Refractive eye surgery is a group of eye surgeries that aim to correct refractive errors and decrease dependency on glasses or contact lenses. There are several types of refractive eye surgery; the most common is LASIK.
What is photorefractive eye surgery?
Most refractive surgeries in use today use a special excimer laser to reshape the cornea (the clear covering on the front of the eye), and are thus called photorefractive eye surgeries. The most common of these are LASIK, LASEK and PRK. Learn more about these procedures by reading further.
In many ways, the eye is similar to a camera. In both an eye and a camera, light rays are focused onto a film (in the eye this is called the retina) to create an image. In both systems, failure to focus the light precisely onto the film will result in a blurred image.
In the eye, the focusing of light is carried out by two structures. The first structure, the cornea, is the clear outer covering of the eye. The cornea is able to partially focus light rays because of its curved surface; it performs most of the focusing. The rest is carried out by the crystalline lens in the inside of the eye. The lens is capable of changing its shape to adjust its focusing power for near and far objects. This is called accommodation, and it declines as we age.
The goal of the cornea and lens is to focus all light onto the light-sensitive back of the eye, the retina (analogous to the film on a camera). Refractive error occurs when the light does not focus on the retina, causing a blurred image. Refractive error can be eliminated with LASIK. There are three types of refractive errors: myopia, hyperopia and astigmatism.
What is myopia?
Myopia, or near-sightedness, results when the light rays are bent (refracted) too much by the cornea and lens. The result is that you will have trouble seeing far-off objects. However, your close vision will remain relatively good.
In myopia (near-sightedness), the image is focused in front of the retina.
What is hyperopia?
Hyperopia, or far-sightedness, results when light rays are not bent (refracted) enough. This is the opposite of myopia: near vision becomes blurred but far vision is not affected.
In hyperopia (far-sightedness), the image is focused behind the retina.
What is astigmatism?
An astigmatism is a refractive error that is caused by an irregularly-shaped cornea or lens. In general, both near and far vision will be affected by astigmatism. A good way to think about astigmatism is that the cornea or lens is in the shape of a football instead of a soccer ball. In some cases, it is possible to have astigmatism combined with either myopia or hyperopia.
In hyperopia, an irregularly shaped cornea causes blurring of vision.
What is LASIK?
LASIK (Laser Assisted In Situ Keratomileusis) is the most commonly performed refractive eye surgery.
Once the eye has been prepared for surgery, a special instrument called a microkeratome is used to cut a thin flap off the surface of the cornea.
Once this flap has been folded to the side, the inner cornea (the stroma) is exposed. An excimer laser is then used to reshape the inner cornea (measurements are taken before surgery to decide exactly where and how much tissue is to be removed).
The actual reshaping of the cornea usually takes less than 1 minute. After this is completed, the corneal flap is folded back into place. Stitches are not required.
What is PRK? PRK (PhotoRefractive Keratectomy) is a photorefractive surgery common in the past, but performed less today. In PRK, the epithelium of the cornea is removed (the epithelium is the extremely thin layer of cells on the surface of the cornea). Next, an excimer laser reshapes the inner cornea (the stroma). The epithelium naturally regenerates in a few days.
What is LASEK?
LASEK (Laser-Assisted Sub-Endothelial Keratectomy) is a photorefractive eye surgery similar to PRK. In LASEK, the epithelium of the cornea is removed but it is persevered during surgery. After the laser has reshaped the stroma of the cornea, the epithelium is replaced.
What medical conditions may exclude me from photorefractive eye surgery?
To ensure a successful procedure and proper wound-healing, it is important that your eyes are healthy at the time of the procedure. Some eye diseases may exclude you from surgery altogether, while others may simply delay your surgery until they are resolved.
Diseases that are known to affect wound healing include: • autoimmune diseases • immunodeficiency disorders • diabetes • certain medications such as steroids
Diseases that can affect the outcome of the procedure or increase risk of complications include: • Herpes simplex virus or Herpes zoster virus in the eye • Glaucoma • Eye disease such as uveitis (inflammation of the eye), keratoconus or blepharitis (inflammation of the eyelids) • Previous eye surgery (including refractive surgery) • Previous eye injuries
Finally, having large pupils or a thin cornea are also risk factors for photorefractive eye surgery. With thin corneas there may not be enough tissue to perform the procedure safely, and having surgery on large pupils can result in side effects such as glare and double vision. Because of the risk factors involved in the surgery, it is important that you discuss with your doctor if you are a good candidate for the procedure.
