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BACKGROUND: To find out the incidence and risk factors of opaque bubble layer (OBL) in eyes with myopia and myopic astigmatism following femtosecond laser-assisted in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE). METHODS: A total of 1076 eyes from 569 patients who had FS-LASIK or SMILE were included in the retrospective research. For each kind of surgery, eyes were separated into two groups: "OBL" groups and "no OBL" groups. In the FS-LASIK group, eyes that developed OBL were split into "hard OBL" and "soft OBL" groups. The incidence and size of OBL were analyzed after watching the surgical procedure videotaped during the operation and taking screenshots. Surgical parameters, including sphere, cylinder, keratometry, corneal thickness, flap thickness, cap thickness, lenticule thickness, and visual acuity, were compared. RESULTS: In the FS-LASIK surgery, the incidence of OBL was 63.2% (347 eyes). A thicker central corneal thickness (CCT) was the only independent risk factor affecting the OBL area (ß = 0.126, P = 0.019). One hundred and thirty of these eyes had hard OBL, and the flap thickness of these eyes was thinner than that of those with soft OBL (P = 0.027). In the SMILE group, 26.6% (140 eyes) developed OBL. A higher flat keratometry (K) and a thicker residual stromal thickness (RST) were risk factors affecting the OBL area (ß = 0.195, P = 0.024; ß = 0.281, P = 0.001). CONCLUSION: The incidence of OBL differs between the FS-LASIK surgery and the SMILE surgery. There are differences in the factors influencing OBL between the two surgeries.

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Introduction: This study aimed to investigate two types of corneal flap thickness on opaque bubble layer (OBL) formation in Visumax femtosecond laser-assisted stromal for situ keratomileusis (FS-LASIK). Methods: This retrospective study analyzed 203 eyes of 103 patients (32 men and 71 women) who underwent Visumax FS-LASIK between January 2020 and June 2020, and according to corneal flap thickness, they were divided into the 100-µm group (64 eyes) and the 110-µm group (139 eyes). Anterior-segment examination revealed no abnormal findings. Preoperatively, intraocular pressure (IOP), central corneal thickness (CCT), residual stromal thickness (RST), spherical power, cylindrical power, flat keratometry (K1), steep keratometry (K2), and biomechanical parameters including deformation amplitude (DA) ratio, Integrated Radius, stiffness parameter at first applanation (SP-A1), and Ambrosio relational thickness to the horizontal profile (ARTh) were evaluated. Primary outcomes were the incidence of OBL formation in the two groups compared by the Chi-square test and the correlation between the incidence of OBL and the above preoperative data by Spearman's Rho test. Secondary outcomes were the comparisons corrected by the generalized estimating equation (GEE) model. Results: The incidence of OBL formation in the 100-µm group was 59.4 %, which was higher than that in the 110-µm group (23.0 %) with a significant difference (χ2 = 25.635, P < 0.001). The thinner corneal flap thickness (r = -0.355, P < 0.001) and higher spherical power (r = -0.142, P < 0.05) correlated with OBL formation. Higher K1 (r = 0.217, P < 0.01) and K2 (r = 0.198, P < 0.01) also correlated with OBL formation. The results of the GEE correction analysis showed higher rates of OBL formation in the 100-µm group (odds ratio [OR] = 4.704, 95 % CI 1.681-13.161, P < 0.01). Conclusions: OBL was more likely to occur with the 100-µm corneal flap than with the 110-µm corneal flap in Visumax FS-LASIK. The risk of OBL formation in the 100-µm group was 4.704 times higher than that in the 110-µm group.

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Modern approach to refractive laser surgery features three main types of lamellar surgery. Two of them are types of open laser keratomileusis (LASIK and femtosecond laser-assisted LASIK), and the third - closed (SMILE). All of these techniques allow achieving good clinical outcomes but differ in possible complications. This article reviews the complications of femto-LASIK and specifically the post-operative cavitation injuries, describes the mechanism of their occurrence, variants of their course, and presents the prevention measures.

