Utility of the Swept Source Optical Coherence Tomography for Measurements of Central Corneal Thickness

PURPOSE: To evaluate the efficacy of swept source optical coherence tomography (SS-OCT) by comparing the measurement of central corneal thickness (CCT) to the measurement obtained using Orbscan II, anterior segment optical coherence tomography (AS-OCT) and ultrasound pachymetry. METHODS: One examiner measured the CCT in 65 eyes of 65 healthy subjects using Orbscan II, AS-OCT, SS-OCT and ultrasound pachymetry. The mean values and correlations were analyzed. RESULTS: The average CCT measurements obtained using Orbscan II, AS-OCT, SS-OCT and ultrasound pachymetry were 534.83 ± 38.46, 517.80 ± 32.48, 528.22 ± 33.71 and 528.02 ± 34.90 µm, respectively. A significant linear correlation was observed among Orbscan II, AS-OCT, SS-OCT and ultrasound pachymetry (r > 0.894, p < 0.001). There was no significant difference between the SS-OCT and ultrasound pachymetry (p = 0.782). CONCLUSIONS: The results of the 4 methods were significantly correlated and the SS-OCT reached a high level of agreement when CCT was determined using ultrasound pachymetry. The CCT measurements using SS-OCT is a better alternative for ultrasound pachymetry than Orbscan II and AS-OCT.

Comparison of Anterior Segment Measurements Using Scanning-Slit Topography and Optical Low-Coherence Reflectometry (OLCR) Biometry

PURPOSE: To compare the results of anterior segment biometry including white-to-white (WTW) between scanning-slit topography (ORBscan IIz(R), Bausch & Lomb), optical low-coherence reflectometry (OLCR) biometry (Lenstar(R), Haag-Streit), and Castroviejo calipers. METHODS: Measurements on 72 eyes of 36 patients that underwent refractive surgery were measured using ORBscan(R), Lenstar(R), and calipers and compared. Ocular biometry parameters used in this study included the WTW, central corneal thickness, anterior chamber depth (ACD), keratometry, and pupil size. RESULTS: The WTW measurements using ORBscan(R) and calipers (11.57 +/- 0.35 mm and 11.58 +/- 0.34 mm, respectively) were statistically similar. However, the measurement using Lenstar(R) (12.05 +/- 0.40 mm) was significantly greater than with the other methods (p < 0.001). Central corneal thickness and keratometry measurements using ORBscan(R) were greater than when using Lenstar(R) (p = 0.01 for both). ACD and pupil size measurement using Lenstar(R) were greater than when using ORBscan(R) (p < 0.001 for both). CONCLUSIONS: Because WTW and ACD measurements using Lenstar(R) were greater than when using ORBscan(R) and calipers, unexpected high-vaulting may be observed due to the selection of a larger-sized posterior chamber phakic intraocular lens. Therefore, the differences in measurements obtained when using these methods should be considered.

Comparison of Anterior Segment Measurements Using Scanning-Slit Topography and Optical Low-Coherence Reflectometry (OLCR) Biometry

PURPOSE: To compare the results of anterior segment biometry including white-to-white (WTW) between scanning-slit topography (ORBscan IIz(R), Bausch & Lomb), optical low-coherence reflectometry (OLCR) biometry (Lenstar(R), Haag-Streit), and Castroviejo calipers. METHODS: Measurements on 72 eyes of 36 patients that underwent refractive surgery were measured using ORBscan(R), Lenstar(R), and calipers and compared. Ocular biometry parameters used in this study included the WTW, central corneal thickness, anterior chamber depth (ACD), keratometry, and pupil size. RESULTS: The WTW measurements using ORBscan(R) and calipers (11.57 +/- 0.35 mm and 11.58 +/- 0.34 mm, respectively) were statistically similar. However, the measurement using Lenstar(R) (12.05 +/- 0.40 mm) was significantly greater than with the other methods (p < 0.001). Central corneal thickness and keratometry measurements using ORBscan(R) were greater than when using Lenstar(R) (p = 0.01 for both). ACD and pupil size measurement using Lenstar(R) were greater than when using ORBscan(R) (p < 0.001 for both). CONCLUSIONS: Because WTW and ACD measurements using Lenstar(R) were greater than when using ORBscan(R) and calipers, unexpected high-vaulting may be observed due to the selection of a larger-sized posterior chamber phakic intraocular lens. Therefore, the differences in measurements obtained when using these methods should be considered.

