Seeing the Bigger Picture

Yet even as we celebrated KLEX’s precision and safety, one question kept coming up in our clinic: could we make good vision even better, particularly in young patients with large pupil sizes who struggled with night vision or glare?

This question led us down a path toward something deceptively simple: making the lenticule just a little bigger.

From PRK to KLEX: a brief (and painful) evolution

Refractive surgery has always been about refining light and reducing the side-effects of that refinement. PRK in the 1980s was revolutionary, but epithelial removal came with a price: slow recovery and potential haze for the patient (2). In the 1990s, LASIK changed the game with a corneal flap that sped healing but introduced biomechanical vulnerabilities like dislocations and dry eye (3,4).

Then keratorefractive lenticule extraction (KLEX) stepped onto the stage: a flapless, minimally invasive technique that uses a femtosecond laser to carve out and remove a thin lenticule from within the cornea (5). It preserves more corneal nerves and biomechanics (6), and shows less postoperative dry eye symptoms (7,8).

The case for going big

In standard KLEX, optical zones typically range from 6.0 to 7.0 mm (10,11). But as every refractive surgeon knows, the human eye is not one-size-fits-all. Some patients, particularly younger ones, have larger pupils, especially under scotopic conditions (13,19). When the pupil dilates beyond the treated zone, light enters through the untreated corneal periphery, leading to aberrations, halos, and reduced contrast sensitivity (14).

This realization sparked our interest in whether larger optical zones could bridge that gap – could we expand the treatment area to match the natural physiology of patients’ pupils, keeping safety and long-term refractive stability intact?

Putting it to the test

To explore that question, we conducted a retrospective case series of 40 eyes from 20 patients, all treated with the VisuMax 800 (Carl Zeiss Meditec). We pushed beyond the standard parameters, performing KLEX with a 7.7 mm optical zone and a 7.9 mm cap diameter – to our knowledge, this was one of the largest reported configurations to date.

Our patient cohort had preoperative spherical equivalents ranging from –1.5 D to –4.75 D and astigmatism up to –3.0 D. Pupil size under photopic, mesopic, and scotopic conditions was measured, with scotopic pupils averaging around 7.0 ± 1.1 mm, consistent with published data in younger adults (19).

Three months after surgery, 100% of eyes were within ±1.0 D of target, 97.5% within ±0.5 D, and all patients achieved 20/20 vision, with 25% reaching 20/16. These findings mirror recent real-world VisuMax 800 outcomes showing excellent safety and predictability (15).

Contrast sensitivity under mesopic conditions remained stable compared to normative data (16). No significant complications or adverse effects were observed.

Why it matters

If the refractive outcomes and contrast sensitivity remain unchanged, what’s the true payoff of enlarging the lenticule? It comes down to the effective optical zone: the real area of corneal reshaping that contributes to clear vision. Studies have shown that the effective zone is typically smaller than the programmed one, shrinking by 1.4–1.7 mm due to biomechanical and epithelial remodeling (17–18).

So a programmed 6.5 mm zone may translate to an effective area closer to 5 mm, an area smaller than many young patients’ pupils. By expanding the programmed optical zone to 7.7 mm, we aim to preserve an effective zone that actually matches or exceeds the patient’s scotopic pupil.

Who stands to benefit

While larger lenticules could theoretically benefit many patients, certain groups stand out:

• Younger patients (<40 years), who naturally have larger pupils (19)

• High myopes, in whom regression risk is higher (20–22)

• Occupationally dependent patients, such as pilots, drivers, or others working in low-light conditions

For these individuals, enlarging the optical zone could make a meaningful difference in everyday visual quality.

Challenges and caveats

Of course, no innovation comes without uncertainty. Larger lenticules mean more tissue removal, and so careful attention to residual stromal bed thickness remains essential. Surgeons must also ensure accurate centration (12) and consistent dissection to avoid any irregularities.

Our own study’s limitations – a small sample size, short follow-up, and lack of postoperative aberrometry – highlight the need for longer-term evaluation to confirm biomechanical stability and determine whether regression truly decreases.

Looking ahead

As refractive surgeons, we often think of “customization” in terms of topography, wavefront, or nomograms. But perhaps it’s time to add optical zone size to that list. Personalizing the lenticule diameter to each patient’s pupil dynamics could represent the next subtle yet significant step forward in refractive surgery outcomes (10,11,17).

When I tell patients we are aiming to “make their SMILE bigger,” they usually laugh. But the truth is: that might be exactly what their vision needs.