Lasik Eye Surgery

Overview

Nowadays, excimer laser surgery is one of the most common ophthalmic operations. Thousands of patients are operated on each year in the United States to repair various refractive problems. Because of their safety and efficacy, LASIK (Laser-assisted in situ keratomileusis) and PRK (Photorefractive keratectomy) have become the most widely done surgical treatments in this field, although both have certain drawbacks.

Post-operative discomfort, blur, and delayed visual recovery are some of the most prevalent problems associated with PRK. LASIK, on the other hand, includes drawbacks such as possible flap-related issues (intra and post-operative), interface-related difficulties, and post-LASIK ectasia.

Laser-assisted in situ keratomileusis definition

The process of laser-assisted in situ keratomileusis (LASIK) is a standard ophthalmologic surgical treatment used to correct refractive defects. Dr. Gholam Peyman invented LASIK in 1989. Dr. Ioannis was the first to publish the use of LASIK inpatient treatment. This surgery quickly gained popularity due to the shorter recovery time and fewer post-surgical problems, with no compromise ineffectiveness.

LASIK has been one of the most inspected and analyzed surgical procedures that have undergone FDA review since its introduction into clinical practice.

Thirty years later, with advances in technique and technology, LASIK continues to produce efficient, predictable, and safe results, with patients reporting satisfaction with the surgery as compared to using spectacles or contact lenses.

A Historical Perspective

Understanding the significance of LASIK in refractive correction necessitates an understanding of its history. Dr. Tsutomu Sato of Japan made the first big advance in refractive treatment in the 1930s with radial keratotomy. The cornea was flattened by making large incisions into Descemet's membrane, which helped correct myopia.

These deep incisions, however, caused a slew of problems, including corneal decompensation. Alternative procedures, like as Dr. Antonio Méndez's hexagonal keratectomy in Mexico, were developed. It was still difficult to repair individuals with astigmatism or an asymmetric cornea at the time.

Keratomileusis is the medical word for corneal reshaping, which was pioneered by Spanish ophthalmologist José Barraquer in the 1950s and 1960s. Initially, he used a microkeratome, a mechanical tool with an oscillating sharp blade that slices the top layer of the cornea away to generate a lenticule and show the underlying stroma.

Anatomy and Physiology

The cornea is responsible for some of the eye's refractive power. It is responsible for around two-thirds of the eye's refraction power. In myopic, hyperopic, and astigmatic patients, LASIK changes the refractive power of the cornea.

The cornea is a half-millimeter-thick tissue that covers the front surface of the eye. A squamous epithelial layer, the anterior basement membrane (Bowman's), a stroma loaded with keratocytes and collagen, and the posterior basement membrane with a single layer endothelium separating it from the anterior chamber of the eye make up the five layers.

LASIK surgery initially alters the cornea's refractive power by forming a hinged corneal flap from the epithelium, Bowman's membrane, and the superficial section of the corneal stroma. The stroma's more posterior layers are exposed for ablation therapy.

As a result, for a myopic treatment, the central corneal curvature is reduced by ablation, and the overall refractive power of the eye is reduced to achieve emmetropia, or normal vision. The paracentral region is flattened for hyperopic therapy, resulting in a steeper central cornea and an increase in refractive power. Following stroma-targeted laser treatment, the flap is replaced, and reepithelialization occurs along the flap margin. Sutures are not required.

Indications

Patients with low to high myopia, with or without astigmatism, may benefit from LASIK. It has been demonstrated that LASIK can improve myopia; nevertheless, it is typically recommended in patients with low to moderate myopia, as these individuals have a higher risk of developing emmetropia.

This technique has also been shown to be safe and effective in individuals with hyperopia and astigmatism. While LASIK can treat hyperopia with more predictable outcomes, it is suggested that LASIK be performed on hyperopic and astigmatic patients.

The type and severity of the refractive error, as well as other factors such as the patient's age, corneal thickness, crystalline lens changes, keratometry, and corneal topography results, all influence the ophthalmic surgeon's decision to perform excimer laser ablation or other treatment options for the patient.

LASIK is now the most used laser therapy for refractive error. Aside from its usefulness for a wide range of refractive problems, patients have very minimal discomfort compared to methods that do not generate a flap, with a recovery period to baseline of only a few days.

