An informational brochure developed by
Bobby Maddox, M.D.
©1994-2001 Robert M. Maddox, M.D.
Last Revision May 5, 2001
No materials herein may be reproduced in any manner without permission.
The Maddox Laser Eye Centers have two Excimer Laser systems -- one in El Paso, Texas and one in Juarez, Mexico -- allowing us to better serve refractive surgery patients on both sides of the border.
Our El Paso center is equipped with the Alcon Summit Autonomous LADARVision Excimer Laser System, "the future of laser vision correction," that combines the first patented eye tracker with unique, small-spot shaping to provide a smooth corneal surface and the potential for an early return to visual stability.
In Juarez, we use the LaserSight LSX Excimer Laser System.
Our two laser systems have enabled us to expand our treatment parameters to all modalities of refractive error, including myopia, hyperopia, astigmatism, and mixed astigmatism.
Dr. Bobby Maddox, an ophthalmologist practicing in El Paso, Texas, since 1975, has always been a pioneer in bringing new technology to benefit his patients. He routinely chose small incision phacoemulsification surgery for his cataract patients more than a decade before other surgeons in the area. In 1982, he established the first in-office outpatient surgery center in El Paso specifically designed for phacoemulsification of cataracts with intraocular lens implant, a procedure now widely used throughout the world as the procedure of choice for cataract surgery. He pioneered the Excimer Laser into Mexico in January, 1992, having brought the first Excimer Laser into the country of Mexico.
Dr. Maddox was born in Austin, Texas, and has spent most of his life in El Paso. As one of the great football legends of the El Paso High Tigers, he received the prestigious Ralph Marmolejo award from El Paso High for his outstanding performance at quarterback, punter, and safety. Along with his athletic prowess in football and track-and-field at El Paso High, Dr. Maddox competed in bodybuilding competitions as well, once capturing third place in the Mr. El Paso contest. Dr. Maddox has continued his lifelong interest in maintaining a strong physical fitness as well as a strong spiritual fitness. He and his family have dedicated themselves and their work to the honor and glory of God through His Son, Jesus Christ. His office is filled with reminders that God is there to carry us through our difficulties and to show us His love, if we would only ask Him, in Jesus' name.
Dr. Maddox received his medical training and his Doctor of Medicine degree from the University of Texas School of Medicine in Galveston, Texas. After a rotating internship in Austin, he completed a 3-year Residency program in Ophthalmology at Brown University and Rhode Island Hospital in Providence, Rhode Island. He was then awarded a Fellowship grant from the National Institutes of Health to participate in a study of laser surgery for the treatment of diabetic retinopathy, or retinal bleeding, which can lead to blindness. The year he spent treating and following the progress of diabetic patients at Massachusetts Eye and Ear Infirmary in Boston provided him with an invaluable experience in laser eye surgery that he continues to use for the benefit of his patients. His love for the border and the international culture of El Paso brought him back to El Paso, where he established his private practice in 1975. In 1981, Dr. Maddox was certified by the American Board of Ophthalmology, and is a Fellow of the American Academy of Ophthalmology.
Because of his commitment to use his profession to serve God, he has always found time to take care of the indigent citizens of El Paso and many communities in Mexico. His dedication to assist the poor has resulted in his receiving special commendation from several governmental authorities and media organizations in Mexico, and culminated in his being presented the Conquistador Award by the Mayor and City Council of El Paso -- the highest honor the city can bestow on an individual. His reputation for quality in the care of his patients resulted in his being invited to become a member of the Society for Excellence in Eyecare, a national organization of highly skilled eye surgeons, and was recently chosen to be a Fellow of the Society for Excellence in Eyecare as well as being invited by the International Institute for Advanced Laser Surgery to become a member of its five-member International Advisory Board for Excimer Laser Surgery. In 1999, Dr. Maddox was recognized as a "Pioneer in Refractive Surgery" by Summit Technology at the annual meeting of the International LASIK Society.
Dr. Maddox is also an internationally recognized educator, having addressed the 8th Congress of Ophthalmology in Lima, Peru, and the Third National Symposium of Optometry in Juarez, Mexico. In 1984, he participated in instructing other ophthalmologists, including some of his own former instructors, at an intensive course on Advanced Techniques in Cataract Surgery and Phacoemulsification, jointly sponsored in Philadelphia by the American Academy of Ophthalmology, Hahnemann University, Temple University School of Medicine, Scheie Eye Institute, and Wills Eye Hospital. His publications include articles detailing his technique for removing difficult cortical material during cataract surgery, published in Ocular Surgery News, as well as extensive patient educational materials. Dr. Maddox discovered a new and very important post-LASIK syndrome called Sands of the Sahara, or SOS. He has also served on physician educational panels, and he has contributed videos of his own surgical techniques to be used as instructional videos for the libraries of several major suppliers of ophthalmic surgery products. He has in the past conducted a nationwide series of physician certification seminars in postoperative care following Excimer Laser Photorefractive surgery.
His love of his profession and his dedication and commitment to the well-being of his patients has always led Dr. Maddox to be a pioneer in bringing his patients the best medical advances and medical technology science has to offer. He began offering Radial Keratotomy to his patients in 1982. In 1989, when he learned of the exciting results of early European and FDA studies of the Excimer Laser for correcting nearsightedness, he wanted to bring this revolutionary technology to his patients. All 46 clinical sites designated for the FDA studies in the U.S. were already assigned, and no new sites were being allowed. So Dr. Maddox sought to take advantage of the international character of El Paso and began an intensive 2-year process to receive a medical license in Mexico and to establish a clinical study for Mexico similar to the FDA study in the United States.
Dr. Maddox began working with the federal regulatory agencies in Mexico City in December, 1989, to establish an Excimer Laser Center in Mexico for the purpose of performing excimer laser surgery for the correction of myopia and corneal abnormalities. Dr. Maddox made a commitment to establish all aspects of the laser center in complete accordance and compliance with the laws of Mexico. In order to be totally within the regulations of the Ministry of Health and all other governmental agencies of Mexico, Dr. Maddox chose to apply for a license to practice medicine in Mexico. After fourteen months, he fulfilled all of the requirements for licensure and, in January, 1991, he was granted his licence to practice ophthalmology. The final step to establishment of the excimer laser center was completed in August, and the Excimer Laser Center began operations in January, 1992. After Dr. Maddox was awarded his license to practice ophthalmology in Mexico, he was also granted a permit by the Ministry of Health to establish an excimer laser site in Juarez, using the excimer laser system manufactured by Summit Technology, Inc., of Waltham, Massachusetts. Both the Ministry of Health and the Mexican Society of Ophthalmology in Mexico approved Dr. Maddox to perform excimer laser surgery and to conduct clinical studies for the Ministry of Health, as well as the protocol developed by Dr. Maddox for the studies to be conducted. These studies substantiated for Mexico the safety, predictability and efficacy of the 193-nanometer excimer laser in correcting refractive insufficiency of the cornea, as previously established in other worldwide studies. Millions of patients have undergone excimer laser photorefractive keratectomy surgery in countries throughout the world.
Corneal epithelium:(approximately 40-50 microns thick) The superficial collection of multiple layers of cells that line the corneal surface. These cells constantly regenerate as do the cells that cover the skin of the body.
Basement membrane: A small membrane laid down by the basal epithelial cells and upon which they rest. This membrane rests on Bowman's membrane.
Bowman's membrane:(approximately 15 microns thick) A membrane layer immediately below the epithelium and basement membrane which rests on the stroma.
Stroma: Makes up the bulk of the cornea; consists of multiple layers of collagen fibers, keratocytes, and water.
Stromal lamellae: Collagen fibers arranged in a transparent fashion within the stroma.
Keratocytes: The stromal cells.
Descemet's membrane: A membrane layer that is located beneath the stroma and above the endothelial cell layer.
