Journal of Refractive Surgery

Original Article Supplemental Data

Suction Stability Management in SMILE: Development of a Decision Tree for Managing Eye Movements and Suction Loss

Dan Z. Reinstein, MD, MA(Cantab), FRCSC; Timothy J. Archer, MA(Oxon), DipCompSci(Cantab), PhD; Ryan S. Vida, OD, FAAO; Glenn I. Carp, MBBCh, FCOphth (SA)

Abstract

PURPOSE:

To develop a comprehensive protocol for suction stability management during small incision lenticule extraction (SMILE).

METHODS:

This was a retrospective video review of all SMILE cases where suction loss occurred or eye movement was noted in the medical record. The different types of eye movement were collated. A suction stability grading scale was derived to represent the magnitude of eye movements. A decision tree protocol was developed to define the management in each scenario depending on the suction stability grading and the femtosecond laser cutting progress.

RESULTS:

Eight types of eye movement were identified: fixation light tracking, Bell's reflex, saccades, oscillations, anxiety/uncooperative patient, nociceptive reflex movement, false suction, and nystagmus. Type I eye movements were defined as small movements that shift the corneal position by a clinically negligible amount. The surgeon may want to pause the femtosecond laser cutting, regain control of the patient, then continue. Type II eye movements were defined as large movements that shift the corneal position by a clinically relevant amount, in which case the surgeon may choose to release suction (ie, a surgeon-initiated suction loss). Type III eye movements were defined as those with sufficient force to break suction (ie, a patient-generated suction loss). A comprehensive decision tree was developed to cover all possible eye movement and suction loss scenarios. Example scenarios outside the preprogrammed machine restart treatment module include converting to laser in situ keratomileusis (LASIK) if there was tracking of the interface and restarting SMILE with a thinner cap if the original cap thickness was 135 μm or greater.

CONCLUSIONS:

With appropriate management, it is possible for the SMILE procedure to be completed on the same day by either continuing with SMILE or converting to LASIK depending on the progress of the femtosecond laser cutting.

[J Refract Surg. 2018;34(12):809–816.]

Abstract

PURPOSE:

To develop a comprehensive protocol for suction stability management during small incision lenticule extraction (SMILE).

METHODS:

This was a retrospective video review of all SMILE cases where suction loss occurred or eye movement was noted in the medical record. The different types of eye movement were collated. A suction stability grading scale was derived to represent the magnitude of eye movements. A decision tree protocol was developed to define the management in each scenario depending on the suction stability grading and the femtosecond laser cutting progress.

RESULTS:

Eight types of eye movement were identified: fixation light tracking, Bell's reflex, saccades, oscillations, anxiety/uncooperative patient, nociceptive reflex movement, false suction, and nystagmus. Type I eye movements were defined as small movements that shift the corneal position by a clinically negligible amount. The surgeon may want to pause the femtosecond laser cutting, regain control of the patient, then continue. Type II eye movements were defined as large movements that shift the corneal position by a clinically relevant amount, in which case the surgeon may choose to release suction (ie, a surgeon-initiated suction loss). Type III eye movements were defined as those with sufficient force to break suction (ie, a patient-generated suction loss). A comprehensive decision tree was developed to cover all possible eye movement and suction loss scenarios. Example scenarios outside the preprogrammed machine restart treatment module include converting to laser in situ keratomileusis (LASIK) if there was tracking of the interface and restarting SMILE with a thinner cap if the original cap thickness was 135 μm or greater.

CONCLUSIONS:

With appropriate management, it is possible for the SMILE procedure to be completed on the same day by either continuing with SMILE or converting to LASIK depending on the progress of the femtosecond laser cutting.

[J Refract Surg. 2018;34(12):809–816.]

Suction loss is the most obvious intraoperative complication of small incision lenticule extraction (SMILE) because this prevents the femtosecond laser cutting of the lenticule interfaces from completing, and it has been reported as a complication since the early development studies.1 In large population studies of more than 1,500 procedures, the incidence of suction loss has been reported as 0.17%,2 0.20%,3 0.41%,4 0.50%,5 0.78%,6 0.93%,7 and 2.10%.8 Suction loss can be managed by continuing with SMILE, converting to laser in situ keratomileusis (LASIK) or surface ablation, or aborting the procedure.

