Lenticule Extraction Procedure Research Articles

Effective optical and treatment zone analysis by means of cross-over differences after lenticule extraction.

To determine the size of the effective optical and treatment zones after lenticule extraction procedures. Retrospective case series. A fully automated method to determine the boundaries of the optical and treatment zones of a lenticule of tissue extracted from a cornea has been developed, in which the boundaries of the corrected area are derived from differences between post and preoperative maps of several corneal metrics by determining the smallest cross-over point along each semi-meridian. The method has been applied to a pilot cohort of 84 eyes, clinical data showing average diameters of 6.56±0.46mm [5.25 to 7.51] and 8.49±0.56mm [6.58 to 9.52] for tangential anterior curvature and corneal thickness, respectively. The method provides a reliable and objective way to determine the size of a lenticule of tissue extracted from a cornea and it can be applied to any topo- or tomographic derived metric. To determine the size of the effective optical and treatment zones after laser vision correction, a fully automated method was developed. The method is simple to implement and can be used to determine the actual size of a corneal correction and help titrating the planned size. The advantages of this algorithm over existing methods are its objectivity; automation; speed; resolution, accuracy and precision; the free-form boundary determination; and finally its support in determining centration and circularity.

Characterization of Disrupted Tissue Interface Thickness for Keratorefractive Lenticule Extraction Procedure With ELITA Femtosecond Laser.

This study identified and compared variables causing changes in corneal tissue structure following the smooth incision lenticular keratomileusis (SILK) procedure using the ELITA Femtosecond Laser System by characterizing the resulting disrupted tissue interface. Seventy-one ex vivo porcine eyes and six human cadaver eyes underwent ELITA SILK with diverse surgical steps, pulse energies, scan overlaps, and surgical methods. Flaps created with the iFS Advanced Femtosecond Laser and ELITA systems were also evaluated. The disrupted interface thickness was determined by imaging corneal layers at different depths through the interface with confocal microscopy and counting layers with elevated backscattered light via computer program-assisted, subject-matter-expert visual judgment with blinding. The disrupted interface thickness for ELITA SILK was 25 ± 3 µm; for the ELITA flap, it was 25 ± 2 µm; and for the iFS flap, it was 32 ± 3 µm. Factors influencing the total ELITA SILK disrupted interface thickness included laser pulse energy (0.11µm/nJ; P < 0.01), scan overlap (5µm; P < 0.01), and mechanical manipulation (7µm; P < 0.01). Varying surgical techniques for mechanical manipulation resulted in a difference in disrupted interface thickness of 4µm (P < 0.01). The ELITA SILK disrupted interface thickness was less than that of the iFS flap and similar to that of the ELITA flap. Assessing disrupted interface thickness identified factors influencing the quality of the corneal interface with SILK. The disrupted interface thickness, a new method for measuring corneal damage, has been used to quantify the potential effects of various refractive surgery factors on surgical outcomes.

Comparative Analysis of Corneal Wound Healing: Differential Molecular Responses in Tears Following PRK, FS-LASIK, and SMILE Procedures.

