Changes in corneal biomechanics and posterior corneal surface elevation after FS-LASIK.

AIM: To investigate the changes in corneal biomechanics and posterior corneal surface elevation after femtosecond laser-assisted in situ keratomileusis (FS-LASIK). METHODS: Totally 197 eyes of 100 patients who underwent the FS-LASIK from April 2022 to November 2022 were included. They were divided into three groups according to the ratio of residual corneal stroma thickness/corneal thickness (RCST/CT): Group I (50%≤RCST/CT<55%, 63 eyes of 32 patients), Group II (55%≤RCST/CT<60%, 67 eyes of 34 patients), and Group III (RCST/CT≥60%, 67 eyes of 34 patients). The intraocular pressure (IOP), corneal compensated IOP (IOPcc), corneal hysteresis (CH) and corneal resistance factor (CRF) were measured immediately, 1, and 3mo postoperatively by ocular response analyzer (ORA) and the posterior elevation difference (PED) was measured by Pentacam. RESULTS: After operation, IOP, CH, CRF, and PED were statistically different among the three groups (F=12.99, 31.148, 23.998, all P<0.0001). There was no statistically significant difference in IOPcc among the three groups (F=0.603, P>0.05). The IOP, IOPcc, CH, and CRF were statistical changed after surgery (F=699.635, 104.125, 308.474, 640.145, all P<0.0001). The PED of Group I was significantly higher than that of Group II (P<0.05), and Group II was significantly higher than that of Group III (P<0.05). The PED value of 3mo after surgery decreased in each group compared with 1mo after surgery, but there was no statistical difference (Group I: t=0.82, P=0.41; Group II: t=0.17, P=0.87; Group III: t=1.35, P=0.18). The correlation analysis of corneal biomechanical parameter changes with PED at 1mo and 3mo after surgery showed that ΔIOP, ΔIOPcc, ΔCH, and ΔCRF were not correlated with PED value in three groups (P>0.05). CONCLUSION: The smaller the RCST/CT, the greater effect on corneal biomechanics and posterior surface elevation. There is no correlation between changes in corneal biomechanics and posterior corneal surface elevation in the range of RCST/CT≥50%.

Efecto de los segmentos anulares intracorneales en la topografía corneal posterior en ojos con queratocono / Effect of intracorneal ring segments on posterior corneal topography in eyes with keratoconus

Objetivo Analizar los cambios en las superficies corneales anterior y posterior medidos con un dispositivo de imágenes Scheimpflug en pacientes con queratocono implantados con segmentos anulares intracorneales y correlacionar esos cambios con los resultados visuales. Métodos Este estudio prospectivo de serie de casos de intervención incluyó 92 ojos de 60 pacientes con queratocono a los que se implantó segmentos anulares intracorneales de Kerarings (Mediphacos, Belo Horizonte, Brasil). Se evaluaron las lecturas queratométricas (K), la asfericidad corneal (valor Q) y las elevaciones de las superficies corneales anterior y posterior mediante un dispositivo de imágenes Scheimpflug antes de la operación y a los uno, 3, 6 y 12 meses después de la misma. Resultados La mejor agudeza visual corregida (MAVC) mejoró de 0,61 a 0,19 logMAR a los 12 meses de la cirugía. Tanto la superficie corneal anterior como la posterior mostraron un aplanamiento significativo con una reducción estadísticamente significativa de la lectura K anterior media en 3,39 D y de la lectura K posterior media en 0,39 D (p<0,001) a los 12 meses. Se observó un cambio estadísticamente significativo del Q anterior a un valor menos negativo (de −1,05 a −0,36) (p<0,001) sin que se produjera ningún cambio significativo en el valor del Q posterior. La mejora del Q anterior se correlacionó significativamente con una mejor MAVC postoperatoria (p=0,03). Una mejor MAVC postoperatoria se correlacionó significativamente con una mejor MAVC preoperatoria, una K anterior y posterior más plana, un valor Q anterior menos prolato y menores elevaciones anteriores. Conclusiones La implantación de segmentos anulares intracorneales tiene un efecto de aplanamiento significativo en las superficies corneales anteriores y posteriores. La mejora de la asfericidad corneal se correlaciona con un mejor resultado visual. Algunos parámetros preoperatorios fueron factores predictivos de la mejora visual postoperatoria (AU)

