Central and peripheral pachymetry measurements according to age using the Pentacam rotating Scheimpflug camera

Cataract Classification Systems: A Review

Cataract is among the leading causes of visual impairment worldwide. Innovations in treatment have drastically improved patient outcomes, but to be properly implemented, it is necessary to have the right diagnostic tools. This review explores the cataract grading systems developed by researchers in recent decades and provides insight into both merits and limitations. To this day, the gold standard for cataract classification is the Lens Opacity Classification System III. Different cataract features are graded according to standard photographs during slit lamp examination. Although widely used in research, its clinical application is rare, and it is limited by its subjective nature. Meanwhile, recent advancements in imaging technology, notably Scheimpflug imaging and optical coherence tomography, have opened the possibility of objective assessment of lens structure. With the use of automatic lens anatomy detection software, researchers demonstrated a good correlation to functional and surgical metrics such as visual acuity, phacoemulsification energy, and surgical time. The development of deep learning networks has further increased the capability of these grading systems by improving interpretability and increasing robustness when applied to norm-deviating cases. These classification systems, which can be used for both screening and preoperative diagnostics, are of value for targeted prospective studies, but still require implementation and validation in everyday clinical practice.

Biomechanical Analysis of Tomographically Regular Keratoconus Fellow Eyes Using Corvis ST

BACKGROUND

Keratoconus is a bilateral, yet asymmetric disease. In rare cases, the second eye may show no signs of tomographic changes. The purpose of this study was to analyze the biomechanical characteristics in tomographically regular keratoconus fellow eyes.

MATERIALS AND METHODS

This retrospective, consecutive case series analyzed 916 eyes of 458 patients who presented to our keratoconus clinic between November 2020 and October 2022. Primary outcome measures included best-corrected visual acuity (BCVA), tomographic Scheimpflug analysis using Pentacam AXL (Oculus, Wetzlar, Germany), and biomechanical assessment using Corvis ST (Oculus, Wetzlar, Germany). Tomographic changes were assessed via analysis of the anterior and posterior curvature, K-max, thinnest corneal thickness (TCT), the Belin/Ambrosio Deviation Display (BAD-D), and the ABCD-Grading. Biomechanical changes were analyzed using Corvis Biomechanical Index (CBI) and Tomographic Biomechanical Index (TBI).

RESULTS

Of 916 eyes, 34 tomographically regular fellow eyes (7.4%) were identified and included in the analysis. Overall, the mean BCVA was - 0.02 ± 0.13 logMAR. Tomographic analysis showed mean K-max of 43.87 ± 1.21 D, mean TCT of 532 ± 23 µm, and mean BAD-D of 1.02 ± 0.43. Biomechanical analysis demonstrated mean CBI of 0.28 ± 0.26 and mean TBI of 0.34 ± 0.30. While normal CBI-values were observed in 16 (47%) of 34 eyes, only 13 eyes (38%) showed a regular TBI and only 7 eyes (21%) showed regular TBI and CBI. The sensitivity of CBI and TBI to detect a tomographically normal keratoconus fellow eye was 53% and 62%, respectively.

CONCLUSION

A highly asymmetric corneal ectasia with regular tomographic finding in a fellow eye is rare among keratoconus patients. In such cases, a biomechanical analysis may be useful in detecting early signs of corneal ectasia. In our analysis, the TBI showed high sensitivity for detecting a biomechanical abnormality in tomographically regular fellow eyes.

Diagnostic Techniques to Increase the Safety of Phakic Intraocular Lenses

Preoperative and postoperative diagnostics play an important role in ensuring the safety of patients with phakic intraocular lenses (pIOLs). The risk of endothelial cell loss can be addressed by regularly measuring the endothelial cell density using specular microscopy and considering the endothelial cell loss rate and the endothelial reserve in accordance with the patient's age when deciding whether to explant a pIOL. The anterior chamber morphometrics, including the anterior chamber depth and the distance between the pIOL and the endothelium, measured using Scheimpflug tomography and anterior segment optical coherence tomography (AS-OCT), can help to assess the risk of the endothelial cell loss. In patients undergoing posterior chamber pIOL implantation, accurate prediction of the vault and its postoperative measurements using AS-OCT or Scheimpflug tomography are important when assessing the risk of anterior subcapsular cataract and secondary glaucoma. Novel approaches based on ultrasound biomicroscopy and AS-OCT have been proposed to increase the vault prediction accuracy and to identify eyes in which prediction errors are more likely. Careful patient selection and regular postoperative follow-up visits can reduce the complication risk and enable early intervention if a complication occurs.