In this study, we aimed to analyze the changes in the expression profiles of selected messenger RNAs (mRNAs) and their encoded proteins in the tears of patients undergoing photorefractive keratectomy (PRK), femtosecond-assisted laser in situ keratomileusis (FS-LASIK), and small-incision lenticule extraction (SMILE) procedures. A total of 120 patients were divided into three groups based on the laser vision correction (LVC) procedure: PRK, FS-LASIK, or SMILE. Tear samples were collected preoperatively and at 1, 7, 30, and 180 days postoperatively. The expression levels of selected messenger RNAs (mRNAs) and proteins were analyzed by using reverse transcription quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA), respectively. PRK and FS-LASIK elicited significantly stronger biological responses than SMILE. Interleukin-15 (IL-15) expression increased notably in the PRK and FS-LASIK groups, with mRNA levels reaching fold changes of 4.65 ± 0.65 and 4.99 ± 0.28, respectively, on day 1, compared with only 2.09 ± 0.23 in the SMILE group. Vascular endothelial growth factor A (VEGFA) levels were also elevated in the PRK (2.98 ± 0.23 fold change) and FS-LASIK groups (3.45 ± 1.09 fold change) on day 1, while the SMILE group showed minimal fluctuations. The protein concentration analysis based on the ELISA confirmed these trends, with IL-15 levels peaking at 54.2 ± 2.5 pg/mL in the PRK group and 52.8 ± 3.1 pg/mL in the FS-LASIK group, compared with 32.4 ± 1.9 pg/mL in the SMILE group on day 1. Similarly, VEGFA protein concentrations were the highest in the PRK (72.4 ± 4.1 pg/mL) and FS-LASIK patients (69.5 ± 3.8 pg/mL) on day 1 but remained low in the SMILE patients (45.6 ± 2.3 pg/mL). By day 180, gene expression and protein levels in all groups had stabilized, returning to near-preoperative values. PRK and FS-LASIK induced more pronounced molecular and protein-level changes during corneal wound healing than the less invasive SMILE procedure, indicating stronger biological responses. These findings suggest that tailored postoperative care based on the specific procedure could optimize healing and patient outcomes. However, further research with larger sample sizes and longer follow-ups is needed to confirm these observations and develop personalized treatment strategies.

Comparing visual outcomes of keratorefractive lenticule extraction, PRK, and LASIK procedures in the military population.

To assess the 6-month visual and refractive outcomes of keratorefractive lenticule extraction (KLEx) as compared with laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK) in a military population at a Joint Warfighter Refractive Surgery Center. Joint Warfighter Refractive Surgery Center (JWRSC), Lackland Air Force Base, San Antonio, Texas. Retrospective study. Patients who underwent KLEx, PRK, or LASIK between 2019 and 2022 were included. Anonymized data collected included demographics, preoperative and postoperative uncorrected and corrected visual acuity, and manifest refraction. Of the 4466 treated eyes, 737 (16.5%) underwent the KLEx, 2801 (62.7%) underwent PRK, and 928 (20.8%) underwent LASIK treatment. Regarding efficacy, there was no statistically significant difference at postoperative month (POM) 6 between the percentage of eyes reaching an uncorrected distance visual acuity of 20/20 or better between the 3 procedures. At POM1 ( P < .001) and POM3 ( P < .001), there were a greater number of eyes in the KLEx group that achieved the same or 1 line better of distance visual acuity than the PRK group. The efficacy indices of KLEx, PRK, and LASIK at POM6 were 1.09, 1.10, and 0.97, respectively. The safety indices for KLEx, PRK, and LASIK at POM6 were 0.96, 1.01, and 0.81, respectively. After the initial recovery period, KLEx demonstrates comparable outcomes in efficacy, safety, and accuracy as compared with LASIK and PRK.

Photorefractive Keratectomy: Technical Evolution, Refractive Outcomes, Corneal Wound Healing Response, and Complications.

Photorefractive keratectomy (PRK) was the first excimer laser procedure developed to treat refractive errors. The safety and efficacy of PRK established it as one of the most performed corneal refractive procedures worldwide. With the introduction of laser in situ keratomileusis (LASIK), and more recently keratorefractive lenticule extraction (KLEx) procedures, many corneal surgeons favor these newer corneal procedures as the first choice due to faster visual rehabilitation and less discomfort during the early postoperative period. Importantly, however, PRK remains a viable alternative for most corneal refractive candidates and there are many situations in which PRK remains the refractive procedure of choice. This review addresses the technical evolution of PRK-mechanical epithelial debridement versus alcohol-assisted epithelial removal versus excimer laser-assisted epithelial debridement (transepithelial) PRK-and reports the PRK refractive outcomes compared to other keratorefractive laser procedures. The corneal wound response associated with each PRK technique and the indications, limitations, and complications of PRK are reviewed to aid refractive surgeons to best position PRK in their overall practice. [J Refract Surg. 2024;40(10):e754-e767.].

