Ectasia after laser in situ keratomileusis

Tomographic Predictors of Ectasia Development After Keratorefractive Surgery

PURPOSE

The aim of this study was to identify the risk factors for postkeratorefractive surgery ectasia in unsuspicious tomographies and to report a new index coined diameter of peak locations (DPLs).

METHODS

All patients who underwent keratorefractive surgery between 2011 and 2018 at Care-Vision Laser Centers, Israel, and later developed ectasia were included. For each ectasia case, 3 matched controls were selected. Demographic and preoperative, intraoperative, and postoperative data were collected. Multivariate analysis was performed to evaluate the interdependence of the variables.

RESULTS

The retrospective study included 19 ectasia and 58 control eyes. There were no significant differences between the groups in ablation depth ( P = 0.73), preoperative spherical equivalent ( P = 0.12), percent tissue altered ( P = 0.71), residual stromal bed ( P = 0.73), and Ectasia Risk Score System ( P = 0.60). The anterior and the posterior symmetry index were significantly higher ( P < 0.001), and DPL was significantly tighter in the ectasia group ( P = 0.01). Binary multiple logistic regression found the symmetry index of the posterior cornea and DPL to be better predictors than age, percent tissue altered, Ectasia Risk Score System, residual stromal bed, and ablation depth.

CONCLUSIONS

A higher posterior symmetry index and a tighter DPL are predictors of ectasia in patients with otherwise normal tomographies. A tight DPL implies a weak area in the cornea, which is thin and slightly bulging, increasing the risk of this area becoming ectatic.

Corneal Collagen Crosslinking for Ectasia After Refractive Surgery: A Systematic Review and Meta-Analysis

Introduction

Corneal ectasia leads to progressive irregular corneal curvature and reduced visual acuity.

Objective

To assess the safety and effectiveness of corneal collagen cross-linking (CXL) for managing corneal ectasia resulting from refractive laser surgery (RSL).

Methods

A systematic review and meta-analysis were realized according to PRISMA guidelines. We searched PubMed, EMBASE, Cochrane, and Web of Science databases for studies on CXL in patients with ectasia after RLS. The outcomes of interest included visual acuity, refractive outcomes, topographic parameters (Kmax, index surface variance (ISV), index of Vertical Asymmetry (IVA), keratoconus index (KI), central keratoconus index (CKI), index of height asymmetry (IHA), index of height decentration (IHD) and Rmin (minimum sagittal curvature)), central corneal thickness, endothelial cell count, and possible adverse events. Statistical analysis was performed using the R software (version 4.2.3, R Foundation for Statistical Computing, Vienna, Austria).

Results

15 studies encompassing 421 patients (512 eyes) were included. The mean age was 32.03 ± 4.4 years. The pooled results showed a stable uncorrected visual acuity post-CXL, with a significant improvement in corrected distance visual acuity (SMD = 0.09; 95% CI: -0.07 to 0.26). The spherical equivalent decreased significantly (SMD = -0.09; 95% CI: -0.35, -0.02). The topographic parameter Kmax decreased significantly (SMD = 0.15; 95% CI:0.01 to 0.28); however, the other parameters, ISV, IVA, KI, CKI, IHA, IHD, and Rmin, did not change significantly. Central corneal thickness decreased significantly (SMD = 0.24; 95% CI:0.07 to 0.41), and the endothelial cell count remained stable The complications were rare.

Conclusion

CXL is a safe and effective technique for managing corneal ectasia after RLS.

Characterization of postoperative LASIK ectasia features on higher-order aberration excimer ablation maps

BACKGROUND

To characterize anterior corneal higher-order aberration (HOA) excimer ablation map patterns in postoperative LASIK ectasia (POE) and to examine correlations between newly identified corneal HOA ablation map features of POE and known topographic indices.

METHODS

Prospective multicenter non-interventional descriptive study. A total of 28 eyes from 22 POE patients were enrolled. The postoperative HOA ablation map was derived from Topolyzer Vario corneal imaging at the time of POE diagnosis. Features that recurred were identified and then analyzed. Correlations to Orbscan indices were studied.

RESULTS

An arrangement of two elliptical paracentral ablation islands, deep inferior and shallow superior, in direct mirror-like opposition to each other, were identified on all HOA maps. The paracentral islands were accompanied by peripheral ablation crescents. The deep paracentral inferior island 'hot spot' coincided with the topographical apical POE cone and was highly reproducible in angular position (249.3 ± 17.3°). There was significant variation in ablation depth (shallow superior island: 11.5 ± 6.9 μm and deep inferior island: 32.5 ± 18.8 μm). The superior crescents had high variability in depth (34.8 ± 18.9 μm). Strong correlations were found between the corneal irregularity index and the ablation depth difference between the deep and shallow paracentral islands (R = 0.96; P < 0.0001).

CONCLUSION

The corneal HOA excimer ablation map revealed a recurring, distinct, easily recognizable pattern in POE eyes. Validated Orbscan POE indices and HOA ablation map islands showed a strong correlation. It is possible to extract useful information from the corneal HOA ablation map, potentially making it suitable for diagnosing and monitoring POE although more studies are needed.

Nonlinear fourth-order elastic characterization of the cornea using torsional wave elastography

Measuring the mechanical nonlinear properties of the cornea remains challenging due to the lack of consensus in the methodology and in the models that effectively predict its behaviour. This study proposed developing a procedure to reconstruct nonlinear fourth-order elastic properties of the cornea based on a mathematical model derived from the theory of Hamilton et al. and using the torsional wave elastography (TWE) technique. In order to validate its diagnostic capability of simulated pathological conditions, two different groups were studied, non-treated cornea samples (n=7), and ammonium hydroxide ([Formula: see text]) treated samples (n=7). All the samples were measured in-plane by a torsional wave device by increasing IOP from 5 to 25 mmHg with 5 mmHg steps. The results show a nonlinear variation of the shear wave speed with the IOP, with higher values for higher IOPs. Moreover, the shear wave speed values of the control group were higher than those of the treated group. The study also revealed significant differences between the control and treated groups for the Lamé parameter [Formula: see text] (25.9-6.52 kPa), third-order elastic constant A (215.09-44.85 kPa), and fourth-order elastic constant D (523.5-129.63 kPa), with p-values of 0.010, 0.024, and 0.032, respectively. These findings demonstrate that the proposed procedure can distinguish between healthy and damaged corneas, making it a promising technique for detecting diseases associated with IOP alteration, such as corneal burns, glaucoma, or ocular hypertension.

Bibliometric and visualized analysis of myopic corneal refractive surgery research: from 1979 to 2022

Background

Myopic corneal refractive surgery is one of the most prevalent ophthalmic procedures for correcting ametropia. This study aimed to perform a bibliometric analysis of research in the field of corneal refractive surgery over the past 40 years in order to describe the current international status and to identify most influential factors, while highlighting research hotspots.

Methods

A bibliometric analysis based on the Web of Science Core Collection (WoSCC) was used to analyze the publication trends in research related to myopic corneal refractive surgery. VOSviewer v.1.6.10 was used to construct the knowledge map in order to visualize the publications, distribution of countries, international collaborations, author productivity, source journals, cited references, keywords, and research hotspots in this field.

Results

A total of 4,680 publications on myopic corneal refractive surgery published between 1979 and 2022 were retrieved. The United States has published the most papers, with Emory University contributing to the most citations. The Journal of Cataract and Refractive Surgery published the greatest number of articles, and the top 10 cited references mainly focused on outcomes and wound healing in refractive surgery. Previous research emphasized "radial keratotomy (RK)" and excimer laser-associated operation methods. The keywords containing femtosecond (FS) laser associated with "small incision lenticule extraction (SMILE)" and its "safety" had higher burst strength, indicating a shift of operation methods and coinciding with the global trends in refractive surgery. The document citation network was clustered into five groups: (1) outcomes of refractive surgery: (2) preoperative examinations for refractive surgery were as follows: (3) complications of myopic corneal refractive surgery; (4) corneal wound healing and cytobiology research related to photorefractive laser keratotomy; and (5) biomechanics of myopic corneal refractive surgery.

Conclusion

The bibliometric analysis in this study may provide scholars with valuable to information and help them better understand the global trends in myopic corneal refractive surgery research frontiers. Two stages of rapid development occurred around 1991 and 2013, shortly after the innovation of PRK and SMILE surgical techniques. The most cited articles mainly focused on corneal wound healing, clinical outcomes, ocular aberration, corneal ectasia, and corneal topography, representing the safety of the new techniques.

