 3 months, 6 months and 12 months post-operation using the Pentacam system. Corneal biomechanical parameters were evaluated at 6 and 12 months with the ORA. RESULTS: PCE change at 3 and 6 months were not significantly different between the two procedures (p=0.064, p=0.109 respectively). At 12 months, PCE change was greater in FS-LASIK than SMILE (p=0.048). One-way ANOVA showed that for either procedure, the change in PCE did not differ at 3, 6 or 12 months post operation. CH and CRF values were reduced after both procedures, with FS-LASIK demonstrating a greater reduction in CRF than SMILE at 6 and 12 months (p=0.037 and p=0.001). Both CH and CRF reduction correlated with PCE increase at 6 and 12 months. CONCLUSION: FS-LASIK demonstrated a greater increase in PCE than SMILE only at 12 months, as well as a greater reduction of CRF than SMILE. There were no significant differences in PCE change over time within either group.

A one-year follow-up study of posterior corneal elevation after FS-LASIK / 实用医学杂志

Objective To study the changes of posterior corneal elevation with one-year follow-up by using Allegro Oculyzer anterior segment diagnostic system in patients who had undergone laser in situ keratomileusis with femtosecond laser (FS-LASIK) for myopia. Methods Ninety eyes of forty-five patients who had undergone FS-LASIK for myopia were included in our study . The spherical equivalent of ametropia was-10.63D to -1.63D. The preoperative and postoperative corneal tomography (including 1, 3, 6 and 12 month after operation ) were collected by Allegro Oculyzer in the posterior corneal elevation and the thickness at central corneal thinnest point of each eye were measured , and the differences of the posterior corneal elevation were calculated. The data were analyzed with ANOVA and Pearson correlation analysis. Results There were no statistically significant differences in the changes of posterior corneal elevation from the preoperative time to the any postoperative follow-up time (F = 1.50, P > 0.05). There were no statistically significant changes of the posterior corneal elevation from the 1st month to 12th month postoperatively (F = 1.47, P > 0.05). There were statistically significant differences in the changes of thickness at central corneal thinnest point from the preoperative to the 12th month postoperative (F = 369.10, P 0.05). Conclusion After strictly followed surgical indications in FS-LASIK, the posterior corneal elevation can keep good stability and has no significant change. Thickness of central cornea thinnest point increases gradually and tends to stablity at the 3th months after surgery.

Modificaciones de la superficie corneal posterior al año de la cirugía / Changes in the posterior corneal surface one year after surgery

Objetivo: describir las modificaciones de la curvatura posterior corneal en pacientes sometidos a cirugía refractiva láser en el Instituto Cubano de Oftalmología Ramón Pando Ferrer en el período de enero-diciembre de 2011. Métodos: estudio descriptivo, longitudinal y prospectivo, con un universo de 257 pacientes (504 ojos) sometidos a cirugía refractiva láser. La muestra quedó conformada por 31 pacientes (59 ojos). Se analizaron las variables: edad, sexo, equivalente esférico, paquimetría preoperatoria, cantidad de ablación, estroma residual y diferencia de elevación posterior corneal, esta última obtenida del mapa de diferencia del tomógrafo Galilei con medición preoperatoria, al mes, 3 meses, 6 meses y 1 año de la cirugía. Con análisis de regresión múltiple se evaluaron dichos cambios con la paquimetría, cantidad de ablación, estroma residual y presión intraocular. Resultados: el equivalente esférico, paquimetría, cantidad de ablación, estroma residual y presión intraocular estaban dentro de los criterios de seguridad. La diferencia promedio de la elevación corneal posterior fue de 15,62 µm al mes y 11,78 µm a los 3 meses, 7,68 µm a los 6 meses y 3,22 µm al año con disminución significativa con el tiempo (p= 0,000). Se observó asociación con la paquimetría preoperatoria, el estroma residual y la presión intraocular. Conclusiones: la cirugía refractiva láser induce un aumento precoz en la elevación corneal posterior, con disminución progresiva en el tiempo. Los factores que más influyeron en estos cambios fueron el estroma residual, la paquimetría preoperatoria y la presión intraocular

Objective: to describe the changes of the posterior corneal curvature observed in patients who underwent laser-assisted refractive surgery at Ramón Pando Ferrer Cuban Institute ofOphthalmology from January through December 2011. Methods: a prospective, longitudinal and descriptive study of a sample of 31 patients (59 eyes) selected from a universe of 257 patients (504 eyes), who underwent laser-assisted refractive surgery. The analyzed variables were age, sex, spherical equivalent, pachymetry before surgery, ablation magnitude, residual stroma and difference in posterior corneal elevation. The latter was obtained from the Galilei´s tomograph difference map with measurements before surgery and one month, three months, six months and a year after surgery. Stepwise multiple regression analysis allowed evaluating such changes with pachymetry, ablation microns, residual stroma and intraocular pressure. Results: spherical equivalent, pachymetry, ablation microns, residual stroma and intraocular pressure were within the set safety criteria. The average difference of the posterior corneal elevation was 15,62 µm at one month, 15,62 µm three months, 7,68 µm six months and 3,22 µm one year after the surgery, with significant reduction as time goes by (p=0.000). Preoperative pachymetry, residual stroma and intraocular pressure were found to be related. Conclusions: laser-assisted refractive surgery causes an early increase of the posterior corneal elevation, with progressive reduction in time. The most influential factors were residual stroma, preoperative pachymetry and intraocular pressure

Modificaciones de la curvatura posterior corneal después de la cirugía refractiva láser / Modifications in the corneal posterior curve after laser refractive surgery