Refractive Coupling Effects in Keratorefractive Lenticule Extraction Procedures: A Machine Learning-Assisted Approach.

To evaluate the impact of refractive couplings in myopia and myopic astigmatism with two different keratorefractive lenticule extraction (KLEx) systems. This was a retrospective evaluation of refractive outcomes with two different lasers studying 2,841 eyes undergoing small incision lenticule extraction (SMILE) (VisuMax 500; Carl Zeiss Meditec) and 2,528 eyes undergoing SmartSight (ATOS; SCHWIND eye-tech-solutions GmbH). Coupling effects (derived from the ratio between partial slopes) were determined for sphere and cylinder and for spherical equivalent, cardinal, and oblique astigmatism separately. Statistically significant coupling effects were observed for both the VisuMax and ATOS systems, as indicated by P values less than .05. For the VisuMax, a coupling effect of 8% of cylinder into sphere and a 2% coupling of sphere into cylinder was found. For the ATOS, the coupling effect of sphere into cylinder was 1%. A 3% coupling effect of oblique astigmatism into cardinal astigmatism in the VisuMax, and conversely, a 0.1% coupling effect of defocus into oblique astigmatism in the ATOS were found. In cases with no astigmatism plan, sphere had a 2% effect on induced astigmatism in the VisuMax and 0.6% in the ATOS. In high astigmatism plans, sphere had a significant 16% impact on cylinder in the VisuMax. Additionally, the effect of defocus on cardinal astigmatism was 6% in the VisuMax and 0.8% on oblique astigmatism in the ATOS. Despite the P values less than .05 indicating statistical significance, the observed coupling effects were consistently low, with magnitudes below 10%, even for astigmatism exceeding 2.50 diopters. These couplings may be partly attributed to cross-effects of torsional eye movements. Coupling values for KLEx were markedly lower than those reported for non-aspheric excimer laser ablations. The results suggest that surgical results may be refined further by optimizing nomograms to mitigate coupling effects. [J Refract Surg. 2024;40(10):e706-e715.].

Changes in the Biomechanical Properties of Corneal Stromal Lens after Collagen Crosslinking Induced by EDC-NHS.

To evaluate the changes of lens antidilatation, antiedema, and antienzymolysis ability after different concentrations of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide (EDC-NHS)-induced collagen cross-linking. Corneal stromal lenticules (n = 100) obtained from small incision lenticule extraction (SMILE) procedures were divided into 5 groups: no treatment (control); EDC/NHS (5%/2.5%); EDC/NHS(5%/5%); EDC/NHS (10%/5%); riboflavin and ultraviolet-A light (UVA). Collagen crosslinking was induced using EDC-NHS and UVA. Biomechanical assessments including inflation test, enzymatic degradation resistance, and light transmittance were evaluated posttreatment. (1) Lenticule apex displacement ranked: control Group > UVA Group > Group (5%/5%) > Group (5%/2.5%) > Group (10%/5%) (Friedman test, p < 0.0001). (2) Light transmittance was significantly higher in the crosslinked groups versus control, with EDC/NHS superior to UVA riboflavin. After 15 minutes in PBS, light transmittance decreased due to swelling; however, crosslinked groups maintained significantly higher transmittance versus control. (3) Following crosslinking, enzymatic resistance improved significantly, with the EDC-NHS crosslinking group was significantly better than the UVA cross-linking group. EDC/NHS crosslinking enhanced lenticule stiffness, antiedema, and enzymatic resistance and without compromising the transparency of the lens. Moreover, EDC/NHS crosslinking efficacy exceeded UVA riboflavin crosslinking in improving lenticule biomechanical properties.

