Vision problems resulting from focusing or refractive errors (nearsightedness, farsightedness, and astigmatism) are typically corrected either with eyeglasses or contact lenses. More recent alternative methods include various surgical techniques noted below:
· Radial Keratotomy
Excimer Laser Vision Correction Procedures
Photorefractive Keratectomy (PRK)
Laser assisted in situ keratomileusis (LASIK)
Wavefront enhanced LASIK
Intracorneal Rings (INTACS)
Phakic Intraocular lenses
Clear lensectomy with Intraocular lens placement
Currently, Excimer Laser Vision Correction Procedures for treating nearsightedness, farsightedness, and astigmatism are the procedure of choice for most people who desire less dependence upon glasses or contact lenses. These techniques use an excimer laser to reshape the cornea using energy from the pulses of ultraviolet light emitted by an excimer laser.
The excimer laser operates at a wavelength of 193 nanometers and does not transmit energy through the cornea to the internal tissues of the eye. Instead, the ultraviolet light is absorbed in the surface cells of the eye giving the excimer laser its unique ability to reshape these surface tissues. As the ultraviolet light is absorbed by the surface of the eye, tissue is vaporized. Essentially no heat is generated in the process; therefore, the risk of scarring the corneal tissues is minimized.
The energy of the laser is controlled so that each pulse precisely removes thin layers of tissue from the cornea, 1/4000 of a millimeter at a time. In fact, it would take about 200 pulses from an excimer laser just to etch through one human hair. The laser is programmed specifically for each patient and is controlled by a computer, which determines the location, number of pulses, and surface area to be impacted by the laser light beam based on that individual patient's particular vision problems and correction needs.
The two techniques using the Excimer laser which have the best overall track record, safety profile and predictability for the treatment of the majority of refractive errors are:
Photorefractive keratectomy (PRK) involves removal of the surface cells of the cornea (epithelium) by laser, chemical, or mechanical means. The laser then treats the layers below the surface cells to reshape the cornea. After the laser treatment, a contact lens and eye drops are used to aid the healing of the surface cells. Initial healing usually takes just a few days.
Laser assisted in situ keratomileusis (LASIK) uses a microkeratome to precisely split the cornea. The top layer remains attached on one side, is folded back, and the excimer laser is used to reshape the underlying stromal tissue. Following laser treatment, the flap is laid back in place. The flap is primarily held in place by the epithelium.
Higher order aberrations cannot be corrected through traditional LASIK or PRK procedures. Similarly, glasses and contact lenses are unable to help with these vision problems. An exciting new procedure, called CustomCornea®, uses WaveFront technology is the first laser vision procedure that's capable of correcting both lower order and higher order aberrations.
Diagnosing higher order aberrations
Higher order aberrations are diagnosed and measured using wavefront maps. These maps are plotted by passing a narrow ray of eye-safe light through the optical system and measuring the optical distortions as the light exits the eye. These patterns are then compared with the flat wavefront associated with normal vision. An ideal wavefront map would be perfectly flat.