The main factor that influences management following a suction loss is which of the four interfaces is being cut at the time that suction is lost. Following the initial experiences with suction loss, a preprogrammed machine restart treatment module was incorporated into the software for the VisuMax femtosecond laser (device version 2.3, therapy assistant version 1.16.2.229; Carl Zeiss Meditec, Jena, Germany) that provides the user with a recommended course of action depending on the progress of the femtosecond laser cutting. The management is divided into five potential stages, as described briefly below.

  1. Lenticule interface (first 10%): Creation of the lenticule interface starts in the periphery, so a small peripheral ring of bubbles will be inconsequential to the treatment. Therefore, SMILE can be restarted with the same settings.

  2. Lenticule interface (10% to 100%): The lenticule interface is the refractive cut, so it follows a curve through the stroma. Attempting to repeat the lenticule interface at the same depth can potentially result in tissue slivers, and hence an irregular lenticule. Therefore, the protocol is to convert to LASIK with a flap thickness equivalent to the planned cap thickness.

  3. Lenticule side cut: The lenticule side cut does not affect the refractive geometry of the lenticule, so SMILE can be restarted from the lenticule side cut with the same settings.

  4. Cap interface: The cap interface is planar or parallel to the corneal surface, meaning that it is possible to repeat the cap interface with the same cap thickness. The bubbles within the region treated during the first pass will have slightly expanded to create a zone, therefore increasing the likelihood of the femtosecond laser pulses of the second pass being attenuated, allowing for a joining with sections where the first pass has already created a separable interface.

  5. Small incision: The small incision does not affect the refractive geometry of the lenticule, so SMILE can be restarted from the small incision.

However, there are some scenarios that are not covered by the restart treatment module, and other scenarios where surgical management may require actions outside the restart treatment module. Most notably, small, or even large, eye movements can occur without breaking suction that cannot be picked up by the software. In such cases, the surgeon may consider initiating a suction loss if the movement has compromised the treatment centration or has created a discontinuity in the bubble pattern. In almost all cases, a suction loss is caused by the patient moving the eye, so the management of eye movements and suction loss are closely connected.

The aim of the current study was to review the cases of suction loss in SMILE within the London Vision Clinic database to classify the cause and develop a suction stability management decision tree to expand the existing restart treatment module to cover all possible scenarios, including those in which eye movements occur without breaking suction.

Patients and Methods

This was a retrospective non-comparative case series of all myopic SMILE procedures treated consecutively between March 2010 and February 2017 by two experienced LASIK surgeons (DZR and GIC) using the VisuMax femtosecond laser at the London Vision Clinic, London, United Kingdom. The videos of all cases of suction loss or where eye movement was noted in the medical record were reviewed.

Informed consent and permission to use their data for general analysis and publication were obtained from each patient prior to surgery as part of our routine protocol. Because this was a retrospective study, an exemption from full institutional review board approval was obtained from the United Kingdom Health Research Authority.

Suction Stability Management Protocol

On reviewing the surgical videos, the different types of eye movement were collated. A suction stability grading scale was then derived to represent the magnitude of eye movements. Finally, a decision tree protocol was developed to define the management in each scenario depending on the suction stability grading and the femtosecond laser cutting progress.

Results

Out of a population of 4,000 eyes treated during the study period, there were 20 cases of suction loss (0.50%). The types of eye movement that were identified are described below. Table 1 shows the breakdown of suction loss according to the type of eye movement.

Incidence of Suction Loss in a 4,000 Eye SMILE Population Categorized by the Cause of Eye Movement

Table 1:

Incidence of Suction Loss in a 4,000 Eye SMILE Population Categorized by the Cause of Eye Movement

Eye Movement Classification

Fixation Light Tracking. Once docking is achieved, the patient is instructed not to follow the green light if it moves. However, if the fixation light is slightly displaced on the retina, the patient may perceive it to be off to one side, causing the eye to turn if he or she tries to focus on it. This acts to shift the light further and ends up in a negative feedback loop, hence moving the eye under suction and potentially causing suction loss (Video 1, available in the online version of this article). This is usually related to anxiety-mediated lack of cooperation where the patient is not focused on the surgeon's instructions.

