Midperipheral Corneal Thickness Research Articles

Association Between Family History and the Corneal Characteristics of Keratoconus in Japan.

The aim of this study was to determine the association between family history and corneal characteristics of keratoconus in Japan. The clinical records of patients with keratoconus who were interviewed regarding family history of keratoconus were retrospectively reviewed. Corneal indices derived from anterior segment optical coherence tomography were compared between the positive and negative family history groups using multiple linear regression analysis adjusted with age, sex, and history of atopy and eye rubbing. A total of 2,701 eyes, including 122 eyes with positive family history, were enrolled. Based on the adjusted multiple linear regression analysis, no significant differences were found between groups with and without a family history except for paracentral and mid-peripheral corneal thickness. The adjusted mean differences in paracentral and mid-peripheral corneal thicknesses between the two groups were -10.33 (95% confidence interval -20.29 to -0.37 P -value <0.05) and -9.78 (95% confidence interval -16.70 to -2.85, P -value <0.01), respectively. There was no significant association between family history and corneal indices in Japanese patients with keratoconus, except for paracentral and mid-peripheral corneal thicknesses. A Japanese patient with keratoconus who had a family history showed significantly lower paracentral and mid-peripheral corneal thicknesses than those with no family history.

Epithelial and stromal thickness profile and lens decentration in myopic orthokeratology

PurposeTo study topographic epithelial and total corneal thickness changes in myopic subjects undergoing successful orthokeratology treatment in connection with the objective assessment of contact lens decentration. MethodsA prospective-observational and non-randomized study in 32 Caucasian myopic eyes undergoing Ortho-k for 3 months. Total, epithelial, and stromal thicknesses were studied before and after Ortho-k treatment, using optical coherence tomography with anterior segment application software. Central, paracentral, and mid-peripheral values are taken along 8 semi-meridians. ResultsThe central average total corneal thickness was 4.72 ± 1.04 μm thinner after Ortho-K. The paracentral corneal thickness showed no significant changes (p = 0.137), while the mid-peripheral corneal thickness was increased by 3.25 ± 1.6 μm associating this increase exclusively to the epithelial plot (p<0.001). When lens centration was assessed, a lens fitting decentration less than 1.0 mm was found for the whole sample, predominantly horizontal-temporal (87.5%) and vertical-inferior (50%) decentring. Corneal topographical analysis revealed a horizontal and vertical epithelial thickness asymmetric change profile with paracentral temporal thinnest values, and mid-peripheral nasal thickest values. ConclusionsThe present study found a central corneal thinning induced by Ortho-k lenses in subjects with moderate myopia, only associated with a change in epithelial thickness, as well as mid-peripheral thickening, that seems to be mainly epithelial in origin. The authors also found a tendency of contact lens decentration toward temporal and inferior areas conditioning an asymmetric epithelial redistribution pattern.

Comparison of Changes in Corneal Thickness and Curvature After Myopia Correction Between SMILE and FS-LASIK.

To comparatively investigate the changes in corneal thickness and curvature between small incision lenticule extraction (SMILE) and femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK). Data were collected preoperatively and postoperatively at 1 week, 1 month, and 3 months, including central corneal thickness (CCT), midperipheral corneal thickness (MPCT), peripheral corneal thickness (PCT), central keratometry (CK), midperipheral keratometry (MPK), and peripheral keratometry (PK), using a dual rotating Scheimpflug analyzer. At 1 week postoperatively, changes in CCT, MPCT, PCT, and PK were significantly greater in the SMILE group than in the FS-LASIK group (P = .003 for CCT and < .001 for MPCT, PCT, and PK), but no significant inter-group differences were found between changes in CK and MPK (P = .883 and .513, respectively). CCT, MPCT, and PK values showed a similar increase in both groups, but significantly more increase in PCT and significantly less increase in CK and MPK was observed in the SMILE group from 1 week to 3 months after surgery. At 3 months postoperatively, CCT and MPCT were significantly thinner in the SMILE group than in the FSLASIK group (P = .018 and .022, respectively), and there was no significant difference in PCT, CK, MPK, and PK between the two groups. SMILE caused significantly more corneal thinning at the center, midperiphery, and periphery, and more corneal flattening at the periphery, compared to FS-LASIK. A different pattern of corneal remodeling was observed between the two surgeries during the 3-month follow-up period. [J Refract Surg. 2023;39(1):15-22.].

