Corneal refractive procedures are widely accepted techniques for refractive correction. Small incision lenticule extraction (SMILE) is characterized by the extraction of a refractive stromal lenticule through a small peripheral corneal incision, and can correct both myopia and astigmatism. There is strong evidence of the safety, efficacy, predictability, and stability of this novel procedure,1–5 which may explain its growing popularity in Europe and Asia.
Complications, including corneal epithelial defects, suction loss, opaque bubble layer, and tears in the corneal cap and stromal lenticule have also been reported.5 In particular, suction loss is one of the SMILE complications that may have a negative impact on postoperative visual outcomes.4,6
To date, the incidence, management, and clinical outcomes of suction loss have been reported in studies with varying sample sizes, ranging from 340 to 4,000.6–10 However, only a few studies analyzed the risk factors for suction loss.8,10 Moreover, in all of the studies quoted above, more than one surgeon performed the SMILE procedures, which may be a confounding factor affecting the incidence of suction loss.
In the current study, we reviewed all SMILE procedures performed by a single experienced surgeon from 2013 to 2016 to evaluate the incidence, management, visual outcomes, and risk factors for suction loss. Also, a novel method to be able to continue the surgery on the same day after suction loss occurrence greater than 10% of the lenticule cut was introduced and analyzed.
Patients and Methods
Patients and Design
This study adhered to the tenets of the Declaration of Helsinki and was approved by the Ethics Committee of the Eye and ENT Hospital of Fudan University. This retrospective study included all eyes that underwent SMILE procedures performed by the same experienced surgeon (XZ) for the correction of myopia or myopic astigmatism between January 2013 and December 2016. Demographic data, manifest refractions, uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), white-to-white (WTW) distance, corneal topographic data, and the surgical parameters of all patients were documented and analyzed. Intraoperative surgical videos of all eyes that developed suction loss were analyzed. Manifest refractions, UDVA, and CDVA were obtained and analyzed preoperatively and postoperatively after 1 day and 12 months. In all patients, the right eye was the first to be operated on.
Eyes that developed suction loss were selected as the study group. A demographically matched group of 54 right eyes that underwent uneventful SMILE surgery during the same study period was selected as the control group according to the ratio of 1:2 (study group vs control group). However, 4 patients in the control group withdrew from the study during follow-up, so a total of 50 eyes of 50 patients were included.
In the event of suction loss, the surgeon evaluated the specific situation and proceeded with the best decision possible. In general, if suction loss occurred during cutting of the lenticule (> 10%), the patient was given the choice of continuing with SMILE surgery or proceeding to laser in situ keratomileusis (LASIK). The surgeon would continue according to the manufacturer's standard protocol if the suction loss occurred during other stages.11
The surgical technique and centration method used for the SMILE procedure in this study have been described previously.12 The attempted treatment center was the first Purkinje reflex. In all eyes, the S-size contact glass was used. Femtosecond laser cutting was performed with a repetition rate of 500 kHz and a pulse energy of 130 nJ. The original intended cap thickness was set to 120 µm as default and 110 µm if the calculated residual stromal thickness was less than 280 µm when using a cap thickness of 120 µm. The width of the cap incision was set to 2 mm at 90° (12-o'clock position). The intended diameter of the lenticule (optical zone) was set between 6.5 and 6.8 mm. The main tissue planes were created in the following sequence: cutting of the refractive lenticule (spiral in), cutting of the lenticule side-cut, cutting of the cap (spiral out), and cutting of the cap incision (Figure A, available in the online version of this article). The refractive lenticule was dissected and removed manually using microforceps. Postoperative medications included 0.3% tobramycin, 0.1% fluorometholone, and artificial tears.
Small incision lenticule extraction femtosecond laser cutting procedure of the corneal lenticule.
The Statistical Analysis System 9.4 statistical software (SAS Institute, Inc.) was used to analyze the data. Continuous variables were reported as mean ± standard deviation. Statistical analysis for visual acuity was based on logMAR units. The Student's t test for two independent samples was used to compare these groups. The paired Student's t test was used for repeated measures in the case of normally distributed data, and the Wilcoxon signed-rank test otherwise. The Shapiro–Wilk test was used to test for normality. A multivariate logistic regression model was constructed to identify the risk factors for the development of suction loss. The regression covariates were checked for multicollinearity before analysis. These models tested age, sex, the order of operated eyes, manifest refraction, flat keratometric readings, steep keratometric readings, keratometric astigmatism, optical zone, central corneal thickness, WTW distance, spherical diopters, cylindrical diopters, cylindrical axis, corneal diameter, and lenticule thickness as possible risk factors. P values less than .05 were considered statistically significant.