Bell's Reflex. There is an involuntary reflex upward movement of the eye to “protect the cornea” by the patient attempting to close the eye (Video 2, available in the online version of this article). As with fixation light tracking, this usually occurs in highly anxious patients not listening closely to the surgeon.

Saccades. If there is a sudden movement of the eye in one direction, this can be strong enough to slightly move the cornea without breaking suction. These movements are often not large enough to create a visually significant discontinuity in the femtosecond laser cut interface, but are visible through the microscope view (Video 3, available in the online version of this article). However, a large saccade can cause a lateral shift large enough to create a discontinuity in the femtosecond laser interface, which may lead to an irregular interface (Figure 1).

Pair of images showing a crescent discontinuity (left image) created in the lenticule interface centrally due to a large eye movement caused by an anxious patient squeezing the eye. The surgeon attempted to continue the femtosecond laser cutting, but another eye movement as the cap interface was started created a second discontinuity (right image), at which point the small incision lenticule extraction procedure was aborted and converted to laser in situ keratomileusis (LASIK). Reprinted with permission from Reinstein DZ, Archer TJ, Carp GI. The Surgeon's Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: SLACK Incorporated; 2018.

Figure 1.

Pair of images showing a crescent discontinuity (left image) created in the lenticule interface centrally due to a large eye movement caused by an anxious patient squeezing the eye. The surgeon attempted to continue the femtosecond laser cutting, but another eye movement as the cap interface was started created a second discontinuity (right image), at which point the small incision lenticule extraction procedure was aborted and converted to laser in situ keratomileusis (LASIK). Reprinted with permission from Reinstein DZ, Archer TJ, Carp GI. The Surgeon's Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: SLACK Incorporated; 2018.

Oscillations. Adrenaline-driven tremor can cause small involuntary eye movements in some extremely anxious patients. In some cases, this can be strong enough to make small oscillatory movements of the cornea under suction due to cardiac balloting of the upper body and head (Video 4, available in the online version of this article).

Anxiety/Uncooperative Patient. Anxious patients may not be able to listen attentively to the surgeon or manage to keep their muscles relaxed and flaccid. Involuntary muscle tension can lead to triggering of the natural protective mechanisms, including pulling or turning the head away or squeezing the eyelids, which can cause the eye to move (Video 5, available in the online version of this article). In extreme cases, such eye movement can break suction by forcing the speculum onto the treatment cone.

Nociceptive Reflex Movement. Although uncommon, there can be a sharp pain sensation during photodisruption despite topical anesthetic (Video 6, available in the online version of this article).

False Suction. Although the suction ports are applied onto the cornea itself, in almost all cases the vacuum ports extend partially onto the conjunctiva in some areas. In extremely rare cases, this can result in false suction, so the eye is not actually immobilized, leading to eye movements and a cascade of conjunctival intrusion and loss of suction (Video 7, available in the online version of this article).

Nystagmus. Patients with nystagmus can be treated by SMILE without consequence because the immobilization provided by the suction nullifies the nystagmus; involuntary eye movements associated with nystagmus are not strong enough to overcome the suction force and shift the cornea. The accurvation of the cornea into the contact glass produces enough force and friction to neutralize the oscillations (Video 8, available in the online version of this article).

Eye Movement Grading

The suction stability grading scale was developed to include three broad categories. Type I includes small eye movements such as small saccades that shift the corneal position by a clinically negligible amount. These can be so subtle as to be unnoticeable without careful observation of the femtosecond laser cutting. A type I eye movement would not be large enough to create a visible discontinuity in the femtosecond laser bubble pattern. Therefore, it is not expected for a type I movement to induce a clinically significant irregularity in the lenticule surface.