Para Incisional Quadrant Saving Dissection in Refractive Lenticule Extraction for Myopia by Reverse Pull using Shearing Applied Force Extraction (SAFE)

There is no standard technique of lenticule separation in Refractive Lenticule Extraction (ReLEx) or Small Incision Lenticule Extraction (SMILE) procedure used for spectacle number treatment by Laser. We present a unique method of lenticule dissection using reverse pull by shearing applied force extraction (SAFE) to ensure complete removal of the lenticule with minimal postoperative inflammation. This technique keeps the lenticule under control of the operating surgeon throughout the dissection. Random separation of lenticule may leave a part of the lenticule attached to the periphery. Separated lenticule overrides the attached part of lenticule. This reduced visibility of the attached part makes further separation difficult and causes excessive manipulation, consumes more time, leads to inflammation and may cause incomplete lenticule removal. This new technique ensures safe and full removal of the lenticule irrespective of its thickness (thin lenticule is difficult to identify and separate while thick lenticule tends to get accumulated on one side) and improves postoperative outcome.

Comprehensive Assessment of Posterior Corneal Asphericity Change Calculated by Tangential Radius of Curvature After FS-LASIK and SMILE.

To evaluate changes in posterior corneal asphericity (ΔQ) using the tangential radius of curvature after femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) procedures. One hundred twenty right eyes of myopic patients who underwent either FS-LASIK or SMILE procedures were analyzed using Sirius 3D corneal topography for assessment. The tangential radius was employed to calculate both preoperative and postoperative posterior corneal Q-values across each semimeridian. After both surgical interventions, the ΔQ value variations across the 360° semimeridional regions of the posterior corneal surface were compared. A marked postoperative increase in the posterior corneal Q-value was documented. No significant differences were noted between the postoperative Q-values or ΔQ-values of the two surgical approaches. Among patients with moderate myopia, postoperative Q-value exhibited considerably lower increases and ΔQ-value significantly smaller than their counterparts with high myopia. Moreover, the fluctuation in ΔQ across semimeridional regions was less evident in patients with moderate myopia than in those with high myopia. Notably, the degree of ΔQ fluctuation across semimeridional regions was similar between both surgical categories. These data offer insights into variations in the posterior corneal surface after refractive surgeries depending on the degree of myopia, illuminating their clinical relevance. Both FS-LASIK and SMILE introduce notable changes to posterior corneal asphericity among patients with different myopia intensities. Furthermore, the influence on the asphericity across the entire posterior surface is similarly distributed between FS-LASIK and SMILE techniques. [J Refract Surg. 2024;40(3):e133-e141.].

Comparison of the accuracy of 9 intraocular lens power calculation formulas after SMILE in Chinese myopic eyes

As of 2021, over 2.8 million small-incision lenticule extraction (SMILE) procedures have been performed in China. However, knowledge regarding the selection of intraocular lens (IOL) power calculation formula for post-SMILE cataract patients remains limited. This study included 52 eyes of 26 myopic patients from northern China who underwent SMILE at Tianjin Eye Hospital from September 2022 to February 2023 to investigate the suitability of multiple IOL calculation formulas in post-SMILE patients using a theoretical surgical model. We compared the postoperative results obtained from three artificial intelligence (AI)-based formulas and six conventional formulas provided by the American Society of Cataract and Refractive Surgery (ASCRS). These formulas were applied to calculate IOL power using both total keratometry (TK) and keratometry (K) values, and the results were compared to the preoperative results obtained from the Barrett Universal II (BUII) formula for the SMILE patients. Among the evaluated formulas, the results obtained from the Emmetropia Verifying Optical 2.0 Formula with TK (EVO-TK) (0.40 ± 0.29 D, range 0–1.23 D), Barrett True K with K formula (BTK-K, 0.41 ± 0.26 D, range 0.01–1.19 D), and Masket with K formula (Masket-K, 0.44 ± 0.33 D, range 0.02–1.39 D) demonstrated the closest proximity to BUII. Notably, the highest proportion of prediction errors within 0.5 D was observed with the BTK-K (71.15%), EVO-TK (69.23%), and Masket-K (67.31%), with the BTK-K showing a significantly higher proportion than the Masket-K (p < 0.001). Our research indicates that in post-SMILE patients, the EVO-TK, BTK-K, and Masket-K may yield more accurate calculation results. At their current stage in development, AI-based formulas do not demonstrate significant advantages over conventional formulas. However, the application of historical data can enhance the performance of these formulas.

