Apical Corneal Thickness Research Articles

Comparison of corneal measurements using two different Scheimpflug analyzers in Sirius and Pentacam devices

The aim was to compare measurements of anterior segment biometry parameters using two Scheimpflug tomographies, Pentacam and Sirius to assess the agreement. Prospective cross-sectional observational study. A total of 60 eyes of 30 healthy subjects were included and evaluated with Pentacam followed by Sirius imaging. Corneal indices were performed with two modalities in both eyes including; apical corneal thickness (ACT), corneal thickness at pupil site(PCT), thinnest corneal thickness (TCT), anterior chamber depth (ACD), chamber angle, chamber volume, cornea volume, mean front keratometry (FKm), the radius of corneal curvature at the anterior and posterior surface in steep and flat meridian, anterior astigmatism values, pupil diameter, and horizontal corneal diameter. The Bland–Altman graph and ICC (intra-class correlation were used to establish an agreement and present the similarity of the findings. Most parameters showed perfect agreement. In both devices, the ICC was more than 0.91 in all measurements except for ACD (ICC = 0.820), cylinder axis (ICC = 0.520), TCT(ICC = 0.881), ACT(ICC = 0.672), PCT (ICC = 0.882), chamber angle (ICC = 0.362), pupil diameter(ICC = 0.137). Pentacam yielded higher values that were significant in five parameters including 3.47 μm for TCT, 4.29 µm for PCT, 10.03 mm3 for chamber volume,2.67 mm3 for cornea volume, and 1.49 mm for pupil diameter but there was only a statistically significant difference in cornea volume and pupil diameter (p-value < 0.001). However, in Pentacam only the chamber angle value was 6.44 mm3 lower than Sirius, with a statistically significant difference (p-value < 0.001). Although these two devices had some statistically different results, it seems that they have a good agreement and correlation in most parameters.

Evaluation of Eyelid, Angle, and Anterior Segment Parameters Using Scheimpflug Camera and Topography System in Obstructive Sleep Apnea Syndrome.

The purpose of the study was to investigate the eyelid hyperlaxity, anterior segment, and corneal topographic parameters in patients with obstructive sleep apnea syndrome (OSAS) using Scheimpflug camera and topography system. In this prospective and cross-sectional clinical study, 32 eyes of 32 patients with OSAS and thirty-two eyes of 32 healthy subjects were evaluated. The participants with OSAS were selected from those with an apnea-hypopnea index ≥ 15. The minimum corneal thickness (ThkMin), apical corneal thickness (ACT), central corneal thickness (CCT), pupillary diameter (PD), aqueous depth (AD), aqueous volume (AV), anterior chamber angle (ACA), horizontal anterior chamber diameter (HACD), corneal volume (CV), simulated K readings (sim-K), front and back corneal keratometric values at 3 mm, RMS/A values, highest point of ectasia on the anterior and posterior corneal surface (KVf, KVb), symmetry indices and keratoconus measurements were taken by combined Scheimpflug-Placido corneal topography and compared with healthy subjects. Upper eyelid hyperlaxity (UEH) and floppy eyelid syndrome were also evaluated. There were no statistically significant difference between groups in terms of age, gender, PD, ACT, CV, HACD, simK readings, front and back keratometric values, RMS/A-KVf and KVb values, symmetry indices, and keratoconus measurements (p>0.05). ThkMin, CCT, AD, AV, and ACA values were significantly higher in OSAS group compared to the control (p<0.05). UEH was detected in two cases in the control group (6.3%) and in 13 cases in the OSAS group (40.6%) and the difference was significant (p<0.001). The anterior chamber depth, ACA, AV, CCT, and UEH increase in OSAS. These ocular morphological changes occurring in OSAS may explain why these patients prones to normotensive glaucoma.

Correlations among Corneal Biomechanical Parameters, Stiffness, and Thickness Measured Using Corvis ST and Pentacam in Patients with Ocular Hypertension.

