Corneal ectasia after myopic laser in situ keratomileusis: a long-term study

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.

Tel-Aviv Protocol for Postrefractive Surgery Corneal Ectasia: A Case Series

PURPOSE

The aim of this study was to describe the safety and efficacy of the Tel-Aviv Protocol (epithelial photorefractive keratectomy and corneal cross-linking) as a treatment for postrefractive surgery corneal ectasia.

METHODS

This study includes 8 eyes from 7 patients, each diagnosed with postrefractive surgery ectasia years after refractive surgery and treated with the Tel-Aviv Protocol. The procedure included transepithelial PRK using the EX500 excimer laser, a 50-μm laser ablation of the epithelium and anterior stroma, delivered on the visual axis with cyclotorsion correction, treating up to 50% of refractive astigmatism. After the epithelial photorefractive keratectomy, all patients underwent corneal cross-linking.

RESULTS

The mean keratometry (K) and maximal K both decreased [from 43.37 ± 2.23 to 41.84 ± 2.01 ( P = 0.03) and from 44.95 ± 3.08 to 42.78 ± 2.19 ( P = 0.03), respectively]. Astigmatism was significantly reduced (from 3.53 ± 2.36 to 0.88 ± 0.89 diopter; P = 0.02). Uncorrected visual acuity improved significantly in all patients from a mean of 0.56 ± 0.32 to 0.15 ± 0.14 logMAR ( P = 0.01). Best-corrected visual acuity improved from 0.22 ± 0.24 to 0.06 ± 0.06 logMAR ( P = 0.07; 1-tail P = 0.04). All patients maintained visual acuity during the follow-up period, up to 25 months, mean = 329 days. The Tel-Aviv Protocol was found to be safe [mean safety index: 1.63 ± 1.03 (range: 1.00-4)] and effective [mean efficacy index: 1.29 ± 0.66 (range: 0.71-2.1)].

CONCLUSIONS

The Tel-Aviv Protocol, developed initially for keratoconus treatment, is a safe and promising procedure to stop postrefractive surgery ectasia progression while significantly improving vision, thereby avoiding keratoplasty.

Factors associated with changes in posterior corneal surface following laser-assisted in situ keratomileusis

PURPOSE

To identify factors associated with changes in the posterior corneal curvature following laser-assisted in situ keratomileusis (LASIK).

METHODS

This retrospective study included myopic astigmatic eyes that underwent LASIK between January and December 2013 at Care-Vision Laser Center, Tel-Aviv, Israel. The average posterior keratometry was measured with the Sirius device at a radius of 3 mm from the center. The correlations between the surgically induced change in average posterior keratometry and preoperative parameters such as preoperative sphere, cylinder, spherical equivalent, central corneal thickness (CCT), refraction, Baiocchi Calossi Versaci (BCV) index, ablation depth, percent of tissue altered (PTA), and residual stromal bed (RSB) are reported.

RESULTS

A total of 115 eyes with a mean age of 32.5 ± 8.3 years (range 22-56 years) were included. Central corneal thickness (p < 0.005), preoperative sphere (p < 0.001), spherical equivalent (p < 0.005), and preoperative posterior inferior/superior ratio (p < 0.05) were all significantly correlated with the percentage of change in the mean posterior K. According to ranked stepwise multiple regression analysis, 22% of the variance of change in posterior K could be explained by the examined factors. The factors that remained significant were the percentage of change in posterior inferior/superior ratio, preoperative subjective sphere, and preoperative mean posterior K (for all, p < 0.001).

CONCLUSIONS

The percentage of change in posterior inferior/superior ratio, subjective sphere, and preoperative mean posterior K are all correlated with change in the mean posterior K after LASIK. Understanding of the variables that can influence posterior corneal changes following refractive surgery may play a role in the prevention of iatrogenic keratectasia.

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.

Assessment of the specificity of corvis biomechanical index-laser vision correction (CBI-LVC) in stable corneas after phototherapeutic keratectomy

PURPOSE

The Corvis Biomechanical Index-Laser Vision Correction (CBI-LVC) is a biomechanical index to detect ectasia in post-refractive surgery patients (PRK, LASIK, SMILE). This study aims to evaluate the distribution of the CBI-LVC in stable patients who underwent Phototherapeutic Keratectomy (PTK) compared to PRK patients.

METHODS

Patients who underwent PRK and PTK performed between 2000 and 2018 in Humanitas Research Hospital, Rozzano, Milan, Italy and remained stable for at least four years post-surgery were included. All eyes were examined with the Corvis ST (Oculus, Germany), whose output allows the calculation of the CBI-LVC. The distribution and specificity of the CBI-LVC in the two populations were estimated using a Wilcoxon Mann-Whitney test and compared.

RESULTS

175 eyes of 148 patients were included (85 eyes of 50 PTK patients and 90 eyes of 90 PRK patients). The distribution of CBI-LVC in the two groups showed a minor difference, with a median value in PRK patients of 0.000 (95% CI 0.000; 0.002) and 0.008 (95% CI 0.000; 0.037) in PTK patients (Mann-Whitney U test p = 0.023). The statistical analysis showed that the CBI-LVC provided a specificity of 92.22% in the PRK group, while in the PTK group it was 82.35%. Nevertheless, this difference was not statistically significant (Chi-squared test with Yates, p = 0.080).

CONCLUSION

CBI-LVC provided similar specificity in stable PTK patients compared to those who underwent PRK. These results suggest that the CBI-LVC could be a useful tool to aid corneal surgeons in managing PTK patients.

Outcomes and Complications in Patients With Hypermobile Ehlers-Danlos Syndrome Who Have Undergone Laser In Situ Keratomileusis Surgery

PURPOSE

The purpose of this study was to determine the safety and outcomes of myopic laser in situ keratomileusis (LASIK) in patients who were secondarily diagnosed with hypermobile Ehlers-Danlos syndrome (EDS).

METHODS

We conducted a case series study on patients with hypermobile EDS who underwent myopic LASIK surgery. Visual acuity, manifest refraction, a full dilated eye examination, biometry measurements, and Scheimpflug imaging were performed in the Wilmer outpatient clinic.

RESULTS

There were 24 eyes of 12 patients included in this study. All participants were White women with a mean age of 46.58 years (SD 8.91 years). Participants were seen at an average of 13.83 years (SD 4.3 years, range 6-21 years) after undergoing LASIK. None of the patients in the series had a diagnosis of hypermobile EDS before LASIK surgery. Overall, 92% of patients were happy they got LASIK. The uncorrected distance visual acuity was 20/20 or better in 68% of eyes, and the best-corrected visual acuity was 20/20 or better in 92% of eyes. Manifest refraction was within 1 diopter of plano in 79% of patients. Dry eye symptoms were present in 83% of patients, and 46% of eyes had either punctate epithelial erosions or decreased tear break-up time. One of the 12 patients developed corneal ectasia in both eyes.

CONCLUSIONS

Patients with hypermobile EDS are generally satisfied with myopic LASIK correction, with good visual acuity outcomes and low rates of myopic regression. However, the risk of corneal ectasia may prevent laser vision correction from being a viable treatment option in these patients. Further studies are needed to make a definitive recommendation.

Novel Technique to Improve the Efficacy of Corneal Cross Linking in Cases of Post LASIK Ectasia

Purpose

The aim of the present study was to validate the use of a novel technique that can improve the efficacy of corneal cross-linking (CXL) in cases with post LASIK ectasia.

Methods

This is a retrospective, comparative study that was conducted on patients who sought medical advice at Ain Shams University Hospitals and Maadi Eye Subspeciality Center, Cairo, Egypt. It included two groups of patients with post LASIK ectasia. Group 1 included patients who performed our proposed protocol (topo-guided PRK, followed by customized phototherapeutic keratectomy "PTK" to transmit the laser treatment to the corneal stroma, then CXL). For group 2, accelerated CXL was performed. Subjective refraction and relevant topographic/tomographic parameters (Sirius topographer) compared between the two groups. Recorded follow-ups included the 2 to 3-month follow-up visit and the last visit (mean ± SD of 17.2 months ± 10.2).

