Overview of Small Incision Lenticule Extraction
The invention of the femtosecond (FS) laser has dramatically changed the way we perform eye surgery. Since it started being used in 2003, the FS laser is now a critical tool in many procedures. One of these is laser in situ keratomileuses (LASIK), a common surgery technique to correct vision issues. This laser has also opened doors for new methods such as FS lenticule extraction (FLEx) that was introduced in 2007. FLEx is different from LASIK because it only uses the FS laser, making the procedure quicker and less costly for healthcare institutions.
When using LASIK, the surgeon creates a flap in the cornea (the clear front part of the eye) with a corneal flap and then reshapes the cornea. However, when using FLEx, the process is a bit different. While a corneal flap is still made, the cornea is not reshaped. Instead, the surgeon makes a careful cut inside the cornea and removes a small piece of it called a lenticule. This new method offers a great benefit in vision-correcting surgery and brings a new option aside from the regular techniques.
Another promising eye surgery technique is Small incision lenticule extraction (SMILE). This technique is different from others because it does not create a flap in the cornea. Instead, the surgeon makes a tiny cut in the cornea to remove the lenticule. SMILE is thought to help maintain the cornea’s natural structure better than LASIK or FLEx because, with SMILE, most of the cornea’s strength-supporting part is not disturbed. This technique is also hypothesized to cause less damage to the nerve and avoids issues related to the cornea flap.
SMILE was first used in 2008 and has since become increasingly popular among eye surgeons. It is now seen as a standard treatment option for vision corrections. It provides a similar level of results, safety, and predictability as FS-LASIK, making it a top choice for treating nearsightedness and astigmatism. Patients also report high satisfaction with their vision quality after the surgery. On the downside though, SMILE is believed to be more challenging to master for beginners. A step-by-step approach involving observation, practice, and actual experience with other lenticule extraction methods like FLEx and pseudo-SMILE is suggested for a safer and more effective learning process.
As SMILE continues to gain popularity around the world, proposed changes to the technique are aimed to make the lenticule-removing process easier. This ongoing improvement in SMILE surgery is critical to make sure they can execute the procedure safely and effectively, no matter their level of expertise.
Anatomy and Physiology of Small Incision Lenticule Extraction
Laser eye surgeries, such as SMILE, focus on the cornea. The cornea is the clear, dome-like layer that covers the front of your eye. During these procedures, a specific type of laser called an FS laser is used to create a small, lens-shaped piece of tissue within the cornea by making several precise cuts. Then, another cut is made on the outer edge of the cornea, usually towards the upper or upper side area. This second cut is needed to remove the lens-shaped tissue that was created.
Why do People Need Small Incision Lenticule Extraction
In 2016, the US Food and Drug Administration (FDA) approved a procedure called Small Incision Lenticule Extraction (SMILE) to treat nearsightedness (myopia), a vision problem where you can see close objects clearly, but items further away might be blurry. Specifically, it was approved for people aged 22 and older with myopia between -1 and -8 units (diopters) and astigmatism, a condition that causes blurry or distorted vision, of up to -0.5 diopters. Later, in 2018, the treatment was extended to myopic astigmatism up to 3 diopters. Currently, a specific SMILE platform can correct up to 6 diopters of astigmatism. However, the person should not have more than -8.25 diopters of astigmatism.
Europe has approved SMILE to treat stronger myopic cases, covering vision imperfections of up to -11.5 diopters, which includes -10 diopters of myopia and -3 diopters of myopic astigmatism.
In practice, doctors also check several other factors to ensure the person is a good candidate for the SMILE procedure. These factors include having pupils smaller than 7 mm in low light conditions (mesopic pupil size), having a thick enough cornea (the clear surface at the front of your eye), your corneal thickness must be above 475 microns, and your vision should have been stable for at least 1 year.
The doctor will also carry out an assessment to make sure your eyes are healthy before the procedure. They will look for abnormalities in the cornea and check for a condition called keratoconus, which causes the cornea to thin and bulge outwards. They’ll also calculate the percentage of corneal tissue that will be altered (PTA), aiming to keep it below 40%.
If you suffer from dry eyes, SMILE might be the best choice for you, as it causes less disruption to the surface of the eye. Also, dry eye symptoms, if they do develop, tend to be milder and heal faster with SMILE as compared to other vision correction surgeries. The regeneration of the nerve fibers, located just below the surface of the cornea, also occurs at a faster rate with SMILE.
From a mechanical perspective, SMILE is stronger than LASIK (another eye surgery used to correct vision), which might make it a better option for people with high vision errors. It’s also a good choice for people who play contact sports, as there is no risk of a flap (a thin slice of eye tissue) being dislodged because SMILE does not create a flap.