Discrepancy of sulcus-to-sulcus diameter and its relationship with white-to-white diameter in high myopic eyes / 中华实验眼科杂志

Background Horizontal sulcus-to-sulcus (STS) and white-to-white diameter are important parameters for designing the proper size of collamer implantable contact lens (ICL).Inappropriate size of ICL may induce the complications postoperatively.Several previous studies compare horizontal STS and white-to-white diameter in normal eyes have been reported,but seldom in high myopic eyes.Objective This study was to investigate the discrepancy of STS diameters in 4 axes and analyze the relationship between horizontal STS diameter and white-towhite diameter in high myopia eyes.Methods The STS diameters in 4 axes (45,90,135 and 180 degrees) and the white-to-white diameters were measured in 48 eyes of 26 high myopia patients using the 50 MHz ultrasound biomicroscopy (UBM),the Orbscan-Ⅱ topography system,and the IOL Master,respectively.The mean spherical was (-12.93±3.87) diopters (D) (-8 to-20 D).Statistical evaluation was performed using the one-way ANOVA for comparison of measurement.The agreement of three devices was assessed using the Bland and Altman method.Results The mean STS diameter at 45,90,135 and 180 degrees was (12.06±0.50) mm,(12.27±0.50)mm,(12.03±0.46) mm and (11.84±0.47)mm,respectively.The 90 degree STS was significantly larger than other STS diameters (all at P＜0.05).The 180 degrees STS was significantly shorter than other STS diameters (all at P＜0.05).However,there was no significant difference between 45 degree STS and 135 degree STS (P=0.817).The mean WTW was (11.56±0.40) mm with Orbscan Ⅱ z topography system and (11.98±0.41) mm with IOLMaster.The WTW measured with Orbscan Ⅱ z was significantly shorter than the 180 degrees STS (t =-4.384,P =0.000).The WTW measured with IOLMaster was significantly larger than the 180 degrees STS (t =2.368,P =0.000).Bland-Altman analysis showed not very well agreement for measurements of WTW,STS between Orbscan Ⅱz and UBM,IOLMaster and UBM,Orbscan Ⅱ z and IOLMaster,the width of 95％ confidence interval (CI) were-0.57 to 1.12 mm,-0.96 to 0.67 mm,-0.73 to-0.13 mm,respectively.Conclusions The STS diameters in 4 different axes are not identical with each other in high myopia eyes.The longest STS is in the vertical meridian,the shortest STS is in the horizontal meridian.The WTW diameter measured with both Orbscan Ⅱ z and IOLMaster are not precise for calculating the horizontal STS in high myopia eyes.Three instruments cannot be interchanged for calculating the size of ICL.

Comparison of ocular anterior segment parameters measured by three kinds of biometric measuring methods in myopic eyes / 中华实验眼科杂志

