Background Accurate measurement of corneal thickness is very important during the pre-and post-operative management of corneal surgical procedures,especially laser-assisted in-situ keratomileusis (LASIK),which is the most popular approach to the correction of refractive errors currently.This may be particularly important for the patients who have undergone previous laser refractive surgery with suboptimal outcomes and are being considered for an enhancement procedure.Objective This study was to compare the measuring outcomes of corneal thickness by slit-scanning pachymetry,non-contact specular microscope,anterior segment optical coherence tomography (AS-OCT)and ultrasound pachymetry,with a focus on central and midperipheral (from the central 3.0 mm) region of cornea in post-LASIK eyes.Methods Sixty-four right eyes of 64 patients who received LASIK were collected in Henan Eye Institute,Henan Eye Hospital from March to June 2011 with the equivalent spherical diopter of (-4.75±2.38)D and horizontal corneal diameter of (11.36±0.32)mm.Central corneal thickness was measured on each eye by using non-contact specular microscope (Topcon SP-3000P),slit-scanning pachymetry (Orbscan Ⅱ),AS-OCT and A-type ultrasound pachymetry,respectively,and the paracentral corneal thickness including 12:00,2:00,6:00 and 10:00 meridian was measured using Orbscan Ⅱ,non-contact specular microscope and AS-OCT.The measuring values and the agreement from different instruments were compared and evaluated.Results The mean central corneal thickness was (467.12±31.10)tμm for AS-OCT,(466.67±30.99)μm for ultrasound pachymetry,(441.84 ± 33.65) μm for specular microscopy and (422.51 ± 44.09) μm for Orbsan Ⅱ,respectively,showing a significant difference among the four methods (F =23.730,P =0.000).The central thickness value of the A-type ultrasound pachymetry was significantly higher than that of Orbsan Ⅱ or non-contact specular microscope (q =6.940,6.720,both at P =0.000).Compared with Orbscan Ⅱ,the measuring values of non-contact specular microscope and AS-OCT were significantly higher (q =-5.54,6.940,both at P =0.000),and the measuring value of AS-OCT was significantly higher that of non-contact specular microscope (q =6.800,P =0.000).The lowest difference value (25.3 μm)and the best agreement was found between the ultrasound pachymetry and AS-OCT.The paracentral corneal thickness values in 12:00,2:00,10:00,6:00 meridians were highest for Orbsan Ⅱ and the next for AS-OCT,and non-contact specular microscope had the lowest values,with significantly differences among them (F =5.020,22.950,67.890,18.850,all at P ＜ 0.01).Conclusions The corneal thickness values vary with the different instruments.Orbsan Ⅱ underestimates the central corneal thickness and overestimates the midperipheral corneal thickness,and non-contact specular microscope underestimates both the central and midperipheral corneal thickness.The measuring outcome from AS-OCT has a good agreement with ultrasound pachymetry and therefore they can be used interchangeably.

