Small incision lenticule extraction (SMILE) lenticule thickness readout compared to change in axial length measurements with the IOLMaster
To compare theoretical values from the small incision lenticule extraction (SMILE) lenticule thickness readout with change in axial length measurements taken with the IOLMaster.
We prospectively studied 214 eyes from 107 patients undergoing bilateral SMILE surgery for myopia or myopic astigmatism between December 2014 and May 2017 at an ophthalmological practice in Singapore. All eyes were examined pre-operatively and 1 and 3 months post-operatively with the IOLMaster following SMILE surgery. Achieved lenticule thickness was taken as the change in axial length after surgery. A linear mixed-effects model was used to examine changes in axial length, spherical equivalent and acuity over time. The relationships between change in axial length and theoretical lenticule thickness and spherical equivalent were examined with multiple linear regression analyses, and model prediction was assessed with adjusted R2 statistics.
Mean (95% confidence interval [CI]) spherical equivalent pre-operatively was − 5.25 (95% CI − 5.38 to − 5.12) diopters (D), at 1 month was 0.04 (95% CI − 0.09 to 0.17) D (p < 0.001), and at 3 months was − 0.02 (95% CI − 0.15 to 0.11) D (p < 0.001). Mean (95% CI) pre-operative axial length was 27,726 (95% CI 25,595 to 25,857) μm. Post-operative axial length at 1 month was significantly shorter at 25,595 (95% CI 25,464 to 25,726) μm (p < 0.001) with no change thereafter (p = 0.647). Pre-operative mean ± standard deviation (SD) refractive target was 0.24 (± 0.3) D, and mean difference between target and post-operative spherical equivalent at 1 month was 0.20 D (95% CI 0.16 to 0.25 D, p < 0.001). Multiple regression analysis showed that change in axial length at 1 month was, on average, 5% lower than theoretical lenticule thickness, indicating an average difference of 5.4 μm (95% CI 5.2 to 5.6 μm). Preoperative spherical equivalent predicted negative association with change in axial length at 1 month (β = − 14.8, 95% CI − 18.2 to − 11.3, adjusted R2 = 0.457, p < 0.001).
Calculated lenticule thickness values were less than expected, and post-operative refractive outcomes at 1 month showed a slight under-correction. Further research in this area is needed to validate these findings.
KeywordsSMILE Lenticule Thickness Refractive IOLMaster
No funding was received.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed were in accordance with the ethical standards of the local institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Human and animal rights and informed consent
Informed consent was obtained from all individual participants included in the study.
- 2.SMILE—laser vision correction. Carl Zeiss Meditec AG website. https://www.zeiss.com/meditec/int/c/smile/laser-vision-correction.html. Accessed December 10, 2018.
- 4.Sekundo W, Kunert KS, Blum M (2011) Small incision corneal refractive surgery using the small incision lenticule extraction (SMILE) procedure for the correction of myopia and myopic astigmatism: results of a 6 month prospective study. Br J Ophthalmol 95:335–339. https://doi.org/10.1136/bjo.2009.174284 CrossRefPubMedGoogle Scholar
- 13.Hulley SB, Cummings SR, Browner WS, Grady DG, Newman TB (2013) Designing clinical research. Lippincott Williams & Wilkins, PhiladelphiaGoogle Scholar
- 18.Reinstein DZ, Archer TJ, Gobbe M, Johnson N (2010) Accuracy and reproducibility of artemis central flap thickness and visual outcomes of LASIK with the Carl Zeiss Meditec VisuMax femtosecond laser and MEL 80 excimer laser platforms. J Refract Surg 26:107–119. https://doi.org/10.3928/1081597X-20100121-06 CrossRefPubMedGoogle Scholar
- 23.Reinstein DZ, Archer TJ, Gobbe M (2014) Lenticule thickness readout for small incision lenticule extraction compared to Artemis three-dimensional very high-frequency digital ultrasound stromal measurements. J Refract Surg 30:304–309. https://doi.org/10.3928/1081597X-20140416-01 CrossRefPubMedGoogle Scholar
- 34.Vestergaard A, Ivarsen A, Asp S, Hjortdal JØ (2013) Femtosecond (FS) laser vision correction procedure for moderate to high myopia: a prospective study of ReLEx(®) flex and comparison with a retrospective study of FS-laser in situ keratomileusis. Acta Ophthalmol 91:355–362. https://doi.org/10.1111/j.1755-3768.2012.02406.x CrossRefPubMedGoogle Scholar
- 38.Agca A, Ozgurhan EB, Yildirim Y, Cankaya KI, Guleryuz NB, Alkin Z, Ozkaya A, Demirok A, Yilmaz OF (2014) Corneal backscatter analysis by in vivo confocal microscopy: fellow eye comparison of small incision lenticule extraction and femtosecond laser-assisted LASIK. J Ophthalmol 2014:265012. https://doi.org/10.1155/2014/265012 CrossRefPubMedPubMedCentralGoogle Scholar
- 39.Uçakhan OO, Ozkan M, Kanpolat A (2006) Corneal thickness measurements in normal and keratoconic eyes: Pentacam comprehensive eye scanner versus noncontact specular microscopy and ultrasound pachymetry. J Cataract Refract Surg 32:970–977. https://doi.org/10.1016/j.jcrs.2006.02.037 CrossRefPubMedGoogle Scholar
- 42.Reinstein DZ, Yap TE, Archer TJ, Gobbe M, Silverman RH (2015) Comparison of corneal epithelial thickness measurement between Fourier-domain OCT and very high-frequency digital ultrasound. J Refract Surg 31:438–445. https://doi.org/10.3928/1081597X-20150623-01 CrossRefPubMedPubMedCentralGoogle Scholar