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AIM: To investigate the effect of different preoperative corneal curvature on the size of optical deformation area after femtosecond laser small incision lens extraction(SMILE).METHODS:A prospective study was conducted on 108 consecutive patients who underwent SMILE surgery in our hospital from February 2021 to January 2022. Considering the association between both eyes, only the left eye of each patient was studied. According to the average anterior corneal surface curvature in preoperative, the patients were divided into three groups: Km<42.0D group(n=30), Km>47.0D group(n=26)and conventional corneal curvature group(n=52)with 42.0D≤Km≤47.0D. All patients underwent standardized SMILE surgery, and the laser ablation diameter was 6.5mm. The diameters of optical deformation areas in the three groups were compared at 6mo after operation.RESULTS:There was no significant difference in preoperative data among the three groups except for the mean curvature of the anterior corneal surface(all P>0.05), and there was no significant difference in uncorrected distance visual acuity(UDVA)and subjective refraction at 6mo after operation(all P>0.05). The diameters of the optical deformation zone in the Km<42.0D group, Km>47.0D group and the conventional corneal curvature group were 6.54±0.14, 6.32±0.13, 6.45±0.15mm respectively(F=19.238, P<0.05). The optical area diameter of the group with flat corneal curvature was larger than that of the group with conventional corneal curvature and the group with steeper corneal curvature(P<0.05). The diameter of optical zone in the conventional curvature group was larger than that in the Km>47.0D group(P<0.05).CONCLUSION: When the preset laser cutting diameter is the same, the steeper the corneal curvature before operation, the smaller the diameter of the optical deformation area after operation.
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AIM: To evaluate the effect of preoperative degrees of myopic astigmatism and anterior corneal curvature on the functional optical zone(FOZ)after transepithelial photorefractive keratectomy(TransPRK).METHODS: Retrospective study was conducted on 78 patients(130 eyes)with myopia and myopic astigmatism who underwent TransPRK, and they were divided into control group(cylinder 0D), moderate astigmatism group(-0.50～-2.00D)and high astigmatism group(>-2.00～<-6.00D). The FOZ was measured and compared among the three groups 6mo after operation. The correlations between attempted correction, anterior corneal curvature, corneal aberrations, Q value, and the FOZ were analyzed.RESULTS: At 6mo after operation, the mean FOZ was 5.16±0.12mm in the control group, 5.29±0.23mm in the moderate astigmatism group, and 5.49±0.23mm in the high astigmatism group(P<0.001), and the FOZ of the high astigmatism group was significantly higher than moderate astigmatism and control group(P<0.05, P<0.001); Pearson correlation analysis showed that the changes in spherical equivalent, total corneal higher-order aberrations(HOAs), coma, and spherical aberration were all negatively correlated with FOZ(all P<0.05); and FOZ positively correlated with changes in the steep curvature(K2), mean curvature(Km), corneal astigmatism, and Q value(all P<0.01). Multiple linear regression analysis showed that there was still positive correlation between preoperative K2 and FOZ after adjusting for other risk factors(P<0.001).CONCLUSION: Patients with high astigmatism can obtain a larger FOZ and less induced coma after TransPRK. A larger FOZ can be achieved in eyes with steeper keratometry.
