Similar to PRK, this technique involves preserving a flap of epithelium (discarded in PRK) and replacing at the end of the procedure. Alcohol is used to loosen the epithelium so it can be preserved, but the alcohol may cause the epithelial flap to deteriorate. Proponents originally felt that this technique would have faster, less painful healing than PRK and less chance for haze in the cornea. In actuality, it is no better than PRK on these issues and in fact, may be worse since the epithelial flap may deteriorate and become a source of infection.
Similar to LASEK, the epithelial flap is removed by a modified microkeratome (epikeratome) rather than with the use of alcohol. The epithelial flap is less likely to deteriorate during healing, but it is difficult to get the epikeratome to consistently “cut” at the proper depth; too shallow or too deep can lead to problems. When properly performed, healing may be slightly faster than with PRK
Radial Keratotomy – an incisional procedure for nearsightedness and astigmatism performed commonly until about the early-mid 1990’s. Radial incisions were made in the mid-peripheral cornea to produce the effect. No actual tissue was removed. The effect and recovery were rapid, but for up to 30% of patients, long term stability became an issue.
Astigmatic Keratotomy – an incisional procedure, it was often combined with RK to correct astigmatism. A variation (limbal relaxing incisions – LRI) is sometimes performed in conjunction with cataract surgery to reduce pre-existing astigmatism.
Hexagonal Keratotomy – an incisional procedure performed briefly in the early 1990’s by a few practitioners for the correction of farsightedness and to produce nearsightedness for monovision by steepening the cornea. This procedure was very difficult to perform accurately and often produced hard-to-correct irregular astigmatism. Glare and haloes were significant.
Conductive Keratoplasty – a treatment originally designed to treat hyperopia, but more recently used for producing nearsightedness in one eye for monovision. The effect is accomplished by steepening the cornea by placing marks in the midperipheral cornea with a special type of radio frequency probe. Each mark produces collagen shrinkage and thereby, corneal steepening. Although seen to be less invasive than LASIK, it is less accurate, less stable, cannot correct astigmatism (in fact may produce new astigmatism), but may produce a form of monovision that may work well for selected patients. Because of regression, it often needs to be repeated.
Laser thermal keratoplasty – much like CK but even less stable with faster regression. The marks were applied all at once by a special type of laser. Largely abandoned in about 2003.
Scleral expansion bands – a treatment for presbyopia (reading vision); these were implants placed partial depth in the white of the eye (sclera) as a treatment for presbyopia. The idea was that these implants would expand the diameter of the eye and apply more stretch to the lens, aiding accommodation. A long, involved operation, brief duration of effect and frequent extrusion of the implants lead to its eventual demise.
Anterior ciliary sclerotomy – intended to accomplish the same thing as SEB’s but by making radial incisions in the white of the eye (sclera). Fairly rapid and predictable effect but very short-lived; numerous efforts to try to prolong the effect have failed.
Myopic keratomileusis – an extremely complex procedure developed in Bogota in the 1970’s for high degrees of myopia (nearsightedness). This procedure served as the foundation for all subsequent lamellar refractive surgeries (such as LASIK). The process involved removing a disc of tissue from the anterior (front) cornea with a microkeratome. The disc of corneal tissue was placed on a cryolathe, cut to the proper shape to correct the nearsightedness and then resutured back onto the surface of the cornea. Healing and stabilization were fairly prolonged, the sutures often produced astigmatism, but for patients with extreme myopia, the results for their day could be miraculous.
Photorefractive keratectomy – the original excimer laser procedure. Surface tissue (epithelium) is removed and discarded, the treatment is applied to the layer directly beneath the epithelium and it then takes about 3 to 4 days for the epithelium to regenerate. Eventually provides the same results as LASIK and usually utilized in patients who are not good candidates for LASIK
Laser assisted in-situ keratomileusis – the most commonly performed vision correction procedure in which an attached (hinged) flap is created in the cornea with either a microkeratome or a femtosecond laser (Intralase), the underlying corneal surface is then reshaped with an excimer laser and then the flap is replaced. Healing and comfort are usually achieved in 6-8 hours with visual stability for most within 3-4 days.
A generic term applied to excimer laser treatments that are wavefront-driven or wavefron-guided.
The proprietary name VISX gives to their system of wavefront-guided treatment.
