Four categories of refractive surgery include:
- Excimer laser procedures
- Implant procedures
- Thermal procedures
- Other refractice procedures
Excimer Laser Procedures
LASIK (Laser In Situ Keratomileusis) LASIK combines two techniques of surgery to correct refractive error. First, a laser called a femtosecond laser or a surgical blade called a microkeratome creates a thin flap in the cornea. Next, an excimer laser sculpts the underlying cornea into a new shape to correct the refractive error. The flap is then repositioned and adheres on its own without sutures after only a few minutes. Eyedrops and/or ointment are placed in the eye to facilitate the healing process. Vision recovery typically is rapid, and there is little or no post-operative pain.
LASIK with microkeratome making corneal flap
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The microkeratome blade cuts
a thin flap of corneal tissue;
|the flap is lifted and the laser resculpts |
the exposed surface of the cornea;
| the tissue flap is replaced.|
LASIK with laser making corneal flap
Epi-LASIK (Epithelial LASIK) is a refractive surgery procedure very much like LASIK. Epi-LASIK is an alternative for patients with thin corneas who would not otherwise be candidates for the conventional LASIK procedure.
The Epi-LASIK procedure uses a specific type of microkeratome, called an Epi-keratome. The Epi-keratome precisely separates the thin epithelial sheet—much thinner than a LASIK flap—from the rest of the cornea. Once the epithelium is separated from the rest of the cornea, the thin sheet of epithelial cells is lifted to one side. After a laser is used to treat the cornea, the thin sheet is then moved back into place, where it will self-adhere. After the procedure, a transparent bandage contact lens is placed on the cornea to promote healing. The reshaped cornea then focuses light more accurately on the retina.
One of the keys to a successful LASIK procedure is the measurement your ophthalmologist takes to determine your refractive error. Small imperfections in the eye may cause some light to travel through the eye at different angles, making light strike the retina in different places. Collectively, these imperfections are called optical aberrations.
Wavefront measurement can be described as a "fingerprint of your eye." Wavefront measurements capture tiny, subtle variations in the way light passes through your eyes. These variations can be as unique as your fingerprints.
Wavefront-guided LASIK uses a measuring device to create a "map" of how your eye focuses light, to precisely assess the unique irregularities and variations in your eye.
The wavefront map is very detailed: instead of simply creating a general description of your eye's focusing power (for example, nearsightedness, farsightedness or astigmatism), it records every subtle distortion in the pathway of light moving through your eye. In addition, subtle measurements of the corneal shape itself can be done with a surface topographer.
The benefit of having wavefront-guided LASIK instead of conventional LASIK is that it reduces the possibility that you will have quality-of-vision complaints, such as poor night vision, difficulty driving at night, glare, halos and blurry images after surgery. Also, there are some optical aberrations that can distort your vision that can not be corrected with glasses and contacts. They can only be measured with wavefront analysis.
How Is the Wavefront Measurement Taken?
If you are having wavefront-guided LASIK, your ophthalmologist maps both of your eyes using a wavefront scanner, called an analyzer or aberrometer. The aberrometer produces a very precise, detailed map of light rays as they travel through your eye, highlighting imperfections in your vision.
A targeted beam of light will be sent through your eye and focused on the retina. A wave of light rays is reflected back from the retina through the eye's lens, pupil and cornea. A sensor will measure the irregularities in the wavefront pattern of light as it emerges from your eye. Using this measurement, the wavefront computer creates an accurate, three-dimensional map of the light rays created by your eye’s optical system.
This wavefront data will be used to program the laser, allowing your ophthalmologist to customize the reshaping of your cornea during the LASIK procedure.
PRK (Photorefractive Keratectomy)
PRK reduces low to high myopia, low to moderate hyperopia, and astigmatism. In PRK, the epithelium, the layer of cells covering the cornea, is removed and the excimer laser sculpts the cornea to correct refractive error. A bandage contact lens is usually placed on the eye following the procedure to speed the epithelial healing process, which usually takes three to four days. Because PRK sculpts the outer surface of the cornea, patients experience some discomfort after surgery and recovery time lasts for a period of several weeks. PRK has been largely displaced by LASIK because LASIK provides less discomfort, faster vision recovery, and the ability to enhance or refine the outcome easily in as little as three months following the initial surgery. However, PRK is sometimes recommended instead of LASIK because it does not create a flap in the cornea and may be a better option for people who have thin corneas or whose occupation makes it more dangerous to have a flap.
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|The epithelium, the layer of cells covering |
the cornea, is removed.
| The excimer laser resculpts the surface of the cornea.|
LASEK (Laser Epithelial Keratomileusis)
LASEK corrects nearsightedness, farsightedness, and astigmatism. It is similar to PRK except that the surface layer (the epithelium) is replaced after surgery. Both PRK and LASEK are similar to LASIK in that they use the excimer laser to shape the cornea, but unlike LASIK neither procedure preserves the surface layers. PRK and LASEK are sometimes recommended instead of LASIK for people with thin corneas because they do not penetrate as deeply into the eye's surface.
