Small incision lenticule extraction (SMILE) and femtosecond laser LASIK: comparison of corneal wound healing and inflammation

Development of low laser energy levels in small-incision lenticule extraction: clinical results, black area, and ultrastructural evaluation

PURPOSE

To evaluate the outcomes of 4 low laser energy levels after small-incision lenticule extraction (SMILE) surgery.

SETTING

Zhongshan Ophthalmic Center, Guangzhou, China.

DESIGN

Prospective randomized clinical trial.

METHODS

This study evaluated consecutive patients who had SMILE to correct myopia or myopia with astigmatism. Eyes were placed into groups based on the laser energy used during surgery (ie, 105 nJ, 110 nJ, 115 nJ, or 120 nJ). All patients had a thorough ophthalmic examination preoperative and at 4 timepoints over 3 months postoperatively. Black areas and surface regularity of the extracted lenticules were observed and evaluated qualitatively and quantitatively.

RESULTS

The study comprised 124 eyes of 62 patients (40 women, 22 men), with 31 eyes in each laser energy group. The incidence of black areas was 45.16% (14 of 31 eyes), 12.90% (4 of 31 eyes), 16.13% (5 of 31 eyes), and 12.90% (4 of 31 eyes) for 105 nJ, 110 nJ, 115 nJ, and 120 nJ, respectively. The mean time for lenticule creation was the longest in the 105 nJ group (P = .015). The greatest increase in corneal thickness postoperatively occurred with 105 nJ (P < .05). Regression was highest in the 105 nJ group at 3 months (P < .01). However, corneal horizontal coma (C8) was lowest in the 105 nJ group at 1 week (P = .032). The lenticular surface in the 110 nJ group was the smoothest (P = .011). All contrast sensitivity values varied with time and recovered to preoperative levels by 1 week or 1 month. In all eyes, the uncorrected distance visual acuity and corrected distance visual acuity were good, with no statistically significant differences between the 4 energy groups.

CONCLUSIONS

The 105 nJ group, in which the lowest energy was used, had the highest risk for black areas, serious postoperative corneal edema, and a significant healing response.

Early biological responses in ocular tissue after SMILE and LASIK surgery

We studied the early protein profile in the ocular tissue extracted after LASIK and SMILE surgery. SMILE and LASIK was performed in contralateral eyes and stromal tissue samples were collected from 10 eyes of 5 donors. The stromal tissue samples were analyzed using label free quantification approach and ITRAQ labelling approach in LC-MS/MS. Combined functional analysis revealed many differentially expressed proteins which were involved in important biological processes. About 117 unique differentially expressed proteins were identified using two different proteomic approaches. Collagens, proteoglycans, corneal crystallins were enriched and showed differential expression in SMILE and LASIK as compared to the non-surgical control. Apart from these, 14-3-3 class of proteins, Lysozyme (LYZ), Macrophage Migratory Inhibitory Factor protein (MIF), Pigment Epithelial Derived Factor (PEDF) were differentially expressed when compared between LASIK and SMILE. Peroxiredoxin 1 (PRDX1) expression was found to be reduced in LASIK as compared to SMILE. The expression of Lysozyme C and Macrophage Migratory Inhibitory Factor inflammatory response was found to be less in SMILE as compared to LASIK. Western blot validation of specific markers such as Collagen IV (COL4), Keratocan (KERA), Lumican (LUM), Aldehyde dehydrogenase 3 A1 (ALDH3A1), Lysozyme C (LYZC) confirmed the differences in the protein levels observed in SMILE and LASIK operated tissues as compared to non-surgical controls. In conclusion, this study revealed the early molecular changes occurring in the cornea resulting from these two surgical procedures which may have implications on managing post-operative complications.

Dry Eyes After SMILE

Dry eyes is one of the most common complications after laser vision correction. Small incision lenticule extraction (SMILE) is a flapless procedure with a smaller corneal incision, less corneal nerves are transected during, making it theoretically less prone to dry eyes. Both SMILE and femtosecond-laser-assisted in situ keratomileusis (FS-LASIK) induce a transient worsening in dry eye parameters, but there is evidence showing that SMILE holds promises to have fewer negative impacts on the ocular surface parameters and allow an earlier recovery. SMILE-treated eyes may also have shown less corneal denervation and better corneal sensitivity compared with FS-LASIK eyes. This review summarizes the mechanisms of dry eyes after laser vision correction, the short-term (≤6 months) and long-term (>6 months) results in changes to dry eyes signs and symptoms, and corneal sensitivity of SMILE, as compared with FS-LASIK. Limitation of the studies and reasons accounting for their discrepancies will be discussed. Future randomized controlled trials with standardized postoperative regime are needed for better evaluation of dry eyes after SMILE.

Presbyopia and the aging eye: Existing refractive approaches and their potential impact on dry eye signs and symptoms

Every part of the human body is subject to aging, including the eye. An increased prevalence of dry eye disease with age is widely acknowledged. Aging threatens ocular surface homeostasis, altering the normal functioning of the lacrimal functional unit and potentially leading to signs and symptoms of dry eye. Additional age-related processes take place within the crystalline lens, leading to presbyopia and cataractogenesis. Correction strategies for presbyopia and cataracts may directly or indirectly challenge the ocular surface. Contact lenses disturb the normal structure of the tear film and can interact negatively with the ocular surface, further deteriorating an already unbalanced tear film in presbyopes, however, newer contact lens designs can overcome some of these issues. Moreover, cataract and corneal refractive surgeries sever corneal nerves and disrupt the corneal epithelium and ocular surface, which can influence surgical outcomes and aggravate dryness symptoms in older age groups. This review summarises the current understanding of how the invasive nature of contact lens wear and cataract and refractive surgery influence signs and symptoms of ocular dryness in an aging population.

Fluctuation in straylight measurements during the visual recovery phase after small incision lenticule extraction

PURPOSE

To investigate the postoperative straylight changes during the visual recovery phase after small incision lenticule extraction (SMILE) and their association.

METHODS

Seventy consecutive eyes from 37 patients with a mean age of 30.92 ± 7.26 years and a mean preoperative spherical equivalent of -5.24 ± 1.90 dioptres undergoing myopic or myopic astigmatism SMILE correction were included in this prospective study. Patients were followed up at days 1, 3, 7, 14, 21 and 28 after standard SMILE. Straylight was measured using the C-Quant straylight meter (Oculus GmbH, Germany) preoperatively and at each postoperative visit.

