What do the studies say about SMILE, LASIK and dry eye?

SMILE and LASIK reshape the cornea to correct refractive error, but they do so in different ways. LASIK uses a flap and an excimer laser to reshape tissue beneath it. In SMILE, a femtosecond laser creates a small disc of corneal tissue (a lenticule), which the surgeon removes through a small incision. A smaller incision is a difference in technique; by itself, it does not prove that an individual will have fewer symptoms or a better result.

Both procedures can affect corneal nerves and the tear-film surface. Studies therefore measure more than one outcome: corneal sensation, clinical signs such as tear break-up time (TBUT) or surface staining, and symptoms reported by the person having surgery. These measures are related, but they are not interchangeable. A difference in a tear test or a nerve measurement does not necessarily mean a noticeable difference in symptoms.

What a paired-eye dry-eye trial found

Ma and Manche conducted a prospective randomised contralateral-eye trial at Stanford involving 40 people with myopia (80 eyes). Each person received wavefront-guided femtosecond LASIK in one eye and SMILE in the other. Corneal sensitivity was measured with Cochet–Bonnet esthesiometry before surgery and at 1, 3, 6 and 12 months; participants also completed the Ocular Surface Disease Index (OSDI), a symptom questionnaire scored from 0 to 100.

Cochet–Bonnet esthesiometry is a tactile test of corneal sensitivity; the authors report the response as nylon-filament length in centimetres. A longer reading indicates that a lighter touch was detected. Readings were lower after LASIK than after SMILE at 1 month (mean 2.1 vs 3.6 cm), 3 months (3.5 vs 5.4 cm) and 6 months (4.7 vs 5.7 cm); all three comparisons had P<.001. By 12 months, both groups had returned to 5.9 cm and did not differ (P=.908). OSDI scores did not differ between procedures at any visit. Mean OSDI improved from 15.3 before surgery to 8.6 at 12 months after LASIK (P=.020), and from 15.1 to 9.5 after SMILE (P=.029). Thus, this small trial found a temporary difference in measured corneal sensation, but not in reported dry-eye symptoms between procedures. [1]

The trial followed participants for one year and compared each person’s eyes, which helps control for person-level differences. Its 40-person sample was small, and a questionnaire about a person’s symptoms cannot assign each symptom to one eye as cleanly as an eye-specific test can. The finding does not establish that either operation prevents dry eye or that symptoms will follow the group average.

What tear-film measurements and biomarkers add

Liu and colleagues studied 70 people in a randomised paired-eye trial at the Singapore National Eye Centre. Each participant had SMILE in one eye and femtosecond LASIK in the other. The team collected tears before surgery and at 1 week, then 1, 3, 6 and 12 months. At each visit, they measured tear break-up time (TBUT), the time before a dry spot first appears on the cornea after a blink (seconds; average of three tests), fluorescein staining on the Oxford scale (0 absent to 5 severe), and Schirmer I tear production (mm over 5 minutes). Thirty pairs of tear samples were randomly selected for SWATH mass spectrometry; a separate random sample of 40 participants was used for neuromediator ELISA.

SMILE eyes had longer mean TBUT than LASIK eyes at 1 week (8.4±3.2 vs 6.1±2.7 seconds, P=.0028), 1 month (9.3±2.6 vs 7.0±2.3 seconds, P<.001) and 3 months (10.0±2.6 vs 8.3±3.2 seconds, P=.011). The reported ± values are standard deviations (SDs), describing spread among participants rather than confidence intervals. Oxford staining scores favoured SMILE at 1 week and 1 month, while Schirmer I results did not differ significantly at any measured visit. By 6 months, the difference in TBUT was no longer reported as significant; the authors state that clinical dry-eye measures were comparable at later follow-up. Some tear-protein and neuromediator profiles still differed. Four participants were lost to follow-up by 6 months and six by 12 months. The study did not include a subjective dry-eye symptom questionnaire, and its clinical comparisons used P<.05 without adjustment for multiple comparisons. The paper reports correlations between mucin-like protein 1 and TBUT (r=−0.47), and between substance P and TBUT (r=−0.49). These laboratory associations are not a diagnostic test or proof that a particular person will feel less dry. A tear profile is a biological measure rather than a direct measure of comfort or quality of life. [2]

Visual recovery is a different outcome

A separate Stanford randomised contralateral-eye trial compared visual outcomes after wavefront-guided LASIK and SMILE in people with myopia and low levels of astigmatism. Of 44 participants (88 eyes) enrolled, 37 participants (74 eyes) completed 12 months. At month 12, 94% of LASIK eyes and 83% of SMILE eyes achieved uncorrected distance visual acuity of 20/20 or better (P<.05). The study reported no significant difference in mean spherical equivalent, higher-order aberrations or several other refractive measures. Its authors reported faster visual recovery and better low-contrast visual acuity after wavefront-guided LASIK in this sample. This study did not compare dry-eye symptoms, and its selected, single-centre population is not a prediction for everyone. [3]

“Recovery” can refer to different things: how quickly vision becomes clear, how stable refraction is, how the eye feels, or how the ocular surface measures. A result on one of these outcomes should not be presented as a result on all of them.

