(Photo Refractive Keratectomy)
Benefits:
* Bowman's layer is spared.
* No removal of the corneal surface tissue is necessary and therefore post-operative pain is substantially reduced.
* Post-operative visual acuity is restored within a few days rather than weeks.
* Less corneal scarring in the long term, less change due to healing (regression) and thus greater stability of the correction.
When comparing only the benefits of Lasik over PRK the first impression is that Lasik has the potential to be a superior procedure. There is however, a very significant list of potential complications or risks and these include:
* Failure of automated instrument to leave a hinge on the corneal flap, with the first incision.
* Loss of the corneal flap during the operation.
* Loss of the corneal flap after the operation.
* Slipping of the flap and healing off center.
* First incision too deep (perforation of the eye) or too shallow, causing a hole in the flap.
* Invasion of the surface tissue into the central tissue of the cornea.
* Infection of the cornea.
* Loss of visual acuity - from scarring or from decentration of the PRK.
* Technical problems with complex and finicky automated diamond cutting devices.
* The procedure is much more dependent upon surgeon's operating skills, than the computerized precision of the PRK procedure.
The overall complication rate for the ALK-E or LASIK in Febuary 1995 was still in the order of 10% in the hands of the world leading innovators in the technique.
Friday, November 6, 2009
Laser Manufacturers
Aesculapx- Meditec GMBH
MEL 60- This is an Argon Fluoride 193 nm excimer scanning system. The scanning beam is rectangular and measures 1mm by 10 mm. The system uses a limbal suction cup mechanism to fix centration and computer controlled rotating masks which fit into the suction cup mechanism. The mask for simple myopia is an f-stop like mechanism. There are different masks used for myopia with astigmatism, hyperopia, and for pure astigmatism. The masks rotate within the suction cup in order to control any axis of extra ablation as needed for astigmatism correction. Laser calibration is done by visual inspection of a 1um thick metal foil which requires 9 laser passes for removal. There is a layer of red under the silver foil making efficacy of removal easily monitored. Watch this space for a future "quick-time" or "M-peg" clip of calibration, and actual treatment of hyperopia, myopia, and astigmatism.
ALCON
LADARVision® System and CustomCornea® - The LADARVision® System consists of the LADARVision® 4000 laser and the LADARWave® Aberrometer. The LADARVision excimer laser is a small-spot scanning laser with a laser radar tracking device. FDA approved for wavefront-guided ablations.
Bausch & Lomb Technolas 217 Excimer Laser with PLANOSCAN
Technolas 217 Workstation - this is an Argon Fluoride 193 nm excimer scanning system. The scanning beam is a circular spot which can be size adjusted. Centration is accomplished by an active "pupil" tracking mechanism which locks on to the pupil image and will have the laser follow any movement by the patient's eye. Active Infra-red Eye Tracker and passive monitor interrupts laser beam on movement in excess of 3 mm range (1.5 mm radius). Astigmatism, myopia and hyperopia can be treated by software adjustment of the beam scans.
LaserSight Technologies, Inc.
The new LaserScan LSX utilizes LaserSight's patented scanning delivery system integrating new leading edge technology. The LaserScan LSX uses a patented scanning system to deliver a 1-mm low energy "flying spot" in a proprietary alternating, multi-zone, multi-pass strategy. With each pass, about 2 microns of tissue are precisely removed to produce a finely polished corneal surface. Unlike older broad beam technologies, no rings or ridges are produced. Studies now show that smoother ablations may produce less haze, faster healing and more stable clinical results. Integral to each system is flexibility in treatment parameters including gently tapered transition zones.
Manufacture and sales of refractive laser systems, keratome systems, keratome blade products, and aesthetic lasers. LaserSight pioneered refractive laser systems using 193 nm, high resolution, scanning delivery. Both patient fixation and an optional automated tracking system are available. Astigmatism, hyperopia and myopia can be treated with software adjustments of the scanning mechanism. Watch this space for a future " quick-time" or "M-peg" clip of calibration, and actual treatment of myopia, astigmatism and hyperopia.
The LaserHarmonic-1 and LaserHarmonic-2 are solid state lasers still in the development stage. The former is flash lamp pumped and employs the fifth harmonic of a Nd:Yag at 213nm, and the latter is a diode pumped fifth harmonic Nd:YLF laser at 209nm.
Nidek, Inc.
EC-5000 This is an Argon Fluoride 193 nm excimer scanning system. The scanning beam is a rectangular slit which both scans, dynamically rotates, and overlaps. The rotation of the scan is designed to eliminate circular f-stop ridges and increase the smoothness of the ablation. Centration is controlled by the surgeon with a "joy" stick mechanism to follow the patient's eye. Astigmatism and myopia can be treated by software adjustment of the beam scans. At the time of writing we do not have any result data for this machine. Watch this space for a future "quick-time" or "M-peg" clip of calibration, and actual treatment of myopia, and astigmatism.
Novatec LASER SYSTEMS INC
Lightblade (TM) This is an solid state c. 208nm non excimer scanning system based upon the fourth harmonic of a titanium sapphire crystal. The scanning beam is a 200-300um variable size spot. Centration is accomplished by an active tracking mechanism which locks to have the laser follow movement by the patient's eye. Astigmatism and hyperopia can also be treated by software adjustment of the spot scans. At the time of writing we do not have any result data for astigmatism of hyperopia treatment. Watch this space for a future "quick-time" or "M-peg" clip of calibration, and actual treatment of hyperopia, myopia, and astigmatism.