Results

Patients of group 1 (22 eyes of 22 patients) experienced significant improvements in most of the evaluated parameters at the 2- to 3-month follow-up visit and showed stability of the ectatic condition at the last follow-up visit, whereas patients of group 2 (10 eyes of 10 patients) showed stability of their ectatic condition at the 2- to 3-month follow-up visit, and one patient developed ectasia progression at the last follow-up visit.

Conclusion

The present study validates the use of our novel protocol in cases having post LASIK ectasia with proven efficacy, safety, and stability, providing regularization for the corneal surface while simultaneously avoiding the unnecessary loss of cross-linking effect within the LASIK flap that no longer shares in the corneal biomechanical strength.

Three-Year Outcomes of Under-flap Stromal Bed CXL for Early Post-LASIK Ectasia

PURPOSE

To investigate the 36-month clinical outcomes of under-flap stromal bed CXL (ufCXL) and report on its ability to stabilize post-laser in situ keratomileusis (LASIK) ectasia.

METHODS

This case series included 20 eyes with diagnosed early post-LASIK ectasia treated with ufCXL. Inclusion criteria were early, mild post-LASIK ectasia, defined as new-onset postoperative manifest refraction cylinder of 1.50 diopters (D) or less, with new topographic inferior steepening consistent with ectasia, uncorrected distance visual acuity of 20/40 or better, and corrected distance visual acuity of 20/25 or better. The existing LASIK flap was lifted, 0.25% isotonic riboflavin was applied directly to the stromal bed, the flap was repositioned, and 18 mW/cm² ultraviolet light was applied for 5 minutes to the corneal flap surface. Post-ufCXL ophthalmic data were compared to pre-ufCXL baseline measurements.

RESULTS

Visual outcomes were maintained pre-ufCXL to 36 months post-ufCXL, with preserved safety index (P = .6545), efficacy index (P = .4980), spherical equivalent accuracy (P = .1536), defocus equivalent accuracy (P = .1032), central corneal thickness (P = .5196), and corneal irregularity indices at 3 mm (P = .8548) and 5 mm (P = .3399). Refractive astigmatism significantly decreased from 0.83 to 0.55 D pre-ufCXL to post-ufCXL (P = .0439), as did maximum keratometry from 42.40 to 42.00 D pre-ufCXL to post-ufCXL (P = .0420). The ufCXL demarcation line depth was 336 ± 21 µm post-ufCXL, with normal endothelial cell density (2,574 ± 203 cells/mm²). Only 1 of 20 eyes showed evidence of progression of 1.00 D in maximum keratometry.

CONCLUSIONS

The ufCXL procedure shows promise in stabilizing early post-LASIK ectasia. Visual function, refractive astigmatism, maximum keratometry, and corneal irregularity indices were statistically maintained at 36 months postoperatively. [J Refract Surg. 2022;38(8):511-519.].

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.

Genetic prescreening of a candidate for laser refractive surgery identifies risk for inadequate tissue response: a case report

Background

Inadequate response to corneal laser refractive surgery, e.g., ectatic corneal diseases, may not be identified by conventional examinations, hence creating therapeutic uncertainty. Herein we demonstrate the application of genetic prescreening to augment preassessment for corneal laser refractive surgery and highlight the ability to prevent the possibility of enrolling a subject at risk for developing ectatic corneal diseases.

Case presentation

Preoperative tests were performed alongside deoxyribonucleic acid (DNA) sequencing of 75 genes specific to the structure and health of the eye of a 44-year-old Caucasian male candidate for corneal laser refractive surgery. The patient had no medical, family, or psychosocial history, nor symptoms that could lead to suspect any corneal abnormalities, and conventional preoperative tests confirmed that no corneal abnormalities were present. The sequencing results uncovered rare DNA variants within the ADGRV1, PTK2, ZNF469, and KRT15 genes. These variants were considered potential risk factors for inadequate response in the patient post corneal laser refractive surgery. Subsequent reevaluation with three different last-generation corneal tomographers identified in the left eye a “warning” for a deformity of the posterior profile of the cornea.

Conclusions

Genetic prescreening identifies potential risk of inadequate response to corneal laser refractive surgery where current technologies in use may lead to a hazardous predictive diagnostic uncertainty.

Long-Term Follow-Up of Accelerated Transepithelial Corneal Crosslinking for Post-LASIK Ectasia: A Pilot Prospective Observational Study

Background: Keratectasia after corneal refractive surgery is a rare but serious postoperative complication, and reports on accelerated transepithelial corneal crosslinking (ATE-CXL)-based treatment of patients with post-laser-assisted in situ keratomileusis (LASIK) ectasia are limited. Therefore, this study evaluated the long-term efficacy and safety of ATE-CXL for progressive post-LASIK ectasia.

Methods: This prospective observational study was conducted at the Eye and ENT Hospital, Fudan University, Shanghai, China, and 25 eyes from 25 patients with post-LASIK ectasia undergoing ATE-CXL were examined. Clinical examinations were conducted preoperatively and postoperatively to assess parameters such as manifest refraction, corrected distance visual acuity (CDVA), endothelial cell density; keratometry, corneal thickness, posterior elevation and topometric indices were measured using Pentacam; sectoral pachymetry and epithelial thickness were evaluated using optical coherence tomography. A paired t-test, Wilcoxon rank-sum test, Kruskal-Wallis test, and repeated measures analysis of variance were used for statistical analysis.

Results: Participants were examined for an average of 46 months. No severe complications occurred during or after ATE-CXL. CDVA improved from 0.25 ± 0.31 preoperatively to 0.15 ± 0.17 postoperatively (p = 0.011). Maximum keratometry decreased from 55.20 ± 8.33 D to 54.40 ± 7.98 D, with no statistical significance (p = 0.074), and the central corneal thickness increased from 414.92 ± 40.96 μm to 420.28 ± 44.78 μm (p = 0.047) at the final follow-up. Posterior elevation, pachymetry, and epithelial thickness remained stable (p > 0.05) throughout the follow-up. No significant differences were noted in topometric indices, except the central keratoconus index, which decreased significantly (p < 0.001) at the final follow-up.

Conclusion: Improvements in CDVA and stabilization in corneal keratometry and posterior elevation after ATE-CXL were noted at the 46-months follow-up, demonstrating that ATE-CXL is a safe and effective treatment for progressive post-LASIK ectasia.

Ectasia After Corneal Refractive Surgery: A Systematic Review

INTRODUCTION

The incidence of ectasia following refractive surgery is unclear. This review sought to determine the worldwide rates of ectasia after photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE) based on reports in the literature.

METHODS

A systematic review was conducted according to modified Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Publications were identified by a search of eight electronic databases for relevant terms between 1984 and 2021. Patient characteristics and preoperative values including manifest refractive spherical refractive equivalent (MRSE), central corneal thickness (CCT), anterior keratometry, postoperative residual stromal bed (RSB), and percent tissue altered (PTA) were summarized. In addition, annual rates of each refractive surgery were determined, and incidence of post-refractive ectasia for each type was calculated using the number of ectatic eyes identified in the literature.

RESULTS

In total, 57 eyes (70 eyes including those with preoperative risk factors for ectasia) were identified to have post-PRK ectasia, while 1453 eyes (1681 eyes including risk factors) had post-LASIK ectasia, and 11 eyes (19 eyes including risk factors) had post-SMILE ectasia. Cases of refractive surgery performed annually were estimated as 283,920 for PRK, 1,608,880 for LASIK, and 96,750 for SMILE. Reported post-refractive ectasia in eyes without preoperative identifiable risk factors occurred with the following incidences: 20 per 100,000 eyes in PRK, 90 per 100,000 eyes in LASIK, and 11 per 100,000 eyes in SMILE. The rate of ectasia in LASIK was found to be 4.5 times higher than that of PRK.

