Laser Vision Correction, commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and astigmatism. The Laser Vision Correction surgery is performed by anophthalmologist who uses a laser or microkeratome to reshape the eye’s cornea in order to improve visual acuity. For most patients, Laser Vision Correction provides a permanent alternative to eyeglasses or contact lenses.
Laser Vision Correction is most similar to another surgical corrective procedure, photorefractive keratectomy (PRK), and both represent advances over radial keratotomy in the surgical treatment of refractive errors of vision. For patients with moderate to high myopia or thin corneas which cannot be treated with Laser Vision Correction and PRK, the phakic intraocular lens is an alternative. As of 2011, over 11 million Laser Vision Correction procedures had been performed in the United States and as of 2009 over 28 million have been performed worldwide.
Wavefront-guided Laser Vision Correction is a variation of Laser Vision Correction surgery in which, rather than applying a simple correction of only long/short-sightedness and astigmatism (only lower order aberrations as in traditional Laser Vision Correction), an ophthalmologist applies a spatially varying correction, guiding the computer-controlled excimer laser with measurements from a wavefrontsensor. The goal is to achieve a more optically perfect eye, though the final result still depends on the physician’s success at predicting changes that occur during healing and other factors that may have to do with the regularity/irregularity of the cornea and the axis of any residual astigmatism. Another important factor is whether the excimer laser can correctly register eye position in 3 dimensions, and to track the eye in all the possible directions of eye movement. If a wavefront guided treatment is performed with less than perfect registration and tracking, pre-existing aberrations can be worsened. In older patients, scattering from microscopic particles (cataract or incipient cataract) may play a role that outweighs any benefit from wavefront correction. Therefore, patients expecting so-called “super vision” from such procedures may be disappointed.
When treating a patient with preexisting astigmatism, most wavefront-guided Laser Vision Correction lasers are designed to treat regular astigmatism as determined externally by corneal topography. In patients who have an element of internally induced astigmatism, therefore, the wavefront-guided astigmatism Laser Vision Correction may leave regular astigmatism behind (a cross-cylinder effect). If the patient has preexisting irregular astigmatism, wavefront-guided Laser Vision Correction approaches may leave both regular and irregular astigmatism behind. This can result in less-than-optimal visual acuity compared with a wavefront-guided Laser Vision Correction approach combined with vector planning, as shown in a 2008 study. Thus, vector planning offers a better alignment between corneal astigmatism and Laser Vision Correction, and leaves less regular astigmatism behind on the cornea, which is advantageous whether irregular astigmatism coexists or not.