Iatrogenic Keratectasia after Refractive Surgery - Causes, Prophylaxis, Therapy

Iatrogenic keratectasia is induced thinning and protrusion of the cornea after laser refractive surgery. Known risk factors include an excessively thin postoperative residual stromal bed, a thicker flap, or preoperatively undetected evidence of preexisting subclinical keratoconus. The rate of post-refractive ectasia in eyes without identifiable preoperative risk factors is 20 per 100 000 eyes for photorefractive keratectomy, 90 per 100 000 eyes for laser in situ keratomileusis, and 11 per 100 000 eyes for small incision lenticule extraction. Traditional screening tools for preoperative risk include the ectasia risk score system and percentage of tissue alteration. More recent methods include corneal elastography and epithelial mapping, in addition to Artificial Intelligence methods for data analysis. Therapy includes contact lenses, cross-linking, implantation of intracorneal ring segments, penetrating or lamellar keratoplasty, and, in early studies, implantation of corneal lenticules.

Clinical Outcomes Comparison of Combined Small Incision Lenticule Extraction with Collagen Cross-Linking Versus Small Incision Lenticule Extraction Only

Purpose

To evaluate clinical outcome during 24 months follow-up between small incision lenticule extraction combined with cross-linking (SMILE Xtra) and small incision lenticule extraction (SMILE) only. Setting. Ophthalmology Division of San Rossore Medical Center, Pisa, Italy.

Design

Retrospective comparative case series.

Methods

The study comprised 70 eyes (35 patients); 40 eyes were corrected using SMILE and 30 eyes were corrected using SMILE Xtra using a low energy protocol. The outcomes were compared at 1, 6, 12, and 24 months postoperatively.

Results

The mean spherical equivalent (SEQ) reduced from −7.18 ± 1.21 D to −0.01 ± 0.09 D in the SMILE group and from −6.20 ± 2.99 D to −0.04 ± 0.1 D postoperatively in SMILE Xtra (p < 0.05). At 24 months the mean SEQs were −0.01 ± 0.24 D for SMILE and −0.15 ± 0.33 D for SMILE Xtra (p > 0.05). At 1, 6, 12, and 24 months, there were no statistically significant differences between the SMILE and SMILE Xtra groups in logarithm of the minimum angle of resolution (logMAR) uncorrected distance visual acuity (UDVA), safety, and efficacy index (p > 0.05). The mean average keratometry (K-avg) at 1, 6, 12, and 24 months after surgery did not shown any statistically significant difference between SMILE and SMILE Xtra group (p > 0.05). The mean maximum keratometry (K-max) readings at 1, 6, 12, and 24 months were not statistically significant between SMILE and SMILE Xtra group (p > 0.05). The preoperative mean thinnest point pachymetry (TTP) was 543.90 ± 22.85 μm in the SMILE group and 523.40 ± 37.01 μm in the SMILE Xtra group (p < 0.05). At 1, 6, 12, and 24 months the mean TTP was not statistically significant between the SMILE and SMILE Xtra groups (p > 0.05). At 24 months, the TTP was 408.29 ± 38.75 μm for the SMILE group and 402.22 ± 37 μm for the SMILE Xtra group (p > 0.05). In the preoperative period, the mean maximum posterior elevation (MPE) was 8.63 ± 4.35 μm for SMILE and 8.13 ± 2.54 μm for SMILE Xtra (p > 0.05). After the surgical procedure, both groups showed a statistically significant increase of the MPE (p < 0.05). At 24 months, the MPE was 11.00 ± 4.72 μm for SMILE Xtra and 10.14 ± 3.85 μm for the SMILE group (p > 0.05). In the preoperative period, the means of the root mean square (RMS) of high-order aberration (HOA) were 0.08 ± 0.03 μm for the SMILE group and 0.08 ± 0.03 μm for the SMILE Xtra group (p > 0.05). At 24 months, the RMS of HOA was 0.13 ± 0.07 μm for the SMILE group and 0.14 ± 0.07 μm for the SMILE Xtra group (p > 0.05). In the preoperative period, the root mean square of coma aberration (RMS-Coma) aberration was 0.06 ± 0.09 μm for the SMILE group and 0.04 ± 0.03 μm for the SMILE Xtra group (p > 0.05). At 24 months, the coma aberration of SMILE group was 0.12 ± 0.21 μm and 0.16 ± 0.25 μm for SMILE Xtra group (p > 0.05).

Conclusions

SMILE Xtra procedure is a safe and simple procedure that can be offered to patients with high corneal ectasia risk because there were no differences in the indices of ectasia compared to the group treated only with SMILE which has a low corneal ectatic risk.

Central Corneal Thickness of a Saudi Population in Relation to Age, Gender, Refractive Errors, and Corneal Curvature

Background In this study, we aimed to investigate the relationship between central corneal thickness (CCT) and age, gender, refractive errors, and corneal curvature in a Saudi population. Methodology In this randomized, hospital-based, retrospective study, data were collected from Dr. Sulaiman Al Habib Hospital and Imam Medical Center, Riyadh. A total of 1,005 eyes were included and recruited from patients referred to the refractive surgery clinic for Lasik assessment. The study included patients aged between 17 and 57 years with no history of any ocular pathology, eye surgeries, and systemic disease, as well as all groups with stable refractions. The identifying data were the age and gender of the patients, as well as their CCT, refraction, and corneal curvature. CCT and corneal curvature were measured by ultrasound pachymeter Pentacam. Results The distribution of CCT was 543.81 ± 34.47 μm. A significant difference in the mean CCT was observed across different refractive errors (p = 0.004). Patients with astigmatism had the lowest CCT, followed by myopic and hyperopic patients. An association between the spherical equivalent of patients with myopia and CCT (p = 0.001) was noted. Conclusions In the Saudi population, we found no significant association between mean corneal curvature and CCT in all three groups. Spherical equivalent in myopic patients was significantly associated with CCT. A significant difference in the mean CCT was observed across different refractive errors. There was a significant negative and weak correlation between age in myopic and astigmatism patients and CCT. Gender was significantly associated with CCT in patients with astigmatism.

Inter-changeability Between Anterior Segment Optical Coherence Tomography and Scheimpflug Imaging in the Evaluation of Corneal Opacity

Purpose

To compare the results of corneal evaluation, either the total corneal thickness and corneal opacity depth by both technologies AS- OCT and Scheimpflug imaging by Sirius Scheimpflug placido topography.

Methods

sixty-eight eyes of sixty- eight consecutive patients with corneal opacities were examined by both AS-OCT and Sirius Scheimpflug imaging. Corneal thickness and corneal opacity depth were measured and compared determining the interchangeability using Bland–Altman plotting.

Results

Total corneal thickness was (470.32±62.10) and (463.47±56.47) by AS. OCT and Sirius Scheimpflug imaging, respectively (P value = 0.8).

While the actual measurement of corneal opacity, corneal opacity depth was (135.39±119) and (85.45±128) by AS-OCT and Siris Scheimpflug imaging respectively with P value (0.004).

Conclusion

AS-OCT and Scheimpflug imaging Sirius may be used interchangeably for measuring both total corneal thickness, while in the determination of corneal opacity depth. the AS-OCT is superior to Scheimpflug imaging in the accuracy of determination of actual boundaries of the corneal opacity.

Visual and Topographic Outcomes of Corneal Collagen Cross Linking for Post LASIK Ectasia

Purpose

To assess the topographic and visual outcomes of corneal cross-linking (CXL) for post-LASIK ectasia.

Methods

A retrospective case series of patients who had progressive post-LASIK ectasia, with at least 2 years of follow-up. They had epithelium-off CXL. Topographical and visual changes were recorded.

Results

The study included 21 eyes of 11 patients. At month 24, the final logMAR corrected distance visual acuity (CDVA) and spherical equivalent (SE) were stable compared to baseline (0.16, and −2.0 diopter (D), respectively). The final Kmean and Kmax were 42.5 and 47.4 D, respectively. Stability or improvement in CDVA, SE, and Kmax was seen in 17 eyes (81%). Significant corneal thinning was seen (438 vs 457 microns, p = 0.003). Thinning by 2% or more was seen in 12 eyes (57.1%). Failure of CXL was seen in 4 eyes (19%). No other ocular complications were seen.

