What are the advantages of SMILE (Small Incision Lenticule Extraction) over PRK (Photorefractive Keratectomy) for vision correction?

Advantages of SMILE Over PRK for Vision Correction

SMILE (Small Incision Lenticule Extraction) offers better ocular surface outcomes, faster recovery time, and less postoperative discomfort compared to PRK (Photorefractive Keratectomy), while maintaining similar visual outcomes and potentially better biomechanical stability for high myopia patients.

Comparative Advantages of SMILE vs PRK

Recovery and Comfort

• SMILE provides intermediate recovery time between PRK and LASIK, but significantly faster than PRK 1
• PRK has the longest recovery time and most uncomfortable postoperative experience among the major refractive procedures 1
• PRK patients may experience significant pain during the first 24-72 hours post-procedure, while SMILE patients typically experience minimal discomfort

Corneal Biomechanics and Stability

• SMILE demonstrates superior corneal biomechanical strength compared to LASIK, and comparable strength to PRK/LASEK 2
• PRK has traditionally offered the strongest biostability, but SMILE provides comparable biomechanical outcomes without the drawbacks of surface ablation 1
• SMILE appears to have a lower rate of ectasia than both LASIK and PRK, though it's not completely protective against ectasia 3

Visual Outcomes

• Both procedures show similar effectiveness in correcting myopia, with comparable uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) 4
• In high myopia correction (>-6.00D), SMILE may have particular advantages over other procedures 3
• SMILE performs better in mesopic conditions (low light) for high myopia correction, while PRK may have advantages in photopic conditions 5

Complications and Side Effects

• PRK carries a risk of corneal haze that is not present with SMILE 1
• SMILE avoids the epithelial healing issues associated with PRK, reducing infection risk
• SMILE complications are primarily associated with surgeon inexperience and include difficulties with lenticule extraction 3

Corneal Higher Order Aberrations (C-HOAs)

• For moderate myopia, SMILE induces less increase in total C-HOA, coma, and spherical aberration in the 6-mm zone compared to PRK 5
• For high myopia, SMILE shows less increase in mesopic spherical aberration but greater increase in photopic total C-HOA and trefoil compared to PRK 5

Clinical Considerations for Patient Selection

Ideal Candidates for SMILE

• Patients with moderate to high myopia, especially those with refractive error >-6.00 diopters 3
• Patients who cannot tolerate prolonged recovery time or postoperative discomfort
• Patients with concerns about corneal haze
• Patients with active lifestyles who need quicker visual recovery

Limitations of SMILE

• SMILE lacks cyclotorsion-compensation system, eye-tracking system, and customized treatment profile for high astigmatism or irregular corneal surface 1
• SMILE has a longer learning curve for surgeons compared to PRK 3
• Limited options for retreatment compared to PRK

Long-term Outcomes

• Long-term studies (minimum 5 years for SMILE, 10 years for PRK) show that both procedures maintain high levels of safety with rare late complications 6
• Neither procedure shows clear superiority in direct long-term comparisons 6
• Both procedures demonstrate good stability within recommended indications 6

Management of Irregular Astigmatism

• For patients with irregular astigmatism, thorough evaluation with corneal topography/tomography is essential before any refractive procedure 7
• PRK with topography-guided ablation may be more suitable for treating specific patterns of irregular astigmatism 7
• SMILE is generally not recommended as first-line treatment for irregular astigmatism due to lack of customized treatment profiles 1

Practical Recommendations

• For patients prioritizing faster recovery and minimal discomfort: Choose SMILE over PRK
• For patients with high myopia (>-6.00D): SMILE may offer better outcomes
• For patients with irregular corneal surfaces or high astigmatism: Consider PRK with topography-guided ablation
• For patients concerned about corneal biomechanics: Both procedures offer good stability, with SMILE potentially offering advantages for higher corrections

Both procedures have proven long-term safety and efficacy, with the choice between them depending primarily on patient-specific factors including refractive error magnitude, recovery time preferences, and corneal characteristics.