Suction loss during SMILE surgery is a potential intraoperative complication, which might negatively influence the postoperative visual acuity. When suction loss occurs, management strategies include postponing surgery or immediate redocking [4,13]. However, the drawbacks of immediate continuance using a redocking technique include increased patient anxiety, difficulties in observing the pupil center due to the presence of air bubbles, risks for treatment decentration due to difficulties in pinpointing, risks for uneven lamellar cuts , and increased anxiety of the surgeon. Therefore, correct and accurate responses based on guidelines and experience are important for good prognosis of visual acuity after suction loss.
After reviewing all cases of suction loss in our SMILE database, we found several factors that lead to suction loss, including head and eye movements during laser cutting, which can be associated with the tension and anxiety of the patients. Therefore, during preoperative education, we should not only instruct patients on how to gaze, but also emphasize the importance of not moving their heads and eyes. The correct placement of the body and the head is crucial. Thus, in addition to adjusting the headrest, soft pads may be placed under the patient’s head when necessary. In general, we must maintain the patient’s head at a horizontal level, which will help the patient to remain still during surgery and to refrain from raising or lowering their chin.
During the waiting period before the surgery, we observed some body language signals that might predict possible intraoperative suction loss. Some patients showed signs of anxiety, such as fidgeting, looking around, and talking endlessly, especially among the male patients. Our study shows that male patients (76.7%) had a significantly higher incidence of suction loss than female patients (23.3%). We should pay more attention on providing the necessary comfort and guidance to anxious patients as they may fail to follow the doctor’s instructions and to track the fixation light with their eyes, and they might make small oscillatory movements due to the enhanced arterial pulse of their upper body and head. In addition, we observed that suction loss occurs more frequently during the cap cutting periods. In our study, suction loss in 19 (61.3%) eyes occurred during the cap interface stage and 8 (25.8%) during the creation of small incision. The respective numbers were 45% and 15% as reported by Reinstein  and 51% and 3% as reported by Liu . One possible explanation for this phenomenon is that the air bubbles generated from lenticule cutting obscure the patient’s vision. The patient loses sight of the green fixation light and panics, hence the movement.
Other risk factors, including the lack of surgical experience, increase the incidence of suction loss. The reported incidence of suction loss varies among studies. A review by Reinstein reported that the average global incidence of suction loss during SMILE surgery is 0.72% . In studies involving large population of more than 1000 cases, the reported incidence of suction loss ranges from 0.17% to 2.10% [3,6,8,10,11,13,14]. As doctors become more experienced, the incidence of suction loss decreases. In our study, the incidence of suction loss in the six consecutive years were 0%, 2.13%, 0.34%, 0.24%, 0.22%, and 0.25%, with an average incidence of 0.37%. The incidence was highest in 2015, during which the number of SMILE surgery performed in our facility rapidly increased. In the four subsequent years, the incidence of suction loss remained relatively low as the surgeon gained more experience. This phenomenon also reflects the learning curve of the surgeons (experience in surgical skills as well as communication techniques during the procedure). Osman reported that the incidence of suction loss decreased with surgical experience. In their first year, the incidence was 5.06%, whereas in their fifth year the number dropped to 1.84% . However, the increase in surgical experience did not eliminate suction loss completely, which could not be fully explained by their learning curve，because suction loss often related to patient anxiety or movement .
According to Osman , some risk factors, such as a larger cap diameter and higher cylinder, might be related to a weaker grasp on the cornea by the suction cone or to a lower shape compatibility between the cornea and the cone. However, CCT, residual stromal thickness, cap thickness, and optical zone were not identified as important risk factors for suction loss. In other studies, smaller palpebral fissures, steep corneas, smaller corneal diameter, and conjunctival chemosis were identified as risk factors . In our study, we observed that the first operative eye and male were important risk factors for suction loss, and this finding was supported by the result of a binary logistic regression analysis. The incidence of suction loss in the right eye (the first operative eye) is 23 (74.2%) eyes, consistent with Liu’s finding (77%) . Thus, we should enhance preoperative education, especially among male patients.
This study stresses the importance of patient head stability in addition to controlling eye movement during the procedure. Surgeons should focus not only on the eyes, but also on the patient’s anxiety and body language.
This study has several limitations. First, the retrospective comparative case control design is at higher risk of selection bias. However, this design is more suitable to reflect the learning curve of a surgeon. Secondly, we have hypothesized that patient anxiety is a possible risk factor for suction loss, without statistical support. Future studies will assess the preoperative, intraoperative and postoperative patient anxiety levels. Finally, the number of patients who experienced suction loss was small. A larger sample would provide a better insight into the risk factor and causes of suction loss.