Conclusion

CXL for post LASIK ectasia is a safe and effective modality. Despite corneal thinning, there was stability or improvement in topographic parameters and CDVA over the 2-year follow-up period.

Torsional wave elastography to assess the mechanical properties of the cornea

Corneal mechanical changes are believed to occur before any visible structural alterations observed during routine clinical evaluation. This study proposed developing an elastography technique based on torsional waves (TWE) adapted to the specificities of the cornea. By measuring the displacements in the propagation plane perpendicular to the axis of the emitter, the effect of guided waves in plate-like media was proven negligible. Ex vivo experiments were carried out on porcine corneal samples considering a group of control and one group of alkali burn treatment (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {NH}_\text {4}$$\end{document}NH4OH) that modified the mechanical properties. Phase speed was recovered as a function of intraocular pressure (IOP), and a Kelvin-Voigt rheological model was fitted to the dispersion curves to estimate viscoelastic parameters. A comparison with uniaxial tensile testing with thin-walled assumptions was also performed. Both shear elasticity and viscosity correlated positively with IOP, being the elasticity lower and the viscosity higher for the treated group. The viscoelastic parameters ranged from 21.33 to 63.17 kPa, and from 2.82 to 5.30 Pa s, for shear elasticity and viscosity, respectively. As far as the authors know, no other investigations have studied this mechanical plane under low strain ratios, typical of dynamic elastography in corneal tissue. TWE reflected mechanical properties changes after treatment, showing a high potential for clinical diagnosis due to its rapid performance time and paving the way for future in vivo studies.

Pentacam versus anterior segment OCT in measuring intended versus achieved ablation depth post-myopic LASIK correction

Background

Accurate quantitative measurements of central corneal thickness (CCT) provide valuable, clinical information for preoperative assessment, surgical planning, and follow-up in myopic patients who have undergone LASIK correction. Typically, an ultrasound is used to measure such parameters. However, noncontact devices such as the Visante anterior segment optical coherence tomographer [AS-optical coherence tomography (OCT)] and Pentacam are becoming more popular to measure ocular parameters. It is important to assess the level of similarity between these two optical devices to compare between the intended and achieved ablation depth after LASIK procedures in cases of myopia and myopic astigmatism.

Methods

This cross-sectional, prospective study included 80 eyes of 40 patients attending Beni-Suef University Hospital between November 2018 and November 2019. All patients underwent LASIK surgery for the correction of myopia with or without myopic astigmatism with spherical equivalent ranging from − 1.5 to − 12 diopters.

Results

No statistically significant difference was observed between the intended ablation depth and the clinically measured ablation depth calculated by Pentacam and AS-OCT 3 months after surgery (P > 0.05).

Conclusion

When planning corneal refraction surgery, ablation depth readouts calculated by the computer software of the excimer laser used in this study are reliable. Both Pentacam and AS-OCT are accurate, sensitive, and specific in measuring the CCT and calculating ablation depth. Pentacam provides slightly higher accuracy and sensitivity compared with AS-OCT. LASIK is a safe, predictable, and effective procedure in the treatment of simple myopia and myopic astigmatism.

Comparison of Anterior Segment Measurements between Scheimpflug-Placido Camera and New Swept-source Optical Coherence Tomography

Purpose: We compared anterior segment measurements obtained using a Scheimpflug-Placido topographer (SIRIUS®, Costruzione Strumenti Oftalmici, Florence, Italy) and a new anterior module for a swept-source optical coherence tomography system (ANTERION®, Heidelberg Engineering Inc., Heidelberg, Germany).Methods: Anterior segment measurements were evaluated in 74 eyes of 101 patients with the two devices. Central corneal thickness (CCT), anterior chamber depth (ACD), corneal refractive power (K), J0 (Jackson cross-cylinder with axes at 180° and 90°), J45 vector (Jackson cross-cylinder with axes at 45° and 135°), and white-to-white corneal diameter (WTW) measurements obtained using the SIRIUS® system and the new anterior segment module of ANTERION® were compared.Results: The mean CCTs measured by SIRIUS® and ANTERION® were 558.69 ± 44.65 and 540.26 ± 36.57 μm, respectively. The difference was statistically significant (p < 0.005), and there were high correlations between the two methods (r = 0.915, p < 0.001). The mean ACD measurements were 3.34 ± 0.53 and 3.34 ± 0.51 mm (p = 0.856), respectively, for SIRIUS® and ANTERION®. The measurements were strongly correlated (r = 0.966, p < 0.001). The measurements of WTW, total mean K, and J0 obtained with the two systems differed significantly (p < 0.005, p = 0.017, and p < 0.005, respectively), with high correlations between the two systems (r = 0.875, r = 0.967, and r = 0.933, respectively; all p < 0.001).Conclusions: There were significant differences in measurements of K, CCT, WTW, and J0 between the two devices. Agreement analysis suggests that SIRIUS® and ANTERION® should not be used interchangeably.

Update and Review of Diagnosis and Management of Post-Refractive Surgery Ectasia

ABSTRACT

Post-Refractive Surgery Ectasia is a serious, sight-threatening, and highly - avoided complication seen after the following procedures: Laser in situ Keratomileusis, Photorefractive Keratectomy, Small Incision Lenticule Extraction, Radial and/or Arcuate Keratotomy. Specific risk factors may include age, corneal thickness, degree of refractive error, corneal topographic changes including irregular astigmatism, percent tissue ablation, and residual stromal bed. Biomarkers may be a new option to help indicate who is at greatest risk for ectasia. Visual aids including glasses or contacts lenses are often required to achieve optimal vision. Collagen crosslinking is the only treatment thought to stop progression of ectasia and prevent keratoplasty. Other surgical options may include topography-guided phototherapeutic keratectomy and intrastromal corneal ring segments. Ultimately an "ounce of prevention is a pound of cure" so careful preoperative screening and ultimately offering the safest and most effective treatments for patients is arguably the most important job of the refractive surgeon.

Logistic Regression Model Using Scheimpflug-Placido Cornea Topographer Parameters to Diagnose Keratoconus

Purpose

Diagnose keratoconus by establishing an effective logistic regression model from the data obtained with a Scheimpflug-Placido cornea topographer.

Methods

Topographical parameters of 125 eyes of 70 patients diagnosed with keratoconus by clinical or topographical findings were compared with 120 eyes of 63 patients who were defined as keratorefractive surgery candidates. The receiver operating character (ROC) curve analysis was performed to determine the diagnostic ability of the topographic parameters. The data set of parameters with an AUROC (area under the ROC curve) value greater than 0.9 was analyzed with logistic regression analysis (LRA) to determine the most predictive model that could diagnose keratoconus. A logit formula of the model was built, and the logit values of every eye in the study were calculated according to this formula. Then, an ROC analysis of the logit values was done.

Results

Baiocchi Calossi Versaci front index (BCV_f) had the highest AUROC value (0.976) in the study. The LRA model, which had the highest prediction ability, had 97.5% accuracy, 96.8% sensitivity, and 99.2% specificity. The most significant parameters were found to be BCV_f (p=0.001), BCV_b (Baiocchi Calossi Versaci back) (p=0.002), posterior rf (apical radius of the flattest meridian of the aspherotoric surface in 4.5 mm diameter of the cornea) (p=0.005), central corneal thickness (p=0.072), and minimum corneal thickness (p=0.494).

Conclusions

The LRA model can distinguish keratoconus corneas from normal ones with high accuracy without the need for complex computer algorithms.

Post-LASIK keratectasia in the context of a thicker than intended flap detected by anterior segment optical coherence tomography

The corneal flap created in LASIK is responsible for most of its advantages in comparison with surface ablation. However, lamellar dissection of the corneal layers in LASIK can also result in serious complications such as corneal ectasia. A 23-year-old man underwent LASIK for correction of −4.75 −2.00@15 in the right eye and −4.50 −2.00@160 in the left eye with a preoperative thinnest corneal thickness of 518 µm/right eye and 513 µm/left eye in 2009. An intended flap thickness and ablation depth in both eyes were 160 µm and 94 µm, respectively, and subsequently, residual stromal bed thickness was 264 µm/right eye and 259 µm/left eye. Several years after surgery, he was referred for the decreased vision. His corrected-distance visual acuity was 0.50 in both eyes. A scissoring reflex was found in retinoscopy. Orbscan imaging was compatible with keratoconus. Anterior segment optical coherence tomography was performed to measure the LASIK flap. It was much thicker (200 µm) than intended (160 µm), and therefore, the residual stromal bed thickness was much thinner. In summary, keratectasia may develop in cases where thicker than expected flaps result in excessive thinning of the residual stromal bed. The obtained results from this case emphasize and remind the importance of intraoperative measurement of flap thickness and using femtosecond and new criteria for patient selection to avoid post-LASIK keratectasia.