Repeatability of corneal pachymetry and epithelial thickness measurements with spectral-domain optical coherence tomography (SD-OCT) and correlation to ocular surface parameters

PURPOSE

To assess the repeatability of corneal pachymetry and epithelial thickness measurements with spectral-domain optical coherence tomography (SD-OCT) and identify correlations between epithelial thickness and ocular surface parameters.

METHODS

Adults who happened to have prolonged computer use were recruited, excluding those with conditions interfering with corneal measurements or tear production. All subjects filled in the ocular surface disease index (OSDI) questionnaire. Three consecutive measurements of central and peripheral corneal and epithelial thickness were performed with SD-OCT (RTVue XR). Schirmer test I and tear film break-up time (TBUT) were performed. Repeatability was evaluated with intraclass correlation coefficient (ICC), coefficient of variation and repeatability limit. Spearman correlation was used for non-parametric variables.

RESULTS

113 eyes of 63 subjects were included in the study. ICC was ≥ 0.989 for all corneal and ≥ 0.944 for all epithelial pachymetry segments. The best repeatability was found centrally and the worst superiorly both for corneal and epithelial measurements. Central epithelial thickness was weakly correlated with Schirmer test I (rho = 0.21), TBUT (rho = 0.02), OSDI symptoms and OSDI score (rho <|0.32|). OSDI symptoms and OSDI score were weakly correlated with Schirmer test I (rho <|0.3|) and TBUT (rho <|0.34|).

CONCLUSION

RTVue XR measurements of corneal and epithelial thickness are highly repeatable in all segments. The lack of correlation between epithelial thickness and ocular surface parameters could suggest the assessment of epithelial integrity with reliable methods such as SD-OCT.

Investigation of the Sectorized Corneal Thickness of Eyes With Corneal Endothelial Dysfunction Using Anterior-Segment Optical Coherence Tomography

PURPOSE

The aim of this study was to investigate the sectorized corneal thickness of eyes with corneal endothelial dysfunction using anterior-segment optical coherence tomography.

METHODS

We retrospectively collected anterior-segment optical coherence tomography data conducted before endothelial keratoplasty on 53 eyes of 53 patients with corneal endothelial dysfunctions including Fuchs endothelial corneal dystrophy, bullous keratopathy (BK) after trabeculectomy, and BK after laser iridotomy and from 18 normal eyes of 18 subjects. The imaging points were divided into 17 sectors. The mean for each sector was calculated and compared with the corresponding superior/inferior and temporal/nasal sectors.

RESULTS

In the normal eyes, the superior sectors were thicker than the inferior and the temporal sectors thinner than the nasal. In the diseased eyes, the superior sectors were thicker than the inferior in all subgroups; however, this tendency was no longer observed after the values were divided by the mean for the normal eyes. No significant differences were found on horizontal comparisons; however, after the values were divided by the mean for the normal eyes, the temporal sectors were thicker than the nasal. When comparing the values between the with-hole and the without-hole sides in the BK after laser iridotomy eyes, the sectors on the with-hole side were thicker than the other side.

CONCLUSIONS

Corneal thickness of endothelial dysfunction was thicker in the superior sectors than the inferior but at a similar level to normal eyes. No significant differences were found for horizontal comparisons but, based on comparison with the normal eyes, the temporal sectors were thicker than the nasal.

Comparison of Mean Corneal Power of Annular Rings and Zones Using Swept-Source Optical Coherence Tomography