Background It is essential to measure and assess the parameters of ocular anterior segment for refractive surgery in myopic eyes.Some different imaging devices can be used for biometric measurement of ocular anterior segment,but which is more accurate and convenient is still under investigation.Objective This study was to compare the anterior segment parameters in myopic eyes measured by anterior segment optical coherence tomography (AS-OCT),Orbscan topography and ultrasonic pachymetry (US).Methods One hundred and forty eyes of 70 myopic subjects with the diopter of-0.75 to-10.25 D,who intended to receive corneal refractive surgery in the Second Affiliated Hospital of Zhejiang University School of Medicine from November 2011 to May 2012,were retrospectively analyzed.Central corneal thickness (CCT) was measured using AS-OCT,Orbscan Ⅱ and US,respectively,and anterior chamber depth (ACD) was measured by AS-OCT and Orbscan Ⅱ,and the angle to angle (ATA) distance and corneal white-to-white corneal distance (WTW) were measured by AS-OCT and Orbscan Ⅱ,respectively.The parameters from different apparatuses were statistically compared.Results The mean CCT were (516.57±30.25) μm in AS-OCT,(523.68±31.87) μm in US and (514.69±38.40) μm in Orbscan Ⅱ,without significant difference among them (F =2.775,P =0.063).Then the patients were divided into three groups based on the US measurement of CCT (＜500 μm group,500-569 μm group,and ≥ 570 μm group).In the ＜500 μm group,there was a significant difference in the CCT among the three methods (F =22.236,P =0.000),significant differences were found between AS-OCT and Orbscan Ⅱ,or Orbscan Ⅱ and US(both at P＜0.05).In the 500-569 μm group,there was no significant difference in the CCT among the three methods (F =3.011,P =0.051).In the ≥ 570 μm group,there was a significant difference in the CCT among the three methods (F =4.133,P =0.021),a significant difference was found between AS-OCT and US(P＜0.05),but there was no significant difference between AS-OCT and Orbscan Ⅱ (P＞0.05).The ACD values measured by AS-OCT was (3.83±0.21) mm,which was higher than (3.75 ± 0.21) mm by Orbscan Ⅱ,with a significant difference between them (t =-8.520,P =0.000).In addition,the ATA value by AS-OCT (12.43 mm±0.74 mm) was higher than the WTW value (11.42 mm±0.33 mm) by OrbscanⅡ,with a significant difference between them(t=-18.088,P=0.000).Conclusions AS-OCT,US and Orbscan Ⅱ can offer accurate CCT value,and they can provide references to one another before refractive surgery.However,the ACD,ATA and WTW values by AS-OCT and Orbscan]Ⅱ have large differences.

Comparison of different methods for the measurement of central and paracentral corneal thickness in post-LASIK eyes / 中华实验眼科杂志

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.

Comparison of Anterior Chamber Depth Obtained from Applanation and Optical Principle Devices

PURPOSE: To assess the reproducibility and reliability of applanation A-scan ultrasonography (Pacscan 300A, Sonomed Inc., Chicago, IL, USA) and optical measurements with IOL Master(R) (Carl Zeiss Meditec, Germany), Pentacam(R) (Oculus, Wetzlar, Germany), and Orbscan II(R) (Orbtek Inc., Laredo, TX, USA) when measuring anterior chamber depth (ACD). METHODS: In this study of 188 eyes of 94 patients, ACD estimation prior to cataract surgery was preformed by the applanation A-scan method and IOL Master(R), Pentacam(R), and Orbscan II(R) optical methods. Repeatability from each device was evaluated by coefficient of variation, standard deviation, and intraclass correlation coefficient. RM-ANOVA on Ranks was used to compare the differences in ACD among the devices. The Bland-Altman plot was performed to assess agreement in measurements between the devices. RESULTS: The mean ACD according to the applanation A-scan method and IOL Master(R), Pentacam(R), and Orbscan II(R) optical methods were 2.89 +/- 0.49 mm, 3.25 +/- 0.45 mm, 3.21 +/- 0.46 mm, and 3.19 +/- 0.47 mm, respectively, and the differences were statistically significant (p < 0.01). The coefficient of variation for the 4 methods was 2.50% in the A-scan, 0.87% in the IOL Master(R), 1.25% in the Pentacam(R), and 1.04% with Orbscan II(R), and reproducibility was higher with the optical principle devices. The correlation coefficient between A-scan and IOL Master(R) was 0.65, between IOL Master(R) and Pentacam(R) 0.91, between IOL Master(R) and Orbscan II(R) 0.90, between A-scan and Pentacam(R) 0.69, between A-scan and Orbscan II(R) 0.71, and between Pentacam(R) and Orbscan II(R) 0.93. CONCLUSIONS: Applanation A-scan provided lower measurements for ACD compared with IOL Master(R), Pentacam(R) and Orbscan II(R). There was good agreement between results obtained with the latter 3 methods, and reproducibility was high with optical measurements. The coefficient of variation was low for IOL Master(R).