To preliminary explore the correlations among corneal biomechanical parameters, stiffness, and thickness in patients with ocular hypertension (OHT) before and after treatment with topical antiglaucoma medications. This was a retrospective study that included 35 eyes with newly diagnosed OHT. Axial length (AL), apical corneal thickness, and minimum corneal thickness were measured using Pentacam. The lengths, velocities, and times of the first and second corneal applanations (A1L, A1V, A1T, A2L, A2V, and A2T, respectively); the highest concavity radius; highest concavity peak distance (PDHC); highest concavity deformation amplitude (DAHC); highest concavity time (HCT); pachymetry (PACH); stress-strain index (SSI); stiffness parameter-A1 (SP-A1); deformation amplitude ratio (DA ratio); integrated radius (IR); Ambrosio's relational thickness horizontal (ARTh); corneal biomechanical index; noncorrected intraocular pressure (IOPnct); and biomechanically corrected IOP (bIOP) values were measured using the corneal visualization Scheimpflug technology (Corvis ST/CST). After 5 weeks of treatment, Goldman applanation tonometer-IOP, IOPnct, bIOP, PACH, A1T, A2V, SSI, SP-A1, and ARTh decreased, but A1V, A2T, PDHC, DAHC, DA ratio, and IR increased significantly (all p < 0.05). SP-A1 and A1T were positively associated with premedication IOP and IOP changes, whereas A1V, A2T, PDHC, and IR were negatively associated (all p < 0.05). DAHC and DA ratio had significantly negative correlations with IOP variations. PDHC was found to be positively correlated with AL (p < 0.05). A positive relationship was noted between SP-A1 and HCT before medication (p < 0.05). SP-A1 was significantly and consistently associated with IOP. HCT might be correlated with SP-A1. SP-A1 and CST parameters could serve as potential biomarkers for evaluating OHT treatment efficacy.

Long-Term Outcome of Corneal Collagen Crosslinking with Riboflavin and UV-A Irradiation for Keratoconus*

Purpose To evaluate long-term outcomes of corneal collagen crosslinking (CXL) using riboflavin and UV-A irradiation and to determine when to repeat CXL. Methods In this retrospective consecutive interventional case series 131 eyes of 131 patients (95 male, 36 female, mean age 29.7 ± 11.4 years) between 2006 and 2016 received standard CXL (Dresden protocol, epithelium-off) for progressive keratoconus. Corrected distance visual acuity (CDVA) and corneal tomography (K1, K2, K max) were repeatedly recorded 1 year (n = 103 eyes) to 10 years (n = 44) postoperatively. Only one eye per patient was included. Paired t-test or Wilcoxon matched-pairs signed rank test was used for parametric and nonparametric data, respectively. Results 1–3 years preoperatively, median K2 significantly increased by 1.1 D (p < 0.001). Postoperatively, median K2 increased by 0.1 D after 1 year, then decreased over the remaining postoperative period by 0.85 D (p = 0.021). K max fluctuated without significant change. Median apical corneal thickness decreased by 16 µm (p = 0.012) after 5 years and then returned to preoperative values. Mean CDVA showed a significant improvement (decrease in logMAR 0.08 after 10 years, p = 0.010). CXL non-responders, defined by a postoperative increase in K max>2 D, increased from 16% after 5 to 33% after 10 years. Risk factors for non-response were young age, high astigmatism (>4.3 D), thin cornea (<480 µm), poor initial visual acuity (CDVA ≥0.3 D), and atopic dermatitis. 4 eyes were re-treated 3–4 years after first CXL without complications and keratoconus stabilized thereafter. Conclusions CXL can slow or stop keratoconus progression. However, as the number of responders declines after 5 years, especially patients with risk factors may require re-treatment.

Matched comparison of corneal higher order aberrations induced by SMILE to femtosecond assisted LASIK and to PRK in correcting moderate and high myopia: 3.00mm vs. 6.00mm

BackgroundThe refractive surgeries induce corneal higher order aberrations (C-HOAs). In this study, change of C-HOAs after small-incision lenticule extraction (SMILE) compared to femtosecond assisted laser in situ keratomileusis (femto-LASIK), and to photorefractive keratectomy with mitomycin-C (PRK) under photopic and mesopic conditions.MethodsIn this prospective study, age, gender, and apical corneal thickness (ACT) matched cases with moderate myopia [spherical equivalent (SE) 3.00 to 6.00D) to high myopia (SE > 6.00D)] were enrolled. In addition to visual acuity and refraction, total C-HOA, coma, spherical aberration (SA), and trefoil in the 3- and 6-mm zones were measured before and 3 and 6 months after surgery.ResultsOverall, 372 moderate myopia cases (124 eyes of 124 individuals in each surgical group) and 171 high myopia cases (57 eyes of 57 individuals in each surgical group) were enrolled. At baseline, the differences in age, gender, ACT, uncorrected and corrected visual acuity, and SE were not statistically significant between subgroups of surgical methods within each myopia group (all P > 0.05). At 12 months, in the moderate myopia group, there was less increase in 6-mm zone total C-HOA, coma, and SA with SMILE compared to the other groups (all P < 0.05). In the high myopia group, there was greater increase in photopic total C-HOA and trefoil and less increase in mesopic SA with SMILE (all P < 0.05).ConclusionsIn correction of moderate myopia, SMILE has better results in mesopic condition. In high myopia correction, femto-LASIK and PRK have better results in photopic and SMILE in mesopic condition.