This study aims to investigate differences in the mean corneal power of annular zones (corneal power measured over the inner annular zone of difference diameters) and rings (corneal power measured over a ring of different diameters) centered on the corneal apex using the swept-source optical coherence tomography technique. The mean anterior axial curvature (AAC), posterior axial curvature (PAC), and total corneal power (TCP) centered on the corneal apex with the annular rings (0−2 mm, 2−4 mm, 4−6 mm, and 6−8 mm) and zones were assessed using the ANTERION device. The paired-sample t-test was used for data comparison. For the 0−2 mm comparison, the AAC, PAC, and TCP values of rings and zones were interchangeable. For the 2−4 mm comparison, the AAC of the rings was lower than that of the zones (p = 0.004), and the TCP values of the rings were higher than that of the zones (p < 0.001). For the 4−6 mm comparison, the AAC of the rings was lower than that of the zones (p < 0.001), and the PAC and TCP values of the rings were higher than that of the zones (both p < 0.001). For the 6−8 mm comparison, the AAC of the rings was lower than that of the zones (p < 0.001), and the PAC and TCP values of the rings were higher than that of the zones (both p < 0.001). Comparisons between AAC and TCP in each sub-region showed significant differences both in the rings (p < 0.001) and the zones (p < 0.008). Differences in the AAC, PAC, and TCP measured at different diameters (2−4 mm, 4−6 mm, and 6−8 mm) of the rings and zones, centered on the corneal apex, should be noticed in clinical practice. As the diameter increases, the difference between the rings and the zones in terms of AAC, PAC, and TCP increase as well. Clinicians should also pay attention to differences between AAC and TCP for the rings and the zones within the same annular region.

Comparison Study of the Two Biometers Based on Swept-Source Optical Coherence Tomography Technology

This research aimed to investigate the potential differences in the parameters, including axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), lens thickness (LT), flat keratometry (Kf), steep keratometry (Ks), mean keratometry (Km), astigmatism, white-to-white (WTW) distance, acquired rate, and intraocular lens (IOL) power, between the two swept-source optical coherence tomography (SS-OCT) biometers, the ANTERION (biometer A) and IOLMaster 700 (biometer B). In a prospective observational comparative case series study, we enrolled 198 eyes undergoing cataract surgery. The AL, CCT, ACD, LT, Kf, Ks, Km, astigmatism, WTW, acquired rate, and IOL power were assessed. McNemar tests compared the acquired rate, and the paired sample t-test compared the quantitative measurement results between the groups. Nineteen eyes were excluded owing to missing AL data for either biometer. Finally, data from 179 eyes were analyzed. Between the two devices, no significant difference was found in AL, astigmatism magnitude, J0, and J45, while significant differences existed in CCT, ACD, LT, Kf, Ks, Km, WTW, astigmatism axis, and IOL power; no statistical significance was found in the AL acquired rate (biometer A, 90.9% and biometer B, 93.9%). Approximately 65.4% of eyes demonstrated ≥0.5-D difference in IOL power between the two biometers. In conclusion, the two biometers showed significant differences in all measurements (CCT, ACD, LT, K, WTW, astigmatism axis, and IOL power), except for AL.

Detecting subclinical keratoconus by biomechanical analysis in tomographically regular keratoconus fellow eyes

PURPOSE

To analyze the tomographically non-affected second eyes of keratoconus patients using the Corvis ST to detect any biomechanical abnormalities or subclinical keratoconus.

METHODS

In this retrospective, single-center, consecutive case series 244 eyes of 122 keratoconus patients were analyzed between November 2020 and February 2021. Fourteen fellow eyes fulfilled the inclusion criteria and showed no clinical or tomographic signs of keratoconus. Main outcome measures included best-corrected visual acuity, tomographic and biomechanical analyses using Scheimpflug imaging: Pentacam and Corvis ST (Oculus, Wetzlar, Germany). Tomographic analyses included anterior and posterior simulated keratometry, K-Max, central corneal thickness, thinnest corneal thickness, Belin/Ambrosio Ectasia Display, and the ABCD grading system. For biomechanical analyses, the corneal biomechanical index (CBI) and tomographic biomechanical index were used.

RESULTS

The mean best-corrected visual acuity was 0.01 ± 0.10 logMAR. Mean K-Max was 43.79 ± 1.12 D, mean central corneal thickness 529 ± 25 µm, mean thinnest corneal thickness 524 ± 23 µm, and mean Belin/Ambrosio Ectasia Display 1.0 ± 0.32. The mean CBI was 0.30 ± 0.21. Regular CBI values were found in six of 14 patients. The mean tomographic biomechanical index was 0.47 ± 0.22 with regular values observed in only two of 14 patients. No signs of tomographic or biomechanical abnormalities were shown in only one of 14 keratoconus fellow eyes, with regular ABCD, Belin/Ambrosio Ectasia Display, CBI and tomographic biomechanical index values.

CONCLUSIONS

Tomographically normal fellow eyes of keratoconus patients are rare. In these cases, a biomechanical analysis of the cornea may help detect a subclinical keratoconus. The tomographic biomechanical index was the most sensitive index to verify a mild ectasia.