Summit Technology
Excimed, Omnimed, Apogee, Apex These are Argon Fluoride 193 nm excimer wide beam systems. The 1990 version of the Eximed machine had optical zones of only 4.5 and 5.0 mm. The Omnimed and Eximed versions increased the optical zone to 6.0 and 6.5mm. (The Apex machine has an optical zone of 6.5mm blending out to 9.4mm transition zone. The mask for simple myopia is an f-stop like mechanism located internally in the beam path. Summit has chosen to use custom crafted ablatable masks in the rail or beam path for the astigmatism and hyperopic correction. These masks protect the corneal tissue under them until the tapered mask is removed by laser pulses. The area without a mask will receive the full laser ablation. We have no data at the time of writing concerning the effectiveness of the ablatable masks for the astigmatic element of myopia treatment. Laser calibration is done by an internal 2 minute beam profile test. Watch this space for a future "quick-time" or "M-peg" clip of calibration, and actual treatment of hyperopia, myopia, and astigmatism.
VisX
20/15, 20/20, STAR (TM) These are Argon Fluoride 193 nm excimer wide beam systems, the STAR(TM) version being the most recent evolution of the machine. The STAR machine has a standard 6mm optical zone which is expandible to 8mm for future applications. The mask for simple myopia is an f-stop like mechanism located internally in the beam path. The astigmatic module masks and hyperopic module masks are located internally in the beam path. The hyperopic module has an ablation zone of 9mm. Laser calibration is performed automatically at the start of each day, and between cases. A plastic test card read on a standard lensometer verifies the calibration. Watch this space for a future "quick-time" or "M-peg" clip of calibration, and actual treatment of hyperopia, myopia, and astigmatism.
Automated Lamellar Keratectomy (ALK) vs
ALK-E or LASIK or "FLAP and ZAP"
As a preamble to discussion of ALK (and RK) it is nessary to remark that as of January 1996 ALK is a anomaly largely confined to the USA. The reason is simple- the FDA in its "wisdom" has only approved one laser machine for PRK use, and only to -7.00 diopters correction. Mechanical surgical operations on the other hand are "approved" and thus American Ophthalmologists effectively have one hand tied behind their backs. They are allowed to perform ALK and RK but not PRK. The precision and efficacy of refractive laser technology have rendered ALK and RK essentially extinct in the rest of the world.
ALK is a purely mechanical method of changing the refractive power of the cornea. It involves removing a top layer of cornea with an automated instrument and then making a second incision (the refractive incision) in order to remove tissue for myopia or adding tissue (i.e. donor cornea) for hyperopia. The first incision is meant to remove a circular button of cornea c. 8mm in diameter, but to leave one edge hinged so that after the refractive portion of the operation is complete the hinged corneal surface flap can be repositioned. The first incision is easier to perform because the cornea which is only 0.55 mm thick can be flattened and thus held without moving so that a diamond knife can make a slice of uniform thickness from one side leaving the opposite side hinged. In the case of myopia a second incision must be made to remove a curved (lens shaped) piece of tissue from the cornea's middle tissue (stroma). This tissue can be removed from the back surface of the slice or the front surface of the remaining cornea. The first slice, which is usually hinged (i.e. not completely removed) is then replaced on the cornea and held in place with or without a contact lens until the flap can reattach itself to the rest of the cornea - i.e. heal with a change in the shape of the corneal surface equivalent to the change in lens needed to satisfy the refractive needs.
The more difficult technical problem with the mechanical ALK procedure is the (second) refractive incision which must remove an extremely thin slice of corneal tissue complete with tapered edges. There is a jelly-like consistency to the corneal tissue underneath the surface and this leads to significant limits to the precision of the procedure.
An improved method of making the refractive incision is to use the excimer laser. This method is called ALK-E OR LASIK rather than ALK (Automated Lammellar Keratectomy - Excimer laser or Laser in Situ Keratomileusis). The use of the laser to sculpt either a - (myopic) or + (hyperopic) lens in the remaining corneal tissue allows the extreme precision of the refractive laserÍs surgical ability to significantly enhance the technique. Since the first or surface incision with the microkeratome is technically easier than the second or refractive incision it makes good sense to use the extreme optical precision of the refractive laser to achieve the desired correction of the corneal refraction. This technique allows preservation of the corneal basement epithelial layer knows as Bowman's membrane and in the absence of complications from the reattachment and healing of this flap, the refractive results can be rapid and superb.
MEL 60- This is an Argon Fluoride 193 nm excimer scanning system. The scanning beam is rectangular and measures 1mm by 10 mm. The system uses a limbal suction cup mechanism to fix centration and computer controlled rotating masks which fit into the suction cup mechanism. The mask for simple myopia is an f-stop like mechanism. There are different masks used for myopia with astigmatism, hyperopia, and for pure astigmatism. The masks rotate within the suction cup in order to control any axis of extra ablation as needed for astigmatism correction. Laser calibration is done by visual inspection of a 1um thick metal foil which requires 9 laser passes for removal. There is a layer of red under the silver foil making efficacy of removal easily monitored. Watch this space for a future "quick-time" or "M-peg" clip of calibration, and actual treatment of hyperopia, myopia, and astigmatism.
