Overview of Photorefractive Keratectomy

Photorefractive keratectomy (PRK) is a type of laser eye surgery used to correct vision problems like nearsightedness (myopia), farsightedness (hyperopia), and astigmatism. PRK was created by Dr. Steven Trokel and his team in 1983 and was first carried out by Dr. Theo Seiler in Berlin in 1987. The US Food and Drug Administration (FDA) gave its approval to PRK in 1996.

For a short time, PRK was the top choice for treating ametropia, a condition where the eye has a problem focusing light properly. This is because PRK delivered more reliable and steady results than incisional keratotomy, a surgery that involves cutting the cornea. However, towards the end of the 1990s, a new type of eye surgery called LASIK became more popular, leading to fewer PRK procedures. Today, LASIK is the most common type of vision correction surgery. Still, there are certain situations where PRK might be a better option.

Anatomy and Physiology of Photorefractive Keratectomy

Laser eye surgeries, like PRK, work on the surface of the cornea. The cornea is the clear, dome-like, outer layer that covers the front of your eye. For the surgery to start, the top layer of the cornea has to be completely removed down to a certain layer called Bowman’s layer. After that, a special kind of laser, called the excimer laser, is used to reshape the surface of the cornea.

After the surgery, your cornea will start to heal itself. This is done through a process where cells called fibroblasts move to the area and start to rebuild the corneal layer using collagen, a type of protein that helps with healing. We’ll talk more about the excimer laser in the following sections.

Why do People Need Photorefractive Keratectomy

Photorefractive Keratectomy (PRK), a type of eye surgery, can be considered for people with nearsightedness up to a -12 diopter level, astigmatism up to 6 diopter, and farsightedness up to 5 diopter. The more severe the vision problem, the more likely it is that the results might not be as long-lasting and the cornea (the clear front of the eye) may get cloudy.

PRK might be a more appealing option than other types of surgery for fixing vision problems, for a few reasons:

* People might be fearful of procedures that involve making a flap in the eye because of risks like the flap not being cut properly, issues with reattaching the flap, or problems with the epithelium (the outer layer of the eye) growing incorrectly.
* PRK might be a better option for people whose jobs involve higher risks of the flap created in other types of surgeries (like LASIK) dislodging. This includes people like pilots and professional athletes.
* Eye doctors who do not often perform vision correction surgeries might choose to do PRK over more complex procedures like LASIK.

In some cases, PRK might be the only option for vision correction surgery. This can be the case for people with a thin cornea, issues with the epithelial basement membrane (the structure that connects the cornea to the outer layer of the eye), a history of repeated corneal erosions (scratches on the cornea), a scleral buckle placed towards the front of the eye, or very flat or very curved corneas. PRK might also be used to further correct eyesight after other eye surgeries such as corneal transplantation, penetrating keratoplasty (another type of corneal transplant), LASIK, cataract surgery, or other eye surgeries. Studies have shown PRK can be a safe and effective option in these cases.

When a Person Should Avoid Photorefractive Keratectomy

There are certain conditions and concerns that may stop a person from getting laser eye surgery, guidelines for which are provided by the FDA and the American Academy of Ophthalmology (AAO). For someone to qualify for this type of surgery, their vision prescription should not have changed more than +/- 0.5 D in the last year.

Certain conditions absolutely stop a person from getting this type of laser eye surgery known as PRK. These include significant cataract (clouding of the eye lens), unstable glaucoma (a group of eye diseases causing a damage to the optic nerve), external eye diseases like blepharitis (an inflammation of the eyelids causing them to become red, irritated and itchy), dry eye syndrome, and allergies. Any abnormalities of the cornea, that’s the clear front surface of the eye, like corneal thinning, swelling, abnormal growths and extensive blood vessel formation also prevent someone from getting PRK. If a person has systemic connective tissue diseases like lupus or rheumatoid arthritis, they are also poor candidates as these conditions may cause increased risk of cornea clouding and melting. However, an exception is made for patients with a condition known as keratoconus, in which the cornea thins and bulges out in a cone shape, who have adequate corneal thickness. A study found that PRK could improve vision and did not make keratoconus worse in such patients.