Type II eye movements include large eye movements that shift the corneal position by a clinically relevant amount. Type II movements are visually obvious and require an immediate management action. The visual cues are a sudden relative shift in the bubble layer already created, a meniscus forming at the edge of the contact glass, intrusion of the conjunctiva within the contact glass, or a distortion or discontinuity in the femtosecond laser bubble pattern (Figure 1). It is possible for a large movement to occur but for the eye to return to its original position, in which case the treatment can be continued. Alternatively, if the movement is such that the lenticule regularity is deemed to have been compromised, the surgeon may choose to release suction (ie, a surgeon-initiated suction loss).

Type III eye movements include an eye movement with sufficient force to break suction (ie, a patient-generated suction loss).

Suction Stability Management Protocol

The full suction stability management protocol is presented as a decision tree in Figure 2. The reasoning behind the protocol is described below.

Flow chart outlining the suction stability management protocol, which combines the management of small (type I) and large (type II) eye movements together with suction loss (type III). This protocol incorporates the restart treatment module built in to the VisuMax laser software (Carl Zeiss Meditec, Jena, Germany), but also provides additional scenarios where surgeons can use their clinical judgment to follow the optimal path. SMILE = small incision lenticule extraction; OCT = optical coherence tomography; LASIK = laser in situ keratomileusis. Reprinted with permission from Reinstein DZ, Archer TJ, Carp GI. The Surgeon's Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: SLACK Incorporated; 2018.

Figure 2.

Flow chart outlining the suction stability management protocol, which combines the management of small (type I) and large (type II) eye movements together with suction loss (type III). This protocol incorporates the restart treatment module built in to the VisuMax laser software (Carl Zeiss Meditec, Jena, Germany), but also provides additional scenarios where surgeons can use their clinical judgment to follow the optimal path. SMILE = small incision lenticule extraction; OCT = optical coherence tomography; LASIK = laser in situ keratomileusis. Reprinted with permission from Reinstein DZ, Archer TJ, Carp GI. The Surgeon's Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: SLACK Incorporated; 2018.

Type I Eye Movements. As indicated in the top section of the flow chart, if there are small eye movements, regardless of when they occur during the femtosecond laser cutting, the treatment can be continued without stopping. If small movements persist, the surgeon may decide to pause to verbally regain control of the patient before continuing. We refer to this as pause, regain control, continue (P/R/C) (Videos 1 and 3).

Before Starting the Femtosecond Laser Cutting. For type II, if an eye movement occurs before the femtosecond laser cutting has started, the surgeon can delay initiating laser cutting to evaluate whether centration has been compromised. If centration is deemed to still be suitable and suction appears stable, then treatment can be continued. Otherwise, the surgeon can release suction and restart the docking process.

For type III, if a patient-generated suction loss occurs before the femtosecond laser cutting has started, there is no risk of creating tissue slivers and the procedure can be safely restarted without affecting the final outcome. If there are residual meibomian oil droplets or debris from the tear film on the contact glass, it may be worth replacing the contact glass to avoid the formation of black spots.9,10

During the Lenticule Interface (First 10%). For type II (well centered), if there is a large eye movement, the first aspect to consider is whether the eye is still centered in the contact glass. It is possible for the eye to move back and forth and end up approximately where it started. P/R/C may be used to regain control of the patient before continuing. When the femtosecond laser cutting restarts, the bubble pattern will be regular and continuous if the centration was close enough to the original position. If not, there will be a visible discontinuity in the bubble pattern, indicating that the centration had been altered, in which case the surgeon should initiate a suction loss. Because more than 10% of the lenticule interface would then have been created, the restart treatment module will load the option to convert to thin flap LASIK. Alternatively, if the original cap thickness was 135 μm or greater, a new SMILE treatment can be planned using a thinner cap. Performing SMILE at least 20 to 25 μm more superficially will avoid the new lenticule interface crossing the aborted interface.

For type II (shift in centration), if the position of the cornea has shifted, then the surgeon should release suction to avoid a decentered treatment. This will initiate the restart treatment module, which will offer the option to restart SMILE with the same settings.

For type III, if there is a patient-generated suction loss, the restart treatment module will be loaded with the recommended option to restart SMILE with the same settings.

For type III (tracked interface), if a patient-generated suction loss occurs but the femtosecond laser cutting was continued leading to the interface tracking upward through the cornea (Figure 3, Video 6), the default option provided by the restart treatment module to restart SMILE with the same settings should be ignored in preference for converting to thin-flap LASIK.