Visual and Refractive Outcomes
The visual and refractive outcomes of both groups are shown in Figures 1–2. A total of 12,057 eyes were treated, of which 27 (0.22%) developed suction loss intraoperatively. The baseline demographic data did not differ between the groups, as shown in Table 1.
The Standard Graphs for Reporting Refractive Surgery of eyes that developed suction loss. (A) Twelve-month postoperative cumulative percentage of eyes attaining specified cumulative levels of uncorrected distance visual acuity (UDVA); all eyes showing emmetropia as the target refraction. (B) Percentage of eyes with postoperative UDVA equal to or better than the preoperative corrected distance visual acuity (CDVA). (C) Gain and loss of CDVA. (D) Attempted spherical equivalent (SE) refractive change plotted against the achieved SE refractive change. (E) Percentage of eyes attaining specified differences in attempted versus achieved correction. (F) Stability of manifest spherical equivalent. D = diopters
The Standard Graphs for Reporting Refractive Surgery of eyes that underwent uneventful surgeries. (A). Twelve-month postoperative cumulative percentage of eyes attaining specified cumulative levels of uncorrected distance visual acuity (UDVA); all eyes showing emmetropia as the target refraction. (B). Percentage of eyes with postoperative UDVA equal to or better than the preoperative corrected distance visual acuity (CDVA). (C) Gain and loss of CDVA. (D) Attempted spherical equivalent (SE) refractive change plotted against the achieved SE refractive change. (E) Percentage of eyes attaining specified differences in attempted versus achieved correction. (F) Stability of manifest spherical equivalent. D = diopters
Preoperative Patient Demographics
At 12 months postoperatively, 25 of 27 eyes (93%) in the study group and 48 of 50 eyes (96%) in the control group (Figure 1A) had a UDVA of 20/20 or better (P = .22). The UDVA of the study and control groups was −0.041 ± 0.064 and −0.050 ± 0.058 logMAR, respectively (P = .52). The CDVA of the study and control groups was −0.056 ± 0.051 and −0.062 ± 0.049 logMAR, respectively (P = .59). As shown in Figure 1B and Figure 2B, 25 of 27 eyes (93%) in the study group and 48 of 50 eyes (96%) in the control group had postoperative UDVA equal to or better than the preoperative CDVA. In terms of postoperative CDVA, 26 eyes (96%) showed no change and 1 eye (4%) gained one line in the study group (Figure 1C), whereas 49 eyes (98%) showed no change and 1 eye (2%) gained one line in the control group (Figure 1C). A scatterplot of the attempted versus achieved spherical equivalent correction is shown in Figure 1D and Figure 2D. Comparison of the spherical equivalent refraction errors showed that the eyes in the study group had more overcorrection compared with those in the control group (P < .01). As shown in Figure 1E and Figure 2E, 93% of the eyes in the study group and 92% of those in the control group were within ±0.50 diopters (D) of the targeted correction (P = .79).