What non-medical conditions may exclude me from photorefractive eye surgery?
Apart from medical conditions, there are important personal and lifestyle criteria that may not make you a good candidate for photorefractive eye surgery.
Firstly, like all types of surgery there is always a risk that a complication could occur. This may result in worse vision than before surgery. If a bad outcome would jeopardize your career, or you are not comfortable with taking a small risk than surgery may not be for you.
Additionally, photorefractive eye surgery is not recommended for patients who have had recent (in the last 6 months) changes in their eye prescription, or who are under the age of 18 (in fact in most countries it is prohibited to have photorefractive eye surgery performed on persons under the age of 18). Other exclusion criteria include participation in contact sports (especially with contact to the head and eyes) and concern over the cost of the procedure.
Why can’t I wear contact lenses before surgery?
Contact lenses can alter the refractive error, hence they must be stopped to ensure that the corneal curve is stable before surgery.
Because the cornea has no blood vessels (the cornea must be transparent to function properly), it must absorb oxygen from the tear film that flows across the front of the eye. Unfortunately, contact lenses serve as a barrier between the cornea and the tear film, blocking the flow of oxygen to the cornea. As a result, blood vessels sometimes invade the cornea to help deliver oxygen. This is called corneal neovascularization.
Corneal neovascularization causes problems for photorefractive eye surgery- it increases inflammation during surgery and increases healing time due to more bleeding.
What type of anesthesia is used for photorefractive eye surgery?
Photorefractive eye surgery is performed with a mild sedative and eye drops to numb the eye. This means that the patient will be awake during surgery, but will experience little if any discomfort.
Could I go blind from surgery?
Going blind from having photorefractive eye surgery is next to impossible. For example, even though there have been tens of millions of LASIK procedures performed, there is not a single case of blindness due to the procedure.
What complications could result from photorefractive surgery?
Like any surgery, there is always a small chance a complication could occur from photorefractive eye surgery. Fortunately, most complications are exceedingly rare and easily treated if they do occur.
The exact chance of having a complication varies according to factors such as the skill of the surgeon, the quality of equipment, refractive error of the patient, patient’s age, degree of astigmatism, and the anatomy of the patients orbit. If you are considering photorefractive eye surgery, it is a good idea to ask your doctor about complication rates at the centre.
The most common complications are: • Inflammation • Infection • Over-correction • Under-correction • Flap complications (most common with LASIK)
How much does photorefractive eye surgery cost?
Photorefractive eye surgery is cosmetic surgery; therefore patients have to pay themselves, but recently some private insurance plans are covering part of the procedure costs.
The exact cost of the procedure depends on where it is taking place. Typically, you can expect to pay at least several hundred to two thousand dollars per eye. However, it should be noted that these surgeries can save money in the long term from avoiding costs associated with glasses or contact lenses.
How should I pick a doctor for the procedure?
Again, it is important to not base your decision of doctor on simply the cost alone. It is important for you to research various doctors, as the risk will vary according to their experience and equipment. Do not be shy to inquire about success rates.
Will I still need glasses or contact lenses after surgery?
It is important that patients undergoing photorefractive eye surgery have realistic expectations about the success of the surgery. Unfortunately, not everyone will achieve perfect 20/20 vision without glasses, especially those who had large refractive errors prior to surgery.
Sometimes, the doctor may feel the need for a “retreatment” to perfect the vision, but this may have additional risks. As well, patients who used reading glasses before surgery will most likely continue to require them after surgery.
Nonetheless, most patients having photorefractive eye surgery (especially who are young) will have a great result and will not require glasses or contact lenses.
What are other types of refractive surgery?
Although photorefractive is the most common and popular type of refractive surgery, there are other procedures to repair refractive errors.
In Radial Keratotomy (RK), a sharp knife is used to reshape the cornea by removing “slits” of tissue. A final type of refractive surgery is thermokeratoplasty, in which heat is used via a laser to reshape the cornea.
As well, there are also various non-surgical techniques to correct refractive errors. An example of such a procedure is orthokeratology. In orthokeratology, special contact lenses are used that also attempt to reshape the cornea.