Comparison of Colvardpupillometer, ORBScan II and Sirius in Determining Pupil Size for Refractive Surgery

PURPOSE: To compare pupil size measured by Colvard(R)pupillometer, ORBScan II(R), Sirius(R) and analyze correlation between pupil size and night vision disturbance after refractive surgery according to measuring methods. METHODS: Two hundred eyes of one hundred patients who underwent refractive surgery were retrospectively evaluated. Pupil size was measured with Colvard(R)pupillometer, Sirius(R) in the scotopic light condition and with ORBScan II(R), Sirius(R) in the photopic light condition. Patients filled out questionnaire about night vision disturbance at postoperative three months. Correlation between pupil size according to measuring methods and night vision disturbance was evaluated. RESULTS: The mean age of patient was 26 years and number of male patients was 36. In scotopic light condition, pupil size measured with Colvard(R)pupillometer (6.76 mm) was significantly larger than that of Sirius(R) (6.53 mm) (p < 0.001). In photopic light condition, pupil size measured with ORBScan II(R) (3.98 mm) was significantly smaller than that of Sirius(R) (4.41 mm) (p < 0.001). Night vision disturbance were correlated with pupil size and Sirius(R) in the scotopic light condition had strongest correlation among three measuring method (r = 0.44). CONCLUSIONS: Sirius(R) tends to measure pupil size smaller than Colvard(R)pupillometer in the scotopic light condition. The correlation between night vision disturbance and pupil size was highest in Sirius(R).

Estimation of Corneal Spherical Aberration from Topography

PURPOSE: To formulate an equation to estimate corneal spherical aberration using Orbscan (Bausch & Lomb Surgical, Rochester, NY, USA) parameters. METHODS: The study was carried out retrospectively. The participants were 76 eyes of 76 senile cataract patients with the mean age of 57.37 +/- 17.63 years. Both Orbscan and KR-1W (Topcon Corp, Tokyo, Japan) were taken as preoperative examinations. Correlation analysis between various parameters from Orbscan and corneal spherical aberrations for a 6 mm pupil by KR-1W was performed. And multivariable linear regression was performed with the significantly correlated Orbscan parameters from the correlation analysis. RESULTS: The mean corneal spherical aberration from KR-1W system was 0.25 +/- 0.08 microm. As a result of the multivariable linear regression, we could generate following equations. If the Q-value was available, estimated corneal spherical aberration = 0.389 x Q-value + (0.022 x Axial power 3 mm) - 0.633 (R2 = 0.436). If the Q-value was not available, estimated corneal spherical aberration = 0.184 x (Mean power 5 mm - Mean power 3 mm) + (0.02 x Axial power 3 mm) - 0.563 (R2 = 0.429). By using the equations, 93.4-94.7% of subjects were in the error range of 0.10 microm. CONCLUSIONS: Even when equipped with Orbscan only, an appropriate aspheric intraocular lens can be selected using the estimated corneal apherical aberration by the equations.

Interval analysis of anterior corneal surface by Q-value calculation on tangential topography / 中华实验眼科杂志

Background Q-value is used to express the asphricity of the anterior corneal surface.As a optical surface,the optial morphology of cornea is composed of a series of tangential sections that cut-off through the optical axial.Therefore,tangential section could represent the true optical morphology of the corneal surface,and Q-value calculation by tangential radius can better represent the asphericity.Objective This study was to calculate Q-value of meridian section of the anterior corneal surface by tangential radius of the tangential topography and analyze the corneal asphericity in horizontal interval.Methods Ninety right eyes of 90 myopia subjects aged 16-30years and with mean spherical equivalent of (-5.45 ± 2.75) D received corneal topography examination using Orbscan Ⅱ system.The subjects were assigned to low myopia group,moderate myopia group and high myopia group based on their diopter and 30 eyes for each group.The tangential curvatures on meridian section at a 0.1 mm interval from apex to periphery of the anterior surface were accepted and the Q value of the semimeridian section was calculated by linear regression mathematical formulas of the tangential radius.Mydriatic optometry,intraocular pressure,keratometer and fundus examinations were performed on the subjects.Written informed consent was obtained from each subject before any medical examination.Results The coefficients of determination in all the semimeridians were over 0.5.The average calculated Q-values in the nasal and temporal horizontal interval were -0.32±0.11 and-0.30±0.12,with a significant difference between them (t =2.009,P＜0.05).The vertex radius of curvature was (7.78±0.27)mm and (7.72±0.25)mm respectively in the nasal and temporal horizontal interval,showing a significant difference(t=-1.016,P＞0.05).No significant difference was seen in Q values of both nasal and temporal areas among three myopic groups (nasal:F =0.192,P =0.825 ; temporal:F =0.912,P =0.406).The average Q value of the nasal and temporal principal meridian was-0.33±0.14 and-0.30±0.13 respectively,and the r0 was 7.76±0.30 and 7.74±0.24 respectively.A weak positive correlation was found between r0 and mean Q value of nasal meridian (r=0.320,P＜0.05),but no significant correlation was found between r0 and mean Q-value of temporal meridian (r=0.104,P＞0.05).No significant differenees were seen in the Q values between nasal meridian and nasal zone (t=0.349,P＞0.05) as well as between temporal meridian and temporal zone(t=-0.373,P＞0.05).Conclusions The study analyzes the calculated Q-value of the semimeridian section in borizontal area with myopia by linear regression mathematical formulas of tangential radius on tangential topography.The anterior surface of the cornea is proved to be prolate ellipse in shape in the subjects with myopia.

