Customizing the flap dimensions appears to have several advantages over traditional LASIK. In our experience, visual recovery is significantly faster and retinal image quality is higher following this LASIK approach, as compared with PRK. The femtosecond laser further provides us with control over many variables in flap customization.

Customizing parameters such as thickness, diameter, shape, hinge-width and side-cut architecture of the flap in a LASIK procedure is a new development that has been proven to maximize residual corneal thickness, which also decreases the risk of post-LASIK ectasia. We refer to the control of this constellation of variables as Custom-Tailored All Laser LASIK.

Can we mimic the eye's natural anatomy?

Technology is improving, and more patients than ever before are opting for LASIK. Because of this, we believe it is important to continue exploring how to create LASIK flaps — using the femtosecond laser — that are a better match for the anatomy of individual eyes. Better matching the flap to the patient improves the exposed stromal bed area and could even diminish the incidence of opaque bubble layers (OBLs).

We have been very excited about femtosecond technology, because these lasers can cut thin flaps precisely, further reducing the likelihood of ectasia. The technology also offers us the possibility of reducing the incidence of dry eye and decreasing enhancement rates, and facilitates the performance of future enhancements. The widened hinge capability further reduces the potential for epithelial ingrowth or formation of striae.

Figure 1

Before we attempt to customize the flap, we must first consider anterior segment morphology, taking into account that the cornea is oval in shape, not circular, and the pupil tends to be superior and nasally displaced. Therefore, housing the hinge complex in either of these quadrants (nasal or superior) is not very logical, since these are the most cramped quadrants of the cornea. Furthermore, the limbal region is also the most immunologically active portion of the cornea: placing the flap margin close to the limbus increases the degree of marginal infiltrates and the likelihood of peripheral Diffuse Lamellar Keratitis (DLK). Hinge ablation is yet another issue to consider; placing a hinge cover over the stromal surface of a superior hinge is not an ideal option, as it does not allow us to apply the full (intended) diameter of the laser ablation to the stromal bed, which is the optimal way to perform the procedure.

Superior vs. temporal

Figure 2

As we have explored in the past,¹ it is possible to create a round flap with a temporal hinge by performing a 90° rotation of a metal microkeratome. Even in the presence of a widened hinge, this technique provides the surgeon with larger bed exposure. In our new study, we evaluated this same process using the IntraLase femtosecond laser (AMO); this laser has the capacity of a second order centration correction, centring the flap over the entranced pupil. In our original study, we had noted a significant difference between temporal and superior hinges (Figures 1 & 2) , in favour of temporal; these results were corroborated by our subsequent study. We therefore now recommend creating temporal rather than superior hinged flaps in most patients.