Agreement Between Predicted and Actual Measured Ablation Depth After FS-LASIK Using Different Rotating Scheimpflug Cameras and OCT.

PurposeTo compare the predicted ablation depth (AD) with the postoperatively measured corneal ablation depth (postop-AD) at central, paracentral, and midperipheral locations using two rotating Scheimpflug analyzers and a Fourier-domain optical coherence tomographer in eyes that underwent femtosecond laser-assisted LASIK (FS-LASIK).MethodsThe values of corneal thickness were measured preoperatively and postoperatively at one and three months. The difference between preoperative and postoperative was defined as postop-AD. Measurements were performed at the corneal vertex and mid-peripheral area. The mid-peripheral corneal thickness was measured at the superior, inferior, nasal, and temporal locations at a distance of 1.0 or 2.5 mm from the corneal vertex. The predicted AD was calculated by ORK-CAM software (Schwind eye tech-solutions GmbH, Kleinostheim, Germany), and the difference between the predicted AD and postop-AD was defined as Δ-AD. Paired t-test analysis was employed to evaluate the differences, agreement was assessed by the Bland-Altman method.ResultsForty-two eyes of 42 patients were investigated. At one month, the predicted AD in the central and paracentral areas was underestimated by the Pentacam HR (Oculus, Wetzlar, Germany), Sirius (Costruzione Strumenti Oftalmici, Florence, Italy) and RTVue OCT (Optovue Inc., Freemont, CA, United States), whereas Δ-AD was negative as established by all devices and predominantly statistically significant. The Δ-AD values approximated zero at three months. The mean difference of Δ-AD at three months at the corneal vertex was 0.67 ± 9.39 mm, −7.92 ± 9.05 mm and −1.36 ± 8.31 mm, respectively. The mid-peripheral measurements had positive values at one month and even more highly positive at three months (with statistically significant differences in most of the cases). The agreement between the predicted and postop-AD was moderate with all devices, but slightly better with RTVue.ConclusionThe predicted AD seems to be underestimated in the central and paracentral corneal area and overestimated in the mid-periphery.Translational RelevanceThe study could help to partly explain and prevent the refractive errors after FS-LASIK.

Reliability and agreement of the central and mid-peripheral corneal thickness measured by a new Scheimpflug based imaging.

BackgroundTo assess the intra-observer repeatability and inter-observer reproducibility of central corneal thickness (CCT) and mid-peripheral corneal thickness (MPCT) measurements using a new Scheimpflug imaging instrument (Scansys) and compare the agreement with the rotating Scheimpflug corneal tomographer (Pentacam HR).MethodsThe same well-trained operator performed the measuring using the two devices, after which Scansys measurements were repeated by another operator. Both instruments required three consecutive measurements per subject. Corneal thickness measurements were obtained by each instrument, including CCT, thinnest corneal thickness (TCT), pupil corneal thickness (PCT), and MPCT. Test-retest repeatability (TRT), within-subject coefficient of variation (CoV), and intra-class correlation coefficient (ICC) were used to evaluate repeatability and reproducibility. A paired t-test was used to compare the differences between Scansys and Pentacam, and the agreement was compared with Bland-Altman plots.ResultsThis study enrolled 112 healthy subjects. The CoV were <0.91% and 0.55% for repeatability and reproducibility, respectively. The ICC was close to 1 in all measurements. For intra-observer repeatability in the CT2mm region, TRT was <10.30 µm. Moreover, TRT was <15.26 µm within the CT5mm region. The paired t-test showed significant differences in all corneal thickness measurements (P<0.001). The central region and CT2mm agreement were high, but the largest range of 95% limits of agreement (LoA) appeared in the CTnasal-5mm.ConclusionsThe new Scheimpflug imaging instrument showed excellent intra-observer repeatability and inter-observer reproducibility for corneal thickness measurements. The agreement analysis suggested that Scansys and Pentacam could be interchangeably used between the central region and CT2mm, except CT5mm.

