Refractive lenticule extraction is becoming the procedure of choice for the management of myopia and myopic astigmatism owing to its precision, biomechanical stability, and better ocular surface It has similar safety, efficacy, and predictability as femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and is associated with better patient satisfaction The conventional technique of small incision lenticule extraction (SMILE) involves docking, femtosecond laser application, lenticule dissection from the surrounding stroma, and extraction It has a steep learning curve compared to conventional flap-based corneal ablative procedures, and the surgical technique may be challenging especially for a novice surgeon As SMILE is gaining worldwide acceptance among refractive surgeons, different modifications of the surgical technique have been described to ease the process of lenticule extraction and minimize complications Good patient selection is essential to ensure optimal patient satisfaction, and novice surgeons should avoid cases with low myopia (thin refractive lenticules), difficult orbital anatomy, high astigmatism, or uncooperative, anxious patients to minimize complications A comprehensive MEDLINE search was performed using "small incision lenticule extraction," "SMILE," and "refractive lenticule extraction" as keywords, and we herein review the patient selection for SMILE and various surgical techniques of SMILE with their pros and cons With increasing surgeon experience, a standard technique is expected to evolve that may be performed in all types of cases with optimal outcomes and minimal adverse effects

/pdf/small-incision-lenticule-extraction-smile-techniques-patient-4gfp9vusjz.pdf

Small incision lenticule extraction (SMILE) techniques: patient selection and perspectives.

Enhancement of the skin-protective activities of Centella asiatica L. Urban by a nano-encapsulation process.

Purpose: The objective of this study is to evaluate the in vivo corneal biomechanical response to three laser refractive surgeries. Methods: Two hundred and twenty-seven patients who submitted to transepithelial photorefractive keratectomy (tPRK), femtosecond laser-assisted in-situ keratomileusis (FS-LASIK), or small-incision lenticule extraction (SMILE) were included in this study. All cases were examined with the Corvis ST preoperatively (up to 3 months) and postoperatively at 1, 3, and 6 months, and the differences in the main device parameters were assessed. The three groups were matched in age, gender ratio, corneal thickness, refractive error corrections, optical zone diameter, and intraocular pressure. They were also matched in the preoperative biomechanical metrics provided by the Corvis ST including stiffness parameter at first applanation (SP-A1), integrated inverse radius (IIR), deformation amplitude (DA), and deformation amplitude 2 mm away from apex and the apical deformation (DARatio2mm). Results: The results demonstrated a significant decrease post-operation in SP-A1 and significant increases in IIR, DA, and DARatio2mm (p < 0.05), all of which indicated reductions in overall corneal stiffness. Inter-procedure comparisons provided evidence that the smallest overall stiffness reduction was in the tPRK group, followed by the SMILE, and then the FS-LASIK group (p < 0.05). These results remained valid after correction for the change in CCT between pre and 6 months post-operation and for the percentage tissue altered. In all three surgery groups, higher degrees of refractive correction resulted in larger overall stiffness losses based on most of the biomechanical metrics. Conclusion: The corneal biomechanical response to the three surgery procedures varied significantly. With similar corneal thickness loss, the reductions in overall corneal stiffness were the highest in FS-LASIK and the lowest in tPRK.

/pdf/biomechanical-effects-of-tprk-fs-lasik-and-smile-on-the-3f7bk0q1.pdf

Biomechanical Effects of tPRK, FS-LASIK, and SMILE on the Cornea

Small-incision lenticule extraction (SMILE) is an effective and safe procedure for the correction of myopia due to minimally invasive and noncorneal flap surgery. However, the SMILE procedure has certain requirements for corneal cap thickness, attempted refractive correction, residual stromal bed thickness, and optical zone diameter, which sometimes make surgeons hesitant to choose SMILE or other refractive surgeries. The requirements limit its use in patients with high myopia. The purpose of this review was to find the optimal parameters of SMILE through discussing the best optical zone for high myopic patients, the visual quality of different optical zones, the choice of corneal cap thickness, and their effects on corneal biomechanical parameters, so surgeons can provide reference recommendations for patients with high myopia in choosing a reasonable and safe procedure.

The best optical zone for small-incision lenticule extraction in high myopic patients.

