ETM Experimental and Therapeutic Medicine 1792-0981 1792-1015 D.A. Spandidos ETM-30-4-12936 10.3892/etm.2025.12936 Articles Morphological changes after corneal stromal lenticule excimer laser shaping WangXiaoxuan 1 LiuXiaopeng 1 HouJie 2 LiuSijun 3 YangShirui 2 LeiYulin 2 Department of Ophthalmology, Binzhou Medical University, Binzhou, Shandong 256603, P.R. China Department of Ophthalmology, Jinan Mingshui Eye Hospital, Jinan, Shandong 250200, P.R. China Department of Ophthalmology, Weifang Eye Hospital, Weifang, Shandong 261072, P.R. China Correspondence to: Professor Yulin Lei, Department of Ophthalmology, Jinan Mingshui Eye Hospital, 5601 Longquan Road, Zhangqiu, Jinan, Shandong 250200, P.R. China leiyulin642@126.com 102025 05082025 30 4 186 11 04 2025 24 06 2025 Copyright © 2025, Spandidos Publications 2025

The present study aimed to investigate the feasibility and design of producing a parallel/concave lenticule using an excimer laser on a convex corneal matrix lenticule in vitro. Optical coherence tomography was used to measure the thickness of the corneal stromal lenticules. Lenticules were cut using an excimer laser. The lenticules were divided into three groups: 1:1, 1:1.5 and 1:2 cuttings. After cutting, the lenticule thickness was measured again. Thickness changes in the three groups were compared before and after the cuts. Significant differences were observed among the three groups in central thickness, thickness changes (1.5 mm) and the difference between central thickness and thickness (2 mm from the centre) before and after cutting. However, thickness changes at 2 and 2.5 mm from the centre were not statistically significant. The differences between the central thickness and thickness at 2 mm from the centre after shaping (with interquartile ranges) were as follows: 38 (28, 53.5) µm in Group Ⅰ, 6 (-3,15.5) µm in Group II and -10 (-16.5, -5) µm in Group III. In conclusion, excimer cutting at different proportions affected thickness changes at the centre and 1.5 mm from the centre. Furthermore, it did not affect the thickness change at 2 and 2.5 mm from the centre. The lenticule obtained by a 1:1 cutting ratio was convex and the lenticule formed by a 1:1.5 cutting ratio retained a convex shape. However, the centre was very close to the parallel lenticule. The lenticule obtained using a 1:2 cutting ratio was concave.

 corneal stromal lenticule excimer laser cutting keratoconus OCT parallel lenticule concave lenticule Funding: No funding was received. Introduction

Femtosecond laser, as an infrared laser, has the advantages of a short action time, high instantaneous power and a small thermal effect area. Thus, it can achieve high-precision incisions (1). Small-incision lenticule extraction (SMILE) uses a femtosecond laser to perform three-dimensional scanning of the corneal stroma to form a lenticule. The lenticule was then removed from the corneal stroma through a small (2-4 mm) incision to correct myopia. The SMILE procedure is safe, effective and highly predictable. Studies have shown that it has better corneal biomechanics compared to traditional surgery (2). Owing to its significant clinical advantages, SMILE is being increasingly adopted by experts. The corneal stromal lenticule is a biological material that can be used to correct hyperopia (3,4) and treat corneal ulcers, perforations (5,6) and keratoconus (7-9).

Conical cornea is a common, progressive, non-inflammatory corneal degeneration disease that typically develops in adolescents (10). Early refractive correction involves the use of frames and rigid gas-permeable (RGP) lenses, whereas disease progression is controlled by corneal collagen cross-linking. Corneal collagen cross-linking uses chemical principles to increase the connections between collagen fibres, thereby enhancing the biomechanics of the cornea and controlling keratoconus progression (11,12). High-energy UV irradiation can damage the corneal endothelium and lenticule. Therefore, the cornea must be 400 µm or greater in thickness before the cross-linking procedure to minimise damage to the corneal endothelium and lenticule (13). Consequently, patients with advanced keratoconus and thin corneas face significant treatment limitations. Treatment options for this group of patients include corneal transplantation or lenticule implantation, depending on the degree of scarring (14).

