Re-treatment enhances vision

November 15, 2010

Some patients who have had previous wavefront-optimized laser vision correction present with quality-of-vision complaints, such as halo and glare, despite having 20/20 visual acuity.

Laser vision correction options

In the United States, laser vision correction has evolved into two different schools of thought. One is based upon a customized wavefront-guided treatment (iLASIK Suite, Abbott Medical Optics [AMO]) in which the patient's wavefront map is used to create a customized treatment pattern that conforms to the degree of spherical aberration, coma, and other higher-order terms that the particular patient has. The iLASIK Suite includes the STAR S4 Iris Registration System with the WaveScan System, and iFS femtosecond laser. The advantage of using this type of system is that it is literally customized to the individual characteristics of each patient's eye. However, it can be more labor intensive. A good wavefront map needs to be obtained on all patients and that requires an added step in the process of working up a patient.

Wavefront-optimized treatment (Allegretto Wave Eye-Q Excimer Laser, Alcon Laboratories) is the other form of modern laser vision correction in the United States today. This type of laser vision correction has a more simple approach. Wavefront measurements are not required and this procedure can be performed by only using the refractive error of the patient. However, assumptions are made regarding the degree of spherical aberrations present in any given eye. As a result, the spherical aberration correction is good enough to produce excellent results for a portion of patients undergoing treatment with an optimized platform, but in some patients the spherical aberration correction is insufficient and in other patients the pre-set spherical aberration correction actually makes the situation worse. An example of this would be a case in which a patient starts out with negative spherical aberration and then an additional negative spherical aberration is added using the ablation.

Overall, both forms of laser vision correction provide very good results for most patients, but customizing the ablation to the individual patient has some important advantages. Some have argued that correcting higher-order aberrations on the cornea might create issues as a patient experiences future lens changes with age. Careful study of the wavefront treatment algorithm in the AMO VISX laser shows that the majority of the wavefront-guided customization is applied to spherical aberration and asymmetrical astigmatism (coma), and correcting those two factors is very likely to serve a patient well throughout the course of a lifetime.

Re-treatments

In my practice, I have come across a number of patients who were initially treated with a wavefront-optimized platform with an extremely good result in terms of their lower-order aberrations. These patients had an essentially zero refractive error, and yet some were fairly unhappy with the quality of their vision. Typically in these patients the lower-order aberrations are small and their entire problem is with higher-order aberrations. Even though their residual refractive error was trivial, we re-treated some of these patients using a wavefront-guided ablation, and their symptoms, such as glare and halo, resolved. This is an indication of the superiority of wavefront-guided treatment in cases like this. With a wavefront-optimized laser, there would be nothing to enter into the treatment plan with such a patient, since the refractive error is essentially nonexistent.