Comparison of total corneal power measurements obtained with different devices after myopic keratorefractive surgery

AIM:To analyze the differences,agreements,and correlation among total corneal power parameters generated by different instruments after myopic keratorefractive surgery.METHODS:The prospective cross-sectional study included patients who underwent myopic keratorefractive surgery and received measurements of corneal power 3mo after surgery.Automated keratometer was used for the measurement of simulated keratometry(Sim K),sweptsource optical coherence tomography(SS-OCT)based biometer for total keratometry(TK),anterior segment-OCT for real keratometry(RK),and Scheimpflug keratometer for the true net power(TNP),the total corneal refractive power(TCRP)and equivalent K-readings(EKR).The differences among these parameters were analyzed,and the agreements and correlation between Sim K and other total corneal power parameters were investigated.RESULTS:A total of 70 eyes of 70 patients after myopic keratorefractive surgery were included.The evaluated corneal power parameters were as follows:Sim K 38.32±1.93 D,TK 37.54±2.12 D,RK 36.64±2.09 D,TNP 36.56±1.97 D,TCRP 36.70±2.01 D,and EKR 37.55±2.00 D.Pairwise comparison showed that there were significant differences(P<0.001)among all parameters except for between TK and EKR,RK and TNP,RK and TCRP(P=1.000,1.000,1.000,respectively).The limits of agreement between Sim K and TK,RK,TNP,TCPR,and EKR were 1.08,1.08,1.43,1.48,and 1.73 D,respectively.All parameters showed good correlation with Sim K,and the correlation coefficients were 0.995,0.994,0.983,0.982,and 0.975.CONCLUSION:Among the corneal power parameters after myopic keratorefractive surgery,the value of Sim K is the largest,followed by TK and EKR,with TCRP,RK,and TNP being the smallest.The differences among the parameters may be attributable to the different calculation principles.Correct understanding and evaluation of corneal power parameters can provide a theoretical basis for taking advantage of the total corneal power to improve the accuracy of intraocular lens calculation after keratorefractive surgery.

Comparison of correcting myopia and astigmatism with SMILE or FS-LASIK and postoperative higher-order aberrations

AIM:To compare the effect of myopia and astigmatism correction and postoperative change in higher-order aberration as results of receiving small-incision lenticule extraction(SMILE)and femtosecond laser-assisted in situ keratomileusis(FS-LASIK).METHODS:A prospective and non-randomized controlled study was conducted.The subjects are divided into two groups according to different operations received:229 eyes of 116 patients in the SMILE group and 168 eyes of 86 patients in the FS-LASIK group.All subjects were followed up for 3 mo by monitoring their uncorrected visual acuity(UCVA),best-corrected visual acuity(BCVA),spherical equivalent,higher-order aberrations,and the preoperative and postoperative complications.RESULTS:At 1 wk,1,and 3 mo post-surgery,224 eyes(97.8%),227 eyes(99.1%)and 229 eyes(100%)had UCVA≥20/20 in the SMILE group,while 165 eyes(98.2%),167 eyes(99.4%)and 167 eyes(99.4%)had UCVA≥20/20 in the FS-LASIK group,respectively(χ^(2)=0.146,2.135,and 1.124;all P>0.05).BCVA reduction was not observed in both groups at 1 and 3 mo of post-surgery(χ^(2)=0.734 and 1.898,P>0.05).There was no statistically significant difference in the spherical equivalent between the two groups at 1 and 3 mo post-surgery,though the percentage of the spherical equivalent within±0.50 D at 3 mo postsurgery was 98%in the SMILE group,which was higherthan that of the FS-LASIK group(92%,χ^(2)=1.872,P>0.05).The root mean square(RMS)values of total high-order aberration,coma,and spherical aberration of the two groups increased significantly in the early postoperative period and decreased after 3 mo,but the values were still higher than the preoperative levels(P<0.05);there was no significant difference between the two groups in the RMS values of total higher-order aberrations and specific higherorder aberrations(P>0.05).The incidence of complications in the SMILE group was lower than that in the FS-LASIK group(χ^(2)=14.52,P<0.05).CONCLUSION:SMILE and FS-LASIK can effectively treat myopia,significantly improve visual acuity,and increase the total high-order aberration,spherical aberration,and coma.The incidence of complications after SMILE is relatively low.