Another benefit of SMILE is that it causes fewer vision disturbances or ‘higher-order aberrations’ such as shadows or glare after the operation. Consequently, it can be a better choice for people with large pupils who might suffer from these issues at night when their pupils enlarge. However, SMILE can be a more challenging procedure for surgeons to perform, especially during the early stages of learning, as compared to surgeries like LASIK.
While LASIK is often used for farsighted people (hyperopia) or people with irregularities on their cornea, SMILE has shown to be a better option for people with myopia or astigmatism without other issues such as irregularities on the corneal surface. The chances of experiencing glare or halos, often a problem for patients with larger pupils undergoing LASIK, are comparatively less with SMILE. However, for surgeons, early stages of performing SMILE can be challenging as compared to LASIK.
When a Person Should Avoid Small Incision Lenticule Extraction
For some patients, the Small Incision Lenticule Extraction procedure (known as SMILE) may not be the best option. This can depend on a variety of reasons. For instance:
People who have a certain thinning disorder of the cornea, a part of the eye’s surface, known as keratoconus, or a thin cornea (less than 475 µm thickness) are not advised to undergo SMILE. This is primarily to reduce the chance of post-surgery complications such as a bulging cornea.
Conditions like unmanaged glaucoma or uveitis, significant cataracts, corneal scarring, seeing with only one eye, active eye inflammation or infection, severe dry eye or ocular allergy disqualify patients from getting SMILE laser procedure.
Women who are pregnant or breastfeeding are advised not to get the procedure. This is due to hormone changes that can affect the focus of the vision.
People who had previous cases of herpes simplex keratitis (a viral eye infection) can still go through SMILE provided they get antiviral treatment before and after the surgery. However, this group falls under what doctors call “relative contraindication” meaning it’s a matter of balancing risks and benefits.
Patients with irregular cornea, irregular corneal astigmatism (an oval-shaped cornea), disorders in their immune systems, certain eye surface irregularities, history of autoimmune diseases, and mild dry eye or ocular allergies also fall into the relative contraindication category, which requires careful consideration.
Patients with unmanaged diabetes should be cautious as this can slow down the corneal wound healing process.
SMILE surgery can be more challenging for beginners, especially those with certain considerations like low cases of nearsightedness. People with challenging eye features such as deep-set eyes and narrow gaps between the eyelids, or noticeable noses might be at higher risk of challenges during the surgery. Patients who tend to move their eyes and head a lot can also make the surgery difficult for beginners.
Patients with high eye astigmatism may experience rotation of the eye, so they should be handled by an experienced surgeon.
Equipment used for Small Incision Lenticule Extraction
The medical device used to correct vision, known as the intrastromal refractive lenticule, is created with a special laser commonly found in the industry. This specific laser emits light particles at a specific wavelength and speed.
The machine used for this procedure is designed to create a piece within your eye to help correct vision. It’s made with a computer, a laser, and a foot switch to control the operation. The machine also comes with built-in lighting systems, and uses a one-time contact lens, known as the treatment pack, for easy operation.
The treatment pack comes in different sizes: small, medium, and large. The machine is capable of pre-set modes, namely standard, fast, and expert to cater to different needs. Good for beginners, the standard mode comes with factory settings. Fast mode allows the user to adjust the settings meeting specific needs. Expert mode is for advanced users, it allows full customization for each case providing a high level of control. Though Initially, consulting with the engineer is recommended.
The laser machine allows customization of various parameters including spacing between laser spots, distance between laser spots in adjacent tracks, size of bubbles produced during laser cuts, and the amount of energy per pulse. For the procedure, the direction of the laser is set to spiral inward for the back plane and outward for the front plane.
Who is needed to perform Small Incision Lenticule Extraction?
When a special type of medical laser, known as an FS laser, is used for procedures like SMILE (a type of eye surgery to correct vision problems), various types of healthcare professionals work together. Each of them has specific skills and responsibilities. Depending on the hospital or healthcare center, some roles may vary, but mostly the team consists of the following people:
A doctor called an ophthalmologist or refractive surgeon who is responsible for doing the surgery.
A surgical technologist or a scrub nurse who helps the surgeon during the operation. They make sure that all the surgical tools are available and sterilized.
A biomedical engineer or a laser technician who ensure that the FS laser is working correctly. This is very important as the laser is the main tool for this surgery.
Then there is an application specialist, whose job is to ensure that all the technology and equipment used in the surgery is being used correctly and safely.
Nursing staff is also involved—they look after your general care and comfort during your hospital stay.
An anesthesiologist or anesthetist who administers medication to prevent you from feeling pain during the procedure.
Each of these professionals has your safety and well-being in mind during the procedure, so ensure you feel comfortable and safe.