Purpose To analyze the changes in the anterior and posterior corneal surfaces measured with a Scheimpflug imaging device in keratoconus patients implanted with intracorneal ring segments and to correlate those changes with the visual outcomes. Methods This prospective interventional case series study included 92 eyes of 60 patients with keratoconus who underwent Kerarings (Mediphacos, Belo Horizonte, Brazil) intracorneal ring segments implantation. Keratometric (K) readings, corneal asphericity (Q value) and elevations of both anterior and posterior corneal surfaces were evaluated using a Scheimpflug imaging device preoperatively and at one, 3, 6 and 12 months after surgery. Result The mean best corrected visual acuity (BCVA) improved from 0.61 to 0.19 logMAR at 12 months after surgery. Both anterior and posterior corneal surfaces showed significant flattening with statistically significant reduction of the mean anterior K reading by 3.39 D and the mean posterior K reading by 0.39 D (P<.001) at 12 months. Statistically significant change of the anterior Q to a less negative value (from −1.05 to −0.36) was observed (P<.001) with no significant change of the posterior Q value. Improvement of the anterior Q was significantly correlated to better postoperative BCVA (P=.03). Better postoperative BCVA significantly correlated to better preoperative BCVA, flatter preoperative anterior and posterior K, less prolate anterior Q value and lower anterior elevations. Conclusions Implanted with intracorneal ring segments implantation has a significant flattening effect on both anterior and posterior corneal surfaces. Improvement of corneal asphericity is correlated to better visual outcome. Certain preoperative parameters were predictive factors of the postoperative visual improvement (AU)

Effect of intracorneal ring segments on posterior corneal topography in eyes with keratoconus.

PURPOSE: To analyze the changes in the anterior and posterior corneal surfaces measured with a Scheimpflug imaging device in keratoconus patients implanted with intracorneal ring segments (ICRS) and to correlate those changes with the visual outcomes. METHODS: This prospective interventional case series study included 92 eyes of 60 patients with keratoconus who underwent Kerarings (Mediphacos, Belo Horizonte, Brazil) ICRS implantation. Keratometric (K) readings, corneal asphericity (Q value) and elevations of both anterior and posterior corneal surfaces were evaluated using a Scheimpflug imaging device preoperatively and at 1, 3, 6 and 12 months after surgery. RESULTS: The mean best corrected visual acuity (BCVA) improved from 0.61 to 0.19 logMAR at 12 months after surgery. Both anterior and posterior corneal surfaces showed significant flattening with statistically significant reduction of the mean anterior K reading by 3.39 D and the mean posterior K reading by 0.39 D (p<0.001) at 12 months. Statistically significant change of the anterior Q to a less negative value (from -1.05 to -0.36) was observed (p<0.001) with no significant change of the posterior Q value. Improvement of the anterior Q was significantly correlated to better postoperative BCVA (p=0.03). Better postoperative BCVA significantly correlated to better preoperative BCVA, flatter preoperative anterior and posterior K, less prolate anterior Q value and lower anterior elevations. CONCLUSIONS: ICRS implantation has a significant flattening effect on both anterior and posterior corneal surfaces. Improvement of corneal asphericity is correlated to better visual outcome. Certain preoperative parameters were predictive factors of the postoperative visual improvement.

Long-term evaluation of posterior corneal surface parameters after accelerated corneal cross-linking with a comparison with uncross-linked keratoconic eyes.

PURPOSE: To evaluate the 36 months changes in posterior corneal surface parameters in keratoconic eyes after accelerated corneal cross-linking and to compare the data with uncross-linked progressive and non-progressive keratoconic eyes. METHODS: Thirty five cross-linked, 30 uncross-linked progressive, and 30 uncross-linked non-progressive keratoconic eyes were included. Maximum keratometry (Kmax), thinnest pachymetry, minimum radius of curvature back (Rminback), asphericity back, posterior elevation and corneal densitometry, back corneal higher order aberrations (HOAs), back surface deviation (Db), final D, posterior radius of curvature (PRC) and 'B' unit values were recorded at baseline and at the 12, 24, 36 months follow-up. Data were analyzed with repeated measures ANOVA and paired t-tests. RESULTS: Kmax and thinnest pachymetry were significantly changed in the cross-linked and progressive uncross-linked groups. Rminback, asphericity back, and HOAs did not change in either group. Total posterior corneal densitometry improved; posterior elevation, Db and B unit worsened in the cross-linked group and did not change in the uncross-linked groups. PRC and final D worsened in the cross-linked and progressive uncross-linked groups, and did not change in the non-progressive group. CONCLUSION: Despite a decreased Kmax, the posterior corneal surface parameters, posterior elevation values were determined to have significantly worsened in the cross-linked group and this increase was higher than in progressive uncross-linked eyes.

Unintended changes in ocular biometric parameters during a 6-month follow-up period after FS-LASIK and SMILE.

BACKGROUND: Corneal refractive surgery has become reliable for correcting refractive errors, but it can induce unintended ocular changes that alter refractive outcomes. This study is to evaluate the unintended changes in ocular biometric parameters over a 6-month follow-up period after femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE). METHODS: 156 consecutive myopic patients scheduled for FS-LASIK and SMILE were included in this study. Central corneal thickness (CCT), mean curvature of the corneal posterior surface (Kpm), internal anterior chamber depth (IACD) and the length from corneal endothelium to retina (ER) were evaluated before and after surgery over a 6-month period. RESULTS: Both the FS-LASIK and SMILE groups (closely matched at the pre-surgery stage) experienced flatter Kpm, shallower IACD and decreased ER 1 week post-surgery (P < 0.01), and these changes were larger in FS-LASIK than in SMILE group. During the 1 week to 6 months follow up period, Kpm, IACD and ER remained stable unlike CCT which increased significantly (P < 0.05), more in the FS-LASIK group. CONCLUSIONS: During the follow up, the posterior corneal surface became flatter and shifted posteriorly, the anterior chamber depth and the length from the corneal endothelium to retina decreased significantly compared with the pre-surgery stage. These unintended changes in ocular biometric parameters were greater in patients undergoing FS-LASIK than SMILE. The changes present clear challenges for IOL power calculations and should be considered to avoid affecting the outcome of cataract surgery.