Endothelial cells: A mosaic of cells lined up on Descemet's membrane. They cover the entire inner surface of the cornea and are responsible for keeping the cornea transparent.
1949 - Jose Barraquer (Bogata, Columbia): Keratophakia
1963 - Jose Barraquer (Bogata, Columbia): Microkeratome (freeze MKM)
Late 60's - Purresquin (Russia): Corneal flap and trephination of the bed
1977 - Troutman and Swinger (USA): First Americans to perform Keratophakia
1977 - C. Swinger (USA): First American to do freeze MKM
1986 - Luis Ruiz (Bogata, Columbia): Performed the first in situ Keratomileusis using the
manual microkeratome
1989 - Gholam Peyman (USA): Erbium-Yag laser on corneal bed, under the cap - animal
model.
1989 - Ioannis Pallikaris (Greece): Performed the first LASIK on a human eye (July).
Coined the term LASIK (Laser In Situ Keratomileusis).
1989 - Lucio Baratto (Milan, Italy): 250-300 micron cap. First Excimer Laser to cap on
human eye
1991 - Luis Ruiz (Bogata, Columbia): Developed the microkeratome.
Therapeutic lamellar Keratoplasty has been done for well over 100 years, predating the first corneal graft.
LASIK is a very special technique that has been developed for correcting myopia, hyperopia, and astigmatism, based on the work done by Dr. Jose Barraquer and Dr. Luis Ruiz of Bogota, Columbia. Since 1949, Dr. Barraquer has been working on a procedure to reshape the cornea. The cornea, or clear front part of the eye, is responsible for about 2/3 of the correcting power, or refracting power, of the eye. The cornea is the delicate transparent structure that is altered by LASIK in order to bring the unfocused light rays into focus. Please refer to the diagram "Illustration of the Cornea" for understanding the corneal anatomy. One micron is equal to one one-thoundsandth of a millimeter (.001 mm). One human cell is approximately 10 microns tall. One single human hair is approximately 50 microns thick. The central cornea is approximately 500 microns in thickness. This translates to about one-half of a millimeter (.5 mm). As you can see in the diagram, the surface of the cornea is covered by four to five layers of epithelial cells, generally 40 to 50 microns thick, which protect the front surface of the cornea. The main structure of the cornea is referred to as the stroma, which is made up of approximately 70% water. It also consists of multiple layers of collagen fibers (stromal lamellae) and keratocytes. The term "lamellar surgery" is derived from the stromal portion of the cornea, which is filled with stromal lamellae. The stromal lamellae are actually collagen fibers arranged in a transparent fashion within the stroma itself, analagous to the layers of an onion. The endothelial cells line the inner portion of the cornea and are responsible for keeping the cornea transparent.
Dr. Jose Barraquer of Bogota, Columbia, has been involved in lamellar refractive surgery since 1949. His first work was with keratophakia--that is, steepening the cornea by adding donor lamellar tissue (corneal stromal tissue) to the cornea. Therefore, lamellar refractive surgery has been around for more than forty years. Dr. Barraquer developed a small microkeratome with a tiny blade which rapidly oscillates and acts like a carpenter's plane. This microkeratome was used to correct large degrees of myopia by reshaping the front surface of the eye and has been used for that purpose since 1963. At that time, it was referred to as MKM, or myopic kerato-mileusis. HKM, or hyperopic keratomileusis, was also developed to correct hyperopia. In 1963, an approximate 300 micron cap of corneal tissue was resected with the micro-keratome; it was frozen and then placed on a contact lens lathe, and a curve was carved on the back surface of the corneal cap. After the correcting curve was placed on the corneal cap, it was referred to as the corneal lenticle. The corneal lenticle was immediately thawed, laid back on the corneal bed, and sutured into place. I actually began doing this procedure in 1984.
During LASIK, the surgeon uses the Excimer Laser to recontour the corneal bed. Keep in mind that we still have to create a corneal flap and apply the Excimer Laser to the corneal stromal bed in order to effect the corrective change. In the case of myopia, the cornea is flattened; and in the case of hyperopia, the cornea is steepened. In the case of astigmatism, the steeper meridian of astigmatism is reduced or eliminated or the flatter meridian is steepened, or a combination of both.
We know we have over 40 years of history on lamellar refractive surgery, and over 30 years of MKM, or myopic keratomileusis, for high myopia. The combination of Excimer Laser is relatively new, and on-going clinical studies with the use of Excimer Laser and the microkeratome will be necessary to determine the long-term safety and efficacy of this aspect of the procedure. Excimer Laser Photorefractive Keratectomy (PRK) has been used in clinical trials all over the world, beginning in 1988. It has been used to correct low, moderate, and high degrees of myopia and astigmatism, as well as hyperopia. In general, the Excimer Laser PRK has been applied to the surface of the cornea in clinical trials. Only since 1993 has this been used in combination with the microkeratome to treat the bed underneath the surface rather than treating the surface itself. I have been performing Excimer Laser PRK to the surface of the cornea since January 8, 1992. Results of our clinical trials in Mexico have shown that about 98% of our patients between -1.00 and -6.00 diopters have uncorrected vision of 20/40 or better at 12 months. This means that about 98% of these patients are driving a car now without glasses. Due to the recent advancements in laser technology, we are able to achieve better results in patients with myopia higher than 6 diopters.
I would like to refer you to the appendix for a brief discussion of the history and physics of the Excimer Laser and Excimer Laser Photorefractive Keratectomy (PRK).
1. Significant irregular astigmatism and loss of best corrected visual acuity
Irregular astigmatism differs from regular astigmatism in the following way. If one has astigmatism, one is generally born with it. This is regular astigmatism. This procedure does not normally induce regular astigmatism. Regular astigmatism generally refers to the shape of the cornea, in that the cornea is shaped like an oval rather than a sphere. Irregular astigmatism differs from regular astigmatism in that the general shape of the cornea can be spherical; however, surface irregularities are present which can diminish the best corrected visual acuity. Normally, irregular astigmatism does not remain permanently; however, occasionally it can. One must have a perfectly smooth corneal surface in order to have the best corrected visual acuity, especially the smooth surface over the visual axis (line of sight) of the eye. The incidence of significant irregular astigmatism with the hinge, or flap, technique and Excimer Laser to the corneal bed is unknown at this time. However, it could be 1% or higher, depending on the degree of attempted correction. When one develops significant irregular astigmatism, one can lose one, two, or more lines of best corrected visual acuity. One of the major problems of irregular astigmatism is the fact that spectacle correction will not adequately correct the vision. The only way to adequately correct the vision would be with a rigid, gas-permeable contact lens. If the contact lens was not a satisfactory alternative and the irregular astigmatism was severe, then a penetrating keratoplasty, or corneal transplant, may have to be performed. Therefore, permanent, significant irregular astigmatism is difficult to correct surgically once induced. Most people who develop irregular astigmatism following this type of surgery improve over time.
2. Significant incomplete or irregular micro-keratome flap or cap resection (uneven cut).
This rarely occurs, but if it does, the surgeon will normally put the cap or flap down on the bed in its original position and not proceed with the second refractive laser ablation in the corneal bed. Normally no harm is done and the vision returns to preop levels in a few days to a few weeks. The surgery can be postponed for 3 to 6 months and then the flap resection with the microkeratome can be repeated in order to achieve an acceptable flap resection. The most common reason for this incomplete microkeratome resection would be poor suction with the suction ring or a break in suction, for whatever reason, during the micro-keratome pass.
3. Decentration of the Excimer Laser beam
Decentration is rare but could occur. A small amount of decentration is of no consequence, but a large de-centration problem could induce large amounts of astigmatism, both regular and irregular, and decrease one's best corrected visual acuity. The eye tracker can decrease the incidence of this problem.