Corneal cross-linking versus standard care in children with keratoconus \u2013 a randomised, multicentre, observer-masked trial of efficacy and safety (KERALINK): a statistical analysis plan

BackgroundThe KERALINK trial tests the hypothesis that corneal cross-linking (CXL) treatment reduces the progression of keratoconus in comparison to standard care in patients aged 10–16 years. This article describes the statistical analysis plan for this trial as an update to the published protocol. It is written before the end of the patient follow-up, while the outcome of the trial is still unknown.Design and methodsKERALINK is a randomised controlled, observer-masked, multicentre trial in progressive keratoconus comparing epithelium-off CXL with standard care, including spectacles or contact lenses as necessary for best-corrected acuity. Keratoconus is a disorder of the shape of the cornea in which the normally round dome-shaped clear front window of the eye (cornea) thins progressively leading to a cone-like bulge. This impairs the ability of the eye to focus properly, causing reduced vision which requires spectacle or contact lens wear or, in a minority of patients, eventually corneal replacement by a transplant for best vision. The primary outcome measure is the between-group difference in K2 at 18 months adjusted for K2 at baseline examination. K2 is the value of the steepest corneal meridian as measured on Pentacam topography. Secondary outcomes are keratoconus progression, time to keratoconus progression, visual acuity, refraction, apical corneal thickness and adverse events. Patient-reported effects will be explored by questionnaires. We describe in detail the statistical aspects of KERALINK: the outcome measures, the sample size calculation, general analysis principles, the planned descriptive statistics and statistical models, and planned subgroup and sensitivity analyses.DiscussionThe KERALINK statistical analysis will provide comprehensive and precise information on the relative effectiveness of the two treatments. The plan will be implemented in May 2020 when follow-up for the trial is completed.Trial registrationEudraCT, 2016-001460-11. Registered on 19 May 2016.

Mapping the corneal thickness and volume in patients with Down syndrome: a comparative population-based study.

To measure the central-to-peripheral corneal thickness and its volume according to age and gender in 10-30-year-old patients with Down syndrome (DS) and in matched individuals without DS. In the report, 202 normal pattern right eyes of patients with Down syndrome and 190 right eyes of individuals without Down syndrome and compared averages using independent sample t-tests and multiple linear regression models. The measured variables included the apical corneal thickness; the minimum corneal thickness; the average thickness on rings at 2 mm (R2), 3 mm (R3), and 4 mm (R4); the corneal volume in the central zones at 2-, 3-, 4-, and 10-mm diameters; Ambrosio's relational thickness; and the pachymetric progression indices. The mean age of the participants was 16.99 ± 4.70 and 17.22 ± 4.54 years (p=0.636). The means ± SD were 516.7 ± 33.0 and 555.7 ± 33.1 µm for apical corneal thicknesses, 508.0 ± 33.5 and 549.0 ± 40.6 µm for minimum corneal thicknesses, 543.0 ± and 588.4 ± 33.8 µm for R2s, 584.9 ± 35.6 and 637.0 ± µm for R3s, 646.9 ± 38.5 and 707.6 ± 37.1 µm for R4s, 396.4 ± 102.3 and 462.7 ± 96.2 µm for Ambrosio's relational thicknesses, 1.36 ± 0.37 and 1.22 ± 0.18 for pachymetric progression index maximums, 1.62 ± 0.11 and 1.74 ± 0.11 mm3 for corneal volume at 2 mm, 3.73 ± 0.24 and 4.01 ± 0.24 mm3 for corneal volume at 3 mm, 6.76 ± 0.44 and 7.30 ± 0.43 mm3 for corneal volume at 4 mm, and 57.03 ± 3.44 and 61.51 ± 3.40 mm3 for total corneal volume in the Down syndrome and control groups, respectively (all p<0.001). All the above indices were inversely related to age, but not to gender. Ambrosio's relational thickness maximum and the pachymetric progression index maximum were independent of age and gender. Non-keratoconic patients with Down syndrome had thin corneas with a homogeneous distribution. Therefore, the reference ranges of cornea thickness and volume should be re-defined for this patient population.

A randomised, controlled, observer-masked trial of corneal cross-linking for progressive keratoconus in children: the KERALINK protocol

IntroductionThe KERALINK trial tests the hypothesis that corneal cross-linking (CXL) treatment reduces the progression of keratoconus in comparison to standard care in patients under 17 years old. KERALINK is a...