Cornea and anterior eye assessment with placido-disc keratoscopy, slit scanning evaluation topography and scheimpflug imaging tomography.

Current corneal assessment technologies make the process of corneal evaluation extremely fast and simple and several devices and technologies allow to explore and to manage patients. The purpose of this special issue is to present and also to update in the evaluation of cornea and ocular surface and this second part, reviews a description of the corneal topography and tomography techniques, providing updated information of the clinical recommendations of these techniques in eye care practice. Placido-based topographers started an exciting anterior corneal surface analysis that allows the development of current corneal tomographers that provide a full three-dimensional reconstruction of the cornea including elevation, curvature, and pachymetry data of anterior and posterior corneal surfaces. Although, there is not an accepted reference standard technology for corneal topography description and it is not possible to determine which device produces the most accurate topographic measurements, placido-based topographers are a valuable technology to be used in primary eye care and corneal tomograhers expanding the possibilities to explore cornea and anterior eye facilitating diagnosis and follow-up in several situations, raising patient follow-up, and improving the knowledge regarding to the corneal anatomy. Main disadvantages of placido-based topographers include the absence of information about the posterior corneal surface and limited corneal surface coverage without data from the para-central and/or peripheral corneal surface. However, corneal tomographers show repeatable anterior and posterior corneal surfaces measurements, providing full corneal thickness data improving cornea, and anterior surface assessment. However, differences between devices suggest that they are not interchangeable in clinical practice.

Posterior corneal surface differences between non-laser in situ keratomileusis (LASIK) and 10-year post-LASIK myopic eyes.

PURPOSE: To evaluate the posterior corneal surface differences between non-laser in situ keratomileusis (LASIK) and 10-year post-LASIK myopic eyes. METHODS: The study included 130 eyes from 65 patients, who were treated with myopic LASIK 10 years ago. In addition, 130 eyes from 65 unoperated myopic patients of matching present age and preoperative refraction were divided into control group. Data on the posterior corneal surface and anterior chamber were obtained from Pentacam software and compared between the groups. Postoperative visual acuity (VA) and refractive error were also analysed. RESULTS: The mean preoperative spherical equivalent (SE) was -6.99 ± 1.78 dioptre (D) in the LASIK group. Ten years after surgery, the mean SE was -0.45 ± 1.22 D, the efficacy index was 0.98, and the safety index was 1.01. The posterior corneal elevations of the LASIK group at 2 mm corneal diameter were significantly lower than those of the control group. However, posterior corneal elevations at 6 mm corneal diameter were higher in the LASIK group than the controls (p < 0.01 for all). The mean Q-values of posterior corneal surface demonstrated significant positive direction compared to that of control eyes at 6 and 7 mm corneal diameters (p < 0.05 for both). At the thinnest point of the cornea, the anterior chamber depths were shallower in the LASIK group than in controls. Meanwhile, the anterior chamber volumes (ACV) were smaller in the LASIK group than in the control group. CONCLUSION: Our results demonstrated that the posterior corneal surface tends to show signs of central flattening and peripheral steepening 10 years after myopic LASIK surgery compared to that of non-operated myopic eyes.

Characteristics of posterior corneal astigmatism and aberration in cataract patients with high myopia / 中华实验眼科杂志

Objective This study was to investigate the characteristics of posterior corneal astigmatism (PCA) and aberration in cataract patients with high myopia.Methods A retrospective study was designed.Two hundred and eighty-two eligible eyes of 190 cataract patients were enrolled in Eye and ENT Hospital of Fudan University from September to December,2014.The eyes were classified into two groups according to axial length (AL):high myopia group with 139 eyes (AL≥26 mm) and control group with 143 eyes (AL was 20 to 25 mm).The mean keratometric mid-radius of curvature (Km),corneal central thickness (CCT),astigmatism and aberrations were measured by the rotating Scheimpflug System (Pentacam),and the AL were measured by the partial coherence interferometry (IOL Master).This study followed the Helsinki declaration,and was approved by the Ethic Committee of Eye and ENT Hospital,Fudan University.Informed consent was signed from each patient.Results In high myopia group,the mean PCA was 0.3 D (range 0 ～ 0.9 D) and 92.8％ eyes had PCA values ＜0.5 D.The steep corneal meridian was aligned vertically (60°～ 120°) in 87.1％ eyes for the posterior corneal surface.There was no significant difference in PCA between the high myopia group and the control group (P =0.797).Significant positive linear correlations was found between PCA and anterior corneal astigmatism (ACA),PCA and anterior corneal root mean square (RMS),PCA and anterior lower-order RMS,PCA and posterior corneal RMS,PCA and posterior high-order RMS,PCA and posterior lower-order RMS (r =0.235,P =0.005;r =0.217,P =0.010;r =0.229,P =0.007;r =0.395,P =0.000;r =0.243,P =0.004;r =0.384,P =0.000).Compared with total corneal astigmatism (TCA),anterior corneal measurements overestimated with-the-rule astigmatism (WTR) by a mean of (0.27 ± 0.18) D in 65.67％ eyes,underestimated against-the-rule astigmatism (ATR) by (0.27 ± 0.18) D in 88.10％ eyes and underestimated oblique astigmatism (Obl) by (0.22 ± 0.10) D in 63.33％ eyes.Compared with total corneal aberrations,anterior corneal aberrations measurements overestimated by (0.275 ±0.176) μm in 87.05 ％ eyes,and the anterior corneal astigmatism types had no effect on the result.Conclusions In high myopia group,92.8％ eyes had PCA values ＜0.5 D and the main astigmatism type in posterior corneal surface was ATR.The posterior corneal astigmatism and aberration were needed to consider in choosing intraocular lens (IOL) before cataract surgery.