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PURPOSE: To evaluate the incidence of an opaque bubble layer (OBL) in femtosecond laser-assisted in situ keratomileusis (FS-LASIK) flaps created with VisuMax Flap 2.0 as a result of a modification in the parameters of the flap programming. METHODS: This retrospective study was comprised of 1400 eyes of 715 patients who received FS-LASIK surgery. OBLs were measured and reported as a percentage of the flap area to identify the incidence and extent. Flap creation, which is a modification technique, was performed with 8.1-mm flap diameters plus 0.3-mm enlarged interlamellar photodisruption (group Flap 2.0). The same flap diameters without extra photodisruption as the previous standard setting were also implemented (group Flap 1.0). The preoperative measurements, including sphere, cylinder, keratometry, and intraoperative characteristics such as flap size and thickness, were documented. Possible risk factors for the occurrence of OBLs were investigated in this study. RESULTS: The incidence of an OBL was reduced when using the Flap 2.0 program (31.4%) compared to the Flap 1.0 program (63.7%). The area of hard and soft OBLs created by the Flap 2.0 program is smaller than those created by the Flap 1.0 program (P = 0.007 and P < 0.001). Multivariate logistic regression indicated that a thinner flap (P = 0.038) and a higher sphere (P = 0.001) affected the chance of hard OBLs occurring. CONCLUSION: The VisuMax Flap 2.0 program promotes gas venting by enlarging the interlamellar photodisruption size. The incidence and extent of OBLs appear to be reduced significantly when the Flap 2.0 program is applied.

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Femtosecond laser-assisted laser in situ keratomileusis(FS-LASIK)and small incision lenticule extraction(SMILE)are the mainstream corneal refractive surgeries at present. Despite efficacy, safety and predictability they have showed in refractive error correction, there are still complications relating to femtosecond laser, such as suction loss and opaque bubble layer(OBL), due to that the production of corneal flap or lenticule is dependent on the femtosecond laser. OBL is a complication that is unique to femtosecond laser surgery and the bubbles are generated from photo-disruptive effect towards corneal tissues which consisted of water vapor and carbon dioxide, and OBL gradually formed when the bubbles are trapped in the stroma. The bubbles can influence the intraoperative manipulation and postoperative visual quality. This review discusses the mechanism, grading, classification, and influencing factors of OBL and its effects on intraoperative manipulations and postoperative recovery, in the hope of providing reference and basis for further clinical studies.

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[This corrects the article DOI: 10.3389/fmed.2023.1156677.].

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Purpose: To evaluate the possible risk factors of opaque bubble layer (OBL) formation in small incision lenticule extraction (SMILE) surgery and its effects on visual quality. Methods: Fifty-six eyes from 28 patients were included in this study. The preoperative parameters and intraoperative designs were recorded. Corneal high-order aberrations (HOAs), point spread function (PSF), and modulation transfer function (MTF) were measured using iTrace at pre-operation, 1 week, 1 month, and 3 months after SMILE. Generalized Estimating Equation and Linear Mixed Effects Model were employed for statistical analysis. Results: The mean OBL area in SMILE surgery was 2.75% ± 1.25%. The patients were divided into groups based on whether the OBL was greater than the mean group or less than the mean group. Compared to the group with a smaller OBL area, the group with the larger OBL area had steeper corneal curvature and thinner cap thickness, the OBL area was positively correlated with the preoperative keratometry (r = 0.21, p = 0.04) and preoperative spherical value (r = 0.47, p = 0.01). The group with the larger OBL area induced more corneal SA and trefoil at 1 week postoperatively, but the difference was not significant at 1 month and 3 months postoperatively. Conclusion: A steep corneal curvature, thin cap thickness, and high preoperative spherical value are possible risk factors for OBL formation in SMILE surgery. The OBL increased the ocular and corneal HOAs postoperatively for a short period (1 week), while it did not affect the long-term outcomes.