Comparative analysis of IOL power calculations in postoperative refractive surgery patients: a theoretical surgical model for FS-LASIK and SMILE procedures

BackgroundAs the two most prevalent refractive surgeries in China, there is a substantial number of patients who have undergone Femtosecond Laser-assisted In Situ Keratomileusis (FS-LASIK) and Small Incision Lenticule Extraction (SMILE) procedures. However, there is still limited knowledge regarding the selection of intraocular lens (IOL) power calculation formulas for these patients with a history of FS-LASIK or SMILE.MethodsA total of 100 eyes from 50 postoperative refractive surgery patients were included in this prospective cohort study, with 25 individuals (50 eyes) having undergone FS-LASIK and 25 individuals (50 eyes) having undergone SMILE. We utilized a theoretical surgical model to simulate the IOL implantation process in postoperative FS-LASIK and SMILE patients. Subsequently, we performed comprehensive biological measurements both before and after the surgeries, encompassing demographic information, corneal biometric parameters, and axial length. Various formulas, including the Barrett Universal II (BUII) formula, as a baseline, were employed to calculate IOL power for the patients.ResultsThe Barrett True K (BTK) formula, demonstrated an mean absolute error (AE) within 0.5 D for both FS-LASIK and SMILE groups (0.28 ± 0.25 D and 0.36 ± 0.24 D, respectively). Notably, the FS-LASIK group showed 82% of results differing by less than 0.25 D compared to preoperative BUII results. The Barrett True K No History (BTKNH) formula, which also incorporates measured posterior corneal curvature, performed similarly to BTK in both groups. Additionally, the Masket formula, relying on refractive changes based on empirical experience, displayed promising potential for IOL calculations in SMILE patients compared with BTK (p = 0.411).ConclusionThe study reveals the accuracy and stability of the BTK and BTKNH formulas for IOL power calculations in myopic FS-LASIK/SMILE patients. Moreover, the Masket formula shows encouraging results in SMILE patients. These findings contribute to enhancing the predictability and success of IOL power calculations in patients with a history of refractive surgery, providing valuable insights for clinical practice. Further research and larger sample sizes are warranted to validate and optimize the identified formulas for better patient outcomes.

Ten-year outcomes following small incision lenticule extraction for up to -10Dioptres myopia

ABSTRACT Clinical relevance More than 6 million small-incision lenticule extraction (SMILE) procedures have been performed worldwide since 2011. Therefore, its long-term safety and efficacy should be investigated. Background This study aimed to evaluate 10-year refractive outcomes, corneal stability, axial length, and wavefront aberrations in patients who underwent SMILE to correct myopia. Methods Thirty two patients (32 eyes) who underwent SMILE-based myopic correction. Corrected distance visual acuity, uncorrected distance visual acuity, corneal stability, axial length, and wavefront aberrations were evaluated preoperatively and at 1 month and 1, 5, and 10 years postoperatively. Results At 10 years postoperatively, the safety and efficacy indices for the patients included in this study were 1.19 ± 0.21 and 1.04 ± 0.27, respectively. For 26 (81%) and 30 eyes (94%), correction to within ±0.50 D and ±1.00 D of the target was achieved, respectively. Over the 10-year follow-up duration, a mean −0.32 ± 0.56 D regression was observed (−0.03 ± 0.06 D/year). Relative to baseline, horizontal and vertical comas significantly increased, as did the incidence of higher-order aberrations (all P < 0.001), whereas axial length and corneal elevation remained stable during follow-up. Conclusion These results indicate that the SMILE-based correction for myopia of up to -10 Dioptres is safe, effective, and stable, with relatively constant wavefront aberrations and corneal stability over time after treatment.