Repeatability and agreement of corneal thickness measurements by three methods of pachymetry in small incision lenticule extraction eyes

ABSTRACT Background: The accurate evaluation of corneal thickness (CT) post small incision lenticule extraction (SMILE) is clinically relevant to reduce the risk of complications. We aimed to analyze repeatability and agreement of central corneal thickness (CCT), thinnest corneal thickness (TCT), and mid-peripheral corneal thickness (MPCT) measurements using Scheimpflug imaging, anterior segment swept-source optical coherence tomography (AS-SS-OCT, CASIA 1000, Tomey), and ultrasound pachymetry (USP, SP-3000, Tomey) in eyes with previous SMILE. Methods: Ninety-one eyes of 91 patients were included. Within-subject standard deviation (Sw), test-retest repeatability (TRT), intraclass correlation coefficient (ICC), and coefficient of variation (CoV) were used to evaluate repeatability. Agreement was assessed by repeat-measurement analysis of variance and Bland–Altman analysis. Results: The above three instruments revealed that Sw was <5.91 µm, CoV was <1.08%, TRT was <16.38 µm, and ICC was >0.94. The 95% limits of agreement were relatively narrow and Bland–Altman plots were more concentrated at the CCT, at the TCT, and at the CT2mm. However, it was shown to be wide at the CT5mm. Conclusions: The three devices provide good repeatability of CT measurements in patients who undergone SMILE. Agreement between measurements at the CCT, TCT, and CT2mm were high, but measurement agreements among CT5mm revealed poor agreement.

The precision and agreement of corneal thickness and keratometry measurements with SS-OCT versus Scheimpflug imaging

PurposeTo assess the repeatability and reproducibility of swept-source optical coherence tomography (SS-OCT) and Scheimpflug system and evaluate the agreement between the two systems in measuring multiple corneal regions in children.MethodsPachymetric and keratometric maps for both systems were evaluated. Central, midperipheral and peripheral corneal thickness (CT), keratometry and astigmatism power vectors were recorded. The three outcomes yielded by the same observer were used to assess intraobserver repeatability. The differences in the mean values provided by each observer were used to evaluate interobserver reproducibility. Within-subject standard deviation, test-retest repeatability (TRT) and coefficient of variation (CoV) were used to analyze the intraobserver repeatability and interobserver reproducibility. Paired T-test and Bland-Altman were used to appraise interdevice agreement.ResultsSeventy-eight eyes of 78 children were included. The CoV was ≤2.12 and 1.10%, respectively, for repeatability and reproducibility. TRT and CoV were lower for central and paracentral CT measurements than for peripheral measurements. The SS-OCT device generated higher precision when acquiring CT data, whereas Scheimpflug system showed higher reliability when measuring corneal keratometry. Although the CT readings measured using SS-OCT were significantly thinner than Scheimpflug device (P < 0.001), the central and thinnest CT values were still of high agreement. The interdevice agreement of keratometry measurement was high for the central corneal region and moderate for the paracentral and peripheral areas.ConclusionsThe precision of CT measurements by SS-OCT was higher, while the reliability of keratometry measurements by the Scheimpflug system was higher in children. Apart from the measured values in the central corneal region, the thickness and keratometry readings should not be considered interchangeable between the two systems.

Evaluation of Central and Peripheral Corneal Thicknesses in Patients with Systemic Lupus Erythematosus.