CONCLUSION

Post-refractive ectasia occurs at lower rates in eyes undergoing PRK than LASIK. Although SMILE appears to have the lowest rate of ectasia, the number of cases already reported since its recent approval suggests that post-SMILE ectasia may become a concern. Considering that keratoconus is a spectrum of disease, pre-existing keratoconus may play a larger role in postoperative ectasia than previously accounted for in the literature.

Pain Control Following Photorefractive Keratectomy: A Prospective Clinical Trial Comparing Codeine Versus Oxycodone for the Management of Postoperative Pain

PURPOSE

To compare the efficacy of oral codeine plus acetaminophen versus oxycodone plus acetaminophen for severe pain control following photorefractive keratectomy (PRK).

METHODS

This single-center trial randomized 200 patients to receive codeine 30 mg/acetaminophen 325 mg (codeine group) or oxycodone 5 mg/acetaminophen 325 mg (oxycodone group)every 4 hours as needed for severe pain for 4 days following PRK. Patients recorded postoperative pain, tablet consumption, and tetracaine use. Patients were monitored at postoperative 1 day, 1 week, and 1, 3, and 6 months for visual acuity and follow-up. Study outcomes were mean postoperative pain, treatment and tetracaine use, and visual acuity.

RESULTS

Analysis of 197 patients who completed the trial (97 codeine group and 100 oxycodone group) showed mean pain scores were lower in the codeine group throughout the intervention period. Mean pain scores were higher in the oxycodone group than the codeine group on postoperative days 2 and 4 (P = .017 and P = .034, respectively). The oxycodone group consumed more tablets than the codeine group, with a difference on postoperative day 2 (P = .019), and used a greater number of tetracaine drops (P = .015). Repeated measures analysis of variance showed significant improvement in visual acuity in both groups with no difference in visual outcomes (P = .81).

CONCLUSIONS

Codeine/acetaminophen is as effective and safe as oxycodone/acetaminophen for pain control following PRK, with no clinical difference in overall pain control and long-term visual outcomes. This implies that treating postoperative pain after PRK with a Schedule III opioid (codeine) is effective and potentially decreases the risk of misuse by a higher regulated Schedule II opioid (oxycodone), lowering the potential for abuse and dependence. [J Refract Surg. 2021;37(9):582-589.].

Factors associated with changes in posterior corneal surface following photorefractive keratectomy

PURPOSE

To identify factors associated with changes in the posterior cornea curvature following laser refractive surgery.

MATERIALS AND METHODS

This retrospective study included myopic astigmatic eyes that underwent PRK between January 2013 and December 2013 at Care-Vision Laser Centers, Tel-Aviv, Israel. The average posterior K was measured with the Sirius device at a radius of 3 mm from the center. The correlations between the surgical induced change in average posterior k and preoperative parameters such as central corneal thickness (CCT), refraction, Baiocchi Calossi Versaci index (BCV), ablation depth, percent tissue altered (PTA), and residual stroma bed (RSB) were analyzed.

RESULTS

A total of 280 eyes with a mean age of 24.9 ± 6.1 years (range, 18-47 years were included in this study. The mean PTA was 14.8 ± 6.0%. A greater change in posterior K was found in females (p = 0.01), smaller treatment zones of 6.0 mm (p = 0.02) and PTA > 20% (p < 0.001). A lower CCT (r =  - 0.24, p < 0.001), higher myopia (r =  - 0.34, p < 0.001), higher astigmatism (r =  - 0.17, p < 0.001), higher total BCV (r = 0.13, p = 0.03), lower back BCV (r =  - 0.12, p = 0.05), higher front BCV (r = 0.16, p = 0.01), higher posterior I-S ratio (r = 0.16, p = 0.01), and a lower RSB (r =  - 0.42, p < 0.001) were all significantly correlated with percentage of change in mean posterior K. In ranked stepwise multiple regression analysis, 26.2% of the variance of change in posterior K could be explained by the examined factors. The factors that remained significant were PTA (p < 0.001), CCT (p = 0.001), and posterior I-S ratio (p = 0.001). PTA alone accounted for 15% of the variance in posterior K changes in multivariate analysis.

CONCLUSIONS

Understanding of factors affecting a change in posterior cornea after refractive surgery may have an important practical value for the prevention of iatrogenic keratectasia. Preoperative CCT, posterior I-S ratio, and PTA were significantly associated with changes in posterior K after PRK. PTA was the strongest predictor of posterior corneal changes (p < 0.001).

Corneal Biomechanical Assessment with Ultra-High-Speed Scheimpflug Imaging During Non-Contact Tonometry: A Prospective Review

BACKGROUND

In recent years, increasing interest has arisen in the application of data from corneal biomechanics in many areas of ophthalmology, particularly to assist in the detection of early corneal ectasia or ectasia susceptibility, to predict corneal response to surgical or therapeutic interventions and in glaucoma management. Technology has evolved and, recently, the Scheimpflug principle was associated with a non-contact air-puff tonometer, allowing a thorough analysis of corneal biomechanics and a biomechanically corrected intraocular pressure assessment, opening up new perspectives both in ophthalmology and in other medical areas. Data from corneal biomechanics assessment are being integrated in artificial intelligence models in order to increase its value in clinical practice.

OBJECTIVE

To review the state of the art in the field of corneal biomechanics assessment with special emphasis to the technology based on ultra-high-speed Scheimpflug imaging during non-contact tonometry.

SUMMARY

A meticulous literature review was performed until the present day. We used 136 published manuscripts as our references. Both information from healthy individuals and descriptions of possible associations with systemic diseases are described. Additionally, it exposed information regarding several fields of ocular pathology, from cornea and ocular surface through areas of refractive surgery and glaucoma until vascular and structural diseases of the chorioretinal unit.

The Role of Corneal Biomechanics in the Assessment of Ectasia Susceptibility Before Laser Vision Correction

Purpose

To describe the tomographic and corneal biomechanical status of a sample of eyes excluded from LVC and to present the differences in biomechanical behavior in relation to cutoffs of clinical- and tomography-based screening methods used in clinical practice.

Patients and Methods

Observational cross-sectional study including 61 eyes from 32 consecutive patients who were excluded from LVC in our department. Clinical and demographic data were collected from the patients’ clinical records. Tomographic data was assessed with a Scheimpflug camera (Pentacam, OCULUS^®). Ablation depth (µm) and residual stromal bed (µm) were calculated by the WaveLight^® EX500 laser system software (Alcon, EUA). The corneal biomechanical assessment was made through ultra-high speed Scheimpflug imaging during noncontact tonometry (Corvis ST, OCULUS^®). Several ectasia risk scores were analyzed.

Results

Mean age was 31.0±6 years old and mean manifest spherical equivalent was −2.01 ± 2.3D. Belin–Ambrósio deviation index was the tomographic parameter with higher proportion of eyes within the ectasia high risk interval. In the biomechanical assessment, more than 95% of eyes met the criteria for ectasia susceptibility in four of the first generation and in two of the second generation parameters. In a cutoff based comparative analysis, eyes with Kmax ≥45.5 D, eyes with VCOMA <0 and eyes with ARTmax ≤350 presented significantly softer corneal biomechanical behavior.

Conclusion

The majority of eyes excluded from LVC in the present study met the criteria for ectasia susceptibility in several biomechanical parameters, validating the clinical and tomographic based screening prior to LVC in our center. Differences found in the biomechanical assessment regarding cutoffs used in clinical practice highlight its differential role in characterizing risk profile of these patients. Tomography should not be overlooked and the integration of all data, including treatment-related parameters, can be the future of risk ectasia screening prior LVC.