It is critical to discuss realistic LASIK expectations with the patient. These operations are frequently expensive and are not covered by insurance since businesses deem them aesthetic rather than medically required. The usage of two lasers (excimer laser and femtosecond laser) in most clinics accounts for the high cost, which ranges from $1,500 to $2,500 per eye.

Furthermore, the patient should be advised that LASIK does not address presbyopia and that reading glasses may still be required. At a later age, a myopic shift with cataract development is possible.

Contraindications

Absolute Contraindications

• Refractive Instability

Instability is defined as changes more than 0.5 D in the previous year, and LASIK is not suggested for patients since it is a permanent operation, and operating on quickly changing eyes may result in serious consequences such as postoperative ectasia. Pregnancy, lactation, and uncontrolled diabetes mellitus are all factors that might contribute to refractive instability, according to the FDA's LASIK recommendations.

• Corneal Ectasia

A typical corneal thickness is between 540 and 550 microns. The chance of developing keratectasia increases by 5% if the preoperative cornea is less than 500 microns or the postoperative residual stromal thickness is less than 250 microns.

• Keratoconus

Because of the possibility of corneal ectasia, a cone-shaped cornea is an absolute contraindication to LASIK. A practitioner should also be mindful of subclinical keratoconus, such as forme fruste keratoconus (FFK), which is keratoconus that is not identifiable with slit-lamp and corneal topography tests. As a result, it might be a false negative.

• Uncontrolled Systemic Diseases

SLE, Sjögren syndrome, rheumatoid arthritis, Graves disease, Crohn's disease, and other disorders that induce keratoconjunctivitis sicca or other kinds of ocular pathology.

• Active Infection

Bacterial blepharitis and keratitis can increase the risk of spreading infection and inflammation through the cornea into the eye.

Relative Contraindications

• Age

While LASIK is typically not recommended for youngsters owing to refraction changes throughout puberty, it has been effective in individuals under the age of 18 who have significant myopia or other serious diseases.

• Herpes Zoster Ophthalmicus or Herpes Simplex Keratitis

Active Herpes infection should be treated before surgery. A research found that operating on individuals with a history of ocular Herpes is safe; nevertheless, it is suggested that patients wait one year for the virus to be in remission before undergoing surgery.

• Cataract

Patients with minor cataracts may still get LASIK surgery, but if the cataract advances, visual acuity may be compromised despite LASIK. Following cataract surgery, intraocular lens implantation is an indicated alternate method to LASIK.

• Glaucoma

Patients with glaucoma who have LASIK surgery may experience a misleading drop in intraocular pressure (IOP) as a result of decreased corneal thickness. Furthermore, advanced glaucoma patients have a higher risk of optic nerve injury after surgery due to the transitory increase in intraocular pressure caused by the first suction administered to the cornea.

• Corneal Dystrophy (CD)

Certain disorders, such as Fuchs endothelial corneal dystrophy, can be sped up by surgical procedures like LASIK. Patients with various types of corneal dystrophies, such as granular corneal dystrophy and lattice corneal dystrophy, may benefit after LASIK, although disease recurrence is possible.

• Keloidosis

Some sources claim that individuals having a history of keloids may have their surgical outcomes hampered by the condition. It has been noted, however, that individuals with keloids who undergo refractive surgery have satisfactory results.

• Pupil Size

It has previously been noted that patients with bigger pupil sizes are more likely to experience post-surgical visual problems such as halos/star-bursting with light and glare. However, with the introduction of new technology lasers, wider ablation zones, and blend/transition zones, the link between high pupil size and visual difficulties is weakening.

Equipment

• Excimer Laser

The United States Federal Drug Administration (US FDA) has authorized many excimer lasers, each having benefits that may be chosen based on the patient's needs. Lasers differ in terms of beam size, repetition speed, and other features such as eye-tracking.

Today, custom-LASIK is often used, either utilizing topography-guided (using the measured corneal topography to set the laser) or wavefront-guided (calculating the light refraction off of the cornea to configure the laser) techniques. These customized lasers can be used in combination with spot or slit-scanning lasers to assist reduce post-surgical problems by precisely sculpting the cornea.