Posterior Corneal Curvature Assessment after Epi-LASIK for Myopia: Comparison of Orbscan II and Pentacam Imaging

PURPOSE: To compare the changes in posterior corneal curvature using scanning slit topography (Orbscan II) and Scheimpflug imaging (Pentacam) before and after Epi-laser in situ keratomileusis (LASIK) for myopia. METHODS: In a prospective observational case-series study, 20 myopic patients having undergone Epi-LASIK were examined serially with two different devices, Orbscan II and Pentacam, preoperatively and one month postoperatively. Posterior central elevation (PCE) and posterior maximal elevation (PME) were compared between the two devices, and the changes in parameters after Epi-LASIK were analyzed using a difference map. RESULTS: All parameters (preoperative and postoperative PCE and preoperative and postoperative PME) that were measured using the Orbscan II were significantly greater compared to those of the Pentacam (for all p < 0.001). PCE and PME were significantly increased one month postoperatively in the Orbscan II measurements (p < 0.05) but were not significantly increased in the Pentacam measurements. Also, DeltaPCE and DeltaPME, in the difference map obtained by each serial scanning, were significantly greater in the Orbscan II measurements than with the Pentacam (p = 0.012, p = 0.016). CONCLUSIONS: The Pentacam measurements displayed significantly reduced values in all parameters related to posterior corneal elevation compared to those of the Orbscan II. The Pentacam showed no significant change in posterior corneal curvature after Epi-LASIK, based on the difference map.

Comparison of corneal curvature, anterior chamber depth and axial length measured by IOLMaster, Orbscan Ⅱ and ultrasound before and after LASIK / 中华实验眼科杂志

BackgroundIt is important to measure the corneal curvature, anterior chamber depth (ACD) and axial length accurately for calculating IOL power. The interchange outcomes from different measuring methods and apparatus will cause unreliable IOL power. ObjectiveThe present study was to compare the differences of corneal curvature, anterior chamber depth (ACD) measured by IOLMaster and Orbscan Ⅱbefore and after laser in situ keratomileusis(LASIK) and further compare the axial length measured by IOLMaster and A-ultrasound. Methods One hundred and thirty eyes from 65 consecutive myopic patients before LASIK and 56 eyes of 28 cases with 1-month follow-up duration after LASIK in Henan Eye Institute were enrolled in this study. The K value, ACD between IOLMaster and Orbscan Ⅱ as well as results of axial length between IOLMaster and A-ultrasound were compared by using paired t test. The agreements of the measured values among IOLMaster, Orbscan Ⅱ and A-ultrasound were evaluated using Bland-Altman plot. ResultsBefore LASIK,the K value measured by IOLMaster,Orbscan Ⅱ were ( 43.32 ± 1.52 ) D and ( 42.99 ± 1.45 ) D respectively with the difference value of( 0. 33 ±0. 03 ) D, showing a significant difference(t=10. 380,P=0.000) and a positive relation between them(r=0.971,P=0.000). After LASIK,the K value measured by IOLMaster, Orbscan Ⅱwere(39. 02±2. 14) D and ( 38.91 ±2. 04) D with the difference value (0. 12±0. 33 ) D, presenting a significant differences between them (t =2.715, P =0.009). Bland-Altman plots indicated the disagreement in K value and uninterchangeable. Before LASIK, the ACD measured by IOLMaster,Orbscan Ⅱ and A-ultrasound were ( 3.72 ± 0. 22 ) mm, ( 3.69 ±0. 22 ) mm and ( 3.75± 0.27 )mm respectively and no significant differences were found between them (P ＞ 0. 05 ). Axial length measured by IOLMaster significantly prolonged in comparison with A-ultrasound(25.59± 1. 01 mm vs 25.22±0.99 mm ) , and the difference was( -0. 37 ±0. 30 ) mm, showing significant difference ( t =- 14. 098, P =0. 000 ) and positive correlation ( r =0. 954, P =0. 000 ). Axial length values measured by IOLMaster were ( 25.54 ± 1.05 ) mm in preoperation and ( 25.48 ± 1.01 ) mm in postoperation with the difference (0.052±0. 412)mm, showing statistically insignificant difference between them (t=0. 946,P=0. 348). ConclusionsKeratometries measured by IOLMaster,Orbscan Ⅱ are much more different. Therefore,these two methods are not recommended to use interchangely. ACD measured by IOLMaster,Orbscan Ⅱ and A ultrasound are proved to obtain the similar results and is clinically interchange. Axial length measured by IOLMaster is longer than that measured by A-ultrasound.