PurposeTo evaluate the corneal pachymetric and topographic parameters of systemic Lupus Erythematosus (SLE) patients using Dual Scheimpflug Imaging.MethodsThis observational cross-sectional controlled study included the right eye of 30 SLE patients and 30 age-matched controls. Corneal measurements were acquired by dual Scheimpflug imaging including anterior and posterior corneal curvatures, central, mid-peripheral corneal thickness (measured at the 5 mm zone) and peripheral pachymetry (measured at the 7 mm zone). SLE disease activity index (SLEDAI) was calculated and correlated with corneal pachymetry.ResultsSLE patients had significantly thicker corneal periphery than controls. Mean central corneal pachymetry was 530.4± 27.3 microns (SD) in SLE and 547.5±31.5 microns (SD) in control group, p = 0.032. The corneal periphery – except superiorly – was significantly thicker in SLE patients than controls (p ˂0.001). Nasal peripheral corneal thickness positively correlated with disease activity index SLEDAI (p=0.03).ConclusionSLE patients present with thicker corneal periphery than controls characteristically sparing the superior quadrant. Possible corneal photosensitivity leading to peripheral immune complex deposition as well as flatter posterior corneal surface at the periphery are proposed explanations for these findings.

Effects of artificial tear treatment on corneal epithelial thickness and corneal topography findings in dry eye patients

To investigate the effects of artificial tear treatment on central corneal epithelial thickness, and central, mid-peripheral and peripheral corneal thicknesses in patients with dry eye disease (DED). Patients with DED underwent ocular examinations, including Schirmer-2 test, slit lamp examination for tear break-up time (BUT), corneal topography (CT) for measuring mean central, mid-peripheral and peripheral corneal thickness values and anterior segment optic coherence tomography (AS-OCT) for obtaining central corneal epithelial thickness. After artificial tear treatment (carboxymethylcellulose and sodium hyaluronate formulations) for one month, patients were examined again at a second visit and the results were compared. Sixty-one eyes of 33 female dry eye patients (mean age: 38.3±5.7 years) were enrolled. The mean follow-up time was 36.4±3.3 days. The mean tear BUT and Schirmer-1 tests revealed significant improvement after treatment (P=0.000, P=0.000, respectively). Central corneal epithelium and mean mid-peripheral corneal thicknesses measured significantly higher after treatment (P=0.001, P=0.02). Changes in central and peripheral corneal thicknesses were not statistically significant. Artificial tear treatment in dry eye patients seems to increase central corneal epithelial and mid-peripheral corneal thicknesses. Measurement of corneal epithelial thickness can be a useful tool for evaluation of treatment response in dry eye patients. Further long-term prospective studies are needed to investigate this item.

The effect of oxybuprocaine on corneal thickness as measured with optical coherence tomography

Background: No previous study in South Africa has used optical coherence tomography (OCT) in assessing corneal thickness changes following the instillation of an anaesthetic.Aim: The purpose of this study was to investigate the short-term effects of oxybuprocaine 0.4% on corneal thickness.Setting: The study was conducted at a university eye clinic in Westville, KwaZulu-Natal.Methods: A total of 34 (N = 34) participants, of both genders, aged 18–25 years participated in the study. Data collection commenced once ethical clearance was obtained. Baseline measurements of central corneal thickness (CCT) (within 0 mm – 2 mm of the corneal apex) and mid-peripheral corneal thickness (MPCT) (within 2 mm – 5 mm of the corneal apex) were taken using the Optovue iVue 100 OCT. Measurements were obtained using the standard iVue 100 corneal pachymetry map. One drop of oxybuprocaine was then instilled using a sterile technique in the right eye (RE) of each participant. Central and MPCT measurements were obtained using the OCT at time intervals of 30 s for the first 2 min and then for 60-s intervals up until 5 min. Baseline central and MPCT were then measured for the left eye (LE) using the OCT. The effect of two drops of oxybuprocaine on CCT was also investigated on the left eye only using the same procedure as on the right eye.Results: There were minimal fluctuations of the CCT and MPCT in the 5 min following instillation of either one or two drops of oxybuprocaine. The fluctuation of both the CCT and MPCT was within 10 µm irrespective of dosage and returned to baseline thickness after 5 min.Conclusion: Clinically, short-term CCT and MPCT changes following the instillation of oxybuprocaine are not large enough to affect the accuracy of Goldmann applanation tonometry.

