Comparison of corneal biomechanics after myopic small-incision lenticule extraction compared to LASIK: an ex vivo study

Figures & data

Figure 1 Fitting of the corneal specimen on the BioTester device rake battery just prior to testing.

Figure 2 Young’s modulus E linear regression fitting performed on stress–strain curves.

Notes: Data illustrate stress (shear force ÷ cross-section, expressed in kPa) versus relative displacement (strain, reported as %). From left to right, top to bottom, Group A (SMILE-3D), Group B (SMILE-8D), Group C (LASIK-3D), and Group D (LASIK-8D). Young’s modulus corresponds to the slope, which is indicated by the numeric factor preceding variable x in each trend-line function per group, expressed in kPa and converted to MPa in the data listed in Table 1.
Abbreviation: SMILE, small-incision lenticule extraction.

Table 1 Comparative tensile measurements between the six groups

Metric	Young’s modulus @ 10% (MPa)	Young’s modulus @ 15% (MPa)	Stress @ 10% (kPa)	Stress @ 15% (kPa)
Group E SMILE control
Mean	5.09	8.17	248	580
SD	±0.78	±0.92	±54	±75
Group A SMILE-3D
Mean	3.24	5.28	160	376
SD	±0.85	±1.06	±66	±98
Group B SMILE-8D
Mean	2.58	4.03	123	287
SD	±0.55	±0.81	±35	±72
Group F LASIK control
Mean	5.63	9.34	266	632
SD	±0.65	±0.91	±68	±92
Group C LASIK-3D
Mean	4.43	7.36	210	498
SD	±0.81	±1.16	±77	±108
Group D LASIK-8D
Mean	2.88	4.14	142	313
SD	±0.59	±0.48	±47	±69

Note: Data represent mean and standard deviation between all corneas within each group.

Abbreviations: SD, standard deviation; SMILE, small-incision lenticule extraction.

Figure 3 Summary of biomechanical tensile test differential results per group studied.

Note: Young’s modulus (units MPa) and stress results (units kPa) calculated at 10% and 15% strain.
Abbreviation: SMILE, small-incision lenticule extraction.

Table 2 Comparative analysis of tensile results

	Young’s modulus @ 10% (MPa)	Young’s modulus @ 15% (MPa)	Stress @ 10% (kPa)	Stress @ 15% (kPa)	Average Δ
Δ within procedure
SMILE-3D vs control	−36.3%	−35.4%	−35.5%	−35.2%	−35.6%
SMILE-8D vs control	−49.3%	−50.7%	−50.4%	−50.5%	−50.2%
SMILE-8D vs -3.00	−20.4%	−23.6%	−23.1%	−23.7%	−22.7%
LASIK-3D vs control	−21.3%	−21.2%	−21.1%	−21.2%	−21.2%
LASIK-8D vs control	−48.9%	−55.7%	−46.6%	−50.5%	−50.4%
LASIK-8D vs -3.00	−35.1%	−43.7%	−32.4%	−37.1%	−37.1%
Δ between same dioptric correction
SMILE-3D vs LASIK-3.00	−27%	−28%	−24%	−24%	25.9%
SMILE-8D vs LASIK-8.00	−10% (*)	−3% (*)	−13% (*)	−8% (*)	−8.7% (*)

Notes: Δ: relative (%) difference between metrics;

* difference was not statistically significant (P>0.05). Average Δ is the numeric average of the four metrics (Young’s modulus @ 15%, stress @ 10%, and stress @ 15%).

Abbreviation: SMILE, small-incision lenticule extraction.