A physical/optical construct which is measured as a method of assessing the quality of an optical system. A wavefront measurement is generated by a Hartmann-Shack aberrometer. This device shines a beam of light through an optical system and by analyzing how it exits the other end of the optical system generates a wavefront; a perfectly flat wavefront indicates perfect optics; any irregularities in the wavefront which are a result of photons exiting faster of slower than the reference photons, indicate irregularities in the optical system.
This system has been applied to the human eye and the measured wavefront irregularities constitute what are called higher order aberrations (nearsightedness, farsightedness and astigmatism are lower order aberrations). In custom treatments, the laser ablation is modified to correct the higher order aberrations and improve the quality of the wavefront. The wavefront measurement for each eye is unique, so that wavefront-guided treatments are likewise unique.
The proprietary name VISX gives to their aberrometer (see wavefront).
Advanced surface ablation – another term for PRK. Usually implies the use of some sort of newer technique for epithelial removal (e.g., alcohol) and haze prevention.
This term applies to the vaporization of corneal tissue caused by the excimer laser.
This is a mathematical term that applies a curved shape, or arc, that is steeper in the center and flatten towards the periphery. Corneas that have not undergone refractive surgery are generally prolate. Most wavefront-based treatments are designed to preserve a more prolate shape with a resulting better quality of vision. Some non-wavefront-based treatments are also prolate. (see also oblate)
This is a mathematical term that applies a curved shape, or arc, that is flatter in the center and steepens towards the periphery. Most corneas that have undergone surgery for nearsightedness are at least somewhat oblate. Older excimer technologies produced more “oblateness” which translated into more visual symptoms such as glare, halo, and reduced vision in dim light.
Another term for PRK
Intraocular contact lens – a lens that is implanted in the eye for the correction of high refractive errors or for patients who are not good candidates for PRK or LASIK. Two models have been FDA approved. They have a completely different risk/benefit ratio than the excimer-based procedures and patients need to consider these options very carefully. Many patients have reported very good results, but compared to excimer procedures, case volume is small, and long term effects are unknown.
Same as ICL.
A prolate-based laser system manufactured by Wavelight. Manufactured in Germany and first approved in this country in 2004.
An excimer laser company which evolved from Summit technologies, the first recipient of FDA approval for PRK in 1995. First company to achieve FDA approval for wavefront-driven ablation in late 2002.
One of the original early excimer laser developers; continues to be the US market leader in terms of procedure volume and market share.
Nearsightedness; in which light rays are in focus in front of the retina (and out of focus on the retina). The cornea is too steep in relation to the length of the eye. Without glasses or contacts, distant objects will be blurry and there will be a point at near where objects will be clear. In pure myopia, all incoming light rays will be focused to the same point within the eye.
Farsightedness; in which light rays are in focus behind the retina, if that were actually possible, (and out of focus on the retina). The cornea is too flat in relation to the length of the eye. In low amounts and young patients there may be no discernible visual deficit. Often becomes manifest as the individual ages and will eventually cause blurry distance and near vision.
Refractive error in which light rays are focused at different points in the eye’s optical system. Usually a result of the cornea being shaped more like part of a football than part of a basketball and thus having areas of different curvatures leading to the different focal points. Usually present to some degree since birth, but can be induced by certain ocular surgeries and/or trauma. (see irregular astigmatism)
A catch-all term usually used to describe an irregularly shaped cornea. In regular astigmatism, the cornea has a steepest meridian (axis) separated by 90 degrees from a flattest merdian. An example of irregular astigmatism is when these two meridia are not 90 degrees apart. There are many ways in which a cornea can have irregular astigmatism. Glasses and conventional LASIK do not specifically correct the irregular component of astigmatism if present. However, certain cases of irregular astigmatism can be corrected by wavefront-guided treatment.
The loss of an eye’s ability to focus at near. This usually occurs sometime between the age of 40 and 50. It will happen regardless of the underlying refractive error (myopia, hyperopia, astigmatism) and is a result of loss of flexibility of the eye’s natural lens. If the vision at distance is good, usually only reading glasses are necessary.
The condition in which an eye needs corrective lenses to see clearly. Expressed numerically in terms of degree of nearsightedness/farsightedness and astigmatism.
The opinions herein expressed are those of Dr. Lusby and are based on his clinical experience. Alternate opinions may exist.