Refractive Surgery

What Is Refractive Surgery?

Refractive surgery refers to a group of surgical procedures designed to correct refractive errors of the eye, thereby eliminating or reducing the need for glasses or contact lenses. These errors include:

Myopia (nearsightedness—difficulty seeing objects at a distance).

Hyperopia (farsightedness—difficulty seeing objects up close).

Astigmatism (distorted vision caused by an irregular corneal shape).

Presbyopia ("age-related vision loss"—the loss of the ability to focus on near objects, typically occurring after age 40).

How Does It Work?

The eye focuses light through the cornea and the crystalline lens. If the shape of these structures is not ideal, light does not focus correctly on the retina, resulting in blurred vision.

Refractive surgery works in two primary ways:

• By modifying the cornea (using a laser or other techniques).

• By replacing or adding an intraocular lens (in cases involving high prescriptions or when the cornea is not suitable for other procedures).

Types of Refractive Surgery

1. Corneal Refractive Surgery (Ablative)

This approach uses a laser (excimer or femtosecond) to reshape the cornea and correct how the eye focuses light.

Common techniques include:

• PRK (Photorefractive Keratectomy): Involves removing the corneal epithelium and applying a laser to the underlying stroma.

• LASIK: Involves creating a corneal "flap," applying a laser, and then repositioning the flap.

• SMILE: Involves removing a small piece of corneal tissue (a lenticule) without creating a flap (a minimally invasive procedure).

Advantages:

• Rapid recovery (especially with LASIK and SMILE).

• Effective for myopia, hyperopia, and astigmatism.

Limitations:

• Not suitable for thin corneas or cases of keratoconus.

Does not fully correct presbyopia. Evolution of Ablative Refractive Surgery: From the 1st to the 3rd Generation

Refractive surgery has evolved dramatically since its inception, transitioning from invasive techniques with unpredictable outcomes to precise, minimally invasive, and personalized procedures. Below, we detail the three generations of ablative surgery and their impact on the correction of visual defects (myopia, hyperopia, astigmatism, and presbyopia).

Radial Keratotomy (RK) – Scalpel-based Surgery

Years: 1970–1990.

Technique: Radial incisions made with a diamond scalpel to flatten the cornea and correct myopia.

Limitations:

• Serious complications: Corneal ectasia, induced hyperopia, and opacities.

• Unpredictable results: Dependent on the manual healing process.

• Legacy: Now obsolete; it remains a cause for corneal transplants.

1st Generation: PRK (Photorefractive Keratectomy) – Excimer Laser Surgery

Years: 1990s.

Technique: Use of an excimer laser to reshape the corneal surface (without incisions).

Advantages:

• More precise than Radial Keratotomy (RK).

• No risk of corneal rupture.

Disadvantages:

• Postoperative pain.

• Slow recovery (up to 1 month).

• Current Status: Still used for thin corneas or in cases following prior RK.

2nd Generation: LASIK (Laser-Assisted In Situ Keratomileusis) – Excimer Laser Surgery

Year: 1991 (revolutionized in the 2000s).

Technique:

Creation of a corneal flap (using a microkeratome or a femtosecond laser). Application of an excimer laser to the stroma to reshape the cornea.

Advantages:

• Rapid recovery (24–48 hours).

• Less pain than PRK.

• Corrects myopia, hyperopia, and astigmatism.

Limitations:

• Risk of flap-related complications (dislocation, "wrinkled flap" syndrome).

• Not suitable for thin corneas or keratoconus.

3rd Generation: Lenticular Surgery (SMILE, SmartSight, and others; surgery using a femtosecond laser).

Techniques that eliminate the use of an excimer laser and avoid the creation of a corneal flap.

A. SMILE (Small Incision Lenticule Extraction)

Year: 2011 (FDA-approved in 2016).

Technique:

A femtosecond laser creates an intrastromal lenticule (no flap).

The lenticule is extracted through a 2–4 ​​mm micro-incision.

Advantages:

• No flap: Lower risk of ectasia and dry eye.

• Safer for thin corneas.

• Recovery similar to LASIK.

Limitations:

• Does not treat hyperopia (only myopia and astigmatism).

• Requires a higher level of surgical expertise.

B. SmartSight (A technique similar to SMILE, but with greater customization)

Differences:

Uses advanced algorithms to adapt to irregular corneas.

Greater precision for high levels of astigmatism.

Lenticular surgery results in less dry eye compared to LASIK (30% fewer cases).

The Future of Ablative Refractive Surgery

More precise lasers (customization based on aberrometry).

Combined techniques (e.g., SMILE + crosslinking for early-stage keratoconus).

Artificial intelligence for surgical planning. What Is the Best Option for Ablative Refractive Surgery Today?

✔ Thick corneas and high prescriptions: LASIK.

✔ Thin corneas and dry eye: SMILE.

✔ Maximum safety without a flap: Advanced PRK (TransPRK).

2. Intraocular Lens Surgery (Non-Ablative)

A lens is implanted inside the eye without altering the cornea.

Types of lenses:

• Phakic (ICL): Placed without removing the eye’s natural lens (ideal for high myopia or thin corneas).

• Pseudophakic: Replace the eye’s natural lens (as in cataract surgery).

  • Monofocal: Focus at one distance (far).

  • EDOF

  • Multifocal