Comparison of Eyemetrics and Orbscan automated method to determine horizontal corneal diameter.

Purpose: To compare horizontal corneal diameter measurements using the Orbscan Eyemetrics function and Orbscan corneal topographer. Materials and Methods: Seventy-three eyes of 37 patients were included in the study. In all cases, the automated white-to-white (WTW) measurements were obtained using Orbscan by two observers. Using the Eyemetrics function, the WTW was measured manually by the same observers from limbus to limbus using the digital caliper passing through the five point corneal reflections on the Orbscan real image. The data was analyzed using SPSS software for correlation, reliability and inter-rater repeatability. Results: The mean horizontal corneal diameter was 11.74 ± 0.32mm (SD) with the Orbscan and 11.92 ± 0.33mm (SD) with Eyemetrics Software-based measurement. A good positive correlation (Spearman r = 0.720, P = 0.026) was found between these two measurements. The coefficient of inter-rater repeatability was 0.89 for the Orbscan and 0.94 for the Eyemetrics software measurements on the anterior segment images. The Bland and Altman analysis showed large limits of agreement between Orbscan WTW and Eyemetrics WTW measurements. The intra-session repeatability scores for repeat measurements for the Orbscan WTW and Eyemetrics measurements were good. Conclusion: Eyemetrics can be used to measure WTW and the Eyemetrics measured WTW was longer than the WTW measured by Orbscan.

Central Corneal Thickness Measured by Four Different Methods in Normal and Post-Femtosecond Laser-Assisted LASIK Eyes

PURPOSE: To compare corneal pachymetry assessment using four measurement methods in normal and post-femtosecond laserassisted LASIK eyes. METHODS: Central corneal thickness was measured sequentially using Orbscan II, Pentacam, Galilei and ultrasonic pachymetry in 30 normal, non-surgical eyes (Group I), 30 eyes one to six months after femtosecond laser-assisted LASIK (Group II), and 30 eyes six months or longer after femtosecond laser-assisted LASIK (Group III). RESULTS: In Group I, corneal thickness measurements were similar for all four methods (P=0.202, one way ANOVA). In Groups II and III, corneal thickness measurements were significantly different (P=0.000, respectively, one way ANOVA). Compared to the Pentacam, Galilei and ultrasonic pachymetry, Orbscan significantly underestimated the corneal thicknesses in Groups II and III (P<0.005, respectively, one way ANOVA). CONCLUSIONS: Central corneal thicknesses of normal eyes were similar for all four measurements, therefore corneal thickness measurements before refractive surgery using all four measurements is suitable. However measurements obtained with the Orbscan II were thinner than those obtained with the Pentacam, Galilei or ultrasonic pachymetry in post femtosecond laserassisted LASIK eyes. Further studies are needed to determine which instrument is more accurate in measuring central corneal thickness before and after refractive surgery.

