Lasik!
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Lasik Technology development
The LASIK technique was made possible by Jose Barraquer (Colombia), who around 1960 developed the first microkeratome, used to cut thin flaps in the cornea and alter its shape, in a procedure called keratomileusis. This procedure was developed and pioneered by the Barraquer Clinic, based in Bogot', Colombia.In 1981, Rangaswamy Srinivasan discovered that an ultraviolet excimer laser could etch living tissue in a precise manner with no thermal damage to the surrounding area. He named the phenomenon Ablative Photodecomposition (APD). Srinivasan and his co-inventors ran tests using the excimer laser and a conventional, green laser to etch organic matter. They discovered that while the green laser produced rough incisions, damaged by charring from the heat, the excimer laser produced clean, neat incisions. In 1983, Srinivasan collaborated with an ophthalmic surgeon to develop APD to etch the cornea.
LASIK surgery was developed in 1990 by Lucio Buratto (Italy) and Ioannis Pallikaris (Greece) as a melding of two prior techniques, keratomileusis and photorefractive keratectomy. It quickly became popular because of its greater precision and lower frequency of complications in comparison with these former two techniques.
In 1991, LASIK was performed for the first time in the United States by Stephen Brint and Stephen Slade. The same year, Thomas and Tobias Neuhann successfully treated the first German LASIK patients with an automated microkeratome.
Today, faster lasers, larger spot areas, bladeless flap incision, and wavefront-optimized and -guided techniques have significantly improved the reliability of the procedure as compared to that of 1991. Nonetheless, the fundamental limitations of excimer lasers and undesirable destruction of the eye's nerves have spawned research into many alternatives to "plain" LASIK, including all-femtosecond correction (FLIVC), LASEK, Epi-LASIK, wavefront-guided PRK, and modern intraocular lenses. Furthermore, the long term effects of LASIK surgery still remain unknown.
Lasik Procedure
Lasik Preoperative
Patients wearing soft contact lenses typically are instructed to stop wearing them approximately 7 to 10 days before surgery. One industry body recommends that patients wearing hard contact lenses should stop wearing them for a minimum of six weeks plus another six weeks for every three years the hard contacts had been worn. Before the surgery, the surfaces of the patient's corneas are examined with a computer-controlled scanning device to determine their exact shape. Using low-power lasers, it creates a topographic map of the cornea. This process also detects astigmatism and other irregularities in the shape of the cornea. Using this information, the surgeon calculates the amount and locations of corneal tissue to be removed during the operation. The patient typically is prescribed an antibiotic to start taking beforehand, to minimize the risk of infection after the procedure.Lasik Operation
The operation is performed with the patient awake and mobile; however, the patient typically is given a mild sedative (such as Valium) and anesthetic eye drops.Lasik is performed in two steps. The initial step is to create a flap of corneal tissue. This process is achieved with a mechanical microkeratome using a metal blade, or a femtosecond laser microkeratome (procedure known as IntraLASIK) that creates a series of tiny closely arranged bubbles within the cornea. A hinge is left at one end of this flap. The flap is folded back, revealing the stroma, the middle section of the cornea. The process of lifting and folding back the flap can be uncomfortable.
The second step of the procedure is to use an excimer laser (193 nm) to remodel the corneal stroma. The laser vaporizes tissue in a finely controlled manner without damaging adjacent stroma by releasing the molecular bonds that hold the cells together. No burning with heat or actual cutting is required to ablate the tissue. The layers of tissue removed are tens of micrometers thick.
During the second step, the patient's vision will become very blurry once the flap is lifted. He/she will be able to see only white light surrounding the orange light of the laser. This can be disorienting.
Currently manufactured excimer lasers use a computer system that tracks the patient's eye position up to 4,000 times per second, redirecting laser pulses for precise placement. After the laser has reshaped the cornea, the Lasik flap is repositioned over the treatment area by the surgeon. The flap remains in position by natural adhesion until healing is completed.
Performing the laser ablation in the deeper corneal stroma typically provides for more rapid visual recovery and less pain.
Lasik Post Operative
Patients are usually given a course of antibiotic and anti-inflamitory eye drops. These are gradually scaled down to nothing in the weeks following surgery.Patients are also given a darkened pair of goggles to protect their eyes from rubbing when asleep. It is advised to wear these from four to eight weeks depending on the nature of the surgery.
Lasik Industry concerns
There are many concerns and movements to change the way the LASIK industry operates. Primarily these are based on the distribution of information by surgeons to potential patients. It is often argued that patients are not given sufficent information regarding the possible complications, their side effects, and final outcomes. A survey in the United Kingdom indicated that most LASIK patients expected their vision to become at least 20/20 after surgery and few knew it could potentially be worse.This section is a stub. You can help by adding to it.