RESULTS

Preoperatively, the mean straylight measurement was 1.16 ± 0.16. After SMILE, the mean straylight values were 1.12 ± 0.14 and 1.13 ± 0.13 at days 7 and 14, which were significantly reduced compared to preoperative values (p ≤ 0.028). Straylight returned to baseline by week 3 (p = 0.160) and remained stable onwards (p = 0.651). A lower ablation ratio was associated with less straylight level at days 1, 3, 14 and 21 (p ≤ 0.0497) in the multivariable regression model. Likewise, better visual acuity was associated with lower straylight at days 7, 14 and 28 postoperatively (p ≤ 0.038). A small proportion of eyes (range: 0-12.86%) had ≥0.30 log(s) increase in postoperative straylight within the first month after SMILE.

CONCLUSIONS

SMILE induced a temporary decrease in straylight. It gradually returned to the preoperative level, which could be related to a number of dynamic processes during corneal healing. In the small proportion of patients with an increase in straylight postoperatively, this can affect their visual recovery during the early postoperative period.

Functional Optical Zone and Centration Following SMILE and LASIK: A Prospective, Randomized, Contralateral Eye Study

PURPOSE

To compare centration and functional optical zone (FOZ) after small incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (LASIK).

METHODS

In this prospective, randomized, single-masked, paired-eyed, clinical trial, 70 patients received SMILE in one eye and LASIK in the other eye for myopia and myopic astigmatism. FOZ was calculated using custom software on 3-month postoperative refractive power maps (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany). Programmed treatment area was defined as the total area of the programmed OZ plus the transition zone. Centration was evaluated by the linear distance between FOZ centroid and the pupil center and the corneal apex.

RESULTS

The average preoperative spherical equivalent (-5.38 ± 1.65 vs -5.45 ± 1.61 diopters [D]), postoperative spherical equivalent (0.05 ± 0.39 vs 0.06 ± 0.39 D), uncorrected distance visual acuity (0.01 ± 0.13 vs 0.00 ± 0.08 logMAR), and corrected distance visual acuity (-0.07 ± 0.10 vs -0.07 ± 0.10 logMAR) were comparable in SMILE- and LASIK-treated eyes of the 60 patients with complete datasets (P > .419). Postoperative increase in spherical aberration was lower in SMILE than in LASIK (0.08 ± 0.16 vs 0.17 ± 0.18 µm, P = .002). The FOZ area was significantly larger in SMILE than in LASIK (30.25 ± 3.60 vs 29.21 ± 3.72 mm²), despite the smaller programmed OZ diameter (6.48 ± 0.08 vs 6.52 ± 0.11 mm) and smaller programmed treatment area (33.87 ± 0.81 vs 46.30 ± 2.61 mm², P < .037). Pupil centration (0.43 ± 0.21 vs 0.41 ± 0.22 mm) and apex centration (0.48 ± 0.24 vs 0.48 ± 0.22 mm) were comparable between SMILE and LASIK (P > .694).

CONCLUSIONS

SMILE created a larger FOZ than LASIK, despite the smaller programmed OZ. This may be due to a difference in the biomechanical response between the two procedures. Visual outcome and centration were comparable between SMILE and LASIK. [J Refract Surg. 2019;35(4):230-237.].

Postoperative Corneal Complications in Small Incision Lenticule Extraction: Long-Term Study

PURPOSE

To investigate the incidence and clinical results of corneal complications after small incision lenticule extraction (SMILE).

METHODS

A retrospective cohort study including 3,223 patients (6,373 eyes) who were treated for myopia or myopic astigmatism was conducted. Postoperative corneal complications were recorded. Postoperative follow-up visits were scheduled on days 1 and 7 and months 1, 3, 6, and 12.

RESULTS

Of the 6,373 cases, 432 eyes (6.8%) developed at least one corneal complication postoperatively. These included punctate epithelial erosions (3.26%), diffuse lamellar keratitis (DLK) (2.17%), corneal infiltrates (0.39%), interface debris/secretion (0.30%), interface haze (0.17%), interface foreign body (0.24%), corneal striae (0.14%), corneal edema (0.09%), and epithelial ingrowth (0.02%). Of cases with corneal complications, 308 (71.3%) had an uncorrected distance visual acuity (UDVA) of better than 20/25 and 49 (11.3%) eyes lost two or more lines of corrected distance visual acuity (CDVA) on the first day after surgery. By 3 months, only 2 eyes (0.9%) had lost two or more lines of CDVA. At 6 months, 1 eye (1.0%) did not achieve a UDVA of 20/25 as a result of stage 3 DLK, but achieved 20/20 by 1 year. The postoperative spherical equivalent in cases without complications was lower than that in cases with complications at 1 day and 1 and 3 months (P = .001, .011, and .001, respectively), but there was no statistical difference at 6 and 12 months.

CONCLUSIONS

In this large cohort study, a variety of corneal complications were noted after SMILE. Although some of these complications may temporarily affect visual recovery, most resolve with appropriate treatment. [J Refract Surg. 2019;35(3):146-152.].

Refractive surgery

Refractive surgery has evolved beyond laser refractive techniques over the past decade. Laser refractive surgery procedures (such as laser in-situ keratomileusis), surface ablation techniques (such as laser epithelial keratomileusis), and photorefractive keratectomy have now been established as fairly safe procedures that produce excellent visual outcomes for patients with low-to-moderate amounts of ametropia. Additionally, a broader selection of options are now available to treat a wider range of refractive errors. Small incision lenticule extraction uses a femtosecond laser to shape a refractive lenticule, which is removed through a small wound. The potential advantages of this procedure include greater tectonic strength and less dry eye. In the future, intracorneal implants could be used to treat hyperopia or presbyopia. Phakic intraocular implants and refractive lens exchange might be useful options in carefully selected patients for correcting high degrees of ametropia. Thus, physicians are now able to provide patients with the appropriate refractive corrective option based on the individual's risk-benefit profile.

CIRCLE Software for the Management of Retained Lenticule Tissue Following Complicated SMILE Surgery

PURPOSE

To describe the therapeutic use of CIRCLE software (Carl Zeiss Meditec, Jena, Germany) for the management of retained lenticule tissue after complicated small incision lenticule extraction (SMILE).

METHODS

Two patients were referred for consultation and treatment due to intraoperative complications during SMILE. In case 1, a black patch during laser delivery caused the lenticule to be torn irregularly from the undersurface during extraction and a sliver of it was retained in the pocket. Case 2 presented with false plane dissection and a completely retained lenticule on anterior segment optical coherence tomography. Both cases were managed using the CIRCLE software by converting the cap into a flap, thus making access to the interface possible.

