The Difference Between LASIK and PRK

The Difference Between LASIK and PRK

If you’re one of the many bespectacled or be-contact-lensed individuals who have considered your options for no longer being bespectacled or be-contact-lensed, it’s likely you’ve come across the terms LASIK and PRK before. Though the ultimate goal of both laser eye surgery techniques is the same – to render you without spectacle nor contact lens (at least for a period of time) – LASIK and PRK differ on several points.

The Similarities Between LASIK and PRK

Because looking for ways in which we are the same is generally better than pointing out the ways we’re different, let’s start with this.

Both LASIK (laser assisted in situ keratomileusis) and PRK (photorefractive keratectomy) are laser-based methods of refractive surgery. Refractive surgeries are procedures that correct the refractive error of an eye. Refractive errors are more commonly known as conditions such as far-sightedness (hyperopia), near-sightedness (myopia), and astigmatism. In addition to laser eye surgery, other refractive procedures that don’t involve a laser tool include implantable contact lenses and refractive lens exchange.

Both LASIK and PRK work on the premise of reshaping the cornea. The cornea is the clear dome of tissue at the front surface of the eye; behind it you see the colored iris with the black pupil at the center. The cornea and the thin layer of tear fluid that covers it are responsible for the majority of the bending (or refraction) of light as it enters the eye. Accurately bending light such that it focuses to a sharp point on the retina is as crucial for clear vision as bending the soccer ball like Beckham is to winning matches. In far-sightedness, the focus of light is too late, coming to a point behind the retina. In near-sightedness, light comes to a point too early, in front of the retina. In astigmatism, everything is blurry and light actually focuses at two separate points due to an uneven cornea bending different planes of light to different degrees.

The laser tool used in both the LASIK and PRK laser eye surgery techniques vaporizes selective areas of corneal tissue to change its curvature. By modifying the shape of the cornea, the refracted path of light is adjusted to come to a clear focal point right on the retina. The result is clear vision without needing eyeglasses or contact lenses.

Both techniques are considered to be generally safe, effective methods of surgical vision correction, but both have their own pros and cons. Some people may be suitable for either LASIK or PRK, while others may be steered towards one that is deemed safer by their eye surgeon.

LASIK vs PRK: Technique

While both LASIK and PRK involve the use of an excimer laser tool for reshaping the cornea under a local anesthetic, they differ significantly on the finer details of the procedure.

LASIK starts with creating a flap of the outermost corneal layers. Out of the five layers that make up the cornea – epithelium on the outer surface, Bowman’s layer, stroma, Descemet’s membrane, and endothelium facing the iris – the corneal flap is thick enough to include all those top layers plus some stromal tissue. This flap of corneal tissue can be created either using a bladed instrument called a microkeratome, or another laser tool called a femtosecond laser. Either way, the flap is not removed entirely but is left connected to the eye via a small hinge of tissue. Opening the flap allows the surgeon to apply the excimer laser to the remaining corneal stroma for the reshaping process. Once this computer-guided step is complete, the flap is placed back over the newly sculpted cornea and allowed to self-seal during the healing process.

Conversely, PRK involves removing only the topmost layer of cells from the cornea, the epithelium, in a process called debridement. There are a number of ways to perform epithelial debridement, including using a handheld tool to scrape off the tissue, using a chemical solution, or with the excimer laser. Once the epithelium is out of the way, the excimer laser can perform its best work on your eyes. At the end, a bandage contact lens is placed over your naked corneas until the epithelial layer can regenerate.

LASIK vs PRK: Eligibility Criteria

LASIK and PRK share much of the same factors that surgeons look for in a suitable candidate:

  • Over the age of 18 (an indication that your eyes are likely to have stopped growing)
  • A refractive error that has been stable for at least the last year
  • No other significant eye diseases that affect your vision (which would limit the effectiveness of laser eye surgery)
  • No systemic diseases that may affect your ability to heal
  • Not pregnant, breastfeeding, or going through any other major hormonal changes (as this has the potential to temporarily affect your prescription)

The treatment range for both PRK and LASIK are roughly the same:

  • Near-sightedness of approximately -1.0 to -12.00 diopters
  • Far-sightedness up to approximately +5.0D
  • Astigmatism up to approximately -3.0D

A major factor that separates those suitable for LASIK or for PRK is the thickness of the cornea. Remember the corneal flap created as part of the LASIK procedure? And how cutting out this flap takes a little nibble of the corneal stroma? To retain the stability of the cornea post-operation, there is a minimum requirement for the remaining corneal tissue after laser eye surgery. The higher your prescription, the more corneal tissue that needs to be removed to correct your vision. If your corneas are not thick enough to leave the minimum amount of tissue after LASIK, it may mean PRK is your only option. Since PRK only involves debriding the epithelium, there’s more stromal tissue to work with without compromising the corneal post-op integrity. However, in the case of exceptionally thin corneas, it could be possible you’re ineligible for either PRK or LASIK.

There are a few other factors that may cause you to lean one way or the other. People with dry eyes are better served with PRK as the flap created in LASIK can exacerbate (or instigate) dry eye. For people whose hobbies or occupation involve a risk of head or face trauma (contact sports, armed forces, etc), PRK may be the better option to avoid the potential of the LASIK flap dislodging or dislocating. Conversely, if the idea of a short recovery time is appealing, LASIK trumps over PRK.

LASIK vs PRK: Recovery

The road to recovery is much faster in LASIK compared to PRK. Vision can be clear within as little as a few hours after LASIK and most people can return to their normal low-intensity activities the following day. In PRK, the initial recovery to functional vision typically takes a few days, and it may be closer to a week before you can go back to work. Some people feel that their vision is only truly sharp after about a month.

Both LASIK and PRK involve some light sensitivity, and irritation or burning of the eyes immediately after the operation, however, this discomfort lasts for longer with PRK. Fortunately, this irritation can typically be managed with over-the-counter pain medications and lubricant eye drops.

For full recovery, it can take a few months for the cornea and vision to stabilize completely.

Post-op guidelines during the recovery period are similar for both PRK and LASIK. In general, they include:

  • Avoid heavy lifting or intense activities after your procedure
  • Use your eye drop medications
  • Keep the eye area clean, avoiding dust and debris
  • Avoid swimming pools, spas and saunas
  • Be on the look out for any decrease to your vision, discharge from the eye, or increasing eye redness – if you notice any of these, contact your surgeon immediately; don’t wait for your next scheduled review appointment

Bespectacled and be-contact-lensed individuals interested in being as such no longer can consider reaching out to a refractive eye surgeon. An initial examination can tell you whether LASIK or PRK might be more suitable for you. If neither is ideal, fear not, there are still other refractive surgery options to consider.