SMILE Pro and Dry Eyes: What the Evidence Shows

Dry eye is the most discussed side effect in refractive surgery, and also the one most often reduced to a slogan. “SMILE is better for dry eyes” is a claim you will see in clinic marketing, and like most slogans it is partly true, importantly incomplete, and unhelpful if you are the person with dry eyes considering surgery.

Here is what is actually established, and where the uncertainty sits.

Why would a flapless procedure affect dry eye differently?

The cornea is densely innervated. Fine nerve fibres run through the surface layers, and they do two things: they provide sensation, and they drive the reflex that tells the eye to produce tears. Interrupt the nerves and both functions can be affected temporarily: reduced sensation, less tear production, and a surface that dries more quickly.

A LASIK flap is created by cutting through the surface layer of the cornea, which severs a proportion of those nerves across a broad area. A SMILE incision is a small arc at the edge of the cornea, so far fewer fibres are cut and the surface layer remains substantially continuous.

That mechanism is straightforward, and it is the reason the difference was predicted rather than merely observed.

What do the studies show?

Comparative studies and meta-analyses have generally reported differences favouring SMILE on measures such as corneal sensation, tear film stability and dry-eye symptom scores in the early post-operative period. Several have found that the difference narrows over the following months.

There are also studies that find smaller differences, or none, and the way a study defines and measures dry eye materially affects its conclusions. Symptom questionnaires, staining, tear break-up time and sensation testing are four different measurements of four related but distinct things.

The honest summary is: a difference is plausible, mechanistically supported, and reported by several studies, but it is a relative advantage in a risk that exists for both procedures. It is not a licence to ignore dry eye.

Why is dry eye assessed before surgery?

Two reasons, and the second is underappreciated.

Comfort afterwards. Someone entering surgery with a compromised tear film is more likely to notice symptoms during recovery, and possibly beyond it.

Measurement accuracy. A dry or unstable tear film distorts the cornea and makes topography and refraction less repeatable. If your measurements vary between visits, your correction may be planned on unreliable numbers, which is a problem for accuracy, not just comfort.

Because of the second point, an unstable surface can affect the quality of the surgery itself, not only the experience of recovering from it.

What happens if you have dry eyes?

Usually, a sequence rather than a no:

1. Assess and measure. Tear break-up time, staining, meibomian gland assessment and symptoms.
2. Treat the surface. Lubricants, lid hygiene, prescription drops, punctal plugs, treatment of blepharitis or meibomian gland dysfunction: the specific treatment follows the specific cause.
3. Reassess. Often after several weeks. If the measurements have become stable and repeatable, surgery can be reconsidered.
4. Adjust the plan. Sometimes the procedure choice changes; sometimes the plan moves to a different approach entirely.

Being asked to treat a dry eye for a month and come back is a sign of a careful assessment. It is also the point at which some people discover their dry eye was a longstanding, under-treated condition, which is worth knowing whether or not they proceed.

What does dry eye feel like after surgery?

Commonly: a gritty or sandy sensation, watering (which sounds contradictory but is common), a feeling that vision wavers and clears when you blink, and discomfort that worsens over a screen-heavy day.

It is usually most noticeable in the first weeks and improves as the surface recovers. For some people it lasts longer, and for a small number it persists.

There is also a measurement problem in the other direction: reduced corneal sensation can mean the eye feels normal while being dry, which is why follow-up appointments look at the surface rather than relying on symptoms alone.

What this means for you

If you already know you have dry eyes, do not accept a clinic’s reassurance that SMILE Pro will not be a problem for you. Ask what the assessment found, what the treatment plan is before surgery, and what the clinic’s experience has been with patients who had a similar baseline.

If you have no particular dry-eye symptoms, that is a good starting position, but it is still worth asking how your tear film was assessed, because the answer affects the accuracy of everything measured afterwards.

Our risks page covers the broader side-effect picture, and the comparison page shows how dry-eye considerations differ between SMILE Pro, LASIK and PRK.