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@#AIM: To explore the changes and influencing factors of effective optical zone(EOZ)after femtosecond laser small incision lenticule extraction(SMILE)in patients with different degrees of myopia.<p>METHODS:Retrospective study. From October 2019 to October 2020, fifty patients(92 eyes)with myopia who underwent SMILE surgery in the Affiliated Eye Hospital of Nanchang University and whose preoperative optical zone diameter was designed to be 6.5mm were selected. According to the preoperative equivalent spherical diopter, the patients were divided into three groups: low myopia group(-0.50D to -3.00D, 18 cases, 34 eyes), moderate myopia group(>-3.00D to -6.00D, 20 cases, 36 eyes)and high myopia group(>-6.00D, 12 cases, 22 eyes). The uncorrected visual acuity, best corrected visual acuity, manifest refraction spherical equivalent, optical zone diameter, corneal Q-value and high-order aberrations(HOA)were collected before and 3mo after operation.<p>RESULTS:The postoperative 3mo EOZ of patients with low, moderate and high myopia were 5.07±0.69, 5.08±0.43 and 4.50±0.58 mm, respectively, and the corneal Q-values were 0.22±0.17, 0.57±0.34 and 0.63±0.73, there were significant differences among the three groups(all <i>P</i><0.05). The diameter of effective optical zones after operation in all three groups was lower than that predicted by 6.5mm before operation(<i>P</i><0.001). There were significant differences in postoperative total HOA, spherical aberration(Z40)and vertical coma(Z3-1)among the three groups(<i>P</i><0.05). The diameter of effective optical zone after SMILE was positively correlated with preoperative manifest refraction spherical equivalent and residual corneal thickness(<i>r</i>=0.357, 0.275,all <i>P</i><0.05), and negatively correlated with central corneal ablation depth and postoperative corneal Q-value(<i>r</i>= -0.316, -0.353, all <i>P</i><0.05). After operation, ΔZ40 was negatively correlated with ΔEOZ(<i>r</i>= -0.336, <i>P</i><0.05).<p>CONCLUSION:The EOZ after SMILE was lower than that expected before operation, and the higher the myopia was, the smaller the optical area was and the more the postoperative corneal spherical aberration increased. In addition, the depth of corneal ablation, residual corneal thickness and aspheric changes of cornea can affect the size of EOZ after operation.
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@#AIM: To investigate differences between 6.0mm and 6.5mm optical zones in visual quality after FS-LASIK. <p>METHODS: This was a prospective study. Totally 25 patients(50 eyes)treated with FS-LASIK were included and they were classified into 6.0mm group and 6.5mm group according to optical zone. Objective visual quality was evaluated by OQASⅡoptical quality analysis system(including OSI, Strel Ratio, MTF cut off, OV100%, OV20%, OV9%)and by Sirius to obtain the higher order aberrations parameters(including total HOAs, spherical aberrations, trefoil and coma)at 3mm, 5mm and 7mm pupil sizes. OSDI questionnaire was applied to evaluate patients' subjective visual quality. <p>RESULTS: At 3mo postoperatively, there were no significant differences in total HOAs, spherical aberrations, trefoil and coma under 3mm pupil size(all <i>P</i>>0.05). Significant differences were only observed in spherical aberrations at 5mm pupil size(<i>P</i><0.05), and in total HOAs and spherical aberrations at 7mm pupil size(<i>P</i><0.05).However, there were no significant differences in OSDI scores and OQAS visual quality parameters(<i>P</i>>0.05).<p>CONCLUSION: HOAs under scotopic conditions could be less with 6.5mm optic zone after FS-LASIK, however, both 6.0mm and 6.5mm optical zones could achieve good subjective and objective visual quality after FS-LASIK.
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We performed eight radial line cuts in anterior radial keratotomy(RK) employing the Russian style and the American style incisions on 103 eyes from August/ 1989 to March/ 1990. To analyze the results of myopic correction according to the size of the central optical zone and the incision length in RK, we chose the central optical zone size according to the degree of myopia (4.0 mm from -1.50D to -2.75D, 3.5mm from -30D to -3.75D and 3.0mm above -4.0D) and measured the length of each of the eight radial incisions of the cornea. The results were as follows: 1. In determining the average length of each corneal incision in RK, the longest was the superior and superior-nasal incision and the shortest was the temporal and inferior-temporal incision, regardless of the central optical zone size. 2. The total length of each of the eight incisions in each eye ranged from the longest at 3.0mm of central optical zone and the shortest at 4.0mm of central optical zone Undoubtedly, total incision length affected clinical results not significantly (p>0.05). 3. Assessing the clinical effect of myopic correction according to the optical zone size, smaller diameter clear zones produce a greater flattening of the cornea than larger ones. 4. The clinical result was not significantly affected by the direction of the incision (p>0.05).