Crosslinking + PRK / PTK: Trans-PRK/CXL – Healing keratoconus & correcting visual defects at the same time

The treatment of keratoconus is no longer just about stopping the disease – modern procedures such as Trans-PRK/Crosslinking offer the possibility of significantly improving vision at the same time. The combination of crosslinking, which stabilizes the cornea, and PTK or PRK, which corrects the shape of the cornea, can not only prevent the progression of the disease, but also optimize vision. In this article, you will learn how this innovative treatment works, who it is suitable for and the impressive benefits it offers – from improving visual acuity to long-term stabilization of the cornea.

What is PRK or PTK + CXL?

PRK (Photorefractive Keratectomy) and PTK (Phototherapeutic Keratectomy) are both procedures that use the excimer laser to treat the top layer of the cornea, but with different goals:

• PRK (photorefractive keratectomy): This is a refractive laser treatment used to correct refractive errors such as nearsightedness, farsightedness and astigmatism. The excimer laser is used to reshape the cornea and improve the refraction of light so that the light is correctly focused on the retina. It is an alternative to other refractive procedures such as LASIK. With PRK, the corneal epithelium is removed before the laser sculpts the underlying tissue. After the treatment, the epithelium regenerates.
• PTK (phototherapeutic keratectomy): This procedure is mainly used to treat corneal diseases such as corneal scars, corneal dystrophies or irregular corneal surfaces. The aim of PTK is to smooth the surface of the cornea and remove irregularities in order to improve the quality of vision. As with PRK, the epithelium is removed and the excimer laser is used precisely to remove or smooth pathological tissue.

Both procedures can be performed in combination with corneal crosslinking (CXL) to stabilize the cornea and improve long-term treatment outcomes for conditions such as keratoconus.

What is CXL (Corneal Crosslinking)?

Corneal Crosslinking (CXL) is a treatment developed to strengthen and stabilize the cornea in progressive conditions such as keratoconus. The process uses a combination of riboflavin eye drops (vitamin B2) and UV light to strengthen chemical bonds between the collagen fibers in the cornea (called “crosslinks”). The aim is to make the cornea stiffer and prevent the progression of deformation.

How does the combination of PRK/PTK and CXL work?

The combination of PRK/PTK with crosslinking is often used in the treatment of keratoconus or other corneal diseases. The main reason for combining the procedures is to normalize the corneal shape and at the same time increase stability through crosslinking.

• In the PRK/CXL combination, the excimer laser is first used to reshape the cornea (PRK) by removing the epithelium and sculpting the underlying cornea. This is followed by crosslinking to “freeze” the new shape of the cornea and stop the progression of the disease. This offers an improvement in both visual acuity and corneal stability.
• In the PTK/CXL combination, PTK is used to treat irregular areas of the cornea and then crosslinking is performed to strengthen the cornea.

How does it differ from conventional crosslinking?

The difference between the combination of PRK or PTK with crosslinking (CXL) and ordinary crosslinking (CXL) lies mainly in the functionality and treatment goal of the combined procedures. Here are the main differences:

1. aims of the treatment

• Common crosslinking (CXL):
  • Objective: The main function of traditional crosslinking is to stabilize the cornea and stop the progression of keratoconus or other ectatic diseases (such as corneal deformities).
  • No attempt is made to actively change the shape of the cornea or correct visual defects. The CXL “freezes” the cornea in its current state to prevent further damage.
  • Above all, it helps to prevent the progression of the disease, but the deformation of the cornea that has already occurred largely remains.
• Combination PRK/PTK with crosslinking (CXL):
  • Objective: This combination stabilizes the cornea (as with ordinary CXL), but in addition the cornea is sculpted by laser treatment to normalize the corneal shape and improve visual defects.
  • PRK or PTK helps to smooth or correct the irregularities of the corneal surface. Crosslinking then stabilizes the reshaped cornea to ensure that the improvements last and the condition does not deteriorate further.