Then, there are some conditions that do not absolutely stop a person from getting PRK but require extra considerations. For example, the surgery is usually avoided in women who are pregnant or nursing as hormonal changes can influence the vision prescription. More so, any medicines given after the surgery might affect the fetus or nursing infant. It’s also a bit risky for those who have only one functioning eye, or any other eye conditions that limit their vision. People with excessively curved corneas or irregularly shaped corneas also require caution. Those suffering from uncontrolled dry eye, uveitis (an inflammation inside the eye), and glaucoma are advised to approach with caution. If a person had a history of herpes simplex keratitis, an eye condition caused by herpes virus, they can have the surgery after taking antiviral medicines for a few months to reduce the risk of the condition returning. Patients with diabetes that is not under good control are at higher risk of unpredictable vision changes or poor wound healing after the surgery. Those taking medications known to have harmful effects on the eye, like amiodarone, isotretinoin, sumatriptan, etc., are generally advised to avoid laser eye surgery.

Equipment used for Photorefractive Keratectomy

PRK, or Photorefractive keratectomy, is a type of eye surgery that uses a specific kind of laser (193 nm argon fluoride excimer laser) to reshape the front part of the cornea, which is the clear outer layer of the eye. This laser is so powerful that a single burst of light can split the chemical bonds that hold together the cornea’s structure. With each burst, the laser breaks the cornea into smaller pieces, and a certain amount of tissue is removed from the surface of the eye.

The first step in the procedure involves removing the outer layer of cells (epithelium) from the cornea. This can be done in a few different ways – with a small tool called a spatula, with another type of laser (femtosecond laser), by applying a diluted alcohol solution, or with a rotating brush.

Each of these techniques has its own pros and cons, which will be explained further.

Preparing for Photorefractive Keratectomy

Before having laser eye surgery, there are several steps doctors need to take to ensure the patient has the best chance of a good result and a smooth recovery. This includes giving the patient all the information they need about the procedure, what it involves, and what they can expect afterwards. This helps to make sure the patient knows what to expect and can help reduce any worries they might have.

The patient’s medical history and current medication list are checked to make sure there are no reasons they shouldn’t have the surgery. It is very important that patients have a realistic understanding of what the surgery can achieve. The purpose of laser eye surgery is to reduce the patient’s need for glasses or contact lenses – it’s not always able to completely correct their vision.

Before the surgery, the doctor needs to take a close look at the patient’s eyes. They’ll measure how much the patient’s eyes need correcting (their ‘refraction’) and check for things like unevenness of the eye surface (astigmatism). They’ll check for differences between what the patient can see with their own focus (manifest refraction) and what they can see when their focus is helped with eye drops (cycloplegic refraction). If there is a big difference between these two measurements, the doctor will need to reassess. This can happen when a patient’s focus isn’t relaxed, which is common in people in their middle age. Patients who need correction to a high degree should know that the result may not be as predictable and there is a higher risk of issues like scarring and poorer vision following the surgery.

The doctor will also check the patient’s cornea for scars, inflamed areas, or abnormal blood vessels. They need to measure the size of the patient’s pupils because large pupils can cause glare and rings of light (haloes) after the surgery. A detailed look at the front of the eye (slit-lamp examination) is necessary to rule out significant eye issues such as abnormal blood vessels in the cornea, keratoconus (where the cornea thins and bulges outwards), scarring, or cataracts.

The thickness of the cornea will be measured (corneal pachymetry) to detect keratoconus or other types of abnormal shape. The doctor will examine the eyelids and the layer of tears on the front of the eye for signs of inflammation of the eyelid (blepharitis) or dry eyes. The shape of the cornea will be mapped on a computer (computed corneal topography) to allow the detection of irregular astigmatism and keratoconus.

Patients should not wear soft contacts for three days and hard contacts for two weeks before evaluation as they cause changes in the shape of the cornea, which affects the accuracy of pre-surgery measurements. Pressure inside the eye is measured to identify glaucoma. The doctor also looks at the back of the eye (fundoscopy) to rule out a retinal hole and other issues.

Before having the surgery, patients will typically be given some medications in the 20 minutes beforehand. To reduce pain after the operation, eye drops like ketorolac tromethamine 0.5% or diclofenac 0.1% are used, one drop given three times every ten minutes. Anesthetic eye drops, like proparacaine hydrochloride 0.5%, are also put onto the eye to numb it. Special antibiotic eye drops, such as moxifloxacin 0.5% and gatifloxacin 0.3%, are given to help lower the chance of getting an infection. Some patients may be sedated during the procedure, but this is usually not recommended.