Five-Year Changes of Anterior Corneal Indices in Diabetics versus Non-Diabetics: The Shahroud Eye Cohort Study

ABSTRACTPurpose: To compare 5-year changes of central and peripheral corneal thickness, corneal volume, and keratometry between diabetic and non-diabetic individuals (>40 years) in a population-based study.Materials and Methods: Right eye corneal indices of the 333 diabetic persons were compared with 2865 non-diabetics. Studied indices included the apical corneal thickness (ACT), minimal corneal thickness (MCT), thickness values on corneal rings of 4 mm, 6 mm, and 8 mm in diameter, the volume of the 10 mm of the corneal diameter, and the central 3 mm keratometry in two steep (Kmax) and flat (Kmin) axes as measured with Pentacam (Oculus, Inc, Lynnwood, WA).Results: In the diabetic and non-diabetic groups, respectively, the 5-year change was +0.1 ± 11.9 and −1.2 ± 11.9 μm (p = 0.035) for ACT, −1.1 ± 12.1 and −2.4 ± 11.9 μm (p = 0.056) for MCT, −3.9 ± 12.6 and −5.1 ± 12.3 μm (p = 0.007) for the 4 mm ring, −5.0 ± 15.3 and −7.5 ± 14.5 μm (p = 0.006) for the 6 mm ring, and −7.0 ± 20.1 and −10.8 ± 19.2 μm (p = 0.011) for the 8 mm ring. The diabetic group showed less reduction in corneal volume (−0.5 ± 1.8 mm3) compared to non-diabetics (−0.8 ± 1.6 mm3) (p = 0.030). Kmax (+0.3 ± 0.5D vs. +0.4 ± 0.5, p = 0.028) and Kmin (+0.4 ± 0.5D vs. +0.5 ± 0.5, p = 0.005) showed less change in diabetics compared to non-diabetics.Conclusions: The overall patterns of change in corneal thickness and shape in over 40-year old diabetics are similar to non-diabetics, such that with aging, reduced thickness and increased keratometry take the cornea towards a prolate shape. However, the age-related changes in central and peripheral corneal thickness, volume and corneal shape are less pronounced in diabetic subjects.

Single session, intrauser repeatability of anterior chamber biometric and corneal pachy-volumetric parameters using a new Scheimpflug + Placido device

PurposeTo analyze single session, intrauser reliability of a Scheimpflug device for anterior chamber (AC) and corneal parameters. MethodsIn this observational study, 100 normal candidates underwent Scheimpflug analysis with Sirius 3D Rotating Scheimpflug Camera and Topography System (Costruzione Strumenti Oftalmici, Italy). Two scans in dark room conditions were performed by the same experienced user. The candidates were asked to keep both eyes closed for 5min before the scans. Exclusion criteria were previous ocular surgery, corneal scarring and anterior segment/posterior segment anomalies. Only the right eyes were used for the analysis. Both corneal (central, minimum, and apical thickness, volume, horizontal visible iris diameter, and apical curvature) and anterior chamber (volume, depth, angle, horizontal diameter) measurements were evaluated. ResultsThere was no difference in the means of repeated measurements (p>0.05, ANOVA). Intraclass correlations between the measures were high and ranged from 0.995–0.997 for corneal to 0.964–0.997 for anterior chamber (AC) parameters. The precision of repeatability measures (1.96×Sw) was approximately 5μ for the central and minimum corneal thickness, 8μ for the apical corneal thickness, 0.06mm for AC (anterior chamber) depth and less than 2° for the AC angle. ConclusionsSirius Scheimpflug system has high repeatability for both corneal and AC parameters in normal eyes.

Evaluation of corneal thickness using a Scheimpflug–Placido disk corneal analyzer and comparison with ultrasound pachymetry in eyes after laser in situ keratomileusis

