Until recently, if you were one of the millions of people with a refractive error, eyeglasses and contact lenses were the only options for correcting vision. But with the arrival of refractive surgery, some people with myopia (nearsightedness), hyperopia (farsightedness), or astigmatism (a cornea with unequal curves), may have their vision improved through surgery.
Laser assisted in situ keratomileusis, or LASIK, is a refractive procedure that uses a ‘bladeless’ all-laser method (femtosecond and excimer laser) to permanently reshape the cornea.
LASIK is usually performed as an outpatient procedure using topical anesthesia with drops. The procedure itself generally takes about fifteen minutes. The surgeon creates a flap in the cornea with femtosecond laser beam. The flap is lifted to the side and the cool beam of the excimer laser is used to remove a layer of corneal tissue. The flap is folded back to its normal position and sealed without sutures. The removal of corneal tissue permanently reshapes the cornea.
The initial step of LASIK, the flap creation, is traditionally done with a microkeratome (mechanical microsurgical knife). Compared to a microkeratome, flap creation with the femtosecond laser is more precise and can create a thinner flap. Because it is computer controlled, the corneal flap created by laser is consistently- and precisedly-shaped, and is of a uniformly thin thickness, hence preserving more corneal tissue for added long term safety. There is also no risk of a blade-related corneal flap problem. Moreover, previous studies had suggested femtosecond flaps has less induced optical aberration when compared to the corneal flaps created with microkeratome.
For improved outcomes and enhanced safety, in our centre, corneal flap creation for LASIK is performed using the technologically advanced femtosecond laser. The subsequent step of cornea reshaping is performed with the latest generation excimer laser.
A shield protects the flap for the first day and night. Vision should be clear by the next day. Healing after surgery is often less painful than with other methods of refractive surgery since the laser removes tissue from the inside of the cornea and not the surface. If needed, eyedrops can be taken for pain and usually are only needed up to one week.
Some people experience poor night vision after LASIK. The surgery may result in undercorrection or overcorrection, which can often be improved with a second surgery. More rare and serious complications include a dislocated flap, epithelial in-growth and inflammation underneath the flap. Most complications can be managed without any loss of vision. Permanent vision loss is very rare.
The ideal candidate for LASIK has a stable refractive error within the correctable range, is free of eye disease, is at least eighteen years old and is willing to accept the potential risks, complications and side effects of LASIK.
Advanced Surface Ablation (ASA)
Not every patint is an ideal LASIK candidate. If a patient is prone to eye trauma or has thin / irregular cornea, LASIK may not be the appropriate surgery. In these cases, the surgeon may recommend advanced surface ablation, which is an effective alternative for many people.
ASA is an outpatient procedure, done under topical anesthetic eyedrops. It takes about fifteen minutes. The epithelium, the outer cell layer of the cornea, is removed with a blade, alcohol or a laser. An excimer laser, which produces ultraviolet light and emits high-energy pulses, is used to remove a thin layer of corneal tissue. Your ophthalmologist enters your vision correction information in a computer and the laser beam vaporizes the surface of the cornea up to that precise depth. By breaking the bonds that hold the tissue molecules together, your cornea is reshaped, correcting the refractive error. Because no incisions are made, the procedure does not weaken the structure of the cornea.
Immediately following surgery, a bandage contact lens is placed on the eye. After ASA, vision is blurry for 3 days to one week. It may take a month or longer to achieve one's best vision. Patients may be on eyedrops for up to three months.
Possible complications of ASA surgery include undercorrection, overcorrection, poor night vision and corneal scarring. Permanent vision loss is very rare. In recent studies monitored by the FDA, 95% of eyes were corrected to 20/40, the legal limit for driving without corrective lenses in most states.
To be a candidate for the procedure you must have a stable and appropriate refractive error, be free of eye disease, be at least eighteen years old and be willing to accept the potential risks, complications and side effects of ASA.
Phototherapeutic Keratomy (PTK)
PTK is an excimer laser surgical procedure that removes roughness or cloudiness from the cornea. The cornea is the smooth clear window of the eye in front of the colored iris that helps bend light rays so they focus directly on the retina, the light-sensing layer of cells at the back of the eye. If the corneal surface is rough or cloudy, the rays of light do not focus properly on the retina and images are blurry.
Until recently, the rough cornea was scraped smooth with a surgical blade, while the cloudy cornea required a partial or full corneal transplant. More recently, phototherapeutic keratectomy, or PTK, is an option.
The excimer laser allows some abnormal corneas to be treated with a cool beam of light that evaporates tissue. The principal advantage of laser surgery over conventional surgery is the laser is able to create a smoother corneal surface than a blade and smaller amounts of tissue can be removed.
Potential complications after PTK include poor wound healing, excessive corneal flattening resulting in changes of refractive error, and irregular astigmatism or poor vision that cannot be corrected completely with glasses.