Knowlegde about Safety of Laser Eye Surgery
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Generally, the success rate of the procedures of LASIK (Laser-Assisted In Situ Keratomileusis), IntraLASIK (Femtosecond Laser Microkeratome Lasik), LASEK (Laser-Assisted Subepithelial Keratectomy), Epi-LASIK and PRK (Photorefractive Keratectomy) for laser vision correction of the eye is claimed to be 95%. But this relates to a range of ±1 diopters and includes not the risks mentioned below.
The LASIK procedure starts with anaesthetic drops to have a painless frontal eye section. Afterwards the surgeon places a device between the upper and lower lid that blocks blinking. Then the surgeon uses an instrument called microkeratome to cut a thin circular flap of corneal tissue, opens the flap like a hinged door, vaporizes the targeted tissue in the corneal stroma beneath it with the excimer laser, and then replaces the flap. For IntraLASIK, the microkeratome is not used. Instead the flap is cut with a femtosecond laser which allows a thinner flap ( >90 µm) for more laser ablation.
In contrast to LASIK, no sharp cornea cut is carried out during the so-called surface procedures like LASEK, Epi-LASIK and PRK. By using alcohol (LASEK) or a blunt blade (Epi-LASIK) the uppermost epithelium layer is shoved aside before the laser treatment is started. The initial procedure, invented many years ago, is called PRK (Photorefractive Keratectomy). For this procedure the epithelium is scraped off, then the tissue is ablated by a laser. Because the protective epithelial flap is missing postoperatively, this operation is accompanied by more pain and a longer recuperation period compared to LASEK, Epi-LASIK and especially comfortable LASIK. It is, however, a good option for patients with less than -4 diopters who are reluctant to have a cut in the cornea. The results of LASIK and PRK are comparable, so apart from being less painful and allowing for faster recuperation LASIK is not superior to PRK. [1]
The risk associated with the above-mentioned laser eye surgery procedures has not yet been determined in detail and with statistical precision. The following facts seem to refute a success rate of 95 %:
- According to some studies, about 75 % [2], 20% [3] or 5 % [4] of the patients suffer postoperatively from restricted twilight and night vision due to halos, double vision (ghosting), loss of contrast sensitivity (foggy vision), starburst and glare (=> images section)
- Between 5% and 28% of all patients need follow-up treatment after laser eye surgery. This percentage depends on the patients’
risk factors, the surgeon´s experience and the individual patient’s expectations. [5]
- In numerous cases there is an over- or undercorrection in the short or long term. Disturbed wound healing can result in dangerous complications. In single cases a bulged cornea (keratectasia) is reported, which may be followed by a transplantation of the cornea. [6], [7], [8], [9]
- A postoperative uncorrected visual acuity 20/40 (50%) without glasses is still termed successful. This is achieved for more than 90% myopic patients with initial values between -1 and -5 diopters. [4] A more realistic assessment of a successful laser eye surgery has been demanded for many years because it is not possible to cover all complications that may occur with a simple eyesight check. In order to measure the real success of a laser eye surgery it is necessary to include, for instance, the determination of contrast sensitivity, the determination of starburst sensitivity (measurement of the eyesight under special light conditions) als well as low contrast vision testing.
- The risk for a patient of suffering from disturbing visual side effects like halos, double vision (ghosting), loss of contrast sensitivity (foggy vision), starburst and glare after LASIK depends on the degree of ametropia before the laser eye surgery and other risk factors [4]. Visual side effects will occur with a probability of >1% for slightly nearsighted patients with only up to -1 diopters, whereas the risk for patients with -1 to -5 diopters increases to 5%, for severely nearsighted patients with -10 diopters even up to 50%.
As a result, since the risk of visual side effects after a laser eye surgery statistically also depends on individual risk factors, e.g. the dioptric value, it is necessary to include individual factors in the consultation of patients. For this reason, it is important to take into account the individual risk potential of a patient and not just the average probability for all patients [10].
Based on this knowledge, severely nearsighted patients should not be treated with LASIK anymore. The risk of postoperative visual side effects is too high. Alternatives to laser eye surgery procedures in these cases may be the implantation of anterior chamber lenses (iris-clip lenses) or posterior chamber lenses (ICL). A conservative alternative are well-adjusted rigid gas permeable (RGP) contact lenses made by experienced contact lens fitters. Candidates for refractive surgery often complain that they are unabele to tolerate rigid gas permeable (RGP) contact lenses but they probably have not found the fitting model yet.
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