Corneal Power Estimation Using Orbscan II Videokeratography in Eyes With Previous Corneal Refractive Surgeries

PURPOSE: To report three cases of corneal power estimation for intraocular lens power calculation using Orbscan II videokeratography in eyes with previous corneal refractive surgeries. CASE SUMMARY: In three eyes of three patients with previous corneal refractive surgeries, corneal power values were respectively measured at three, four, five, six mm-diameter zones of total mean, axial, tangential, and optical maps using Orbscan II videokeratography. Then, intraocular lens power values were calculated via the SRK/T formula. After cataract surgeries, back-calculated corneal power (BCK) values were estimated from post-phacoemulsification refraction data, and compared with those measured at three, four, five, six mm-diameter zones of each map in Orbscan II videokeratography. The postoperative refractive values after cataract surgeries were achieved within 1.5D of the target refraction in all eyes by using five mm total axial power and four mm total optical power for intraocular lens power calculation. Orbscan II parameters including three mm, four mm total axial power, and three mm total optical power were the least different from the BCK (0.69+/-0.49D, 1.08+/-0.54D, and 1.10+/-0.44D, respectively). CONCLUSIONS: If historical data are not available, Orbscan II videokeratography can be useful for estimating corneal power for intraocular lens power calculations in patients with previous corneal refractive surgeries.

Comparison of Corneal Thickness and Anterior Chamber Depth Measured With Orbscan, Pentacam, and Ultrasound Pachymetry

PURPOSE:We compared the measurements of corneal thickness and anterior chamber depth (ACD) using three different methods Orbscan, Pentacam and ultrasound pachymetry. METHODS: In healthy volunteers, central corneal thickness was measured with Orbscan, Pentacam and ultrasound pachymetry. Estimation of peripheral corneal thickness and ACD were done by Orbscan and Pentacam. All results were compared statistically. RESULTS: The mean central corneal thickness of 64 eyes measured by Orbscan, Pentacam and ultrasound pachymetry were 509.1+/-61.0 microm, 539.2+/-51.7 microm and 527.4+/-48.3 microm, respectively. There were statistically significant differences in the results among the three methods (repeated-measures analysis of variance (ANOVA), p0.90, p<0.05). The temporal and nasal peripheral corneal thicknesses were thinner in the Pentacam than in the Orbscan (paired t-test, p<0.05). The superior and inferior corneal thickness and ACD were not significantly different. CONCLUSIONS: The results of the three instruments have significant correlations with each other, so all methods are clinically useful.

Effects of artificial tears on corneal thickness in adult myopia / 国际眼科杂志(Guoji Yanke Zazhi)

AIM: To study the effects of Sodium Hyaluronate (HA) and Bion Tears on corneal thickness in adult myopic patients.METHODS: A total of 38 cases (76 eyes) were involved in this study. Three consecutive corneal measurements (the thinnest point of the cornea,THN) were evaluated before and half an hour after the instillation of one drop of HA in one eye and Bion Tears in the other at random with the Orbscan Corneal Topography System II (Orbscan,Inc,Salt Lake City,UT,USA,Version 3.00E).RESULTS: There were no significant between-group differences in baseline variable (t=0.264). Thirty minutes after the instillation of HA and Bion tears,THN were significantly increased by 5.57±7.00μm (t=4.906,P<0.01) and 7.89±7.64μm (t=6.369,P<0.01) respectively. However,there were no between-group differences in THN changes(t=1.381,P>0.05).Increase in the corneal thickness were found in 32 eyes (84%) and 33 eyes (87%) for the HA and Bion tears group,respectively.CONCLUSION: Artificial tears including HA and Bion Tears can significantly increase the corneal thickness in a short period of time. Corneal thickness can be used as one of the objective indices for evaluating the quality and therapeutic role of artificial tears.