PURPOSE To evaluate the impact of cap thickness for small incision lenticule extraction (SMILE) on changes in corneal curvature and biomechanics. METHODS One hundred eyes (50 patients) were enrolled in this prospective contralateral eye study. The difference in manifest refraction spherical equivalent (MRSE) in the same patient was less than 0.50 diopters. SMILE was performed with a randomized cap thickness of 110 µm in one eye and 140 µm in the other eye. MRSE, uncorrected distance visual acuity (UDVA), and corneal curvature and biomechanics were evaluated. The anterior and posterior surfaces of the corneal curvature (mean keratometry [Km] values 2, 4, and 6 mm from the pupil center) were measured by Pentacam HR (Oculus Optikgerate, Wetzlar, Germany) and changes in corneal biomechanics at 6 months postoperatively by Scheimpflug technology. RESULTS There was no significant between-group difference in UDVA or MRSE postoperatively. Postoperative changes in Km at the anterior surface (ΔKm-ant) in the 4-mm zone were significantly higher in the 110-µm group than in the 140-µm group at 1 day and 1, 3, and 6 months postoperatively (P = .043, .045, .003, and .049, respectively); at 3 months, the ΔKm-ant in the 6-mm zone was higher in the 110-µm group (P = .035). The changes in second appla-nation time, deformation amplitude, and integrated radius were significantly less in the 110-µm group (P = .031, .049, and < .001, respectively). CONCLUSIONS A thicker corneal cap caused less change in anterior surface curvature after SMILE for moderate or low myopia, with no significant difference in UDVA and MRSE. [J Refract Surg. 2020;36(2):82-88.].

Influence of Cap Thickness on Corneal Curvature and Corneal Biomechanics After SMILE: A Prospective, Contralateral Eye Study

Observe the influence of femtosecond laser cutting on corneal biomechanics during small-incision lenticule extraction (SMILE) or femtosecond-assisted laser in situ keratomileusis (FS-LASIK) and assess the biomechanical changes following the operation. Prospective, non-randomized study. A total of 80 eyes from 80 patients were treated with either SMILE or FS-LASIK. Parameters of inverse concave radius, deformation amplitude ratio 2 mm or 1 mm (DA ratio 2 mm or 1 mm), highest concavity radius (HC radius), biomechanically corrected intraocular pressure (bIOP), and central corneal thickness (CCT) measured by Corvis ST II were recorded at 1 day preoperatively, immediately after the lenticule or flap creation, during subsequent lenticule extraction or excimer laser ablation, and during follow-up at 1 week, 1 month and 3 months postoperatively. After lenticule creation, the DA ratio 2 mm or 1 mm was bigger (p   0.05) after operation. The variations in bIOP (ΔbIOP) after operation were significantly less than those in Δnon-contact IOP (p < 0.001) in two groups. Femtosecond laser cutting during lenticule creation has a greater impact on corneal biomechanics than flap creation. Both the femtosecond laser cutting and removal of tissue degrade corneal biomechanics; however, these effects may be predominantly a result of tissue removal. SMILE and FS-LASIK have no differences in corneal biomechanics when the same CCT is consumed. bIOP is more reliable after the operation, but further study is essential.

Changes in corneal biomechanics during small-incision lenticule extraction (SMILE) and femtosecond-assisted laser in situ keratomileusis (FS-LASIK)

Purpose. To evaluate the effect of corneal cap thickness on visual acuity and corneal biomechanics in small incision lenticule extraction (SMILE) for the treatment of myopia. Methods. Forty eyes of 20 patients undergoing SMILE for the treatment of myopia were enrolled in this prospective controlled study. The patients with 510 μm–560 μm central corneal thickness (CCT) and a refractive spherical equivalent of −3.00 D to −8.00 D were included. It was designed randomly to undergo SMILE with a 110 μm cap thickness in one eye and 150 μm cap thickness in the other. Ophthalmic examinations included best-corrected and uncorrected visual acuity (UCVA); refractive status, contrast sensitivity, and objective visual quality were evaluated at 2 h, 4 h, and 24 h postoperatively; while at 3 months after the procedure, corrected intraocular pressure (IOP), higher order aberrations (HOAs), and morphologic modifications of corneal architecture of both eyes were assessed. Results. Compared with the 150 μm group, the incidence of OBL was significantly higher in the 110 μm cap thickness group ( ), and UCVA, Strehl ratio (SR), objective scatter index (OSI), modulation transfer function (MTF) cutoff frequency, and photopic and scotopic contrast sensitivity at medium spatial frequency were all significantly better in 110 μm group at 2 h and 24 h postoperatively ( ). Corneal spherical aberration and corrected IOP by Corvis ST were significantly higher in the 110 μm group at 3 months postoperatively ( ). No statistically significant differences were found in manifest refraction, UCVA, SR, OSI, MTF cutoff, and mesopic and photopic contrast sensitivity at low frequency, photopic contrast sensitivity at high frequency, endothelial density, corneal coma, and total HOAs at 3 months after the procedure. No visual decline was found in the patients in this study. Conclusions. Both 110 μm and 150 μm cap thickness in SMILE were safe and effective for treatment of myopia. A 110 μm cap thickness demonstrated better visual outcomes during early and late postoperative periods with higher corneal spherical aberration and corrected IOP at 3 months postoperatively. This trial is registered with ChiCTR-IOR-17013369 .

