Many patients do not realize that the eye is an imperfect optical system. As light rays from distant objects pass through the individual optical components of the eye, they are subject to being distorted by the imperfections found in the cornea and the crystalline lens.
The distortions that are created are referred to as "aberrations." The vast majority--90% or more--of these aberrations create common refractive errors, such as nearsightedness, farsightedness and astigmatism, which can be treated by optical devices, like glasses and contact lenses, or by Laser Eye Surgery, using the conventional methods of LASIK, PRK or LASEK. The remaining 10% of optical aberrations create images which are altered by chromatic aberration, spherical aberration, diffraction, curvature of field, coma, trefoils and quadrifoils--collectively known as "higher order aberrations."
These higher order aberrations only occur in a visually significant manner in 10% to 15% of the general population. When they do occur, they are entirely unique to a particular patient--much like a fingerprint. For these patients, the use of a wavefront-guided laser eye surgery technique to create a completely customized reshaping of the surface of the cornea may be the best treatment option.
To achieve a customized corneal shaping, it will require measuring the higher order optical aberrations using a wavefront analysis system called an Aberrometer and then digitally interfacing it with a laser, using high speed computerized control to direct the delivery of a very tiny beam of laser energy across the cornea.
The Aberrometer System lets the surgeon see refractive aberrations in clear and accurate, rotating 3-D images. How does the Aberrometer do this? First, the Aberrometer sends low-energy laser light into the eye. The light reflects off the retina and travels back through the lens and cornea as an outgoing wavefront. This wavefront is captured by the Aberrometer, which then measures it to determine both higher and lower order aberrations of the entire optical system. The aberrations are then displayed on-screen in precise 3-D images.
To then create a customized corneal ablation from the Aberrometer measurements we digitally interface that data with the Excimer Laser Eye Surgery System. The Excimer Laser Eye Surgery System incorporates the use of a high-speed computerized eye tracking method that helps the Laser Eye Surgeon enhance your treatment by providing precise registration of the laser beam to create a customized ablation surface. Since your eyes are continually making very fine jumping movements - called "saccadic" movements which are beyond your control, no matter how hard you concentrate the tracking system assists the surgeon by scanning the eye thousands of times per second. Then, using computer control, it makes micro-adjustments at speeds many times per second to reposition the pinpoint laser beam between pulses of light, tracking even the smallest and quickest movements of your eye during treatment.
In addition, the Excimer Laser Eye Surgery System uses an ultra-small beam of cool laser light - one that's less than a millimeter wide, a spot much smaller than the thickness of a single human hair. Using high-speed computer control, the Excimer Laser Eye Surgery System moves this tiny beam of light across the surface of the cornea very rapidly in a tiny, non-sequential and overlapping pattern. This helps the surgeon deliver a smooth customized corneal shape to provide you quick visual recovery and individualized correction of your prescription.
Important Custom LASIK Note:Custom Wavefront Guided LASIK should not be confused with Wavefront Optimized Laser Eye Surgery. Spherical aberration is one of the most common aberrations that we find in the eye as well as optical systems such as cameras, telescopes and microscopes. For that reason, optical device manufacturers and certain laser manufacturers include a simple correction for the spherical aberration in their systems. So a Wavefront Optimized LASIK is only useful for correcting spherical aberration and NOT the full spectrum of higher aberrations that can affect your vision. To have a truely Custom LASIK procedure requires a measurement with the aberrometer as described above, and then directly programming the Excimer Laser by using those measurements. For some less complex prescriptions, Custom Wavefront Optimized LASIK is sufficient. For more complex prescriptions, a true Custom Wavefront Guided LASIK will be the procedure of choice.