Comparison of corneal curvature parameters obtained from two different instruments—Pentacam and VX120

AIM: To explore whether the same corneal curvature parameters and anterior chamber depth measured by Pentacam and VX120 have a good consistency and can replace each other. METHODS: This study enrolled 140 eyes of 70 patients ranging in age from 19 to 53 y. All eyes underwent a comprehensive ophthalmologic examination including an anterior segment analysis with the VX120 system(Visionix-Luneau Technologies, Chartres, France) and Pentacam(Oculus Optikgerate GmbH) respectively. The comparison on corneal curvature parameters was done between Pentacam and VX120 using clustered signed rank test;the interclass correlation coefficients(ICC) with 95% confidence intervals(CI) was calculated for each parameter between Pentacam and VX120;the BlandAltman plot of each parameter was supplemented. RESULTS: The anterior corneal curvature measured by VX120 was Ks: 44.00±1.78 D, KsAt: 89.45±22.18, Kf: 42.84±1.58 D, KfAt: 93.91±79.34;which measured by Pentacam was Ks: 43.80±1.82 D, KsAt: 91.17±21.40, Kf: 42.61±1.64 D, KfAt: 91.16±78.69. There was statistical difference between Pentacam and VX120 for anterior corneal curvature parameter(P<0.001). The posterior corneal curvature measured by VX120 was Ks:-6.42±1.23 D, KsAt: 91.00±23.45, Kf:-5.85±1.24 D, KfAt: 95.93±79.11;which measured by Pentacam was Ks:-6.44±0.32 D, KsAt: 92.24±11.75, Kf:-6.01±1.05 D, KfAt: 74.43±80.64. There was statistical difference between Pentacam and VX120 for posterior corneal curvature parameters(P<0.001). Anterior chamber depth(ACD) measured by Pentacam and VX120was statistically different. Pentacam and VX120 achievedhigh consistency only on corneal anterior surface, including Ks and Kf. The ICCs were 0.96(95%CI: 0.95, 0.97) and 0.95(95%CI: 0.94, 0.97) respectively. For other corneal surface curvature parameters, all ICCs of between Pentacam and VX120 were below 0.87. Bland-Altman plots indicated oflow consistency of corneal surface curvature parameters measured by Pentacam and VX120. CONCLUSION: The corneal curvature parameters and anterior chamber depth measured by Pentacam and VX120 were statistically different. Data measured by Pentacam and VX120 is not suggested to replace each other, mixing data measured by Pentacam and VX120 together is not suggested either.

Comparison of clinical outcome of small-incision lenticule intrastromal keratoplasty and FS-LASIK for correction of moderate and high hyperopia

AIM:To compare the clinical outcome of small-incision lenticule intrastromal keratoplasty(s LIKE)and femtosecond laser-assisted in situ keratomileusis(FS-LASIK)for correction of moderate and high hyperopia.METHODS:A case-controlled clinical study was performed.Twenty right eyes of 20 moderate and high hyperopia patients underwent s LIKE(s LIKE group)and 22 right eyes of 22 moderate and high hyperopia patients underwent FS-LASIK(FS-LASIK group)were enrolled in this study from October 2015 to October 2017.Visual acuity,refractive error,corneal thickness,and keratometry were compared between the groups before and 1 y postoperatively.RESULTS:The postoperative uncorrected near visual acuity(UNVA)and uncorrected distance visual acuity(UDVA)were improved in the two groups.The UNVA reached J1 in 15 eyes(75.0%)in the s LIKE group and 5 eyes(22.7%)in the FS-LASIK group 1 y after surgery(χ2=11.476,P=0.001).The UDVA was equal or better than the preoperative CDVA in 16 eyes(80.0%)in the s LIKE group and 8 eyes(36.4%)in the FS-LASIK group,respectively(X2=8.145,P=0.004).No eyes lost any line of best-corrected visual acuity(BCVA)in either group.The amount of postoperative residual hyperopia in the s LIKE group was significantly less than in the FS-LASIK group(Z=-2.841,P=0.004).The postoperative keratometry and corneal thickness were significantly higher in the s LIKE group than in the FS-LASIK group(t=4.411,10.279,P<0.001).The SRI and SAI of the s LIKE group were significantly higher than that in the FS-LASIK group.There was no statistically significant difference in mean decentration between the two groups.CONCLUSION:s LIKE has better visual and refractive outcome than FS-LASIK for correction of moderate and high hyperopia.

Evaluation of preoperative dry eye in people undergoing corneal refractive surgery to correct myopia