ALCON
LADARVision® System and CustomCornea® - The LADARVision® System consists of the LADARVision® 4000 laser and the LADARWave® Aberrometer. The LADARVision excimer laser is a small-spot scanning laser with a laser radar tracking device. FDA approved for wavefront-guided ablations.
Bausch & Lomb Technolas 217 Excimer Laser with PLANOSCAN
Technolas 217 Workstation - this is an Argon Fluoride 193 nm excimer scanning system. The scanning beam is a circular spot which can be size adjusted. Centration is accomplished by an active "pupil" tracking mechanism which locks on to the pupil image and will have the laser follow any movement by the patient's eye. Active Infra-red Eye Tracker and passive monitor interrupts laser beam on movement in excess of 3 mm range (1.5 mm radius). Astigmatism, myopia and hyperopia can be treated by software adjustment of the beam scans.
LaserSight Technologies, Inc.
The new LaserScan LSX utilizes LaserSight's patented scanning delivery system integrating new leading edge technology. The LaserScan LSX uses a patented scanning system to deliver a 1-mm low energy "flying spot" in a proprietary alternating, multi-zone, multi-pass strategy. With each pass, about 2 microns of tissue are precisely removed to produce a finely polished corneal surface. Unlike older broad beam technologies, no rings or ridges are produced. Studies now show that smoother ablations may produce less haze, faster healing and more stable clinical results. Integral to each system is flexibility in treatment parameters including gently tapered transition zones.
Manufacture and sales of refractive laser systems, keratome systems, keratome blade products, and aesthetic lasers. LaserSight pioneered refractive laser systems using 193 nm, high resolution, scanning delivery. Both patient fixation and an optional automated tracking system are available. Astigmatism, hyperopia and myopia can be treated with software adjustments of the scanning mechanism. Watch this space for a future " quick-time" or "M-peg" clip of calibration, and actual treatment of myopia, astigmatism and hyperopia.
The LaserHarmonic-1 and LaserHarmonic-2 are solid state lasers still in the development stage. The former is flash lamp pumped and employs the fifth harmonic of a Nd:Yag at 213nm, and the latter is a diode pumped fifth harmonic Nd:YLF laser at 209nm.
Nidek, Inc.
EC-5000 This is an Argon Fluoride 193 nm excimer scanning system. The scanning beam is a rectangular slit which both scans, dynamically rotates, and overlaps. The rotation of the scan is designed to eliminate circular f-stop ridges and increase the smoothness of the ablation. Centration is controlled by the surgeon with a "joy" stick mechanism to follow the patient's eye. Astigmatism and myopia can be treated by software adjustment of the beam scans. At the time of writing we do not have any result data for this machine. Watch this space for a future "quick-time" or "M-peg" clip of calibration, and actual treatment of myopia, and astigmatism.
Novatec LASER SYSTEMS INC
Lightblade (TM) This is an solid state c. 208nm non excimer scanning system based upon the fourth harmonic of a titanium sapphire crystal. The scanning beam is a 200-300um variable size spot. Centration is accomplished by an active tracking mechanism which locks to have the laser follow movement by the patient's eye. Astigmatism and hyperopia can also be treated by software adjustment of the spot scans. At the time of writing we do not have any result data for astigmatism of hyperopia treatment. Watch this space for a future "quick-time" or "M-peg" clip of calibration, and actual treatment of hyperopia, myopia, and astigmatism.
Summit Technology
Excimed, Omnimed, Apogee, Apex These are Argon Fluoride 193 nm excimer wide beam systems. The 1990 version of the Eximed machine had optical zones of only 4.5 and 5.0 mm. The Omnimed and Eximed versions increased the optical zone to 6.0 and 6.5mm. (The Apex machine has an optical zone of 6.5mm blending out to 9.4mm transition zone. The mask for simple myopia is an f-stop like mechanism located internally in the beam path. Summit has chosen to use custom crafted ablatable masks in the rail or beam path for the astigmatism and hyperopic correction. These masks protect the corneal tissue under them until the tapered mask is removed by laser pulses. The area without a mask will receive the full laser ablation. We have no data at the time of writing concerning the effectiveness of the ablatable masks for the astigmatic element of myopia treatment. Laser calibration is done by an internal 2 minute beam profile test. Watch this space for a future "quick-time" or "M-peg" clip of calibration, and actual treatment of hyperopia, myopia, and astigmatism.
VisX
20/15, 20/20, STAR (TM) These are Argon Fluoride 193 nm excimer wide beam systems, the STAR(TM) version being the most recent evolution of the machine. The STAR machine has a standard 6mm optical zone which is expandible to 8mm for future applications. The mask for simple myopia is an f-stop like mechanism located internally in the beam path. The astigmatic module masks and hyperopic module masks are located internally in the beam path. The hyperopic module has an ablation zone of 9mm. Laser calibration is performed automatically at the start of each day, and between cases. A plastic test card read on a standard lensometer verifies the calibration. Watch this space for a future "quick-time" or "M-peg" clip of calibration, and actual treatment of hyperopia, myopia, and astigmatism.