Peripheral corneal thickness and associated factors - results from the population-based German Gutenberg Health Study

PURPOSE

Changes in peripheral corneal thickness are described in various corneal diseases such as corneal ectasia. However, few data exist describing the increase in corneal thickness from central to peripheral and reporting the normal distribution of corneal thickness in rings around the corneal centre. The aim of this study was to report these cornea characteristics and investigate associated factors in a population-based setting.

METHODS

The Gutenberg Health Study is a prospective, population-based study examining participants in a 5-year follow-up (age range 40-80 years) using Scheimpflug imaging. Corneal thickness was assessed in each participant at the apex, as well as in the corneal centre (thinnest corneal thickness) and in rings with 2, 4, 6, 8 and 10 mm diameter around the corneal centre, and the increase in corneal thickness towards the periphery. The relationship between corneal thickness at these locations and possible associated factors was determined using linear regression models. For this purpose, general and ocular parameters were included.

RESULTS

A total of 9729 participants were included in the present analysis (4874 women, age 59.2 ± 10.8 years). Multivariable analysis showed a correlation between the increase in corneal thickness in the circles from 0 to 10 mm (diameter) and the following parameters: age (B = -0.24 µm per year, p < 0.001); body height (B = -0.04 µm, p = 0.005); smoking (B = -0.72 µm, p < 0.001); spherical equivalent (B = -0.70 µm per dioptre, p < 0.001); white-to-white distance (B = -0.75 µm/mm, p < 0.001); mean corneal radius (B = -3.61 µm/mm, p < 0.001); intraocular pressure (B = -0.12 µm/mmHg, p < 0.001); glaucoma (B = -1.94 µm, p < 0.001); and pseudophakia (B = 0.89 µm, p < 0.001).

CONCLUSION

The results of the present study suggest that several general and ocular parameters are associated with peripheral corneal thickness. In the context of diagnosing glaucoma, a smaller increase in corneal thickness towards the periphery might be a new additional marker.

Comparison between different tonometers following intrastromal corneal ring segments implantation

PURPOSE

To compare different intraocular pressure (IOP) readings in corneas with intrastromal corneal ring segments (ICRS) taken by three different tonometers; Goldmann applanation tonometry (GAT), air puff tonometer, and ocular response analyzer (ORA) corneal-compensated IOP (ORA-IOPcc) and determine the relation of these measurements to different corneal parameters taken by Pentacam.

METHODS

An observational cross-sectional analytic study included patients who underwent ICRS keraring implantation at 3 months. In each eye, the two rings were placed using the femtosecond laser assisted technique 5.5 or 6 mm from the center. IOP was measured using three different tonometers; GAT, air puff tonometer, and ocular response analyzer (ORA) corneal-compensated IOP (ORA-IOPcc).

RESULTS

Fifty eyes of 30 patients (20 males and 10 females) aged 27.56 ± 6.38 years were included. IOP measurements by GAT, air puff tonometer, and ORA-IOPcc were 13.28 ± 2.13 mmHg, 10.47 ± 2.55 mmHg, and 13.19 ± 2.78 mmHg, respectively. Comparisons between air puff and each of GAT and ORA-IOPcc were statistically highly significant (p-value <0.001).

CONCLUSION

IOP measurements taken by air puff tonometer were significantly lower than those taken by GAT and ORA-IOPcc. These differences were not constant across the pressure range but increased as the pressure values determined using GAT and ORA increased. ORA-IOPcc and GAT showed similar readings. No correlation was found between any of the IOP readings taken by the three tonometers and the central corneal thickness.

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

Background

To 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).

Methods

The 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.

Results

This 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 CT_2mm region, TRT was <10.30 µm. Moreover, TRT was <15.26 µm within the CT_5mm region. The paired t-test showed significant differences in all corneal thickness measurements (P<0.001). The central region and CT_2mm agreement were high, but the largest range of 95% limits of agreement (LoA) appeared in the CT_nasal-5mm.

Conclusions

The 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 CT_2mm, except CT_5mm.

