Laser In Situ Keratomileusis
Karl Stonecipher
Jessica Mathew
Stephen Brint
Laser in situ keratomileusis (LASIK) is the combination of using the excimer laser with a device used for making a flap of corneal tissue. More than 60 years ago, Jose I. Barraquer, M.D., created the initial concept of in situ keratomileusis (cornea/carving), which really consisted of adding, removing, or altering corneal tissue to modify the refractive power of the eye.1 Keratomileusis in situ initially started over 50 years ago with the creation of a corneal lamellar disc (surface), also called lamellar keratoplasty, with a device called a keratome. By 1962, Dr. Barraquer looked at addition, subtraction, or modification of the corneal tissue. Initially, this started with the development of the cryolathe where he would freeze the removed lamellar disc and alter its shape to reduce the refractive error of the patient. However, this was fraught with complications including but not limited to corneal scarring and irregular astigmatism.2,3,4,5,6,7,8,9,10 Fast forward to the late 1980s and early 1990s when Pallikaris started animal studies using an excimer laser combined with a microkeratome with both Pallikaris and Burrato doing the early human trials and Peymon patenting what is known as LASIK today (Fig. 7.1).11,12,13,14,15,16,17,18,19,20 A more detailed history of LASIK can be found in an article by Reinstein et al.21
INDICATIONS
Myopia
Hyperopia
Myopic astigmatism
Hyperopic astigmatism
Mixed astigmatism
Presbyopic treatments
Laser vision correction was designed to reduce or eliminate refractive errors of essentially normal corneas. However, there are more advanced laser vision correction options now available that can also reduce or eliminate higher-order aberrations. The primary goal of LASIK is to allow the patient to see postoperatively equal to or better than their present refractive correction (glasses, contact lens, etc.) while providing a safe procedure with low to no complications or repeat procedures, known commonly as enhancements.
 FIGURE 7-1 Copy of an image of the first U.S. Patent of LASIK in 1989. |
CONTRAINDICATIONS FOR LASER IN SITU KERATOMILEUSIS
Keratoconus
Corneal scarring or opacification
Pellucid marginal degeneration
Corneal ectasia
Various corneal dystrophies
Unstable refraction
Contact lens warpage
Uncontrolled ocular surface disease
Uncontrolled systemic diseases (i.e., diabetes, thyroid, etc.)
Uncontrolled connective tissue disease
Uncontrolled intraocular inflammation (i.e., uveitis, etc.)
The screening process for LASIK continues to evolve. Initially, the screening process consisted primarily of a routine eye examination to include manifest refraction, cycloplegic refraction, and topography. Today, additional diagnostics are included, such as tomography, corneal hysteresis, corneal aberrometry, corneal pachymetry, ray tracing, and others are added to the mix but not necessarily all inclusive. Standard of care ranges from country to country but basics include a refraction, corneal thickness, corneal topography, and/or corneal tomography as an addition to a routine eye exam.
PATIENT-INFORMED CONSENT PROCESS
Following are some free consent form resources with more detailed information:
1. https://www.omic.com/lasik-consent-forms/
2. https://www.omic.com/lasik-bilateral-simultaneous/
3. https://www.omic.com/lasik-off-label/
4. https://www.omic.com/lasik-assumption-of-post-op-care/
Informed Consent of the Patient
Consent documents received by the patient
Consent documents reviewed by the patient
Surgeon discussion with the patient
Risks and benefits of the procedure reviewed with the patient
Questions answered for the patient
Consent signed and placed in the chart
It is mandatory to discuss the procedure in detail, the benefits of the procedure, the alternatives to the procedure including no surgery at all.22 The risks of the procedure should also be discussed and include blindness, failure of the procedure, risk of loss of the eye or eyes, infection, and even death as a potential complication. Explaining and detailing the contents of the informed consent document to the patient is imperative. The patient should have an opportunity to ask questions and to have them answered in an understandable format. The patient and the doctor should verbally confirm that they understand what is about to take place and that they have agreed
to proceed with the planned procedure. Personally, the authors believe this discussion is a legally binding contract between the patient and the doctor and is the surgeon’s responsibility to undertake control of the informed consent process and should not be delegated.22,23,24 If co-management is to be part of the process, the patient must be informed of the individual duties of the comanaging clinician versus the surgeon, and follow-up procedures must be discussed in detail and agreed upon by the patient prior to surgery (Fig. 7.2).25
to proceed with the planned procedure. Personally, the authors believe this discussion is a legally binding contract between the patient and the doctor and is the surgeon’s responsibility to undertake control of the informed consent process and should not be delegated.22,23,24 If co-management is to be part of the process, the patient must be informed of the individual duties of the comanaging clinician versus the surgeon, and follow-up procedures must be discussed in detail and agreed upon by the patient prior to surgery (Fig. 7.2).25