Evaluating the Ectasia Risk Score System in Cancelled Laser In Situ Keratomileusis Candidates

Purpose

To evaluate the ectasia risk score system in cancelled laser in situ keratomileusis (LASIK) candidates at an academic hospital.

Methods

LASIK candidates who had been cancelled by a surgeon considering the patient age, preoperative central corneal thickness, residual stromal bed thickness, or preoperative manifest refraction spherical equivalent were retrospectively reviewed, and their Randleman ectasia risk score system score was calculated.

Results

The mean ectasia score of 194 eyes (97 patients) was 4.5 ± 2.67; 40 (20.6%), 46 (23.7%), and 108 (55.7%) eyes were classified as low-, moderate-, and high-risk eyes, respectively. The topography was abnormal in 69% of the patients. The mean manifest refraction spherical equivalent, central corneal thickness, and estimated residual stromal bed thickness were 4 (+0.50 to –15.50) diopters, 520 (439 to 608) µm, and 312.38 (61.5 to 424.12) µm, respectively. The main cause of cancellation in low- and moderate-risk patients (86 eyes) was the presence of unstable refractive error in the past year.

Conclusion

Although promising, some other criteria, such as stable refraction, should be added to this scoring system to achieve greater practicality since a main cause of cancelling LASIK candidates in this study was the presence of unstable refraction.

Post-FDA Approval Results of Epithelium-Off, Full-Fluence, Dresden Protocol Corneal Collagen Crosslinking in the USA

Introduction

The purpose of this non-comparative, prospective, observational study was to evaluate the post-US Food and Drug Administration approval outcomes of epithelium-off, full-fluence, Dresden protocol corneal collagen crosslinking (CXL) for the treatment of progressive keratoconus (KCN) and post-refractive corneal ectasia at a US academic tertiary medical center.

Methods

This study involved 125 eyes of 97 patients with KCN and 13 eyes of 12 patients with post-refractive ectasia which underwent CXL between November 2016 and September 2019. Best spectacle-corrected visual acuity (BSCVA) and corneal topographic parameters were measured preoperatively, at postoperative month 1 (POM-1), and between postoperative months 3 and 24 (POM 3–24).

Results

Best spectacle-corrected visual acuity, flat keratometry, steep keratometry, and mean corneal power worsened at POM-1 (p < 0.01) with a return to preoperative values at POM 3–24. Maximum keratometry (Kmax) steepened at POM-1 and then improved beyond preoperative levels at POM 3–24 (p < 0.01 and p = 0.03, respectively). Pachymetry at the apex and pupil decreased at POM-1 and POM 3–24 (p = 0.03). Pachymetry at the thinnest point decreased at POM-1 and trended toward reduction at POM 3–24 (p < 0.001 and p = 0.06, respectively). Visual and tomographic outcomes were similar between pediatric and adult populations, and between KCN and post-refractive ectasia patients.

Conclusions

Real-world results of CXL in the USA are similar to those reported in prior studies, demonstrating an initial worsening of BSCVA, pachymetry, and keratometry followed by corneal flattening and preservation of visual acuity. Improvements in Kmax and stability in visual acuity were observed over 24 months in children and adults with progressive KCN or post-refractive ectasia.

Safety and Efficacy of Myopic LASIK performed on Thin Corneas

Purpose:

The aim was to report on the visual outcomes and safety of myopic LASIK performed in patients with corneas of central thickness below average(<540μm) and normal topography.

Methods:

This is a retrospective cohort study conducted at a private practice setting on Mexican Hispanic patients who underwent myopic LASIK between January 2014 and January 2015. An analysis of records of patients >18 years-old with previous normal topography, stable refraction, corrected visual acuity ≥ 20/20 (Snellen), Central Corneal Thickness (CCT) < 540μm and at least 12 months follow up after surgery was conducted. The main outcome measures were standard visual outcomes (efficacy, safety, refractive stability) and Percent Tissue Altered (PTA) analysis was conducted.

Results:

A total of 51 patients (102 eyes) were included; 56% (n=57) were female. The mean age was 26.52 ± 8.06 (range 18-55 years) with a mean follow up of 13.9 ± 1.2 months. Preoperative CCT was 515.44 ± 17.87μm (range 452- 540μm), with a mean refractive spherical equivalent (SEQ): -4.08 ± 2.17 D (range -0.75 to -9.75 D), and mean refractive cylinder: -1.44 ± 1.29 D (range 0.00 to -6.00 D). Mean predictability of postoperative SEQ was -0.20 ± 0.40 D (range -1.25 to +1.25). Postoperative SEQ was ±0.50 D in 71%, ±1.00 D in 93% of the eyes. Postoperative uncorrected distance visual acuity was ≥20/20 in 78% and ≥20/25 in 95%. One line of CDVA was lost in 3% of the eyes, no eyes lost ≥2 lines. No ectasia cases were observed during follow-up.

Conclusion:

LASIK surgery in Mexican Hispanic patients with thinner than “normal” corneas (<540 μm) is safe, efficient and predictable at 1 year follow up for myopic refractive corrections with no evidence of postoperative keratectasia.

The Role of Corneal Biomechanics for the Evaluation of Ectasia Patients

Purpose: To review the role of corneal biomechanics for the clinical evaluation of patients with ectatic corneal diseases. Methods: A total of 1295 eyes were included for analysis in this study. The normal healthy group (group N) included one eye randomly selected from 736 patients with healthy corneas, the keratoconus group (group KC) included one eye randomly selected from 321 patients with keratoconus. The 113 nonoperated ectatic eyes from 125 patients with very asymmetric ectasia (group VAE-E), whose fellow eyes presented relatively normal topography (group VAE-NT), were also included. The parameters from corneal tomography and biomechanics were obtained using the Pentacam HR and Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany). The accuracies of the tested variables for distinguishing all cases (KC, VAE-E, and VAE-NT), for detecting clinical ectasia (KC + VAE-E) and for identifying abnormalities among the VAE-NT, were investigated. A comparison was performed considering the areas under the receiver operating characteristic curve (AUC; DeLong’s method). Results: Considering all cases (KC, VAE-E, and VAE-NT), the AUC of the tomographic-biomechanical parameter (TBI) was 0.992, which was statistically higher than all individual parameters (DeLong’s; p < 0.05): PRFI- Pentacam Random Forest Index (0.982), BAD-D- Belin -Ambrosio D value (0.959), CBI -corneal biomechanical index (0.91), and IS Abs- Inferior-superior value (0.91). The AUC of the TBI for detecting clinical ectasia (KC + VAE-E) was 0.999, and this was again statistically higher than all parameters (DeLong’s; p < 0.05): PRFI (0.996), BAD-D (0.995), CBI (0.949), and IS Abs (0.977). Considering the VAE-NT group, the AUC of the TBI was 0.966, which was also statistically higher than all parameters (DeLong’s; p < 0.05): PRFI (0.934), BAD- D (0.834), CBI (0.774), and IS Abs (0.677). Conclusions: Corneal biomechanical data enhances the evaluation of patients with corneal ectasia and meaningfully adds to the multimodal diagnostic armamentarium. The integration of biomechanical data and corneal tomography with artificial intelligence data augments the sensitivity and specificity for screening and enhancing early diagnosis. Besides, corneal biomechanics may be relevant for determining the prognosis and staging the disease.

Analysis of cases and accuracy of 3 risk scoring systems in predicting ectasia after laser in situ keratomileusis

PURPOSE

To identify risk factors for ectasia after laser in situ keratomileusis (LASIK) by comparing the accuracy of the Ectasia Risk Score System (ERSS), Screening Corneal Objective Risk of Ectasia (SCORE) Analyzer, and percentage of tissue altered (PTA) in predicting the occurrence of ectasia.

SETTING

Multiple centers in 8 countries.

DESIGN

Retrospective case series.

METHODS

Previously unpublished post-LASIK ectasia cases were analyzed. Consecutive patients who had LASIK performed at least 5 years previously with no resultant ectasia were used as controls. Axial maps from preoperative Orbscan IIz topographies were analyzed in a masked fashion, and examination files tested with the SCORE Analyzer. The PTA values and ERSS scores were generated using available preoperative and perioperative data. Only eyes with subjectively identified normal preoperative topography were tested with the PTA. Threshold values for the SCORE, ERSS, and PTA were more than or equal to 0, 4, and 40, respectively.