Current Developments in Corneal Topography and Tomography

Introduction: Accurate assessment of the corneal shape is important in cataract and refractive surgery, both in screening of candidates as well as for analyzing postoperative outcomes. Although corneal topography and tomography are widely used, it is common that these technologies are confused. The aim of this study was to present the current developments of these technologies and particularly distinguish between corneal topography and tomography. Methods: The PubMed, Web of Science and Embase databases were the main resources used to investigate the medical literature. The following keywords were used in various combinations: cornea, corneal, topography, tomography, Scheimpflug, Pentacam, optical coherence tomography. Results: Topography is the study of the shape of the corneal surface, while tomography allows a three-dimensional section of the cornea to be presented. Corneal topographers can be divided into large- and small-cone Placido-based devices, as well as devices with color-LEDs. For corneal tomography, scanning slit or Scheimpflug imaging and optical coherence tomography may be employed. In several devices, corneal topography and tomography have been successfully combined with tear-film analysis, aberrometry, optical biometry and anterior/posterior segment optical coherence tomography. Conclusion: There is a wide variety of imaging techniques to obtain corneal power maps. As different technologies are used, it is imperative that doctors involved in corneal surgery understand the science and clinical application of devices for corneal evaluation in depth.

The possible causes for tomography suspect Keratoconus in a Chinese cohort

Background

To explore the possible causes of tomography suspect keratoconus (TSK) marked by Tomography in screening keratoconus in a Chinese cohort, and the reasonable range of corneal horizontal diameter and thickness for decreasing the proportion of TSK.

Methods

Nested case-control study from a single center prospective cohort. All subjects were selected from the Peking University Third Hospital Ectasia Cornea Disease Cohort Project database, which included myopic patients seeking corneal refractive surgical corrections since 2013. Demographic information, basic eye examination, and auxiliary equipment examination including refraction, IOL-master, Pentacam, Sirius, and Topolyzer were recorded. In this study, all cases were classified into two groups: TSK group and normal control (NC) group, and all of them were followed up at least 2 years. The former is consisted of those whose screening examinations of tomography are abnormal, the latter is those whose screening examinations are normal. All of them have already been followed up at least 2 years without abnormalities after excimer laser corneal refractive surgeries. Unpaired t tests and Chi-square tests were used to compare the differences of indices from the tomography between the two groups.

Results

Of 183 TSK eyes (109 patients) and 160 NC eyes (83 patients), the mean age is 28.0 and 26.3 years old respectively. The corneal horizontal diameter is 11.5–11.8 mm in TSK group and 11.8–12.0 mm in NC group. The central corneal thickness is nearly 520 μm in the former and 550 μm in the latter. For Sirius, the TSK ratio of indices of SIf and SIb is 41.5 and 39.9% respectively in TSK group. For Pentacam, the TSK ratio of index IHD is 59.0% and “final D” is 72.7%.

Conclusions

Corneal horizontal diameter and central corneal thickness have great influences on the results of corneal tomography in detecting the suspect keratoconus.

Lenstar LS 900 versus Pentacam-AXL: analysis of refractive outcomes and predicted refraction

Analysis of refractive outcomes, using biometry data collected with a new biometer (Pentacam-AXL, OCULUS, Germany) and a reference biometer (Lenstar LS 900, HAAG-STREIT AG, Switzerland), in order to assess differences in the predicted and actual refraction using different formulas. Prospective, institutional study, in which intraocular lens (IOL) calculation was performed using the Haigis, SRK/T and Hoffer Q formulas with the two systems in patients undergoing cataract surgery between November 2016 and August 2017. Four to 6 weeks after surgery, the spherical equivalent (SE) was derived from objective refraction. Mean prediction error (PE), mean absolute error (MAE) and the median absolute error (MedAE) were calculated. The percentage of eyes within ± 0.25, ± 0.50, ± 1.00, and ± 2.00 D of MAE was determined. 104 eyes from 76 patients, 35 males (46.1%), underwent uneventful phacoemulsification with IOL implantation. Mean SE after surgery was − 0.29 ± 0.46 D. Mean prediction error (PE) using the SRK/T, Haigis and Hoffer Q formulas with the Lenstar was significantly different (p > 0.0001) from PE calculated with the Pentacam in all three formulas. Percentage of eyes within ± 0.25 D MAE were larger with the Lenstar device, using all three formulas. The difference between the actual refractive error and the predicted refractive error is consistently lower when using Lenstar. The Pentacam-AXL user should be alert to the critical necessity of constant optimization in order to obtain optimal refractive results.

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

Purpose

To 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.

Methods

Pachymetric 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.

Results

Seventy-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.

Conclusions

The 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.