4. Significant decen-tration of the corneal flap or disc (decentration of corneal resection with microkeratome)
This refers to decentration of the flap or disc following the resection of the corneal flap or disc. This problem is also rare, but if it did occur and the corneal bed were regular and smooth, one still may be able to proceed with the Excimer Laser application to the corneal bed for the refractive ablation step. If this could not safely be done, the surgery would have to be postponed for 3 to 6 months and then start all over again. Usually, no harm is done and the vision returns to the preop level a few days to weeks afterwards.
5. Displaced cap or flap
If the corneal cap or flap is not perfectly aligned at postop day #1, it will need to be repositioned under topical anesthesia. A displaced cap may occur from the following reasons:
6. Lost cap of corneal tissue.
This is an exceedingly rare complication since we are now using the flap or hinge technique. Prior to the hinge technique, the surgeon routinely removed the corneal cap, or disc, completely, perform the Excimer Laser photoablation on the stromal side of the "free" cap instead of the corneal bed, and then place the free corneal cap, or lenticle, back onto the corneal bed without sutures. Occasionally the cap would fall off the eye, and sometimes could not be found. If it were found, it could be placed back on the eye into position, and usually sutured into place. If the lost cap could not be found, then what is called a homoplastic lamellar graft, taken from another person, would be used to replace the original lost cap. This latter procedure sometimes takes several months to heal, but one may do quite well with this technique.
7. Attempting the corneal flap and ending up with a free corneal disc
At the present time, we are leaving a hinge, creating a corneal flap, when we do the microkeratome resection. We then lay that corneal flap back, exposing the corneal bed. Sometimes, due to various factors and circumstances, the microkeratome will resect the corneal cap completely free rather than leaving the small hinge. If that were to happen, we still could have just as good a result as we could have had with the hinge technique; however, we do run the slight risk of cap decentration or dislocation without sutures. Under those circumstances, we would do the sutureless technique; however, we would tape the eyelids shut until the following day. If the cap did dislodge, we would normally be able to find it, if the lids have been securely closed for that period following surgery. It is unusual for a free corneal disc to occur when we are aiming for the corneal flap.
8. Subconjunctival Hemorrhage (Bloodshot eye)
A subconjunctival hemorrhage may occur secondary to the suction ring that is placed on the eye prior to the microkeratome pass. This certainly is not a serious condition and merely presents as a bloodshot eye on the first postop day. If this happens, the subconjunctival hemorrhage will normally clear over the next couple of weeks and is of no visual consequence. A subconjunctival hemorrhage refers to the presence of small, splotchy, superficial hemorrhages underneath the transparent tissue that covers the white part of the eye, or sclera. Sometimes the splotches can enlarge or spread over the first day or two, but then normally stabilize.
9. Pain
The operation itself is painless. One receives only topical anesthetic drops prior to the procedure. One feels pressure, not pain, while the suction ring is on the eye. One may have a mild to moderate foreign body sensation for a few hours following surgery, but after about 4-6 hours the eye normally feels comfortable. During this period, you may take your appropriately prescribed pain medication for this. It would probably be a good idea to take a nap following surgery. Normally, when you wake up the discomfort is gone.
Remember, this is one of the least painful of all refractive procedures following surgery.
10. Undercorrection
The higher the refractive error, the less accurate is this LASIK operation. It is more accurate in the lower to moderately high refractive errors. Therefore, if one is going to be overcorrected versus undercorrected, it is much better for one to be undercorrected. In other words, it is better to remain a little bit nearsighted versus farsighted. If the residual undercorrection is not that much, then a reoperation, or enhancement, may not be necessary. However, if the undercorrection is excessive, then an enhancement can be done six weeks to three months later.
11. Reoperation (touch-up or enhancement)
It will be quite common to need an enhancement in order to fine-tune the vision correction, especially in the extremely high myopes. This is usually done by lifting the original flap and placing more laser treatment in the bed. Usually, one enhancement takes care of the correction; but, rarely a third surgery could be necessary. Dr. Maddox prefers to lift the flap and reapply laser for the enhancement. It is usually done 36weeks to to 3 months post-op. Generally, it will not be necessary to make a new flap with the microkeratome. Each patient should be mentally prepared for an enhancement procedure, if necessary.
12. Will I be able to wear contact lenses after LASIK?
If you remain partially undercorrected and you choose to wear a contact lens after LASIK, it would be extremely unusual for you not to be able to tolerate a contact lens after LASIK, especially if you could tolerate contact lenses prior to surgery.
13. Overcorrection
Since overcorrection is undesireable, we strive to avoid this condition following LASIK. Actually, one may become temporarily overcorrected initially, but this is usually substantially reduced or gone by the first 2 to 3 months postop. If one has a mild overcorrection that is permanent, this is not usually something that has to be corrected. If one has a significant overcorrection, Dr Maddox prefers to lift the flap at 6 weeks to 3 months and retreat the bed.
14. Glare, starburst, contrast sensitivity problems
Significant night glare could occur in a small percentage of the population; however, the glare is usually not any worse than glare prior to surgery, especially when wearing contact lenses. Night glare could be debilitating, but this would be rare.
One commonly experiences some night glare and halos immediately following LASIK. Normally, by 3 to 9 months post-op, night glare is significantly reduced or eliminated.
One may experience glare and star burst without glasses at night following surgery if a significant residual refractive error remains. The glare can be reduced merely by using a light pair of prescription glasses when driving at night.
Those individuals who have very large and dilated pupils at night will complain more about night glare, halos, etc. than those who have small or moderately dilated pupils at night.The new laser system allows for a larger optical zone treatment diameter, thus reducing nighttime glare and halo problems. The pupil size will be carefully evaluated prior to surgery.
15. Sands of the Sahara
Occassionally, one may develop excessive inflammation between the flap and corneal bed. This is usually eliminated with the use of potent and frequent steroid eye drops. Occassionally, the flap has to be raised, the inner side of the flap and surface of the bed have to be cleaned, and the flap has to be repositioned in order to prevent corneal melt and irregular astigmatism.
16. Epithelium in the interface (between the corneal flap, or disc, and corneal bed)
Possibly 2 or 3% of the time, the corneal epithelium may be found to be present in the interface. The corneal epithelium consist of 4 or 5 cell layers that normally cover the surface of the cornea and protect it. For example, if the corneal flap has a loose edge, say the first day postop, the epithelium may choose to grow under the flap in that particular area and cause problems with vision and stability of the corneal flap. The flap will become loose and can induce significant amounts of astigmatism. This epithelium can be 20 to 70 microns thick. Therefore, we know that epithelial ingrowth can be significant, and we must repair the edge defect and rid the epithelium from underneath the flap. This can usually be done quite easily under topical anesthetic drops; however, if this is not easily fixed, then the flap may have to be lifted up to give access to the epithelial cells, and be vigorously cleaned. Afterwards, the flap is either repositioned without sutures or with temporary sutures. This will usually take care of the problem, but if it doesn't, the procedure can be repeated until the epithelium is eradicated from beneath the flap. Sometimes there is a localized island of epithelium under the flap that is tiny, and we just observe it and do nothing unless it grows to 2 mm or larger, and then we would remove it. If we left it and allowed it to continue to grow, it could cause a localized corneal melt problem anterior, or in front of, the epithelial island, or plaque. Normally, the epithelium under the flap is more of a nuisance than anything else; and we can generally remove it without it growing back.
17. Particulate matter under the cap or flap
We sometimes see particulate matter, or tiny filaments in the interface, but they are usually of no consequence. At the time of surgery, we try to remove it; however, if we see them at the slit lamp biomicroscope the next day, we can either leave them or remove them at that time. Occasionally, we see a small amount of blood in the interface. If this occurs, it would come from prior long-term contact lens wearers where tiny superficial blood vessels have grown into the superficial peripheral corneal area. This is of no consequence and will disappear in a few weeks.
18. Mechanical failure of the microkeratome or Excimer Laser
If either the micro-keratome or the Excimer Laser malfunctioned, surgery would have to be temporarily postponed.
