There are many ways to present patient outcomes after refractive surgery, and the difference in numbers can be confusing. Some doctors may talk about the percentage of patients who achieve 20/20 vision after the first treatment, while others may present data on the number of patients who achieve 20/40 vision. Still others may discuss their results based on patients who have had enhancement procedures (if necessary). What are the important numbers and how can you interpret these outcomes?
First of all, to drive legally without glasses you need to have 20/40 vision. This is an important number. However, it is also important to know your chance of achieving 20/20 vision or your best potential vision without correction by glasses or contacts. Additionally, it is important to know the likelihood that you will need an enhancement (retreatment) procedure. These numbers depend on your initial prescription and are also somewhat surgeon dependent. Patients with higher degrees of nearsightedness or farsightedness have a higher likelihood of needing an enhancement procedure.
The statistics provided below are based on a study including 820 eyes treated by Ernest W. Kornmehl, MD, and provide a good guideline for what you can expect. Keep in mind that the patients in the statistics below who do not achieve 20/20 vision without correction are usually quite happy. They can do most things, including drive a car, without any correction. And when it is absolutely necessary for them to fine-tune their vision, they can use a thin pair of glasses to do so. Some patients appreciate a small amount of myopia in one or both eyes to help with near vision and, thus, do not request an enhancement.
Mild myopia is defined as less than three diopters (-3.00), with or without astigmatism. The chance that a patient with mild myopia will need an enhancement procedure is approximately two percent. The chance of achieving 20/20 vision without correction is ninety-four percent after an enhancement procedure (if necessary). The chance of achieving 20/40 or better without correction and being able to drive is nearly one hundred percent.
Moderate myopia is defined as a refractive error between -3.00 and -6.00 diopters. There is a six percent chance of needing an enhancement procedure if you fall into this category. Based on the data, eighty-two percent of patients achieve 20/20 vision or better, and ninety-nine percent achieve 20/40 or better.
Severe myopia is defined as a refractive error between -6.00 and -9.00 diopters. These patients have approximately a nine percent chance of needing an enhancement procedure, after which they have a ninety-nine percent chance of seeing 20/40 or better and a sixty-nine percent chance of seeing 20/20 or better.
Extreme myopia is defined as refractive error higher than -9.00. The enhancement rate for this group of patients varies from twelve to fifteen percent. Many patients do extremely well; however, other variables such as the thickness and the steepness of the cornea come into play. Patients in this group need to thoroughly discuss the risks and benefits of the LASIK procedure, as well as other options, with their doctor. Although enhancement rates are higher in this group of patients, there may be limitations on what can be done due to other variables of the eye, such as corneal thickness.
Patients with mild astigmatism (1.00 diopter or less) can expect nearly identical outcomes and enhancement percentages, as can patients with pure myopia. The presence of moderate or high degrees of preoperative astigmatism will reduce your chance of achieving 20/20 vision after the initial procedure, making it more likely that an enhancement will be desired.
A multicenter trial done for FDA approval for the VISX STAR S2 laser for the treatment of hyperopia in the range of +1.00 to +6.00 provides us with a good general benchmark. In this study, ninety-one percent of the patients saw 20/40 or better, and fifty-three percent saw 20/20 without glasses after the procedure.
Patients being treated for hyperopia should be aware that their healing time is slightly longer than for those patients with myopia, and the chance that they will need an enhancement is slightly higher. Again, these numbers are variable, depending on the patient’s original prescription and the surgeon.
Summary LASIK Statistics
From the data presented above, you can see that while refractive surgery is an exciting new procedure, it is not for everyone. It should not be thought of as a guarantee to eliminate one’s need for glasses. Rather, it should be thought of as a way to dramatically reduce one’s dependency on glasses and contact lenses.