Repeatability of central and peripheral corneal thickness measurements with the iVue100 optical coherence tomographer

Background: Accurate assessment of corneal thickness is essential in corneal refractive surgery, contact lens wear and corneal pathology.Aim: To assess the repeatability (intra-observer, inter-observer and inter-session) of central (0 mm – 2 mm), mid-peripheral (2 mm – 5 mm) and peripheral (5 mm – 6 mm) corneal thickness measurements using the iVue 100 spectral domain optical coherence tomographer (SD-OCT).Setting: Optometry Eye Clinic at the University of KwaZulu-Natal (UKZN).Methods: Corneal thickness measurements were taken on 50 healthy participants by two observers independently. A second set of readings was taken by one observer on another session. Repeatability was assessed using Bland–Altman analysis, the intraclass correlation coefficient, coefficient of variation and one-way analysis of variance (ANOVA) analysis.Results: For all corneal regions, the intraclass correlation coefficients for observer one ranged from 0.942 to 0.999 and that for observer two ranged from 0.946 to 0.999, indicating good intra-observer repeatability. Using linear regression, the corneal thickness measurements were found to be comparable (within 1 µm of each other) in all regions with the exception of the nasal and temporal mid-periphery and periphery. The inter-session repeatability was based on the measurements of observer one only with the mean differences ranging from 0.02 µm to 0.63 µm. Linear regression revealed no significant differences between session 1 and session 2 (p &gt; 0.05) except for the measurement of minimum corneal thickness.Conclusion: This study found evidence of good intra-observer, inter-observer and intersession repeatability of central, mid-peripheral and peripheral corneal measurements with the iVue 100 SD-OCT.

Assessment of corneal thickness and tear meniscus during contact-lens wear.

To assess the effect of seven different daily disposable contact lenses upon corneal thickness, as well as upon tear meniscus volume, by using optical coherence tomography (OCT). Thirty-four young healthy subjects wore seven different types of daily disposable soft contact lenses, each for a period of 12h: Delefilcon A, Nelfilcon A, Omafilcon A, Filcon II3, Narafilcon A, Etafilcon A and Hilafilcon B. Central and mid-peripheral corneal thickness and lower tear meniscus volume (TMV) were measured using an OCT device during contact-lens wear at 4-h intervals throughout a 12-h period. Measurements were also recorded without any contact lenses being worn during a day. In the no-lens scenario a small but significant (p<0.05) thinning in the cornea was observed after the 12-h period. Overall, as for contact-lens wear, it was the Hilafilcon B lens that caused the greatest thickness increase in the central area, whereas the Etafilcon A caused it in the mid-peripheral cornea. Delefilcon A was the lens that showed the most similar behavior to the naked eye. As for TMV, it decreased with all the lenses, but it was the Delefilcon A lens the one that caused the smallest drop in TMV (p=0.007). OCT makes it possible to evaluate both corneal thickness variations and TMV changes as a result of contact-lens wear. The changes in corneal thickness hereafter presented are not clinically significant. On the other hand, TMV drop could indicate discomfort for contact-lens users.

Comparison of different methods for the measurement of central and paracentral corneal thickness in post-LASIK eyes

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. Key words: Corneal thickness; Laser-assisted in-situ keratomileusis; Specular microscope; Anterior segment optical coherence tomography; Orbscan Ⅱ ; Ultrasound pachymetry

Central and midperipheral corneal thickness measured with Scheimpflug imaging and optical coherence tomography.