Compression Sutures to Treat Acute Hydrops in a Case of Bilateral Post-Laser In Situ Keratomileusis Ectasia

ABSTRACT

This a case report of acute hydrops with interface fluid syndrome in a patient with post-laser in situ keratomileusis (LASIK) ectasia treated with compression sutures. A patient with post-LASIK ectasia presented with acute hydrops and fluid accumulation in the LASIK flap-stromal interface sequentially in both eyes. Full thickness compression sutures were applied to appose the edges of the Descemet tear, and this resulted in a rapid resolution of stromal edema and interface fluid. The patient had best distance visual acuities of 20/40 and 20/60 at the last follow-up in the right and left eyes, respectively. Hydrops along with fluid in the interface needed early intervention to prevent complications such as epithelial ingrowth and interface haze. Compression sutures were useful in this case to help bridge the gap between the margins of Descemet tear, hastening the resolution of stromal edema and interface fluid.

Refractive surgery with simultaneous collagen cross-linking for borderline corneas - A review of different techniques, their protocols and clinical outcomes

Simultaneous corneal cross-linking (CXL) has been proposed as an adjunct therapy to corneal refractive procedures to prevent future ectasia, especially when performed in borderline corneas. This review analyses the currently available literature (minimum follow-up 6 months) on corneal refractive surgery and simultaneous CXL (PRK Xtra, LASIK Xtra, and SMILE Xtra) to evaluate the overall results including the safety, efficacy, and potential complications associated with these procedures. A comprehensive literature search of various electronic databases (PubMed, PubMed Central, Cochrane database, and MEDLINE) was performed up to 20^th May 2020. Four relevant studies were found for PRK Xtra, 12 for LASIK Xtra, and 3 for SMILE Xtra. The total number of eyes included in this review was 1,512: 294 for PRK Xtra, 221 for PRK-only, 446 eyes for LASIK Xtra, 398 eyes for LASIK-only, 91 for SMILE Xtra and 62 for SMILE-only. Current literature suggests that refractive surgery and simultaneous CXL is generally safe and delivers comparable results in terms of visual and refractive outcomes than refractive surgery alone. However, there is no consensus on a standard cross-linking protocol, and complications such as diffuse lamellar keratitis, central toxic keratopathy, and corneal ectasia following Xtra procedures have been reported. It is therefore suggested that surgeons exercise caution in case-selection and counsel their patients regarding the potential risks and benefits with Xtra procedures. Also, further studies are required to standardize the UV-A irradiation protocols and to evaluate the long-term effect on safety, refractive predictability, and stability of these procedures.

Myopic regression and recurrent Salzmann nodule degeneration after laser in situ keratomileusis in Ehlers Danlos Syndrome

PURPOSE

We describe the first case of Ehlers Danlos Syndrome (EDS) reported in the English language ophthalmic literature to have undergone Laser In Situ Keratomileusis (LASIK) surgery.

OBSERVATIONS

We review our patient's specific postoperative complications of myopic regression, Salzmann nodular degeneration, and dry eye syndrome, as well as the risks and consequences of performing LASIK on patients with this collagen disorder.

CONCLUSIONS AND IMPORTANCE

Refractive errors may prompt EDS patients to seek laser vision correction, placing them at increased risk for complications such as myopic regression, keratectasia, and dry eye syndrome. Aberrant wound healing and collagen dysfunction may have influenced our patient's myopic regression and Salzmann nodule degeneration post-LASIK. Currently, EDS is considered a relative contraindication in LASIK due to a presumed higher risk of postoperative keratectasia; however, we believe it is possible that not all forms of EDS need to be an absolute contraindication to LASIK. More research is warranted to determine preoperative risk stratification for laser vision surgery in each subtype of EDS.

Laser in situ keratomileusis (LASİK) in patients with superior steepening on corneal topography: Is it safe and predictable?

BACKGROUND

Attention is usually given to inferior steepening on corneal topography in the evaluation of a patient's suitability for LASIK surgery. The aim of this study is to investigate long-term refractive results with superior steepening.

METHODS

Patients who underwent LASIK surgery between 2015 and 2019 in our refractive surgery department were retrospectively reviewed. The patients with a ≥ 1.0 D superior-inferior (S-I) quadrant difference in the tangential map, using a Scheimpflug camera with a Placido disc topographer (Sirius), were included in the study. Preoperative and postoperative best-corrected and uncorrected visual acuity (Snellen), cylindrical refraction values, and spherical equivalent (SE) values were compared. Adverse events were recorded.

RESULTS

Fifty eyes of 28 patients participated in the study. The mean age of the patients was 27.5 ± 8.0 (19-59). Sixteen patients were female (57.1%), and 12 (42.8%) patients were male. The average follow-up time was 29.8 ± 11.1 months (12-61). Average central corneal thickness was 549.4 ± 26.0 (498-602) μm. Average minimal corneal thickness was 549.1 ± 26.9 (497-598) μm. Preoperative S-I quadrant difference (D) was 1.87 ± 0.7 (1.0-3.99). Posterior elevation (Kvb) was 11.2 ± 1.9 (9-17) μm. The preoperative SE value was - 1.7 ± 2.1 (- 6.25-3.25) and improved to - 0.3 ± 0.44 D (- 1.25-0.75) (p < 0.001). Preoperative cylindrical refraction values were - 2.04 ± 1.7 (- 6.25-0), and postoperative values were - 0.47 ± 0.4 (- 2-0) D (p < 0.001). Uncorrected visual acuity was median 1.0 (0.4-1.0) with 38 eyes (76%) having 20/20 postoperative uncorrected visual acuity. No sight threatening complications or ectasia findings were observed during the 2 years postoperative follow-up time.

CONCLUSIONS

Abnormal corneal topographies with (S-I) asymmetry result in predictable results after LASIK.

Management of acute corneal hydrops after laser in situ keratomileusis

A 43-year-old man developed acute corneal hydrops after laser in situ keratomileusis (LASIK). A persistently fluid-filled interface between the corneal flap and stroma (without flap dehiscence or wound leakage) did not respond to the conservative treatment. To avoid keratoplasty, the subflap fluid was drained by an air injection into the anterior chamber; the surgery also included suturing of the corneal flap and stroma. The corrected distance visual acuity improved rapidly after resolution of the fluid-filled interface and corneal stromal edema, and no leakage was observed. Thus, a minimally invasive surgery to drain the subflap fluid by an air injection was effective for treating a persistently fluid-filled interface in a case of acute corneal hydrops after LASIK.

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.

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.

Eighteen-year prospective audit of LASIK outcomes for myopia in 53 731 eyes

BACKGROUND

To assess the outcomes of laser-assisted in situ keratomileusis (LASIK) performed for the treatment of myopia in terms of safety, efficacy and predictability in an 18-year clinical audit.

METHOD

In this single-centre, prospective, non-randomised study, preoperative and postoperative refractions, uncorrected (UCVA), best-corrected Snellen visual acuity (BCVA) and complications of all eyes undergoing myopic LASIK were recorded. Safety, efficacy, refractive predictability, treatment trends, retreatment rates and complication rates were evaluated.

