Posterior Corneal Elevation Research Articles

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

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

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.

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.

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

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). 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. 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. 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.

Evaluation and Comparison of Posterior Corneal Elevation Parameters in Different Grades of Keratoconus by Pentacam

To evaluate and compare posterior corneal elevation data and anterior segment parameters in different grades of keratoconus by Pentacam. 114 eyes of 114 keratoconic patients (85 men and 56 women) with a mean age of 31.6±4.7 years were evaluated with a Pentacam Scheimpflug camera. Keratoconic eyes were divided into 3 groups or grades according to the maximum keratometry reading: mild or grade I (K=50 or less than 50 diopters [D]), moderate or grade II (K=50.0 to 55.0 D), and severe or grade III (K=55.0 D or higher). The posterior corneal parameters were obtained posterior. There were no statistically significant differences between keratoconus grades in terms of sex (P=0.661). Also, there were no statistically significant differences between 3 grades in terms of age (P=0.214). There were statistically significant differences in anterior keratometry readings (K), anterior chamber depth (ACD), anterior chamber angle (ACA), and all pachymetric corneal measurements between all groups. With the progression of the disease, posterior K readings and all posterior elevation measurements were statistically different between the three grades. However, there were no significant differences in pupil diameter, anterior chamber volume (ACV), and corneal volume (CV) between the three grades of keratoconus. According to the results of this study, height data of posterior elevation, when combined with corneal anterior segment parameter, could provide a useful keratoconus severity classification tool.

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

PurposeTo evaluate the changes in posterior corneal elevation in thin corneas after small incision lenticule extraction (SMILE).MethodsIn 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.ResultsNo 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).ConclusionsWith 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.SynopsisCareful preoperative assessment and suitable surgical design should be taken to ensure posterior corneal stability after SMILE in thin corneas.

Posterior corneal elevation changes and characteristic analysis 1year after corneal collagen cross-linking for keratoconus.

To investigate the changes in posterior corneal elevations (PCEs) in the circular areas and local points after corneal collagen cross-linking (CXL) for the treatment of keratoconus. Method 1 divided the cornea into 0-2, 2-4, 4-6, and 6-8mm regions centering on the apex. Method 2 obtained other 34 PCE values of local point that were identified on the nasal, supra-nasal, sub-nasal, superior, inferior, temporal, supra-temporal, and sub-temporal sides of the circle with diameters of 2, 4, 6, and 8mm, and the apex and thinnest point. Method 1 showed a forward displacement of PCE at 1month after CXL and then a backward displacement at 3months. In Method 2, the points on the temporal side of 2mm and 4mm showed the same trend. The backward displacements of PCE on the temporal side of 2mm at 6months and on the temporal side of 4mm at 12months after CXL were both statistically different than those at 1month after CXL (P < 0.05). No significant forward displacement of PCE was found in all local points in different quadrants at 1year after CXL. The PCEs in circular areas and characteristic points of different diameters in keratoconic eyes after CXL change with time. Local point assessment of the PCE is more clinically significant. In points selected in different quadrants of the cornea, the change in temporal points was more significant after CXL.

Changes in Anterior and Posterior Corneal Elevation in Patients With Allergic Conjunctivitis.

Purpose: To evaluate corneal elevation changes in patients with allergic conjunctivitis (AC) and to analyze their correlations with ocular allergy signs and corneal biomechanical alterations.Methods: Thirty patients (30 eyes) with AC and twenty normal subjects (20 eyes) were included in this prospective study. All participants underwent a complete ocular examination, including corneal tomography by Pentacam and corneal biomechanics evaluation by Corvis ST. AC patients were evaluated for their eye rubbing frequency and ocular allergic signs.Results: The elevation at the thinnest location (TE) and the central location (CE), the elevation difference at the thinnest location (TED) and the central location (CED), and the mean value of elevation difference in the central 4 mm zoom (MED) of both the anterior and posterior corneal surface were significantly higher in the AC group than in the normal group (p < 0.05 for all). In AC patients, only anterior corneal elevation parameters were positively correlated with eye rubbing frequency and ocular allergy sign severity (p < 0.05 for all), while the tomography and biomechanical index (TBI) was positively correlated with the elevation parameters of both the anterior and posterior corneal surfaces (p < 0.05 for all).Conclusion: AC patients carry an increased risk of corneal ectasia. Posterior corneal elevation parameters are sensitive and reliable predictors of keratoconus (KC) risk in AC patients.Clinical Trial Registration: https://clinicaltrials.gov/ct2/show/NCT04299399, identifier [NCT04299399].