• Femtosecond Laser

Flaps can be created using a variety of techniques, as discussed in the method section; however, the usual strategy with LASIK at the moment is to produce the flap using a femtosecond laser. The benefit of using a laser over mechanical procedures is that the flap may be generated thinner and with more accuracy, resulting in better outcomes and fewer flap-related issues following surgery.

Preparation

Contact lenses should be temporarily discontinued 1 to 2 weeks before a screening test to allow the corneal surface to settle, allowing for more precise measurements. To assist detect any contraindications to LASIK, a full history and physical examination should be done. Prior to contemplating surgery, a comprehensive eye examination must be conducted in addition to visual acuity tests. This exam should include a slit-lamp exam, fundoscopic exam, dry eye examination, and intraocular pressure measurement.

Keratometry and pachymetry are used to assess the cornea. A normal corneal thickness of around 550 microns is required for LASIK candidates. Topography and tomography are critical for excellent refractive screening and have become the standard of care for pre-operative keratoconus screening.

The Randleman criteria can assist select individuals who are at high risk of developing post-surgical corneal ectasia for a more complete examination of eligibility. Topographical findings, corneal thickness, age, and spherical manifest refraction are all factors considered. A score of 4 or above indicates a significant likelihood of developing post-LASIK ectasia.

Once a patient has been authorized for LASIK, the Munnerlyn formula is used to compute the ablation zone and depth for LASIK therapy, which takes into account the thickness of the ablated tissue, the diameter of the optic zone, and the dioptric correction. The percentage of tissue changed (PTA), which takes into account corneal thickness, ablation depth, and flap thickness, also aids clinicians in predicting the likelihood of post-LASIK corneal ectasia; a PTA of 40% or above has been linked to the formation of ectasia. 

Technique

Pre-Surgery

All equipment should be thoroughly inspected for safety and to guarantee that patient topographical data is input into the excimer laser. The patient should be educated on the procedure's routine before signing an informed permission agreement.

Surgical Technique

LASIK surgery is typically conducted as follows: the patient is taken to the table and positioned in a comfortable supine posture. The other eye is taped shut, and the operating eye is held open with a speculum. Eye drops are used to anesthetize the eye. A suction ring is put on the cornea, and either a microkeratome or a femtosecond laser is used to mark the cornea for flap development.

The laser is used to outline the flap by generating micro-cavitation bubbles in a cleavage plane. The flap's diameter, thickness, side-cut angle, hinge length, and hinge location may all be modified. For flap formation, the femtosecond laser has essentially supplanted the microkeratome.

Following the creation of the flap, the surgeon gently reflects the flap to show the underlying stroma. The surgeon places and activates the excimer laser to shape the stromal surface by photoablation. The flap is subsequently replaced in its original location by the surgeon. It is safe for the patient to have LASIK surgery on both eyes on the same day.

Post-Surgery

Because dry eyes are a typical side effect of surgery, the patient uses preservative-free artificial tears. Patients are encouraged to use artificial tears on a regular basis, but if problems continue, punctal plugs may be administered. In addition, the patient is given antibiotics and steroidal eye drops to utilize for 5 to 14 days following the procedure.

The patient returns to their surgeon as directed by their practice, and following evaluation, may require extra small LASIK modifications to rectify remaining refractive error, referred to as an enhancement surgery, generally within a year of the first procedure. Enhancement operations are performed on around 10% of patients, with a higher frequency in patients with high initial corrections, over 40 years old, or with astigmatism.

Alternate Procedures

Other laser-assisted treatments may be available to patients with refractive problems. Furthermore, as technology has advanced, variants to LASIK have been effectively adopted in practice.

PRK

According to one study, whereas LASIK produces higher visual acuity outcomes sooner after surgery, PRK patients tend to keep better refraction years later. Another research found that PRK had better results in patients with low to high myopia, with fewer problems, than LASIK, despite earlier studies finding that LASIK had superior outcomes. Multiple studies demonstrate that both techniques produce comparable but great results.

In determining which surgery would result in the best outcomes for the patient, the physician must apply clinical judgment. While discomfort has always been cited as a drawback of PRK, the combination of bandage contact lenses and NSAIDs has resulted in a pain-free post-op recovery.