RESULTS

In case 1, after lifting the flap a small sliver of tissue was found in the interface, which was dissected, following which a 20-µm phototherapeutic keratectomy was done to smooth the interface. In case 2, after lifting the flap the edge of the retained lenticule was identified by using an endoilluminator and the lenticule was separated and subsequently removed. Both cases showed significant improvement in uncorrected distance visual acuity, corrected distance visual acuity, and Objective Scatter Index score on day 1 after repair surgery.

CONCLUSIONS

CIRCLE software may be successfully used for managing retained lenticule tissue apart from performing enhancement after SMILE. [J Refract Surg. 2019;35(1):60-65.].

Comparison of changes in refractive error and corneal curvature following small-incision lenticule extraction and femtosecond laser-assisted in situ keratomileusis surgery

Purpose

To compare visual acuity, refractive error, corneal curvature, and the stability of these parameters during the early postoperative period following small-incision lenticule extraction (SMILE) and femtosecond laser-assisted in situ keratomileusis (FS-LASIK) surgery.

Methods

One hundred and five eyes and 110 eyes were enrolled in SMILE and FS-LASIK group, respectively. Uncorrected and best-corrected distance visual acuity (UCVA and BCVA), manifest refraction, corneal curvature, intraocular pressure, and slit-lamp examinations were performed preoperatively, 1 day, 1 week, 1 month, and 3 months postoperatively.

Results

No significant differences in postoperative UCVA or BCVA were observed between the SMILE and FS-LASIK groups at any time point. SMILE group had significant better postoperative spherical equivalent (SE) values than FS-LASIK group at 1 day, 1 week, and 1-month follow-up. However, there was no significant difference in postoperative SE values at 3-month follow-up. Significant differences in mean postoperative corneal curvature were observed during all follow-up examinations.

Conclusion

SMILE surgery was associated with more accurate postoperative refractive correction up to 1 month following surgery. SMILE surgery also resulted in less significant corneal curvature changes than FS-LASIK. Furthermore, FS-LASIK was associated with decreased stability of postoperative refractive error and corneal curvature relative to SMILE.

Clinical outcomes of small-incision lenticule extraction and femtosecond laser-assisted wavefront-guided laser in situ keratomileusis

Small-incision lenticule extraction and wavefront-guided femtosecond-assisted laser in situ keratomileusis (LASIK) provide good visual outcomes and an efficacious correction of myopia or myopic astigmatism with similar levels of safety. Some differences in predictability and the percentage of eyes gaining lines of corrected distance visual acuity are present. A higher level of coma is present after small-incision lenticule extraction, with no clear differences between techniques in spherical aberration. Better contrast sensitivity is achieved in the early postoperative period after wavefront-guided femtosecond laser-assisted LASIK, possibly because of less intrastromal light backscattering and Bowman layer microdistortions. Corneal sensitivity decreased less after small-incision lenticule extraction because of less severe decrease in subbasal nerve density, which has a significant effect on symptomatology and dry-eye tests (P < .05). Significant corneal biomechanical changes occurred after both techniques (P < .05), with no scientific evidence supporting the superiority of 1 technique over the other.

FINANCIAL DISCLOSURE

Dr. Piñero received an unrestricted educational grant from Abbott Medical Optics, Inc. Neither author has a financial or proprietary interest in any material or method mentioned.

Wound Healing, Inflammation, and Corneal Ultrastructure After SMILE and Femtosecond Laser-Assisted LASIK: A Human Ex Vivo Study

PURPOSE

To assess the wound healing, inflammation, and tissue ultrastructure in the human corneal stroma after small incision lenticule extraction (SMILE) and femtosecond laser-assisted LASIK (FS-LASIK).

METHODS

Sixteen corneoscleral discs of 16 human donors unsuitable for corneal transplantation were obtained from an eye bank. Eight eyes underwent SMILE with -5.00 diopters (D) of myopic correction; in 3 of them the lenticule was not extracted. Further 5 donor corneas were subjected to FS-LASIK with -5.00 D ablation, and 3 eyes served as the control group without surgical intervention. Postoperatively, specimens were incubated in organ culture medium for 72 hours before being subjected to immunofluorescence staining for CD11b, Ki67, fibronectin, terminal deoxynucleotidyl transferase-mediated dUTP-digoxigenin nick-end labelling assay, and high-magnification scanning electron microscopy.

RESULTS

Keratocyte apoptosis, keratocyte proliferation, and infiltration of immune cells were generally mild and comparable between FS-LASIK and SMILE (irrespective of surgical lenticule extraction). By staining for fibronectin, we observed a trend toward milder fibrotic response in the corneal stroma after SMILE than after FS-LASIK. On the contrary, scanning electron microscopy analysis revealed a smoother, more regular ultrastructural appearance of the residual corneal bed after FS-LASIK.

CONCLUSIONS

Corneal stromal wound healing after SMILE and FS-LASIK was virtually identical with respect to keratocyte proliferation and apoptosis in the human donor eye model. Although reactive fibrosis adjacent to the laser application site appeared less marked after SMILE, the stromal bed after LASIK exhibited a smoother surface texture. [J Refract Surg. 2018;34(6):393-399.].

Corneal remodeling and spatial profiles following small incision lenticule extraction

PURPOSE

To evaluate the three-dimensional corneal spatial profiles following small incision lenticule extraction (SMILE) based on corneal asphericity, thickness, and volume.

MATERIALS AND METHODS

Eighty-three eyes in 83 patients who underwent SMILE were examined before and 1 and 6 months after surgery. The asphericity of the anterior and posterior corneal surfaces was analyzed. Corneal volume (CV) was measured in corneal regions measuring 3.0 mm, 5.0 mm, and 7.0 mm in diameter. Mean corneal thickness (CT) values were acquired at the apex (0.0 mm) and in four concentric radial zones from the apex (with diameters of 2.0, 4.0, 6.0, and 8.0 mm).

RESULTS

The mean anterior Q value increased from - 0.32 preoperatively to 0.67 at 1 month and 0.62 at 6 months postoperatively. The mean posterior Q value decreased from - 0.30 preoperatively to - 0.26 at 1 month and to - 0.25 at 6 months postoperatively. The CV increased by 0.05 ± 0.06 mm³ (1.40%), 0.06 ± 0.11 mm³ (0.83%), and 0.09 ± 0.17 mm³ (0.73%) along the radial zones with respective diameters of 3.0 mm, 5.0 mm, and 7.0 mm. The CT increased by 6.02 ± 6.48 µm (1.36%) at the apex and then decreased with increasing distance from the center, i.e., to 5.52 ± 6.31 µm (1.20%) at 2.0 mm, 4.72 ± 6.55 µm (0.92%) at 4.0 mm, 4.47 ± 7.86 µm (0.75%) at 6.0 mm, and 4.86 ± 10.31 µm (0.70%) at 8.0 mm. No correlations were observed between changes in CV and CT and refractive fluctuation between 1 month and 6 months postoperatively.