Analysis of Suction Loss
Table 2 provides detailed information regarding all of the eyes that experienced suction loss. Among these 27 eyes, suction loss occurred in 13 during the cutting of the lenticule (cases 1 to 13). One eye (case 1) experienced suction loss after less than 10% of the lenticule cut had been performed, and laser cutting was reinitiated using the same parameters. Ten eyes (cases 2 to 11) developed suction loss after more than 10% of the lenticule cut had been performed. Although the surgical procedure could have been converted to femtosecond laser–assisted LASIK or postponed, the novel methods described below were applied instead. In 8 eyes (cases 3 to 10), the surgeon checked the cornea 1 to 2 hours after the occurrence of suction loss to ensure that the surgical induced gas bubbles and corneal edema had disappeared. A modified design that increased the cap thickness by 10 to 20 µm (the original cut was included within the new lenticule; Figure B, available in the online version of this article) was applied. Because one eye (case 2) had a residual stromal thickness of 260 µm, the lenticule diameter was increased in the modified design from 6.4 to 6.5 mm (lenticule thickness increased from 128 to 132 µm), with a final designated residual stromal thickness of 256 µm. Case 11 experienced suction loss during the cutting of the lenticule. Because only 0.01 mm was left uncut, it was deemed adequate to fully achieve the intended correction. One hour later, a LASIK flap cut setting (with the same diameter and thickness) was used to create the 2-mm cap incision (ie, a large hinge was programmed with an incision of just 2 mm). Because there was no lenticule side-cut, a spatula was used to bluntly dissect the layers. The lenticule was separated and removed without complications. Case 12 experienced a partial suction loss: The right eye moved during the cutting of the lenticule, prompting an automatic pause of the laser cut, following which the eye returned to the initial position and laser cutting continued automatically. In case 13, the patient refused to attempt SMILE surgery again, and laser-assisted subepithelial keratomileusis (LASEK) was performed after 2 weeks.
Analyses and Management of Eyes With Suction Loss
Cutting of the new lenticule with deepened cap thickness showing the unfinished lenticule cut (first cut when suction loss occurred, red dotted line) included inside the new lenticule (second cut).
Eight eyes (cases 14 to 21) experienced suction loss during cutting of the cap. Cases 14 to 20 underwent the “repair” procedure after developing suction loss. In case 21, the creation of the cap had exceeded the edge of the lenticule before suction loss occurred, such that the surgeon decided to manually create a small cap incision using a diamond knife.
In 6 eyes (cases 22 to 27), suction loss occurred during the cutting of the small cap incision. The unfinished or uncut small cap incisions were created using a spatula or a diamond knife.
All surgeries were completed without further postoperative complications.
Analysis of Suction Loss Risk Factors
The incidence of suction loss was 0% (0 of 966) in 2013, 0.15% (4 of 2,674) in 2014, 0.56% (19 of 3,386) in 2015, and 0.08% (4 of 5,031) in 2016, respectively. The overall average incidence was 0.22% (27 of 12,057).
Multivariate logistic regression revealed that the eye operated on first (the right eye) had a significantly higher risk of developing suction loss (P = .02; odds ratio [OR] = 0.34; 95% confidence interval [CI] = 0.14 to 0.84). Additionally, thinner lenticules for low myopias had a significantly higher risk of developing suction loss (P = .006; OR = 0.98; CI = 0.96 to 0.99). No other demographic characteristics were found to be significant risk factors.
Suction loss is an uncommon intraoperative complication of SMILE, with an overall incidence of 0.22% (27 of 12,057) in the current study. Although the incidence varies in the literature, the value we report is one of the lowest among studies. Wong et al9 reported an overall incidence of 4.4% (8 of 183), whereas Osman et al8 reported 2.1% (70 of 3,376) and Park and Koo7 reported 0.24% (28 of 11,762). The low incidence noted in our study may be due to thorough preoperative and intraoperative communication with the patients and good centration of the suction cone because of the extensive experience of the surgeon.
It has been noted that several factors can predispose a patient to have intraoperative suction loss.9 Both the longer duration of suction required during SMILE compared to femtosecond laser–assisted LASIK and the relatively weaker vacuum suction of the VisuMax system are inherent risks for suction loss. A small palpebral aperture, loose corneal epithelium, and excessive reflex tearing on the ocular surface can also contribute to suction loss.9 Osman et al8 found that eyes with a larger cap diameter were significantly more likely to develop suction loss (P = .023; OR = 9.60), whereas surgical experience significantly decreased the risk. Multivariate logistic regression in our study indicated that the eye operated on first had a significantly higher risk of developing suction loss. The patient's psychological status could be a possible explanation for this observation. When suction was applied to the first eye, some patients became nervous and, as a result, uncontrollable and significant eye movements occurred. A thinner lenticule was associated with significantly higher risk of developing suction loss, possibly due to the fact that patients with lower myopia are less used to blurry vision without glasses than patients with higher myopia during preparation, such that some of these patients with low myopia would be more anxious and more likely to move their eye and try to find the moving or disappearing green fixation light during laser scanning. Therefore, it is important for surgeons to be aware that suction loss tends to occur in the first operated eye and patients with low myopia, and accordingly provide thorough preoperative and intraoperative communication to relieve patient tension. If the surgeon suspects that suction loss may occur, the surgeon could maintain suction on the patient's eye for several seconds before proceeding to ascertain the ability of the patient to cooperate. With this technique, we managed to keep the suction loss incidence to a relatively low 0.22%.