Postoperative changes of posterior corneal surface height after small incision lenticule extraction and femtosecond laser <i>in situ</i> keratomileusis / 国际眼科杂志(Guoji Yanke Zazhi)

@#AIM: To explore the posterior corneal surface height after femtosecond laser small incision lenticule extraction(SMILE)or femtosecond laser <i>in situ</i> keratomileusis surgery(Fs-LASIK). <p>METHODS: A retrospective analysis of 113 cases of patients(226 eyes)with myopia underwent laser corneal refractive surgery in our hospital from January to December 2016 was taken. There were 51 cases(102 eyes)with SMILE and 62(124 eyes)with Fs-LASIK. Postoperative posterior corneal surface height, uncorrected visual acuity, spherical equivalent change, operation safety were analyzed and compared between the two groups.<p>RESULTS: The preoperative posterior corneal surface height had no statistical difference between the two groups(<i>P</i>>0.05). Corneal surface height at 1, 3 and 6mo after operation were significantly higher than those before operation(<i>P</i><0.05), but the differences between the two groups at different time points after operation were not significant(<i>P</i>>0.05). Preoperative uncorrected visual acuity had no statistical difference between the two groups(<i>P</i>>0.05); postoperative uncorrected visual acuity at 1, 3 and 6mo were significantly better than those before operation(<i>P</i><0.05), but the differences between the two groups at different time points after operation were not significant(<i>P</i>>0.05). Preoperative spherical equivalent had no statistical difference between the two groups(<i>P</i>>0.05); postoperative spherical equivalent at 1wk were significantly better than those before operation(<i>P</i><0.05), but the differences between the two groups after operation were not significant(<i>P</i>>0.05). Postoperative incidence of adverse reactions such as corneal edema, corneal infection, diffuse lamellar keratitis and postoperative glare had no statistical difference between the two groups at 6mo after operation(<i>P</i>>0.05).<p>CONCLUSION: SMILE and Fs-LASIK can be safely and effectively correcting visual acuity, but posterior corneal surface partial forward occurred after either operation.

Value of posterior keratometry in the assessment of surgically induced astigmatic change in cataract surgery.

PURPOSE: To investigate the value of posterior keratometry in the assessment of surgically induced astigmatic change (AC) in cataract surgery, with particular emphasis on the influence of test-retest variability. METHODS: Seventy-seven eyes of 77 cataract patients scheduled for routine cataract surgery were enrolled. All patients received a 2.2-mm self-sealing scleral incision (n = 24), single-plane clear corneal incision (SPCCI; n = 29) or biplanar clear corneal incision (BPCCI; n = 24). Measurements of anterior and posterior corneal astigmatism were performed with a rotating Scheimpflug camera (Pentacam HR) preoperatively and postoperatively. Two repeated readings were taken preoperatively to assess the role of the test-retest effect. Astigmatic change (AC) was analysed according to the polar value method. RESULTS: On the anterior corneal surface, SPCCIs and BPCCIs caused a statistically significant mean flattening of the incisional meridian of 0.37 and 0.27 dioptres (D), respectively. Scleral incisions on average did not cause AC, although steepening, flattening or torque beyond the test-retest effect was observed in individual cases. On the posterior surface, mean power changes in the incisional meridian were below 0.1 D for all incisions, and these changes were of the same order of magnitude as the test-retest effect. CONCLUSION: Surgically induced AC of the posterior corneal surface after cataract surgery is of negligible clinical relevance. Moreover, it is of the same order of magnitude as the test-retest variability of the measurement device and therefore cannot (yet) be reliably assessed.

Aberration compensation between anterior and posterior corneal surfaces after Small incision lenticule extraction and Femtosecond laser-assisted laser in-situ keratomileusis.