Femtosecond laser-assisted lenticule transplantation is used to treat keratoconus by implanting a surgically acquired stromal lenticule into the recipient's stromal capsular bag through a small 2-4 mm incision (15). This surgical procedure is flapless, minimally invasive, single-step and does not require postoperative sutures. Therefore, suture scarring can be avoided. The increased thickness of the cornea postoperatively also enhances its biomechanical strength to a certain extent. Corneal stromal lenticule implantation for keratoconus has several advantages and limitations. SMILE-derived lenticules, used in myopia correction, are convex, with a thick centre and thin edges (15). In comparison, patients with keratoconus are characterised by a central anterior protrusion and an increase in curvature (16). Therefore, the curvature does not improve or even become increasingly steep despite an increase in the thickness. This phenomenon may result in intolerance to postoperative framed lenticules. It may also cause a poor RGP fit, difficulty in refractive reconstruction and poor patient satisfaction (7,8). The excimer laser can cut corneal tissues with high precision without affecting tissues outside the cutting area, making it highly safe (17). In the present study, excimer laser cutting of the corneal stromal lenticule was performed. Thus, a corneal stromal lenticule is produced, which is either parallel or concave. Consequently, the thickness of the corneal cone can be increased while avoiding excessive curvature during the postoperative period. This outcome is conducive to refractive reconstruction.

 Patients and methods <sec> <title>Study objective and grouping

A total of 75 patients (111 eyes) who underwent SMILE surgery at Jinan Mingshui Eye Hospital (Jinan, China) between September 2023 and April 2024 were selected for this study. All patients voluntarily came to Jinan Mingshui Eye Hospital for refractive surgery, and none had received any treatment for an eye condition. A complete ophthalmological examination was performed before the surgery. The surgically designed spherical equivalent lenticule was -6.75 [interquartile range (IQR): -7.00, -6.38; range: -8.13, -5.00] D. Astigmatism in each eye did not exceed 1.00 D. A complete preoperative ophthalmological examination was conducted. The lenticules were randomly divided into three groups at a ratio of 1:1:1 using a random number table. Each group consisted of 37 lenticules. Group I was cut using a 1:1 ratio according to the equivalent spherical mirror of the lenticule itself (diopters of the excimer laser cutting=equivalent spherical power of the lenticule). Group II was cut using a 1:1.5 ratio (excimer laser cutting diopter=1.5 times the equivalent spherical lenticule). Group III was cut at a 1:2 ratio (diopters of excimer laser cutting=2 times the equivalent spherical power of the lenticule). After cutting, the thickness measurements of the centre of the corneal stromal lenticule were repeated at distances of 1.5, 2 and 2.5 mm from the centre. The interval between pre- and post-cutting measurements was recorded as the time T. The research protocol complied with the principles of the Declaration of Helsinki and was approved by the Medical Ethics Committee of Jinan Mingshui Eye Hospital (Ref. Ethics/2024/004). Informed consent was obtained from all adult participants and the guardians of juvenile participants. A pre-experiment was conducted before the main experiment, in which the degree of expansion of the corneal stromal lenticule in the balanced salt solution was measured. Based on this, the ratios were designed as a reference.

 Corneal stromal lenticule acquisition process

All patients underwent a detailed ophthalmological examination before surgery and the same experienced physician performed all of the surgeries. Levofloxacin eye drops (levofloxacin bromofenac sodium; Ruilin Medicince) were routinely administered for 1 day before surgery, with a total dosage of 5 ml. Furthermore, local anaesthetic proparacaine hydrochloride eye drops were applied for surface anaesthesia after rinsing the conjunctival sac and routinely disinfecting the periocular area during preoperative preparations, with two applications, each containing one drop (~0.1 ml in total; concentration, 0.5%). Femtosecond laser lenticule production and small-incision parameters included the following: Visumax 500 kHz femtosecond Laser System (Carl Zeiss AG); laser pulse frequency, 500 kHz; energy, 130 nJ; lenticule cutting diameter, 6.5 mm; corneal cap thickness, 120 µm; and small-incision length, 2 mm (18). The removed stromal lenticules were placed on a flat surface of a Petri dish. Subsequently, one to two drops of balanced salt solution were added to flatten the stromal lenticules.