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BACKGROUND: Opaque bubble layer (OBL), which generates from photo-disruptive procedures on the cornea, has been a common phenomenon during femtosecond laser-assisted refractive surgeries and it would potentially impact eye tracking and flap lifting. And we have observed that an updated flap-making pattern could form less OBL clinically than the traditional pattern, which needed further approval. Thus, the purpose of this study is to prove our observation and investigate the possible risk factors related to the occurrence and type of OBL in laser in situ keratomileusis (LASIK) flaps using the Visumax laser system. METHODS: This prospective study included 167 eyes of 86 patients (mean age: 27.5 ± 6.1 years) undergoing bilateral femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) for myopia/myopic astigmatism by the same surgeon from April 2020 to August 2020. Preoperative data on refraction, central corneal thickness (CCT), and keratometry as well as intraoperative data were included for analysis. A new flap-making pattern creating an offset between flap-cut and side-cut was adopted to compare with the traditional pattern. The operation video of flap formation was analyzed to identify the existence and type of OBL. The area covered by OBL and the ratio of OBL to flap were calculated using Image J software. RESULTS: Among 167 eyes, 54 eyes (32.3%) developed OBLs, consisting of 31 as hard OBL coexisting with soft OBL, and 23 as soft OBL alone. The OBL incidence was significantly reduced in eyes with the new flap-making pattern compared with the traditional pattern (13.8% vs. 52.5%, P < 0.001). Hard OBLs had larger area ratios than soft OBLs (14.3 ± 8.3% vs. 1.1 ± 1.8%, P < 0.001). Univariate analyses revealed that eyes with more myopia, thicker CCT, and traditional flap-making patterns were more likely to develop OBLs. Multivariate analysis further confirmed that more myopia, thicker CCT, and traditional flap-making pattern were risk factors for OBLs. A Larger corneal diameter was associated with a higher incidence of hard OBL when applying the traditional flap-making process. CONCLUSION: More myopia, thicker CCT, and larger corneal diameter were risk factors for OBL development during flap creation, whereas a flap-making pattern with an offset between flap-cut and side-cut could reduce the incidence of OBL.

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@#AIM: To explore the effect of different energy parameters of femtosecond laser small incision lenticule extraction(SMILE)on stage Ⅰ opaque bubble layer(OBL)and visual quality. <p>METHODS: A retrospective analysis of the clinical data of 216 patients(432 eyes)who came to our hospital for SMILE surgery from July 2018 to December 2019. According to whether stage Ⅰ OBL occurred, they were divided into OBL group(42 eyes)and non-OBL group(390 eyes). The age, visual acuity parameters, corneal parameters, microlens parameters and energy parameters were compared between the two groups, and multivariate regression analysis was used to analyze the relationship between the difference in energy settings and the OBL of stage Ⅰ. The uncorrected visual acuity(UCVA), best corrected visual acuity(BCVA), and modulation transfer function cut-off spatial frequency(MTF_cut-off), Strehl Ratio(SR)and Objective Scattering Index(OSI)with energy parameters of 130, 135, 140, 145, and 150 nJ before and 1mo after surgery were compared. The correlation between energy parameters and stage Ⅰ OBL, UCVA, BCVA, MTF_cut-off, SR, OSI were analyzed. <p>RESULTS: Multivariate regression analysis showed that the energy setting with a difference of 5nJ did not show an association with stage Ⅰ OBL. In the different energy parameter groups, LogMAR UCVA, MTF_cut-off, and OSI at 1mo after surgery were improved compared with preoperatively(<i>P</i><0.05), and the difference between the groups were statistically significant(<i>F</i>=75.712, 15.304, 26.293, all <i>P</i><0.05). SMILE intraoperative energy parameters were negatively correlated with UCVA(<i>r</i>=-0.272), MTF_cut-off(<i>r</i>=-0.132), and OSI(<i>r</i>=-0.151)1mo after surgery(<i>P</i><0.05). <p>CONCLUSION: When using a 4.5μm dot pitch, in the usual energy range, the lower the energy, the better the postoperative visual quality, but it does not significantly affect the incidence of stage Ⅰ OBL during SMILE surgery.