 FIGURE 7-2 Sample informed consent created by Ophthalmic Mutual Insurance Company. |
PREOPERATIVE PREPARATION FOR LASER IN SITU KERATOMILEUSIS
Medical history
Allergies
Medication history
Past medical history
Ocular history
Surgical history
Ocular surface disease assessment and treatment
Contact lens discontinuation prior to evaluation
A full ocular examination, complete with medical history, current medications, and allergies, is performed prior to the procedure. Patients will be documented in the chart as candidates or noncandidates. Confirmation that the patient’s refraction is stabilized is imperative. This requires that contact lens wear be discontinued for an appropriate amount of time. Typically, soft single vision contact lenses should be discontinued for one week, while soft toric/astigmatic and multifocal contact lenses should be discontinued for two weeks. Rigid gas permeable lens wear can cause more of a challenge for reaching stability of the patient’s refraction due to reshaping of the corneal surface. On average, about one month per decade of lens wear is generally needed for the cornea to return to its original shape and for the refraction to reach stabilization. It goes without saying that ocular surface disease, glaucoma, and retinal diseases must be evaluated and treated prior to surgery, and patients must understand their candidacy or noncandidacy depends on this diagnostic work-up. The diagnostic devices and the refraction used for treatment depend on stabilization of the aforementioned for stable outcomes.26,27,28
As already mentioned, risks and benefits of the operation must be discussed in depth with each patient as well as quality of life after surgery. It is of utmost importance to appropriately set patient expectations prior to LASIK.29 In most patients, LASIK is overwhelmingly successful; however, postoperative refractive error including astigmatism, myopia, and hyperopia following LASIK can occur depending on individual patient healing and/or laser data entry errors.30
SETTINGS AND PROCEDURE
Sedation
Pre-procedure preparation
Flap preparation
Flap lift
Laser ablation
Flap repositioning
Flap assessment at the end of the procedure and post-procedure prior to patient departure for position confirmation
The LASIK procedure consists of flap creation with a mechanical keratome or a femtosecond laser.31 Data from the previously measured refraction and diagnostic devices, along with the aid of a nomogram, are utilized to determine the
amount of refractive error needed to treat lower- and, possibly, higher-order aberrations. The laser shot file is then transferred to the excimer laser. After making a flap with a mechanical microkeratome or a femtosecond laser, the stromal bed is treated with the patient-specific treatment profile created by the inputted data in a conventional fashion (Figs. 7.3, 7.4, 7.5, 7.6, 7.7).
amount of refractive error needed to treat lower- and, possibly, higher-order aberrations. The laser shot file is then transferred to the excimer laser. After making a flap with a mechanical microkeratome or a femtosecond laser, the stromal bed is treated with the patient-specific treatment profile created by the inputted data in a conventional fashion (Figs. 7.3, 7.4, 7.5, 7.6, 7.7).
 FIGURE 7-3 Creation of a 100 micron flap, which is 9 mm in diameter and has been created in 9 seconds. |
 FIGURE 7-4 The surgeon in this figure is lifting the flap that was just created to prepare for excimer laser ablation of the stromal bed. |
 FIGURE 7-5 The flap is hinged and the flap is being lifted by the surgeon in this figure. |
 FIGURE 7-6 The laser pulses are fired on to the stromal bed using either a topography-guided profile, an aberrometry-guided profile or wave front-optimized profile. |
 FIGURE 7-7 The flap is replaced to its original anatomical position, and pharmaceuticals are applied as per the surgeon’s protocol. |
POSTOPERATIVE CARE/CO-MANAGEMENT (FOLLOW-UP SCHEDULE)
Postoperative day 1
Postoperative week 1 (in person or telemedicine)
Postoperative month 1 (in person or telemedicine)
Postoperative months 3 (in person for data point for future nomogram development)
Postoperative year 1 (some include a six-month visit if indicated by the three-month exam)
Postoperative examinations are performed either by the surgeon or the comanaging doctor at 1 day, 1 week, and 1, 3, 6, and 12 months in most instances but vary based on surgeon or comanaging doctor preference.32 With current nuances with COVID-19, telemedicine has been included as part of the option to care and co-manage these patients to allow for reduced exposure of both the staff and the patients.33
POTENTIAL COMPLICATIONS AND THEIR TREATMENT
Complications for Laser In Situ Keratomileusis
Complications for LASIK can occur at any step (preoperative or postoperative) and vary based on timing, techniques, and technology used. The authors felt it was best to define the events in an easily regimented format using the Sentinel Article to define
the complications as outlined below. The references referred to below provide the reader with more detailed discussion, description, prevention and potential treatment for each event listed.
the complications as outlined below. The references referred to below provide the reader with more detailed discussion, description, prevention and potential treatment for each event listed.