Preparing for Small Incision Lenticule Extraction
When preparing for an eye treatment called SMILE, it’s important for doctors and patients to have detailed discussions about the procedure. SMILE stands for Small Incision Lenticule Extraction, which is a type of laser eye surgery. It’s crucial for patients to know both the benefits and risks of this procedure. They also need to know what to expect during the surgery, like what they might hear, feel, see, and smell. Getting the patient’s agreement or “informed consent” to do the surgery is a necessary part of this process. Patients should also understand that the main goal of this surgery is not to make their vision perfect, but to reduce their need for glasses or contact lenses.
Before the surgery, doctors need to check the patient’s health history to make sure there are no conditions that could cause problems during or after the surgery. They also need to make sure the patient has realistic expectations about what their vision will be like after the surgery.
The doctor will also perform an in-depth preoperative eye examination. This includes checking the eyelids and tear film for dry eye or eyelid inflammation, two conditions that might affect the success of the surgery. The doctor will measure the patient’s refractive error, which causes blurry vision, using manifest and cycloplegic refraction.
Other parts of the examination include inspecting the cornea for any issues, measuring pupil size, and running a slit-lamp exam to check for abnormalities in the cornea. The doctor will also measure the thickness of the cornea, a process known as corneal pachymetry, and check the shape of the ocular surface or corneal topography. Measuring intraocular pressure is necessary to identify glaucoma, a condition that damages the optic nerve. Lastly, the doctor will perform a fundoscopy to check for any issues at the back of the eye.
Just before the SMILE procedure, the doctor will give the patient eye drops containing antibiotics and a topical anesthetic to numb the eye. It’s important not to use too much anesthetic, as it can loosen the top layer of the cornea and potentially increase the risk of complications.
How is Small Incision Lenticule Extraction performed
The SMILE (Small Incision Lenticule Extraction) procedure is a surgical operation aimed at correcting issues with the vision. The procedure mainly involves docking (aligning the eye with the surgical equipment), creating a lens-shaped piece of tissue (called a lenticule) with the help of a special laser, separating this lenticule from the surrounding tissue, and finally removing it. The lenticule is separated carefully with a special tool, and this dissection starts with a small cut. This is done first on the front layer of the eye, followed by the back layer.
Before the procedure, it is essential for the patient to be well-positioned to ensure they are comfortable throughout the surgery. It’s also important that they fully understand the whole procedure and provide informed consent. For pain relief, a topical anesthetic (a numbing cream) is applied to both eyes before surgery. It’s important to take care not to use too much, as this could loosen the top layer of the eye, leading to complications.
During the surgery, the patient will be asked to lie still and avoid sudden movements. They will also be instructed to take shallow breaths to minimize head movement. Keeping the patient’s head well-positioned is crucial to ensuring the surgery is carried out accurately.
When it comes to docking, the patient lies flat and is directly beneath the laser equipment. A disposable curved lens is used to ensure accurate positioning. The lens aligns properly with the surface of the eye. The patient is then asked to keep their gaze fixed on a green blinking light. This ensures accurate placement of the laser beam.
The laser is then used to create sequential cuts or incisions deep in the cornea, to create the lenticule and a small cut for accessing and removing the lenticule. After the laser makes the cuts, the surgeon uses a thin tool to separate the lenticule from the surrounding tissue. The lenticule is then removed using a special instrument.
The laser settings and parameters can be customized based on the surgeon’s preference and the specifics of the case. Generally, the standard settings include a certain depth, cut width, and minimum thickness of the lenticule.
During the SMILE procedure, the laser creates the lenticule by making a cut from the outside to the inside, followed by side cuts and finally an inside-out cut. This final cut is performed last in this procedure.
After the laser cuts, a thick visible bubble is formed in the cornea. Inside this bubble, there are two visible rings, which guide the surgeon in identifying the edge of the lenticule and the necessary dissection. After dissecting the lenticule, it is removed.
It’s notable that extracting the lenticule is a particularly tricky task for surgeons who are not experienced in this procedure. Incorrect identification of the tissue plane can result in it sticking to the top layer of the cornea. One technique to avoid this is the “meniscus sign,” which is a method used to identify the back plane during the creation of the back layer channel.
In some cases, if the lenticule is not dissected correctly, it is important to distinguish between the edge of the lenticule and the front dissection plane. This helps to minimize the risk of causing any unwanted damage to the eye during the surgery.
Possible Complications of Small Incision Lenticule Extraction
SMILE (Small Incision Lenticule Extraction) eye surgery can have some complications related to the learning curve of the doctors performing the surgery and the complexity of the procedure. These complications can be split into three main areas:
1. Creating the lenticule (a piece of eye tissue)
2. Separating the lenticule from the rest of the eye
3. Removing the lenticule.
Creating the Lenticule
When creating the lenticule, there can be complications like the loss of suction on the eye, a layer of bubbles, minor bleeding, and black spots. If the suction is lost, typically caused by sudden patient eye movement, redocking and recentering are recommended if less than 10% of the lenticule has been cut. However, if more than 10% has been cut, the surgery should switch to using a different type of eye laser (excimer).