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@#AIM: To evaluate the effect of opaque bubble layer(OBL)on the ocular cylotorsion compensation during FS-LASIK procedures. <p>METHODS: Prospectively clinical study. From July 2019 to September 2019, two-hundred FS-LASIK patients(400 eyes)were randomly included into this study. The total OBL incidence, flap-out OBL incidence, flap-in OBL incidence, incidence of dynamic cyclotorsion component(DCC)and incidence of static cyclotorsion component(SCC)were statistically analyzed. <p>RESULTS: OBL developed in 183 eyes of 400 FS-LASIK eyes, with a total OBL incidence of 45.8%. DCC was successfully performed on 397 eyes, with a total DCC incidence of 99.2%. SCC was successfully performed on 293 eyes, with a total SCC incidence of 73.2%. Neither flap-out OBL nor flap-in OBL could disturb the successful implementation of DCC during the operation(<i>P</i>>0.05). Both flap-out OBL and flap-in OBL could impact the SCC implementation and make it fail(<i>P</i><0.05).<p>CONCLUSION: OBL can result in failure of SCC implementation during the FS-LASIK procedures.

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The procedure of small incision lenticule extraction (SMILE) was introduced in 2011, and since then there has been an increase in the number of cases undergoing this procedure worldwide. The surgery has a learning curve and may be associated with problems in the intraoperative and postoperative periods. The intraoperative problems during SMILE surgery include the loss of suction, the occurrence of altered or irregular opaque bubble layer and black spots, difficulty in lenticular dissection and extraction, cap perforation, incision-related problems, and decentered ablation. Most of the postoperative problems are similar as in other laser refractive procedures, but with decreased incidence. The identification of risk factors, clinical features, and management of complications of SMILE help to obtain optimum refractive outcomes.

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AIM: To investigate the predictive factors of the opaque bubble layer (OBL) compared to the fellow eye of same patients in FS200 femtosecond laser assisted laser in situ keratomileusis (FS-LASIK). METHODS: This study consisted of 60 consecutive patients (120 eyes) with unilateral OBL during FS-LASIK. Eyes were divided into OBL (the OBL eyes) and OBL-free groups (the fellow eyes) based on the occurrence of OBL. The preoperative demographic data, refraction, keratometry, corneal astigmatism, pachymetry, intraocular pressure and intraoperative data including the outlet location of gas diffusing canal were collected. Conditional logistic regression analysis was performed to find the associated factors with OBL in the two groups by determining odds ratios (OR) and 95%CI. RESULTS: The preoperative demographic data, mean spherical errors, mean K value, suction time, intraocular pressure and central cornea thickness were not significantly different between the two groups. The outlet location of gas diffusing canal (P<0.01, OR 7.16, 95%CI 2.53-20.32) and the corneal astigmatism (P=0.013, OR 0.13, 95%CI 0.03-0.65) were significantly associated with the incidence of OBL by multivariate logistic regression analysis. Visual acuity, efficacy, and safety were comparable between the two groups two months after surgery except for a slightly lower predictability value for the hard OBL eyes. CONCLUSION: The reduction of the incidence of OBL is obvious when the outlet of gas diffusing canal located at the posterior border of the corneoscleral limbus. This is probably consequent to more effectiveness of gas diffusing canal. Corneal astigmatism is also an independent protective factor for OBL formation.