Suitability depends on an eye examination

The American Academy of Ophthalmology’s Refractive Surgery Preferred Practice Pattern calls for a comprehensive eye evaluation before refractive surgery, including assessment of the tear film and ocular surface. It also says that risks, benefits and alternatives should be discussed, including possible development or worsening of dry-eye symptoms. This supports an individual assessment rather than choosing a procedure from a general SMILE-versus-LASIK claim. [4]

The FDA’s 2016 Summary of Safety and Effectiveness Data for the VisuMax SMILE system describes a prospective, multicentre, single-arm study of 336 treated subjects at five sites, followed for 12 months. The enrolled population had defined age, refractive-stability and corneal criteria; clinically significant dry eye unresolved by treatment was an exclusion criterion, and severe dry eye was listed as a contraindication for the device’s myopia indication. These are study eligibility and device-labelling conditions, not a complete current assessment of every laser platform or a personal eligibility decision. The report also lists dry eye among potential adverse effects. [5]

During an assessment, ask how your current symptoms and ocular-surface findings will be evaluated, whether any dry-eye condition should be treated before measurements are final, and how corneal shape, thickness, prescription stability and your visual needs affect the available options. Ask what outcomes each procedure is expected to address, which risks remain, and what follow-up care is planned.

Questions to ask when comparing options

If you are comparing LASIK and PRK laser eye surgery prices in Turkey with SMILE laser eye surgery prices in Turkey, ask which procedure, clinical assessments and follow-up services each listing describes. Likewise, a LASIK and PRK laser eye surgery package and a SMILE laser eye surgery package describe their listed package scope; package wording does not establish clinical suitability or comparative safety. PRK appears in those LASIK/PRK listings, but the cited SMILE-versus-LASIK studies did not compare PRK with either procedure.

What the evidence can and cannot tell you

The strongest direct comparisons here use randomised paired eyes, but their questions differ. One small trial measured corneal sensitivity and OSDI symptoms; another tracked clinical tear-film measures and molecular markers; a separate trial compared visual outcomes. These studies cannot be combined into a promise that SMILE prevents dry eye, that LASIK is always more comfortable, or that one method suits a particular eye. The FDA study was single-arm, so it does not establish comparative superiority. The guideline supports a comprehensive assessment and informed discussion, not a procedure ranking. Results also depend on the laser platform, treatment plan, baseline eye health and the outcome being measured.

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References

1. Ma, Kevin K., & Manche, Edward E. “Corneal Sensitivity and Patient-Reported Dry Eye Symptoms in a Prospective Randomized Contralateral-Eye Trial Comparing Laser In Situ Keratomileusis and Small Incision Lenticule Extraction.” American Journal of Ophthalmology. Published online 18 May 2022; 2022 Sep;241:248–253. doi: 10.1016/j.ajo.2022.05.010. PMID: 35594919. Abstract and metadata accessed; full text not available in this review.
2. Liu, Y.-C., Yam, G. H.-F., Lin, M. T.-Y., Teo, E., Koh, S.-K., Deng, L., Zhou, L., Tong, L., & Mehta, J. S. “Comparison of tear proteomic and neuromediator profiles changes between small incision lenticule extraction (SMILE) and femtosecond laser-assisted in-situ keratomileusis (LASIK).” Journal of Advanced Research. Published online 5 November 2020; 2021 Mar;29:67–81. doi: 10.1016/j.jare.2020.11.001. PMID: 33842006; PMCID: PMC8020296. Full text.
3. Chiang, Bryce, Valerio, Gabriel S., & Manche, Edward E. “Prospective, Randomized Contralateral Eye Comparison of Wavefront-Guided Laser In Situ Keratomileusis and Small Incision Lenticule Extraction Refractive Surgeries.” American Journal of Ophthalmology. Published online 14 November 2021; 2022 May;237:211–220. doi: 10.1016/j.ajo.2021.11.013. PMID: 34788593. Abstract and metadata accessed; full text not available in this review.
4. Jacobs, Deborah S., Lee, Jimmy K., Shen, Tueng T., Afshari, Natalie A., Bishop, Rachel J., Keenan, Jeremy D., & Vitale, Susan, on behalf of the American Academy of Ophthalmology Preferred Practice Pattern Refractive Management/Intervention Panel. “Refractive Surgery Preferred Practice Pattern®.” Ophthalmology. Published online 19 December 2022; 2023 Mar;130(3):P61–P135. doi: 10.1016/j.ophtha.2022.10.032. PMID: 36543604. Publisher full text.
5. U.S. Food and Drug Administration, Center for Devices and Radiological Health. “Summary of Safety and Effectiveness Data (SSED): VisuMax Femtosecond Laser, PMA P150040.” FDA, 13 September 2016. Full regulatory report, especially sections II–III and X.