 Measurement of corneal stromal lenticules

Measurements were taken using an optical coherence tomography (OCT) scanner (RTVue100-2; Kelin Instrument Co., Ltd.). Preparations and measurements were conducted at the same suitable temperature (temperature, 20±0.5˚C; humidity, 42±2%). The excess liquid on the surface and sides of the lenticule was absorbed using a surgical sponge. The preparation process was completed in 1 min. The Petri dish was then fixed to the homemade fixation device made from foam, which was positioned in front of the OCT. The thickness of the corneal stromal lenticule was measured at the centre and 1.5, 2 and 2.5 mm from the centre. Immediately after the measurement, the flat dish was placed on an Amax excimer machine for excimer cutting and the optical zone of the cutting was set to 4 mm.

 Data processing

The change in central thickness was represented by the central thickness change (ctc). The thickness changes at 1.5, 2.0 and 2.5 mm from the centre were denoted as 1.5tc, 2tc and 2.5tc, respectively. Lenticule concavity was expressed as the difference between the central thickness and thickness at 2 mm from the centre (ct-2t). ct-2t values #x003C;-3 µm indicate a concave lens, values between -3 and 3 µm indicate a parallel lens and values >3 µm indicate a convex lens.

 Statistical analysis

All data were analysed using SPSS version 27.0 (IBM Corp.). The Shapiro-Wilk test was used to assess the normal distribution of data. If the normal distribution and χ2 criteria were met, a one-way ANOVA was used with the Least Significant Difference post hoc test. If the assumptions were not met, the data were analysed using the Kruskal-Wallis test and the Dunn's test was employed as the post hoc test. The χ2 test was used for sex in Table I. P#x003C;0.05 was considered to indicate a statistically significant difference.

 Results <sec> <title>Basic information statistics of patients

Participants were aged 17-35 years (23.15±4.982 years). The surgically designed equivalent spherical lenticule was -6.75 (-7.00, -6.38) (range, -8.13 - -5.00 D). Astigmatism in each eye did not exceed 1.00 D. Basic information statistics showed no statistically significant differences in age, sex or diopters among the three groups (Table I).

 Comparison of pre-plastic thickness in the three groups

No statistically significant differences were found among the three groups in the plastic anterior centre, thickness at distances of 1.5, 2 and 2.5 mm from the centre, or ct-2t (Table II).

 Comparison of the three groups

The cuttings of the three groups are shown in Fig. 1. The difference between the two measurement intervals (T) in the three groups was not statistically significant (Table III). The difference in ctc and 1.5tc of the three groups was statistically significant. No statistically significant differences were observed in the 2tc or 2.5tc values of the three groups. The difference in ct-2t after laser plasticity was statistically significant among the three groups (Table III).

 Postplasticisation ct-1/4t

After laser plasticity, Group I had a ct-2t of 38 (IQR, 28, 53.5) µm, Group II had a ct-2t of 6 (IQR, -3, 15.5) µm and Group III had a ct-2t of -10 (IQR, -16.5, -5) µm (Table III).

 Discussion

Femtosecond laser-assisted corneal lenticule transplantation has achieved good results in the treatment of conical corneas. Zhao et al (7), Wang et al (8) and Sun et al (9) used surface lenticule transplantation combined with corneal collagen cross-linking to treat patients with advanced keratoconus and thin corneas. The postoperative surface lenticules were well-adhered, with increased corneal thickness, and a significant reduction of irregular astigmatism. Furthermore, the mean keratometry (K) value, steep K value and maximal postoperative surface height value stabilised from the third month. Li et al (19) reported a case of corneal dilatation after laser-assisted in situ keratomileusis (LASIK). SMILE allogeneic lenticule lamellar transplantation was performed first, followed by corneal collagen cross-linking surgery 4 months postoperatively. Follow-up was maintained for 30 months. Therefore, the corneal thickness increased and the corneal morphology stabilised. Previous studies have collectively demonstrated the safety and efficacy of corneal stromal lenticule implantation combined with corneal collagen cross-linking for the treatment of keratoconus.