Corneal topography and hyperopia / 国际眼科杂志(Guoji Yanke Zazhi)

AIM: To evaluate Orbscan II corneal topography in hyperopic cases.METHODS: A retrospective, observational, consecutive, clinical case series in two hundred and ninety five eyes of hyperopic patients who undergo a LASIK evaluation. The information that was reviewed included age and sex of the patients and the Orbscan II corneal topographic maps. Refractive powers and the following test indices produced by Orbscan II were analyzed: keratometry, corneal diameter, pupil diameter and anterior chamber depth. RESULTS: The total mean corneal thickness was 546.3±35.5μm.It was found ; 547.3±38.4μm in 17-29 years old, 553.4±38.3μm in 30-44 years old and 546.2±29.3μm in older than 45 years old .The mean corneal thickness was found 551.5±35.9μm in female, and 542.6±34.7μm in male. The total mean depth of anterior chamber was 2.57±0.40mm and in 17-29 years old patients was 2.82±0.39mm. In 30-44 years old patients was 2.49±0.39mm and in patients older than 45 years old was 2.37±0.40mm. The mean depth of anterior chamber was 2.53±0.40mm in female and 2.60±0.40mm in male. A reverse significant relation between corneal thickness and keratometry were found. Refractive error severity had a reverse correlation with depth of anterior chamber and a correlation with keratometry (P=0.061,r=0.108).Corneal thickness had a reverse correlation with keratometry (P=0.005,r=0.160), and correlation with pupil diameter (P=0.013, r=0.144).CONCLUSION: This study provides a description and analysis of Orbscan II findings in hyperopic patients. These show mean corneal thickness 546.3±35.5μm and anterior chamber depth 2.57±0.40mm in hyperopic patients.

Screening of the Previous Photorefractive Surgery Using the Minimum Distance Between the Anterior Best Fit Sphere and the Center of the Anterior Corneal Surface

PURPOSE: To develop a screening test based on the difference (Diff) between the anterior corneal surface and the anterior best fit sphere in the central region of the Orbscan IIz topography as a way of detecting previous myopic photorefractive surgery. METHODS: From 1623 patients who had no refractive surgery and no corneal disease, 3132 topographies were defined as normal. From 120 patients who had Orbscan IIz topography after myopic photorefractive surgery, 238 topographies were defined as eyes that had undergone refractive surgery. The first objective was to determine the difference (Diff) between the anterior corneal surface and the anterior best fit sphere in the central region. The second objective was to classify the anterior elevation map of Orbscan IIz topography. RESULTS: The Diff value of the center of the anterior cornea surface averaged 0.008+/-0.003 mm in normal eyes, and all values were over 0 mm. However, in eyes that had previous refractive surgery, the average was 0.014+/-0.009 mm, and all values in this group were less than 0. The specificity and sensitivity was 100 % in both groups. The spherical equivalent of the degree of myopic correction and the Diff value of the center of the anterior cornea surface showed a linear relationship. Consequently, we could derive a formula to determine the degree of myopic correction with a known Diff value of the center of the anterior corneal surface. CONCLUSIONS: The screening test, based on the Diff value of Orbscan IIz topography, is quite useful in determining whether an eye has undergone previous myopic photorefractive surgery.

Comparison of Corneal Thickness Measured by Specular, US Pachymetry, and Orbscan in Post-PKP Eyes

PURPOSE: To compare the accuracy and reproducibility of central corneal thickness measured by non-contact specular microscopy, ultrasound pachymetry, and Orbscan in the post-penetrating keratoplasty eyes. METHODS: Central corneal thickness was prospectively measured in eyes that had recieved penetrating keratoplasty at least 1 month before. One experienced technician measured all eyes using three methods; non-contact specular microscopy (Topcon SP-2000P; Topcon Corporation, Tokyo, Japan), Orbscan IIz (Orbtek; Bausch & Lomb, Rochester, USA), and ultrasound pachymetry (AL-2000; Tomey, Erlangen, Germany). Three consecutive measurements were performed using each method and the mean values and coefficient of variation were compared. RESULTS: The mean values of central corneal thickness were 550.7+/-63.3 micrometer with specular microscopy, 548.2+/-72.5 micrometer with ultrasound pachymetry, and 472.5+/-151.7 micrometer with Orbscan. There was no significant difference between the measurements obtained by specular microscopy and ultrasound pachymetry (p=0.53), and both methods showed high reproducibility. The corneal thickness measured by Orbscan was remarkably variable and in some patients, Orbscan was unable to measure corneal thickness. CONCLUSIONS: Non-contact specular microscopy appears to be an effective technique, potentially replacing ultrasound pachymetry for measuring central corneal thickness in the post-penetrating keratoplasty eyes.