Lasik Higher-order aberrations
Higher-order aberrations are visual problems not captured in a traditional eye exam which only tests for acuteness of vision. Severe aberrations can effectively cause significant vision impairment. These aberrations include starburts, ghosting, halos, double vision, and a number of other post-operative complications listed below.Concern has long plagued the tendency of refractive surgeries to induce higher-order aberration not correctible by traditional contacts or glasses. The advancement of LASIK technique and technologies has helped reduce the risk of clinically significant visual impairment after the surgery. One of the major discoveries was the correlation between pupil size and aberrations: Effectively, the larger the pupil size, the greater the risk of aberations. This correlation is the result of the irregularity between the untouched part of the cornea and the reshaped part. Daytime post-lasik vision is optimal, since the pupil is smaller than the LASIK flap. But at night, the pupil may expand such that light passes through the edge of the LASIK flap into the pupil which gives rise to many aberrations. There are other currently unknown factors in addition to pupil size that also affect higher order aberrations.
In extreme cases, where ideal technique was not followed and before key advances, some people could suffer rather debilitating symptoms including serious loss of contrast sensitivity in poor lighting situations.
Over time, most of the attention has been focused on spherical aberration. LASIK and PRK tend to induce spherical aberration, because of the tendency of the laser to undercorrect as it moves outward from the center of the treatment zone. This is really only a significant issue for large corrections. There is some thought if the lasers were simply programmed to adjust for this tendency, no significant spherical aberration would be induced. Hence, in eyes with little existing higher order aberrations, "wavefront optimized" lasik rather than wavefront guided LASIK may well be the future. Regardless, most patients with even the low to medium corrections remain highly satisfied even with conventional LASIK, however patients requiring higher corrections often complain about night vision.
Lasik Wavefront-guided LASIK
Wavefront-guided LASIK is a variation of LASIK surgery where, rather than apply a simple correction of focusing power to the cornea (as in traditional LASIK), an ophthalmologist applies a spatially varying correction, using a computer-controlled high-power UV laser guided by measurements from a wavefront sensor. The goal is to achieve a more optically perfect eye, though the final result still depends on the physician's success at predicting changes which occur during healing. Nor are wavefront aberrations the factor to degrade vision; especially in older patients, scattering from microscopic particles plays a major role. Hence, patients expecting so-called "super vision" from such procedures may be disappointed. However, while unproven, surgeons claim patients are generally more satisfied with this technique than with previous methods, particularly regarding lowered incidence of "halos", the visual artifact caused by spherical aberration induced in the eye by earlier methods.Lasik Complications
A subconjunctival hemorrhage is a common and minor post-LASIK complication.The incidence of refractive surgery patients having unresolved complications six months after surgery has been estimated from 3% to 6%. The following are some of the more frequently reported complications of LASIK:
Dry eyes
Overcorrection or undercorrection
Visual acuity fluctuation
Halos or starbursts around light sources at night
Light sensitivity
Ghosts or double vision
Wrinkles in flap (striae)
Decentered ablation
Debris or growth under flap
Thin or buttonhole flap
Induced astigmatism Epithelium erosion
Posterior vitreous detachment
Macular hole
Complications due to LASIK have been classified as those that occur due to preoperative, intraoperative, early postoperative, or late postoperative sources:
Lasik Preoperative sources of complications
Lasik Intraoperative complications
The incidence of flap complications has been estimated to be 0.244%. Flap complications (such as displaced flaps or folds in the flaps that necessitate repositioning, diffuse lamellar keratitis, and epithelial ingrowth) are common in lamellar corneal surgeries but rarely lead to permanent visual acuity loss; the incidence of these microkeratome-related complications decreases with increased physician experience . This risk is further reduced by the use of IntraLasik and other non-microkeratome related approaches.A slipped flap (a corneal flap that detaches from the rest of the cornea) is one of the most common complications. The chances of this are greatest immediately after surgery, so patients typically are advised to go home and sleep, to let the flap heal. Flap interface particles are another finding whose clinical significance is undetermined A Finnish study found that particles of various sizes and reflectivity were clinically visible in 38.7% of eyes examined via slit lamp biomicroscopy, but apparent in 100% of eyes using confocal microscopy.
Lasik Early postoperative complications
The incidence of diffuse lamellar keratitis (DLK), also known as the Sands of Sahara syndrome, has been estimated at 2.3%. When diagnosed and appropriately treated, DLK resolves with no lasting vision limitation. The incidence of infection responsive to treatment has been estimated at 0.4%. Infection under the corneal flap is possible. It is also possible that a patient has the genetic condition keratoconus that causes the cornea to thin after surgery. Although this condition is screened in the preoperative exam, it is possible in rare cases (about 1 in 5,000) for the condition to remain dormant until later in life (the mid-40s). If this occurs, the patient may need rigid gas permeable contact lenses, Intrastromal Corneal Ring Segments (Intacs), Corneal Collagen Crosslinking with Riboflavin or a corneal transplant. The incidence of persistent dry eye has been estimated to be as high as 28% in Asian eyes and 5% in Caucasian eyes. Nerve fibers in the cornea are important for stimulating tear production. A year after LASIK, subbasal nerve fiber bundles remain reduced by more than half.The incidence of subconjunctival hemorrhage has been estimated at 10.5%.
