Lasik

LASIK (Laser Assisted In-Situ Keratomileusis) surgery involves reshaping the cornea with a laser, allowing light to be refocused and vision improved. In LASIK, a corneal flap is created by using a laser or a mechanical approach. The flap is repositioned after the corneal reshaping. LASIK can correct varying degrees of nearsightedness (myopia) farsightedness (hyperopia) and astigmatism and is generally the treatment of choice for patients with high myopia.

LASIK can correct varying degrees of nearsightedness (myopia) farsightedness (hyperopia) and astigmatism and is generally the treatment of choice for patients with high myopia. LASIK is currenlty the most widely used technique to correct most refractive errors because of its safety and its predictability, that lead to satisfactory outcomes for both patients and surgeons. It has been refined over the years and still undergoes continuous improvements.

LASIK for Low to Moderate Myopia
Myopic excimer laser treatments achieve their effect by flattening the central cornea. Low myopia is diagnosed in patients having a refractive error of -4.00 diopters (D) or less. Patients who are between -4.00 to -7.00 D are categorized as having moderate myopia.

Those with low or moderate myopia represent the largest population of patients undergoing refractive surgery.The LASIK technique for these patients is safe and effective, and patient satisfaction is extremely high. Grouped data from the FDA-approved laser platforms showed that 96% of patients with low or moderate myopia had a postoperative vision equivalent to 20/40, 72% of patients had vision equal or better than 20/20.

LASIK for High Myopia
High myopia is diagnosed for patients with a refractive error of more than -7.00 D. Any patient with high myopia presenting clinical and/or topographic evidence of corneal abnormalities such as keratoconus, forme frusts keratoconus, and pellucid marginal degeneration should be excluded from LASIK surgery.

In normal corneas, the depth of ablation is an important factor to consider, especially in patients with thin corneas. FDA data showed that 89% of patients were 20/40 or better. Combined data from the non-FDA set showed that 94% of patients were 20/40 or better; 64% were 20/20 or better.

LASIK for Hyperopia
In comparison to myopic correction, in which the goal is to flatten the central cornea, in hyperopia the central cornea is to be steepened to increase its optical power. Therefore, for hyperopic LASIK ablations most of the laser energy is directed at the periphery of the treatment zone with a relative sparing of the central cornea.

Grouped data from the FDA approved non-custom laser platforms showed that 90% of patients were 20/40, 63% of patients had vision equal to or better than 20/20. In FDA-approved custom laser platform 97% of patients were 20/40 and 66% of patients had vision equal to or better than 20/20. The factor that negatively influences the outcome of hyperopic LASIK is the degree of hyperopia corrected. Better outcomes are expected when the magnitude of hyperopia equal to or less than +4 D.

LASIK for Presbyopia
Presbyopia is an age-related refractive condition in which the eye is no longer able to focus over a broad enough range to allow for both functional near and distance vision correction. LASIK surgery can treat the symptoms of presbyopia through the use of a technique termed monovision. In monovision, one eye is set for distance vision and the other eye for nearer vision.

There are no FDA trials for the use of LASIK for monovision. Non-FDA data suggest that about 80% of patients will adapt to monovision, and that most patients will adapt to monovision within 3-4 weeks. Perhaps the most important factor for obtaining good outcomes with this technique is proper selection of patients and adequate counselling before the procedure.

Patients must understand that improved functional vision, if it does arise, will come only after the adaptation period. When the patient is unhappy, the undercorrected eye can undergo re-treatment or initial treatment (when the myopic eye was untreated) to balance the eyes. The patient will then need to use reading glasses for near tasks.

References:
Sakimoto T, Rosenblatt MI, Azar DT. Laser eye surgery for refractive errors. Lancet 2006; 367:1432-47.

Gatinel D. LASIK for myopia, hyperopia and astigmatism. In: Azar DT (editor), Gatinel D, Hoang-Xuan T (Associate editors). Refractive Surgery 2nd edition. Mosby Elsevier: 2007, P:165-182.