Automated Lamellar Keratectomy (ALK) vs
ALK-E or LASIK or "FLAP and ZAP"
As a preamble to discussion of ALK (and RK) it is nessary to remark that as of January 1996 ALK is a anomaly largely confined to the USA. The reason is simple- the FDA in its "wisdom" has only approved one laser machine for PRK use, and only to -7.00 diopters correction. Mechanical surgical operations on the other hand are "approved" and thus American Ophthalmologists effectively have one hand tied behind their backs. They are allowed to perform ALK and RK but not PRK. The precision and efficacy of refractive laser technology have rendered ALK and RK essentially extinct in the rest of the world.
ALK is a purely mechanical method of changing the refractive power of the cornea. It involves removing a top layer of cornea with an automated instrument and then making a second incision (the refractive incision) in order to remove tissue for myopia or adding tissue (i.e. donor cornea) for hyperopia. The first incision is meant to remove a circular button of cornea c. 8mm in diameter, but to leave one edge hinged so that after the refractive portion of the operation is complete the hinged corneal surface flap can be repositioned. The first incision is easier to perform because the cornea which is only 0.55 mm thick can be flattened and thus held without moving so that a diamond knife can make a slice of uniform thickness from one side leaving the opposite side hinged. In the case of myopia a second incision must be made to remove a curved (lens shaped) piece of tissue from the cornea's middle tissue (stroma). This tissue can be removed from the back surface of the slice or the front surface of the remaining cornea. The first slice, which is usually hinged (i.e. not completely removed) is then replaced on the cornea and held in place with or without a contact lens until the flap can reattach itself to the rest of the cornea - i.e. heal with a change in the shape of the corneal surface equivalent to the change in lens needed to satisfy the refractive needs.
The more difficult technical problem with the mechanical ALK procedure is the (second) refractive incision which must remove an extremely thin slice of corneal tissue complete with tapered edges. There is a jelly-like consistency to the corneal tissue underneath the surface and this leads to significant limits to the precision of the procedure.
An improved method of making the refractive incision is to use the excimer laser. This method is called ALK-E OR LASIK rather than ALK (Automated Lammellar Keratectomy - Excimer laser or Laser in Situ Keratomileusis). The use of the laser to sculpt either a - (myopic) or + (hyperopic) lens in the remaining corneal tissue allows the extreme precision of the refractive laserÍs surgical ability to significantly enhance the technique. Since the first or surface incision with the microkeratome is technically easier than the second or refractive incision it makes good sense to use the extreme optical precision of the refractive laser to achieve the desired correction of the corneal refraction. This technique allows preservation of the corneal basement epithelial layer knows as Bowman's membrane and in the absence of complications from the reattachment and healing of this flap, the refractive results can be rapid and superb.
PRK Laser Types
Current PRK lasers are best classified by laser source (either Argon-Fluoride excimer lasers or solid state) and beam type (broad beam or scanning beam). Laser technology and computer control software has evolved significantly since the first normally sighted eyes were treated in 1987. Initial PRK treatments used 3.5 and 4mm optical zones so as to minimize the depth of ablation. Since many pupils dilate to 5mm it is not surprising that edge glare and light sensitivity were common complications. Ablation diameter increase with edge smoothing has been implemented to solve many edge glare problems. Wide or broad beam machines initially had problems caused by the use of nitrogen flow to disperse vaporized tissue and with the occurrence of unvaporized central islands. Stoppage of nitrogen flow and modification of computer generated treatment regimes has largely eliminated these problems.
The US Food & Drug Administration (FDA) has been cautious, rigid, and slow to approve PRK for widespread use within the USA. There has been speculation that the reason for the current caution is embarrassment over a previous premature approved of the surgical procedure of radial keratotomy (RK). Many observers have feared that the apparent bureaucratic rigidity might impede the implementation of future needed changes to equipment or procedures prior to long and inflexible testing schedules. However, recently the FDA surprised its critics when, with the final approval of the Summit Laser, they insisted upon increasing the size of the optical zone from that tested in the preapproval trials. In the US a number of other laser manufacturers are progressing or almost through FDA trials. In contrast, most other jurisdictions including Europe and Canada, have, without the "benefit" of as vigorous an approval process, had the freedom to amend and improve equipment and treatment regimes as improvements presented themselves. There is now worldwide a large and expanding experience with many varied laser machines and evolving technical improvements.
The US Food & Drug Administration (FDA) has been cautious, rigid, and slow to approve PRK for widespread use within the USA. There has been speculation that the reason for the current caution is embarrassment over a previous premature approved of the surgical procedure of radial keratotomy (RK). Many observers have feared that the apparent bureaucratic rigidity might impede the implementation of future needed changes to equipment or procedures prior to long and inflexible testing schedules. However, recently the FDA surprised its critics when, with the final approval of the Summit Laser, they insisted upon increasing the size of the optical zone from that tested in the preapproval trials. In the US a number of other laser manufacturers are progressing or almost through FDA trials. In contrast, most other jurisdictions including Europe and Canada, have, without the "benefit" of as vigorous an approval process, had the freedom to amend and improve equipment and treatment regimes as improvements presented themselves. There is now worldwide a large and expanding experience with many varied laser machines and evolving technical improvements.
PRK Laser Energy
Visible light and all other forms of electromagnetic radiation carry energy. Light passes through windows, radio waves pass through buildings and x-rays pass through people, but each of these energy forms can also interact and thus release the energy. Beneficial or harmful effects will occur depending upon the wavelength of the energy source, the strength of the radiation, and what substance interacts or is struck.
