If you have myopia, distant objects appear blurred because light entering the eye is focused in front of the retina rather than directly on it. Glasses and contact lenses correct this by changing how light enters the eye. SMILE eye surgery takes a different approach: it permanently changes the shape of the cornea so that incoming light is focused more accurately on the retina.
SMILE, or Small Incision Lenticule Extraction, uses a femtosecond laser to create a tiny piece of tissue called a lenticule within the cornea. The surgeon then removes this lenticule through a small incision. Removing the precisely shaped tissue changes the curvature and focusing power of the cornea, reducing myopia.
This article explains exactly how that process works and why removing a small amount of corneal tissue can improve distant vision. For a broader overview of the procedure, see the SMILE Eye Surgery guide.
First, What Happens in a Myopic Eye?
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
To understand how SMILE corrects myopia, it helps to understand how the eye normally focuses light. The cornea is the clear, curved surface at the front of the eye. Together with the natural lens inside the eye, it bends incoming light and directs it toward the retina at the back of the eye.
In a normally focused eye, light rays from a distant object converge on the retina, producing a clear image. In myopia, the eye's focusing system is too strong for its length, or the eyeball is relatively longer than the optical power of the cornea and lens requires. As a result, light from distant objects comes to a focus in front of the retina. The image reaching the retina is therefore blurred.
How Do Glasses Correct Myopia?
Myopia is usually expressed in negative diopters, such as -2.00 D or -5.00 D. Minus-powered glasses and contact lenses spread incoming light rays slightly before they enter the eye.
This compensates for the eye's excessive focusing power and moves the focal point backward onto the retina. SMILE works differently. Instead of placing an optical lens in front of the eye, it modifies the eye's own optical system by changing the shape of the cornea.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
How Does SMILE Change the Cornea?
The cornea provides a large proportion of the eye's focusing power. Even a carefully controlled change in its curvature can therefore produce a meaningful change in the eye's refractive power.
During SMILE, the femtosecond laser creates a precisely shaped lenticule inside the middle layer of the cornea, known as the stroma.
The lenticule has a thickness and shape calculated according to the refractive correction required. The surgeon then separates and removes it through a small incision.
Once the lenticule is removed, the corneal tissue above it settles into a new shape. This changes the curvature of the central cornea and reduces its refractive power. The result is that incoming light is redirected so that it can focus closer to the retina rather than in front of it.
What Is a Corneal Lenticule?
The word lenticule refers to a small, lens-shaped piece of corneal tissue. In SMILE, the femtosecond laser creates this tissue within the corneal stroma. The shape of the lenticule is not the same for every patient.
Its dimensions are planned according to the individual's refractive error and the desired correction. Think of it as a precisely designed piece of tissue that the surgeon needs to remove to alter the optical shape of the cornea.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
How Is the Lenticule Created?
SMILE uses a femtosecond laser, which creates extremely precise laser cuts within the cornea. The laser creates the boundaries of the lenticule inside the corneal tissue. It also creates a small opening that connects the treatment area with the surface of the cornea.
Unlike LASIK, SMILE does not require the creation of a large corneal flap. The lenticule is accessed through a small incision, generally around 2–3 mm in the commonly described SMILE technique.
The laser itself creates the tissue planes; the surgeon then carefully separates the lenticule from the surrounding cornea and removes it through the small opening.
What Happens When the Lenticule Is Removed?
This is the key step that corrects myopia. Before the procedure, the cornea has a particular curvature and refractive power. The lenticule represents a precisely calculated amount of tissue that needs to be removed to reduce that optical power.
Once the lenticule has been extracted, the central cornea becomes flatter. A flatter corneal surface bends incoming light less strongly. This reduces the eye's overall refractive power and shifts the focal point backward toward the retina.
In a successfully corrected myopic eye, distant light can therefore be focused much closer to the retinal surface, improving uncorrected distance vision.
Why Does Removing Such a Small Amount of Tissue Matter?