Preoperative Events
Refraction accuracy (manifest and cycloplegic)
Stable refractions are mandatory prior to surgical intervention.
Topographic issues:
Irregular astigmatism
Contact lens “warpage”34
Pupil size
Pupil size is a debated issue. Some suggest counseling patients about the additional risks of postoperative dysphotopsias with pupils larger than 8 mm.38
Corneal pachymetry
The original limitations of 250 microns of the stromal bed were a theoretical assumption with keratomileusis procedures. Current thought surrounds the evaluation of the percent tissue altered as to judge the candidacy of a patient or lack thereof.39
LASIK is contraindicated in granular corneal dystrophy type 2 (Avellino corneal dystrophy).
Intraoperative Events
Suction loss
Suction loss with a mechanical microkeratome can result in devastating complications; however, this issue is less of an event with the femtosecond laser.40
Decentered flap
Flap decentration was not uncommon early on with mechanical keratomes (especially those in which blind passes were made). With newer centration technology, decentration is a rare event. With highly astigmatic, short, and long eyes, the surgeon centration is more of a challenge and requires diligence in these eyes.41
Opaque bubble layer (OBL)
The creation of an OBL occurs when the expanding gases created by the femtosecond laser become trapped in the stroma. It is related to settings on the laser and poor venting of the expanding gases through the channel or pocket depending on the type of laser used.42
Difficult flap lift/side cut tags
During flap creation, poor separation of the corneal tissues by the laser can occur. The reasons are multifactorial and are rare occurrences with today’s laser systems.43
Gas bubbles in anterior chamber (AC bubbles)
The presentation or migration of AC bubbles is a rare occurrence during flap creation with the femtosecond laser. The etiology is debated but may be anatomically related or laser setting related. Interference with tracking on the laser systems is an issue and waiting for resolution is recommended.44
Gas breakthrough
Gas breakthrough can be related to suction, anatomy (i.e., corneal scars), and thin flap settings of a variety of multifactorial issues. Depending on the severity, continuing the case must be managed on a case-by-case basis.45
Vertical gas breakthrough
Horizontal gas breakthrough
Postoperative Events
Day 1
Epithelial defects/desiccation
Epithelial defects and surface issues related to corneal dystrophy or ocular surface disease was not uncommon with mechanical keratomes. While still possible, the femtosecond laser has reduced the overall presentation of this complication. Management is on a case-by-case basis.46
Debris/foreign bodies in interface
Interface debris is related to foreign or organic matter. Inflammatory reactions to the debris or foreign bodies are the main issue, and surgeon’s vary on their management of these cases.47
Flap slippage
The postoperative day-1 visit is imperative because flap slippage if caught early does not result in reduced outcomes. These can occur idiopathically or traumatically in the early postoperative period. Striae in the flaps are defined as visually significant or visually insignificant and management is on a case-by-case basis; however, with visually significant flap slippage, it is considered an urgent if not emergent intervention.48
Diffuse lamellar keratitis
Diffuse lamellar keratitis (DLK) is graded from 1 to 4 and grade 4 is considered a toxic event. Management is discussed at length in reference [49], and when present, it needs to be addressed urgently and followed diligently.49
Week 1
Dislocated flap (trauma)
As mentioned earlier, movement of the flap can occur traumatically. Surgical intervention is considered urgent if not emergent to warrant a good outcome without loss of best corrected visual acuity (BCVA). When a flap is lost completely, then a bandage contact lens (BCL) is placed and the patient is managed like a postoperative photorefractive keratectomy (PRK). With resolution and refractive stability, outcomes can be surprisingly good.50
Infectious keratitis
A complete book could be written on the etiology and management of infectious keratitis after any type of refractive surgery. Reference [51] is a nice summary of the options.51
Diffuse lamellar keratitis
This results from accumulation of inflammatory cells in the interface between the LASIK flap and corneal stroma and should be treated quickly. Management of this occurrence can be found in reference [49].
Refractive error
Retreatment or enhancements after refractive surgery have been reduced with better lasers, ablation profiles, diagnostics, and postoperative regimens. Retreatments should occur after refractive stability and only in patients with appropriate anatomy postoperatively.52
Months 1 to 12
Dislocated flap
Late flap dislocation should be treated as an ocular emergency and handled quickly. Blunt or penetrating trauma is usually the issue, and lateral damage to other ocular structure should be investigated and ruled out.50
Flap melt
Flap melting is related to severe inflammation or autoimmune disease. Screening prior to surgery will help reduce this postoperative risk.53,54
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