Introduction to LASIK

LASIK is an acronym for laser in situ keratomileusis. It is a very common corneal laser surgery used to treat a wide range of refractive problems of the eye including near and far sightedness and astigmatism, and thus reduce dependence on glasses. The advantages include less recovery period, less painful and less intense healing response. Disadvantages are some serious side effects which may cause blindness. Besides, the procedure is expensive and needs highly skilled people for safe operation.

Earlier, eye laser surgeries were done by a procedure termed photorefractive keratectomy or PRK. This procedure had drawbacks like, delayed recovery time, discomfort and significant reduced vision problems in a few cases. LASIK surgery is an improvement on PRK in most respects.

LASIK surgery

The surgery is performed by an excimer laser. At its simplest, the procedure uses an instrument called a microkeratome or more recently, a femtosecond laser. An epithelialstromal flap is cut and left attached to the corneal periphery by a hinge of uncut tissue. This flap is lifted and the high energy pulses of the excimer laser are applied on the stromal area to get the desired surgical outcomes. After the operation, the flap is returned to its original position. No sutures are needed to heal the cut.

Benefits of LASIK

LASIK performed by skilled and experienced surgeons improves vision substantially, in most cases, even if vision acuity of 20/40 is not achieved. The chances of getting a desired level of vision correction are inversely related to baseline level of correction. For example, in an eye with 2 dioptres of myopia the chances of getting a 20/20 vision is 70% to 80%, and the chances of achieving 20/40 or better is greater than 98%. Whereas, in an eye with myopia of 9D, the odds of getting 20/20 vision are 40% to 55% and odds of getting 20/40 vision are 95% to 98%.

Depending on surgeon expertise and the initial correction attempted, a repeat enhancement laser ablation surgery is needed in 5% to 20% cases, to obtain best outcomes. In LASIK, the tendency to lose the surgical effects over time is comparatively less.

Risks from LASIK surgery

LASIK can result in several complications. These are visual disturbances, such as, starbursts, halos, distorted images, and multiple images commonly seen during the night. The chances of these complications occurring is more when excimer laser is used or when corrections are higher than 7 to 8 dioptres of myopia and 2 to 3 dioptres of hyperopia. Improved laser technology and pre-operative screenings have reduced the incidence of such complications to1% of patients treated, according to a rough estimate. Other complications like, infection and ectasia are seen in less than 1% cases.

Unique to LASIK are the flap- induced complications, not found in PRK or other laser surgeries since they do not involve flaps. It is mainly due to flap complications that LASIK carries a higher risk of losing 2 or more lines of visual acuity in Snellen’s chart. Flap formations in LASIK also induce transient dry eyes in LASIK.

Haze in the anterior stroma due to wound is rare. By and large, LASIK offers better comfort and vision after a few days of surgery. Complications it appears are less with more experienced surgeons.

Pre-operative screening for LASIK surgery

Pre-operative screening is critical for good surgical outcomes. Patients are comprehensively examined for normal, healthy eyes. LASIK is performed only on those above 21 years of age. And even in these cases, refraction should have been relatively stable in the previous two years. This may be difficult to verify and the surgeon may have to rely on patient history.

LASIK is not considered a suitable option in people with systemic diseases, such as, rheumatoid arthritis and immune related disorders associated with healing problems, such as, corneal melting. Pregnant and lactating women also should not opt for LASIK due to changes in refraction at that time. Patients with moderate to severe dry eyes are not suitable candidates for LASIK.

Corneal thickness, which is normally between 490 micro meters to 650 micro meters, should be taken into account before opting for LASIK. LASIK should be avoided if corneal thickness is inadequate, even where corneal topography is normal.

Also important is pupil diameter in the dark. Greater the pupil diameter in the dark, greater is the likelihood of glare, halos and other visual disturbances, especially in eyes with high myopia. Therefore, measurements performed during the pre-operative eye screening are especially vital in determining the presence of myopia or hyperopia.

Topographic maps of the cornea should not show any signs of diseases where progressive thinning of the cornea occurs over time. Otherwise, poor results would turn up in LASIK.