Background Researches showed that femtosecond laser corneal small incision lenticule extraction (SMILE) was used in the correction of myopia and myopic astigmatism due to its fast recovery,good shortterm efficacy and few complications.However,few research focused on its long-term efficacy.Objective Thisstudy was to evaluate the effectiveness,safety,predictability,stability and complications of SMILE.Methods A serial cases-observational study was carried out under the approval of Ethic Committee of Henan Eye Institute and informed consent of patients.Sixty-seven eyes of 34 patients with myopia and myopic astigmatism were included in Henan Eye Institute from January to June 2013.All the patients received SMILE and followed-up for 2-year duration.The uncorrected visual acuity (UCVA),best corrected visual acuity (BCVA),automatic optometry,intraocular pressure and corneal topography were examined before surgery and 1 day,1 week,1 month,3 months,1 year and 2 years after surgery and calculated the spherical equivalent (SE).The long-term efficacy of SMILE included effective index (preoperative BCVA/postoperative UCVA),safety index (postoperative BCVA/ preoperative BCVA),predictability (linear regression analysis between actual SE and attempted SE) and refractive stability (SE changes at postoperative time points).Results The preoperative BCVA was ≥ 20/20 in 60 eyes with the percentage of 89.55％.UCVA≥ 20/20 were found in 61 eyes and 60 eyes in postoperative 3 months and 2 years respectively (91.04％ and 89.55％).The effective index was 1.038±0.182 and 1.029±0.231 in postoperative 3 months and 2 years respectively,showing an insignificant difference between them (t =0.400,P ＞ 0.05).Compared with the preoperative BCVA,8.96％ (6/67) and 10.45％ (7/67) eyes lost 1 line at 3 months and 2 years after surgery,respectively.The safety indexes were 1.141±0.193 and 1.312±0.242 at 3 months and 2 years after surgery,with no significant difference between them (t =0.414,P＞0.05).A linear correlation was found between actual SE and attempted SE both at postoperative 3 months and 2 years,with the linear regression equations of Y=0.897 1X-0.440 8 (R2 =0.914 2,P＜0.05) and Y =0.893 7X-0.382 3 (R2 =0.915 7,P＜0.05),respectively.The SE was (0.013±0.578),(-0.033±0.489),(-0.106±0.508),(-0.103±0.375),(-0.154±0.518) and (-0.147±0.366)D 1 day,1 week,1 month,3 months,1 year and 2 years after surgery,respectively,and there were no significant difference among different time points (F =0.185,P =0.176).Eighteen in the 67 eyes occurred opaque bubble layer after surgery.Diffuse lamellar keratitis appeared in 6 eyes and punctate keratitis was in 2 eyes.These complications were cured 1 month after administration of drugs.Conclusions SMILE is good in effectiveness,safety,predictability and refreactive stability and has fewer complications during 2-year following-up.

Objective To study the sensitivity and specificity of parameter Corvis biomechanical index (CBI)— a new biomechanical index of Corvis ST in the diagnosis of keratoconus and evaluate the role of CBI in the diagnosis of keratoconus and the change of biomechanic.Methods A diagnostic trial study was adopted,and 66 eyes from 49 keratoconic patients (keratoconus group) and 91 right eyes from 91 myopic patients (control group) from April in 2018 to August in 2018 in Henan Eye Hospital were enrolled.Pentacam and Corvis ST examinations were performed by the same operator after the basic eye examinations.Using the evaluation of diagnostic test,consistency test,and receiver operating characteristic (ROC) curve analysis,gain the outcome of the sensitivity,specificity,consistency,Youden index,and area under the ROC curve of the parameter CBI.This study protocol was approved by Ethic Committee of Henan Eye Hospital and followed the Declaration of Helsinki.Written informed consent was obtained from each patient prior to any medical examination.Results Sixty eyes were diagnosed as keratoconus by the parameter CBI of Corvis ST.Evaluation of diagnosis test:the sensitivity was 97.0％,and the specificity was 97.8％;consistency check:Kappa =0.948,P＜0.05.ROC curve analysis:the sensitivity was 98.5％,the specificity was 96.8％,Youden index was 96.3％,P＜0.000 1 and AUC was 0.996.Conclusions CBI can separate healthy eyes from keratoconic eyes with highly sensitivity and specificity,which was highly consistency with results of Rabinowitz keratoconus diagnostic criteria.CBI could be used as a new biomechanical indicator for the diagnosis of keratoconus.