RESULTS

Ectasia occurred in 31 eyes (22 patients); 79 eyes (44 patients) were used as controls. In all eyes, the sensitivity and specificity for predicting ectasia, respectively, were 67.7% and 79.7% for the ERSS and 64.5% and 100% for the SCORE. In eyes with normal topography (ectasia group, 12 eyes; controls, 64 eyes), the PTA yielded sensitivity of 33.3% and specificity of 85.9%. The area under the receiver operating characteristic curve was highest for SCORE (0.911) followed by the ERSS (0.844) and PTA (0.557).

CONCLUSIONS

The SCORE was most predictive of ectasia, achieving the best specificity; the ERSS had the best sensitivity. Further studies are required to validate the PTA as a screening metric for ectasia.

[Bandage lamellar-optical keratoplasty for post-excimer laser keratectasia]

INTRODUCTION

According to various sources, occurrence rate of keratectasia (KE) after Laser in situ Keratomileusis (LASIK) ranges from 0.04 to 0.2%. No known technique for keratorefractive surgery eliminates the probability. Neither corneal cross-linking, nor implantation of polymeric segments can completely prevent its development.

PURPOSE

To treat KE after LASIK with bandage lamellar-optical keratoplasty (BLOK) surgery and to evaluate the results.

MATERIAL AND METHODS

The study included 22 patients with KE after LASIK divided into two groups. The first group consisted of 6 patients; they underwent BLOK surgery using a segment transplant 1.5 mm in width and 180-220 µm in thickness. The second group included 16 patients who underwent BLOK surgery using 2.75 mm wide, 290-350 µm thick allogeneic transplant of individual length. The follow-up lasted 4 years.

RESULTS

In the first group, uncorrected visual acuity (UCVA) improved by 0.4±007, in the second group - by 0.46±0.15. After two years, two patients had their transplant exchanged for a wider one due to ectasia progression. Corneal refraction was stable at 45.36±1.47 Diopters in all other patients of the first group. In the second group, it was consistently between 40.6 and 45.7 Diopters. The main complication of the BLOK surgery was displacement of the edge of the corneal flap formed during LASIK - occurred in 4 patients.

CONCLUSION

Bandage lamellar-optical keratoplasty proved effective in treating patients with KE after LASIK, leading to improvement of visual acuity, strengthening of the cornea and normalization of its surface; it slows further progression of ectasia.

Corneal refractive surgery combined with simultaneous corneal cross-linking: Indications, protocols and clinical outcomes-A review

Corneal refractive surgery is one of the most common approaches for correction of refractive errors. Combined corneal refractive surgery and corneal cross-linking (CXL) has been proposed as a method to achieve better refractive stability and to prevent iatrogenic corneal ectasia. However, there are concerns regarding its indications, surgical safety, standardization of protocols and long-term effect on corneal tissue. This review article aims to discuss the current knowledge and recent updates on combination of CXL and refractive surgery.

Long term efficacy and stability of corneal collagen cross linking for post-LASIK ectasia: an average of 80mo follow-up

This study was designed to evaluate efficacy and stability of corneal collagen crosslinking (CXL) in halting the progression of post-laser in situ keratomileusis (LASIK) ectasia and provide long-term follow-up results with an average of 80mo. Patients with post-LASIK ectasia were treated with CXL between December 2007 and January 2012. Main outcome measures were uncorrected distance visual acuities (UDVA) and corrected distance visual acuities (CDVA), minimum and maximum keratometry (K) values, spherical and cylindrical refraction, and corneal thickness. The study evaluated 17 eyes for 13 patients (8 men, 5 women) with mean age of 31y (range 23 to 39) and mean follow-up of 80.7±15 (range 57 to 102)mo. UDVA and CDVA improved from logMAR 0.53±0.36 (20/63) to 0.49±0.4 (20/50) (P=0.43) and from 0.18±0.17 (20/28) to 0.16±0.16 (20/27) (P=0.55) respectively. In 15 eyes UDVA and in 13 eyes CDVA either remained stable or improved ≥1 Snellen lines (88.2%) and (76.5%) respectively. Although statistically insignificant, spherical and cylindrical refraction decreased post-CXL from -1.26±2.87 to -0.38±2.32 diopters (D) (P=0.054) and from -3.80±2.47 to -3.04±2.18 D (P=0.13) respectively. Kmax significantly decreased from 44.23±3.76 to 42.85±3.08 D (P=0.013) and Kmin decreased from 41.07±3.61 to 40.00±2.65 D (P=0.057). Corneal thickness decreased from 470±42 to 460±41 µm, but was statistically non-significant (P=0.063). Therefore, CXL is effective in halting and partially reversing the progression of post-LASIK ectasia on the long-term (mean follow-up of more than 80mo), thus highlighting the stability and maintained effect of CXL for such cases.

Post-LASIK Ectasia: Twenty Years of a Conundrum

Corneal ectasia has emerged as a serious complication of laser vision correction (LVC) procedures since the first report by Seiler in 1998. Thereby, its prevention has become a major concern for refractive surgeons. Ectasia occurs due to biomechanical decompensation of the stroma, which may be related to a severe impact on corneal structure (i.e., attempted treatment for high myopia) or the altered biomechanical properties preoperatively. The current understanding is that a combination from those factors determines stability or ectasia progression after LVC. Abnormal corneal topography has been the most important surrogate for lower biomechanical properties, but novel imaging technologies such as tomography and biomechanical assessment have proven to enhance the ability for detecting mild ectatic disease, such as in the eyes with normal topography from patients with clinical ectasia in the fellow eye. Bohac and associates in a retrospective case series analyzed data from 30,167 eyes from 16,732 documented ten eyes (0.033%) of seven patients that developed post-LASIK ectasia. This data supports the concept that the actual incidence of ectasia has decreased from 0.66% reported by Pallikaris in 2001. This has been the result of major development related to the advanced screening strategies. Nevertheless, mysterious cases of ectasia still challenge the field and stimulated research in this field. Ocular allergy and eye rubbing may be a factor that triggered ectasia in such series. Artificial intelligence (AI) and machine-learning algorithms may play a definitive role for further enhancing ectasia risk assessment. Reporting ectasia after LVC is needed.

Central corneal thickness measurement using ultrasonic pachymeter, optical coherence tomography, and TMS-5 topographer

AIM:

This study aimed to compare the central corneal thickness (CCT) measurements using Optical Coherence Tomography (OCT) and TMS-5 topographer with that taken with the gold standard digital Ultrasonic pachymeter (USP).

MATERIALS AND METHODS:

A total of 61 subjects (122 eyes) were prospectively and consecutively studied in a period from June 2016 to June 2017 at Sudan Eye Centre (SEC), Khartoum, Sudan. Besides the visual and refractive data, measurements of CCT were taken using OCT, TMS-5 and USP. Data analyzed using SPSS software for windows (IBM SPSS 20, IBM Corp., Armonk, NY).

RESULTS:

A statistically significant differences in mean CCT was detected between the three instruments (P < 0.001). USP was found to measure the CCT 29μm thicker than OCT and 22μm thicker than TMS-5 topographer. A significant difference was also found between OCT and TMS-5. OCT found to give the lower values of CCT compared to both USP and TMS-5 topographer. Further analysis showed that the three procedures were significantly and strongly correlated to each other (USP vs OCT, r = 0.77), (USP vs TMS-5, r = 0.78) and (OCT vs TMS-5, r = 0.80).

CONCLUSION:

Mean central corneal thicknesses (CCT) were comparable among OCT, TMS-5 topographer and the gold standard USP. However, there is a reproducible systematic difference between CCT measurements taken with the three devices. It is important to note in clinical practice, that measurements acquired by these three modalities are not directly interchangeable.

Incidence and Clinical Characteristics of Post LASIK Ectasia: A Review of over 30,000 LASIK Cases

PURPOSE

To report the incidence of postoperative ectasia after laser in situ keratomileusis (LASIK).

METHODS

A retrospective case review of 30,167 eyes (16,732 patients) was conducted following LASIK between August 2007 and August 2015. The follow-up was between 2 and 8 years. Tomography was performed after 2 years postop. After identifying cases of ectasia, the charts of these patients were examined to identify any common factors that may have predisposed them to develop ectasia.