2. vision correction

• Common crosslinking (CXL):
  • Visual acuity does not usually improve significantly after CXL treatment alone, as it is primarily aimed at stabilizing the structure of the cornea, not correcting it.
  • Patients often have to continue wearing contact lenses or glasses to correct the visual impairment caused by keratoconus.
• Combination PRK/PTK with crosslinking (CXL):
  • This combination can lead to better visual acuity, as PRK or PTK smoothes the corneal surface and improves its shape, which can optimize vision in glasses or contact lenses.
  • Transepithelial PRK (TransPRK) is designed to remove minimal tissue depths, which is particularly important for patients with keratoconus as their corneas are often already thin. The combination of PRK and CXL therefore not only improves the quality of vision, but also provides the necessary stability.

3. procedure and approach

• Common crosslinking (CXL):
  • The epithelium (the uppermost cell layer of the cornea) is either removed(Epi-off CXL) or left in place(Epi-on CXL), and then riboflavin (vitamin B2) is applied to the cornea. The cornea is then irradiated with UV light to promote crosslinking.
  • There is no additional treatment of the corneal surface or refractive error.
• Combination PRK/PTK with crosslinking (CXL):
  • In this method, the cornea is first sculpted using an excimer laser:
    • PRK smoothes and shapes the cornea to correct vision defects such as short-sightedness, long-sightedness and astigmatism.
    • PTK smoothes the cornea and treats irregularities (such as scars or dystrophies).
  • After the laser treatment, crosslinking is performed to stabilize the newly formed cornea and prevent further deformation.

4. depth and extent of corneal treatment

• Common crosslinking (CXL):
  • In CXL treatment, the entire cornea is treated evenly with riboflavin and irradiated evenly with UV light. There is no targeted approach to influence certain areas of the cornea more strongly.
  • No cornea is removed or shaped.
• Combination PRK/PTK with crosslinking (CXL):
  • Here, the cornea is specifically shaped, in particular the conical deformation in keratoconus. The laser treatment removes the epithelium and precisely reshapes the underlying corneal tissue to improve the quality of vision.
  • This combined treatment makes it possible to selectively concentrate more UV energy on certain parts of the cornea (as in the case of the keratoconus tip), resulting in greater flattening and regularization of the corneal shape.

PRK/CXL Advantages

1. Stabilization of the cornea: Crosslinking prevents the progression of keratoconus by making the cornea stiffer and more stable through crosslinking.
2. Improved visual acuity: PRK smoothes and sculpts the cornea, which can lead to improved visual quality, especially in patients with irregular corneal surfaces.
3. Reduction of corneal deformations: PRK helps to reduce the deformation of the cornea in keratoconus and bring it closer to its normal shape.
4. Prevention of corneal transplants: The combination can often prevent the need for a corneal transplant, as the progression of the disease is halted and the quality of vision is improved.
5. Improving the quality of vision in spectacles/contact lenses: The treatment ensures better visual acuity in spectacles or contact lenses and often makes hard, gas-permeable lenses superfluous.
6. Long-term stability: CXL “freezes” the cornea reshaped by PRK, which ensures the long-term stability of the cornea.
7. No tissue removal: Compared to other refractive procedures, only a minimal amount of corneal tissue is removed, which is important for patients with thin corneas.
8. Treatment of advanced cases: PRK/CXL can also be used in advanced keratoconus to stabilize the cornea and alleviate vision problems.
9. Synergy effect: The combination of the two procedures has a reinforcing effect that leads to better results than if the procedures were carried out separately.
10. Prevention of further visual deterioration: CXL stops the progression of keratoconus, preventing further vision loss.

Who is this option best suited for?

PRK/CXL is particularly suitable for patients with keratoconus or other corneal deformities who require a combination of vision improvement and corneal stabilization. This method is ideal for people whose keratoconus is still progressive and who already have visual problems such as astigmatism, glare or ghost images. It is also suitable for patients with thin corneas where other refractive procedures such as LASIK are not possible, and for those who wish to halt the progression of the disease before a corneal transplant becomes necessary. PRK/CXL is also beneficial for patients who want to improve vision quality despite a stabilized cornea and reduce dependence on hard contact lenses.