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Objective: To investigate the influence of corneal biomechanical properties on opaque bubble layer (OBL) in small incision lenticule extraction (SMILE). Methods: In this nested case control study, 20 patients (31 eyes) were enrolled in OBL group, while 51 patients (98 eyes) were included in non-OBL group. The parameters were obtained by Pentacam HR and Corvis ST examinations. Independent t test was used to analyze the difference of corneal biomechanical parameters between the two groups and multivariable logistics regression was applied to analysis the influence of corneal biomechanical properties on OBL. Results: This study enrolled 129 eyes in 71 cases including 30 males and 41 females, with a mean age of (22.50±5.18) years old. It has shown that the spherical equivalent (SE) [(-4.64±1.33) and (-5.78±1.61) D], central corneal thickness (CCT) [(572±29) and (550±32)µm], residual stromal thickness (RST)[(356±31) and (325±36 µm)], and lenticule thickness (LT) [(96±23) and (115±25) µm] were significantly different between OBL group and non-OBL group (t=3.58, -3.43, -5.68 and 3.64, respectively, P<0.05). There were significant differences in deflection amplitude at the first applanation and highest concavity (A1 DefA and HC DefA), deflection area at the highest concavity (HC DefArea), maximum deformation amplitude (DAmax), maximum deflection amplitude (DefAmax) and stiff parameter (SP) (108.85±13.77 and 100.19±14.13) between the two groups (t=-2.75, 2.41, 3.62, 4.09, 2.22 and -2.99, respectively, P<0.05). The OR and 95% confidence interval of SP in crude and adjusted logistics models were 1.04, (1.01-1.07) (P=0.005), and 1.01, (1.00-1.05) (P=0.426), respectively. Conclusions: The occurrence of OBL could be influenced by various corneal biomechanical factors. The thicker CCT, thicker RST and the stiffer cornea may increase the risk for the occurrence of OBL. Fully acknowledgement on the relationship between corneal biomechanics and surgical outcomes and evaluation of the occurrence of OBL in SMILE surgery is of great importance for improving the safety and predictability of SMILE. (Chin J Ophthalmol, 2019, 55:115-121).

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PURPOSE: To evaluate the effects of the central corneal thickness (CCT) and residual stromal thickness (RST) on the formation of opaque bubble layer (OBL) during small-incision lenticule extraction (SMILE). METHODS: A total of 345 eyes from Refractive Surgery Center database at Tianjin Eye Hospital that had been subjected to SMILE surgery and followed for 6 months were included in this study and divided into OBL and OBL-free groups. Preoperative, intraoperative, and postoperative data for all eyes were evaluated and analyzed using multivariate regression analysis. After adjustment for several confounding factors, potential associations of CCT and RST with OBL were elucidated by determining odds ratios (ORs) and 95% confidence intervals (CIs). RESULTS: In total, 22 of the 345 eyes developed various degrees of OBL during the femtosecond laser scanning phase of SMILE surgery. After adjustment for age, sex, and refractive errors, significant relationships were detected between CCT and RST and OBL formation (OR 1.04; 95% CI 1.02-1.06; OR 1.03; 95% CI 1.02-1.05, respectively, P < 0.001). Smooth curve fitting revealed an increased risk of OBL in the presence of an increased CCT or RST. However, visual outcomes were comparable between the two groups at both 3 and 6 months postoperatively. CONCLUSIONS: The results suggest that OBL formation during SMILE surgery is more likely in eyes with a thicker cornea. CCT and RST can be considered independent risk factors for OBL formation. Although this phenomenon may disturb the surgical procedure, it is unlikely to affect the postoperative visual outcome.

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The purpose of this study was to evaluate the incidence of opaque bubble layer (OBL) in femtosecond laser-assisted in situ keratomileusis (LASIK) flaps created with the support of Visumax Carl Zeiss femtosecond laser, planned with different flap diameters (7.90, 8.0, and 8.20 mm) and the same laser energy and power settings. Incidence of intraoperative OBL in flaps of consecutive 108 patients (216 eyes) subjected to bilateral femtosecond-assisted LASIK was considered. Flap creation was performed with the same laser design parameters (spot distance and energy offset) and different presetting diameters of 7.90 mm (72 eyes, group 1), 8 mm (72 eyes, group 2), and 8.20 mm (72 eyes, group 3). The incidence of OBL was considered and its extension was reported measuring involvement of different four corneal flap quadrants in which was theoretically divided the entire flap area; based on these data, OBL presence was classified as none (no evidence of OBL), minimal (minimal presence in not more that one quadrants corneal flap), mild (OBL presence in almost two or three quadrants without tendency to invade central cornea), and moderate (OBL presence in almost three quadrants with tendency to invade central cornea). In group 1, the incidence of OBL was of 23.6 % (17 eyes) with a mild/moderate presence; in group 2, incidence was 20.8 % (15 eyes) with mild presence. Group 3 presented a reduced OBL incidence (4.1 %, 3 eye) with a minimal presence. No statistically significant difference was found between group 1 and 2 (p = 0.8414).We found statistically significant differences between group 1 and group 3 (p = 0.0012) and between groups 2 and 3 (p = 0.0044). A significant reduction and extension of OBL incidence were evident when LASIK flap settings diameter was increased, and flap edge was closer to the contact glass border; this is probably consequent to a more effective gas dispersion outside of corneal flap.