In LASEK, the epithelium is loosened and peeled back to expose the cornea. The excimer laser then reshapes the cornea, the epithelium is placed back into position and a bandage contact lens is placed on the eye to facilitate healing. Like LASIK, recovery time is rapid but discomfort is somewhat increased compared to LASIK.
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| The epithelium is loosened and peeled back;|
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| the excimer laser resculpts the exposed |
surface of the cornea;
| the epithelium is placed back into position.|
Intrastromal Corneal Ring Segments (INTACS)
Intrastromal corneal ring segments (Intacs) are semicircular pieces of plastic that are implanted within the cornea to treat mild forms of myopia. They also are sometimes used for other conditions affecting the cornea, such as keratoconus. They are designed to change the shape of your cornea, adjusting the focusing power of your eye so that light is focused onto your retina. The Intacs are inserted through a small incision near the upper edge of the cornea. The incision is closed with two small sutures that are usually removed two to four weeks after surgery.
Unlike laser eye surgeries, Intacs are reversible; if they are removed, your cornea usually returns to its original shape after a few weeks.
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|Intacs are inserted within the cornea to change the shape of the cornea. || View of Intacs in a real patient.|
Phakic Intraocular Lenses (Phakic IOLs)
Until recently, refractive surgery for some people with high degrees of myopia or hyperopia has not been an option. The amount of correction needed could not be achieved safely through surgical procedures involving reshaping the cornea. However, cataract surgery patients have been treated successfully with plastic lenses (called intraocular lenses or IOLs) implanted in the eye for many years. In cataract surgery, the natural lens is removed and the IOL is inserted in its place, replacing the focusing ability of the natural lens and also offering cataract patients correction for myopia and hyperopia.
Using a similar approach, a different style of IOL known as phakic IOL can be used to treat patients who do not have cataracts but need correction for refractive errors that exceeds the safe range of excimer laser procedures such as LASIK. In order to preserve the focusing ability needed for reading vision, the natural lens is not removed from the eye. The phakic IOL, sometimes referred to as an implantable contact lens or ICL, is surgically implanted inside the eye in front of the eye's natural lens.
Phakic IOLs are being used around the world with multiple intraocular lens styles. Since phakic IOLs involve entering the eye, unlike LASIK and PRK, the risk of complications is higher.
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|A small incision is made in the |
peripheral (side) cornea;
|the phakic IOL is placed in front of the |
eye's natural lens;
| the incision is closed with sutures.|
Conductive Keratoplasty (CK)
CK is generally used for people who are farsighted or who are over age 40 and have difficulty focusing on objects up close (commonly referred to as presbyopia, or "aging eye"). CK does not involve making an incision but instead applying heat to cause the peripheral (outside edge) area of the cornea to tighten like a belt and make the central cornea steeper. CK cause little or no discomfort or irritation and vision improvement is almost instantaneous. However, unlike other types of refractive surgery such as LASIK, correction from CK may be temporary and re-treatment may be necessary later.
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|With CK, a tiny probe releases controlled amounts of radiofrequency to apply heat to the peripheral (side) portion of the cornea.|
Other Refractive Surgery Procedures
Accommodative and Multifocal Intraocular Lenses
Used to treat nearsightedness (myopia), farsightedness (hyperopia) and the inability to focus at near with age (presbyopia), accommodative and multifocal IOLs are artificial lenses surgically implanted in the eye, replacing the eye’s natural lens. These lenses enable your eye to regain its focusing and refractive ability.
Refractive Lens Exchange (RLE)
Refractive Lens Exchange (RLE) is used to treat moderate to high degrees of nearsightedness, farsightedness and patients who are not candidates for the LASIK procedure. This is a non-laser procedure where the natural, clear lens of the eye is removed and replaced with an artificial intraocular lens (IOL). As with accommodative and multifocal IOLs, the cornea is not reshaped in the RLE procedure.
RK (Radial Keratotomy)
RK is a surgical procedure sometimes still used to correct low degrees of nearsightedness and astigmatism. Using a diamond scalpel, a calculated number of spoke-like cuts are made on the surface of the eye to flatten and reshape the cornea and reduce refractive error. RK has been largely displaced by LASIK, which is a more accurate procedure capable of correcting a larger range of myopia without structurally weakening the eye.
A calculated number of spoke-like cuts are made on the surface of the cornea to reshape the cornea.
Monovision is a refractive surgery technique for people with presbyopia. Many people use reading glasses to correct presbyopia but only use the glasses for close-up vision and take them off when they need to see objects farther away. While there are refractive surgeries to reduce nearsightedness and farsightedness, these procedures do not help correct presbyopia. Monovision is a compromise that refractive surgery can offer people with presbyopia. The technique uses refractive surgery to enable one eye to focus at close proximity, and the other eye is left untreated or, if needed, treated to be able to focus at a distance. Having each eye configured for different focusing distances can reduce or eliminate the need for eyeglasses or contacts. It may seem difficult to get used to at first, but about six to eight weeks after the monovision procedure your brain is able to adjust to the different focusing ability of your eyes. A preoperative trial with contact lenses is a useful test to see if a patient will adapt to the intended refractive outcome.