To evaluate the repeatability and reproducibility of corneal thickness measurements in post-laser in situ keratomileusis (LASIK) eyes using a rotating Scheimpflug camera combined with a Placido disk corneal topographer (Sirius) and compare the results with those of ultrasound (US) pachymetry. Eye Hospital of Wenzhou Medical College, Wenzhou, China. Comparative evaluation of a diagnostic test or technology. Patients were examined 3 times with the Scheimpflug-Placido topographer by 2 examiners. The central pupil corneal thickness (CTpupil), apical corneal thickness (CTapex), and thinnest corneal thickness (CTthinnest) were recorded. After noncontact examinations, US pachymetry was used to obtain the central corneal thickness (CCT). The Scheimpflug-Placido topographer showed high intraoperator repeatability as indicated by a test-retest repeatability of less than 8.5 μm for CTpupil, CTapex, and CTthinnest, The coefficients of variation (CoV) were less than 0.7%, and the intraclass correlation coefficient was higher than 0.99. Excellent results were also obtained for interoperator reproducibility. All CoVs were less than 0.5%. The 95% limits of agreement between the Scheimpflug-Placido measurement and the US pachymetry measurements were narrow (-16.62 to 12.44 μm for CTpupil versus US pachymetry CCT; -17.49 to 12.16 μm for CTapex versus US pachymetry CCT; -18.59 to 10.90 μm for CTthinnest versus US pachymetry CCT). The Scheimpflug-Placido topographer showed excellent intraoperator repeatability and interoperator reproducibility of CTpupil, CTapex, and CTthinnest measurements in post-LASIK eyes. The CCT measurements obtained using the device were in high agreement with those obtained by US pachymetry, suggesting that the 2 devices are interchangeable. No author has a financial or proprietary interest in any material or method mentioned.

Comparison of corneal thickness measurement with the Pentacam, the PARK1 and an ultrasonic pachymeter

Purpose: The aim was to determine the agreement between PARK1 pachymetric readings and measurements made with the Pentacam and ultrasonic pachymetry.Methods: In this prospective study, we enrolled refractive surgery patients free of other ocular conditions and performed Pentacam and PARK1 acquisitions followed by ultrasonic pachymetry. We recorded pachymetric readings on the centre, apex and thinnest point with the Pentacam, corneal thickness values of the apex and minimum readings from the PARK1, and the central corneal thickness with the ultrasonic system. Data were compared using t‐tests, and the Pearson correlations and 95% limits of agreement (LoA) of all pairs were determined.Results: The mean age of the 47 participants was 32 ± 10.4-years and data from their right eyes were used. Overall, ultrasonic measurements were significantly higher than all readings from the PARK1 and the Pentacam. The smallest difference was between the PARK‐apex and Pentacam‐apex readings (0.2 ± 11 µm); the 95% LoA of this pair gave a width of 43.7 µm (‐21.7 to 22.0 µm). The smallest width pertained to the Pentacam‐centre and ultrasound‐centre paired readings; the width was 32.5 µm (‐21.8 to 11.8 µm), while the mean difference was ‐5.54 ± 8 µm.Conclusion: The PARK1 measurements of the apical corneal thickness can be a substitute for central corneal pachymetry with an ultrasonic device, provided that the range of agreement is taken into consideration in the interpretation of the results. Similar studies on populations with different corneal conditions such as keratoconus are needed.

Corneal pachymetry in normal and keratoconic eyes: Orbscan II versus ultrasound

Purpose: To compare corneal thickness measurements using Orbscan II (OII) and ultrasonic (US) pachymetry in normal and in keratoconic eyes. Setting: Eye Department, Heartlands and Solihull NHS Trust, Birmingham, United Kingdom. Methods: Central corneal thickness (CCT) was measured by means of OII and US pachymetry in 1 eye of 72 normal subjects and 36 keratoconus patients. The apical corneal thickness (ACT) in keratoconus patients was also evaluated using each method. The mean of the difference, standard deviation (SD), and 95% limits of agreement (LoA = mean ± 2 SD), with and without applying the default linear correction factor (LCF), were determined for each sample. The Student t test was used to identify significant differences between methods, and the correlation between methods was determined using the Pearson bivariate correlation. Bland-Altman analysis was performed to confirm that the results of the 2 instruments were clinically comparable. Results: In normal eyes, the mean difference (± 95% LoA) in CCT was 1.04 μm ± 68.52 (SD) ( P>.05; r = 0.71) when the LCF was used and 46.73 ± 75.40 μm ( P = .0001; r = 0.71) without the LCF. In keratoconus patients, the mean difference (± 95% LoA) in CCT between methods was 42.46 ± 66.56 μm ( P<.0001: r = 0.85) with the LCF, and 2.51 ± 73.00 μm ( P>.05: r = 0.85) without the LCF. The mean difference (± 95% LoA) in ACT for this group was 49.24 ± 60.88 μm ( P<.0001: r = 0.89) with the LCF and 12.71 ± 68.14 μm ( P = .0077; r = 0.89) when the LCF was not used. Conclusions: This study suggests that OII and US pachymetry provide similar readings for CCT in normal subjects when an LCF is used. In keratoconus patients, OII provides a valid clinical tool for the noninvasive assessment of CCT when the LCF is not applied.