Series of images showing a suction loss almost immediately after starting the femtosecond laser cutting of the lenticule interface due to the patient reacting to nociceptive pain. Due to the suddenness of the resulting eye movement, the femtosecond laser cutting created an interface that tracked vertically through the stroma to the surface (arrow) within the pupil border. Reprinted with permission from Reinstein DZ, Archer TJ, Carp GI. The Surgeon's Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: SLACK Incorporated; 2018.

Figure 3.

Series of images showing a suction loss almost immediately after starting the femtosecond laser cutting of the lenticule interface due to the patient reacting to nociceptive pain. Due to the suddenness of the resulting eye movement, the femtosecond laser cutting created an interface that tracked vertically through the stroma to the surface (arrow) within the pupil border. Reprinted with permission from Reinstein DZ, Archer TJ, Carp GI. The Surgeon's Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: SLACK Incorporated; 2018.

During the Lenticule Interface (10% to 100%). For type II, the management in this scenario is exactly the same as that described for 10% of the lenticule interface: pause the femtosecond laser cutting, regain control, consider the centration, and check for any discontinuity. The surgeon should initiate a suction loss if either the centration or femtosecond laser bubble pattern is unsatisfactory (Video 5). The options are then to restart SMILE with a thinner cap (if the original cap thickness was 135 μm or greater) or use the restart treatment module to convert to thin-flap LASIK. If there is no discontinuity, it might be worth obtaining an optical coherence tomography (OCT) scan to review the geometry of the interfaces before proceeding to extract the lenticule, particularly if the eye movement occurred when the bubble pattern creation was nearing the visual axis. However, micro-irregularities in the stromal surface will be at least partially, and sometimes completely, masked by epithelial remodeling.11–15

For type III, if there is a patient-generated suction loss, the restart treatment module will be loaded with the recommended option to convert to LASIK with the flap thickness set to the programmed cap thickness (Video 7). However, it is usually preferable to reduce the flap thickness to maximize the residual stromal thickness. If the cap thickness was 135 μm or greater, the alternative option is to restart SMILE with a thinner cap (Figure A, available in the online version of this article).

Optical coherence tomography B-scan the day after small incision lenticule extraction (SMILE) in which suction loss occurred during femtosecond laser cutting of the lenticule interface (yellow). The treatment was completed by reprogramming SMILE with a thinner cap of 110 μm (blue), reduced from 135 μm as originally planned. Reprinted with permission from Reinstein DZ, Archer TJ, Carp GI. The Surgeon's Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: SLACK Incorporated; 2018.

Figure A.

Optical coherence tomography B-scan the day after small incision lenticule extraction (SMILE) in which suction loss occurred during femtosecond laser cutting of the lenticule interface (yellow). The treatment was completed by reprogramming SMILE with a thinner cap of 110 μm (blue), reduced from 135 μm as originally planned. Reprinted with permission from Reinstein DZ, Archer TJ, Carp GI. The Surgeon's Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: SLACK Incorporated; 2018.

For type III (tracked interface), if a patient-generated suction loss occurs but the femtosecond laser cutting was continued, leading to the interface tracking upward through the cornea, this would usually rule out the possibility of restarting SMILE with a thinner cap. Therefore, the restart treatment module should be used to convert to LASIK, again after adjusting the flap thickness to the preferred thickness. An OCT scan is recommended to verify the extent of the interface deviation away from the intended plane.

During the Lenticule Side Cut. For type II, the treatment can be continued and completed even if an eye movement is large enough to induce a misalignment between the lenticule interface and the lenticule side cut. The location of the lenticule side cut will not affect the refractive power of the lenticule and the gap can usually be punched through manually by the surgical instrument. The cap interface will also consequently be slightly decentered. This, in principle, will not affect the lenticule geometry because the cap interface is planar to the surface. P/R/C may also be used to regain control of the patient before continuing.

For type III, if a patient-generated suction loss occurs, the restart treatment module should be used to restart SMILE from the lenticule side cut.