Simultaneous procedure or separate interventions

Whether the simultaneous procedure (simultaneous performance of PRK and CXL) or separate procedures (first CXL, then PRK after a waiting period) is better depends on the individual circumstances of the patient. Both approaches have advantages and disadvantages:

Advantages of the simultaneous procedure:

1. Faster overall healing: The cornea only needs to heal once, as both procedures are performed in one session, which shortens the recovery time.
2. Stronger synergy effects: The combination of PRK and CXL in one step can lead to greater flattening of the cornea, which is particularly beneficial in the treatment of keratoconus.
3. Fewer procedures: Patients only have to undergo one procedure, which reduces stress and the number of visits to the doctor.
4. Efficient stabilization: Crosslinking immediately stabilizes the cornea reshaped by PRK, which reduces the risk of further deformation.

Advantages of separate interventions:

1. Safer corneal thickness: With a separate approach, the cornea can be fully stabilized after crosslinking before proceeding with PRK. This is particularly important for very thin corneas in order to increase safety.
2. Predictable results: Because the cornea has time to stabilize after crosslinking (12 to 18 months), refractive correction can be more precise.
3. Reduced risk of complications: Because crosslinking strengthens the corneal tissue before PRK, there is less risk of over-flattening or other biomechanical problems after refractive surgery.

The simultaneous procedure is ideal for patients who prefer fast treatment and healing and where the corneal thickness is sufficient. It offers a strong synergy between PRK and CXL and is particularly suitable for moderate cases of keratoconus.

Separate procedures are more suitable for patients with very thin corneas or when a stabilized cornea is desired before refractive work is performed. It is safer for advanced cases of keratoconus and for patients who expect more precise refractive results after stabilization.

The choice between a simultaneous or separate procedure should always be made in consultation with the ophthalmologist and based on the patient’s individual circumstances.

Alternatives to PTK/PRK and crosslinking

1. corneal crosslinking (CXL) alone

• Epi-off CXL: In this standard procedure, the corneal epithelium is removed to allow better uptake of riboflavin and deeper cross-linking. It is effective for stabilizing the cornea in early stages of keratoconus.
• Epi-on CXL: This method leaves the epithelium intact, resulting in faster healing and less discomfort. Epi-on CXL is a painless alternative, but may be less effective than Epi-off CXL. It is increasingly used for early or stable stages of keratoconus.

2. intracorneal ring segments (ICRS)

• ICRS are small, arc-shaped plastic implants that are inserted into the cornea to reduce the curvature of the cornea and improve the quality of vision. This procedure is an alternative for patients with moderate to advanced keratoconus who are either unsuitable for PRK or who require greater shape correction. ICRS can be combined with crosslinking to increase stability if required.

3. topography-guided PRK without CXL

• Topography-guided PRK is often used for refractive correction and to treat irregular corneal surfaces. In some cases, this can be performed without crosslinking if there is no risk of keratoconus progression, especially in patients with an already stable cornea.

4. phakic intraocular lenses (ICL)

• Phakic intraocular lenses (ICL) are soft, implantable lenses that are inserted into the eye without removing the natural lens. This option is suitable for patients with stabilized keratoconus and severe ametropia, where the cornea does not require further treatment but an improvement in visual acuity is desired.

5. corneal transplantation (keratoplasty)

• In very advanced cases of keratoconus, when other treatment options are not sufficiently effective, a corneal transplant (complete or partial) may be necessary. This involves replacing the diseased cornea with a healthy donor cornea. This is usually a last option for patients whose vision is severely impaired and who have no other treatment options.

6. glasses or contact lenses

• In early or stable stages of keratoconus, correction with spectacles or soft contact lenses may be sufficient. In advanced keratoconus, hard, gas-permeable contact lenses are often used to improve vision. This solution is non-invasive, but does not cure or stabilize the keratoconus.

What are the risks of trans-PRK/crosslinking?

Trans-PRK/Crosslinking carries some risks, but these are usually rare or temporary. The most common include pain and discomfort during the healing phase, which lasts around 5-7 days, as well as temporary visual disturbances such as blurred vision or halos. There is a risk of infection as the cornea is more sensitive after epithelial removal. Scarring and over- or undercorrection may occur in rare cases. Other risks include delayed epithelial healing, possible deterioration of vision due to inflammation or infection and rare cases of endothelial cell loss. Dry eyesor regression of the vision correction may also occur. Regular aftercare and precise postoperative care can minimize these risks.