PURPOSE: To investigate the aberration compensation between anterior and posterior corneal surfaces after SMILE and FS-LASIK. METHODS: Fifty-five subjects (55 eyes) undergoing SMILE and 51 subjects (51 eyes) undergoing FS-LASIK were enrolled in this study. Wavefront aberrations of anterior and posterior corneal surfaces and the whole cornea at 6 mm in diameter were measured using a Scheimpflug Camera preoperatively and one, three and 6 months postoperatively. The compensation factor (CF), where CF = 1 - (aberration of the whole cornea/aberration of anterior corneal surface), was calculated. RESULTS: Spherical aberration of the posterior surface and the whole cornea remained stable after SMILE. However, spherical aberration of posterior surface increased significantly at 6 months in the FS-LASIK group. The total higher-order aberration (tHOA) of the anterior surface and the whole cornea was lower at 6 months than at one and 3 months (p = 0.001 and 0.001, respectively) in the FS-LASIK group. Meanwhile, in the SMILE group, no significant difference in tHOA was found between various postoperative time points. There were significant decreases in the CF of tHOA compared with preoperative values in both groups. The CF of spherical aberration reduced significantly in both groups at 3 and 6 mm in diameter one, three and 6 months postoperatively. Significant decreases in the CF of vertical coma were found at three and 6 months postoperatively in the FS-LASIK group compared with preoperative values at 6 mm in diameter (p = 0.021 and 0.008, respectively). The change in CF (ΔCF) of spherical aberration was smaller in the SMILE group than in the FS-LASIK group at one and 3 months postoperatively (p = 0.003 and p < 0.0001, respectively). The ΔCF of spherical aberration was significantly lower in moderately myopic subjects than in subjects with high myopia at 1 month in the SMILE group (p = 0.041) and at one, three and 6 months in the FS-LASIK group (p = 0.014, 0.020, and 0.004, respectively). CONCLUSIONS: The posterior corneal surface plays an important role in compensating for spherical aberration of the anterior corneal surface. The compensation mechanisms of spherical aberration and higher-order aberration between anterior and posterior corneal surfaces were disrupted by the SMILE and the FS-LASIK procedures. The change in the CF of spherical aberration was smaller in the SMILE group compared with the FS-LASIK group, especially in subjects with high myopia.

Impact of Posterior Corneal Surface on Toric Intraocular Lens (IOL) Calculation.

PURPOSE: To quantify the impact of posterior cornea on toric IOL calculation accuracy using Placido-topography of anterior corneal surface and Scheimpflug measurements of corneal thickness. MATERIALS AND METHODS: Three-hundred seventy-nine non-selected eyes undergoing cataract surgery with non-toric intraocular lens (IOL) implantation were measured with TMS-5 (Tomey, Japan), IOLMaster (Zeiss, Germany) and Lenstar (Haag-Streit, Switzerland). Anterior, posterior and total measured corneal astigmatisms were compared with astigmatisms from postoperative refraction by calculating vector differences. RESULTS: The average absolute vector difference between anterior astigmatism and total astigmatism combining the measurements of anterior and posterior cornea was only 0.3 ± 0.2 D, with a median of only 0.27 D, but a maximum of 1.5 D. Measurements of anterior cornea alone show a systematic difference from refractive cylinder of 0.3-6 D at 90, 0.38 D at 89° and 0.28 D at 91° (IOLMaster, Lenstar and anterior TMS5), whereas the total TMS5 cylinder differs on average by only 0.14D at 81° from the refractive cylinder. With-the-rule (WTR) corneal astigmatism is slightly reduced and against-the-rule (ATR) astigmatism slightly increased on average when posterior corneal surface is taken into account additionally. This could also be confirmed by the calculation of an average pachymetry of all eyes in which the thinnest central part shows an ellipsoidal shape with horizontally long axis. CONCLUSION: Measurements of posterior cornea have on average only a small but significant impact on the outcome of toric IOL calculation, however, they are nevertheless recommended to detect outliers in which corneal irregularities (e.g. beginning keratokonus) may be overlooked.

Caracterización morfológica de la superficie corneal posterior en córneas normales / Morphological characterization of the posterior corneal surface in normal corneas

Objetivo: describir las características de la superficie corneal posterior en córneas normales y las modificaciones de esta en pacientes a quienes se les realizó queratomileusis con láser in situ. Métodos: fue realizado un estudio descriptivo, longitudinal y prospectivo en 282 ojos de pacientes que asistieron a la consulta de cirugía refractiva. Las variables estudiadas fueron: queratometría media central posterior, equivalente esférico, paquimetría óptica en la posición más delgada, astigmatismo topográfico anterior y posterior, astigmatismo refractivo y variación morfológica del mapa topográfico de elevación posterior respecto a la esfera de mejor ajuste. Fueron escogidos 27 ojos, los cuales reunían los criterios para cirugía refractiva láser y se les realizó la técnica queratomileusis con láser in situ. Se analizaron también las variables cantidad de ablación, estroma residual y diferencia de elevación posterior corneal, esta última obtenida del mapa de diferencia del tomógrafo Pentacam HR. Resultados: la queratometría media posterior fue de -6,37 ± 0,22 dioptrías; la correlación entre la queratometría media posterior con respecto a la paquimetría óptica fue muy significativa (p= 0,008). La media de la diferencia de elevación máxima con respecto a la esfera de mejor ajuste posterior fue 5,33 µm; el 93,3 por ciento de la muestra se encontraba dentro de valores normales. La diferencia de elevación posterior a través del tiempo fue de 18,38 µm ± 7,47 al mes y 14,95 µm ± 10,02. Se observó relación con la paquimetría y el estroma residual.Conclusiones: la queratomileusis con láser in situ determina modificaciones en la superficie corneal posterior. El estroma residual es el factor más relacionado con estas modificaciones(AU)