However, the process of effectively controlling the further development of keratoconus can lead to a further increase in corneal curvature in patients with the disease, thereby resulting in difficulty in postoperative refractive reconstruction. For instance, Zhao et al (7) used surface lenticule implantation combined with corneal collagen cross-linking to treat a patient with advanced keratoconus who could not tolerate an RGP contact lens. Preoperatively, the steep K was 62.7 D and the average K was 55.4 D. At three years postoperatively, the steep K was 63.8 D, with an average K value of 61.9 D. Wang et al (8) reported that surface lenticule implantation combined with cross-linking for thin corneal cone treatment resulted in a corneal curvature that was significantly higher than that at 1 and 3 months after surgery. Li et al (19) reported that in patients with corneal dilatation after LASIK, the preoperative flat keratometry (K1), steep keratometry (K2) and maximum keratometry (Kmax) values were 57.5, 67.2 and 74.9 D, respectively. Simultaneously, the postoperative K1, K2 and Kmax values were 59.7, 71.7 and 82.7 D, respectively. Sun et al (9) reported that preoperative K1 was 55.26 D, K2 was 64.80 D and the mean K value was 59.65 D. One year after surgery, the K1, K2 and mean K values were 62.44, 64.04 and 63.23 D, respectively. These values were significantly higher than the preoperative values. In a recent domestic study, Gao et al (20) used parallel lenticule row corneal transplantation to avoid these problems. Furthermore, a statistically significant decrease in anterior central corneal elevation and an increase in central corneal thickness were observed in the postoperative period. However, the scarcity of corneal sources and shortage of donor sources for corneal transplantation have not changed for a long time (21). The corneal stromal lenticule is an anterior layer of tissue in the central region of the corneal stroma. It is composed of collagen fibres arranged in an orderly fashion, and its normal anatomical structure and physiological functions are essential for maintaining corneal transparency and biomechanics. The excimer laser can cut corneal tissue with high precision without affecting tissues outside the cut area. Therefore, this approach is considered safe (22). In the present study, an excimer laser was used to cut the corneal stromal lenticule, which was either parallel or concave.

In the present study, an excimer laser was used to cut three groups of lenticules at ratios of 1:1, 1:1.5 and 1:2. The optical zone was 4 mm, and the thickness at 1.5 mm from the centre was within the cutting range. Furthermore, a thickness of 2 mm from the centre represents the boundary of the cutting zone, with the lenticule's centre at the centre of cutting. When the three groups were compared, the differences between the ctc and 1.5 tc among the three groups were caused by the different cutting ratios. No differences were observed in the 2tc and 2.5 tc of the three groups. This finding indicates that thicknesses of 2 and 2.5 mm were probably not affected by cutting. Because all other conditions of the three groups were consistent except for the different cutting ratios, 2tc and 2.5tc were probably only caused by dehydration. No difference in ct-2t was observed before laser plastination in the three groups because ct-2t was affected by the diopters. No differences were observed in the refraction of the lenticules incorporated into any of the three groups. However, a significant difference in ct-2t was observed after laser plastination. One group had a ct-2t of 38 (IQR: 28, 53.5) µm after laser plasticity, with a distinct convex lenticule at the centre. The second group had a ct-2t of 6 (IQR, -3, 15.5) µm after laser plasticity, which was still a convex lenticule in the centre but was already very close to a parallel lenticule compared with the two other groups. The third group had a ct-2t of -10 (IQR: -16.5, -5) µm after laser plasticity, with a distinct concave lenticule at the centre. This may be because the amount of tissue ablation is affected by the corneal stromal lenticule, which swells because of in vitro water absorption (23). This finding shows that excimer cutting changed the morphology of the centre of the stromal lenticule. Given the water-absorbing swelling of the stromal lenticule in vitro, a 1:1.5 ratio of excimer cutting can be used to obtain a stromal lenticule with a centre close to a parallel lenticule. Similarly, a 1:2 excimer cutting ratio can be used to obtain a stromal lenticule with a concave lenticule at the centre. We hypothesize that this technology can also customize the corneal stromal lenticule according to the different needs of patients and then reuse it, thus transforming the traditional corneal laser surgery from the ‘subtraction’ mode of ‘thinning and weakening’ to the ‘addition’ mode of ‘thickening and strengthening’. Additionally, we hypothesize that this transformation not only provides a new treatment approach for patients with thin corneal refractive errors, but also opens up new possibilities for the treatment of corneal diseases. Our experimental results indicated that the use of excimer laser-plasticised corneal stromal lenticules for keratoconus treatment is highly conducive to refractive reconstruction because it avoids excessive postoperative curvature while adding thickness to the conical cornea.