How is Photorefractive Keratectomy performed

When preparing for eye surgery, comfort is key. This means patients should rest in a relaxed position, with their legs uncrossed and their neck straight. Breathing should be shallow and slow. When the eye speculum (a tool to hold open the eye during surgery) is inserted, equal parts of the white of the eye should be visible above and below the iris (the colored part of the eye). If the surgery is only happening in one eye, the other should be covered or gently closed while the one being operated on is clearly labeled. The skin of the eye area is usually cleaned using alcohol wipes or a disinfecting solution called povidone-iodine, and a small cloth pad can be used to catch any fluid that might run off during the procedure.

The excimer laser, which is the device used to perform the surgery, needs to be properly set up on the day of the procedure. Its settings are calibrated for each patient and specific details like the patient’s name, the power level of the laser, the corrections intended to be made, or the areas to be affected during surgery are inputed.

It’s crucial during eye surgery that the pupil (the black dot at the center of the eye) stays still. Doctors ensure this steadiness through several techniques. The most popular method is to have patients focus on a light during the surgery. Modern lasers even have built-in systems that pause the operation if the eye wanders off too much. Throughout this, it’s paramount that the doctor continues to carefully watch the eye and quickly halt the procedure if the patient’s eye loses its focus.

Throughout, doctors should constantly reassure the patient, helping them stay calm and relaxed. Just like in any surgical environment, there should be minimum background noises that could cause disruption or distraction.

In PRK eye surgery, the first step is to gently remove the outer layer of the eye, or the epithelial cells. This can be done in several ways, each trying not to damage a layer deeper inside the eye called Bowman’s layer. Some techniques include mechanical debridement, where doctors use a blunt spatula to scrape off the patient’s epithelium layer, and transepithelial technique, where a blue fluorescent light indicates when ablation (the removal process) is complete. This approach doesn’t require manual scraping. Another method involves using a diluted alcohol solution to remove the epithelium. Finally, a rotary brush could be used, which removes the epithelium without injuring Bowman’s layer.

Once this layer is removed, the laser then is positioned and focused on the necessary areas. If the patient is nearsighted, the laser targets more of the center of the eye and less of the edges; if farsighted, it’s the other way around. The laser operations aim to reshape cornea to improve vision.

Sometimes, PRK surgery is combined with a procedure called collagen cross-linking (CXL) in cases of certain eye conditions like keratoconus and post-LASIK ectasia. This process is thought to strengthen the cornea. Lastly, a substance called topical mitomycin-C (MMC) can also be applied after PRK.

Possible Complications of Photorefractive Keratectomy

After you get refractive surgery to correct your vision, you might feel some minor pain or discomfort, similar to the sensation of having sand in your eye. Dry eye, where the eye doesn’t produce enough tears to stay properly lubricated, is also a possibility. Dry eyes are more common in older people and women, and can be addressed by using artificial tears, taking omega-3-fatty acids, or using certain kinds of eye drops.

A rare complication from this type of surgery is an infection in the cornea, the clear front part of the eye. If your eye care provider suspects an infection, they may try to grow bacteria from your eye on a lab dish to confirm and might treat the infection with antibiotic eye drops.

In the first few days after the surgery, the surface (epithelium) of the cornea heals. If you notice lasting blurry vision, it might be because this healing is delayed. Other complications can include “pseudodendrites,” which look like tiny fingers reaching out over the surface of your cornea; the “halo effect,” where you see bright circles around sources of light (this usually improves over time); central corneal islands, which are irregularities in the cornea that might cause blurry vision; and ectasia, where the cornea thins and begins to bulge outward, though this is very rare.

Another potential issue during surgery is decentration, where the treatment area isn’t centered correctly. This can lead to problems with seeing glare, haloes, and other visual distortions, but it’s less likely to happen these days as better technology is used.

Persistent corneal erosion, where the cornea keeps having small tears, could cause pain and tearing up, especially when you wake up. This complication can be managed by using certain kinds of eye drops and ointments.

Lastly, corneal haze is a late complication where the cornea becomes less clear due to deposits in the tissue, usually peaking 1-2 months after surgery and disappearing within 6-12 months. It can be treated using certain types of medication. The risk of corneal haze is higher in patients with extreme near-sightedness or far-sightedness.

What Else Should I Know About Photorefractive Keratectomy?