/pdf/corneal-cap-thickness-and-its-effect-on-visual-acuity-and-1m2w8zi3dp.pdf

Corneal Cap Thickness and Its Effect on Visual Acuity and Corneal Biomechanics in Eyes Undergoing Small Incision Lenticule Extraction.

Visual outcomes after balanced salt solution infiltration during lenticule separation in small-incision lenticule extraction for myopic astigmatism.

PURPOSE Use immunohistochemical staining and Western Blot analysis to observe and compare the accurate dynamic changes of type I, III, V, VI collagen in the wound healing processes of the rabbit cornea which underwent LASEK or PRK to investigate the possible mechanism of corneal haze and myopic regression. METHODS New Zealand White rabbits were divided into 8 groups: normal control group (n=6), 1 day, 7 days, 1, 3, 4, 5 and 6 month groups (n=14). Every rabbit underwent LASEK in one eye while the other one with PRK. We use immunohistochemical staining and Western Blot analysis to compare the wound healing process of dynamic change of the type I, III, V and VI collagen in rabbit cornea of every time point. The results were analysised with data analysis software. RESULT Immunohistochemical staining and Western Blot analysis showed that after LASEK, the cornea wound healing with type I and III collagen were much faster than PRK, and the wound response was also much weaker. Whereas for type V and VI collagen, their dynamic changes were resemble between LASEK and PRK, they both reached the peak value after 3 months since the surgery, but LASEK group returned to normal earlier than PRK. The value of these two types of collagen after PRK were higher than LASEK. The changes of these four types of collagen may offer us at least partial explaination to the difference between formation between corneal haze and refractive regression. CONCLUSIONS There were significant differences between LASEK and PRK on type I, III, V and VI collagens or the time of reacting, reaching apex and returning to normal . LASEK had slighter intensity of reaction. The results indicate that there is excessive aggradation of collagens after PRK, it may be the histological foundation of obvious haze and myopia regression.

[Western Blot analysis of type I, III, V, VI collagen after laser epithelial keratomileusis and photorefractive keratectomy in cornea of rabbits].

Objective
To investigate the effectiveness of topography-guided FS-LASIK in treating asymmetrical corneal astigmatism.


Methods
Forty-one patients(72 eyes)were prospectively enrolled in the study and were treated with FS-LASIK at the Daping Hospital. They were randomly divided into a T-CAT group(37 eyes)that underwent topography-guided FS-LASIK and a WF-optimized group(35 eyes)that underwent wavefront-optimized FS-LASIK. Preoperative and postoperative best corrected visual acuity(BCVA), uncorrected visual acuity(UCVA), vertical coma(C7), horizontal coma(C8)and total third order coma were measured and the differences between the two groups were compared with paired t tests or independent t tests.


Results
The postoperative UCVAs of the T-CAT group and WF-optimized group were 5.03±0.05 and 5.00±0.05, respectively, and the difference was statistically significant(t=3.00, P<0.01). Postoperative vertical coma and total third order coma were significantly reduced in the T-CAT group(t=14.801, 8.429, respectively, both P<0.01), and were significantly lower than that for the WF-optimized group(t=-7.799,-6.737, P<0.05).


Conclusion
Topography-guided FS-LASIK can be an effective treatment for patients with asymmetrical corneal astigmatism. Treatment using this surgical technique significantly improved the visual acuity of patients.


Key words: 
Topography; Keratomileusis, laser in situ; Femtosecond laser; Asymmetrical astigmatism; Wavefront aberration

The effectiveness of topography-guided FS-LASIK in treating asymmetric corneal astigmatism

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