AIM: To investigate the incidence of preoperative dry eye and related factors in patients undergoing corneal refractive surgery to correct myopia.METHODS: A total of 141 patients with myopia who underwent corneal refractive surgery were surveyed by questionnaires, tear film break-up time(BUT) test, Schimer I test(SIt), corneal fluorescein staining(FL) test and diagnosed according to the currently recognized domestic diagnostic criteria for dry eye. Correlation analysis of factors such as age, gender, regular wearing of contact lens(CL), diopter(spherical equivalent), corneal thickness, and corneal curvature that may affect the onset of dry eye was carried out to clarify the main influencing factors. RESULTS: There were 64 patients(45.39%) diagnosed with dry eye. The male patients(20.31%) was significantly less than that of non-dry eye subjects(41.56%;χ~2=7.260, P=0.007);the proportion of patients with dry eye wearing CL(81.25%) was significantly higher than that of non-dry eye subjects(51.95%;χ~2=13.234, P<0.001);the median diopter level of dry eye patients was-6.59(IQR:-8.87,-4.58) D, and the median diopter level of non-dry eye subjects was-5.69(IQR:-7.15,-4.03) D. The diopter level of dry eye patients was significantly higher(Z=-2.086, P=0.019). However, the age, best corrected visual acuity, and intraocular pressure of dry eye patients were not statistically different from those of non-dry eye subjects(t=-0.257,-0.383 and 0.778, P=0.798, 0.702, and 0.438);the corneal thickness and corneal curvature(K1 and K2) were also not statistically different either(Z=-1.487,-1.036 and-1.707, P=0.137, 0.300, and 0.088). The research further analyzes the three significant factors in the single factor analysis(gender, CL wear, and diopter) in a multi-factor way: CL wear and diopter were the influencing factors of dry eye disease. Among them, CL wear increased the risk of dry eye by 2.934 times compared with no CL wear;for every 1 D increase in diopter, the risk of dry eye increased by 0.761 times.CONCLUSION: Preoperative dry eye is relatively common in patients who undergo corneal refractive surgery to correct myopia, especially in patients who have a history of CL wear and a high diopter level before surgery. Therefore, it is necessary to carry out preoperative screening and timely treatment of dry eye to obtain the best treatment outcome and postoperative satisfaction.

Comparison of corneal flaps created by Wavelight FS200 and Intralase FS60 femtosecond lasers

AIM：To assess and compare the morphology of corneal flaps created by the Wavelight FS200 and Intralase FS60 femtosecond lasers in laser in situ keratomileusis（LASIK）.METHODS：Four hundred eyes of 200 patients were enrolled in this study and divided into Wavelight FS200 groups（200 eyes） and Intralase FS60 groups（200 eyes）.Fourier-domain optical coherence tomography（RTVue OCT） was used to measure the corneal flap thickness of 36 specified measurements on each flap one week after surgery.Results were used to analyze the regularity,uniformity and accuracy of the two types of LASIK flaps.RESULTS：The mean thickness of corneal flap and central flap was 105.71±4.72 μm and 105.39±4.50 μm in Wavelight FS200 group and 109.78±11.42 μm and 109.15±11.59 μm in Intralase FS60 group,respectively.The flaps made with the Wavelight FS200 femtosecond laser were thinner than those created by the Intralase FS60 femtosecond laser（P=0.000）.Corneal flaps in the 2 groups were uniform and regular,showing an almost planar configuration.But the Wavelight FS200 group has more predictability and uniformity of flap creation.The mean deviation between achieved and attempted flap thickness was smaller in the Wavelight FS200 group than that in the Intralase FS60 group,which were 5.18±3.71 μm and 8.68±7.42 μm respectively.The deviation of more than 20 μm was 0.2% measurements in Wavelight FS200 group and 8.29% measurements in Intralase FS60 group.CONCLUSION：The morphologies of flaps created by Wavelight FS200 are more uniform and thinner than those created by Intralase FS60.

Comparison of Ziemer FEMTO LDV "Classic" and " Crystal Line" femtosecond laser flap quality by Fourierdomain optical coherence tomography

AIM:To compare the regularity and accuracy of laser in situ keratomileusis(LASIK) flaps created by the Ziemer FEMTO LDV 'Classic'(Ziemer 'Classic') and Ziemer FEMTO LDV Crystal Line femtosecond laser(Ziemer Crystal Line). METHODS:Fourier-domain optical coherence tomography(RTVue OCT) was used to measure the morphology of 200 LASIK flaps of 100 consecutive patients created with the Ziemer Classic(100 flaps) or the Ziemer Crystal Line(100 flaps) at one week postoperatively.Flap thickness was evaluated at 36 specified measurement points on each flap.For all procedures with both lasers,the nominal flap thickness was 110μm.RESULTS:The mean flap thickness of the Ziemer Crystal Line group(102.49±2.68μm) was thinner than that of the Ziemer Classic group(107.65±5.09μm)(P【0.01).Average thickness of all flaps was uniform within 4μm at all measurement points.The flaps in the Ziemer Crystal Line group were more regular than those in the Ziemer Classic group when measured from the center to the periphery.The maximum deviation from the nominal 110μm of 36 measurements was 8μm in the Ziemer Classic group,while in the Ziemer Crystal Line group it was 9μm.Within the 3 600 measurements on the 100 eyes,differences greater than 20μm were observed 0.14% in the Ziemer Classic group,and 0.04% in the Ziemer Crystal Line group. CONCLUSION:The flaps created with the Ziemer FEMTO LDV Crystal Line femtosecond laser are more uniform and thinner than those created by the Ziemer FEMTO LDV Classic femtosecond laser.