Lasers are a method of producing an intense beam of energy with a precise wavelength. The first optical laser appeared in 1960 (1). The early medical lasers (2) produced visible light wavelengths which relied upon the transfer of heat energy to burn or photo coagulate tissue. Later lasers (3) used infrared (IR) wavelengths whose heat and energy was sufficient to either photo vaporize or photo disrupt (explode) tissue. Ultraviolet (UV) lasers were first suggested in 1975 (4) and subsequently a class of lasers known as Excimer lasers has evolved. The argon fluoride (ArF) version emits radiation of 193.3 nm wavelength. This is the laser which has revolutionized refractive surgery because when this laser interacts with tissue it removes only a fraction of the cell with virtually no damage to surrounding cells. A recent Ophthalmology textbook (5) has excellent comprehensive reviews showing collections of pioneering photomicrographs. We hope soon to receive permission to reproduce extraordinary photographs of grooves in a human hair (6), and laser incisions in human cornea (7). The remarkable feature is incredibly smooth incisions with no evidence of heat damage in immediately adjacent tissue. This could be called a cold laser. It turns out that wavelengths in the 200 nm range deliver just the right energy to break intermolecular bonds and simply ablate tissue without collateral damage to immediately adjacent cells. A longer wavelength such as a 248 nm (KrF Excimer) radiation burns a wide path of adjacent tissue in addition to the directly affected tissue. Since longer UV wavelengths (UV-B) are known to increase the occurrence of skin cancer a number of scientific studies have been done to study the possibility of 193 nm (UV-C) radiation causing cancer and each one has shown that 193 nm radiation does not damage DNA (8). Wavelengths shorter than 100 nm enter the X-Ray bands. X-Rays pass through cell and can also cause Cancer. Excimer 193 nm rays strike a cell surface and ablate only 0.25 (9) um of tissue. Since the distance from cell wall to nucleus in a corneal epithelial cell is 1.5 to 3.0 um (10) it is thought that the nuclei are either shielded from the radiation or destroyed with little potential for mutagenesis (cancer production).
The action of 193 nm excimer radiation is even more elegant than ablating 0.25 um of tissue. It turns out that after each laser pulse the remaining cell elements are resealed by the formation of a pseudo membrane or new layer or membrane. It is helpful to think of corneal cells as rather like grapes with a liquid center and surrounding membrane which holds the liquid center in. You can imagine each laser pulse removing 1/10 of the grape and resealing the portion of the grape (cell) not ablated or destroyed! To place the 0.25 um ablation in perspective, some corneal epithelial cells are 18 um tall and the depth of the cornea at center is 500 um.
Lasers are a method of producing an intense beam of energy with a precise wavelength. The first optical laser appeared in 1960 (1). The early medical lasers (2) produced visible light wavelengths which relied upon the transfer of heat energy to burn or photo coagulate tissue. Later lasers (3) used infrared (IR) wavelengths whose heat and energy was sufficient to either photo vaporize or photo disrupt (explode) tissue. Ultraviolet (UV) lasers were first suggested in 1975 (4) and subsequently a class of lasers known as Excimer lasers has evolved. The argon fluoride (ArF) version emits radiation of 193.3 nm wavelength. This is the laser which has revolutionized refractive surgery because when this laser interacts with tissue it removes only a fraction of the cell with virtually no damage to surrounding cells. A recent Ophthalmology textbook (5) has excellent comprehensive reviews showing collections of pioneering photomicrographs. We hope soon to receive permission to reproduce extraordinary photographs of grooves in a human hair (6), and laser incisions in human cornea (7). The remarkable feature is incredibly smooth incisions with no evidence of heat damage in immediately adjacent tissue. This could be called a cold laser. It turns out that wavelengths in the 200 nm range deliver just the right energy to break intermolecular bonds and simply ablate tissue without collateral damage to immediately adjacent cells. A longer wavelength such as a 248 nm (KrF Excimer) radiation burns a wide path of adjacent tissue in addition to the directly affected tissue. Since longer UV wavelengths (UV-B) are known to increase the occurrence of skin cancer a number of scientific studies have been done to study the possibility of 193 nm (UV-C) radiation causing cancer and each one has shown that 193 nm radiation does not damage DNA (8). Wavelengths shorter than 100 nm enter the X-Ray bands. X-Rays pass through cell and can also cause Cancer. Excimer 193 nm rays strike a cell surface and ablate only 0.25 (9) um of tissue. Since the distance from cell wall to nucleus in a corneal epithelial cell is 1.5 to 3.0 um (10) it is thought that the nuclei are either shielded from the radiation or destroyed with little potential for mutagenesis (cancer production).
The action of 193 nm excimer radiation is even more elegant than ablating 0.25 um of tissue. It turns out that after each laser pulse the remaining cell elements are resealed by the formation of a pseudo membrane or new layer or membrane. It is helpful to think of corneal cells as rather like grapes with a liquid center and surrounding membrane which holds the liquid center in. You can imagine each laser pulse removing 1/10 of the grape and resealing the portion of the grape (cell) not ablated or destroyed! To place the 0.25 um ablation in perspective, some corneal epithelial cells are 18 um tall and the depth of the cornea at center is 500 um.