RESULTS

Between 1998 and 2015, 53 731 eyes of 27312 patients underwent myopic LASIK. Patients' median age was 31.6 years (mean, 32.6±7.3 years); there were 9703 males (35.5%). Patients were predominantly ethnic Chinese (87.4%). Mean follow-up time was 78±75.6 days (median, 86 days). Overall efficacy index was 0.91 with >99% of eyes achieving UCVA of ≥20/40 and >70% achieving 20/20 since 2010. 95.43% of eyes had no loss of vision postoperatively and 4.2% and 0.37% lost 1 and ≥2 lines BCVA, respectively. From 2010 the safety index has been >1.05. More than 94.0% of eyes achieved within ±1.0 D of target refraction and at least 70% achieved within ±0.50 D of target from 2010 onwards. Retreatment rate was 2.55% and after retreatment 98.4% of eyes achieved ≥20/40 UCVA and 63.5% achieved ≥20/20 UCVA. The overall complication rate is 0.98%, and since 2010, the annual complication rate has been <0.8%.

CONCLUSIONS

Myopic LASIK performed in Asian eyes is safe and effective with high refractive predictability in a comprehensive LASIK programme with appropriate clinical audit.

Continuous intracorneal ring implantation for treatment of myopic astigmatism

We report a case of myopic astigmatism, not eligible for laser vision correction and with an anterior chamber depth below that recommended for application of phakic implantable collamer lens. In this case, the only refractive surgery option that remained for the patient was intracorneal ring implantation. The aim of the current presentation was to document the clinical and refractive outcomes after continuous intracorneal ring implantation in both eyes in this patient with myopic astigmatism. The results presented were collected during a 4-year follow-up period. Surgery was performed at Lasik specialty center, Baghdad, Iraq, in 2013.

[SMILE (Small Incision Lenticule Extraction) among the corneal refractive surgeries in 2018 (French translation of the article)]

Refractive surgery is a field in constant evolution. In recent years, a new procedure has appeared under the name SMILE (Small Incision Lenticule Extraction). This technique, carried out solely with a femtosecond laser, should make it possible to better preserve corneal innervation and biomechanics. After a detailed review of the technique itself, we then focus on the scientific evidence for the safety and efficacy of SMILE and its current indications. Advantages of SMILE will be discussed in comparison to disadvantages of the conventional techniques, particularly concerning dry eye and the risk of corneal ectasia with LASIK. Lastly, the current limitations of SMILE (indications, retreatment) are discussed, and future applications are considered regarding improvements in the technique.

SMILE (Small Incision Lenticule Extraction) among the corneal refractive surgeries in 2018

Refractive surgery is a field in constant evolution. In recent years, a new procedure has appeared under the name SMILE (SMall Incision Lenticule Extraction). This technique, carried out solely with a femtosecond laser, should make it possible to better preserve corneal innervation and biomechanics. After a detailed review of the technique itself, we then focus on the scientific evidence for the safety and efficacy of SMILE and its current indications. Advantages of SMILE will be discussed in comparison to the conventional techniques, particularly concerning dry eye and the risk of corneal ectasia related to LASIK. Lastly, the current limitations of SMILE (indications, retreatment) are discussed, and future applications are considered regarding new improvements in the technique.

Corneal Biomechanical Properties after FS-LASIK with Residual Bed Thickness Less Than 50% of the Original Corneal Thickness

Background

The changes in corneal biomechanical properties after LASIK remain an unknown but important topic for surgical design and prognostic evaluation. This study aims to observe the postoperative corneal biomechanical properties one month after LASIK with amount of corneal cutting (ACC) greater than 50% of the central corneal thickness (CCT).

Methods

FS-LASIK was performed in 10 left rabbit eyes with ACC being 60% (L60) and 65% (L65) of the CCT, while the right eyes (R) were the control. After 4 weeks, rabbits were executed and corneal strip samples were prepared for uniaxial tensile tests.

Results

At the same strain, the stresses of L65 and L60 were larger than those of R. The elastic moduli of L60 and L65 were larger than those of R when the stress was 0.02 MPa, while they began to be less than those of R when stress exceeds the low-stress region. After 10 s relaxation, the stress of specimens L65, L60, and R increased in turn.

Conclusion

The elastic moduli of the cornea after FS-LASIK with ACC greater than 50% of the CCT do not become less under normal rabbit IOP. The limit stress grows with the rise of ACC when relaxation becomes stable.

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.

Scanning-slit topography in patients with keratoconus

AIM

To evaluate the anterior and posterior corneal surfaces using scanning-slit topography and to determine the diagnostic ability of the measured corneal parameters in keratoconus.

METHODS

Orbscan II measurements were taken in 39 keratoconic corneas previously diagnosed by corneal topography and in 39 healthy eyes. The central minimum, maximum, and astigmatic simulated keratometry (K) and anterior axial power values were determined. Spherical and cylindrical mean power diopters were obtained at the central and at the steepest point of the cornea both on anterior and on posterior mean power maps. Pachymetry evaluations were taken at the center and paracentrally in the 3 mm zone from the center at a location of every 45 degrees. Receiver operating characteristic (ROC) analysis was used to determine the best cut-off values and to evaluate the utility of the measured parameters in identifying patients with keratoconus.

RESULTS

The minimum, maximum and astigmatic simulated K readings were 44.80±3.06 D, 47.17±3.67 D and 2.42±1.84 D respectively in keratoconus patients and these values differed significantly (P<0.0001 for all comparisons) from healthy subjects. For all pachymetry measurements and for anterior and posterior mean power values significant differences were found between the two groups. Moreover, anterior central cylindrical power had the best discrimination ability (area under the ROC curve=0.948).

CONCLUSION

The results suggest that scanning-slit topography and pachymetry are accurate methods both for keratoconus screening and for confirmation of the diagnosis.

Corneal Collagen Cross-Linking Complications

Corneal cross-linking was approved by United States Food and Drug Administration for the treatment of progressive keratoconus in April 2016. As this approach becomes more widely used for the treatment of keratoconus and post-laser in situ keratomileusis (LASIK) ectasia, the medical community is becoming more familiar with potential complications associated with this procedure. This article aims to review the reported complications of collagen cross-linking for the treatment of keratoconus and post-LASIK ectasia.

Risk profiles of ectasia after keratorefractive surgery

PURPOSE OF REVIEW

To identify and evaluate the risk factors of iatrogenic ectasia after refractive surgery.

RECENT FINDINGS

We reviewed recently published papers that identified various risk factors associated with ectasia after LASIK, photorefractive keratectomy, small incision lenticule extraction, and other refractive surgical procedures. We also attempted to evaluate the relative contributions of these factors to the development of ectasia following refractive surgery. Forme fruste keratoconus, genetic predisposition to keratoconus, low residual stromal bed thickness (through high myopia, thin preoperative cornea, or thick LASIK flap), and irregular corneal topography have been identified as risk factors for keratectasia development after refractive surgical procedures. A newly proposed metric, percentage tissue altered, has been reported to be a robust indicator for post LASIK ectasia risk calculation. Several cases of keratectasia have also been reported 6 to 12 months following minimally invasive small incision lenticule extraction procedure. Other risk factors associated with iatrogenic ectasia include eye rubbing, young age, and pregnancy.

SUMMARY

Ectasia after refractive surgery is a relatively rare complication which can lead to sight-threatening complications if not detected and treated in time. It is important to continue our quest to improve our methods of identifying absolute and relative risk factors of ectasia and their cut-off values following various keratorefractive surgical procedures.

Laser-assisted subepithelial keratectomy (LASEK) versus laser-assisted in-situ keratomileusis (LASIK) for correcting myopia

BACKGROUND

Near-sightedness, or myopia, is a condition in which light rays entering the eye along the visual axis focus in front of the retina, resulting in blurred vision. Myopia can be treated with spectacles, contact lenses, or refractive surgery. Options for refractive surgery include laser-assisted subepithelial keratectomy (LASEK) and laser-assisted in-situ keratomileusis (LASIK). Both procedures utilize a laser to shape the corneal tissue (front of the eye) to correct refractive error, and both create flaps before laser treatment of corneal stromal tissue. Whereas the flap in LASEK is more superficial and epithelial, in LASIK it is thicker and also includes some anterior stromal tissue. LASEK is considered a surface ablation procedure, much like its predecessor, photorefractive keratectomy (PRK). LASEK was developed as an alternative to PRK to address the issue of pain associated with epithelial debridement used for PRK. Assessing the relative benefits and risks/side effects of LASEK and LASIK warrants a systematic review.