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AlM: To compare the impact of different thickness of corneal cap design on small incision lenticule extraction ( SMlLE) operation.METHODS: Forty-six cases of myopia patients ( 92 eyes) intends to SMlLE operation in our hospital were collected , and were randomly divided into 2 groups:corneal cap thickness design for 110μm in group A and 120μm in group B. Other operation parameters designs were consistent. All patients were surgeried by the same surgeon. The incidence of opaque bubble layer ( OBL ) , the ratio of difficult separation of lens, uncorrected visual acuity ( UCVA ) of each time points, and spherical equivalent ( SE) were compared.RESULTS: lntraoperative OBL incidence rate of 110μm group was higher than that of 120μm group with significant difference between the two group (P0. 05). SE were compared at 7d and 6mo after operation, showed no significant difference (P>0. 05)CONCLUSlON: Compared with 120μm group, corneal cap design SMlLE operation in 110μm group are more prone to OBL and difficult separation of lens, thus affects UCVA and postoperative recovery rate. There is no significant difference in long-term UCVA.

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BACKGROUND: The purpose of this study is to evaluate the extent and incidence of opaque bubble layer (OBL) using laser-assisted in situ keratomileusis (LASIK) flaps created with the Alcon/WaveLight® FS200 femtosecond laser as a result of a recent change in flap programming parameters aiming to reduce further the incidence and extent of OBL. METHODS: Intraoperative digital images of flaps from 36 consecutive patients (72 eyes) subjected to bilateral femtosecond-assisted LASIK were analyzed using a proprietary computerized technique. The incidence and extent of OBL was measured and reported as a percentage of the entire flap area. Flap creation was performed with a 1.7 mm wide canal, implemented as an updated design intended to reduce the extent of OBL (group A). The same OBL parameters were investigated and compared in an age-matched and procedure-matched patients in whom the previous standard setting of a 1.3 mm wide canal was implemented (group B). RESULTS: In group A, the average extent of OBL was 3.69% of the flap area (range 0%-11.34%). In group B, the respective values were 6.06% (range 0%-20.24%). We found the difference to be statistically significant (one-tailed P = 0.00452). CONCLUSION: This study suggests that there is a significant reduction in the incidence and extent of OBL when novel LASIK flap ventilation canal parameters of width and spot line separation are used.

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BACKGROUND: The purpose of this study was to determine flap parameter accuracy, extent of the opaque bubble layer, and incidence of skip lines in femtosecond laser-assisted stromal in situ keratomileusis (LASIK) using the WaveLight(®) FS200 laser and optoelectronic clinical measurements. METHODS: Images from 101 flaps were automatically recorded during consecutive routine LASIK procedures performed using the WaveLight FS200 femtosecond laser and the EX500 excimer laser. Digital processing of these images was used to evaluate objectively the diameter of FS200-created flaps, by comparing planned versus achieved procedures and to evaluate the incidence and extent (area) of the opaque bubble layer. RESULTS: The intended flap diameters were between 8.00 mm and 9.50 mm. The achieved flap diameters showed extremely high precision, and were on average -0.16 ± 0.04 mm smaller for a 8.00 mm intended flap diameter, -0.12 ± 0.03 mm smaller for a 8.50 mm flap, and up +0.06 ± 0.06 mm wider for a 9.50 mm flap. With an average flap area of 72.4 mm(2), the mean area of the opaque bubble layer (4.1 ± 4.3 [range 0-14.34] mm(2)) corresponded to a 6% opaque bubble layer-to-flap area. Specifically, 80% of the femtosecond-created flaps had an essentially zero opaque bubble layer (<2.7% of the flap area). CONCLUSION: In our clinical experience, flaps created using FS200 and this novel highly objective assessment technique demonstrate both precision and reproducibility. The incidence of opaque bubble layer was minimal.