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Photo Refractive Keratectomy

Photo Refractive Keratectomy 

Did you read the above, roll your eyes and say to yourself, “What in the world does this mean?” Don’t go hunting for that alien-human translation dictionary yet…

What is Photo Refractive Keratectomy?

PRK is a Laser eye Surgery, the lesser known cousin of LASIK and is done to give you freedom from glasses or contact lenses.

When is PRK indicated?

It can be used in mild to moderate degrees of near-sightedness, far-sightedness and astigmatism (a vision condition that causes blurred vision).

 1. Age 18 years or older
 2. Stable refraction error: Change in refraction of less than or equal to 0.5 Diopters /year for at least 1 year before surgery.
 3. -1.0 to -6.0 Diopters of Myopia
 4. 0.75 to 3.0 Diopters of Astigmatism
 5. +1.0 to +4.0 Diopters of Hyperopia
 6. Correction of refractive errors after other eye surgery (However, Lasik is generally chosen over PRK)
 7. Corneas previously treated with Lasik.

When is PRK Contra-indicated?

1. Systemic auto-immune or immune-deficiency disorders (e.g., Collagen vascular diseases, Diabetes, Rheumatoid Arthritis)
2. Eye disease (e.g., Dry eye, Glaucoma, Granular corneal dystrophy type II)
3. History of side effects from steroids
4. Pregnancy or Breast feeding
5. Medications like isotretinoin or amiodarone.

How does PRK work?

 

 

PRK uses an excimer laser beam (which is a laser that emits ultra violet light) to reshape the surface layer of your cornea. This helps to change the curvature of the cornea, enabling light rays to focus onto your retina thus helping you achieve clear vision.

With nearsighted people, the aim is to flatten the too-steep cornea; with farsighted people, a steeper cornea is required. In astigmatism, it smoothens an irregular cornea into a more normal shape.

The top most layer of the cornea (called the epithelium) is gently removed using alcohol or blade. Excimer laser treatment is then performed to ablate (remove by vaporisation) the outermost layer below the epithelium (called the anterior stroma). Fascinating isn’t it?

The cornea is then covered with a bandage contact lens. Over the next 1 to 3 days, the surface cells gradually grow back over the central cornea and vision improves. During this time, there is a little irritation to the eyes as the surface cells regenerate.

What is the procedure exactly?

Before PRK:

Your doctor will examine your eyes to determine exactly how much laser ablation is needed and what kind of vision correction you require.

During PRK:

You walk into the surgery centre, have PRK and walk out again. In fact, the actual surgery usually takes only a few minutes, and you're awake the whole time.

Did you just go: Awake?!! Your eyes are anesthetized with special drops and you do not feel any pain. A kind of retainer is placed to keep your eyelids open — which is not uncomfortable.

The doctor uses a computer to adjust the laser for your eye. You will be asked to look at a target light for a short time while he scans your eye through a microscope.

The laser machine will make a steady clicking sound as the laser painlessly reshapes your cornea, and you may notice a slight odour during the tissue removal. Don't worry, that's normal.

If you're having both eyes done the same day, the surgeon will probably do the other eye after a short while.

After PRK:

After a little rest, you are all good to go home (escorted). Once home, relax for at least a few hours.

It is advisable to take a couple of days break from work. It is also advisable to avoid strenuous exercise for a week, as this can traumatize the eye and affect healing.

Use all prescribed medications (antibiotics and anti-inflammatory drops) as directed and call your doctor immediately if you suspect a problem.

Avoid rubbing your eye. Your eye doctor will examine your eye the day after surgery and few times thereafter to ensure proper healing. Your vision can fluctuate for as long as up to six months after surgery.

A peek into History:

The first PRK was done in 1987 by Dr Theo Seiler in Germany.  Yes, it’s that old!

PRK v/s Lasik:

PRK is less invasive than Lasik as PRK only alters the surface of the cornea without the creation of a flap through the substance of the cornea. Thus, PRK does not create the risk of dislocated corneal flaps which may occur due to trauma after Lasik. This is important for people engaged in activities like boxing and martial arts that have eye injury risks.

PRK remains useful for treating patients with corneas too thin to perform LASIK and when treating a refractive error associated with an uneven corneal surface

PRK has more discomfort and a longer healing process as compared to Lasik.

There also is a greater risk of eye infection after PRK compared with LASIK, and a greater risk of temporary or permanent haziness of the cornea affecting vision.

However, studies show that visual results of PRK and LASIK 6 months after surgery are comparable.

What are the possible Complications?

-Delayed healing period
-Corneal Haze: In many cases it does not affect the visual acuity.
-Night glare (starbursts or halos that are most noticeable when viewing lights at night).
-Under- or over-correction especially in those with severe myopia
-Increased Intra-ocular pressure which reverts to normal after stopping steroids.
-Steroid induced herpes simplex keratitis.
-Corneal Melting and Perforation: This occurs in patients with connective tissue diseases.
-Reduced best corrected visual acuity (BCVA). However, PRK results in improved BCVA about twice as often as it causes a loss.

However, technical improvements in the design of excimer machines like eye-tracking devices have minimized complications.

What is my Prognosis?

In myopic PRK, refractive stability achieved at 1 year was maintained up to 12 years.

After hyperopic PRK, refractive stability achieved at 1 year was maintained up to 7.5 years.

PRK for severe anisometropic amblyopia in children resulted in long-term stable reduction in refractive error and improvement in visual acuity.