During the Cap Interface. For type II, because the cap interface is programmed to be parallel to the surface, it is somewhat tolerant to a shift in position, so the treatment can be continued after P/R/C. If there is a visible discontinuity in the bubble pattern, an OCT scan would be useful to confirm that the interface is regular before extracting the lenticule. If the discontinuity is deemed large enough, a surgeon-initiated suction loss can be considered to bring up the restart treatment option of restarting the cap interface.

For type III, if a patient-generated suction loss occurs, the restart treatment module can be used to restart SMILE from the cap interface using the same thickness.

For type III (outside lenticule diameter), if a patient-generated suction loss occurs but the cap interface progress has passed the lenticule diameter, there is no need to recreate the whole cap interface as recommended by the restart treatment module. One option is to create only a small incision. Alternatively, an incision might be created manually using a diamond knife.

For type III (tracked interface), if a patient-generated suction loss occurs but the femtosecond laser cutting was continued, leading to the interface tracking upward through the cornea, continuing with SMILE, as indicated by the restart treatment module, may not be appropriate due to the risk of tissue slivers, the creation of false planes, and an irregular lenticule. Instead, the restart treatment module can be aborted to convert the procedure to thin-flap LASIK after waiting for the bubbles to dissipate. An OCT scan can be used to verify the extent of the interface deviation away from the intended plane.

During the Small Incision. For type II, there is no real need to stop the femtosecond laser cutting if there is an eye movement during the small incision because it will always be possible to manually bridge any gap.

For type III, the restart treatment module can be used to restart only the small incision. The surgeon may choose to slightly reduce the cap diameter and incision depth to ensure that the incision intersects the cap interface. If more than 50% of the incision has been created, then it is possible to manually complete the incision by blunt dissection or using a surgical knife.

Discussion

In reviewing all cases of suction loss within our SMILE database, we derived a classification of the types of intraoperative eye movements experienced and developed a structured suction stability management protocol. Because the femtosecond laser cutting only takes approximately 35 seconds, there is limited time available for making clinical decisions, so it is useful to have a clear decision process prepared. In preparing this protocol, several areas were identified where the appropriate action deviated from the preprogrammed machine restart treatment module.

Reviewing the suction loss cases highlighted the link between eye movements and suction loss, which led to the understanding that managing patient comfort and cooperation was paramount in minimizing the incidence of suction loss. This introduced the technique of P/R/C, whereby any small movement increases alertness to the patient becoming uncooperative and the patient can be managed proactively to prevent a suction loss occurring.

The importance of monitoring eye movements was also highlighted by this case review because there can be clinically significant eye movements without a break in suction. Therefore, the surgeon must be prepared to intentionally release suction when appropriate (a surgeon-initiated suction loss), such as if the treatment centration has been affected or if a significant discontinuity in the bubble pattern has formed. If a patient is particularly uncooperative, intentionally releasing suction can be considered at an advantageous point during the sequence of interfaces; for example, breaking suction during the lenticule side cut will have essentially no impact on restarting and completing the treatment.

Another point related to eye movements is the option to use an OCT scan to assess the regularity of the lenticule interfaces before proceeding to the interface separation part of the procedure. If significant irregularities are visible on the lenticule interfaces, the procedure can be converted to LASIK or surface ablation (Figure B, available in the online version of this article).

Optical coherence tomography B-scan (vertical) immediately following treatment in which small incision lenticule extraction (SMILE) was aborted due to significant eye movements creating discontinuities in the lenticule and cap interfaces. The treatment was converted to laser in situ keratomileusis (LASIK) using a 90-μm flap thickness, which was successfully completed. The two interfaces were clearly visible, with both showing significant undulations caused by the eye movements during femtosecond laser cutting. These undulations would have resulted in an irregular lenticule if the SMILE procedure had been continued. However, a non-uniform LASIK flap does not affect the outcome because the flap fits together with the stromal bed in a lock-and-key fashion. Reprinted with permission from Reinstein DZ, Archer TJ, Carp GI. The Surgeon's Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: SLACK Incorporated; 2018.

Figure B.