CONCLUSIONS

The corneal profile displayed a less oblate shift on the anterior surface; however, the posterior surface showed a slight backward shift during the postoperative period. The CV and CT steadily increased after surgery and mainly within the operative zones. Refraction remained stable postoperatively and was not affected by the corneal remodeling.

Functional Optical Zone After Small-Incision Lenticule Extraction as Stratified by Attempted Correction and Optical Zone

PURPOSE

To compare the functional optical zone (OZ) with different levels of myopia and different OZ groups after small-incision lenticule extraction.

METHODS

This retrospective study included 249 patients (120 men) after small-incision lenticule extraction correction. We grouped participants according to attempted correction [low: spherical equivalent (SE) > -3.0 D; moderate: -6.0 D ≥ SE ≥ -3.0 D; high: SE ≥ -6.0 D] and planned functional optical zone (PFOZ) (OZ-1: PFOZ ≤ 6.3 mm; OZ-2: 6.3 mm < PFOZ ≤ 6.5; OZ-3: PFOZ > 6.5 mm), and we compared the achieved functional optical zone (AFOZ) and total corneal aberration, using Scheimpflug imaging, 1 month postoperatively. Correlations between corneal aberration and AFOZ were analyzed.

RESULTS

The AFOZ was smaller than the PFOZ in all 3 refraction groups (reduction: low, 0.78 ± 0.72 mm; moderate, 1.22 ± 0.60 mm; and high: 1.49 ± 0.58 mm, P < 0.001). There was no difference in the AFOZ among the 3 OZ groups. Total corneal aberration increased more in the high myopia group (total higher-order aberration, coma, and spherical aberration, P < 0.001), which also correlated with the AFOZ.

CONCLUSIONS

The discrepancy between the AFOZ and PFOZ increased with greater attempted correction. Attempted correction and AFOZ influence corneal aberration.

Three-year outcomes of small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for myopia and myopic astigmatism

Aims

To compare long-term clinical outcomes following small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for myopia and myopic astigmatism correction.

Methods

In this retrospective study, we enrolled a total of 101 patients (101 eyes) who underwent SMILE or FS-LASIK 3 years prior. Measured parameters included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction and corneal wavefront aberrations.

Results

No significant differences in patient characteristics were found between the two groups. At the 3-year follow-up, UDVA was better than or equal to 20/20 in 90% and 85% (p=0.540) of the eyes; the efficacy indexes were 1.05±0.19 and 1.01±0.21 in the SMILE and FS-LASIK groups, respectively (p=0.352). Safety indexes were 1.19±0.17 and 1.15±0.20 in the SMILE and FS-LASIK groups, respectively (p=0.307). Eighty per cent and 65% of eyes were within ±0.50 D of the attempted spherical equivalent correction after SMILE and FS-LASIK, respectively (p=0.164). Vector analysis revealed no significant differences in astigmatic correction between the two groups (p>0.05). Surgically induced spherical aberration was higher in the FS-LASIK group than in the SMILE group (p<0.001).

Conclusion

Long-term follow-up analysis suggested that both SMILE and FS-LASIK were safe and equally effective for myopic and astigmatic correction.

Comparison of the efficiency of femtoLASIK and ReLEx SMILE in terms of dioptric error reduction

BACKGROUND AND AIMS

Refractive eye surgery is a rapidly expanding field of ophthalmology and corneal surgery is undergoing constant development leading to less invasive technologies. The goal of this study was to compare the most common femtoLASIK surgery with the newer ReLEx SMILE surgery which is gentler to the cornea. The comparison was made in terms of dioptric error reduction.

METHODS

The studied cohort of patients consisted of two major groups: 30 patients who underwent femtoLASIK surgery and 30 who underwent ReLEx SMILE surgery. -30 patients, 60 eyes. All patients were aged 18-45 years with moderate myopia or astigmatism ranging from -3.25 to -6.0 spherical diopters and from 0 to -1.0 cylindrical diopters. In all, the best corrected visual acuity measured prior to surgery was 1.0. Pachymetry was not comparable because each surgical method was performed at a different time point and the introduction of an innovative method into practice led to a change in selection criteria.

RESULTS

During postsurgical check-ups, the ReLEx SMILE method (0.74) led to lower values of non-corrected visual acuity compared to the femtoLASIK method (0.88), (P<0.001). However, the results changed at the one-year post-surgery check-up, when ReLEX SMILE patients achieved non-corrected visual acuity of 0.97 compared to femtoLASIK patients, who scored 0.83, (P=0.007). Based on data analysis from the automatic refractometer, the average spherical diopters of the femtoLASIK (-0.32 D) were higher than those of the ReLEx SMILE (-0.07 D), (P<0.001). The results for the cylindrical diopters were also significant, (P=0.021). When we compared the spherical equivalent one year after surgery, the difference between methods was significant. The FemtoLASIK method resulted in an average SE -0.55 D compared to -0.09 D for the ReLEx SMILE method, (P<0.001).

CONCLUSION

This study showed that there was a significant difference in results between the two surgical methods of treatment of moderate myopia and astigmatism, in terms of regression of dioptric error, as well as in achievement and maintenance of visual acuity during the observed period. The ReLEx SMILE had better results.

Short-term Observation of Intraocular Scattering and Bowman's Layer Microdistortions After SMILE-CCL

PURPOSE

To investigate changes in intraocular scattering and Bowman's layer microdistortions after femtosecond laser small incision lenticule extraction using the continuous curvilinear lenticulerhexis technique (SMILE-CCL).

METHODS

In this prospective study, 93 eyes of 93 patients (44 women, 49 men) were treated with SMILE-CCL. Mean age was 26.09 ± 4.39 years and mean spherical equivalent was -6.31 ± 2.16 diopters. The Objective Scatter Index (OSI) was examined with an objective optical quality analysis system. Bowman's layer microdistortions in the central 4-mm optical zone were measured using Fourier-domain optical coherence tomography.

RESULTS

The mean OSI value increased from 0.67 preoperatively to 1.09 at 20 days, and then decreased to 0.84 at 3 months (P < .05). Microdistortions were observed in 62.37% of the eyes at 20 days and 48.39% at 3 months postoperatively (P < .05). The width of the microdistortions per meridian was 283.18 ± 197.19 μm at 20 days; this decreased to 156.00 ± 159.86 μm at 3 months (P < 0.05). Regression analysis models revealed that older age (b = 0.02, P = .03) and higher preoperative spherical equivalent (b = -0.09, P < .05) resulted in higher postoperative OSI values; no significant association was found between postoperative OSI values and microdistortion-related parameters (P > .05). Higher preoperative spherical equivalent (b = -0.28, P = .01) and thinner preoperative corneal thickness (b = -0.02, P = .01) were associated with more microdistortions.