19. Infection
Infection is exceedingly rare after LASIK in general. If one did develop a bacterial infection after LASIK, it most likely could be cured by antibiotic drops. However, if the infection is not discovered until the late stages, one may have to remove the cap or flap and cure the infection and then have a homoplastic corneal cap later on (donor corneal material). The infection could permanently scar the corneal bed and necessitate a corneal transplant. It could also enter the eye and cause loss of the eye, but this would be extremely rare with LASIK.
20. Poor exposure
This is often due to narrow eyelids and/or small orbit with a small eye. Also, deep-set eyes are not as easily accessible. Therefore, if the eye does not protrude enough for the suction ring, an injection around the eye, of balanced salt solution or anesthetic solution, may have to be given in order to expose the eye enough for the surgery. This is rarely done. Sometimes a lateral canthotomy needs to be done in order to widen palpebral fissure area. This is done with a light injection of anesthetic at the lateral corner of the eyelid. Two tiny snips are carried out on the lateral canthal area (the lateral portion of the corner of the lids where the upper and lower lids meet). This also is rarely done.
21. Perforation of the globe and/or retrobulbar hemmorrhage
This is extraordinarily rare, since we do not routinely use a retrobulbar or peribulbar injection to anesthetize the eye. We routinely use topical anesthetic drops. The only time we might do an injection around the eye would be if the eye would not give us good exposure. In other words, if the eye did not naturally protrude enough for application of the suction ring and microkeratone. If this were the case, then 4 to 5 cc of balanced salt solution or local anesthetic solution could be injected around the eye in order to achieve better exposure. This is normally a benign, painless procedure; but, only rarely, this could cause a sight-threatening problem such as perforation of the globe or hemmorrhage behind the eye with possible permanent loss of vision, partial or complete. If we were to do a retrobulbar or peribulbar injection, there is a small risk that the injection fluid used could infiltrate up under the conjunctiva or transparent tissue that surrounds the sclera, or white part of the eye. This is not a dangerous problem in and of itself; but it can interfere with good suction by the suction ring. Therefore, if this occurred, the operation would have to be delayed about an hour or so, or completely postponed in order for the chemosis, or swelling, of the conjunctiva to recede. Also, Surface PRK could be substituted for LASIK under these circumstances.
22. Loss of endothelial cells
The endothelial cells line the inside of the transparent cornea. They play an important role in keeping the cornea transparent. Without these cells, the cornea would become opaque, or lose its transparency. LASIK itself has not been shown to cause any significant endothelial cell loss or damage over the years. Also, Excimer Laser to the corneal bed has thus far not been shown to be harmful to the endothelial cells. Further studies are underway to determine any such longterm effects.
23. Persistent corneal epithelial defect with foreign body sensation and a prolonged healing period and prolonged irritation
Normally, the epithelium covers over the corneal flap edge within 24 hours following LASIK. However, there are those rare cases that may take a bit longer. For the first few weeks post-op, the eye may feel "dry" and you may use non-preserved artificial tear drops as frequently as needed. Even more rare is a persistent localized area of the cornea that causes a foreign body sensation; infrequently this has to be treated in order for it to clear.
24. Cataract formation
Cataract formation has not been a problem with LASIK. The Excimer Laser is an ultraviolet laser with a wave length of 193 nanometers. The maximal penetration is only 1 to 3 microns; hence, it is not believed to cause cataract formation.
25. Corneal Ectasia (excessive structural weakness of the cornea.)
It is believed that one should be left with around 250 microns of corneal bed (excluding the corneal flap) after the LASIK procedure in order to avoid corneal ectasia or loss of structural integrity of the corneal bed. If one leaves a corneal bed less than 250 microns, this may cause the cornea to bow forward ("pseudo-keratoconus") where one would most likely need a corneal transplant. Very careful calculations and ultrasonic pachymetric measurements are made in order to avoid this complication.
26. Temporary Glaucoma or increased intraocular pressure
Temporary glaucoma or increased intraocular pressure has not been a problem with LASIK, especially since drops are only used for approximately 1 week following surgery.
27. Transient iritis (inflam-mation inside the eye)
Usually less than 1% of patients develop iritis during the epithelialization period following LASIK. The iritis normally clears with topical corticosteroid drops, or intramuscular injection of a systemic corticosteroid.
28. Temporary Fluctuation of Vision
This phenomenon may occur during the first few days following LASIK. Once the eye stabilizes, which is usually 1 to 3 months, the fluctuation normally disappears. Longterm fluctuation of vision has not been a problem with LASIK, unless one has a "dry eye".
29. Ptosis or droopy eyelid (usually temporary)
It is felt that use of potent corticosteroids is the most common cause for ptosis, and it usually tends to be reversible. It could be caused from the lid speculum, or from post-op lid edema or swelling. It would be rare to have a permanently droopy eyelid following LASIK. If one developed a permanent droopy eyelid, surgical correction of this condition may be necessary.
30. Dry Eye
There are a number of patients who have undergone LASIK who complain of a dry eye feeling for a few weeks to months following this refractive surgery. We do recommend that these patients use a non-preserved artificial tear drop as often as needed to relieve this sensation.
31. Decompensated Eye Muscle Imbalance (Rare)
Decompensated eye muscle imbalance is rare after LASIK. If one has had a prior history of a crossed eye, but now is straight, this could recur after LASIK treatment, especially if there is a substantial imbalance in the refractive error between the two eyes. Once both eyes are balanced by equal or similar refractive errors, they usually will straighten out. Rarely surgery has to be performed to correct this muscle imbalance.
32. Vascular Occlusion
When the suction ring is applied to the eye prior to the keretectomy, the intraocular pressure is raised to 65mm Hg or greater. This pressure occludes the central retinal artery of the eye and prevents one from seeing until after the keratome pass and release of the suction ring pressure. It would be extremely rare for this pressure to cause damage to the eye. Only a few cases of this have been reported on a world wide basis. I have never seen this happen.
33. Mutagenesis (Cancer)
There have been no reported cases of mutagenesis. Since the Excimer Laser 193 nanometer wave length penetrates only about 1 to 3 microns at the most, it is felt that it does not penetrate deep enough to affect the nucleus of the cell. Animal studies have not indicated any problem with mutagenesis as a result of Excimer Laser photoablation.
34. Retinal radiation effect from the Excimer Laser
Since the 193 nanometer wave length does not penetrate more than 1 to 3 microns, no damage to the retina or other intraocular structure has ever been reported. Some of the ultraviolet fluorescence, other than the 193 nanometer, in the 300 to 400 nanometer range is present to a certain degree; however the exposure during LASIK is no more than that received by the eye when one is walking outside for a few minutes on a bright, sunny day. The retina is the photoreceptor cell lining of the inside of the eye that receives and transmits light energy back to the visual cortex in the brain.
35. Induced regular astigmatism
Significant amounts of astigmatism induced after LASIK are unusual, and it would be rare to be clinically significant. Regular astigmatism occurs when the cornea is shaped like an oval rather than a sphere and requires a special cylindrical lens or contact lens to correct it. Significant amounts of induced regular astigmatism can be reduced or eliminated with a diamond blade or with the Excimer Laser.
We have gone over the most important risks and complications. Even though a serious side effect is unlikely to occur, the remote possibility exists. We believe that the long track record for myopic keratomileusis (MKM) has stood the test of time since 1963. With the recent technological breakthrough on the microkeratome in conjunction with the excimer laser since 1991, it appears that this has made the procedure more accurate, safer, and less complicated for the surgeon to perform. So far, there have been several million of these cases done with impressive results.
(Note to ladies preparing for LASIK surgery: please discontinue application of eye makeup for at least one day prior to the date of surgery. Be sure to clean makeup from the base of the lashes or lid margins, both upper and lower lids. Generally, you may resume eye lid makeup, preferably with new cosmetics, 7 days after surgery has taken place and the eye is comfortable. Be very gentle in applying your eye makeup and be sure not to bump your eye during the process. Use extreme caution with curling irons, makeup brushes, and hair or deodorant spray.)