Optical coherence tomography B-scan (vertical) immediately following treatment in which small incision lenticule extraction (SMILE) was aborted due to significant eye movements creating discontinuities in the lenticule and cap interfaces. The treatment was converted to laser in situ keratomileusis (LASIK) using a 90-μm flap thickness, which was successfully completed. The two interfaces were clearly visible, with both showing significant undulations caused by the eye movements during femtosecond laser cutting. These undulations would have resulted in an irregular lenticule if the SMILE procedure had been continued. However, a non-uniform LASIK flap does not affect the outcome because the flap fits together with the stromal bed in a lock-and-key fashion. Reprinted with permission from Reinstein DZ, Archer TJ, Carp GI. The Surgeon's Guide to SMILE: Small Incision Lenticule Extraction. Thorofare, NJ: SLACK Incorporated; 2018.

The restart treatment module is designed to handle the routine suction loss scenarios, but there are some situations where an alternative action is more appropriate. First, if femtosecond laser cutting was continued as the eye pulled away from the contact glass, the interface will track upward through the cornea. This in turn increases the risk of creating tissue slivers if the new interfaces cross the tracked interface. This cannot be picked up by the restart treatment software, so the surgeon must be aware of this possibility and make an appropriate treatment decision.

Second, the restart treatment module currently forces conversion to LASIK if a suction loss occurs during the lenticule interface. However, if the cap thickness was 135 μm or greater, it is possible to restart SMILE with a thinner cap. This option might be introduced into a future upgrade of the restart treatment module because the software knows the cap thickness used.

There have been improvements over time to the VisuMax laser that have affected the suction loss incidence; the vacuum suction was increased and the laser frequency was increased from 200 to 500 kHz. In addition to the change in frequency, the suction time can be reduced by adjusting the spot and track distance settings. Increasing the spot and track distance reduces the total number of femtosecond laser pulses required and therefore reduces the treatment time. However, optimization of spot and track distance settings must be done in conjunction with adjusting the energy to achieve a balance between visual recovery and ease of lenticule separation.5,16–19

Although suction loss is a potential complication of SMILE, the treatment can be completed as SMILE in the majority of cases without affecting the outcome. We found no difference in visual and refractive outcome between the suction loss cases and the fellow eyes of the same patients for our series.5 The suction stability management protocol described here incorporates intraoperative monitoring of the bubble pattern for eye movements that may require a surgeon-initiated suction loss. This comprehensive protocol allows the surgeon to make confident and efficient decisions during a time-sensitive and pressured part of the SMILE procedure.

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Incidence of Suction Loss in a 4,000 Eye SMILE Population Categorized by the Cause of Eye Movement

Eye Movement TypeSuction Loss
Fixation light tracking6
Bell's reflex10
Anxious patient2
Nociceptive reflex1
False suction1
All suction loss20

Authors

From London Vision Clinic, London, United Kingdom (DZR, TJA, RSV, GIC); the Department of Ophthalmology, Columbia University Medical Center, New York (DZR); Faculty of Medicine, Sorbonne Université, Paris, France (DZR); and Biomedical Science Research Institute, Ulster University, Coleraine, Northern Ireland (DZR).

Dr. Reinstein is a consultant for Carl Zeiss Meditec (Jena, Germany) and has a proprietary interest in the Artemis technology (ArcScan, Inc., Golden, Colorado) through patents administered by the Cornell Center for Technology Enterprise and Commercialization (CCTEC), Ithaca, New York. Drs. Carp and Archer receive travel expenses from Carl Zeiss Meditec. The remaining authors have no financial or proprietary interest in the materials presented herein.

AUTHOR CONTRIBUTIONS

Study concept and design (DZR, TJA, GIC); data collection (DZR, TJA, GIC); analysis and interpretation of data (DZR, TJA, RSV, GIC); writing the manuscript (DZR, TJA); critical revision of the manuscript (RSV, GIC); statistical expertise (DZR, TJA)

Correspondence: Dan Z. Reinstein, MD, MA(Cantab), FRCSC, London Vision Clinic, 138 Harley Street, London W1G 7LA, United Kingdom. E-mail: dzr@londonvisionclinic.com

Received: September 04, 2018
Accepted: October 22, 2018

10.3928/1081597X-20181023-01

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