Objective: To evaluate the repeatability of corneal biomechanics parameters measured by Corneal Visualization Scheimpflug Technology (Corvis ST) and explore the factors that influence the repeatability. Methods: A diagnostic test study was performed.A total of 190 eyes in 95 myopia patients (34 males and 61 females) were enrolled from September to October 2017 in Henan Eye Hospital.All the subjects underwent 5 repeated examinations with the Corvis ST.The intraclass correlation coefficient (ICC), Cronbach α coefficients and repeatability coefficient (RC) were computed to evaluate repeatability of Corvis ST parameters.The multiple linear regression analysis was used to study the factors that affect the magnitude of the test-retest variability (within subject SD) of new Corvis ST parameters.This study was approved by the Ethics Committee of Henan Eye Hospital (HNEECKY-2019[5]), and written informed consent was obtained from each subject. Results: Among the 39 biomechanics parameters, The ICC and Cronbach α were greater than 0.75 for 26 parameters, within 0.60-0.75 for 4 parameters, and lower than 0.60 for deflection amplitude max time (DLAMT). The ICC and Cronbach α of DA ratio max[1 mm], DA ratio max [2 mm], max inverse radius, Ambrósio's relational thickness horizontal (ARTh), biomechanical intraocular pressure (bIOP), integrated radius, stiffness parameter applanation 1 (SPA1) and Corvis biomechanical index (CBI)were all above 0.920.The multivariate regression results indicated that the within subject SD of bIOP increased with the increase of IOP (β=0.210, P=0.010). The within subjects SD of DA Ratio Max [1 mm]decreased with the increase of central corneal thickness (CCT) (β=-0.218, P=0.008). The within subjects SD of DA Ratio Max [2 mm]decreased with the increase of CCT(β=-0.295, P<0.001). The within subject SD of CBI decreased with the increase of astigmatism, axial lengths and CCT (β=-0.190、-0.148、-0.428, all P<0.05). Conclusion The Corvis ST parameters showed favorable measurement repeatability in myopia patients, especially for the new parameters.Astigmatism, axial lengths and CCT significantly affected the repeatability of CBI.

Objective:To investigate the differences in corneal thickness and corneal epithelial thickness measurements by two kinds of high-resolution frequency domain anterior segment optical coherence tomography (OCT), RTVue XR-OCT and Cirrus 5000 HD-OCT, and to analyze the consistency between them.Methods:A cross-sectional study was conducted.Fifty-two patients (52 eyes) who were admitted to Henan Eye Hospital from July to September 2019 were enrolled.The corneal thickness and corneal epithelial thickness in various areas including the central area (C area) (2-mm diameter), and 8 concentric corneal areas of 2 to 5-mm diameter, which were the superior area (S area), the superior nasal (SN area), the nasal side area (N area), the inferior nasal area (IN area), the inferior area (I area), the inferior temporal area (IT area), the temporal area (T area) and the superior temporal area (ST area) above the temporal, were measured by the same examiner using RTVue XR-OCT and Cirrus 5000 HD-OCT.The corneal thickness and corneal epithelial thickness measurements were compared to analyze the difference, correlation and consistency between the two kinds of OCT.This study adhered to the Declaration of Helsinki.The study protocol was approved by an Ethics Committee of Henan Eye Hospital (No.HNEECKY-2021[06]). Written informed consent was obtained from each subject prior to any medical examination.Results:The corneal thickness measured by RTVue XR-OCT in C, S, SN, N, IN, I, IT, T, ST areas were (521.73±29.85), (554.31±32.38), (553.54±33.30), (546.96±32.05), (537.54±32.10), (532.13±31.51), (528.42±30.38), (532.25±30.08), (544.85±30.70)μm, respectively, and the corneal thickness in the 9 areas measured by Cirrus 5000 HD-OCT were (526.77±30.62), (555.13±33.32), (558.08±32.57), (554.46±31.42), (548.29±31.84), (539.69±32.74), (536.19±32.40), (533.38±31.90), (543.83±32.02)μm, respectively.There was no significant difference in corneal thickness of various areas between the two kinds of OCT (all at P>0.05), and there were positive correlations between them ( r=0.99, 0.89, 0.95, 0.97, 0.95, 0.93, 0.96, 0.97, 0.92; all at P<0.01). Bland-Altman analysis showed that there was a good consistency of corneal thickness measurements by the two kinds of OCT.The corneal epithelial thickness in C, S, SN, N, IN, I, IT, T, ST areas measured by RTVue XR-OCT were (52.06±3.26), (52.58±3.48), (53.06±3.56), (53.75±3.49), (53.81±3.40), (53.48±3.35), (52.96±3.32), (52.67±3.19), (53.12±3.15) μm, respectively, and the corneal epithelial thickness in the 9 areas measured by Cirrus 5000 HD-OCT were (46.75±3.25), (47.40±3.36), (47.58±3.64), (48.85±4.48), (48.46±4.54), (48.40±4.96), (48.06±5.12), (47.46±3.91), (48.79±3.90)μm, respectively.There were statistically significant differences in the corneal epithelial thickness of various areas measured by the two kinds of OCT (all at P<0.05), and there was no significant correlation between them ( r=0.17, 0.08, 0.16, 0.28, 0.20, 0.24, 0.19, 0.21, 0.13; all at P>0.05). Bland-Altman analysis showed poor consistency of corneal epithelial thickness measurements between the two kinds of OCT. Conclusions:There is no significant difference in measuring corneal thickness between the two kinds of OCT and the consistency is high, which means that they can be replaced by each other.There are significant differences in corneal epithelial thickness measurement between them and the consistency is poor, so they are not interchangeable.