Objective: to describe the characteristics of the posterior corneal surface in normal corneas and its changes in patients who underwent laser in situ keratomileusis.Methods: prospective, longitudinal and descriptive study of 282 eyes from patients who went to the refractive surgery service. The studied variables were posterior central mean keratomery, spheral equivalent, optical pakimetry at the thinnest position, anterior and posterior topographic astigmatism, refractive astigmatism and morphological variation of the posterior elevation topographic map in relation to the best fit sphere. In this group, 27 eyes were selected, which met the criteria for laser refractive surgery using the laser in situ keratomileusis. Other analyzed variables were ablation amount, residual stroma and posterior corneal elevation difference, being the latter taken from the difference map outlined with the Pentacam HR tomography.Results: mean posterior keratometry was -6,37 ± 0,22 dioptries; the correlation between mean posterior keratometry and optical pakimetry was very significant (p= 0,008). The mean difference of maximum elevation with respect to the best posterior fit sphere was 5,33 µm; 93,3 percent of the sample was within the normal values. The correlation between the posterior elevation and the spheral equivalent was also significant (p= 0,019). The difference of the posterior elevation throughout the period was 18,38 µm ± 7,47 after a month and 14,95 µm ± 10,02 at the end of the period. There was correlation with pakimetry and residual stroma. Conclusions: laser in situ keratomileusis causes changes in the posterior corneal surface. The residual stroma is the factor most related with these changes(AU)

Caracterización morfológica de la superficie corneal posterior en córneas normales / Morphological characterization of the posterior corneal surface in normal corneas

OBJETIVO: describir las características de la superficie corneal posterior en córneas normales y las modificaciones de esta en pacientes a quienes se les realizó queratomileusis con láser in situ. MÉTODOS: fue realizado un estudio descriptivo, longitudinal y prospectivo en 282 ojos de pacientes que asistieron a la consulta de cirugía refractiva. Las variables estudiadas fueron: queratometría media central posterior, equivalente esférico, paquimetría óptica en la posición más delgada, astigmatismo topográfico anterior y posterior, astigmatismo refractivo y variación morfológica del mapa topográfico de elevación posterior respecto a la esfera de mejor ajuste. Fueron escogidos 27 ojos, los cuales reunían los criterios para cirugía refractiva láser y se les realizó la técnica queratomileusis con láser in situ. Se analizaron también las variables cantidad de ablación, estroma residual y diferencia de elevación posterior corneal, esta última obtenida del mapa de diferencia del tomógrafo Pentacam HR. RESULTADOS: la queratometría media posterior fue de -6,37 ± 0,22 dioptrías; la correlación entre la queratometría media posterior con respecto a la paquimetría óptica fue muy significativa (p= 0,008). La media de la diferencia de elevación máxima con respecto a la esfera de mejor ajuste posterior fue 5,33 µm; el 93,3 % de la muestra se encontraba dentro de valores normales. La diferencia de elevación posterior a través del tiempo fue de 18,38 µm ± 7,47 al mes y 14,95 µm ± 10,02. Se observó relación con la paquimetría y el estroma residual. CONCLUSIONES: la queratomileusis con láser in situ determina modificaciones en la superficie corneal posterior. El estroma residual es el factor más relacionado con estas modificaciones.

OBJECTIVE: to describe the characteristics of the posterior corneal surface in normal corneas and its changes in patients who underwent laser in situ keratomileusis. METHODS: prospective, longitudinal and descriptive study of 282 eyes from patients who went to the refractive surgery service. The studied variables were posterior central mean keratomery, spheral equivalent, optical pakimetry at the thinnest position, anterior and posterior topographic astigmatism, refractive astigmatism and morphological variation of the posterior elevation topographic map in relation to the best fit sphere. In this group, 27 eyes were selected, which met the criteria for laser refractive surgery using the laser in situ keratomileusis. Other analyzed variables were ablation amount, residual stroma and posterior corneal elevation difference, being the latter taken from the difference map outlined with the Pentacam HR tomography. RESULTS: mean posterior keratometry was -6,37 ± 0,22 dioptries; the correlation between mean posterior keratometry and optical pakimetry was very significant (p= 0,008). The mean difference of maximum elevation with respect to the best posterior fit sphere was 5,33 µm; 93,3 % of the sample was within the normal values. The correlation between the posterior elevation and the spheral equivalent was also significant (p= 0,019). The difference of the posterior elevation throughout the period was 18,38 µm ± 7,47 after a month and 14,95 µm ± 10,02 at the end of the period. There was correlation with pakimetry and residual stroma. CONCLUSIONS: laser in situ keratomileusis causes changes in the posterior corneal surface. The residual stroma is the factor most related with these changes.