If your evaluation exam proves that you qualify for surgery, we will discuss surgical options with you. If you have the LASIK surgery on one eye, you may wish to have the second eye done several days to weeks later. When the first operated eye is comfortable and sees well, and both the doctor and the patient are satisfied, then evaluation for LASIK surgery on the second eye can be considered.
However, more and more cases of bilateral LASIK are being performed. Patients are opting for both eyes to be done on the same day for obvious reasons. If you desire both eyes to be done on the same day, discuss this with your referring doctor or with Dr. Maddox.
However, if it is determined that you are not a good candidate for the LASIK surgery, you will be given an explanation as to the reasons why you are not a good candidate. It may be recommended that you postpone your refractive surgery until further developments take place with LASIK. You may want to consider an alternative method of refractive surgery, or stay with your glasses or contact lenses for the time being.
1. Computerized Topographical Analysis (Video Keratography)
This is a very sophisticated, computerized, high-tech analysis machine that will record in detail the corneal topography (over approximately 6,000 points on the corneal surface), so that we may be able to see exactly what the corneal shape is prior to surgery and be able to follow that corneal shape after surgery to determine the impact of LASIK on the cornea.
2. Pupil Diameter
3. Pachymetry
Pachymetry will be measured to determine the thickness of the cornea. This measurement will also be done during surgery to determine the flap thickness and the thickness of the corneal bed.
4. Tonometry
Tonometry is taken to determine the intraocular pressure both preoperatively and postoperatively.
5. Endothelial Cell Count (ECC) (on selected patients)
This is a technique employed to determine the number of endothelial cells present on the back of the cornea, as well as the health of the endothelial cells. These measurements may be followed periodically after LASIK. Endothelial cells are responsible for corneal clarity and appropriate hydration of the cornea.
6. Contrast Sensitivity Analysis
This is a contrast sensitivity test that may be done prior to and following the Excimer Laser surgery. Contrast sensitivity measures the ability of the eye to distinguish images under varying degrees of lighting.
7. Horizontal Diameter of the Cornea
8. Eye Dominance
9.Refraction on the Automated Refractometer
10. Tear Test to Rule Out Dry Eye.
11. Complete Eye Exam
12. Others
Prior to surgery, you will be administered a mild sedative; then, your cornea will be marked with a dye mark at the 6 and 12 o'clock meridians. Next, you will be positioned under the microscope, and asked to fixate (concentrate) on a blinking red light. The unoperated eye will be taped shut. Make sure you do not squeeze your unoperated eye shut, because it will affect your ability to hold your operated eye steady. Just act as though the unoperated eye that is taped shut is open. Try to use both eyes together, and this will steady the operated eye.
The eye will be anesthetized with topical anesthetic, an eye drape will be placed over the lashes and lid margins, and an eyelid speculum will be placed between the eyelids in order to hold them open during the procedure.
You will once again be asked to concentrate on the red fixation light under the microscope, and the corneal flap dye marks will be applied. Next, a suction ring will be placed and centered on the eye, and suction will be applied. At this time, you will feel pressure, but no pain. While the suction ring is in place, it will be normal for you not to be able to see out of the eye while the suction is on. Once the suction is released, vision then returns to the eye. It is best to be as relaxed as possible and try not to move your eyes while the suction ring is in place. The suction ring has a tiny groove and track on it for the microkeratome to drive across. Next, the microkeratome will be placed into position onto the suction ring track and groove, and is then driven across 90% of the cornea, resecting approximately 160 microns of cornea tissue, creating a corneal flap, and then is reversed off the suction ring. It is important to realize that when the microkeratome is traveling across the cornea, there is a normal buzzing sound to the keratome itself. It is critical that this buzzing noise does not startle you and cause you to jump or squeeze your eyes while it is passing across the cornea. Once the corneal flap is made, it is hinged back, away from the corneal bed, and the Excimer Laser is then applied to the bed of the cornea or stromal interface in order to correct the refractive error.
Prior to doing the Excimer Laser, you will be asked to fixate on the red blinking fixation light only. Once the Excimer Laser begins, you will perceive this as a mild buzzing sound, and you may smell the odor of the molecules of protein being vaporized from the corneal bed. When fixating on the green light inside of the red ring during the laser treatment, you may see the green light become somewhat blurry, and this would be normal. If during the Excimer Laser treatment, you inadvertently move your eye, the laser beam eye tracking system will take over and will follow small eye movements. Once the Excimer Laser treatment is completed, the corneal flap will be put back into position over the corneal bed, without sutures in most cases. It takes approximately 20 to 30 seconds for the corneal flap to seal itself securely to the corneal bed. A clear plastic shield will be placed over the eye until the next day.
Under no circumstances jump or squeeze your eye. It is critically important that you remember during the operation to relax completely your shoulders, your neck, your chin. Do not clench your hands or make your hands into fists and squeeze them. Doing so can detract from your steadiness. It is best to relax your hands, your legs, your feet. Do not chew gum during the procedure. Do not cross your legs. I will be reminding you about these things throughout the treatment session. The entire procedure usually takes less than 20 minutes to perform.
As we have said, the operation itself is really not painful, and there is usually nothing more than pressure that is felt during the operation. Following surgery, it is unusual to have severe pain, but a prescription for pain medication will be given to you, just in case. Usually, the first day the eye may have a slight foreign body sensation, and nothing more. Sometimes the eye waters, and you may be light-sensitive for a couple of days. It is not unusual, for the first month, to have some mild glare problems at night; but that usually disappears or is significantly reduced over time. Vision may be surprisingly good on the first day postop; however, if it is not, we ask that you not worry about this. Sometimes it takes a few weeks before the vision really gets sharp. Normally, you can see and function quite well without glasses the first post-op day.
It may take at least 1 to 3 months for the operated eye to stabilize and be able to achieve the desired excellent vision. Remember, with high myopia, astigmatism, or hyperopia, one will have a greater chance that an enhancement will be necessary in order to fine-tune the vision. enhancements are usually done from 6 weeks to 3 months postop.
Normally the first day of surgery you will not be required to put drops into the eye; however, you will start the following day. Your drop regimen will be given to you prior to surgery. Normally we don't have to use the drops longer than 1 week. Vision is usually stable at one month, but can change slightly between 1 and 3 months. Stability of vision is affected by the dryness of the eyes--i.e., the dryer the eye, the longer it takes for the vision to stabilize.
The second eye may be operated on when the first eye recovers and sees well. When the visual result is satisfactory and the eye is completely comfortable, one may consider having the second eye treated in order to balance both eyes. This time period between the treatments of each eye may be as little as a few days to as long as a few weeks. However, LASIK on both eyes the same day can be done if desired. You will need to discuss this with Dr. Maddox.
You will need to sleep with a protective shield over the eye while sleeping or napping. This must be done for at least 1 week following surgery. You should not swim for at least 2 weeks, and try not to get the eye wet while bathing or showering for at least a week. One of the things you really don't want to do is rub the eye, especially the first 3 months following the surgery. It probably is not a very good idea for any of us to rub our eye, whether we have had surgery or not. Be extremely cautious about deodorant spray, hair spray, paint, and any other kinds of sprays. The mist from the spray can get on the cornea and cause irritation.
Your eyes may be imbalanced following the surgery if only eye is done. You can wear a contact lens on the unoperated eye until the operated eye gets well in order to balance the eyes. Or, if you prefer, you can wear your glasses, but when you want to read or drive , you will have to patch the operated eye and use the unoperated eye until the operated eye is comfortable and can see well; please realize that you will have todo this for a few weeks if only one eye is done. In most cases, one cannot comfortably balance both eyes together with glasses if one eye is nearsighted and the other eye has been corrected with LASIK. In addition, some individuals who choose this method of dealing with the imbalance prefer using no glasses at all after the operated eye recovers good vision if they are well under 40 years of age. If one is in the presbyopic age group (over 40) and chooses to wear a contact lens on the unoperated eye while the operated eye recovers, one will most likely need reading glasses or bifocals to be worn over the unoperated eye during the recovery phase with or without the contact lens. The imbalance problem is one of the main reasons we prefer to do bilateral laser surgery. Please be prepared to have some blurry vision out of the operated eye for a few weeks.