OBJECTIVES

To assess the effects of LASEK versus LASIK for correcting myopia.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), which contains the Cochrane Eyes and Vision Trials Register (2016, Issue 10); MEDLINE Ovid (1946 to 24 October 2016); Embase.com (1947 to 24 October 2016); PubMed (1948 to 24 October 2016); LILACS (Latin American and Caribbean Health Sciences Literature Database; 1982 to 24 October 2016); the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), last searched 20 June 2014; ClinicalTrials.gov (www.clinicaltrials.gov); searched 24 October 2016; and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en); searched 24 October 2016. We did not use any date or language restrictions in the electronic searches for trials.

SELECTION CRITERIA

We considered only randomized controlled trials (RCTs) for the purposes of this review. Eligible RCTs were those in which myopic participants were assigned randomly to receive either LASEK or LASIK in one or both eyes. We also included paired-eye studies in which investigators randomly selected which of the participant's eyes would receive LASEK or LASIK and assigned the other eye to the other procedure. Participants were men or women between the ages of 18 and 60 years with myopia up to 12 diopters (D) and/or myopic astigmatism of severity up to 3 D, who did not have a history of prior refractive surgery.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened all reports and assessed the risk of bias in trials included in this review. We extracted data and summarized findings using risk ratios (RRs) for dichotomous outcomes and mean differences (MDs) for continuous outcomes. In the absence of clinical and methodological heterogeneity across trials, we used a random-effects model to calculate summary effect estimates. We used a fixed-effect model when including fewer than three trials in a meta-analysis. When clinical, methodological, or statistical heterogeneity was observed across trials, we reported our findings in a narrative synthesis.

MAIN RESULTS

We identified four eligible trials with 538 eyes of 392 participants for the review, but only three trials (154 participants) provided outcome data for analysis. We found no ongoing trials. Two of four trials were from China, one trial was from Turkey, and the location of one trial was not reported. The risk of bias for most domains was unclear due to poor reporting of trial methods; no trial had a protocol or trial registry record. Three trials enrolled participants with mild to moderate myopia (less than -6.50 D); one trial included only participants with severe myopia (more than -6.00 D).The evidence showed uncertainty in whether there is a difference between LASEK and LASIK in uncorrected visual acuity (UCVA) at 12 months, the primary outcome in our review. The RR and 95% confidence interval (CI) at 12 months after surgery was 0.96 (95% CI 0.82 to 1.13) for UCVA of 20/20 or better and 0.90 (95% CI 0.67 to 1.21) for UCVA of 20/40 or better based on data from one trial with 57 eyes (very low-certainty evidence). People receiving LASEK were less likely to achieve a refractive error within 0.5 diopters of the target at 12 months follow-up (RR 0.69, 95% CI 0.48 to 0.99; 57 eyes; very low-certainty evidence). One trial reported mild corneal haze at six months in one eye in the LASEK group and none in the LASIK group (RR 2.11, 95% CI 0.57 to 7.82; 76 eyes; very low-certainty evidence). None of the included trials reported postoperative pain score or loss of visual acuity, spherical equivalent of the refractive error, or quality of life at 12 months.Refractive regression, an adverse event, was reported only in the LASEK group (8 of 37 eyes) compared with none of 39 eyes in the LASIK group in one trial (low-certainty evidence). Other adverse events, such as corneal flap striae and refractive over-correction, were reported only in the LASIK group (5 of 39 eyes) compared with none of 37 eyes in the LASEK group in one trial (low-certainty evidence).

AUTHORS' CONCLUSIONS

Overall, from the available RCTs, there is uncertainty in how LASEK compares with LASIK in achieving better refractive and visual results in mildly to moderately myopic participants. Large, well-designed RCTs would be required to estimate the magnitude of any difference in efficacy or adverse effects between LASEK and LASIK for treating myopia or myopic astigmatism.

Under-flap stromal bed CXL for early post-LASIK ectasia: a novel treatment technique

Purpose

Collagen cross-linking (CXL) for post-laser-assisted in situ keratomileusis (LASIK) ectasia (PLE) is traditionally performed either epi-on or epi-off on the corneal surface. This study describes a novel technique in treating early PLE with under-flap CXL (ufCXL) to the stromal bed and reports on 6-month outcomes.

Patients and methods

Case series of seven patients (eight eyes) with topography-diagnosed early PLE treated with ufCXL. Inclusion criteria were early, mild PLE defined as new-onset postoperative manifest refraction cylinder ≤1.50 D, with new topographic inferior steepening consistent with ectasia, uncorrected distance visual acuity (UDVA) of 20/40 or better, and corrected distance visual acuity (CDVA) of 20/25 or better. Existing LASIK flap was lifted, riboflavin was applied directly to the stromal bed, flap was repositioned, and 18 mW/cm² ultraviolet light was applied for 3 minutes to the corneal surface. Post-ufCXL manifest refraction, UDVA and CDVA, corneal cylinder, K_max, and corneal irregularity index were compared with pre-ufCXL measurements.

Results

Patients had a pre-ufCXL sphere of 0.09±0.48 D and cylinder of −0.78±0.49 D. At 6 months, post-ufCXL sphere (0.06±0.8 D; P=0.89) and cylinder (−1.09±0.76 D, P=0.26) were unchanged. Cumulative post-ufCXL UDVA was unchanged, achieving 20/20, 20/30, and 20/40 in 25%, 88%, and 88%, respectively, compared with 13%, 63%, and 88% pre-ufCXL (P=0.68). Post-ufCXL CDVA was unchanged (P=0.93) with a gain of one line in two eyes, a loss of one line in one eye, and five eyes unchanged. The efficacy index (P=0.76), safety index (P=0.89), K_max (P=0.94), and corneal irregularity index (P=0.73) were also unchanged.

Conclusion

Preliminary results with ufCXL for early PLE are promising, demonstrating maintenance of visual accuracy, efficacy, safety, K_max, and cylinder, with much quicker recovery times than surface CXL.

Effect of femtosecond and microkeratome flaps creation on the cornea biomechanics during laser in situ keratomileusis: one year follow-up

AIM

To compare the corneal biomechanical outcomes at one year after laser in situ keratomileusis (LASIK) with the flaps created by Ziemer and Moria M2 microkeratome with 110 head and -20 blade.

METHODS

Totally 100 eyes of 50 consecutive patients were enrolled in this prospective study and divided into two groups for corneal flaps created by ZiemerFemto LDV and Moria M2 microkeratome with 110 head and -20 blade. Corneal biomechanical properties including cornea resistance factor (CRF) and cornea hysteresis (CH) were measured before and 1, 3, 6, 12mo after surgery by ocular response analyzer. Central cornea thickness and corneal flap thickness were measured by optical coherence tomography.

RESULTS

The ablation depth (P=0.693), residual corneal thickness (P=0.453), and postoperative corneal curvature (P=0.264) were not significant different between Ziemer group and Moria 110-20 group after surgery. The residual stromal bed thickness, corneal flap thickness, CH and CRF at 12mo after surgery were significant different between Ziemer group and Moria 110-20 group (P<0.01);Ziemer group gained better corneal biomechanical results. The CRF and CH increased gradually from 1 to 12mo after surgery in Ziemer group, increased from 1 to 6mo but decreased from 6 to 12mo in Moria 110-20 group. Both CRF and CH at one year after surgery increased with the increasing of residual cornea thickness; pre-LASIK CRF, CRF also increased with residual stromal bed thickness, while CH decreased with the increasing of pre-LASIK intraocular pressure and cornea flap thickness (P<0.01).