Good centration may reduce the risk of suction loss, because poor centration may result in the suction of the bulbar conjunctiva at the corneoscleral limbus and lead to suction loss. Previous studies have shown that corneal vertex centration is superior to pupil centration in terms of induced ocular aberrations and asphericity.13–15 The corneal vertex is also the point of maximum elevation when the patient is fixating on the internal target.16 Thus, it is important that the centration is made on the corneal vertex instead of on the pupil center. Osman et al8 found that corneal diameter, central corneal thickness, residual stromal thickness, keratometric readings, cap thickness, and optical zone were not significant risk factors for the development of suction loss, in agreement with our findings. According to the operation manual provided by the manufacturer11 and a study by Reistein et al,17 standardized practice patterns are recommended on development of suction loss at different stages. Reinstein et al17 recommended the original cap thickness be at least 135 µm (to better preserve corneal nerve plexus and biomechanics) and if suction loss occurred at stage 2 (posterior lenticule cut greater than 10%), a thinner cap SMILE can be performed safely. However, in our study population of highly myopic eyes, most of the original cap cuts were more superficial (110/120 µm). Therefore, we had to proceed in the opposite direction, which is more suitable for populations with higher myopia (ie, repeat the SMILE cut at a deeper plane than the original cut). Thus, a novel method for suction loss management was applied. In 8 eyes (cases 3 to 10), a modified design with an increase in cap thickness of 10 to 20 µm (the original cut before suction loss was included within the new lenticule; Figure B) was employed 1 to 2 hours after suction loss development.
The patient was allowed to rest and surgery was continued after examining the cornea to ensure the disappearance of the gas bubbles and corneal edema. According to the previous literature, the gas bubbles may disappear spontaneously within 30 minutes after lenticule creation,18 whereas if surgery is continued immediately, the gas bubbles could still exist19 and could affect laser energy and surgical accuracy. One study7 showed significant undercorrection of up to −2.00 D with an immediate recut. However, our findings suggest that the patient should wait 1 to 2 hours before a recut so that the corneal endothelium will pump out the fluid to ensure the accuracy of the recut. The visual and refractive results showed that the second cutting was as accurate as in eyes without suction loss. For another eye (case 2), a new SMILE procedure was reinitiated after 2 hours of rest, with the optical zone increased by 0.1 mm, resulting in an increase in lenticule thickness (the original cut before suction loss was included within the new lenticule). One eye developed suction loss during the posterior lenticule cut with only 0.01 mm remaining to finish the cut (case 11): a “flap” procedure was applied with the same parameters as the original cap design in terms of diameter and thickness. All of these eyes had satisfactory visual outcomes.
The surgeon should be wary of the unfinished layer in the new lenticule and avoid entering the unfinished layer during lenticule separation (Figure B). The surgeon should be aware that the accuracy of the standard deviation of the VisuMax laser ranges from 3 to 5 µm.20,21 Ten µm of cap thickness increase is within approximately two standard deviations of the VisuMax laser and there is a 2.5% chance of crossing the original cut. Thus, 20 µm of cap thickness increase is a safer and better choice. In addition, creating deeper caps means deeper lenticule surfaces, which also results in a greater chance of false plane creation and more difficult dissections. It is recommended that only surgeons with considerable SMILE experience attempt the modified procedure. Management of suction loss is on a case-by-case basis and should follow the standard decision protocol to ensure safety, given that the multifactorial dimension of this complication must be integrated.