Influence of corneal spherical aberration on prediction error of the Haigis-L formula

The purpose of this study is to investigate the relationships between corneal asphericity and Haigis-L formula prediction errors in routine cataract surgery after refractive surgery for myopic correction. This retrospective study included 102 patients (102 eyes) with a history of previous PRK or LASIK and cataract surgery. Axial length, anterior chamber depth, and central corneal power were measured using the optical biometer. On the anterior corneal surface, Q-value, spherical aberration, and ecentricity at 6.0 and 8.0 mm were measured using a rotating Scheimpflug camera. The postoperative refractive outcome at 6 months, mean error, and mean absolute error were determined. Correlation tests were performed to determine the associations between pre-cataract surgery data and the prediction error. The Q-values for 6.0 and 8.0 mm corneal diameter were 1.57 ± 0.70 (range: 0.03~3.44), and 0.82 ± 0.5 (range: -0.10~-2.66). The spherical aberration for 6.0 and 8.0 mm diameter was 1.16 ± 0.39 µm (range: 0.24~2.08 µm), and 3.69 ± 0.87 µm (range: 0.91~5.91 µm). eccentricity for 6.0 and 8.0 mm diameter was -1.22 ± 0.31 (range: -1.85 to -0.17), and -0.82 ± 0.39 (range: -1.63 to 0.32). The spherical aberration for 8.0 mm cornea diameter showed the highest correlations with the predicion error (r = 0.750; p < 0.001). When the modified Haigis-L formula considering spherical aberration for 8.0 mm produced smaller values in standard deviation of mean error (0.45D versus 0.68D), mean absolute error (0.35D versus 0.55D), and median absolute error (0.31D versus 0.51D) than the Haigis formula. Corneal asphericity influences the predictive accuracy of the Haigis-L formula. The accuracy was enhanced by taking into consideration the corneal spherical aberration for the 8.0 mm zone at pre-cataract surgery state.

Comparison of Chinese and North American Tomographic Parameters and the Implications for Refractive Surgery Screening

PURPOSE

The aim of this study was to determine whether there are significant clinical variations in the Belin/Ambrosio Enhanced Ectasia Display (BAD display) parameters between Chinese and North American eyes and whether any variations are related to differences in corneal diameter.

DESIGN

Retrospective observational study.

METHODS

Files were generated from patients seeking refractive surgical correction. Patients with previous surgery, evidence of corneal ectasia, or scans representing a non-normal cornea were excluded. Unpaired t tests were performed for all variables. Regression analyses were performed for all variables with respect to corneal diameter, and compared to evaluate the influence of corneal diameter between populations. Data were graphed as standard scores (z scores) to compare different parameters.

RESULTS

127 North American and 49 Chinese patients met study criteria. Statistically significant differences existed for corneal diameter (P < 0.01), anterior elevation at the thinnest point (P < 0.01), and Df (P < 0.01). In both populations, statistically significant correlations existed between corneal diameter and most indices, and most profoundly on pachymetric progression and final D. Regression slopes revealed a statistically significant difference for the influence of corneal diameter on ARTmax (P = 0.04) and was nearly significant for final D (P = 0.06).

CONCLUSIONS

Corneal diameter had the greatest influence on pachymetric progression and final D, and more profoundly in the Chinese. This suggests that incorporating corneal diameter as an additional variable may make the BAD display more universally applicable. Also, the differences in anterior elevation parameters suggest that specific ethnic/geographic normative values may be beneficial for the BAD display.

Comparison of corneal thickness in patients with dry eye disease using the Pentacam rotating Scheimpflug camera and anterior segment optical coherence tomography