However, this study still has certain limitations. The current research is only confined to in vitro experiments of corneal stromal lenticules and has not yet conducted in-depth exploration of the series of changes after their implantation into the recipient's capsular bag. Whether the corneal stromal lenticules, after being shaped by excimer laser, can achieve the ideal refractive correction effect, effectively increase the biomechanical strength of the cornea and their long-term stability and biocompatibility in the body all need to be evaluated through more clinical experiments and long-term follow-ups. Future research can further study the refractive effect and biomechanical changes of corneal stromal lenticules after implantation through animal models or clinical trials; optimize the cutting parameters by comparing the effects of different cutting ratios on the microstructure and biomechanical properties of corneal stromal lenticule; and conduct a comprehensive assessment of the long-term performance of corneal stromal lenticules in the body by combining advanced imaging techniques and biomechanical analysis methods to ensure their safety and effectiveness. These studies are expected to further improve the corneal stromal lenticule implantation technique and provide more reliable and efficient treatment options for refractive and corneal diseases.

 Acknowledgements

Not applicable.

 Availability of data and materials

The data generated in the present study may be requested from the corresponding author.

 Authors' contributions

YL contributed to the study conception and design. JH, SL, SY, XL and XW acquired and interpreted study data. XW conducted the statistical analysis and drafted the manuscript. YL and JH provided critical manuscript revisions and administrative, technical support. YL supervised the study. XW and YL checked and confirmed the authenticity of the raw data. All authors have read and approved the final version of the manuscript.

 Ethics approval and consent to participate

The study protocol conformed to the tenets of Declaration of Helsinki and was approved by the Human Ethics Committee of Jinan Mingshui Eye Hospital (approval no. Ref. Ethics/2024/004). Informed consent was obtained in writing from all adult participants and the guardians of juvenile participants.

 Patient consent for publication

Not applicable.

 Competing interests

The authors declare that they have no competing interests.