In this study, we found that, with appropriate management, suction loss did not affect long-term safety and efficacy. Other studies have also reported that good visual outcomes were achieved with appropriate management and that there were no significant differences compared to the uneventful patients, consistent with our results.6,7,9,22 In the study by Wong et al,9 the recommended protocol was not followed for 3 of 11 cases of suction loss. Although these 3 eyes had good visual outcomes, one required LASIK enhancement. The authors noted that it was difficult to determine whether deviation from the protocol was indeed appropriate. Park and Koo7 compared the predictability and safety of immediate SMILE procedures after suction loss with uneventful SMILE procedures, and found that immediately attempting SMILE with re-applied suction was safe and had clinically predictable long-term outcomes; however, predictability was lower when compared with an uneventful SMILE procedure. Liu et al22 reported that there was no statistically significant difference between re-treatment with SMILE or femtosecond laser–assisted LASIK in terms of safety and efficacy indices, or in terms of third- and fourth-order aberrations at 3 months postoperatively. Reinstein et al10 analyzed 4,000 consecutive SMILE procedures and reported no difference in results for the 20 suction loss eyes and fellow eyes in terms of visual and refractive outcomes.
In this study, a diamond blade knife or spatula was used to handle unfinished small cap incisions, which cannot guarantee the reproducibility. We now use the repair mode of the VisuMax software to recut the small cap incision as our standard procedure, as recommended.11,17
The suction loss rate in our study increased from 2013 to 2015, and decreased in 2016. The rate of the suction loss could not be entirely explained by the learning curve, and although surgical experience decreased the rate of suction loss, it did not eliminate it entirely. Although the rate of suction loss increased to 0.56% in 2015, it was still relatively low. The relatively low total number of suction loss cases may have contributed to the incidence fluctuation. The surgeon in our study was an expert in laser refractive surgery before learning SMILE, and this suction loss rate may not apply to novice surgeons.
There are limitations to this study. First, this was a retrospective study, and the objective visual quality of patients, such as wavefront aberrations, was not evaluated. However, in our study, none of the patients who developed suction loss had complaints of halos, glare, or monocular diplopia. Second, given that we were able to include data from only two postoperative time points, due to the retrospective nature of the study, future studies with a prospective design are needed to help refractive surgeons plan and evaluate management options. Third, we only included a Chinese population in our study; a multi-ethnic study is required to confirm the results in other populations.
The incidence of suction loss during SMILE is low. The novel method of suction loss management (for lenticule cutting) and keeping the patient rested for 1 to 2 hours after the initial suction loss offers an alternative procedure to treat eyes that suffered suction loss, and good visual outcomes can be achieved with proper management. The eye operated on first had a significantly higher risk of developing suction loss, indicating a need for thorough preoperative communication with patients so they fully understand the procedure, as well as good intraoperative communication to relieve patient tension.
- Sekundo W, Kunert KS, Blum M. Small incision corneal refractive surgery using the small incision lenticule extraction (SMILE) procedure for the correction of myopia and myopic astigmatism: results of a 6 month prospective study. Br J Ophthalmol. 2011;95(3):335–339. doi:10.1136/bjo.2009.174284 [CrossRef]
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- Vestergaard A, Ivarsen AR, Asp S, Hjortdal JO. Small-incision lenticule extraction for moderate to high myopia: predictability, safety, and patient satisfaction. J Cataract Refract Surg. 2012;38(11):2003–2010. doi:10.1016/j.jcrs.2012.07.021 [CrossRef]