Corneal stromal lenticule transplantation for the treatment of corneal ulcers.

To evaluate the safety and efficacy of using corneal stromal lenticules (CSLs) obtained during refractive surgery Refractive Lenticule Extraction (ReLEx) with the Small Incision Lenticule Extraction (SMILE) procedure for the treatment of corneal ulcers. This retrospective study included 12 eyes of 12 patients, 7 men and 5 women with varying degrees of corneal ulcer. The mean age was 64 ± 18 (range 34 to 95 years). The monitoring included corrected distance visual acuity (CDVA), slit-lamp biomicroscopy examination, a Seidel test, stability of the graft and anterior segment optical coherence tomography (AS-OCT) inspection. Patients were closely monitored for possible postoperative complications for at least 6 months. In 7/12 (58%) eyes, the corneal ulcer was successfully sealed with CSL and amniotic membrane (AM) without the need for any additional surgical intervention. In 3 eyes, penetrating keratoplasty (PK) was needed in addition to CSL transplantation and in 2 eyes the scleral patch was used to fully seal after CSL transplantation. During the follow-up period no signs of rejection or infection were detected in any patient. The use of CSLs from ReLEx SMILE may be considered as an alternative method for the treatment of corneal ulcers before a more extensive and definitive solution - PK - is used. Our preliminary findings suggest that properly performed CSL transplantation using cryopreserved lenticules is a safe and effective method to temporarily cover the corneal partial-thickness defect or even perforation.

Clinical Evaluation of Corneal Biomechanics following Laser Refractive Surgery in Myopic Eyes: A Review of the Literature.

The role of corneal biomechanics in laser vision correction (LVC) is currently being raised in the assessment of postoperative corneal ectasia risk. The aim of the paper was to evaluate the changes in corneal biomechanics after LVC procedures based on a systematic review of current studies. The results of a search of the literature in the PubMed, Science Direct, Google Scholar, and Web of Science databases were selected for final consideration according to the PRISMA 2020 flow diagram. Included in our review were 17 prospective clinical studies, with at least 6 months of follow-up time. Corneal biomechanical properties were assessed by Ocular Response Analyzer (ORA), or Corvis ST. The results of the study revealed the highest corneal biomechanics reduction after laser in situ keratomileusis (LASIK) followed by small incision lenticule extraction (SMILE) and surface procedures, such as photorefractive keratectomy (PRK) or laser-assisted sub-epithelial keratectomy (LASEK). In SMILE procedure treatment planning, the use of thicker caps preserves the corneal biomechanics. Similarly, reduction of flap thickness in LASIK surgery maintains the corneal biomechanical strength. Future prospective clinical trials with standardization of the study groups and surgical parameters are needed to confirm the results of the current review.

Predictive models for IOPs measured with NCT, GAT, and ORA among patients undergoing SMILE.

Purpose: To develop predictive models for the intraocular pressure (IOP) of patients undergoing small incision lenticule extraction (SMILE) procedures, measured with a noncontact tonometer (NCT), Goldmann applanation tonometry (GAT), and an ocular response analyzer (ORA). Methods: In this prospective study, a total of 104 eyes (-6.23 ± 2.06 diopters) of 52 patients (24.38 ± 4.76years) undergoing SMILE procedures were included. The intraocular pressure was measured (IOPNCT with NCT, IOPGAT with GAT, and IOPcc and IOPg with ORA) before surgery and at postoperative 6months. Information on age, preoperative and attempted spherical equivalent (SE), ablation depth, preoperative values and postoperative changes in central corneal thickness (CCT), K1, K2, Km, corneal hysteresis (CH) and corneal resistance factor (CRF) values was collected in order to predict IOPs. Results: All surgeries were uneventful. At postoperative 6months, the efficacy and safety index were 1.04 ± 0.15 and 1.08 ± 0.18, respectively. Significant decreases were detected in postoperative IOPNCT, IOPGAT, IOPcc, and IOPg compared to preoperative values (all p < 0.001). No relationship was found between any IOP and ablation depth, attempted SE, and preoperative SE, as well as CCTdifference (all p > 0.05). Predictive models for IOPs were constructed to predict preoperative values, and R 2 values were 67.5% (IOPNCT), 64.5% (IOPGAT), 78.7% (IOPcc), and 82.0% (IOPg). The prediction band of IOPNCT and IOPGAT was 7.4-15.1mmHg and 8-16mmHg, respectively. Conclusion: Predictive models for IOP measurements after SMILE procedures can be helpful in clinical practice.