 References AkimotoKTsuichiharaSTakamatsuTSogaKYokotaHItoMGotodaNTakemuraHEvaluation of laser-induced plasma ablation focusing on the difference in pulse durationConf Proc IEEE Eng Med Biol Soc20196987699020193194744610.1109/EMBC.2019.8857085 ReinsteinDZArcherTJRandlemanJBMathematical model to compare the relative tensile strength of the cornea after PRK,LASIK, and small incision lenticule extractionJ Refract Surg2945446020132382022710.3928/1081597X-20130617-03 SunLYaoPLiMShenYZhaoJZhouXThe safety and predictability of implanting autologous lenticule obtained by SMILE for hyperopiaJ Refract Surg3137437920152604670310.3928/1081597X-20150521-03 DongYHouJZhangJLeiYYangXSunFEpithelial thickness remodeling after small incision lenticule intrastromal keratoplasty in correcting hyperopia measured by RTVue OCTBMC Ophthalmol241320243819138110.1186/s12886-023-03272-x WuFJinXXuYYangYTreatment of corneal perforation with lenticules from small incision lenticule extraction surgery: A preliminary study of 6 patientsCornea3465866320152581171810.1097/ICO.0000000000000397 JiangYLiYLiuXWXuJA novel tectonic keratoplasty with femtosecond laser intrastromal lenticule for corneal ulcer and perforationChin Med J (Engl)1291817182120162745323110.4103/0366-6999.186639 ZhaoJShangJZhaoYFuDZhangXZengLXuHZhouXEpikeratophakia using small-incision lenticule extraction lenticule addition combined with corneal crosslinking for keratoconusJ Cataract Refract Surg451191119420193127277510.1016/j.jcrs.2019.03.010 WangKNFuMJZhaoJJWangYCWangJHZhangHRWangRCorneal surface mirror (stromal lens) implantation combined with corneal collagen cross-linking for the treatment of keratoconus: A case reportJ Clin Ophthalmol305525532022 SunXShenDCaiJZhangCNWeiWA case of keratoconus treated by femtosecond laser assisted implantation of corneal allogenic matrix lens combined with corneal collagen crosslinkingChin J Optom Ophthalmol Vis Sci244724742022 FerrariGRamaPThe keratoconus enigma: A review with emphasis on pathogenesisOcul Surf1836337320203223434210.1016/j.jtos.2020.03.006 WollensakGSpoerlESeilerTRiboflavin/ultraviolet-a-induced collagen crosslinking for the treatment of keratoconusAm J Ophthalmol13562062720031271906810.1016/s0002-9394(02)02220-1 PadmanabhanPlsheikhAKeratoconus: A biomechanical perspectiveCurr Eye Res4812112920233574688810.1080/02713683.2022.2088798 WollensakGSpörlEReberFPillunatLFunkRCorneal endothelial cytotoxicity of riboflavin/UVA treatment in vitroOphthalmic Res3532432820031468842210.1159/000074071 MatthyssenSVan den BogerdBDhubhghaillSNKompenCZakariaNCorneal regeneration: A review of stromal replacementsActa Biomater69314120182937460010.1016/j.actbio.2018.01.023 FasoloAGalzignatoAPedrottiEChieregoCCozziniTBonacciEMarchiniGFemtosecond laser-assisted implantation of corneal stroma lenticule for keratoconusInt Ophthalmol411949195720213362565110.1007/s10792-021-01739-8 SunXZhangHShanMDongYZhangLChenLWangYComprehensive transcriptome analysis of patients with keratoconus highlights the regulation of immune responses and inflammatory processesFront Genet1378270920223528182610.3389/fgene.2022.782709 ShahSUGritzDCApplication of the femtosecond laser LASIK microkeratome in eye bankingCurr Opin Ophthalmol2325726320122254347910.1097/ICU.0b013e3283541c76 ReinsteinDZArcherTJGobbeMSmall incision lenticule extraction (SMILE) history, fundamentals of a new refractive surgery technique and clinical outcomesEye Vis (Lond)1320142660535010.1186/s40662-014-0003-1 LiMYangDZhaoFHanTLiMZhouXNiKThirty-month results after the treatment of post-LASIK ectasia with allogenic lenticule addition and corneal cross-linking: A case reportBMC Ophthalmol1829420183041986610.1186/s12886-018-0967-z GaoHLiuMLiNChenTQiXXieLShiWFemtosecond laser-assisted minimally invasive lamellar keratoplasty for the treatment of advanced keratoconusClin Exp Ophthalmol5029430220223506133110.1111/ceo.14047 GainPJullienneRHeZAldossaryMAcquartSCognasseFThuretGGlobal survey of corneal transplantation and eye bankingJAMA Ophthalmol13416717320162663303510.1001/jamaophthalmol.2015.4776 LaurentJMSchallhornSCSpigelmireJRTanzerDJStability of the laser in situ keratomileusis corneal flap in rabbit eyesJ Cataract Refract Surg321046105120061681406910.1016/j.jcrs.2006.02.038 WangQRaoJZhangMZhouLChenXMaYGuoHGuJWangYZhouQSMILE-derived corneal stromal lenticule: Experimental study as a corneal repair material and drug carrier. Cornea: Jan 21, 2025 (Epub ahead of print).

Comparison before and after shaping. Optical coherence tomography scans before shaping (top) and after shaping (bottom). (A) The 1:1 excimer cutting based on the equivalent spherical lenticule of the lenticule itself. The comparison images before and after the cutting process are presented. (B) The 1:1.5 excimer cutting based on the equivalent spherical lenticule of the lenticule itself. the comparison images before and after the cutting process are presented. (C) The 1:2 excimer cutting based on the equivalent spherical lenticule of the lenticule itself. the comparison images before and after the cutting process are presented.