PurposeTo compare corneal thickness measurements using Pentacam (Oculus, Germany), Sirius (CSO, Italy), Galilei (Ziemer, Switzerland), and RTVue-100 OCT (Optovue Inc., USA).MethodsSixty-six eyes of 66 healthy volunteers were enrolled. Three consecutive measurements were performed with each device. The mean value of the three measurements was used for subsequent analysis. Central corneal thickness (CCT), thinnest corneal thickness (TCT), and midperipheral corneal thickness (MPCT; measured at superior, inferior, nasal, and temporal locations with a distance of 1 mm (CT2mm) or 2.5 mm (CT5mm) from the corneal apex) were analyzed. Differences and agreement between measurements were assessed using the repeated-measures analysis of variance (ANOVA) and Bland-Altman analyses, respectively.ResultsStatistically significant differences (p<0.001) among the four devices were revealed in CCT, TCT and CT2mmmeasurements. The CCT, TCT, and CT2mm values were ranked from the thickest to the thinnest as follows: Galilei>Sirius>Pentacam>RTVue OCT. For these measurements, agreement between measurements by Sirius and Pentacam was good, whereas Galilei overestimated and RTVue underestimated corneal thickness compared to Sirius and Pentacam. As regards CT5mm measurements, Pentacam provided the largest values, whereas RTVue OCT yielded the smallest values. Agreement of the CT5mm measurements was good between the Pentacam, Sirius, moderate between Galilei and the other two Scheimpflug systems, and poor between the RTVue OCT and the remaining devices.ConclusionsThe Pentacam and Sirius can be used interchangeably for CCT measurements, while the Galilei and RTVue systematically over- and underestimate CCT, respectively. The three Scheimpflug cameras, but not the RTVue, may be used interchangeably for MPCT measurements.

Relationships between central and peripheral corneal thickness in different degrees of myopia

PurposeTo analyze the relationship between the central corneal thickness (CCT) and mid-peripheral corneal thickness (PCT) with the degree of myopia [axial length (AL) and spherical equivalent refractive error (SE)]. Methods175 right myopic eyes from 175 patients were divided according to the degree of SE: group #1 (n=76, <6.00D), group #2 (n=72, between 6.00 and 12.00D) and group #3 (n=27, >12.00D). The CCT and PCT (3mm from the apex to the superior, inferior, nasal and temporal locations) were measured with the Orbscan-II. Relative peripheral index (RPI) was calculated by dividing the PCT by the CCT. The AL was measured with the IOL Master, and the SE was obtained with subjective refraction. ResultsAL was 25.18±1.16mm, 26.59±1.26mm and 29.45±2.58mm and SE was −3.31±1.40D, −8.32±1.64D and −16.44±4.48D for groups #1, #2 and #3, respectively. Non-statistically significant differences in central and peripheral corneal thickness were found between groups (P>0.05 ANOVA). Non-significant relationship was found between central and peripheral corneal thickness with the AL and SE in the three study groups and in the total sample (r<0.24; P>0.05). The RPI values were similar between groups without significant difference between groups (P>0.05 ANOVA). Linear relationship was found between RPI superior location in group #2 (r=−0.23; P=0.04) and RPI nasal location in group #3 with the EE (r=0.41; P=0.03). ConclusionThere are no significant differences among low, moderate and extremely myopic eyes related to the CCT and PCT. Corneal thickness is very similar in myopic eyes with small differences that are not clinically relevant to myopic patient management.

A Comparison between Scheimpflug Imaging and Optical Coherence Tomography in Measuring Corneal Thickness

To assess the repeatability and reproducibility of 3 rotating Scheimpflug cameras, the Pentacam (Oculus, Wetzlar, Germany), Sirius (Costruzione Strumenti Oftalmici, Florence, Italy), and Galilei (Ziemer, Biel, Switzerland), and 1 Fourier-domain optical coherence tomography (FD-OCT) system, the RTvue-100 OCT (Optovue Inc., Fremont, CA), in measuring corneal thickness. Evaluation of diagnostic test. Sixty-six right eyes of 66 healthy volunteers, whose mean age ± standard deviation (SD) was 35.39±10.06 years (range, 18-55 years). Corneal thickness measurements obtained by each system included central corneal thickness (CCT), thinnest corneal thickness (TCT), and midperipheral corneal thickness (MPCT), measured at superior, inferior, nasal, and temporal locations at a distance of 1 and 2.5 mm from the corneal apex. In the first session, 3 consecutive measurements were performed by the same operator to assess intraobserver repeatability and by a second operator to assess interobserver reproducibility. Measurements were repeated in the second session scheduled 1 day to 1 week later. The mean values obtained in the 2 sessions by the first operator were used to investigate the intersession reproducibility. Intraobserver repeatability and interobserver and intersession repeatability of corneal thickness measurements, as calculated by means of within-subject SD, test-retest repeatability, coefficient of variation (COV), and intraclass correlation coefficients. The precision of CCT, TCT, CT2 mm (midperipheral corneal thickness [MPCT] with a distance of 1 mm from the corneal apex), and CT5 mm (midperipheral corneal thickness [MPCT] with a distance of 2.5 mm from the corneal apex) measurements was high with all 4 systems. The COV was ≤1.16%, 0.94%, and 1.10% for repeatability, interobserver reproducibility, and intersession reproducibility, respectively. The 4 devices offered better interobserver reproducibility than intersession reproducibility for all measurements. The CTsuperior-5 mm (midperipheral corneal thickness [MPCT], measured at superior locations with a distance of 2.5 mm from the corneal apex) measurements showed the poorest repeatability and reproducibility. The Galilei revealed the best precision of CCT, TCT, and CT2 mm measurements. Both Scheimpflug imaging and FD-OCT offer highly repeatable and reproducible measurements of CCT and MPCT. The precision was lower in the midperipheral superior quadrant. The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Investigation of the Human Anterior Segment in Normal Chinese Subjects Using a Dual Scheimpflug Analyzer

