Comparison of myopic astigmatic correction after cross-assisted SMILE, FS-LASIK, and transPRK.

PURPOSE: To compare astigmatic correction among cross-assisted small-incision lenticule extraction (SMILE), femtosecond laser-assisted in situ keratomileusis (FS-LASIK), and transepithelial photorefractive keratectomy (transPRK). SETTING: The Eye Hospital of Wenzhou Medical University, Zhejiang, China. DESIGN: Prospective comparison study. METHODS: 154 right eyes of 154 patients with astigmatism of -1.00 to -2.75 diopters (D) were included in this study. 64 eyes, 42 eyes, and 48 eyes were receiving SMILE, FS-LASIK, and transPRK, respectively. The SMILE group used cross-axial alignment for head positioning for astigmatism correction. In the FS-LASIK and transPRK groups, static and dynamic cyclotorsion control were used. Changes in ocular parameters and vector analysis were assessed at 6 months postoperatively. RESULTS: The safety and efficacy indices were comparable among the 3 groups at 6 months postoperatively. Residual astigmatism was smallest in the SMILE group (-0.23 ± 0.25 D) compared with that in FS-LASIK (-0.40 ± 0.28 D, P = .009) and transPRK groups (-0.42 ± 0.32 D, P = .001). 53 (82.8%), 36 (85.7%), and 37 (77.1%) eyes achieved an angle of error within ±5 degrees, respectively ( P = .55). Notably, vector analysis showed that the difference vector, the magnitude of the error, and its absolute value were significantly smaller in the SMILE group than those in the other groups ( P < .05). In addition, the higher-order aberrations, especially coma, were significantly induced postoperatively in each group ( P < .001). CONCLUSIONS: Residual astigmatism magnitude was smallest by cross-assisted SMILE, followed by FS-LASIK and transPRK, and the astigmatism axial correction was comparable among groups.

Comparison of Astigmatic Correction With and Without Cross-axis Alignment During Small Incision Lenticule Extraction.

PURPOSE: To compare clinical outcomes after astigmatism correction via small incision lenticule extraction (SMILE) with and without cross-axis alignment. METHODS: This prospective study included patients who underwent SMILE with astigmatism of greater than 0.75 diopters (D). In the alignment group, head position was readjusted by cross-axis alignment before the standard SMILE procedure. First, the cross-axis was aligned to corresponding green lines on the headrest. Then, the patient's head was adjusted to align the horizontal line to the outer canthus of both eyes and align the vertical line connecting the midpoints of the eyebrows and the bridge of the nose. Changes in ocular parameters were assessed, and vector analysis was performed 6 months postoperatively. RESULTS: The alignment and control groups included 61 and 54 eyes, respectively. Postoperatively, the safety and efficacy indices were comparable between the two groups. Notably, refractive cylinder differed significantly in the alignment group (-0.23 ± 0.26 D) compared to the control group (-0.36 ± 0.26 D) (P = .007). Forty-eight (78.7%) and 32 (59.3%) eyes in the alignment and control groups (P = .03) achieved an angle of error within ±5°, respectively. Vector analysis showed a significantly lower difference vector and a significantly better index of success in the alignment group than that in the control group (0.24 ± 0.25 vs 0.35 ± 0.24, P = .003 and 0.20 ± 0.22 vs 0.29 ± 0.22, P = .02, respectively). Moreover, the change in corneal trefoil differed significantly between the groups (P < .001). CONCLUSIONS: Cross-axis alignment for head positioning in SMILE significantly minimizes axis misalignment and reduces undercorrection astigmatism in myopic astigmatism correction. This technique is a non-invasive and effective method, especially for beginners. [J Refract Surg. 2022;38(10):624-631.].

Geochemistry and tectonic significance of late Paleoproterozoic A-type granites along the southern margin of the North China Craton.

The Longwangzhuang pluton is a typical example of Paleoproterozoic A-type granite intrusions at the southern margin of the North China Craton. This pluton is composed of arfvedsonite granite and minor aegirine-augite granites. Samples from both granite types display similar zircon U-Pb ages with 207U-206Pb ages of 1612 ± 19 Ma [mean square weighted deviation (MSWD) = 0.66] and 1609 ± 24 Ma (MSWD = 0.5), respectively. The granites exhibit similar high silica (SiO2 = 71.1-73.4 wt.%), high alkaline (Na2O + K2O = 8.10-9.26 wt.%, K2O/Na2O > 1), and low Al2O3 (11.8-12.8 wt. %) contents and metaluminous to weakly peraluminous bulk chemistry. The chemical variations of the Longwangzhuang pluton suggest the effects of mineral fractionation. In addition, all samples show typical characteristics of A-type granites, such as high 10000Ga/Al ratios (4.10-7.28), high FeOtot/(FeOtot + MgO) ratios (0.88-0.99), and high Zr (484-1082 ppm), Ce (201-560 ppm), and Y (78-156 ppm) contents. The εNd(t) values and the (206Pb/204Pb)t, (207Pb/204Pb)t, and (208Pb/204Pb)t ratios of the arfvedsonite granite samples vary from -4.6 to -5.3, 15.021 to 17.349, 15.241 to 15.472, and 33.206 to 36.905, respectively, and those for the aegirine-augite granite sample amount at -0.2, 14.421, 15.175, and 33.706. The distinct and variable Nd and Pb isotope values indicate the presence of heterogeneous protoliths. Based on its geochemistry, its low initial Pb isotope ratios, and its enrichment in Nd isotopes, we infer that the Longwangzhuang A-type granite is the partial melting product of basement rocks such as the Taihua Group gneisses accompanied by some involvement of juvenile material from the mantle. Together with published data from other Paleoproterozoic A-type granite plutons exposed at the southern margin of the craton, our findings suggest that these granites had a similar origin. Furthermore, geochemically, they can be divided into two groups: A2-type, which formed earlier (~1.8-1.6 Ga), and A1-type, which formed later (~1.6-1.5 Ga). Combining this information with the variations in whole-rock Nd and zircon Hf isotopic composition at ca. 1.6 Ga, we propose that tectonic transformation from post-orogenic to anorogenic magmatism occurred at the southern margin of the North China Craton at that time.