Effect of related factors on the stability of posterior corneal surface after LASIK / 国际眼科杂志(Guoji Yanke Zazhi)

AIM:To discuss the related factors that affected the stability of posterior corneal surface after laser in situ keratomileusis ( LASIK) . METHODS:About 64 patients (64 eyes) were enrolled. The correlation among the changes in posterior corneal surface 6 month after LASIK, surgery method, corneal flap thickness ( FT ) , ablation thickness ( AT ) , postoperative residual corneal stroma thickness ( RCST ) , preoperative thinnest corneal thickness ( CT ) , flap thickness/preoperative thinnest corneal thickness ( FT/CT ) , ablation thickness/preoperative thinnest corneal thickness ( AT/CT) , postoperative residual corneal stroma thickness/preoperative thinnest corneal thickness ( RCST/CT) , anterior and posterior preoperative corneal height, the difference of the forward shift in posterior corneal surface ( diff value ) of preoperative and preoperative intraocular pressure were analyzed. RESULTS: The changes of diff value between preoperative and postoperative were related with diopter (r=0.419, P=0.014), AT (r=0.394, P=0.023), AT/CT (r=0.501, P=0.004), Diff value of preoperative (r=0.501, P=0. 004), RCST (r=-0. 385, P=0. 033) and RCST/CT (r=-0. 401, P=0. 025). The changes of height value from posterior corneal surface between preoperative and postoperative were related with diopter (r=0. 520, P=0. 002), AT (r=0.504, P=0. 003), AT/CT (r=0. 442, P=0. 013), Diff value of preoperative (r=0. 624, P=0. 000) and RCST/CT (r=-0. 394, P=0. 028). CONCLUSION: AT, RCST, AT/CT, RCST/CT and diff value of preoperative should be the key index that predicted the stability of posterior corneal surface after LASIK,the further research will give the range of safety value.

Reasearch progress in posterior corneal surface anterior protrusion after the excimer laser corneal refractive surgery / 中华实验眼科杂志

With the mature of techniques and development of equipments in excimer laser corneal refractive surgery,the postoperative complications are decreasing gradually.As the center of cornea become thin after laser in situ keratomileusis (LASIK)and laser subepithelial keratomileusis ( LASEK ),the strength of cornea and the intraocular pressure relatively step down,which can cause cornea anterior protrusion more or less.Because the posterior surface which is not directly affected by surgical process and healing process,so it is usually used to evaluate the protrusion of cornea.As the application of.ophthalmic anterior segment imaging and analysis system,we can get more message of cornea posterior surface.The manifestation,principle and precautionary measures of corneal posterior surface anterior protrusion after the excimer laser corneal refractive surgery were reviewed.

The Changes of Posterior Corneal Surface and High-Order Aberrations after Refractive Surgery in Moderate Myopia

PURPOSE: To compare forward shift of posterior corneal surface and higher-order aberration (HOA) changes after LASIK, LASEK, and wavefront-guided LASEK surgery in moderate myopia METHODS: One hundred eighty four eyes undergoing LASIK, LASEK and wavefront-guided LASEK with VISX STAR S4 were included in this study. The posterior corneal elevation was measured with Orbscan before, 2 and 4 months after surgery. Changes of the elevation were assessed using the difference map generated from preoperative and postoperative elevation maps. The values of higher-order aberrations were evaluated preoperatively and 2 months postoperatively with Wavefront aberrometer. RESULTS: The posterior corneal surface displayed forward shift of 27.2+/-11.45 micrometer, 24.3+/-9.76 micrometer in LASIK group, 23.4+/-10.5 micrometer, 23.6+/-10.55 micrometer in LASEK group, 24.0+/-14.95 micrometer, 28.4+/-14.72 micrometer in wavefront-guided LASEK group at 2 months and 4 months, respectively. There were no statistically significant differences among those three groups, and between 2 and 4 months. The root mean score (RMS) of HOA was increased after LASIK and LASEK (p=0.000, p=0.000, respectively). The mean change of HOA-RMS was significantly smaller in wavefront-guided LASEK than LASIK or LASEK (p=0.000, p=0.000, respectively, Bonferroni-corrected). CONCLUSIONS: The changes of posterior corneal surface forward shift showed no difference among LASIK, LASEK and wavefront-guided LASEK in moderate myopia. HOAs were significantly increased after LASIK and LASEK. The changes of HOAs were significant smaller in wavefront-guided LASEK than LASIK or LASEK.