Femtosecond Lenticule Extraction (FLEx) or Small Incision Lenticule Extraction (SMILE)

The squamous epithelium is removed with the femtosecond laser without leaving a flap. When compared to LASIK, it is advised in individuals with greater myopia. Compared to LASIK, studies have demonstrated comparable clinical results, with lower instances of dry eyes following surgery.

Laser Epithelial Keratomileusis (LASEK)

Lasek is a treatment in which an alcohol solution is used to help remove the superficial corneal layer. To remove the layer, Epi-LASEK employs an epi-microkeratome. Both strategies are PRK versions and can be regarded credible alternatives.

Complications

• Dry Eyes

Dry eyes caused by a lack of tear production is one of the most prevalent transitory adverse effects of LASIK. This is due to the lacrimal reflex being interrupted as a result of nerve tissue being cut during the treatment. According to several studies, dry eyes develop in 85 to 98 percent of patients one week following surgery. After one month, this figure declines to roughly 60%. Until the nerves regrow, artificial tears and/or punctal plugs are used.

• Visual Aberrations

20% of patients will report some kind of visual alteration. Some individuals may experience glare, halo or star-bursting patterns surrounding lights, haze, and diminished contrast sensitivity. According to the FDA, visual impairments usually resolve three to six months following the treatment.

• Diffuse Lamellar Keratitis

Patients may also have blurriness and a foreign body sensation, which might be caused by diffuse lamellar keratitis (DLK), often known as "sands of Sahara" syndrome, a sterile inflammatory reaction. Under the corneal flap interface, inflammatory cell infiltrates occur. This condition may occur in as many as 1 in every 50 LASIK procedures. DLK often appears one to two days after surgery and disappears within one week with adequate corticosteroid therapy.

• Corneal Flap Complications

After surgery, the incidence of microstriae, macrostriae, buttonholing, incomplete cap, free cap, cap dislodgement, and epithelial ingrowth is minimal, with 0.1-4 percent of patients reporting some type of problem. It has been demonstrated that corneal flap problems can result in a decrease of visual acuity. 

• Post-LASIK Ectasia

A thin cornea prior to surgery may increase the chance of developing ectasia or additional corneal thinning. The incidence has been observed to range between 0.04 and 0.6 percent. Because of the narrower flaps formed by femtosecond-assisted LASIK, this problem can be avoided. The Randleman criteria, as mentioned in the preceding section, can also be used to screen for patients at high risk of developing ectasia. 

• Infectious Keratitis

After LASIK, less than 0.1 percent of patients will develop an infection. Gram-positive organisms such as Staphylococcus species or atypical mycobacteria are the most prevalent causes of infection, especially if illness occurs one to two weeks following surgery.

• Rare Complications

Ischemic optic neuropathy, retinal detachment, vitreous hemorrhage, and posterior vitreous separation are all potential but extremely rare LASIK problems that occur in fewer than 0.1 percent of patients.

Clinical Significance

While LASIK may be used to correct refractive problems, it has been demonstrated that it is most reliable in individuals with myopia of -6.0 D or less and astigmatism of less than 2.0 D. A recent meta-analysis research found that LASIK improves visual acuity and patient safety similarly to other refractive surgery techniques. This surgery offers the extra benefit of allowing for a faster recovery and less postoperative discomfort. Several studies show that individuals who had LASIK surgery were satisfied in 92 percent to 95 percent of cases.

Conclusion 

Various approaches are utilized in LASEK eye surgery to keep the very thin corneal surface layer of cells (epithelium) that is needed to repair the cornea following laser sculpting. LASIK uses a laser or a mechanical instrument (microkeratome) to generate a thicker flap for the laser sculpting.

Ophthalmic surgeons, optometrists, nurses, medical assistants, and technicians are common members of the LASIK treatment team. In the outpatient environment, team members collaborate to find the best candidates for LASIK in order to avoid needless expenditures and issues for the patient. On the day of surgery, the team is responsible for following standard clinical protocols, such as obtaining the patient's informed consent for the procedure, correctly marking which eye will receive which specific treatment, proper placement and preoperative evaluation of necessary equipment for the procedure, a timeout called before the operation, and patient education throughout the treatment process.

Communication among team members is essential for any changes in patient status before, during, or after the surgery, and it improves patient outcomes.