Risks and Complications Associated with Refractive Surgery

Myopia, hyperopia, and astigmatism (together called ametropia) are the top causes of vision impairement worldwide. Refractive surgery, surgical modification of refractive surfaces in the eye, are prominent solutions for treating ametropia. This study made a summary of the risks (poor refractive outcomes of either high residual ametropia after surgery or the postoperative development of refractive errors) and complications associated with seven refractive surgery procedures for ametropia. Risks and complications were summarized and discussed in categorized form, the incidence of each undesirable outcome in percent, rather than in quantified form, the severity of occurrence on average, help readers to identify the chances of undesirable results directly. The incidence of risks and complications were also stratified based on related factors, depending on the availability of data. Brief descriptions and analyses of the results of data summaries were included at the beginning of the discussion of the risks and complications of each refractive surgery procedure; specific data was also included to allow for comparison. In general, laser-assisted in situ keratomileusis (LASIK), laser-assisted sub-epithelium keratomileusis (LASEK), and small incision lenticule extraction (SMILE) procedure were found to yield few undesirable outcomes, while all seven procedures were crucial for the system of solutions for refractive errors.

Evaluation of peripapillary - macular microvascularity and choroidal vascularity index after refractive surgery

BackgroundTo evaluate the microvascularity and choroidal vascularity index (CVI) using optical coherence tomography angiography (OCTA) and OCT following femtosecond laser-assisted in-situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) procedures. MethodsPatients with myopia (<-6.0D sphere) or myopic astigmatism (<-4.0D astigmatism) were enroled. The percentage of vessel density and foveal avascular zone (FAZ) size, optic disc flux index and perfusion were noted and the CVI was calculated before and after surgery. ResultsTwenty-nine eyes of 16 patients in the FS-LASIK group and 30 eyes of 16 patients in the SMILE group were enroled. Macular vessel density, FAZ size, and optic disc flux index were significantly higher on postoperative 1st day compared to preoperative day (p = 0.001, p = 0.007, and p < 0.001, respectively). There was no significant difference in terms of macular and peripapillary CVI between postoperative 1st day and preoperative day (p > 0.05). All microvascular parameters were similar on postoperative 7th day and preoperative day (p > 0.05). ConclusionsIt was detected that there is a transient alteration in macular and peripapillary microvascularity after FS-LASIK/SMILE, whereas choroidal circularity is not significantly affected by these refractive surgeries.

Experiment-Based Validation of Corneal Lenticule Banking in a Health Authority-Licensed Facility.