RESULTS

Ten eyes of seven patients developed post-LASIK ectasia. Eight eyes had been treated for myopia and myopic astigmatism, two eyes for mixed astigmatism. There were no cases of ectasia after LASIK for hyperopia. All 10 cases of ectasia had a flap that was created using the Moria M2 mechanical microkeratome (average flap thickness 118.15 ± 12.88 µm) and refractive error corrected using the Wavelight Allegretto excimer laser. Retrospectively, most prevalent risk factors were thin cornea (≤ 500 µm, 50% of cases), anterior topographic map irregularities (e.g., asymmetric bow tie, 40% of cases), Ectasia Risk Score > 3 (40% of cases), percent tissue thickness alteration ≥ 40% (20% of cases) and low residual stromal bed (≤ 300 µm, 30% of cases). One eye had no identifiable risk factors. In the retrospective chart review 14.97% (4,506) of all the eyes had similar risk factors to the cases that went on to develop ectasia.

CONCLUSION

The incidence of ectasia was 0.033% over 8 years. The incidence could be higher as some cases may destabilize beyond this period and some patients were lost to follow-up asymptomatic of any clinical signs. Other intrinsic factors may trigger the development of post LASIK ectasia. The current widely accepted risk factors are not sufficiently rigorous for screening out potential ectasia from developing after LASIK. There is a need to augment accuracy with higher sensitivity and specificity.

Induction of Controlled Wound Healing with PMMA Segments in the Deep Stroma in Corneas of Hens

Purpose

Polymethylmethacrylate (PMMA) segments are normally used in additive surgery to treat both corneal ectasia post laser-assisted in situ keratomileusis and keratoconus. The aim of this work was to develop an experimental animal model to induce wound healing in the deep stroma in corneas of hens.

Methods

PMMA segments were implanted in the right eyes of 40 adult hens without suture in the wound incision. Animals were randomized for 5 time points to histopathology study (1, 3, 15, 30, and 90 days) being clinically evaluated during the experiment.

Results

Thirty-four eyes (85%) had a successful clinical outcome and intraoperative mistakes occurred in 6 eyes (15%), including anterior chamber perforation resulting in abscess (1), excess of lamellar dissection with segment migration (3), and peripheral incisions evolving with neovascularization (2). At 24 hours, all the epithelial injuries were completed in integrity, but a persistent stromal incision, with a fish mouth form, was observed until day 15. Corneal edema disappeared at the fifth day. Haze, keratocyte cell death, keratocyte proliferation, myofibroblast differentiation, and new matrix production were observed in length around the segment.

Conclusions

Wound healing was induced in the deep corneal stroma by means of PMMA segment implantation in a new animal model developed in hens.

Penetrating Keratoplasty for Corneal Ectasia after Laser in Situ Keratomileusis

Purpose

To improve the visual acuity of patients with progressive keratectasia following laser in situ keratomileusis (LASIK).

Methods

Five eyes of four patients underwent penetrating keratoplasty for ectasia after LASIK. In one patient the second eye was operated on 10 months after the first keratoplasty. The pre- and postoperative refraction, best spectacle-corrected visual acuity, and topographic data were evaluated.

Results

The preoperative refraction was −20.0 diopters (D) with high cylindrical values in all eyes at the time of surgery. After penetrating keratoplasty, mean spherical equivalent was −13.08±3.62 (SD) and mean refractive cylinder was −3.87±1.12 (SD). In one eye Urrets-Zavalia syndrome was noted as an early postoperative complication. In the second operated eye of another patient, there had been graft rejection several times. In this patient, frequent steroid use led to secondary glaucoma and he required filtering surgery.

Conclusions

Penetrating keratoplasty is effective and successful in treating iatrogenic keratectasia after LASIK, but these patients need a close and lifelong follow-up to treat late-term complications such as graft rejection and secondary glaucoma.

Corneal Ectasia After LASIK Combined With Prophylactic Corneal Cross-linking

PURPOSE

To report a case of unilateral corneal ectasia following LASIK surgery combined with prophylactic corneal cross-linking (CXL) in a young patient.

METHODS

Case report.

RESULTS

Preoperative topography was unremarkable in both eyes with a minimum corneal thickness of 554 μm in the right eye and 546 μm in the left eye. Preoperative corrected distance visual acuity (CDVA) was 1.0 (20/20 Snellen) in both eyes with a refraction of +1.25 -2.75 × 10 in the right eye and +0.50 -2.00 × 163 in the left eye. LASIK combined with CXL was uneventful. After 12 months, postoperative topography was unremarkable with an uncorrected distance visual acuity (UDVA) of 1.0 in both eyes. Two years after surgery, the patient presented with a loss of vision (UDVA 0.25) and an inferior steepening on topography in the left eye. Standard CXL was performed to arrest further progression.

CONCLUSIONS

This report illustrates that the currently used prophylactic CXL protocol in combination with LASIK may not be effectively preventing corneal ectasia in every case. [J Refract Surg. 2017;33(1):50-52.].

In vivo confocal microscopy and tear cytokine analysis in post-LASIK ectasia

AIM

Corneal keratectasia is one of the complications associated with laser in situ keratomileusis (LASIK) that results in vision impairment. The pathogenesis of post-LASIK ectasia (PLE) remains underexplored. We report the tear cytokine profile and in vivo confocal microscopy (IVCM) findings in eyes with PLE.

METHODS

This retrospective study included age-matched 7 (14 eyes) post-LASIK controls (PLCs) and 6 (12 eyes) PLE subjects. Corneal topography was used to categorise the subjects into PLC and PLE groups. Ocular Surface Disease Index (OSDI) scores obtained were based on standard questionnaire and IVCM images were used to determine corneal dendritic cells density (DCD) and sub-basal nerve plexus morphology. Inflammatory cytokines/chemokines in the tears were quantified using flow cytometry based cytometric bead array.

RESULTS

Pentacam-based scores, OSDI scores and corneal DCD were significantly (p<0.05) higher in patients with PLE compared with PLC. Discomfort-related subscale of OSDI score exhibited a positive correlation with total corneal DCD in the PLE cohort. The fold difference of chemokine (C-C motif) ligand/monocyte chemotactic protein-1 (CCL2/MCP1) (3.4±0.6) was found to be significantly (p<0.05) higher in the PLE cohorts and a positive correlation between CCL2/MCP1 levels and total corneal DCD was also observed in the PLE cohort.

CONCLUSION

The current study found a significant difference in the tear film cytokine profile between normal and PLE eyes. Presence of increased corneal dendritic cells and altered tear cytokines suggests an ongoing inflammatory response in PLE.

A review and meta-analysis of corneal cross-linking for post-laser vision correction ectasia

PURPOSE

The aim of this study was to review the safety and stability of cornea cross-linking (CXL) for the treatment of keratectasia after Excimer Laser Refractive Surgery.

METHODS

Eligible studies were identified by systematically searching PubMed, Embase, Web of Science and reference lists. Meta-analysis was performed using Stata 12.1 software. The primary outcome parameters included the changes of corrected distant visual acuity (CDVA), uncorrected visual acuity (UCVA), the maximum keratometry value (Kmax) and minimum keratometry value (Kmin), the surface regularity index (SRI), the surface asymmetry index (SAI), the keratoconus prediction index (KPI), corneal thickness, and endothelial cell count. Efficacy estimates were evaluated by weighted mean difference (WMD) and 95% confidence interval (CI) for absolute changes of the interested outcomes.

RESULTS

Seven studies involving 118 patients treated with CXL for progressive ectasia after laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK) (140 eyes; the follow-up time range from 12 to 62 months) were included in the meta-analysis. The pooled results showed that there were no significant differences in Kmax and Kmin values after CXL (WMD = 0.584; 95% CI: -0.289 to 1.458; P = 0.19; WMD = 0.466; 95% CI: -0.625 to 1.556; P = 0.403, respectively). The CDVA improved significantly after CXL (WMD = 0.045; 95% CI: 0.010 to 0.079; P = 0.011), whereas UCVA did not differ statistically (WMD = 0.011; 95% CI: -0.055 to 0.077; P = 0.746). The changes were not statistically significant in SRI, SAI, and KPI (WMD = 0.116; 95% CI: -0.090 to 0.322; P = 0.269; WMD = 0.240; 95% CI: -0.200 to 0.681; P = 0.285; WMD = 0.045; 95% CI: -0.001 to 0.090; P = 0.056, respectively). Endothelial cell count and corneal thickness did not deteriorate (WMD = 12.634; 95% CI: -29.460 to 54.729; P = 0.556; WMD = 0.657; 95% CI: -9.402 to 10.717; P = 0.898, respectively).