Patients generally experience good long-term vision after undergoing PRK, a type of laser eye surgery. According to one study, 15 years after the surgery, more than half of the treated eyes had a vision within one diopter (measurement unit of the lens’ power) of normal, and 85% were within two diopters. Improvements in the laser used for the procedure and a new technique involving the edge of the eye have helped make the results more predictable.

When comparing LASIK and PRK, two types of laser eye surgeries, research shows that they are equally effective for treating mild to moderate nearsightedness in the long run. They both have the same level of accuracy and risks. However, LASIK usually has a shorter healing period and causes less pain after the operation. PRK has a higher chance of causing haze, a cloudiness or loss of transparency in the cornea, likely due to damage to the cornea’s outermost layer. For patients with farsightedness, there isn’t strong evidence to recommend one procedure over the other.

Frequently asked questions

1. What are the potential risks and complications associated with Photorefractive Keratectomy (PRK)? 2. How long is the recovery period after PRK surgery and what can I expect during this time? 3. Will I experience any pain or discomfort during or after the PRK procedure? What can be done to manage this? 4. What are the expected outcomes and success rates for PRK in treating my specific vision problem? 5. Are there any alternative treatment options to PRK that I should consider?

Photorefractive Keratectomy (PRK) will affect you by reshaping the surface of your cornea using an excimer laser. The top layer of the cornea, called Bowman's layer, will be completely removed before the laser is used. After the surgery, your cornea will heal itself as fibroblast cells move to the area and rebuild the corneal layer using collagen.

You may need Photorefractive Keratectomy (PRK) if you have certain conditions or concerns that prevent you from getting other types of laser eye surgery. PRK may be recommended if your vision prescription has not changed more than +/- 0.5 D in the last year. However, there are certain conditions that absolutely prevent someone from getting PRK, such as significant cataract, unstable glaucoma, external eye diseases like blepharitis, dry eye syndrome, allergies, abnormalities of the cornea, and systemic connective tissue diseases like lupus or rheumatoid arthritis. PRK is also not recommended for pregnant or nursing women, those with only one functioning eye or other vision-limiting eye conditions, excessively curved or irregularly shaped corneas, uncontrolled dry eye, uveitis, or glaucoma. If you have a history of herpes simplex keratitis, you may be able to have PRK after taking antiviral medicines for a few months. Patients with poorly controlled diabetes or those taking medications known to have harmful effects on the eye are generally advised to avoid laser eye surgery.

You should not get Photorefractive Keratectomy (PRK) if your vision prescription has changed more than +/- 0.5 D in the last year, if you have conditions such as cataracts, unstable glaucoma, external eye diseases, corneal abnormalities, systemic connective tissue diseases, or if you are pregnant or nursing. Additionally, caution should be taken if you have only one functioning eye, excessively curved or irregularly shaped corneas, uncontrolled dry eye, uveitis, glaucoma, a history of herpes simplex keratitis, poorly controlled diabetes, or if you are taking medications known to have harmful effects on the eye.

The recovery time for Photorefractive Keratectomy (PRK) can vary, but it typically takes about 1 to 3 weeks for the surface of the cornea to heal. During this time, patients may experience discomfort, dryness, and blurry vision. It can take several months for vision to stabilize and for the full benefits of the surgery to be realized.

To prepare for Photorefractive Keratectomy (PRK), the patient should rest in a relaxed position with their legs uncrossed and their neck straight. Breathing should be shallow and slow. The patient's medical history and current medication list will be checked, and the doctor will perform various examinations and measurements of the eyes to ensure the patient is a suitable candidate for the surgery. The patient should also be given all the necessary information about the procedure, its expectations, and potential risks.

The complications of Photorefractive Keratectomy include minor pain or discomfort, dry eyes, infection in the cornea, delayed healing of the cornea, pseudodendrites, halo effect, central corneal islands, ectasia, decentration, persistent corneal erosion, and corneal haze.

There are no specific symptoms mentioned in the text that would require Photorefractive Keratectomy (PRK). PRK is a surgical option for people with nearsightedness, astigmatism, and farsightedness within certain diopter levels, or for those who have specific eye conditions or have undergone other eye surgeries. It is not based on symptoms, but rather on the specific vision problems or conditions that a person may have.

Photorefractive Keratectomy (PRK) is generally avoided in women who are pregnant or nursing. Hormonal changes during pregnancy can influence the vision prescription, and medications given after the surgery may affect the fetus or nursing infant. Therefore, it is considered a bit risky and not recommended during pregnancy.

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