With the expected rise in patients undergoing refractive lenticule extraction worldwide, the number of discarded corneal stromal lenticules will increase. Therefore, establishing a lenticule bank to collect, catalog, process, cryopreserve, and distribute the lenticules (for future therapeutic needs) could be advantageous. In this study, we validated the safety of lenticule banking that involved the collection of human lenticules from our eye clinic, transportation of the lenticules to a Singapore Ministry of Health-licensed lenticule bank, processing, and cryopreservation of the lenticules, which, after 3 months or, a longer term, 12 months, were retrieved and transported to our laboratory for implantation in rabbit corneas. The lenticule collection was approved by the SingHealth Centralised Institutional Review Board (CIRB). Both short-term and long-term cryopreserved lenticules, although not as transparent as fresh lenticules due to an altered collagen fibrillar packing, did not show any sign of rejection and cytotoxicity, and did not induce haze or neovascularization for 16 weeks even when antibiotic and steroidal administration were withdrawn after 8 weeks. The lenticular transparency progressively improved and was mostly clear after 4 weeks, the same period when we observed the stabilization of corneal hydration. We showed that the equalization of the collagen fibrillar packing of the lenticules with that of the host corneal stroma contributed to the lenticular haze clearance. Most importantly, no active wound healing and inflammatory reactions were seen after 16 weeks. Our study suggests that long-term lenticule banking is a feasible approach for the storage of stromal lenticules after refractive surgery. Impact statement Since 2011, close to 3 million refractive lenticule extraction procedures have been performed. The majority of the extracted lenticules are discarded. The lenticules could have been cryopreserved and retrieved at a later date for therapeutic or refractive applications. Therefore, establishing a lenticule bank to collect, catalog, process, cryopreserve, and distribute the lenticules could be advantageous. In this study, we simulated a lenticule banking service in a validated health authority-licensed facility and showed that long-term cryopreservation of the lenticules in the facility was safe and feasible in vivo.

Biomechanical responses of the cornea after small incision lenticule extraction (SMILE) refractive surgery based on a finite element model of the human eye.

To investigate the biomechanical responses of the human cornea after small incision lenticule extraction (SMILE) procedures, especially their effects of SMILE surgery on stress and strain. Based on finite element analysis, a three-dimensional (3D) model of the human eye was established to simulate SMILE refractive surgery procedures. Stress and strain values were calculated by inputting the intraocular pressure (IOP). After SMILE refractive surgery procedures, the stress and strain of the anterior and posterior corneal surfaces were significantly increased. The equivalent stress and strain on the anterior and posterior corneal surfaces increased with increasing diopter and were concentrated in the central area, whereas the values of stress and strain at the incision site on the anterior surface of the cornea were approximately 0. Compared with the anterior corneal surface, the stress and strain of the posterior surface were larger. Increasing IOP caused an approximately linear change in stress and a nonlinear increase in corneal strain. In addition, we found that the incision sizes and direction had less of an influence on stress and strain. In summary, SMILE surgery increased the equivalent stress and strain on the human cornea. The equivalent stress and strain of the anterior and posterior human corneal surfaces increased after SMILE refractive surgery; these increases were particularly noticeable on the posterior surface of the cornea.

Influence of Cap Thickness on Opaque Bubble Layer Formation in SMILE: 110 Versus 140 µm.

To investigate the impact of cap thickness on the formation of an opaque bubble layer (OBL) during small incision lenticule extraction procedures. In total, 100 eyes from 50 patients were prospectively examined. One of two corneal cap thicknesses was randomly assigned to each eye and differed in the contralateral eye: 110 µm in one eye and 140 µm in the other. OBL area and density were quantitatively assessed. The proportion of OBL areas in the anterior lenticule plane was 11.70% ± 7.35% in the 110-µm group, which was significantly higher than the 140-µm group (6.64% ± 4.68%, P < .001). For OBL areas located in the posterior lenticule plane, mean areas for the 110-µm group were also higher than those for the 140-µm group (1.32% ± 1.20% and 0.94% ± 0.59%, respectively; P = .002). Mean gray values of the OBL in the posterior lenticule plane were slightly different between the two groups (P < .001), but no significant difference in OBL of the anterior lenticule plane was observed (P = .055). Eyes with a 110-µm cap thickness had more focal OBLs, revealed by cap scanning (chi-square = 10.256, P = .001). Corneal cap thickness is predictive of opaque bubble layer during small incision lenticule extraction procedures. [J Refract Surg. 2020;36(9):592-596.].