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AIM: To investigate and analyze the changes of corneal biomechanics of normal eyes, forme frusta keratoconus eyes, subclinical keratoconus eyes and clinical keratoconus eyes by Corneal visualization Scheimpflug technology(Corvis ST), and provide clinical basis for early diagnosis of keratoconus. METHODS: Case-control study. We randomly selected 40 normal eyes as normal group, 15 forme frusta keratoconus eyes as forme frusta keratoconus group, 23 subclinical keratoconus eyes as subclinical keratoconus group, and 40 clinical keratoconus eyes as keratoconus group. The biomechanical parameters of each group were measured by Corvis ST. The receiver operating characteristic(ROC)curves was plotted to distinguish keratoconus from the normal cornea. RESULTS: There was no significant difference in the parameters of biomechanics between normal group and forme frusta keratoconus group (P>0.05). Compared to normal group and subclinical keratoconus group, the parameters second applanation length(AL2), first velocity of applanation(AV1), central curvature radius at highest concavity(HC-radius), deformation amplitude(DA)were revealed statistically significant differences(PCONCLUSION: The corneal biomechanical parameters of forme frusta keratoconus group are not changed compared with normal group. The changes between normal group and subclinical keratoconus group should combine with other technology to further improve subclinical keratoconic screening. Compared with normal corneas, keratoconus has a great change in biomechanics, which DA diagnosis of the highest efficiency.

AIM: To demonstrate the changes in ultrastructure and histopathology of the cornea in acute corneal alkaline burns after femtosecond laser-assisted deep lamellar keratoplasty. METHODS: The New Zealand white rabbits treated with alkaline corneal burn were randomized into two groups, Group A (16 eyes) with femtosecond laser-assisted deep lamellar keratoplasty 24h after burn and Group B (16 eyes) without keratoplasty as controls. All eyes were evaluated with transmission electron microscopy (TEM) at 1, 2, 3, and 4wk follow-up, then all corneas were tested by hematoxylin and eosin staining histology. RESULTS: The corneal grafts in Group A were transparent, while those in Group B showed corneal stromal edema and loosely arranged collagen fibers. One week after treatment, TEM revealed the intercellular desmosomes in the epithelial layers and intact non-dissolving nuclei in Group A. At week 4, the center of the corneas in Group A was transparent with regularly arranged collagen fibers and fibroblasts in the stroma. In Group B, squamous cells were observed on the corneal surface and some epithelial cells were detached. CONCLUSION: Femtosecond laser-assisted deep lamellar keratoplasty can suppress inflammatory responses, prevent toxic substance-induced injury to the corneal endothelium and inner tissues with quicker recovery and better visual outcomes.

AIM: To evaluate the visual quality between femtosecond laser small incision lenticule extraction(SMILE)and femtosecond laser in situ keratomileusis(LASIK)in the treatment of myopia. METHODS: This study comprised 22 eyes(11 patients)underwent SMILE and 43 eyes(23 patients)received LASIK with femtosecond laser to correct myopia and myopic astigmatism. The two groups were recorded bydouble-pass optical quality analysis system(OQAS)at preoperative and postoperative 1mo. The two groups were compared: modulation transfer function cutoff frequency(MTF cutoff), strehl ratio(SR), objective scattering index(OSI). The early visual quality after operation between two groups were analyzed and evaluated.RESULTS: The MTF cutoff after operation one month were 34.835±10.113c/deg(SMILE group)and 38.362±10.623c/deg(LASIK group)(t=0.925, P=0.362). The SR after operation one month were 0.204±0.077(SMILE group)and 0.218±0.072(LASIK group)(t=0.557, P=0.582). The OSI after operation one month were 0.608±0.291(SMILE group)and 0.545±0.405(LASIK group)(t=-0.473, P=0.640). CONCLUSION: The double-pass OQAS tell us that there was not statistically significant between femtosecond laser SMILE and femtosecond LASIK in the treatment of myopia.

AIM: To compare the postoperative visual outcomes of VisuMax small incision lenticule extraction(SMILE)and femtosecond laser assisted LASIK(FEMTO LASIK)for myopia. METHODS:Eighty-tree eyes(42 patients)underwent VisuMax SMILE and 94 eyes(47 patients)received FEMTO LASIK to correct myopia were comprised. The safety, efficacy, predictability, stability and adverse events were assessed preoperatively and 1d, 1 week, 1 month, 3 months postoperatively. RESULTS: At 3 months, the mean safety index was 1.10±0.16 in the SMILE group and 1.09±0.16 in the FEMTO LASIK group; the mean efficacy index was respectively 1.10±0.16 and 1.08±0.12; Spherical equivalent(SE)was respectively 0.11±0.23D and 0.08±0.25D within ±1.00D of the targeted SE correction in 82 eyes(98.8%)of the SMILE group and 91 eyes(96.8%)of the FEMTO LASIK group and SE within ±0.50D in 73 eyes(88.0%)of the SMILE group and 78 eyes(83.0%)of the FEMTO LASIK group. There were no significant complications in both groups. CONCLUSION: SMILE and FEMTO LASIK have equal safety, efficacy, predictabilityand stability in the treatment of myopia.

AIM: To observe the predictability of corneal flap creation with the VisuMax femtosecond laser and preliminarily analyze the factors correlated to the thickness and diameter of the flap. METHODS: This retrospective case series study included 300 eyes of 150 consecutive patients. The eyes were assigned to two groups according to intended flap thickness, 100μm(204 eyes)and 110μm(96 eyes), which created with the VisuMax femtosecond laser. Intended flap diameters were 7.9mm and 8.3mm. Difference analysis of flap diameter and intended diameter as well as flap thickness and intended thickness were made. The data were analyzed with SPSS to sum up a multiple stepwise regression formula that could express their quantitative relationship. RESULTS: The 100μm flap group had an average flap thickness of 103.11±4.07μm, while for the 110μm group the average flap thickness was 113.35±5.71μm. The difference between right and left eyes was not statistically significant(t100μm =-0.901, t 110μm=-0.490; P>0.05). Corneal flap thickness was not related to flap diameter(r=0.003, 0.018; P>0.05), preoperative patient age(r=0.022, 0.050; P>0.05), corneal thickness(r=0.051, 0.101; P>0.05), keratometric value K(r=-0.048, -0.136; P>0.05)or intraocular pressure(r=-0.113, 0.047; P>0.05). Preoperative corneal keratometric value K was positively correlated with corneal flap diameter(r=0.359, 0.532; P=0.01, 0.007CONCLUSION:The LASIK flap creation with the VisuMax femtosecond laser has relatively good predictability. There is no influencing factor for flap thickness.