CONCLUSION

In one year follow-up, femtosecond laser can provide better cornea flaps with stable cornea biomechanics than mechanical microkeratome.

Corneal stromal demarcation line after collagen cross-linking in corneal ectatic diseases: a review of the literature

Collagen cross-linking (CXL) is a relatively new conservative approach for progressive corneal ectasia, which is able to strengthen corneal tissue reforming new covalent bonds. Subjective and objective results following this method seem to be promising. In recent years, newer CXL protocols have been developed to perform more effective and less invasive procedures. The increasing diffusion of CXL in the corneal ectatic disease has increased the need to have actual indices regarding the efficacy of the treatment. Evaluation of demarcation line (DL), a transition zone between the cross-linked anterior corneal stroma and the untreated posterior corneal stroma, is considered a measurement of the depth of CXL treatment into the stroma. Some evidence in the literature emphasize that DL could be a measure of effectiveness of the CXL. On the contrary, some authors believe that the “the deeper, the better” principle is rather a simplistic approach for interpreting the clinical importance of the corneal stromal DL.

Unilateral corneal ectasia following small-incision lenticule extraction

We describe a case of unilateral corneal ectasia in a 26-year-old man following small-incision lenticule extraction. The preoperative corneal topography was normal, with a minimum corneal thickness of 511 μm and 513 μm in the right eye and left eye, respectively. Lenticules of 85 μm and 82 μm were fashioned to offer a refractive correction of -3.75 -1.50 × 180 and -3.50 -1.50 × 165 in the right eye and left eye, respectively. Twelve months after small-incision lenticule extraction, the patient presented with early signs of ectasia in the left eye on corneal topography, which had worsened at the 18-month examination. Intrastromal corneal ring segment implantation with corneal collagen crosslinking was performed to arrest further progression and to improve uncorrected distance visual acuity. On the last examination, the corrected distance visual acuity was 20/20(-2).

FINANCIAL DISCLOSURE

Dr. Mahipal S. Sachdev receives travel grants from Carl Zeiss Meditec AG. No author has a financial or proprietary interest in any material or method mentioned.

Combined effects of interleukin-1β and cyclic stretching on metalloproteinase expression in corneal fibroblasts in vitro

Background

Corneal tensile strain increases if the cornea becomes thin or if intraocular pressure increases. However, the effects of mechanical stress on extracellular matrix (ECM) remodelling in the corneal repair process and the corneal anomalies are unknown.

Methods

In this study, the combined effects of interleukin-1β (IL-1β) on matrix metalloproteinases (MMPs) in corneal fibroblasts under cyclic stretching were investigated in vitro. Cultured rabbit corneal fibroblasts were subjected to 5, 10 or 15 % cyclic equibiaxial stretching at 0.1 Hz for 36 h in the presence of IL-1β. Conditioned medium was harvested for the analysis of MMP2 and MMP9 protein production using the gelatin zymography and western blot techniques.

Results and conclusions

Cyclic equibiaxial stretching changed the cell morphology by increasing the contractility of F-actin fibres. IL-1β alone induced the expression of MMP9 and increased the production of MMP2, and 5 % stretching alone decreased the production of MMP2, which indicates that a low stretching magnitude can reduce ECM degradation. In the presence of IL-1β, 5 and 10 % stretching increased the production of MMP2, whereas 15 % stretching increased the production of MMP9. These results indicate that MMP expression is enhanced by cyclic mechanical stimulation in the presence of IL-1β, which is expected to contribute to corneal ECM degradation, leading to the development of post-refractive surgery keratectasia.

Long-Term Clinical Outcomes of Myopic Patients Having Thin Residual Corneal Thickness after Excimer Laser Surface Ablation

PURPOSE

To investigate and compare the long-term safety, efficacy, and accuracy of PRK (photorefractive keratectomy) and LASEK (laser epithelial keratomileusis) in myopic corneas having residual corneal thickness less than 400 micron meters (µm).

METHODS

The medical reports of the patients who had undergone excimer laser surface ablation between 2007-2011 and had a residual corneal thickness less than 400 µm were retrospectively reviewed.

RESULTS

Forty-two eyes of 42 patients with a mean age of 28.79±7.76 years were enrolled into the study. Twenty-two PRK and 20 LASEK procedures were performed. The mean follow-up time was 45.00±11.80 months. At the end of follow-up, no ectasia was detected. Nineteen percent of eyes had trace haze. No eyes lost any lines in corrected distance visual acuity. Eighty-one percent of the patients had an uncorrected distance visual acuity better than 20/40. The regression rate was 16.7%. Sixty-two percent of eyes were within ±1.00 D. The safety and efficacy indexes were 1.19±0.42 and 1.00±0.40, respectively. There was not any difference between LASEK and PRK regarding achieved spherical equivalent refraction, haze ratio, visual acuity, safety, efficacy, and regression.

CONCLUSIONS

Both PRK and LASEK are safe and effective in myopic corneas having thin residual thickness.

Unilateral Post-LASIK Ectasia and Contralateral Spontaneous Ectasia

PURPOSE

To report a case of iatrogenic unilateral post-LASIK corneal ectasia with contralateral spontaneous ectatic evolution.

METHODS

Case report with preoperative and postoperative measurements including uncorrected visual acuity, corrected distance visual acuity, refraction, slit-scanning topographic and pachymetric maps, and differential maps.

RESULTS

Six months after unilateral LASIK, the operated eye progressively developed signs of post-LASIK ectasia with increased inferior corneal steepening and corneal thinning and decrease in corrected distance visual acuity. Five years later, the unoperated eye also developed signs of spontaneous ectatic evolution with increased inferior steepening and corneal thinning.

CONCLUSIONS

LASIK accelerates occurrence of ectasia in ectasia-susceptible and biomechanically fragile eyes.

Keratoconus in Inflammatory Bowel Disease Patients: A Cross-sectional Study

BACKGROUND AND AIMS

Increasing evidence suggests that keratoconus may have an inflammatory component. The possible association of keratoconus with inflammatory bowel disease (IBD) has yet to be determined. The aim of this study was to determine the prevalence of keratoconus and suspect keratoconus in patients with IBD.

METHODS

All consecutive adult IBD patients seen in the Department of Gastroenterology, Nancy, University Hospital, France, between March 2014 and June 2014 were included. Pregnant women, rigid lens wearers, patients with a family history of keratoconus and patients with a history of refractive surgery were excluded. A control group of healthy subjects was included. All included patients underwent a corneal topography (OPD-Scan III, Nidek) to detect keratoconus or suspect keratoconus. Rabinowitz videokeratographic indices were the basis of corneal topography interpretation.

RESULTS

Two hundred and one IBD patients were included, 150 with Crohn's disease and 51 with ulcerative colitis. Mean age was 38.7 years and 121 were women. Mean disease duration was 10.8 years. Two IBD patients were diagnosed with keratoconus (1%) and 38 with suspect keratoconus (18.9%). Overall prevalence of keratoconus and suspect keratoconus was 19.9% (95% confidence interval [CI] 17.5-22.0). None of the 100 healthy subjects had keratoconus, while three were diagnosed with suspect keratoconus (p = 0.0002 versus IBD patients). Only smoking was identified as a risk factor (p = 0.029), especially in Crohn's disease.

CONCLUSION

Inflammatory bowel disease patients may carry an increased risk of keratoconus and suspect keratoconus, smoking further increasing this risk. This supports the hypothesis of an inflammatory origin of keratoconus.