OBJETIVO: Describir las modificaciones de la curvatura posterior corneal en pacientes sometidos a cirugía refractiva láser en el Instituto Cubano de Oftalmología Ramón Pando Ferrer en el período de mayo a octubre de 2010. MÉTODOS: Se realizó un estudio descriptivo, longitudinal y prospectivo, con un universo de 257 pacientes (504 ojos) sometidos a cirugía refractiva láser. La muestra quedó conformada por 31 pacientes (59 ojos). Se analizaron variables como edad, sexo, equivalente esférico, paquimetría preoperatoria, cantidad de ablación, estroma residual y diferencia de elevación posterior corneal, esta última obtenida del mapa de diferencia del topógrafo Galilei, con medición preoperatoria al mes y a los tres meses de la cirugía. Mediante análisis de regresión múltiple fueron valorados dichos cambios de la paquimetría, la cantidad de ablación y el estroma residual. RESULTADOS: El equivalente esférico, la paquimetría, la cantidad de ablación y el estroma residual se encontraron dentro de los parámetros de seguridad establecidos. La diferencia promedio de la elevación corneal posterior fue de 15,62 Ám al mes y de 11,78 Ám a los tres meses, con disminución significativa con el tiempo (p= 0,000). Se observó asociación con la paquimetría preoperatoria y el estroma residual, y se encontró una correlación inversa entre este último y la elevación corneal posterior a los tres meses. CONCLUSIONES: La cirugía refractiva láser induce un aumento precoz en la elevación corneal posterior, con disminución progresiva hacia el tercer mes. Los factores que más influyeron en estos cambios fueron el estroma residual y la paquimetría preoperatoria(AU)

OBJECTIVES: To describe the modifications in the corneal posterior curve in patients underwent laser refractive surgery in the Ramón Pando Ferrer Cuban Institute of Ophthalmology from May to October, 2020. METHODS: A prospective, longitudinal and descriptive study was conducted in an universe of 257 patients (504 eyes) underwent to laser refractive surgery. Sample included 31 patients (59 eyes). Variables analyzed were: age, sex, spherical equivalent, preoperative pachymetry, ablation amount, residual stroma and difference of corneal posterior elevation, this latter achieved from the difference map of Galilei topography, with preoperative measurement at month and at three months after surgery. By multiple regression analysis the changes of pachymetry, the ablation amount and the residual stroma were assessed. RESULTS: The spherical equivalent, the pachymetry, the ablation amount and the residual stroma were within the established safety parameters. The mean difference of posterior corneal elevation was of 15,62 ?m at three months, with a significant decrease in time (p= 0,000). There was association with preoperative pachymetry and the residual stroma and also an inverse correlation between this latter and the posterior corneal elevation at three months. CONCLUSIONS: The laser refractive surgery produces an early increase in the posterior corneal elevation with a progressive decrease at third month. The factors that more influenced in such changes were the residual stroma and the preoperative pachymetry(AU)

Modificaciones de la curvatura posterior corneal después de la cirugía refractiva láser / Modifications in the corneal posterior curve after laser refractive surgery

OBJETIVO: Describir las modificaciones de la curvatura posterior corneal en pacientes sometidos a cirugía refractiva láser en el Instituto Cubano de Oftalmología Ramón Pando Ferrer en el período de mayo a octubre de 2010. MÉTODOS: Se realizó un estudio descriptivo, longitudinal y prospectivo, con un universo de 257 pacientes (504 ojos) sometidos a cirugía refractiva láser. La muestra quedó conformada por 31 pacientes (59 ojos). Se analizaron variables como edad, sexo, equivalente esférico, paquimetría preoperatoria, cantidad de ablación, estroma residual y diferencia de elevación posterior corneal, esta última obtenida del mapa de diferencia del topógrafo Galilei, con medición preoperatoria al mes y a los tres meses de la cirugía. Mediante análisis de regresión múltiple fueron valorados dichos cambios de la paquimetría, la cantidad de ablación y el estroma residual. RESULTADOS: El equivalente esférico, la paquimetría, la cantidad de ablación y el estroma residual se encontraron dentro de los parámetros de seguridad establecidos. La diferencia promedio de la elevación corneal posterior fue de 15,62 Ám al mes y de 11,78 Ám a los tres meses, con disminución significativa con el tiempo (p= 0,000). Se observó asociación con la paquimetría preoperatoria y el estroma residual, y se encontró una correlación inversa entre este último y la elevación corneal posterior a los tres meses. CONCLUSIONES: La cirugía refractiva láser induce un aumento precoz en la elevación corneal posterior, con disminución progresiva hacia el tercer mes. Los factores que más influyeron en estos cambios fueron el estroma residual y la paquimetría preoperatoria

OBJECTIVES: To describe the modifications in the corneal posterior curve in patients underwent laser refractive surgery in the Ramón Pando Ferrer Cuban Institute of Ophthalmology from May to October, 2020. METHODS: A prospective, longitudinal and descriptive study was conducted in an universe of 257 patients (504 eyes) underwent to laser refractive surgery. Sample included 31 patients (59 eyes). Variables analyzed were: age, sex, spherical equivalent, preoperative pachymetry, ablation amount, residual stroma and difference of corneal posterior elevation, this latter achieved from the difference map of Galilei topography, with preoperative measurement at month and at three months after surgery. By multiple regression analysis the changes of pachymetry, the ablation amount and the residual stroma were assessed. RESULTS: The spherical equivalent, the pachymetry, the ablation amount and the residual stroma were within the established safety parameters. The mean difference of posterior corneal elevation was of 15,62 ?m at three months, with a significant decrease in time (p= 0,000). There was association with preoperative pachymetry and the residual stroma and also an inverse correlation between this latter and the posterior corneal elevation at three months. CONCLUSIONS: The laser refractive surgery produces an early increase in the posterior corneal elevation with a progressive decrease at third month. The factors that more influenced in such changes were the residual stroma and the preoperative pachymetry