Objective:To compare the accuracy and stability between corneal topography-guided femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK) and small incision lenticule extraction (SMILE) for myopic astigmatism by vector analysis.Methods:A non-randomized controlled clinical trial was performed.One hundred and twenty patients (214 eyes) with myopic astigmatism who underwent the FS-LASIK or SMILE in Henan Eye Hospital from January 2020 to July 2020 were enrolled.The patients were divided into FS-LASIK group (58 cases, 105 eyes) and SMILE group (62 cases, 109 eyes) according to different surgeries.The visual acuity, refraction, intraocular pressure and corneal topography were examined before and 1 week, 1 month and 3 months after operation.The results of vector analysis between the two groups were compared, including target induced astigmatism vector (TIA), surgically induced astigmatism vector (SIA), magnitude of error (ME), angle of error (|AE|), difference vector (|DV|), correction index (CI), and index of success (IOS) 3 months after operation.This study protocol adhered to the Declaration of Helsinki and was approved by an Ethics Committee of Henan Eye Hospital (No.HNEECKY-2020[25]). Written informed consent was obtained from each patient before operation.Results:Three months after surgery, no astigmatism was found in 11 eyes (10.5%), and with the rule (WTR) astigmatism was in 23 eyes (21.9%), and against the rule (ATR) and oblique astigmatism were in 71 eyes (67.6%) in FS-LASIK group.In SMILE group, no astigmatism was detected in 35 eyes (32.1%), and WTR astigmatism was in 58 eyes (53.2%), and ATR and oblique astigmatism were in 16 eyes (14.7%), showing a statistically significant difference between them ( χ2 =48.20, P<0.05). The postoperative SIA, |AE|, |DV|, CI and IOS values in the SMILE group were lower than those in the FS-LASIK group, showing statistically significant differences between them (all at P<0.05). The ME was -0.20 (-0.37, 0.00)D in FS-LASIK group and 0.20 (0.00, 0.25)D in SMILE group.Within 3 months after operation, there was no significant difference in ME among different time points in the FS-LASIK group (all at P>0.05) and in spherical equivalent (SE) among different time points in the SMILE group (all at P>0.05). There was significant difference in the results of vector analysis among different time points in the two groups (all at P<0.05). Conclusions:Both FS-LASIK and SMILE are effective in the correction of myopic astigmatism.Astigmatism is slightly overcorrected by FS-LASIK and slightly undercorrected by SMILE.The axial error is smaller and the SE is more stable after SMILE within 3 months postoperatively.