Evaluation of Changes in Human Corneas After Femtosecond Laser-Assisted LASIK and Small-Incision Lenticule Extraction (SMILE) Using Non-Contact Tonometry and Ultra-High-Speed Camera (Corvis ST)

PURPOSE

To evaluate theoretical biomechanical advantages of human corneas treated with small incision lenticule extraction (SMILE) compared with femtosecond laser-assisted LASIK (FS-LASIK) Patients and methods: In a prospective, comparative, non-randomized, consecutive case series patients with moderate to high myopia and/or astigmatism underwent corneal refractive surgery. Patients either received standard FS-LASIK or SMILE. Preoperatively and up to 3 months postoperatively data were analyzed including tomography with Pentacam HR, Goldmann tonometry, non-contact tonometry, and deformability of the cornea using an ultra-high-speed camera (Corvis ST). Data were analyzed and p < 0.05 was considered as statistically significant (t-test).

RESULTS

Seventy-three patients (128 eyes) were treated. Forty-eight eyes of 29 patients underwent FS-LASIK and 80 eyes of 44 patients underwent SMILE. Preoperative spherical equivalent (SE) was -3.23 ± 1.64 D (FS-LASIK group) and -4.83 ± 1.63 D (SMILE group) (p < 0.0001). Almost all parameters obtained by Corvis ST between preoperative and postoperative measurements showed significant changes after refractive surgery. Significant changes were seen between both groups postoperatively. However, matched pair subgroup analysis (n = 69; 26 eyes FS-LASIK; 43 eyes SMILE) of eyes with initially equal pachymetry, intraocular pressure, SE, and difference of pre- to postoperative pachymetry (p>0.05), showed no significant changes in parameters measured with Corvis ST (p>0.05).

CONCLUSIONS

Corneal biomechanical parameters measured preoperatively with Corvis ST showed significant differences postoperatively in total and in both groups. In subgroup analysis with homogenous groups, FS-LASIK showed no significant changes in biomechanical data measured with Corvis ST compared with SMILE.

Posterior Corneal Surface Stability after Femtosecond Laser-Assisted Keratomileusis

The purpose of this study was to evaluate posterior corneal surface variation after femtosecond laser-assisted keratomileusis in patients with myopia and myopic astigmatism. Patients were evaluated by corneal tomography preoperatively and at 1, 6, and 12 months. We analyzed changes in the posterior corneal curvature, posterior corneal elevation, and anterior chamber depth. Moreover, we explored correlation between corneal ablation depth, residual corneal thickness, percentage of ablated corneal tissue, and preoperative corneal thickness. During follow-up, the posterior corneal surface did not have a significant forward corneal shift: no significant linear relationships emerged between the anterior displacement of the posterior corneal surface and corneal ablation depth, residual corneal thickness, or percentage of ablated corneal tissue.

Comparison of prophylactic higher fluence corneal cross-linking to control, in myopic LASIK, one year results

Purpose

To compare 1-year results: safety, efficacy, refractive and keratometric stability, of femtosecond myopic laser-assisted in situ keratomileusis (LASIK) with and without concurrent prophylactic high-fluence cross-linking (CXL) (LASIK-CXL).

Methods

We studied a total of 155 consecutive eyes planned for LASIK myopic correction. Group A represented 73 eyes that were treated additionally with concurrent prophylactic high-fluence CXL; group B included 82 eyes subjected to the stand-alone LASIK procedure. The following parameters were evaluated preoperatively and up to 1-year postoperatively: manifest refractive spherical equivalent (MRSE), refractive astigmatism, visual acuity, corneal keratometry, and endothelial cell counts. We plotted keratometry measurements pre-operatively and its change in the early, interim and later post-operative time for the two groups, as a means of keratometric stability comparison.

Results

Group A (LASIK-CXL) had an average postoperative MRSE of −0.23, −0.19, and −0.19 D for the 3-, 6-, and 12-month period, respectively, compared to −6.58±1.98 D preoperatively. Flat keratometry was 37.69, 37.66, and 37.67 D, compared to 43.94 D preoperatively, and steep keratometry was 38.35, 38.36, and 38.37 D, compared to 45.17 D preoperatively. The predictability of Manifest Refraction Spherical Equivalent (MRSE) correction showed a correlation coefficient of 0.979. Group B (stand-alone LASIK) had an average postoperative MRSE of −0.23, −0.20, and −0.27 D for the 3-, 6-, and 12-month period, respectively, compared with −5.14±2.34 D preoperatively. Flat keratometry was 37.65, 37.89, and 38.02 D, compared with 43.15 D preoperatively, and steep keratometry was 38.32, 38.57, and 38.66 D, compared with 44.07 D preoperatively. The predictability of MRSE correction showed a correlation coefficient of 0.970. The keratometric stability plots were stable for the LASIK CXL group and slightly regressing in the standard LASIK group, a novel stability evaluation metric that may escape routine acuity and refraction measurements.

Conclusion

Application of prophylactic CXL concurrently with myopic LASIK surgery appears to contribute to improved refractive and keratometric stability compared to standard LASIK. The procedure appears safe and provides a new potential for LASIK correction.

Association between the percent tissue altered and post-laser in situ keratomileusis ectasia in eyes with normal preoperative topography

PURPOSE

To investigate the association of a novel metric, percent tissue altered, with the occurrence of ectasia after laser in situ keratomileusis (LASIK) in eyes with normal corneal topography and to compare this metric with other recognized risk factors.

DESIGN

Retrospective case-control study.

METHODS

The study included 30 eyes from 16 patients with bilateral normal preoperative Placido-based corneal topography that developed ectasia after LASIK (ectasia group) and 174 eyes from 88 consecutive patients with uncomplicated LASIK and at least 3 years of postoperative follow-up. The following metrics were evaluated: age, preoperative central corneal thickness, residual stromal bed, Ectasia Risk Score System scores, and percent tissue altered, derived from [PTA = (FT + AD)/CCT], where FT = flap thickness, AD = ablation depth, and CCT = preoperative central corneal thickness.

RESULTS

In the ectasia group, percent tissue altered ≥40 was the most prevalent factor (97%), followed by age <30 years (63%), residual stromal bed ≤300 μm (57%), and ectasia risk score ≥ 3 (43%) (P < .001 for all). Percent tissue altered ≥ 40 had the highest odds ratio (223), followed by residual stromal bed ≤ 300 μm (74) and ectasia risk score ≥ 4 (8). Stepwise logistic regression revealed percent tissue altered ≥ 40 as the single most significant independent variable (P < .0001).

CONCLUSIONS

Percent tissue altered at the time of LASIK was significantly associated with the development of ectasia in eyes with normal preoperative topography and was a more robust indicator of risk than all other variables in this patient population.

Risk Factors in Post-LASIK Corneal Ectasia

Purpose. To evaluate the risk factors for post-laser in situ keratomileusis (LASIK) ectasia. Materials and Methods. Medical records of 42 eyes of 28 (10 women, 18 men) patients who developed corneal ectasia after LASIK were retrospectively reviewed. Topographical features and surgical parameters of those patients were evaluated. Results. The mean age of patients was 34.73 ± 6.50 (23–48) years and the mean interval from LASIK to the diagnosis of post-LASIK ectasia was 36.0 ± 16.92 (12–60) months. The following factors were determined as a risk factors: deep ablation (>75 μm) in 10 eyes, FFK (forme fruste keratoconus) in 6 eyes, steep cornea (>47 D) in 3 eyes, pellucid marginal degeneration (PMD) in 2 eyes, thin cornea (<500 μm) in 2 eyes, thin and steep cornea in 2 eyes, thin cornea and deep ablation in 5 eyes, FFK and steep cornea in 2 eyes, and FFK, steep cornea, and deep ablation in 1 eye. However no risk factor has been determined in 9 eyes (21.4%). Conclusion. The findings of our study showed that most of the patients who developed post-LASIK ectasia have a risk factor for post-LASIK ectasia. However, the most common risk factor was deep ablation.