CONCLUSIONS

SMILE induced a temporary increase in OSI values and Bowman's layer microdistortions. The microdistortions did not influence intraocular scattering. [J Refract Surg. 2018;34(6):387-392.].

Evaluation of Human Corneal Lenticule Quality After SMILE With Different Cap Thicknesses Using Scanning Electron Microscopy

PURPOSE

To evaluate the surface characteristics of lenticules created by small-incision lenticule extraction (SMILE) with different cap thicknesses.

METHODS

This prospective study included 20 consecutive patients who underwent bilateral SMILE. Surface regularity of the extracted corneal lenticule was analyzed using scanning electron microscopy (SEM) combined with 2 methods: qualitative and quantitative regularity. Qualitative regularity of SEM images was graded by masked observers using an established scoring system. Quantitative regularity of SEM images was assessed by counting the total number and areas of tissue bridges using Image-Pro Plus software. Four different cap thickness of 120, 130, 140, and 150 μm were compared. Refractive outcomes of patients were measured at baseline and 1 month after surgery.

RESULTS

As 10 specimens were not analyzable, only 30 eyes were included. Postoperatively, all eyes had postoperative uncorrected distance visual acuity of 20/20 or better; 43% had an unchanged corrected distance visual acuity; 43% gained 1 line; 10% lost 1 line. Ultrastructurally, surface irregularity was primarily caused by tissue bridges. The average surface regularity score obtained was 10.87 ± 2.40 for 120 μm, 10.78 ± 2.60 for 130 μm, 8.76 ± 2.16 for 140 μm, and 8.70 ± 2.66 for 150 μm (P < 0.001). The total number and areas of tissue bridges of 120 to 130 μm were significantly less than 140 to 150 μm (P < 0.05). Surface regularity decreased as cap thickness increased (P < 0.05).

CONCLUSIONS

There is smoother appearance of the lenticular surface as seen through SEM when a thin cap is created compared with a thick cap qualitatively and quantitatively.

SMILE Rescue: Delayed Lenticule Removal in a Patient With High Myopia

PURPOSE

To report successful stromal lenticule extraction, 18 weeks after an aborted small incision lenticule extraction (SMILE) procedure.

METHODS

Case report.

RESULTS

SMILE was planned in both eyes in another center to correct high myopia. The right eye was treated uneventfully with immediate lenticule extraction and normal postoperative corneal and topographic appearance. Femtosecond laser treatment was applied to the left eye, but the lenticule could not be removed and the procedure was aborted. Eighteen weeks later, lenticule extraction was attempted again with success. Uncorrected distance visual acuity improved from counting fingers to 20/15, with a successful refractive outcome as planned.

CONCLUSIONS

Delayed lenticule extraction was successful in achieving the target refractive outcome. To the authors' knowledge, this is the first case of successful delayed lenticule extraction following an incomplete SMILE procedure. Target refractive outcomes were achieved and there were no postoperative complications. [J Refract Surg. 2017;33(3):199-202.].

Visual outcomes and management after corneal refractive surgery: A review

Corneal refractive surgery procedures are widely performed to permanently correct refractive errors. Overall, refractive surgeries are safe, predictable and present high rates of satisfaction. Nevertheless, the induced epithelial, stromal and nerve damage alters corneal integrity and function, triggering a regenerative response. Complications that arise from corneal wound healing process might directly impact on visual outcomes of keratorefractive procedures. Most of these complications can be prevented or effectively treated with minimal consequences and minor impact on optical quality. Nevertheless, it is crucial to accurately and timely identify these corneal regeneration-related complications for successful counseling and management. Optometrists, as primary eye care providers, play an essential role in detecting anatomic and functional alterations in vision. It is therefore of great interest for optometrists to be familiar with the principal postoperative complications derived from alterations in regenerative process after corneal laser refractive surgeries. This review aims to provide a basis for optometrists to better understand, identify and manage the main wound healing-related complications after refractive surgery.

Cap morphology after small-incision lenticule extraction and its effects on intraocular scattering

AIM

To investigate cap morphology after small-incision lenticule extraction (SMILE) and its effects on intraocular scattering.

METHODS

Sixty-five eyes of 33 patients undergoing SMILE were enrolled. In addition to regular evaluation, Fourier-domain optical coherence tomography was used to investigate cap thickness at 1d, 1wk, 1 and 3mo postoperatively. The optical quality including modulation transfer function cutoff frequency, Strehl ratio, Optical Quality Analysis System (OQAS) values, and objective scattering index (OSI), were evaluated using OQAS™.

RESULTS

Cap thickness decreased from 1d to 1wk (P<0.001), but remained higher than intended thickness of 120 µm after 3mo (P<0.001). Cap thickness in central area was thinner than that of in the paracentral and peripheral areas (P<0.0001). Total number of microdistortions decreased from 1d to 3mo (P<0.0001). Pearson analysis revealed a weak correlation between OSI and standard deviation of cap thickness at 1d and 1mo, as well as between range of cap thickness and OSI at 1mo. No correlation was found between microdistortion and OSI, but a negative correlation existed between microdistortion and range at 1d and 1moafter surgery.

CONCLUSION

The corneal cap tends to be more accurate and regular with time lapse. Better cap morphology tends to contribute less intraocular scattering in the eyes undergoing SMILE.

Hyperopic refractive correction by LASIK, SMILE or lenticule reimplantation in a non-human primate model

Hyperopia is a common refractive error, apparent in 25% of Europeans. Treatments include spectacles, contact lenses, laser interventions and surgery including implantable contact lenses and lens extraction. Laser treatment offers an expedient and reliable means of correcting ametropia. LASIK is well-established however SMILE (small-incision lenticule extraction) or lenticule implantation (derived from myopic laser-correction) are newer options. In this study we compared the outcomes of hyperopic LASIK, SMILE and lenticule re-implantation in a primate model at +2D/+4D treatment. While re-implantation showed the greatest regression, broadly comparable refractive results were seen at 3-months with SMILE and LASIK (<1.4D of intended), but a greater tendency to regression in +2D lenticule reimplantation. Central corneal thickness showed greater variation at +2D treatment, but central thickening during lenticule reimplantation at +4D treatment was seen (-17± 27μm LASIK, -45 ± 18μm SMILE and 28 ± 17μm Re-implantation; p <0.01) with expected paracentral thinning following SMILE. Although in vivo confocal microscopy appeared to show higher reflectivity in all +4D treatment groups, there were minimal and inconsistent changes in inflammatory responses between modalities. SMILE and lenticule re-implantation may represent a safe and viable method for treating hyperopia, but further optimization for lower hyperopic treatments is warranted.

