Myopia, astigmatism and hyperopia surgeries (laser for myopia, astigmatism and hyperopia respectively) can be performed mainly by the following methods
ASLA (All Surface Laser Ablation) is the only transepithelial single-step treatment (laser for myopia, astigmatism and hyperopia) that avoids the eye coming into contact with any instrument. The clinical application of TransPRK, named ASLA treatment, uses the excimer laser to remove the epithelium, resulting in a more precise and more uniform treatment than what is achieved with either manual or alcohol-assisted debridement. ASLA was introduced in September 2009, and since then this treatment has gone through various evolutions.
TransPRK-ASLA, performed with the SCHWIND AMARIS laser system, applies an epithelial thickness profile that resembles a slight hyperopic treatment (less than 0.75 D). The resultant epithelium is thinner in the center, hereby avoiding or at least reducing hyperopic shift. Because ASLA applies the laser beam directly over the epithelium, it acts as a smoothing agent for the residual stromal bed.
Treating refractive errors (laser for myopia, astigmatism and hyperopia) with ASLA has several advantages.
The single-step approach allows simultaneous ablation of the epithelium and the stroma to shorten the overall treatment time and minimize the risk of corneal dehydration. Beside a faster surgical time, epithelial tissue removal has been optimized to avoid myopic-like corrections (approximately -0.75 D).
This innovative approach treats refractive errors (laser for myopia, astigmatism and hyperopia) by superimposing a defined epithelial thickness profile of approximately 55 µm at the center and 65 µm at the periphery (4 mm radially from center) with a corneal aspheric ablation profile. This defined epithelial thickness can change according to the preoperative measurments of the the patient. Additionally, the diameter of the epithelial removal is calculated to match the ablation zone, thus decreasing the wound surface and speeding up the healing process.
Photo-Refractive Keratectomy (PRK) is another method of surgically reshaping the cornea using the excimer laser (laser for myopia, astigmatism and hyperopia). The primary difference between PRK and LASEK is that for PRK, the surface epithelium is removed entirely in the area of treatment, whereas in LASEK, the epithelium is pushed to the side after being loosened with alcohol and repositioned after laser treatment. In both procedures, healthy corneal cells grow over the treatment zone from the periphery of the cornea towards the center. A contact lens is applied after surgery to improve comfort. During the few days required for healing, the eyes can be sensitive to light and uncomfortable.
Custom ASLA and Custom PRK
The Custom ASLA and Custom PRK methods allow the surgeon to bypass conventional surgery methods (laser for myopia, astigmatism and hyperopia) and achieve better results. New generation technologies using wavefront techniques to measure the whole eye's optics with its aberrations and irregularities and create a three-dimensional map of it.
The map contains detailed information that is unique to each eye, just like fingerprints for everyone. The doctor uses this information to plan the laser beam and adjust the treatment according to the eye characteristics.
Traditional ASLA and PRK techniques refer to common and lower level of difficulty aberrations, Custom ASLA and Custom PRK techniques refer to high-order aberrations such as party, spherical aberrations, and so on which affect the final quality of vision.
Relevant studies show that 5% -10% of patients undergoing these techniques benefit from these, while the remaining percentage is usually less beneficial.
Laser In Situ Keratomileusis (LASIK)
A form of outpatient corneal surgery (laser for myopia, astigmatism and hyperopia), combines incisional and laser surgery to improve myopia (nearsightedness), hyperopia (farsightedness), astigmatism and presbyopia. Once the surgeon has conducted all pre-operative examinations, the eye is anesthetized with numbing eyedrops, the area around the eye is cleaned, and an instrument called a lid speculum is used to hold the eyelids open.
The surgeon will then use a specialized instrument, called a microkeratome, to cut a thin, circular flap - the outermost 20 percent of the thickness of the cornea - to expose the portion beneath. This part of the procedure is called keratectomy.
While the inner cornea (the stroma) exposed, the surgeon will ask the patient to fixate on a specific light source above the patient. This is to ensure that the laser beam is aligned precisely with the center of the patient’s eye. Once the eye is in the correct position, the laser treatment is performed.
The computer-controlled excimer laser removes the tissue under the flap and reshapes the cornea of the eye. In less than 60 seconds, ultraviolet light and high-energy pulses from the excimer laser reshape the internal cornea with accuracy up to 0.25 microns, or 1/4000 of a millimeter. After the pulses of laser energy vaporize the corneal tissue, the flap is put back into its original position.
The surgeon will observe the eye for three to five minutes to ensure bonding. Because the cornea bonds quickly, healing is rapid, and the eye does not require stitches. Results from LASIK are excellent with 95% of patients achieving 20/40 vision or better.
The entire procedure takes only a few minutes. Improved vision is often possible on the day following the surgery. The vast majority of patients return to their daily activities the day following surgery. Eye drops and night protection are necessary for designated periods of time.
Custom LASIK allows the doctor to tailor the LASIK procedure to each individual eye and potentially improve upon the already excellent results available from the conventional procedure (laser for myopia, astigmatism and hyperopia).
This next generation technique uses wavefront technology to measure the entire eye and create a “three-dimensional” map. The map contains detailed optical information that is unique to each eye, much like a fingerprint is unique to each individual.
The doctor uses this information to guide the laser in customizing the treatment to the eye’s particular visual irregularities. While conventional LASIK corrects refractive errors known as lower-order aberrations (myopia, hyperopia and astigmatism) that affect how much we can see, Custom LASIK also has the potential to improve higher-order aberrations (coma, spherical aberration, and others) that affect how well we can see. Studies indicate that 20% of patients significantly benefit from Custom LASIK treatments while other patients may benefit to a lesser degree.
Key features of Custom LASIK