Let us start with some definitions: a wavefront-guided procedure captures the patient’s wavefront with an aberrometer and employs a custom ablation to correct all of the aberrations it finds. The wavefront-optimized procedure is a derivative of the conventional procedure that offers only a spherocylindrical correction; but unlike a conventional ablation, the “optimized” ablation profile is aspheric so as to induce less spherical aberration.

Predicting Performance

Although studies on multiple laser platforms have consistently found better outcomes with custom than conventional ablations, there are few direct studies of custom vs“optimized” ablations. To learn what surgeons can expect from “optimized” ablations, we created a model to predict visual performance with each type of procedure. To construct the model, we used large clinical data sets from wavefront-guided and conventional LASIK and took into account both pre-and postoperative aberrations. The model was designed to simulate the normal variability that occurs in treatment due to differences in healing response, etc.

In creating the model we made two critical assumptions. For “optimized” ablations we assumed the perfect case, ie, that the ablation would produce no change whatever in the patient’s spherical aberration. In addition, we assumed that the optimized ablation would change (increase or reduce) higher order aberrations (HOAs) to precisely the same degree as a conventional ablation.

The model itself is quite robust. It incorporates 10,000 eyes with the same HOA distribution as the normal population. To each model eye we applied an algorithm that predicted the visual outcome with custom,“optimized,” or conventional LASIK.

As expected, the predicted outcome with conventional ablation closely matched clinical data. The same was true of the predicted custom treatment. Using the model, we found that wavefront-guided ablations predicted significantly fewer induced aberrations than “optimized” ablations, which in turn were predicted to induce fewer aberrations than conventional.

Mining the Data

Because its data set (10,000 eyes) was so large, the model allowed us to ask:“Is there a subset of eyes that might do better with an ‘optimized’ than a custom ablation?” For instance, would eyes with very little preoperative HOA do the same or better with“optimized” compared to custom wavefront ablations? We found that, even in eyes with very low levels of preoperative HOA, wavefront-guided ablations were predicted to induce fewer aberrations than “optimized.” (And, “optimized” ablations induced less HOA than conventional.) In eyes with high preoperative levels of HOA, the disparity between wavefront-guided and “optimized” ablations was considerably greater, because custom ablations have a greater effect on eyes with more HOA.

A reasonable question is: “Why perform wavefront-guided procedures on eyes with very little HOA?” The answer is because no procedure, including a custom procedure, is likely to reduce HOA in these eyes , but a custom procedure still induces less HOA increase than an“optimized” or a conventional LASIK.

Clinically Meaningful

Because, in many cases, the differences in postoperative HOA between ablation types was small, we also asked the model: “What is the chance that a procedure will induce a significant amount (defined as > 0.1 micron) of HOA?” We found that conventional ablations were approximately twice as likely as “optimized” to cause a significant increase in HOA. That’s clinically meaningful. But we also found that “optimized” ablations are approximately twice as likely to induce significant HOAs as custom ablations; and that too is clinically meaningful.

The bottom line is that wavefrontguided ablations have roughly the same level of advantage over“optimized” ablations as “optimized” ablations have over conventional. This is true in all cases. Thus, the model predicts that, on average, all patient populations will achieve superior outcomes with custom than with “optimized” ablations.