CONCLUSION

The study showed that CXL is a promising treatment to stabilize the keratectasia after Excimer Laser Refractive Surgery. Further long-term follow-up studies are necessary to assess the persistence of the effect of the CXL.

Photorefractive Keratectomy for Residual Myopia after Myopic Laser In Situ Keratomileusis

Purpose. To evaluate the safety, efficacy, and predictability of photorefractive keratectomy (PRK) on the corneal flap for correction of residual myopia following myopic laser in situ keratomileusis (LASIK). Patients and Methods. A retrospective study on eyes retreated by PRK on the corneal flap for residual myopia after LASIK. All eyes had no enough stroma after LASIK sufficient for LASIK enhancement. Data included spherical equivalent (SE), uncorrected and best corrected visual acuity (UCVA and BCVA), central pachymetry, corneal higher order aberrations (HOAs), corneal hysteresis (CH), corneal resistance factor (CRF), and corneal haze. Results. The study included 64 eyes. Before PRK, the mean central pachymetry was 400.21 ± 7.8 μm, the mean SE was -1.74 ± 0.51 D, and the mean UCVA and BCVA were 0.35 ± 0.18 and 0.91 ± 0.07, respectively. 12 months postoperatively, the mean central corneal thickness was 382.41 ± 2.61 μm, the mean SE was -0.18 ± 0.32 D (P < 0.01), and the mean UCVA and BCVA were 0.78 ± 0.14 (P = 0.01) and 0.92 ± 0.13 (P > 0.5), respectively. The safety index was 1.01 and the efficacy index was 0.86. No significant change was observed in corneal HOAs. Conclusions. Residual myopia less than 3 D after LASIK could be safely and effectively treated by PRK and mitomycin C with a high predictability. This prevents postoperative ectasia and avoids the flap related complications but has no significant effect on HOAs.

Long-term clinical results of posterior chamber phakic intraocular lens implantation to correct myopia

BACKGROUND

The aim of this study was to determine whether implantable collamer lens (ICL) implantation to correct myopia is an effective and safe surgical option even after long-term follow up.

DESIGN

A retrospective observational study was carried out.

PARTICIPANTS

A total of 281 eyes of 145 myopic patients were included in the study.

METHODS

Patients underwent ICL implantation and had the follow-up period of at least 5 years (87 ± 18.9 months).

MAIN OUTCOME MEASURES

Outcome measures included uncorrected and corrected distance visual acuities, refraction for the evaluation of efficacy, safety, stability and predictability, ICL vault and adverse events.

RESULTS

The final mean logMAR uncorrected and corrected distance visual acuities were 0.02 ± 0.19 and -0.12 ± 0.13, respectively. The mean efficacy and safety indices were 1.04 ± 0.32 and 1.20 ± 0.26. The mean spherical equivalent decreased from -8.74 ± 2.27 diopter (D) to -0.58 ± 0.72 D, and there was high predictability with 69.8% and 87.2% having a postoperative refraction within 0.5 D and 1.0 D, respectively. The mean postoperative vault was changed from 2.53 ± 0.6 to 2.00 ± 0.7. Six (2.1%) eyes developed cataract, and the mean endothelial cell loss was 7.8 ± 8.3%. Increased intraocular pressure was found in two (0.7%) eyes that required the exchange of lenses with different sizes.

CONCLUSIONS

Implantable collamer lens implantation to correct myopia was an effective and safe surgery with high predictability and stability during long-term follow up. Slight myopic shift and cataract formation related with change in vault should be further evaluated.

Corneal Deformation Response with Dynamic Ultra-high-speed Scheimpflug Imaging for Detecting Ectatic Corneas

Purpose

To test the ability of metrics derived from corneal response to noncontact tonometry (NCT) to distinguish between normal and ectatic cases.

Materials and methods

The prototype of CorVis ST (Oculus, Wetzlar, Germany) was used for assessing corneal biomechanical response using ultra-high-speed 8 mm horizontal Scheimpflug photography, taking 4,330 frames per second during NCT. Patients were stratified based on clinical data, including rotating Scheimpflug corneal tomography (Oculus Pentacam HR). Biomechanical data from one eye randomly selected of 177 patients with normal corneas (N) and from 79 patients with bilateral keratoconus (KC) were investigated. Group forme fruste keratoconus (FFKC) was composed of 20 eyes with normal topographic patterns from cases with ectasia detected in the fellow eye. Group keratoconus suspect (KCS) had 16 eyes from 16 patients with topographic patterns suspicious of KC but documented stability over 3 years and normal tomographic findings. A combination of deformation parameters using linear regression analysis (Prototype Factor 1, pF1) was created by the BrAIn (Brazilian Artificial Intelligence on Corneal Tomography and Biomechanics) study group in order to provide the best possible separation of KC and normals.

Results

Statistical significant differences were found for N × KC for several parameters, including first and second applanation times, deformation amplitude, and maximal concavity radius (Mann–Whitney, p < 0.001). However, the areas under the receiver operating characteristic curves (AUC) were lower than 0.90. The pF1 had AUC of 0.945 (IC 0.909–0.97; sensitivity = 87.3% and specificity = 89.3%). The pF1 had statistically significant differences between the ectatic (KC and FFKC) and nonectatic groups (N and KCS) (p < 0.05, Kruskall–Wallis Test with post hoc Dunn's test).

Conclusion

Corneal deformation response analysis by ultra- high-speed 8 mm horizontal Scheimpflug photography provides relevant data for distinguishing ectatic and nonectatic corneas but cannot be used independently to detect KC. This data may be integrated with corneal tomography data for enhancing sensitivity and specificity for screening ectasia.

How to cite this article

Salomão MQ, Correia FF, Ramos I, Luz A, Ambrósio R Jr. Corneal Deformation Response with Dynamic Ultra-high-speed Scheimpflug Imaging for Detecting Ectatic Corneas. Int J Kerat Ect Cor Dis 2016;5(1):1-5.

Lamellar changes in the keratoconic cornea

PURPOSE

The purpose of this study was to identify ultrastructural changes associated with ectasia and to determine the association between lamellar count and corneal thinning.

METHODS

Five surgically removed keratoconic corneal buttons and four, non-keratoconic, normal eye bank control corneas were processed for transmission electron microscopy using an established protocol, ensuring minimal tissue distortion. A sequence of overlapping digital images, spanning the full apical cone corneal thickness, was assembled. A seamless digital montage was printed at 5000× magnification. Lamellae were counted in the anterior-posterior orientation, along a linear line, using established criteria for identification of individual lamellae.

RESULTS

The stromal thickness estimated as a 95% confidence interval for the mean, CI (0.95), in the keratoconic corneas was 372 ± 62 μm, while in the normal cornea, it was 446 ± 89 μm. All keratoconic corneas showed ultrastructural evidence of lamellar splitting and a loss of interweaving anterior lamellae. In the keratoconic corneas, the median total linear stromal lamellar absolute count tangential to the corneal surface was 362, (25th percentile; 75th percentile) = (355; 365) lamellae and in the normal cornea, 246, (25th percentile; 75th percentile) = (239; 251). The linear lamellar density in the keratoconic corneas was estimated as CI (0.95) 117 ± 22 and 86 ±19 lamellae per 100 μm in the anterior and posterior portion of the stroma, respectively. In normal cornea, the linear lamellar density was estimated as CI (0.95) 51 ± 8 and 80 ± 20 lamellae per 100 μm. The mean difference of linear lamellar count between the anterior and the posterior portion of the cornea was estimated as CI (0.95) 31 ± 23 for keratoconic corneas and -29 ± 28 for the normal corneas.

CONCLUSIONS

The current morphometric analysis of ultrastructural changes suggests that ectasia and thinning in keratoconus is associated with lamellar splitting into multiple bundles of collagen fibrils and loss of anterior lamellae. These structural changes, possibly in addition to lateral shifting of lamellae due to the pressure gradient over the cornea, are a potential explanation to the central loss of mass.

Higher Order Aberrations and Visual Outcomes in Wavefront-Optimized Sub-Bowman Keratomileusis: Flap Creation Using Femtosecond Laser Versus Mechanical Microkeratome

PURPOSE

The aim of this study was to compare the outcomes of wavefront-optimized sub-Bowman keratomileusis (SBK) performed using the 150 KHz IntraLase femtosecond (IFS) laser (Abbot Medical Optics) with those using the Moria Evo 3 One Use-Plus SBK mechanical microkeratome (Moria SA).

