Comparison of Four Laser Refractive Surgery Procedure: SILK, ReLEx SMILE, Femtosecond LASIK, and SBK LASIK

With advancements in ophthalmic technology, laser vision correction procedures have become safer, more precise, and faster in recovery. SILK, developed by Johnson & Johnson Vision, is an innovative technique alongside established procedures like ReLEx SMILE and LASIK (including Femtosecond and SBK variants). This article compares their surgical procedure, advantages, and limitations to help patients make informed decisions.

1. Surgical Procedure

• SILK (Smooth Incision Lenticule Keratomileusis): Utilizes the latest-generation femtosecond laser (ELITA) to create a biconvex lenticule within the cornea, which is removed through a small 2 mm incision to correct refractive errors.
• ReLEx SMILE: Uses a femtosecond laser (VisuMax) to create a lenticule within the cornea, then removes the tissue via a 2 mm incision without creating a corneal flap.
• Femtosecond LASIK: Uses a femtosecond laser to create a corneal flap, followed by excimer laser ablation to reshape the cornea, correcting refractive errors.
• SBK LASIK: Uses a Moria SBK microkeratome to form a corneal flap, followed by excimer laser ablation to correct refractive errors.

2. Treatment Thresholds

Each surgical method has specific indications and limitations based on the degree of refractive error and corneal thickness, as presented in the table below:

3. Incision Length

• SILK & ReLEx SMILE: Small incision of 2-4 mm for lenticule removal.
• Femtosecond LASIK & SBK LASIK: Corneal flap with a circumference of ~18-20 mm.

4. Duration of the Procedure

All procedures are outpatient-based:

• SILK: Approximately 16 seconds of laser exposure per eye.
• ReLEx SMILE: Approximately 23 seconds of laser exposure per eye.
• Femtosecond LASIK: Approximately 1.3 seconds of laser per diopter treated.
• SBK LASIK: The full procedure takes around 15–20 minutes.

5. Advantages of Each Method

SILK is an advanced refractive surgery method utilizing the latest laser technology, with the following notable features:

• Lowest laser energy: Minimizes thermal impact on corneal tissue, protecting eye structure and reducing heat-related damage.
• Smallest laser spot: Reduces corneal tissue trauma, helping to minimize postoperative dry eye.
• Fastest pulse frequency: Enables smooth and precise incisions, reducing mechanical stress during tissue separation.
• Biconvex lenticule design: Reduces impact on corneal nerves, improving postoperative visual quality.

ReLEx SMILE is an advanced refractive surgery technique using subsurface laser cutting with minimal invasion, offering the following benefits:

• No corneal flap: Reduces postoperative discomfort, shortens recovery time, and provides clear vision.
• Advanced subsurface cutting: Preserves corneal tissue and maintains surface epithelial integrity, preserving the natural corneal structure.
• Small incision: Minimizes corneal surface impact, reducing the risk of dry eye, infection, and complications such as foreign body sensation or halos post-surgery.
• High and stable visual quality: Postoperative vision is typically sharp, consistent, and stable over time.

Femtosecond LASIK is a fully laser-based refractive surgery method, offering high precision and safety:

• Corneal flap creation with femtosecond laser: Allows precise cutting aligned with the eye’s natural curvature, preserving structure and reducing complications.
• High safety and efficacy: Precise control of cutting depth and position ensures stable refractive correction and significantly improved vision post-surgery.

SBK LASIK is a widely applied and clinically proven refractive surgery method, with the following advantages:

• Lower treatment cost compared to other advanced methods: Increases accessibility for a broader range of patients.
• Clinically proven efficacy: Used globally for decades, demonstrating stable and safe vision correction outcomes.

SBK LASIK

• Cost-effective and clinically proven over decades.
• Widely accessible modality with a strong safety track record globally.

6. Visual Recovery

The SILK, ReLEx SMILE, Femtosecond LASIK, and SBK LASIK methods all offer rapid visual recovery with short postoperative periods. Typically, patients can resume normal work and study within 24 hours.

• SILK: Thanks to advanced laser technology with low energy, small laser spot, and fast pulse frequency, SILK enables patients to achieve optimal vision quickly. In some cases, due to the lenticule removal mechanism, patients may experience a temporary foggy vision effect, which resolves as the corneal layers fully heal.
• ReLEx SMILE: Similar temporary foggy vision may occur but resolves quickly as the cornea heals.
• Femtosecond LASIK & SBK LASIK: Recovery may be slightly slower than SILK and ReLEx SMILE due to corneal flap creation and a larger incision circumference.

7. Limitations

• SILK & ReLEx SMILE: Higher costs due to more advanced technology. Temporary foggy vision may occur post-surgery due to lenticule removal. These methods do not treat hyperopia, only suitable for patients with myopia or astigmatism within treatment thresholds.
• Femtosecond LASIK & SBK LASIK: Due to corneal flap creation, there is a higher risk of complications such as flap displacement or wrinkling if postoperative care is inadequate. Dry eye incidence is higher, and visual recovery is slower compared to SILK or SMILE.

8. Regression Rate

• Femtosecond LASIK & SBK LASIK: Regression rates range from 1-2%, remaining within safe limits and providing stable visual outcomes.
• SILK & ReLEx SMILE: Extremely low regression rates, below 1%. Advanced laser technology allows precise corneal intervention, unaffected by environmental factors such as temperature or humidity in the operating room. Additionally, laser exposure time is independent of the degree of myopia, ensuring high accuracy, stable results, and minimal regression risk.

These advantages enable the methods to deliver superior outcomes, helping patients maintain sharp vision over the long term.

9. Conclusion

Each laser refractive surgery method – SILK, ReLEx SMILE, Femtosecond LASIK, and SBK LASIK – has distinct mechanisms, advantages, and treatment limitations. The choice of the most suitable method depends on various factors, including refractive error, corneal thickness, eye health, and individual patient conditions.

To ensure safety and achieve optimal treatment outcomes, patients should undergo a comprehensive examination with a refractive surgery specialist to make the most appropriate decision based on their current eye condition and needs.