The Magic of PRK
The magic of Photo Refractive Keratectomy (PRK) is a surgical precision unprecedented in human history. Excimer Laser power coupled with today's computers allows one laser pulse to remove as little as one quarter (0.25 nm) of a micrometer (or micron) of corneal tissue. This is exquisite control! In PRK the focusing power of glasses or contact lenses is sculpted directly unto the cornea or front window of the eye. The new and special laser actually cleaves individual molecular bonds to remove tissue with no damage to surrounding tissue. Computer programs control the surface sculpting to ensure the highest possible accuracy and success of the intended refractive change.
LASIK - eye surgery
Laser eye surgery was first performed to correct near-sightedness in Germany in 1988. Since then it has quickly spread throughout the world and is available in most developed countries. It has been particularly popular in Europe, Asia, and North America, especially the USA and Canada. In the USA, the FDA first approved an excimer laser to be used for laser eye surgery in 1995. The excimer laser was approved for use in LASIK in the USA in 1998.
LASIK is perhaps the most popular elective surgery available today. It is estimated that over 1,000,000 LASIK procedures are performed annually in the USA.
Availability
LASIK surgeons and clinics are available in all major cities including New York City, Los Angeles, Miami, San Francisco, Las Vegas, San Antonio, San Jose, Milwaukee, Boston, and San Diego.
There are also LASIK clinics and surgeons available in every state in the United States including
New York, California, Colorado, and New Jersey.
There are more than 5,000 LASIK surgeons who are performing LASIK eye surgery.
General Information
With increased interest in LASIK, there have been an increased number of LASIK providers as well. While LASIK eye surgery is considered to be a very safe and effective treatment in general, patients would be advised to select a LASIK surgeon with caution. Despite the increased advantage of advanced technology, the LASIK surgeon is still considered to be a vital and important part of the treatment and the selection process is vital in improving the chances of a good result.
In addition to selecting the correct LASIK surgeon, it is helpful to know the technology that is available today. LASIK technology has changed rapidly over the years and LASIK providers who have not kept up with the advancements could possibly be harming their patients. Good results with your surgery depend upon a variety of factors, including experience, skill, technology, wise decision-making, good patient selection, and good people skills. Each of the factors can affect the results of your surgery.
LASIK eye surgery has brought happiness and freedom from glasses and contact lenses to millions of people. The vast majority of LASIK patients is very satisfied with the results and would recommend their friends to have the procedure. A very small minority experience side effects or complications which leads them to regret their decision to undergo LASIK surgery. These side effects can range from mild temporary irritation to long term visual problems and possibly even loss of vision.
Please consider all the information provided before contacting your local LASIK providers. It is often wise to contact several LASIK surgeons so that you can determine which surgeon is providing the best possible service and will offer the best chance at having good LASIK results. While it is often difficult for someone outside of the business to weigh the factors in making a good decision, this web site will offer a variety of information to offer you a better opportunity for good LASIK results.
More Specific Information
LASIK articles are written periodically with respect to more specific information including information regarding clinics and surgeons in various markets, new technology, what to watch out for, and other information related to LASIK. As a service we also post articles dealing with other eye-related issues not specifically dealing with LASIK but often of interest to our readers.
LASIK is perhaps the most popular elective surgery available today. It is estimated that over 1,000,000 LASIK procedures are performed annually in the USA.
Availability
LASIK surgeons and clinics are available in all major cities including New York City, Los Angeles, Miami, San Francisco, Las Vegas, San Antonio, San Jose, Milwaukee, Boston, and San Diego.
There are also LASIK clinics and surgeons available in every state in the United States including
New York, California, Colorado, and New Jersey.
There are more than 5,000 LASIK surgeons who are performing LASIK eye surgery.
General Information
With increased interest in LASIK, there have been an increased number of LASIK providers as well. While LASIK eye surgery is considered to be a very safe and effective treatment in general, patients would be advised to select a LASIK surgeon with caution. Despite the increased advantage of advanced technology, the LASIK surgeon is still considered to be a vital and important part of the treatment and the selection process is vital in improving the chances of a good result.
In addition to selecting the correct LASIK surgeon, it is helpful to know the technology that is available today. LASIK technology has changed rapidly over the years and LASIK providers who have not kept up with the advancements could possibly be harming their patients. Good results with your surgery depend upon a variety of factors, including experience, skill, technology, wise decision-making, good patient selection, and good people skills. Each of the factors can affect the results of your surgery.
LASIK eye surgery has brought happiness and freedom from glasses and contact lenses to millions of people. The vast majority of LASIK patients is very satisfied with the results and would recommend their friends to have the procedure. A very small minority experience side effects or complications which leads them to regret their decision to undergo LASIK surgery. These side effects can range from mild temporary irritation to long term visual problems and possibly even loss of vision.
Please consider all the information provided before contacting your local LASIK providers. It is often wise to contact several LASIK surgeons so that you can determine which surgeon is providing the best possible service and will offer the best chance at having good LASIK results. While it is often difficult for someone outside of the business to weigh the factors in making a good decision, this web site will offer a variety of information to offer you a better opportunity for good LASIK results.
More Specific Information
LASIK articles are written periodically with respect to more specific information including information regarding clinics and surgeons in various markets, new technology, what to watch out for, and other information related to LASIK. As a service we also post articles dealing with other eye-related issues not specifically dealing with LASIK but often of interest to our readers.