Change of Posterior Corneal Surface after Laser In Situ Keratomileusis; One Year Fallow-up

PURPOSE: To investigate the change of the posterior corneal surface for 1 year after LASIK METHODS: Ninety-nine eyes of 57 patients who underwent LASIK were evaluated retrospectively. The posterior corneal surface was evaluated before surgery and at 1 week, 2 months, 6 months and 1 year postoperatively. The patients were divided into two groups based on the preoperative mean spherical equivalent (Group I; -2.5 ~ -6.0 D, Group II; -6 ~ -10 D) and two groups based on the residual bed thickness (RBT: Group A; 250 ~ 300 micrometer, Group B; 300 ~ 350 micrometer). We also grouped them based on the ablation percentage of the total corneal thickness (P/TCT: Group 1; below 10%, Group 2; 10-15%, Group 3; 15-20%) RESULTS: The posterior corneal surface in Group I was shifted forward 14.19 +/- 8.98 micrometer at 1 week, 7.93 +/- 5.64 micrometer at 1 year after LASIK, and 19.77 +/- 6.97 micrometer and 14.93 +/- 6.95 micrometer in Group II, respectively. It was displayed forward shift 19.48 +/- 8.54 micrometer at 1 week and 13.04 +/- 7.14 micrometer at 1 year in Group A and 11.64 +/- 6.09 micrometer and 7.07 +/- 5.26 micrometer in Group B, respectively. The values at the same times were 8.49 +/- 5.83 micrometer and 5.45 +/- 4.18 micrometer in Group 1, 17.21 +/- 7.73 micrometer and 9.12 +/- 5.26 micrometer in Group 2 and 20.25 +/- 8.16 micrometer and 16.05 +/- 7.24 micrometer in Group 3, respectively. CONCLUSIONS: The posterior corneal surface shifted forward early time after LASIK, but showed a trend toward gradual backward shifted over time. The eyes with higher myopia, thinner RBT and higher P/TCT were more shifted forward the posterior corneal surface at l year after LASIK.

Comparison of Anterior and Posterior Corneal Surface Change after Laser In Situ Keratomileusis and Laser Epithelial Keratomileusis

PURPOSE: To compare the time course of the change in corneal surface between LASIK and LASEK groups, which show the difference in residual bed thickness. METHODS: Twenty-one eyes of 15 patients who underwent LASIK and 20 eyes of 12 patients who underwent LASEK were included in this study and were evaluated on a review retrospectively. Corneal topography was performed preoperatively, 1 week, 2 months, 6 months, and 1 year postoperatively. The change in corneal surface was measured with the Orbscan II. The change in the elevation of the anterior corneal surface was assessed using the difference map produced from the first postoperative week and the subsequent postoperative maps. The elevation of the posterior corneal surface was measured using the difference map generated from the preoperative and postoperative elevation maps. RESULTS: After LASIK and LASEK, the posterior corneal surface was shifted anteriorly by 18.87 +/- 5.91 micrometer and 28.77 +/- 15.46 micrometer at 1 week, 15.43 +/- 6.49 micrometer and 16.03 +/- 11.32 micrometer at 2 months, 15.58 +/- 6.19 micrometer and 15.14 +/- 7.17 micrometer at 6 months, and 16.38 +/- 6.67 micrometer, 12.81 +/- 9.94 micrometer at 1 year, respectively. Compared to the 1 week postoperative measurement, average posterior corneal surface in the LASIK group reduced by 3.44 micrometer at 1 year (p=.175) ; in the LASEK group, it reduced by 23.24 micrometer at 1 year (p=.020). CONCLUSIONS: In conclusion, in both groups, the posterior corneal surface shifted forward in the early time point postoperatively, and thereafter, it showed a trend toward gradual progressive backward shift over time, but not to the preoperative levels. The elevation of the posterior corneal surface was reduced relatively more in LASEK than in LASIK at 1 year after surgery.

Factors Affecting the Anterior Displacement of Posterior Corneal Surface after Laser In Situ Keratomileusis

PURPOSE: To determine factors which influence forward displacement of the posterior surface of conea after performing LASIK with residual corneal thickness greater than 250 micro meter. METHODS: We studied 100 eyes of 50 myopic patients with an expected residual corneal thickness of greater than 250 micro meter after underwent LASIK. Residual corneal thickness, amount of laser ablation, intraocular pressure, spherical equivalent of cornea (keratometer), corneal diameter, corneal thickness, and anterior chamber depth were obtained at the preoperative stage, the postoperative one week, one month. Computed topography of cornea was performed between before and after LASIK. We evaluated the influence the forward displacement of posterior surface of conea by LASIK procedure. RESULTS: Average forward displacement of posterior surface of the cornea was 38+/-12 micro meter, and among preoperative factors, preoperative corneal thickness showed relatively high correlation with r=0.462 (P<0.001), having influence on the forward displacement. The displacement measured 1 month after LASIK was shown to decrease slightly (31+/-8 micro meter) compared that the displacement measured at 1 week after LASIK. CONCLUSIONS: Despite performing LASIK with residual corneal thickness of greater than 250 micro meter, if pre- operative corneal thickness is thin, one should be careful about anterior displacement of corneal posterior surface, and this change usually occurs within 1 week.