It is imperative that you see us, or your own eye doctor, if you have been referred, for your recommended post-operative follow-up visits. In these cases, we recommend that you be seen at 1 week, 1 month, 3 months, 6 months and 1 year. Please note that the cost of eyedrops is not included in the surgery fee. You will be responsible for the cost of all postoperative medications.
We advise that you do not drive an automobile until the eyes are comfortable and you can see well enough. Many people are able to go back to work the next day because their vision is adequate to function at work and they are comfortable. Under these circumstances, it would be okay to return to work the next day after surgery.
Cornea - Transparent, dome-shaped front surface of the eye which overlies the iris. It is analogous to a clear watch crystal that overlies the face and dials of a watch.
Reported Precautions and Dangers of Contact Lens Wear
Contact lenses are not risk free. It has been shown that the risk in contact lens wearers of sight-threatening corneal infection (ulcer; microbial keratitis) is very real. It has been reported that 25% of patients who present with microbial (ulcerative) keratitis (which can lead to permanent loss of eyesight) are contact lens wearers.
Irreversible and permanent corneal warpage, corneal distortion and endothelial damage are real and may occur after years of long-term use of contact lenses.
The annual risk for microbial keratitis (corneal ulceration and infection) is as follows:
Pseudomonas Keratitis associated with contact lens wear is one of the most dangerous organisms that can threaten the integrity of the cornea. If not diagnosed immediately and treated aggressively, it can literally ulcerate and melt through the full thickness cornea in a matter of hours, and can potentially blind the eye or cause permanent loss of vision from corneal scar, which would necessitate corneal transplant. These organisms live very easily in a number of lens solutions, lens cases, oily places, etc.
Little corneal infiltrates with small overlying epithelial erosions in a contact lens wearer are potentially very serious and could lead to permanent vision loss if not treated promptly and aggressively. Therefore, it has to be assumed that the cornea is infected and treated as an ocular emergency until appropriate lab studies come back.
It is therefore obvious that one must use impeccable hygiene in the care and handling of contact lenses.
Pseudomonas Keratitis accounts for 1/3 to 3/4 of the organisms seen in contact lens-associated microbial keratitis. Approximately 25% are due to gram positive cocci such as staph., strep., etc.
1. GPC (Giant Papillary Conjunctivitis) from contact lens wear
One develops multiple tiny, inflammed bumps on the inner side of the upper lid, which can be very irritating to the eyes. This can be caused from protein buildup and accumulation on the surface of the contact lens and/or mechanical rubbing of the contact lens on the inner surface of the upper eyelids as one blinks.
Treatment:
Treatment:
The main concern with contact lens hypoxic keratopathy is that repeat bouts of persistent corneal hypoxia may eventually lead to permanent corneal damage with clinically significant endothelial cell dysfunction. The endothelium is a mosaic of cells that line the entire area of the inside of the cornea and are responsible for maintaining corneal transparency. If they are significantly compromised, then corneal decompensation can take place, the cornea can become opaque and one can experience significant reduction in vision, possibly on a permanent basis. This also predisposes the eye to a greater chance for microbial infection.
Treatment:
Exchange contact lenses for better fit and contacts that allow high Oxygen permeability. If this does not solve the problem, it is best to discontinue contact lens wear.
4. Dry Eye associated with contact lens wear
If one has a "dry eye", it is often difficult to wear contact lenses for long periods of time. Artificial tears without preservative are recommended. Some individuals who desire to wear contact lenses but have even a borderline dry eye situation have difficulty with comfort and clear vision with contact lenses.
5. Neovascularization of the Cornea in association with contact lenses
Superficial and sometimes deep blood vessels can abnormally grow onto the cornea from long-term use contact lenses. Only the examining doctor can see them under the microscope on examination. They grow because of mechanical rubbing and poor oxygenation by the contact lenses. It is undesirable for this to occur. If they proliferate to such a degree that they encroach on the visual axis area, they would cause a decrease in vision, glare, corneal distortion, corneal melt problems, etc.
6. Contact lens, lens case and contact lens solution contaminants
Discomfort and decreased wearing time can result from contact lens, lens solutions, and lens case contaminants.
Some of these contaminants are as follows:
Acanthomoeba is another extremely dangerous microorganism involved in contaminating contact lenses and cases, especially when using the "home made" saline and using tap water or well water to clean contact lenses. Acanthomoeba is very difficult to treat and cure. Some patients with this type of keratitis have to be treated for months to years with a poor prognosis for recovery of sight, in spite of corneal transplantation if it were to become necessary.
7. Contact lenses may cause permanent or irreverisble warpage of the cornea, which could induce permanent astigmatism.
Laser: an acronym for Light Amplification by Stimulated Emission of Radiation.
Photon: a packet of light energy, or quantum.
Excimer: a contraction of the two words Excited and Dimer. The dimer refers to the Fluoride-Argon molecules in the excited state. This dimer does not exist in nature in the unexcited state; in the unexcited state, the two atoms of Argon and Fluorine are not bound together. Fluorine gas is a halogen, and Argon gas is a rare or inert gas. Therefore, the excited dimer consists of atoms of Argon and Fluoride technologically bound together in a highly excited, temporary state to form a diatomic rare gas-halide. The decay of these unstable molecules (Argon-Fluoride) to a stable state results in the emission of a highly energetic photon of ultraviolet light. The emissions wavelength of the Argon-Fluoride Excited Dimer is 193 nanometers (193 nm). (One nanometer is one-billionth of a meter.) The excimer emissions are in a train of individual pulses, typically 10 nanoseconds (10 x 10-9 seconds) long, with a pulse repetition frequency of up to 50 Hertz (Hz), or 50 pulses per second. (Hertz is the international unit of frequency, equal to one cycle per second.) The typical pulse rate is 10 pulses per second, or 10 Hz coming out of the excimer laser.
Non-excimer ophthalmic lasers generally depend on one of two tissue/laser interactions:
1. Photocoagulation (typically achieved with Argon lasers):Photocoagulation occurs when laser light energy is absorbed by a target tissue and converted to heat. The thermal effects range from protein denaturation to vaporization and carbonization.
2. Photodisruption (typically achieved with Neodymium-YAG lasers): In photodisruption, a high-powered laser pulse causes optical breakdown and plasma formation with a resultant shockwave which mechanically disrupts the target tissue.
The excimer laser now offers a third tissue/laser interaction:
3. Photoablation: High powered, pulsed ultraviolet radiation removes tissue with an extremely high degree of precision (.25 microns per pulse, or 1/25000 of an inch per pulse). Initial studies of ultraviolet photoablation of organic polymers showed that such radiation could produce layer-by-layer removal of material and etch patterns with sub-micron precision. Moreover, ultraviolet photons are highly energetic and can directly break chemical bonds. Ultraviolet laser irradiation of biological tissue breaks these large molecules into diatomic and triatomic fragments and monomers which are ejected from the surface of the material being irradiated.