To investigate anterior segment parameters in normal Chinese subjects and study factors influencing these parameters, such as age, gender, and laterality. A prospective observational case series. A total of 291 normal subjects (582 eyes) were included. The anterior segment data were determined with a dual Scheimpflug analyzer. The corneal thinnest-point thickness (CTPT), corneal thinnest-point distribution (CTPD), central corneal thickness (CCT), corneal thickness (CT) in the central 10 mm diameter, pupil diameter (PD), pupil center distribution (PCD), anterior chamber depth (ACD), and anterior chamber volume (ACV, 8-mm diameter) were measured. The mean distance between the thinnest point and the corneal vertex was 0.70 ± 0.32 mm in the right eyes and 0.42 ± 0.25 mm in the left eyes; the thinnest point was located in the inferior temporal region in 71.1% of the right eyes and 55% of the left eyes. The CCT values were thicker than the CTPT values, and they were positively correlated (right eyes r = 0.994, P<0.001; left eyes r = 0.997, P<0.001). The distance between the pupillary center and the corneal vertex was approximately 0.39 ± 0.27 mm in the right eyes and 0.37 ± 0.24 mm in the left eyes. Furthermore, the percentage of pupillary centers located in the superior regions was 72.2% in the right eyes and 73.5% in the left eyes. Age was negatively correlated with the peripheral CT (7-10 mm diameter), PD, ACD, and ACV of both eyes and the mid-peripheral CT (4-7 mm diameter) of the right eye. Laterality correlated with CTPT (P<0.001) and PD (P<0.001), whereas gender correlated with ACD (P<0.001) and ACV (P = 0.009). The majority of the thinnest corneal points were located in the inferior temporal quadrant, and the pupillary center was located in the superior region of the cornea; both differed substantially from the corneal vertex. The CT increased gradually from the center to the periphery. Age, gender, and laterality correlated with some indexes.

Corneal thickness after overnight wear of an intraocular pressure fluctuation contact lens sensor

To assess the effect of overnight wear of a contact lens-based sensor (CLS) for monitoring of 24-hr intraocular pressure (IOP) fluctuations on central corneal thickness (CCT). Changes in the CCT, mid-peripheral corneal thickness and central corneal radius (CCR) during overnight CLS wear in 20 eligible patients with ocular hypertension or established glaucoma were prospectively studied using ultrasound pachymetry and topography. Corneal thickness and CCR changes were evaluated from pre-to-postsleep, with the fellow eye as control. Paired t-test or Wilcoxon signed-rank test was used as appropriate and with α = 0.05. Relationship between the IOP profile recorded by the CLS and the pre-to-postsleep corneal thickness differences was assessed using the Spearman correlation coefficient. After CLS wear, mean CCT had changed from 523 to 537 μm (p = 0.015) in the study eye and from 518 to 522 (p = 0.206) in the fellow eye (n = 15). There was no difference in CCT change between eyes (p = 0.075). There were no statistically significant changes in horizontal or vertical CCR in either eye (p > 0.05 for all). No correlation was found between the pre-to-postsleep differences in the CLS signal and the pre-to-postsleep differences in ultrasound CCT measurements (p = 0.974). The continuous IOP monitoring does not appear to be affected by differences in corneal thickness that occur during overnight CLS wear, although the CLS did induce some corneal swelling. This effect was not statistically significantly different from the control eye and does not seem to influence the CLS IOP profile.