- Shah R, Shah S, Sengupta S. Results of small incision lenticule extraction: all-in-one femtosecond laser refractive surgery. J Cataract Refract Surg. 2011;37(1):127–137. doi:10.1016/j.jcrs.2010.07.033 [CrossRef]
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- Park JH, Koo HJ. Comparison of immediate small-incision lenticule extraction after suction loss with uneventful small-incision lenticule extraction. J Cataract Refract Surg. 2017;43(4):466–472. doi:10.1016/j.jcrs.2016.12.034 [CrossRef]
- Osman IM, Awad R, Shi W, Abou Shousha M. Suction loss during femtosecond laser-assisted small-incision lenticule extraction: incidence and analysis of risk factors. J Cataract Refract Surg. 2016;42(2):246–250. doi:10.1016/j.jcrs.2015.10.067 [CrossRef]
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- Li M, Zhao J, Miao H, et al. Mild decentration measured by a Scheimpflug camera and its impact on visual quality following SMILE in the early learning curve. Invest Ophthalmol Vis Sci. 2014;55(6):3886–3892. doi:10.1167/iovs.13-13714 [CrossRef]
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- Reinstein DZ, Archer TJ, Gobbe M. Is topography-guided ablation profile centered on the corneal vertex better than wavefront-guided ablation profile centered on the entrance pupil?J Refract Surg. 2012;28(2):139–143. doi:10.3928/108159 7X-20111115-01 [CrossRef]
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- Reinstein DZ, Archer TJ, Vida RS, Carp GI. Suction stability management in SMILE: development of a decision tree for managing eye movements and suction loss. J Refract Surg. 2018;34(12):809–816. doi:10.3928/1081597X-20181023-01 [CrossRef]
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Preoperative Patient Demographics
|Parameter||Suction Loss Group||Control Group||P|
| Mean||24.4 ± 7.1||24.8 ± 7.3||.79|
| Range||17 to 40||18 to 41|
|Sex, n (%)|
| Male||14 (51.9)||26 (52)|
| Female||13 (48.1)||24 (48)|
|Eye lateral with suction loss, n (%)|
| First surgery (right)||18 (66.7)||–|
| Second surgery (left)||9 (33.3)||–|
|Mean sphere (D)||−4.55 ± 1.73||−5.19 ± 1.54||.10|
|Mean cylinder (D)||−0.82 ± 0.63||−0.79 ± 0.64||.82|
|Mean CCT (mm)||539 ± 34||535 ± 30||.63|
|Mean flat K (D)||42.55 ± 1.10||42.44 ± 1.08||.78|
|Mean steep K (D)||43.16 ± 1.06||43.15 ± 1.05||.82|
|WTW distance (mm)||12.1 ± 0.4||11.9 ± 0.3||.56|
Analyses and Management of Eyes With Suction Loss
|Case||Eyea||Time Point of Suction Loss||Management|
|1||OD||Lenticule 6.21 mm (< 10%)||Redock with original laser settingsb|
|2||OD||Lenticule 5.42 mm (> 10%)||Optical zone adjusted from 6.4 to 6.5 mm, lenticule thickness increased from 128 to 132 µm, RST 256 µmc|
|3||OD||Lenticule 0.77 mm (> 10%)||Cap thickness adjusted from 120 to 135 µmc|
|4||OD||Lenticule 5.63 mm (> 10%)||Cap thickness adjusted from 120 to 135 µmc|
|5||OD||Lenticule 0.28 mm (> 10%)||Cap thickness adjusted from 100 to 110 µmc|
|6||OD||Lenticule 0.01 mm (> 10%)||Cap thickness adjusted from 120 to 130 µmc|
|7||OD||Lenticule 0.58 mm (> 10%)||Cap thickness adjusted from 110 to 120 µmc|
|8||OS||Lenticule 0.26 mm (> 10%)||Cap thickness adjusted from 110 to 120 µmc|
|9||OD||Lenticule 2.72 mm (> 10%)||Cap thickness adjusted from 120 to 135 µmc|
|10||OD||Lenticule 5.40 mm (> 10%)||Cap thickness adjusted from 120 to 140 µmc|
|11||OD||Lenticule 0.01 mm (> 10%)||Redock with modified flap creation procedure (no lenticule side cut)c,d|
|12||OD||Lenticule (partial suction loss)||Eye was repositioned and laser cutting continued|
|13||OD||Lenticule 3.41 mm (> 10%)||Changed to LASEK after 2 weeks|
|14||OD||Cap 0 mm||SMILE repair procedureb|
|15||OS||Cap 2.82 mm||SMILE repair procedureb|
|16||OS||Cap 2.82 mm||SMILE repair procedureb|
|17||OS||Cap 2.70 mm||SMILE repair procedureb|
|18||OD||Cap 3.12 mm||SMILE repair procedureb|
|19||OS||Cap 2.04 mm||SMILE repair procedureb|
|20||OD||Cap 2.56 mm||SMILE repair procedureb|
|21||OD||Cap 7.39 mm||Incision created using diamond blade knife|
|22||OS||Cap incision 12%||Incision created using diamond blade knife|
|23||OD||Cap incision 99%||Incision created using diamond blade knifee|
|24||OS||Cap incision 10%||Incision created using diamond blade knife|
|25||OS||Cap incision 90%||Incision separated using spatulaf|
|26||OS||Cap incision 99%||Incision separated using spatula|
|27||OD||Cap incision 90%||Incision separated using spatulaf|