Objective:To investigate the clinical characteristics of patients with keratoconus, and to explore the factors influencing keratoconus severity.Methods:A cross-sectional study was performed.A total of 908 patients (1 476 eyes) with primary keratoconus were enrolled in Henan Eye Hospital from January 2019 to December 2021.The medical history data of patients were collected by face-to-face questionnaire survey.Refractive parameters were measured by subjective optometry.Intraocular pressure (IOP) was measured by a non-contact tonometer, and corrected IOP was calculated by Dresden formula.Corneal topography parameters was obtained using Pentacam HR.The subgroup analysis of clinical characteristics of all patients was performed by age (<21 years, 21~<31 years, ≥31 years) and gender.Disease severity was graded based on steep keratometry (Ks), namely mild (Ks<48 D), moderate (48 D≤Ks<55 D) and severe (Ks≥55 D). The influencing factors of disease severity in keratoconus were analyzed by ordered Logistic regression.This study adhered to the Declaration of Helsinki.The study protocol was approved by the Ethics Committee of Henan Eye Hospital (No.HNEECKY-2019[5]). All subjects or guardians were informed of the purpose and significance of the study and written informed consent was obtained.Results:Of the 908 patients, 622 were with bilateral keratoconus and 286 were with unilateral keratoconus.The median age of onset was 20(17, 26) years, and the median age of diagnosis was 21(18, 27) years.The ratio of males to females was 3.05∶1.There were 9.80%(89/908) of the patients having a history of allergy, 25.55%(232/908) having a history of other systemic diseases, and 1.98%(18/908) having a family history of keratoconus.Of the 1 476 affected eyes, 27.57%(407/1 476) were diagnosed as severe keratoconus, and 61.94%(568/917) had a history of eye rubbing.The medians of sphericity, cylindricity, IOP, corrected IOP, Ks, thinnest corneal thickness (TCT), anterior corneal surface elevation (AE) and posterior corneal surface elevation (PE) were -4.00(-7.00, -1.75)D, -3.50(-6.00, -1.50)D, 12.00(10.30, 13.80)mmHg, 15.40(13.60, 17.00)mmHg, 49.85(46.40, 54.90)D, 460.00(425.00, 490.00)μm, 21.00(13.00, 34.75)μm, 51.00(33.00, 75.00)μm, respectively.The spherical refraction, IOP and corrected IOP were lower and the cylindrical refraction was higher in patients at age <21 years than in patients at age 21~<31 years, and the TCT of patients at age <21 years was higher than that at age ≥31 years, and the differences were statistically significant (all at P<0.05). Compared with female patients, male patients had younger onset age, lower spherical refraction, IOP and corrected IOP, as well as higher cylindrical refraction, AE and PE, showing statistically significant differences (all at P<0.05). The spherical refraction and IOP of male patients were lower than those of female patients at age <21 years, and the cylindrical refraction was higher in males than in females among the patients at age 21~<31 years, and the differences were statistically significant (both at P<0.05). Among the patients with onset age <21 years and diagnosis age <21 years, the ratio of males to females in patients with severe keratoconus was higher than those with mild and moderate disease, and the difference was statistically significant (both at P<0.05). Older age of onset was a protective factor for disease severity in keratoconus (odds ratio=0.981, 95% confidence interval: 0.963~0.999). Conclusions:The younger the onset age of keratoconus patients, the more severe the disease.Among the patients with severe keratoconus, there were more male patients, and males have a younger onset age and severer conditions.It is suggested that early screening of keratoconus in children and adolescents should be strengthened in clinical work, and more active prevention and treatment measures should be taken for younger patients, especially males.