Two-years results of small-incision lenticule extraction and wavefront-guided laser in situ keratomileusis for Myopia

PURPOSE

To compare the 2-years visual and refractive outcomes between small-incision lenticule extraction (SMILE) and wavefront-guided laser in situ keratomileusis (LASIK) in eyes with myopia and myopic astigmatism.

METHODS

Our retrospective case-control study examined 30 eyes of 30 patients with the manifest refraction spherical equivalent (MRSE) of -3.71 ± 1.83 dioptres (D) who underwent SMILE and 30 eyes of 30 patients with MRSE of -3.81 ± 1.40 D who underwent wavefront-guided LASIK. We assessed the 2-years clinical outcomes.

RESULTS

Logarithm of the minimal angle of resolution (LogMAR)-corrected distance visual acuity (CDVA) was -0.23 ± 0.07 in the SMILE group and -0.24 ± 0.07 in the wavefront-guided LASIK group 2 years postoperatively (p = 0.82). Logarithm of the minimal angle of resolution-uncorrected distance visual acuity (UDVA) was -0.18 ± 0.09 and -0.15 ± 0.11 (p = 0.30, respectively). In the SMILE and wavefront-guided LASIK groups 2 years postoperatively, 100% and 73% of eyes, respectively, were within 0.5 D of the prompted MRSE correction (p = 0.005). Changes in the MRSE of -0.10 ± 0.30 D and -0.23 ± 0.51 D occurred from 3 months to 2 years (p = 0.40, respectively). We found a significant correlation between myopic regression and the changes in the keratometric readings from 3 months to 2 years after wavefront-guided LASIK (r = -0.48, p = 0.002), but not after SMILE (r = -0.004, p = 0.90).

CONCLUSION

Small-incision lenticule extraction offers better refractive outcomes than wavefront-guided LASIK during a 2-years follow-up for the correction of myopia and myopic astigmatism.

A Three-Year Observation of Corneal Backscatter After Small Incision Lenticule Extraction (SMILE)

PURPOSE

To investigate changes in corneal backscatter after small incision lenticule extraction (SMILE).

METHODS

One eye was randomly selected from 34 patients who underwent SMILE procedures. Corneal backscatter was analyzed using Scheimpflug technology before surgery and at postoperative 1 day, 1 week, 1 month, 3, 6, and 12 months, and 3 years. Three different corneal depths (the anterior 120 µm, the center, and the posterior 60 µm) and three concentric radial zones (0 to 2, 2 to 6, and 6 to 10 mm) were analyzed. Another 40 eyes of 40 patients who underwent femtosecond laser-assisted LASIK (FS-LASIK) were examined before surgery and at postoperative 1 day and 3 years as the control group.

RESULTS

At postoperative day 1, a significant increase in corneal backscatter was detected in the SMILE group compared to preoperative values in the central 0 to 6 mm zone of the anterior layer and the 0 to 2 mm zone of the central layer (all P < .01). This increase was higher than the increase in the FS-LASIK group in the central 0 to 6 mm zone of the anterior and central layers (all P < .01). No significant differences in corneal backscatter were detected between preoperative values and the 1-week, and 1-, 3-, 6-, and 12-month follow-up visits in the SMILE group (all P > .05). Moreover, a significant decrease in corneal backscatter was detected in the three zones of all three layers in the two groups at 3 years postoperatively compared to preoperative values (all P < .001) and no significant difference was found between the two groups (all P < .05).

CONCLUSIONS

Corneal backscatter peaks and declines to the baseline in the early period after SMILE and corneal transparency achieves an improvement within 3 years postoperatively. [J Refract Surg. 2017;33(6):377-382.].

Management and Outcomes of Retained Lenticules and Lenticule Fragments Removal After Failed Primary SMILE: A Case Series

PURPOSE

To describe the management of and report the outcomes following the removal of retained lenticules or lenticule fragments after a complicated small incision lenticule extraction (SMILE).

METHODS

Three patients were referred for consultation due to intraoperative complications during SMILE. In case 1, the lenticule was torn during extraction and a central fragment was retained in the pocket. In case 2, the inferior part of the lenticule remained attached at the anterior plane and its detached, superior part was dislocated and folded at the inferior part of the pocket. In case 3, the lenticule was completely attached at the anterior plane. All cases underwent secondary surgery. The lenticule fragment was detached using the dissector's body and tip and was extracted using the advanced lenticule forceps. The retained lenticules were extracted after dissection of tissue bridges at the anterior plane and periphery.

RESULTS

Postoperatively, all eyes showed improvement of visual acuity and topographic regularization of the anterior corneal curvature. Complete removal of lenticule remnants was accomplished in cases 1 and 2. In case 3, the photodisruption during primary SMILE was incomplete at a peripheral area next to the incision. A small peripheral fragment, corresponding to the described peripheral area, remained attached after the lenticule removal and was left in situ but did not have any impact on visual acuity and quality.

CONCLUSIONS

Retained lenticules or lenticule fragments may induce irregular astigmatism and loss of visual acuity. Prompt removal restores visual acuity and induces the desired effect of the primary SMILE procedure. [J Refract Surg. 2017;33(12):848-853.].

Conventional Versus Inverted Side-cut Flaps for Femtosecond Laser-Assisted LASIK: Laboratory and Clinical Evaluation

PURPOSE

To study the differences in early corneal cellular events and biomechanical properties after femtosecond laser-assisted LASIK performed using conventional or inverted side-cut angles.

METHODS

In the laboratory study, left eyes of 24 rabbits underwent LASIK flap creation with a 70° or 115° side-cut. The contralateral eyes served as controls. The corneas were harvested 24 hours postoperatively. In the clinical study, 2 eyes of each patient (n = 29) were randomized to corneal flap creation with 70° or 115° side-cut angles during LASIK. The Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Depew, NY) was used to assess biomechanical properties of the cornea.

RESULTS

In rabbit eyes, epithelial ingrowth was observed more frequently in flaps with 70° side cuts compared to flaps with 115° side-cuts. Corneas with 70° side-cuts showed significantly increased apoptotic cells compared to 115° side-cuts in the central (P = .001) and peripheral (P = .004) regions. Fifty-eight eyes of 29 patients were included in the clinical study. An overall reduction in Goldmann-correlated intraocular pressure, corneal-compensated intraocular pressure, corneal resistance factor, corneal hysteresis measurements, p1 area, p2 area, and p1 area 1 and p2 area 1 was noted 37 ± 2 months after surgery (P < .001). No significant difference was observed in the change of any of these parameters between both groups (P ≥ .146).

