With the advancement of science and technology, the concept of refractive surgery procedures has been redefined. Instead of merely shifting the focus of an object's image onto the retina, now the outcome of reshaping the cornea is targeted to reduce image from distortion, especially spherical aberration that occurs more in eyes with large pupils. The amount of spherical aberrations increases following standard laser treatments to correct myopic and hyperopic refractions. Conventional laser ablation modifies corneal asphericity, a fact that may explain the observed increase in spherical aberration.

In conventional procedure, the final shape of cornea is oblate. It is because when laser light hits the center of the cornea, it is fully absorbed. However, in the periphery, the angle of incidence resulting from the cornea‘s curved shape will cause energy reflections.

To maintain the patient's refraction and corneal curvature, the excimer laser systems apply additional pulses in these peripheral areas to compensate for the energy loss, and to achieve the desired post-operative aspheric contour even in the outer areas of the cornea. In order to precompensate for the possible induction of spherical aberrations, the laser applies even more pulses depending on the patient‘s individual corneal steepness.

The effect of higher order aberrations increases with pupil size. Hence the effective optical zone size should correspond with the pupil. Large transition zones induce higher order aberrations, thereby fostering vision problems such as halos and glare.

Controlling the peripheral ablation allows the laser to create large, true optical zones with a minimized transition zone.

By treating larger optical zones with a diameter of up to 8 mm, postoperative glare and halos are minimized.

In the ALLEGRETTO WAVE clinical trials conducted by the FDA (U.S. Food and Drug Administration), for instance, many patients reported that their night-driving glare had improved after the treatment.