A comprehensive eye exam is conducted to discover the existing refractive error and the eye doctor determines you have farsightedness (hyperopia), nearsightedness (myopia) and/or astigmatism and prescribes eyeglasses, by specifying the required lens power that can recover the refractive errors.
The prescription of eyeglass qualifies for Lasik on the basis of different factors. The factors usually include the thickness as well as the shape fo the corneas. There are also other factors, like the brand of laser used for the laser surgery and specific kind of technology of Lasik used and parameters of treatment recommended for the laser surgery procedure.
Maximum Eye Power for Lasik
In the United States, FDA approved excimer lasers for the Lasik surgery can correct the refractive error of -11.00 diopters, up to 5.00 diopters of astigmatism and +5.00 diopters of farsightedness.
When the refractive error value is more, one has to notice that the risk of visual side effects, such as halos, night glare and many other issues can be more. So, the patient has to address and discuss these things with the surgeon, while preoperative consultation is made, especially, for the prescription of more than +4.00 D of hyperopia or -8.00 D of myopia.
The best procedure is determined and recommended by the refractive surgeon, during the Lasik consultation, on the basis of whether the prescription is within the range of treatment recommended for Lasik surgery. In case the prescription of you is too high to go for Lasik procedure, alternate laser vision eye surgery procedures, like refractive lens exchange or phkic IOL implants would be recommended.
Technically, the upper limit of power is basically dependent on corneal thickness, to go for Lasik surgery. So, usually, for correcting the powers that range in between +0.5D to +4.0 AND -0.5d TO -8.0, on an average, corneal thickness needed is approximately 530 microns. On the other hand, in certain cases, if the thickness of the cornea is much above the average, Lasik surgery procedure can correct the power of spectacles, above -8.0D and up to -10.0D. And in a very few cases, where the power of spectacle is in between -8.0 to -18.0, the alternative recommended by the surgeon is usually, ICL surgery.
Is the Maximum Power Same Everywhere?
No, the maximum power that is allowed for the treatment of Lasik is not the same. It not only varies from one place to another place, but also from one eye doctor to another. Doctors have different criteria and consider different factors and determine maximum number allowed for the Lasik treatment. While some doctors limit till 10 diopters, others may stretch this maximum limit to 14 diopters. However, there is certain maximum limit set by FDA. For instance the maximum hyperopia power that can be approved according to the FDA is +6 D and usually many of the eye surgeons go till only +4 D as the limit to go for the Lasik surgery. And it also varies according to the laser machine used for the procedure. for example some better laser machines extend the capability of treating the power till +6 D.