CONCLUSIONS

Significant differences in wound healing were observed in rabbit corneas that underwent LASIK with conventional or inverted side-cuts. Variation in flap side-cut angles did not alter the long-term biomechanical properties measured with the ORA in patients after LASIK. [J Refract Surg. 2017;33(2):96-103.].

Lower Laser Energy Levels Lead to Better Visual Recovery After Small-Incision Lenticule Extraction: Prospective Randomized Clinical Trial

PURPOSE

To determine the effect of lowering laser energy on clinical outcomes in small-incision lenticule extraction (SMILE).

DESIGN

Prospective randomized clinical trial.

METHODS

A total of 151 patients (151 eyes) with moderate myopia scheduled for SMILE were included: 58 eyes received SMILE with low energy (100, 105, and 110 nJ; L-SMILE group) and 93 with conventional energy (115-150 nJ; C-SMILE group). Patients received complete ophthalmic examinations preoperatively and over 3 months postoperatively.

RESULTS

Uncorrected distance visual acuity (logMAR UDVA) 1 day and 1 week postoperatively was significantly better in L-SMILE than in C-SMILE (P < .001 and P = .005, respectively). There was no significant difference between the groups at 1 and 3 months. L-SMILE induced significantly fewer corneal aberrations compared with C-SMILE at 1 week and 1 month postoperatively (both P < .01), but there were no significant differences at 3 months. Though there was no difference in logMAR UDVA over the postoperative period between the 100, 105, and 110 nJ subgroups, there was a significant difference in logMAR UDVA on postoperative day 1 between L-SMILE and each subgroup in which an energy level of 115 nJ or higher was used. Furthermore, logMAR UDVA on postoperative day 1 showed a significant correlation with laser energy (r = 0.451, P < .001) and multiple linear regression analysis revealed that energy level was the only independent factor associated with logMAR UDVA on postoperative day 1 (P < .001).

CONCLUSIONS

SMILE using femtosecond energy of less than 115 nJ facilitates better visual acuity with less induction of corneal aberrations in the early postoperative period.

Small Incision Lenticule Extraction for Correction of Myopia and Myopic Astigmatism: First 24-Hour Outcomes

Purpose

To observe the first 24-hour (h) outcomes of the small incision lenticule extraction procedure (SMILE) for myopia and myopic astigmatism.

Methods

Fifty-three eyes (27 patients) scheduled for SMILE were followed immediately (0 h), 2, 4, 6, and 24 h after SMILE. Uncorrected visual acuity (UCVA), conjunctival congestion, pain level, and corneal edema, thickness, and densitometry were recorded.

Results

At 2 h after SMILE, 15.1% of eyes had ≤0.1 LogMAR UCVA; this increased to 62.3%, 98.1%, and 100% at 4, 6, and 24 h, respectively. Some eyes (33.96%) had mild corneal edema immediately after surgery. No 6 h postoperative edema was observed. In the first 24 h after SMILE, corneal thickness gradually decreased. Postoperative corneal densitometry values were significantly higher than preoperative values but gradually decreased during the first postoperative 24 h.

Conclusions

In the first postoperative 24 h, UCVA and corneal status (edema and densitometry) improved quickly.

Corneal Higher-Order Aberrations of the Anterior Surface, Posterior Surface, and Total Cornea After SMILE, FS-LASIK, and FLEx Surgeries

OBJECTIVES

To investigate the corneal higher-order aberrations (HOAs) of the anterior surface, posterior surface, and total cornea after small incision lenticule extraction (SMILE) and compare the results using femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and femtosecond laser lenticule extraction (FLEx).

METHODS

This study included 160 eyes in total; 73 eyes underwent SMILE, 52 eyes underwent FS-LASIK, and 35 eyes underwent FLEx surgery. Corneal HOAs of the anterior surface, posterior surface, and total cornea were evaluated using a Scheimpflug camera over 6-mm diameter preoperatively and 3 months postoperatively.

RESULTS

The anterior and total corneal HOAs significantly increased after SMILE, FS-LASIK, and FLEx surgeries, especially the spherical aberration and coma, whereas most posterior corneal HOAs remained unchanged. The SMILE procedure induced significantly lower anterior corneal and total corneal spherical aberration and third to eighth HOAs compared with FLEx surgery (P<0.01). FLEx surgery induced higher posterior corneal coma than SMILE (P=0.013) and FS-LASIK (P<0.001) surgeries.

CONCLUSIONS

SMILE, FS-LASIK, and FLEx surgeries mainly induced coma and spherical aberrations in the anterior surface and total cornea. The SMILE procedure induced less spherical aberration of the anterior cornea and total cornea than FLEx surgery. The posterior corneal spherical aberration significantly increased after FS-LASIK surgery. The SMILE procedure seems to have fewer effects on posterior corneal coma compared with the FLEx procedure.

Rapid detection of drought stress in plants using femtosecond laser-induced breakdown spectroscopy

Drought stress disrupts the balance of macro- and micronutrients and affects the yield of agriculturally and economically significant plants. Rapid detection of stress-induced changes of relative content of elements such as sodium (Na), potassium (K), calcium (Ca) and iron (Fe) in the field may allow farmers and crop growers to counter the effects of plant stress and to increase their crop return. Unfortunately, the analytical methods currently available are time-consuming, expensive and involve elaborate sample preparation such as acid digestion which hinders routine daily monitoring of crop health on a field scale. We report application of an alternative method for rapid detection of drought stress in plants using femtosecond laser-induced breakdown spectroscopy (LIBS). We demonstrate daily monitoring of relative content of Na, K, Ca and Fe in decorative indoor (gardenia) and cultivated outdoor (wheat) plant species under various degrees of drought stress. The observed differences in spectral and temporal responses indicate different mechanisms of drought resistance. We identify spectroscopic markers of drought stress which allow for distinguishing mild environmental and severe drought stress in wheat and may be used for remote field-scale estimation of plant stress resistance and health.