DESIGN

A prospective comparative clinical trial.

METHODS

Fifty patients had bilateral wavefront-optimized SBK performed for myopia or myopic astigmatism. In 25 patients, the flap was created with the 150 KHz IFS laser (group 1) and in the other 25 with the Moria One Use-Plus SBK mechanical microkeratome (group 2). All other treatment parameters were the same. Results were reported for 1 eye per patient in each group (ie, 25 eyes in each group).

RESULTS

Efficacy, refractive stability, predictability, and safety profiles were comparable between the 2 groups. Although higher order aberrations (HOAs) increased significantly in both groups after laser in situ keratomileusis, intergroup comparison revealed that group 1 was associated with a significantly higher induction of both total HOAs [mean root mean square (RMS), 0.63 ± 0.20 in group 1 vs 0.52 ± 0.14 in group 2; P = 0.031] and spherical aberrations (RMS, 0.37 ± 0.17 in group 1 vs 0.22 ± 0.09 in group 2; P < 0.001) as compared with group 2.

CONCLUSIONS

Flaps created using the Moria Evo 3 One Use-Plus SBK mechanical microkeratome were associated with significantly lower induction of total HOAs and spherical aberrations as compared with 150 KHz IFS flaps at the end of 3 months follow-up.

Clinical Outcomes of Small Incision Lenticule Extraction with Accelerated Cross-Linking (ReLEx SMILE Xtra) in Patients with Thin Corneas and Borderline Topography

Purpose. To study the safety and clinical outcomes of ReLEx SMILE with accelerated cross-linking in individuals with thinner corneas, borderline topography, and higher refractive errors. Methods. Eligible patients first underwent SMILE procedure for correction of myopic refractive error. Following the removal of lenticule, 0.25% riboflavin in saline was injected into the interface and allowed to diffuse for 60 seconds. Finally, eye was exposed to UV-A radiation of 45 mW/cm² for 75 seconds through the cap. Total energy delivered was 3.4 J/cm². Results. 40 eyes of 20 patients with mean age of 26.75 ± 5.99 years were treated. Mean follow-up was 12 months ± 28.12 days. Mean spherical equivalent (SE) was −5.02 ± 2.06 D preoperatively and −0.24 ± 0.18 D postoperatively. The mean central corneal thickness (CCT) and keratometry changed from 501 ± 25.90 µm to 415 ± 42.26 µm and 45.40 ± 1.40 D to 41.2 ± 2.75 D, respectively. Mean uncorrected visual acuity (UCVA) was 20/25 or better in all eyes. No eyes lost lines of corrected distant visual acuity (CDVA). There were no complications like haze, keratitis, ectasia, or regression. Conclusion. Based on the initial clinical outcome it appears that SMILE Xtra may be a safe and feasible modality to prevent corneal ectasia in susceptible individuals.

Cross-linking and intracorneal ring segments--review of the literature

OBJECTIVES

To review and summarize relevant studies on combined use of corneal crosslinking and intracorneal ring segments (ICRS) for the treatment of corneal ectasia.

METHODS

A literature search was performed using the key words "corneal collagen cross-linking" and "intra-corneal ring segments."

RESULTS

Crosslinking is a well-accepted treatment option for corneal ectasia and can be combined with corneal ICRS insertion as needed. The advent of crosslinking has dramatically reduced the number of corneal transplants performed for patients with keratoconus or postrefractive ectasia. Intracorneal ring segments, although flatten the corneal surface, do not prevent the progression of corneal ectasia. This is why the combination of crosslinking and ICRS is potentially synergistic. Previous studies reported that combining these two complementary interventions has been shown to be safe and effective.

CONCLUSIONS

The effects of ICRS are enhanced and stabilized by crosslinking, but the ideal combined technique is not known at present.

A modified risk assessment scoring system for post laser in situ keratomileusis ectasia in topographically normal patients

Purpose:

To evaluate and modify the Randleman Ectasia Risk Score System for predicting post-laser in situ keratomileusis (LASIK) ectasia in patients with normal preoperative corneal topography.

Methods:

In this retrospective study we reviewed data from 136 eyes which had undergone LASIK including 34 ectatic and 102 normal eyes between 1999 and 2009. After determining the sensitivity and specificity of the Randleman system, a modified model was designed to predict the risk of post-LASIK corneal ectasia more accurately. Next, the sensitivity and specificity of this modified scoring system was determined and compared to that of the original scoring system.

Results:

In our sample, the sensitivity and specificity of the Randleman system was 70.1% and 50.5%, respectively. Our modified model included the following parameters: preoperative central corneal thickness, manifest refraction spherical equivalent, and maximum keratometry, as well as the number of months elapsed from surgery. Sensitivity and specificity rates of the modified system were 74.2% and 76.2%, respectively. The difference in receiver operating characteristic curves between the Randleman and modified scoring systems was statistically significant (P<0.001). The best sensitivity and specificity for our model occurred with a cumulative cutoff score of 4.00; a low risk was considered if the score was ≤4.00, and high risk was defined with a score > 4.00.

Conclusion:

Our modified ectasia risk scoring system for patients with normal corneal topography can predict post LASIK ectasia risk with acceptable sensitivity and specificity. However, there are still unidentified risk factors for which further studies are required.

Photorefractive keratectomy results in myopic patients with thin cornea eyes

BACKGROUND

To evaluate the results of visual acuity and quality, and corneal integrity in myopic patients with a thin cornea who received photorefractive keratectomy (PRK).

MATERIALS AND METHODS

In this before-after interventional study, 30 myopic eyes with a myopia -3.76 ± 1.72 (-6.50 to -1.25) D and a corneal thickness of 486.03 ± 11.93 (452-499) μm at the thinnest point received PRK. In myopia was more than 4D, mitomycin C was used with PRK. The surgery was performed with an excimer laser (VISX STAR, Abbott Medical Optics, Abbott Park, US).

RESULTS

The safety and the efficacy index of the surgery was 1.01 ± 0.05 and 1.00 ± 0.05 in these patients, respectively. All the patients were within ±0.5D of emmetropia 1 year after the surgery. Mesopic contrast sensitivity (CS) had a significant increase in two spatial frequencies of six (P = 0.003) and 12 (P = 0.003). Total coma (P < 0.001), spherical aberration (P < 0.001), and total higher-order aberrations (HOA) (P < 0.001) also showed a significant increase. Corneal hysteresis (P < 0.001) and corneal resistance factor (P < 0.001) showed a significant decrease after 1 year.

CONCLUSION

PRK is a safe, effective, and predictable procedure with desirable effects on mesopic CS in patients with corneal thickness <500 μm, which increases HOAs and decreases corneal integrity proportionate to its value before the procedure.

Air-pulse corneal applanation signal curve parameters for characterization of astigmatic corneas

PURPOSE

The aim of this study was to test the 42 parameters of the ocular response analyzer for distinguishing between the biomechanical properties of emmetropic eyes with normal topography and eyes with moderate-to-high with-the-rule astigmatism (WTA) and against-the-rule astigmatism (ATA) that have symmetric bowtie topography.

METHODS

This retrospective case series study included 37 patients (37 studied eyes) with WTA astigmatism and 35 patients (35 studied eyes) with ATA astigmatism. The control group consisted of 70 patients with emmetropia (70 studied eyes) with normal topography. We first tested correlations of the parameters that describe the applanation curve during ocular response analyzer measurements with the maximum keratometry values and the corneal thickness in all 3 groups. We then evaluated the significant parameters among them in search of any group differences in the biomechanical properties of the cornea.

RESULTS

Fifteen parameters correlated with Kmax reading values or corneal thickness values. The correlation coefficients (r) were low. The best correlated parameters were p1area, p2area, h1, dive1, p2area1, h11, h2, and h21. The ATA group had the highest number of parameters (n = 6) with significant differences compared with the control group. Only p2area was predictive for ATA. In contrast, the WTA group had only 1 parameter (p2area1) that was found to be significantly different compared with the control group.

CONCLUSIONS

Some of the new waveform parameters can distinguish between patients with ATA and WTA and normal topography patterns and may delineate the differences in biomechanical properties between these groups that may predict the risk of corneal ectasia after laser in situ keratomileusis.