Objective:To evaluate the consistency of the Chinese three-dimensional anterior visual field analysis system (Scansys), the anterior segment analyzer (Pentacam), the frequency-domain anterior segment optical coherence tomography system (CASIA SS-1000), and a new ultra-high frequency digital ultrasound scanning system (Arcscan Insight100) to measure central vault after implantable collamer lens (ICL) implantation in myopic eyes with crystalline lenses.Methods:A diagnostic test study was conducted.Fifty-six myopic patients (56 eyes) who underwent ICL V4c implantation from June to December 2019 were included.Scansys, Pentacam, CASIA and Arcscan were used to measure the central vault after surgery.The vault measurements were compared.Correlations between the measurements of the four instruments were analyzed using Pearson correlation analysis, and consistency comparisons were analyzed using the Bland-Altman method.This study adhered to the Declaration of Helsinki.The study protocol was approved by the Ethics Committee of Henan Eye Hospital (No.HNEECKY-2021[13]). Written informed consent was obtained from each subject.Results:The central vault measurements by Scansys, Pentacam, CASIA and Arcscan were (481.8±191.6), (476.4±190.6), (619.3±207.5) and (534.0±221.2)μm, respectively, with a statistically significant overall difference ( F=143.301, P<0.001). The vault measurements by Scansys and Pentacam were significantly lower than CASIA and Arcscan, and Arcscan was lower than CASIA, with statistically significant differences (all at P<0.001). There were strong positive correlations in vault measurements between Arcscan and CASIA, Arcscan and Pentacam, Arcscan and Scansys, CASIA and Pentacam, CASIA and Scansys, Pentacam and Scansys ( r=0.982, 0.933, 0.931, 0.942, 0.941, 0.989; all at P<0.001). Intraclass correlation coefficients of vault measurements by Scansys, Pentacam, CASIA and Arcscan were 0.985, 0.975, 0.998, 0.992, respectively.The 95% limits of agreement of vault measurements differences were -170 to 0, 0 to 280, 0 to 280, -110 to 210, -100 to 220 μm, between CASIA and Arcscan, CASIA and Scansys, CASIA and Pentacam, Arcscan and Scansys, Arcscan and Pentacam, respectively, and the maximum absolute value of the difference was beyond the clinically acceptable range, showing poor agreement.The 95% limits of agreement of vault measurement difference was -60 to 50 μm between Scansys and Pentacam, showing a good agreement. Conclusions:The repeatability of the vault after ICL V4c implantation in myopic eyes measured by the four instruments is good.Among them, the vault measurements of Scansys and Pentacam are smaller, showing good consistency, and their results could be substituted for each other.The measurement of CASIA is the largest, followed by Arcscan, which have a large difference from each other, and their results can not be substituted for each other, which should be comprehensively analyzed with the actual situation in clinical work.

Objective:To evaluate the effects of static eyeball rotation and decentration of lenticule on astigmatism correction in femtosecond small incision lenticule extraction (SMILE) by using standardized vector analysis.Methods:A series of case observation study was performed.A total of 128 eyes from 73 myopic astigmatism patients undergoing SMILE from January to April 2019 in Henan Eye Hospital were enrolled.The preoperative spherical equivalent was -2.25 to -7.75 DS, and the astigmatism was -0.25 to -3.75 DC.The absolute value of the static rotation intraoperatively was measured by WASCA aberrometer, CRS master and MEL80 excimer laser system.The decentration of lenticule was measured and calculated according to Pentacam corneal topography and operation video.The visual acuity, refraction, corneal topography, and target induced astigmatism vector (TIA) were measured and calculated preoperatively and 1 week, 1 month and 3 months postoperatively.The results of manifest refraction were used to calculate surgically induced astigmatism vector (SIA), magnitude of error (ME), absolute value of angle of error (|AE|), absolute value of difference vector (|DV|), correction index (CI) and index of success (IS) three months postoperatively.Written informed consent was obtained from each patient before the surgery.This study protocol was approved by Ethic Committee of Henan Eye Hospital.Results:The absolute value of intraoperative static rotation was 2.75° (1.26°, 4.48°), decentration of lenticule was (172±87)μm and TIA was 0.69 (0.44, 1.35) preoperatively.The SIA was 0.67 (0.42, 1.10), ME was 0.10 (0.00, 0.26)DC, |AE|was 0.35° (0.00°, 9.47°), |DV|was 0.25 (0.00, 0.50), CI was 0.91 (0.72, 1.00), IS was 0.23 (0.00, 0.56) three months postoperatively.The differences of static eyeball rotation angle, ME, |DV|, CI between different astigmatism groups, the difference of decentration of lenticule between different static eyeball rotation groups, and the differences of static eyeball rotation angle, ME, |AE|, |DV|, CI and IS between different decentration groups were statistically significant (all at P<0.05). The decentration of lenticule was positively correlated with static eyeball rotation ( r s=0.39, P<0.01), and with |DV| ( r s=0.31, P<0.01). Conclusions:SMILE is effective procedure in correcting astigmatism.The static eyeball rotation and the decentration of lenticule are slight.The decentration of lenticule may have a relationship with static eyeball rotation and the difference vector of astigmatism.