Black spots, caused by debris or air bubbles trapped between the contact lens and the eye, don’t typically affect vision and can be removed by cleaning.
Separating or Removing the Lenticule
Some common issues while separating or removing the lenticule include remaining lenticule pieces, scratches on the cornea, lenticule adhesions, and tears in the cut. These can typically be managed during or after surgery. There can also be scratches on the corner of the eye (a corneal abrasion), which happen in about 5.5% of cases, often due to excessive manipulation.
After the Surgery
After SMILE surgery, you could experience dry eyes, a corneal abrasion (scratch on the eye surface), or infectious keratitis (an infection of the cornea). A post-operation dry eye occurs about 3% of the time due to decreased nourishing influence in the eye’s surface, inflammation, damage to certain cells during suction, and reduced eye-blinking sensation. Research indicates lower dry eye symptoms after SMILE surgery than another type of laser eye surgery, FS-LASIK.
For infectious keratitis, staying with your post-op topical antibiotic regimen can reduce the chances of infection. If you do get the infection, washing out your eyes with a bacteria-killing solution and antibiotics is typically recommended.
In conclusion, the main complications after SMILE surgeries are as follows:
* Loss of suction
* Black spots
* Bubble layer
* Formation of lenticule adhesions
* Remaining lenticule pieces
* Lenticule tears
* Surface scratches of your eye (Epithelial defects)
It’s also important to know that, during a SMILE procedure, doctors look for various signs to understand if there is lenticular adhesion (sticking of the lenticule). For example, the meniscus sign—a gap between the inner ring and the lenticule edge—can be identified when the surgeon slightly pushes the lenticule edge while creating a channel behind the lenticule. Another sign, known as the shimmer sign, can be seen during the cutting phase of SMILE. Bright light reflex is observed around the instrument, and this can help the doctors understand the correct dissection plane. Lastly, the ‘white ring sign’ is where the ring position in relation to the instrument can be seen in clearer light, particularly in the presence of a dark iris. These signs help the surgeons successfully carry out the surgery.
What Else Should I Know About Small Incision Lenticule Extraction?
SMILE and FS-LASIK are two commonly performed eye surgeries. Recent studies showed that 88% and 98% of eyes seen significant vision correction three months after the operation with SMILE. Even more, 61% to 96% of patients had 20/20 vision or better in the long term.
Numerous benefits have been noted for SMILE compared to FS-LASIK. Clinical trials have shown that there is less dryness in the eyes after a SMILE procedure compared to LASIK. Additionally, there are fewer minor visual disturbances due to SMILE possibly creating a more uniform corneal refractive power – the ability of the eye to bend light onto the retina. It is also found that there are fewer inflammatory cells in eyes treated with SMILE than those treated with FS-LASIK, indicating less inflammation post-surgery.
It’s also been found that patients who have undergone SMILE have reported higher satisfaction levels and a significant improvement in vision-related quality of life compared to those who have undergone LASIK. Recent research shows that SMILE offers better corneal mechanical stability than FS-LASIK. This means the cornea, which is the clear front surface of the eye, is more resilient after surgery with SMILE.
However, SMILE isn’t perfect and there are some downsides compared to FS-LASIK. Patients undergoing SMILE may feel more discomfort during tissue manipulation than flap lifting in LASIK. To deal with this, doctors may use more numbing drops or give patients medication to calm them down before surgery. Patients who have had SMILE also reported more issues with light sensitivity and blurry vision one month after the procedure was performed than those with FS-LASIK, but these issues usually resolve after three months. Additionally, the visual recovery may be slower with SMILE compared to FS-LASIK and there may be more light scattering in eyes treated with SMILE three months after the surgery.
SMILE is slightly less effective than LASIK for treating low-to-moderate astigmatism (a common vision condition that causes blurred vision). However, the results for correcting high astigmatism are comparable. A significant proportion of patients undergoing SMILE may have impaired corrected distance visual acuity (sharpness of vision doing distance activities) up to three months after the operation. Therefore, any further surgery to enhance the results should be delayed to allow sufficient time to recover visual function.
Retreatment options after SMILE are subject to ongoing discussion. There is no clear consensus on the best approach, but possibilities include redoing the SMILE procedure, surface ablation (a laser treatment to reshape the cornea), or converting the SMILE cap into a full flap, among other suggestions. These various methods have their pros and cons, so more research is needed for clarity.
SMILE may become more popular for treating farsightedness in the future. Preliminary research shows that SMILE could achieve similar results to LASIK for treating farsightedness. Despite these promising results, more research is needed to confirm the benefits of SMILE over other laser eye surgeries.