Laser eye surgery risks highlighted
Consumer experts have warned that patients undergoing laser eye surgery are not being told about the risks they could be taking with their sight.
Laser surgery, which can cost thousands of pounds, is increasingly popular.
But the investigation by Health Which? also reveals any doctor can carry out the treatment after just a few days of training - they do not need a specialist qualification.
The magazine also found complication rates vary between surgeons and clinics.
Around 100,000 people, tired of wearing glasses or contact lenses, undergo corrective laser eye surgery in the UK every year.
The procedure is seen as quick and simple, and has received many celebrity endorsements.
Health Which? looked at clinics offering the Lasik procedure - the most popular on offer.
But whilst some highlight a low risk of complications with the procedure, others say the risk is non-existent.
'Misleading adverts'
In very rare cases, complications can lead to corneal ectasia, where fluid pressure builds up on the eye.
Patients can need a corneal transplant to correct the condition.
Other complications, though deemed "minor" by clinics, occur "relatively frequently", according to a review by the American Academy of Ophthalmology.
Patients can experience dry eyes or night vision problems, which can affect ability to drive or work in the evening or in dim light.
Health Which? also says that the Medical Defence Union and the Medical Protection Society, both doctors' insurance companies, are raising the fees they charge doctors working in this field because of increased compensation claims by patients.
Questions
David Gartry, a consultant ophthalmologist at Moorfields Eye Hospital has helped draw up Royal College of Ophthalmologist' guidelines on who should carry out laser eye surgery.
The guidelines say that only doctors with specialist training should carry out the procedure.
Mr Gartry told BBC News Online patients should find out as much as possible about the surgeon likely to carry out their operation.
"This is a situation where patients are responding to adverts, or even incentives.
"Patients should be asking the sort of questions they would ask if they were having, say, a hernia operation.
"What are the complication rates? What will happen if something goes wrong? Will I see the surgeon again?"
Dan Reinstein, who is developing safety guidelines for the Medical Protection Society, added: "Expert surgeons are better equipped to avoid complications even if they have not previously seen them.
"And when these do occur, trained experts will have the knowledge and ability to correct them."
'Highest clinical standards'
Sue Freeman, managing editor of Health Which?, said: "Patients shouldn't be taken in by claims about the safety and success rates of laser eye surgery and in particular about so called 'minor complications'.
"While some people will be able to throw away their glasses, this won't be the case for everyone."
She added: "Patients should be fully informed of the possible risks and of the complication rates of clinics and individual surgeons.
"Until patients are able to make informed choice, they need to do a lot of research and ask a lot of hard questions of surgeons and clinics."
Here are a selection of your comments on this subject.
If my wife had known what it was going to be like she would never have had it done
G Fuller, UK
My wife had corrective laser treatment in November 2002 and all the literature she received quoted 'best case' examples of people being back at work the next day. Unfortunately she experienced massive discomfort and complete blindness for a week which failed to be controlled by the painkillers and sleeping pills prescribed by the clinic. In her own words "if she had known what it was going to be like she would never have had it done".
G Fuller, UK
Following surgery at the age of 44, I now have 20-20 vision, can use normal sunglasses (essential in Australia and at high altitude) and no longer have problems with rain or fogging. I saw a specialist surgeon in Belgium who used the latest equipment. I have had one (free) adjustment operation to correct some astigmatism in one eye.
I have experienced some minor double-vision, slight loss of night vision, and initially starbursts/haloes around strong light sources - the latter now much reduced. For me these are very minor compared with the joy of being able to see the stars with the naked eye for the first time. I was given a video recording of the operation but this is not for the squeamish, and best seen afterwards.
Charles Barran, Australia
After many years of consideration I finally took the decision to have laser treatment in December 2001. I opted for Lasek and was talked through all the possible complications and even had to take a little test to ensure I was fully aware of all possible side effects. After a thorough consultation I then had both eyes done simultaneously. I won't pretend the days following the treatment were bliss, I was in some discomfort for 3 to 4 days but after that had passed my eyes soon began to heal.
It was strange but having worn glasses for so long for a month or so afterwards I was still trying to push glasses that weren't there back up the bridge of my nose! It is now over a year since and I have perfect 20/20 vision. Just very occasionally my eyes are a little dry in the morning but I consider this a tiny inconvenience.
Edward Lacey, UK
I'd like to know if Sue Freeman would recommend micro lenses inserted into the eye as a better option than Lasik eye surgery. Would she be so kind as to find out on my behalf. I would like to lose my glasses. I did intend to have Lasik surgery but have now been scared off with the latest news regarding unsuccessful operations.
Vincent Jones, Dorset, UK
I had Lasik surgery last year and it was the best thing I ever did. I was fully informed by the company regarding any potential risks (and clear details on the procedures are on their website anyway). It was great just waking up the next day and not having to fumble around looking for glasses, and no fussing about shoving bits of plastic in my eyes each day!
Dave, UK
I had laser surgery in June 2001 and have been more than satisfied with the results and the service I received. I felt under no pressure to make a decision and that I was able to make an informed choice to go ahead with the procedure. I agree though that you do need to ask questions and be aware that there are risks - but isn't this the case for any sort of medical procedure? It is also essential to use a reputable company, unfortunately there are rouges out there, look at cosmetic surgery.