Repeatability and reproducibility of Orbscan II

This study aimed to determine the repeatability and reproducibility of Orbscan for anterior and posterior best fit sphere (BFS), simulated keratometry (Sim-K), and central (CCT) and mid-peripheral (PCT) corneal thickness measurements in healthy eyes. Orbscan was performed in 40 healthy eyes (20 subjects) three consecutive times on each cornea during three visits scheduled over one week. Repeatability and reproducibility coefficients [Bland and Altman&amp;rsquo;s coefficient (BAC), coefficient of variation (CV) and intraclass correlation (ICC)] were calculated for Orbscan anterior and posterior BFS, Sim-K and corneal pachymetry (central, superior, inferior, nasal and temporal locations). Repeatability was calculated using three consecutive measurements during each visit, while reproducibility was calculated using the average of the measurements obtained at each visit. High repeatability was found for all Orbscan measurements (r2&amp;lt;0.01; P&amp;gt;0.05, two-way ANOVA) with BAC and CV &amp;lt;1% (except in PCT coefficients; from 0.97% to 1.67%) and ICC close to 0.98- 0.99 for all visits. High reproducibility was also found for all Orbscan measurements (r2&amp;lt;0.01; P&amp;gt;0.05 two-way ANOVA). BAC values were less than 1% for both BFS and Sim- K, and between 1.21 and 2.20% for corneal pachymetry. CV values were less than 1% (except in superior, nasal and temporal PCT, where they ranged from 1.06 to 1.30%). ICC was close to 0.98-0.99 for all measurements. The BAC of reproducibility was higher than the CV of reproducibility. PCT showed less repeatability and reproducibility than CCT. The Orbscan provides non-invasive, repeatable and reproducible measurements of anterior and posterior BFS, simulated keratometry. and central and mid-peripheral pachymetry in healthy eyes.

Effect of a proparacaine 0.50%–sodium fluorescein 0.25% mix and contact ultrasound pachymetry on central and midperipheral corneal thickness measured by noncontact optical pachymetry

To assess the effect of a combination of proparacaine 0.50%-sodium fluorescein 0.25% and ultrasound (US) pachymetry on central and midperipheral corneal thickness. School of Optometry and Vision Sciences, Cardiff University, Cardiff, Wales, United Kingdom. Case series. Topographic measurements of corneal thickness in healthy right eyes were obtained using a scanning-slit device (Orbscan IIz) and a Scheimpflug device (Pentacam) before and after application of proparacaine 0.50%-sodium fluorescein 0.25% and US pachymetry. Changes in corneal thickness in the center and 2.5 mm from the center in the temporal, nasal, inferior, and superior locations were assessed. The study evaluated 35 eyes. The scanning-slit and Scheimpflug devices recorded a small but statistically significant increase in corneal thickness at all locations (mean 4.9 ± 14.3 [SD] to 9.1 ± 11.7 μm; P<.05, paired t test). The cornea swelled uniformly across its diameter (scanning slit, P=.934; Scheimpflug, P=.654; analysis of variance); there was no statistically significant difference in the amount of swelling between the 2 devices (P>.05, t test). The 95% limits of agreement were broad (-10 to +30 μm), suggesting a large degree of interindividual variability. Ultrasound pachymetry combined with proparacaine 0.50%-sodium fluorescein 0.25% caused a small (<10 μm) but significant amount of corneal swelling on average. Because the effect on corneal thickness may be greater than -10 to +30 μm in individual cases, clinicians should avoid contact procedures before obtaining topographic maps of corneal thickness using scanning-slit and Scheimpflug devices.