The cornea is highly sensitive to changes in shape. You do not need to remove a large amount of tissue to produce a significant change in refractive power. SMILE is designed to make a controlled alteration to the central cornea based on the patient's measured prescription.
The exact amount and geometry of the lenticule depend on factors such as the degree of myopia, the optical treatment plan and the characteristics of the individual cornea.
This precision is important because removing too much or too little tissue could result in an inaccurate refractive correction.
Does SMILE Remove the Natural Lens of the Eye?
No. This is an important distinction. SMILE changes the shape of the cornea. It does not remove or replace the natural lens inside the eye.
The procedure is therefore fundamentally different from lens-based procedures in which an artificial lens is placed inside the eye or the natural lens is removed.
What Happens to the Cornea After the Lenticule Is Removed?
After the lenticule has been removed, the small incision is left to heal naturally. There is no large corneal flap that needs to be repositioned, as there is with LASIK. The remaining corneal tissue assumes a new shape corresponding to the tissue that was removed.
Although the procedure changes the corneal structure permanently, the cornea remains a living tissue and continues to undergo biological changes after surgery. This is one reason why postoperative follow-up is important even when vision improves quickly.
How Quickly Does Vision Improve After SMILE?
Vision can become noticeably clearer soon after SMILE, but the speed of visual recovery varies between individuals. It is common for vision to fluctuate during the early healing period. Some patients may notice blurring, glare, halos or fluctuations in visual clarity initially, with these symptoms improving as the eye heals.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Final visual stability can take longer than the first noticeable improvement in sight. Your surgeon will monitor your vision during follow-up examinations to determine how the eye is healing and whether the refractive result is stabilizing.
Can SMILE Correct High Myopia?
SMILE can be used for a range of myopic prescriptions, but the exact limits depend on the laser platform, regulatory approval, and whether the patient's eyes meet the required safety criteria.
For example, current U.S. FDA labeling for the VisuMax system includes SMILE for specified ranges of myopia, with or without myopic astigmatism, in appropriately selected adults with stable refraction. The approved range has also been expanded through subsequent regulatory updates.
However, a prescription falling within an approved range does not automatically mean that SMILE is suitable. Corneal thickness and shape, ocular health, tear-film condition, refractive stability and other examination findings also matter.
How Is SMILE Different From LASIK in Correcting Myopia?
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
| Feature | SMILE | LASIK |
|---|---|---|
| How the cornea is reshaped | A corneal lenticule is created and removed | An excimer laser reshapes the exposed corneal tissue |
| Large corneal flap | No | Yes |
| Main laser technology | Femtosecond laser | Femtosecond or mechanical flap creation followed by an excimer laser |
| How tissue is removed | Through a small incision | Through laser ablation of the exposed corneal surface |
| Primary refractive effect | Reduces central corneal curvature by removing a lenticule | Reshapes the corneal surface through controlled tissue ablation |
Does SMILE Cure Myopia Permanently?
SMILE produces a permanent structural change in the cornea, so the correction itself is not like wearing a temporary optical device.
However, it is more accurate to think of SMILE as refractive correction rather than a cure for every biological aspect of myopia.
The procedure does not shorten an elongated eyeball or eliminate the underlying factors that caused myopia. It changes the corneal focusing power to reduce the refractive error.
In addition, the eye can undergo natural changes over time. A person who has undergone successful SMILE may still develop changes in vision later in life for reasons unrelated to the original myopia correction.
The Bottom Line
SMILE corrects myopia by changing the focusing power of the cornea. A femtosecond laser creates a precisely shaped lenticule within the cornea, and the surgeon removes it through a small incision. The resulting change in corneal curvature reduces its optical power, allowing light from distant objects to focus more accurately on the retina.
The procedure does not remove the natural lens, shorten the eyeball or eliminate every biological factor associated with myopia. Instead, it provides a permanent change to the corneal optics that can substantially reduce dependence on glasses or contact lenses in appropriately selected patients.
Whether SMILE is suitable depends on much more than the strength of a person's prescription. Corneal structure, eye health, refractive stability and other individual factors need to be assessed before treatment.