The Argon-Fluoride Excimer Laser is a revolutionary innovation and advanced treatment modality in an attempt to correct myopia, hyperopia and astigmatism, as well as superficial keratectomy to erase corneal scars and irregular corneal surfaces. When the Argon-Fluoride Excimer Laser is used in corneal reshaping to correct refractive errors, it breaks the carbon-to-carbon molecular bonds of the corneal tissue by the ultraviolet 193-nanometer wavelenghth of emission photochemical effect called photoablation. This photoablation effect is extremely superficial. Minimal thermal damage is created by the ultraviolet excimer laser, unlike traditional lasers in which the produced heat causes damaging effects to surrounding tissue. The pulsing excimer laser removes the tissue in microscopic layers, leaving virtually no underlying thermal trauma. The carbon-to-carbon bond holding most of the tissue together has an energy requirement of 3 electron volts. If an excimer laser photon is introduced, it can literally crack that bond. The photon-energy, or energy per photon, of the excimer photon is 6.4 electron volts, or 10-15 millijoules per photon. One laser pulse contains many photons. One excimer laser pulse contains 2.5 x 1016 photons. Therefore, the energy per pulse at the eye is equal to the 10-15 millijoules (single photon energy) times 2.5 x 1016 (number of photons in one pulse), which equals 25 millijoules (mj). (2.5 x 1016 = 25 billion million.) These excimer photons are like "photon scissors", breaking the carbon-to-carbon bonds of the corneal tissue. Hence, the excimer photon is incredibly energetic, having 3 times as much energy as the YAG laser photon and more than twice the energy as the Argon laser photon. The term that has been coined for the effect of the excimer laser on the tissue is photoablation. The key to the excimer laser is the short pulse duration (10 nanoseconds or 10 x 10-9 seconds) with high energy photons (energy per pulse is 25 millijoules at the eye) with the possibility of concentrating large numbers of these photons on tissue to crack the carbon-to-carbon bonding that holds tissue together.
For the first time, a no-touch system, or no-touch scalpel, with the ultimate resolution of a fraction of a micron, is available to surgeons. (One micron equals one one-thousandth of a millimeter.) So, without touching the eye, the excimer can change and sculpt the cornea (photon scissors) incredibly accurately with virtually no collateral damage conducted into the edges of the tissue affected. There is no significant mechanical effect to the surrounding tissues; and no crushing of tissue, as with a knife blade or scalpel.
Photorefractive keratectomy (also referred to as wide area ablation, corneal reprofiling, corneal sculpting, and laser keratomileusis) is the process of using the Excimer Laser to reshape the cornea in an effort to effect a change in the refractive characteristics of the eye and thereby correct or lessen myopia (nearsightedness), hyperopia (farsightedness), and/or astigmatism. Using the Argon-Fluoride Excimer Laser to accomplish photorefractive keratectomy is a dramatic departure from existing refractive procedures. Some of these existing procedures include radial keratotomy, in which multiple deep radial incisions or cuts are made into the cornea with a diamond blade; epikeratophakia for myopia and hyperopia, in which a donor corneal lenticle is reshaped with the corrective prescription and then sutured over the patient's own cornea; and myopic and hyperopic keratomileusis, in which the patient's own cornea or a donor cornea is shaved and reshaped like a contact lens with a corneal lathe and then resutured onto the eye. (Current technological offshoots of keratomileusis include myopic or hyperopic Lamellar Keratoplasty) and Excimer Laser PRK with the microkeratome, or LASIK.)
In photorefractive keratectomy for myopia, hyperopia, and astigmatism, the cornea is reshaped by the Excimer Laser without being cut or incised, normally effecting a change in the refractive properties of the cornea. The Excimer Laser uses photoablation, or high-powered, pulsed ultraviolet radiation (light energy or photons) to remove tissue with an extremely high degree of precision. The Excimer Laser is a unique computerized 193 NM Argon-Fluoride laser which can reshape the front surface of the eye (cornea), acting at the atomic and molecular level, in as little as 20 seconds, without creating significant thermal damage to surrounding tissue. This special characteristic allows the Excimer Laser to be referred to as a "cold" laser. ("Cold" is a relative term, in that other lasers produce larger amounts of heat and thermal damage than does the Excimer Laser.)
In an area of the central cornea, about the diameter of a drinking straw, 25 billion million photons (packets of light energy) per pulse shower down in a parallel fashion onto the cornea, photoablating, or removing, .25 microns of tissue with each laser pulse. [One micron equals one one-thousandth of a millimeter (1/1,000).] One cell (10 microns) has to be hit or pulsed 40 times in order to be completely photoablated at .25 microns, or 1/25000 of an inch, per pulse. The number of pulses needed to correct the myopia depends on the amount of myopia and the ablation zone size. Usually from 3% to 15% of the central corneal tissue is utilized for corneal reshaping for myopic corrections from -1.00 to -6.00.
[An explanation of the size of a micron: The average single human cell is approximately 10 microns in height. The diameter of a single human hair is approximately 50 microns, and the thickness of the central cornea (the front surface of the eye) is a little over 500 microns (half a millimeter). Therefore, only one-tenth of a cell is penetrated by the excimer photons when penetrating one micron.]
Since each photon has energy equivalent to 6.4 electron volts, and the energy required to hold the protein atoms together in corneal tissue is only 3 electron volts, these molecular bonds holding protein molecules together in the cornea are broken, and molecules and atoms of tissue fly away from the cornea, .25 micron layer by .25 micron layer, at supersonic speeds. (This effect is referred to as the "plume of photoablated tissue.") The laser's aperture (mechanical iris) simultaneously expands in a stepped fashion, until the desired optical zone and optical correction are achieved in myopia. Each pulse of 25 billion million photons acts only on those atoms of protein that are bonded together in an area of about 5 or 6 mm or larger, .25 microns in depth, or 1/40th of a single cell. (One cell is only 10 microns.) Each laser pulse lasts approximately 10 nanoseconds, which is 10 billionths of a second, at 10 pulses per second.
Refractive correction is achieved by stepped photoablation in myopia. The Excimer Laser system uses a mechanical iris, or aperture, to control the laser. After each set of laser pulses, the iris diameter widens and the laser ablates, or removes, a slightly larger ring of tissue to effectively flatten the corneal surface, thus creating a stepped curve. In essence, a prescription for glasses or contact lens becomes permanently microetched onto the front surface of the eye.
In most cases it is virtually impossible to detect any change in the cornea several months following surgery, even upon ophthalmic examination through a slit lamp biomicroscope by a well-trained physician. (The only way to detect the change that has occurred in the cornea is with a photokeratoscope.)
Before the Excimer Laser photoablation procedure can be performed, the surgeon must first remove the corneal epithelium (see illustration of cornea). After Excimer Laser photoablation of the cornea, the corneal epithelium will normally regenerate within a period of 48 to 72 hours. Immediately following Excimer Laser photoablation, a pseudomembrane forms, acting as a true osmotic type of barrier to impede water inflow. As soon as the epithelial cells regenerate and cover the area, the cells break down the pseudomembrane and begin to lay down elements of a new basement membrane. Hemidesmosomes anchor the basal epithelial cells down into the basement membrane, locking the newly formed epithelium straight down into the cornea onto the stromal lamellae. Within a period of four to six weeks, the new corneal epithelium stabilizes to the point that to mechanically push the epithelium off the cornea (for instance, by rubbing the eye) would be very difficult.
There is a distinct difference between RK (radial keratotomy) and Excimer Laser PRK (photorefractive keratectomy). RK reshapes the cornea by the surgeon's use of a diamond knife or scalpel to perform multiple deep and relatively wide incisions or cuts (90% corneal depth) into the periphery of the cornea, in a pattern resembling the radial spokes of a wheel, which weakens this area and allows the circumference of the cornea to increase, thus flattening the central cornea. Unfortunately, many people are under the false impression that radial keratotomy (RK) is indeed done with a laser beam. This is not true. Others also mistakenly believe that "laser surgery" reshapes the cornea by making deep incisions or cuts like RK, except that it is done with a laser beam instead of a surgical blade. This also is not true. Excimer Laser PRK and LASIK are considered to be the most technologically advanced methods in the world today for correcting myopia. This advanced technological breakthrough for the correction of myopia allows eye surgery to enter a totally new dimension - a world of its own - never before experienced by eye surgeons.