Kate Austin, England
Laser surgery, which can cost thousands of pounds, is increasingly popular.
But the investigation by Health Which? also reveals any doctor can carry out the treatment after just a few days of training - they do not need a specialist qualification.
The magazine also found complication rates vary between surgeons and clinics.
Around 100,000 people, tired of wearing glasses or contact lenses, undergo corrective laser eye surgery in the UK every year.
The procedure is seen as quick and simple, and has received many celebrity endorsements.
Health Which? looked at clinics offering the Lasik procedure - the most popular on offer.
But whilst some highlight a low risk of complications with the procedure, others say the risk is non-existent.
'Misleading adverts'
In very rare cases, complications can lead to corneal ectasia, where fluid pressure builds up on the eye.
Patients can need a corneal transplant to correct the condition.
Other complications, though deemed "minor" by clinics, occur "relatively frequently", according to a review by the American Academy of Ophthalmology.
Patients can experience dry eyes or night vision problems, which can affect ability to drive or work in the evening or in dim light.
Health Which? also says that the Medical Defence Union and the Medical Protection Society, both doctors' insurance companies, are raising the fees they charge doctors working in this field because of increased compensation claims by patients.
Questions
David Gartry, a consultant ophthalmologist at Moorfields Eye Hospital has helped draw up Royal College of Ophthalmologist' guidelines on who should carry out laser eye surgery.
The guidelines say that only doctors with specialist training should carry out the procedure.
Mr Gartry told BBC News Online patients should find out as much as possible about the surgeon likely to carry out their operation.
"This is a situation where patients are responding to adverts, or even incentives.
"Patients should be asking the sort of questions they would ask if they were having, say, a hernia operation.
"What are the complication rates? What will happen if something goes wrong? Will I see the surgeon again?"
Dan Reinstein, who is developing safety guidelines for the Medical Protection Society, added: "Expert surgeons are better equipped to avoid complications even if they have not previously seen them.
"And when these do occur, trained experts will have the knowledge and ability to correct them."
'Highest clinical standards'
Sue Freeman, managing editor of Health Which?, said: "Patients shouldn't be taken in by claims about the safety and success rates of laser eye surgery and in particular about so called 'minor complications'.
"While some people will be able to throw away their glasses, this won't be the case for everyone."
She added: "Patients should be fully informed of the possible risks and of the complication rates of clinics and individual surgeons.
"Until patients are able to make informed choice, they need to do a lot of research and ask a lot of hard questions of surgeons and clinics."
Here are a selection of your comments on this subject.
If my wife had known what it was going to be like she would never have had it done
G Fuller, UK
My wife had corrective laser treatment in November 2002 and all the literature she received quoted 'best case' examples of people being back at work the next day. Unfortunately she experienced massive discomfort and complete blindness for a week which failed to be controlled by the painkillers and sleeping pills prescribed by the clinic. In her own words "if she had known what it was going to be like she would never have had it done".
G Fuller, UK
Following surgery at the age of 44, I now have 20-20 vision, can use normal sunglasses (essential in Australia and at high altitude) and no longer have problems with rain or fogging. I saw a specialist surgeon in Belgium who used the latest equipment. I have had one (free) adjustment operation to correct some astigmatism in one eye.
I have experienced some minor double-vision, slight loss of night vision, and initially starbursts/haloes around strong light sources - the latter now much reduced. For me these are very minor compared with the joy of being able to see the stars with the naked eye for the first time. I was given a video recording of the operation but this is not for the squeamish, and best seen afterwards.
Charles Barran, Australia
After many years of consideration I finally took the decision to have laser treatment in December 2001. I opted for Lasek and was talked through all the possible complications and even had to take a little test to ensure I was fully aware of all possible side effects. After a thorough consultation I then had both eyes done simultaneously. I won't pretend the days following the treatment were bliss, I was in some discomfort for 3 to 4 days but after that had passed my eyes soon began to heal.
It was strange but having worn glasses for so long for a month or so afterwards I was still trying to push glasses that weren't there back up the bridge of my nose! It is now over a year since and I have perfect 20/20 vision. Just very occasionally my eyes are a little dry in the morning but I consider this a tiny inconvenience.
Edward Lacey, UK
I'd like to know if Sue Freeman would recommend micro lenses inserted into the eye as a better option than Lasik eye surgery. Would she be so kind as to find out on my behalf. I would like to lose my glasses. I did intend to have Lasik surgery but have now been scared off with the latest news regarding unsuccessful operations.
Vincent Jones, Dorset, UK
I had Lasik surgery last year and it was the best thing I ever did. I was fully informed by the company regarding any potential risks (and clear details on the procedures are on their website anyway). It was great just waking up the next day and not having to fumble around looking for glasses, and no fussing about shoving bits of plastic in my eyes each day!
Dave, UK
I had laser surgery in June 2001 and have been more than satisfied with the results and the service I received. I felt under no pressure to make a decision and that I was able to make an informed choice to go ahead with the procedure. I agree though that you do need to ask questions and be aware that there are risks - but isn't this the case for any sort of medical procedure? It is also essential to use a reputable company, unfortunately there are rouges out there, look at cosmetic surgery.
Kate Austin, England
Subscribe to:
Posts (Atom)