Basic information statistics of patients before the operation.

Parameter Total (n=111) Group I (n=37) Group II (n=37) Group III (n=37) H-value P-value
Age, years 22 (19, 25) 22 (21, 23) 20 (18, 23) 20 (20.5, 27.5) 5.342 0.069
Sex         1.510 0.470
     Male 60 (54.1) 18 (48.6) 19 (51.4) 23 (62.2)    
     Female 51 (45.9) 19 (51.4) 18 (48.6) 14 (37.8)    
Diopters -6.75 (-7.00, -6.38) -6.88 (-7.25, -6.57) -6.75 (-7.00, -6.44) -6.5 (-7.00, -6.07) 5.265 0.072
Spherical diopters -6.5 (-6.75, -6.00) -6.75 (-7.00, -6.25) -6.37 (-6.75, -6.06) -6.25 (-6.75, -5.75) 5.595 0.061
Cylindrical diopters -0.5 (-0.75, -0.25) -0.50 (-0.75, -0.25) -0.50 (-0.75, -0.25) -0.50 (-0.75, -0.25) 2.075 0.354

Values are expressed as the median (interquartile range) or n (%).

Comparison of pre-shaping thickness among the three groups and between two groups.

Parameter Group I, µm Group II, µm Group III, µm F/H value P-value
Center [M (P25, P75)] 247 (225.5, 257) 236 (216, 245) 243 (223.5, 253.5) 4.832 0.890
1.5 mm [M (P25, P75)] 205 (184, 220) 189 (180, 203) 197 (184.5, 213.5) 5.054 0.080
2 mm (x̄ ± SD) 173.162±23.367 162.054±18.824 165.622±16.914 3.009 0.053
2.5 mm [M (P25, P75)] 128 (118, 142) 120 (112, 130) 120 (111, 134) 5.086 0.079
ct-2t [M (P25, P75)] 72 (60, 80.5) 69 (61.5, 80.5) 72 (62, 83) 0.663 0.718

Center, the thickness in the center; 1.5 mm, the thickness at a distance of 1.5 mm from the center; 2 mm, the thickness at a distance of 2 mm from the center; 2.5 mm, the thickness at a distance of 2.5 mm from the center; ct-2t, lenticule concavity was expressed as the difference between the central thickness and thickness at 2 mm from the centre. M (P25, P75), median (25th percentile, 75th percentile).

Comparison of post-shaping thickness among the three groups and between two groups.

Considerations Group I Group II Group III F/H value P-value a b c
ctc, µm [M (P25, P75)] 75 (66, 84) 111 (100, 124) 138 (128, 147) 82.082 #x003C;0.001 #x003C;0.001 #x003C;0.001 #x003C;0.001
1.5tc, µm [M (P25, P75)] 54 (47.5, 63.5) 73 (62, 86) 88 (81, 94.5) 51.623 #x003C;0.001 #x003C;0.001 #x003C;0.001 #x003C;0.001
2tc, µm (x̄ ± SD) 48.351±18.662 46.784±14.675 53.162±12.518 1.702 0.187      
2.5tc, µm [M (P25, P75)] 36 (32, 42) 41 (35.5, 53.5) 39 (34, 50) 5.147 0.076      
ct-2t, µm [M (P25, P75)] 38 (28, 53.5) 6 (-3, 15.5) -10 (-16.5, -5) 87.169 #x003C;0.001 #x003C;0.001 #x003C;0.001 #x003C;0.001
T, min [M (P25, P75)] 3.27 (2.67, 4.75) 4.1 (2.94, 4.5) 3.69 (2.51, 4.35) 3.071 0.215      

a, comparison between Group I and Group II; b, comparison between Group I and Group III; c, comparison between Group II and Group III. The change in central thickness was represented by the ctc. The thickness changes at 1.5, 2.0 and 2.5 mm from the centre are denoted as 1.5tc, 2tc and 2.5tc, respectively. ct-2t, lenticule concavity was expressed as the difference between the central thickness and thickness at 2 mm from the centre. T, the interval time between pre- and post-cutting measurements. M (P25, P75), median (25th percentile, 75th percentile).