Corneal Clarity and Visual Outcomes after Small-Incision Lenticule Extraction and Comparison to Femtosecond Laser-Assisted In Situ Keratomileusis

Purpose. To evaluate corneal clarity and visual outcomes after small-incision lenticule extraction (SMILE) and compare them to femtosecond laser-assisted in situ keratomileusis (FS-LASIK). Materials and Methods. Fifty-eight myopic eyes of 33 patients who underwent SMILE were compared to 58 eyes of 33 patients treated with FS-LASIK. All procedures were performed using VisuMax® femtosecond laser and MEL 80® excimer laser (Carl Zeiss Meditec AG, Germany). Pentacam™ (Oculus, Germany) was used for pre- and 3-month postoperative corneal densitometry (CD) analysis. CD was evaluated at 3 optically relevant, concentric radial zones (0–2 mm, 2–6 mm, and 0–6 mm annulus) around the corneal apex and at 3 different anatomical corneal layers (anterior, central, and posterior). Associations of postoperative CD values with the lenticule thickness and ablation depth were examined. Preoperative and postoperative corrected distance visual acuity (CDVA) values were also compared. Results. After SMILE, the total CD (all corneal layers) at 0–6 mm annulus showed no significant change compared to preoperative values (P = 0.259). After FS-LASIK, the total CD was significantly reduced (P = 0.033). Three-month postoperative CD showed no significant differences between the 2 groups for all examined annuli (0–2 mm: P = 0.569; 2–6 mm: P = 0.055; and 0–6 mm: P = 0.686). Total CD after SMILE at 0–6 mm annulus displayed a weak negative association with the lenticule thickness (P = 0.079, R² = 0.0532) and after FS-LASIK displayed a weak negative association with the ablation depth (P = 0.731, R² = 0.0015). Postoperative CDVA was similar for both groups (P = 0.517). Conclusion. Quantification of corneal clarity using the Scheimpflug CD showed similar results before and 3 months after SMILE. Compared to FS-LASIK, no significant differences of corneal clarity and CDVA were found 3 months postoperatively.

The Effect of High Intensity Focused Ultrasound Keratoplasty on Rabbit Anterior Segment

Purpose. To evaluate the safety of high-intensity focused ultrasound keratoplasty as a treatment for presbyopia by examining its effect on the rabbit anterior segment. Methods. The right corneas of 36 New Zealand rabbits were treated with HIFU keratoplasty. The animals were sacrificed at 1, 7, 15, 30, 60, and 90 days after operation. Collagen type I, MMP-2, and MMP-9 were evaluated using immunohistochemistry. For the detection of apoptosis, the TUNEL method was applied. The SOD and MDA levels were analyzed with assay kits. Results. Collagen type I, MMP-2, and MMP-9 levels were altered after the operation but returned to normal within 90 days. The apoptotic index (AI) of the corneal cells decreased from 1 to 30 days gradually. No apoptosis was observed in the epithelial cells of the lens, and the SOD and MDA levels were normal at any time point. Conclusion. After HIFU keratoplasty, the histomorphology of the cornea changed, the corneal collagen type I levels decreased, the corneal MMP-2 and MMP-9 levels increased, and the corneal cells underwent apoptosis for a period of time. Ninety days after the operation, the levels returned to normal, and the lenses were not affected. Thus, HIFU presents good biological safety for eyes.

Wound healing profiles of hyperopic-small incision lenticule extraction (SMILE)

Refractive surgical treatment of hyperopia still remains a challenge for refractive surgeons. A new nomogram of small incision lenticule extraction (SMILE) procedure has recently been developed for the treatment of hyperopia. In the present study, we aimed to evaluate the wound healing and inflammatory responses of this new nomogram (hyperopic-SMILE), and compared them to those of hyperopic-laser-assisted in situ keratomileusis (LASIK), using a rabbit model. A total of 26 rabbits were used, and slit lamp biomicroscopy, autorefractor/keratometer, intraocular pressure measurement, anterior segment optical coherence tomography, corneal topography, and in vivo confocal microscopy examinations were performed during the study period of 4 weeks. The corneas were then harvested and subject to immunofluorescence of markers for inflammation (CD11b), wound healing (fibronectin) and keratocyte response (HSP47). The lenticule ultrastructual changes were also analyzed by transmission electron microscopy. Out results showed that hyperopic-SMILE effectively steepened the cornea. Compared to hyperopic-LASIK, hyperopic-SMILE had less postoperative wound healing response and stromal interface reaction, especially in higher refractive correction. However, compared to myopic-SMILE, hyperopic-SMILE resulted in more central deranged collagen fibrils. These results provide more perspective into this new treatment option for hyperopia, and evidence for future laser nomogram modification.

Advances in femtosecond laser technology

Femtosecond laser technology has become widely adopted by ophthalmic surgeons. The purpose of this study is to discuss applications and advantages of femtosecond lasers over traditional manual techniques, and related unique complications in cataract surgery and corneal refractive surgical procedures, including: LASIK flap creation, intracorneal ring segment implantation, presbyopic treatments, keratoplasty, astigmatic keratotomy, and intrastromal lenticule procedures.

Posterior Corneal Elevation after Small Incision Lenticule Extraction for Moderate and High Myopia

Purpose

To investigate the changes of posterior corneal elevation after small incision lenticule extraction (SMILE) for moderate and high myopia.

Methods

In this prospective study, fifty consecutive eyes of thirty patients (10 male, 20 female) who underwent SMILE for myopia and myopic astigmatism were included. Eyes were divided in two groups based on the preoperative spherical equivalent refraction: high myopia group (32 eyes, range -6.25D to -10.00D) and moderate myopia group (18 eyes, range -3.00D to -6.00D). Posterior corneal surfaces were measured by a Scheimpflug camera (Pentacam, Oculus Germany) preoperatively and 1 month, 3 months, 6 months and 12 months postoperatively. Posterior central elevation (PCE) and posterior mean elevation (PME) at 17 predetermined points in the central-4mm area above the best-fit sphere were analyzed.

Results

No significant difference in the amount of posterior corneal elevation changes in the high myopia group was noted over time (P = 0.23 and P = 0.94 for PCE and PME, respectively). Similarly, the changes in the moderate myopia group before and after SMILE were not significant either (P = 0.34 and P = 0.40 for PCE and PME). A statistically significant correlation was found between the residual bed thickness and the shift of the PCE in the high myopia group at 12 months postoperatively (r = 0.53, P = 0.01).

Conclusions

The results of this study suggest that the posterior corneal surface remain stable within one year after SMILE for both moderate and high myopia. The changes of PCE correlate to the residual bed thickness for high myopia. Long-term changes of posterior corneal surface need further investigation.

Smile--the next generation of laser vision correction

Our paper is an introduction in this new generation of Laser vision correction, called SMILE. It also reveals our experience in the past year, since we started to perform this new procedure in our patients. Small Incision Lenticule Extraction technique is the 3rd generation of Laser vision correction that completely redefines refractive surgery. Being performed entirely with femtosecond laser, SMILE is tissue preserving and very gentle for the eye. In 2011, it was launched internationally. We have started with SMILE in October 2014. Since then, we have performed more than 200 procedures, with the range of corrected diopters between -2 and -10 and astigmatism between -2 and -5. In the near future, hyperopic diopters will be corrected with SMILE.