Although Excimer Lasers were first developed in 1975, the word EXCIMER, a contraction of the words "EXCIted" and "diMER," appeared in scientific literature as early as 1960. At first, the Excimer Laser was not developed for use in the realm of ophthalmology, but was initially used in 1975 in the plastics industry. The laser was developed for etching silicones and other polymers, and later with the hope of using this technology in manufacturing microcircuits and computer chips.
Excimer Laser surgery is a Western-developed surgical breakthrough. The other, more prevalent form of refractive surgery - Radial Keratotomy, or RK - was developed in the Eastern nations of Russia and Japan. Radial keratotomy, or RK, requires deep incisions or cuts into the cornea with a diamond blade, which changes its shape and structural integrity, in order to correct myopia. The Excimer Laser avoids having to make these deep incisions or cuts into the cornea, and therefore does not weaken the corneal structure. The Excimer Laser photoablates, or uses ultraviolet light energy at a specific wave length to break the cellular bonds of microscopic layers of the cornea in order to change the shape of the cornea to correct myopia or nearsightedness and other refractive errors. The technical term for the Excimer Laser in correcting myopia is Excimer Laser Photorefractive Keratectomy, most often referred to as Excimer Laser PRK.
In 1976, Dr. Dave Muller, Ph.D., formerly President of Summit Technology, Inc., built Cornell University's first Excimer Laser. In 1979 Dr. John Taboada, Ph.D. and colleagues initiated a study of the Excimer Laser on animal eyes at Brooks Air Force Base in San Antonio, Texas. A number of discoveries resulted from these studies, some of which were published in 1980 and 1981. The most intriguing was the observation of a smooth beam-shaped indentation on the cornea of rabbits with experimental Excimer treatment. They attributed the effect to a temperature jump in combination with a photochemical process. Subsequently in 1983, Dr. Taboada and Dr. Steve Trokel, M.D., an Ophthalmologist at Columbia University, met in New York City to complete a co-authored book on YAG Microsurgery. At that time, Dr. Taboada, who is now recognized as the originator of Excimer ablation for refractive surgery, apprised Dr. Trokel on the Excimer Laser process and its application to refractive surgery.
Dr. R. Srinivasan, Ph.D., an I.B.M. researcher in Yorktown, New York, demonstrated the precise photoablation capabilities of the Excimer Laser, which made the Excimer unique among lasers. In late September, 1982, and early 1983, Dr. Srinivasan was using the Excimer Laser for microetching microscopic circuit board technology in computer chips. He described the photoablated decomposition of plastic materials without thermal deformation, as well as decomposition of ultraviolet laser irradiation on biological tissues, such as aorta, bone, cartilage, and hair. He also showed that accurate and smooth microscopic grooves could be microetched on a single human hair with submicron precision without significant surrounding thermal damage to the hair. (A single human hair is approximately 50 microns in diameter.) Dr. Srinivasan microetched, or photoablated, about 30 microns of the human hair. He was impressed as to how sharply defined the edges were and how the microetched hair retained its cylindrical shape. This information was also published, and in 1983, Dr. Steve Trokel, M.D., saw the picture of the microetched hair and visited Dr. Srinivasan at his IBM laboratory in July, 1983. There Dr. Trokel did laboratory studies on rabbit eyes and bovine eyes, and confirmed a significant technological breakthrough. He is regarded as the first ophthalmologist to recognize the significance of the Excimer Laser in corneal refractive surgery.
In 1984, Dr. Olivia Serdarevic, M.D., while at Columbia University (Harkness Eye Institute) in New York, was working with laboratory animals. She was the first to apply the Argon-Fluoride Excimer Laser irradiation to create a therapeutic lamellar keratectomy. In the laboratory she was infecting animal corneas with fungal organisms and was applying the Excimer Laser to the surface of these corneas and was able to sterilize or eliminate the infecting organism. At the same time, she created a therapeutic lamellar keratectomy with a very smooth surface.
From that point on, much research and development began to spring up all over the world, especially in Western nations. The early pioneers include the following: Dr. Steve Trokel, M.D., USA; Dr. Francis L'Esperance, M.D., USA; Prof. John Marshall, Ph.D., England; Dr. Malcolm Ker-Muir, M.D., England; Dr. Theo Seiler, M.D., Ph.D., Germany; Dr. Olivia Serdarevic, M.D., USA; Dr. Carmen Puliafito, M.D., USA; Dr. Roger Steinert, M.D., USA; Dr. Marguerite MacDonald, M.D., USA; Dr. Charles Munnerlyn, USA; and others.
In 1983, Dr. Charles Munnerlyn of the United States started a project which resulted in construction of the first clinical prototype Excimer Laser for ophthalmology. He worked out mathematically the depth of ablation, diameter and edge angles. In 1984, Dr. Marguerite MacDonald from LSU started doing animal research with the Excimer Laser.
Dr. Theo Seiler of Germany ordered his first Excimer Laser in early 1984. In January, 1986, he was the first to create linear and arcuate keratectomies in sighted human eyes for the correction of astigmatism. He performed the first series of phototherapeutic keratectomies (PTK) in sighted human eyes in 1986 in cases of Salzmann's Nodular Degeneration, and for smoothing of the cornea after pterygium removal. On February 6, 1987, Dr. Francis L'Esperance, M.D. of Columbia University, New York, performed the first wide area Argon-Fluoride Excimer Laser superficial keratectomies (PRK) on a series of three human eyes. One of the patients had a malignant melanoma in his eye and was going to have the eye removed. The patient agreed to undergo Excimer Laser surgery prior to the removal of the eye for experimental purposes. This patient had 20/20 vision prior to the Excimer Laser; following the Excimer Laser, the eye was left farsighted, or hyperopic (+3.25 diopters), but was corrected to 20/20 with spectacle correction. In 1988, Professor John Marshall,Ph.D., of England, felt that he had sufficient data from laboratory studies to proceed with human exposure. In March, 1988, the first application of the Summit Excimed UV200 Excimer Laser PTK, or Phototherapeutic Keratectomy, in the U.K. was performed on a sighted human eye for "band keratopathy" (corneal opacity) in London at St. Thomas Hospital by Dr. Malcolm Ker-Muir with great success. In 1988, the United States Food and Drug Administration (FDA) recognized that the experimental research data on laboratory animals was sufficient and satisfactory; therefore, the FDA approved human clinical trials to be started at a number of investigative sites in the United States, approximately 46 sites. In July, 1988, Dr. Marguerite MacDonald, M.D., of LSU, performed Excimer Laser PRK on the first sighted eye with the longest follow-up in the world. In 1989, the first bilateral Excimer Laser PRK for myopia was done in Germany by Dr. Theo Seiler. In 1990, Dr. Howard Gimbel, of Calgary, Canada, began the first Canadian clinical trials for Excimer Laser PRK to correct myopia. On August 5, 1991, the Secretaría de Salud in Mexico City approved Excimer Laser PRK clinical trials to begin. The first Excimer Laser PRK for the correction of myopia in the country of Mexico was performed by Dr. Bobby Maddox, M.D., on January 8, 1992, in Juarez, Mexico.
Excimer Laser technology has come a long way, and a continual refinement and enhancement of this technological breakthrough is expected as studies progress. The future of the Excimer Laser is going to be exciting to follow. The use of the Excimer Laser in ophthalmology may provide the greatest use of lasers in medicine during this decade and the decades to come.
Munnerlyn's PRK Formula:
With a 6.00 mm optical zone and a -1.00 diopter correction, one will need to photoablate approximately 18.25 microns of corneal tissue, or about 3%. For a -6.00 diopter correction, one will need to photoablate 78 microns of corneal tissue. The central cornea, without the epithelium, is approximately 500 microns thick. Therefore, with a -6.00 myopic correction, we only have to photoablate about 15% of the entire central corneal thickness. Of course, if one chooses a larger optical zone size, then more photoablation would be necessary.
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