The purpose of this study was to compare central corneal thickness, thinnest corneal thickness, and the thinnest point of the cornea between Pentacam and anterior segment optical coherence tomography (ASOCT) in patients with dry eye disease (DED). This cross-sectional study included 195 participants between November 2015-June 2017. DED was diagnosed using the Asia Dry Eye Society criteria and further divided into mild and severe DED based on kerato-conjunctival vital staining. Central corneal thickness, thinnest corneal thickness, and the thinnest point of the cornea measured by Pentacam and ASOCT were compared, and Pearson's correlation coefficients were estimated. The differences in central corneal thickness and the thinnest corneal thickness between Pentacam and ASOCT were analysed using Bland-Altman and multivariate regression analyses adjusted for age and sex. This study included 70 non-DED subjects and 52 patients with mild and 73 with severe DED. The Pentacam and ASOCT measurements of central corneal thickness and thinnest corneal thickness were strongly correlated, but the respective values were higher when measured with Pentacam. The Bland-Altman analysis revealed differences in central corneal thickness (non DED, 11.8; mild DED, 13.2; severe DED, 19.6) and in thinnest corneal thickness (non DED, 13.1; mild DED, 13.4; severe DED, 20.7). After adjusting for age and sex, the differences in central corneal thickness (β = 7.029 μm, 95%CI 2.528-11.530) and thinnest corneal thickness (β = 6.958 μm, 95%CI 0.037-13.879) were significantly increased in the severe-DED group. The distribution of the thinnest point of the cornea in the cornea's inferior temporal quadrant between Pentacam and ASOCT deviated in severe DED (Pentacam: 90.4% vs. ASOCT: 83.6%). Clinicians should consider that there were significant differences in corneal-morphology assessment between the measurements with Pentacam and ASOCT in severe DED.

Agreement between Pentacam and handheld Auto-Refractor/Keratometer for keratometry measurement

OBJECTIVE

This study was conducted to evaluate the level of agreement in keratometry measurements between a rotating Scheimpflug imaging-based system (Pentacam) and a handheld auto-refractokeratometer (handheld NIDEK ARK-30).

METHOD

This analytical cross-sectional study was conducted in the right eyes of 579 subjects. Keratometry measurements were conducted with the Pentacam and the handheld NIDEK ARK-30 systems. The SPSS Software version 22 and MedCalc V3 were applied to estimate descriptive statistics using paired t-test, Pearson correlation coefficient, 95% limits of agreement (LoA), and Bland-Altman plot.

RESULTS

In the total sample, the inter-device difference in the mean flat and steep keratometry values was -0.266 diopter (D) (P-value<0.001) and 0.052D (P-value=0.093), respectively. There was a significant difference in mean flat keratometry between the two devices in all groups of refractive errors (paired difference <0.5D and P-value<0.001). The difference in mean steep keratometry was significant only in myopic subjects (P-value=0.046). The 95% LoA between the two devices measurements was 2.51D, 3.98D, and 6.37D for flat keratometry and 2.6D, 3.2D, and 3.9D for steep keratometry in emmetropic, myopic, and hyperopic subjects, respectively.

CONCLUSION

Our study showed relatively wide limits of agreement between handheld NIDEK ARK-30 and Pentacam; therefore, these devices cannot be used interchangeably for measuring corneal curvature.

Effects of corneal thickness distribution and apex position on postoperative refractive status after full-bed deep anterior lamellar keratoplasty

OBJECTIVE

To investigate the effects of corneal thickness distribution and apex position on postoperative refractive status after full-bed deep anterior lamellar keratoplasty (FBDALK).

METHODS

This is a retrospective analysis of patients who were diagnosed with advanced keratoconus between 2011 and 2014 in our hospital. The base of the cone in all patients did not exceed the central cornea at a 6-mm range. The FBDALK was performed by a same surgeon. All patients had a complete corneal suture removal and the follow-up records were intact. Patients who had graft-bed misalignment or who were complicated with a cataract or glaucoma were excluded. Uncorrected visual acuity (UCVA), best spectacle corrected visual acuity (BSCVA), and Pentacam examination data were recorded at two years postoperatively. The recorded data included the superior-inferior (S-I) and nasal-temporal (N-T) corneal thickness differences in 2, 4, 6, and 8 mm diameter concentric circles with the corneal apex as the center (S-I_{2 mm}, S-I_{4 mm}, S-I_{6 mm}, S-I_{8 mm}, N-T_{2 mm}, N-T_{4 mm}, N-T_{6 mm}, and N-T_{8 mm}), the linear, X-axis, and Y-axis distance between the corneal pupillary center and the cornea apex, total corneal astigmatism at a zone of 3 mm diameter from the corneal apex (TA_{3 mm}), the astigmatic vector values J₀ and J₄₅, and the corneal total higher-order aberration for 3 and 6 mm pupil diameters (HOA_{3 mm} and HOA_{6 mm}). Statistical analysis was performed by SPSS 15.0.

RESULTS

A total of 47 eyes of 46 patients met the criteria and were included in this study. The mean follow-up time was (28±7) months. The mean UCVA was 0.45±0.23 (logMAR) (MAR: minimum angle of resolution) and the mean BSCVA was 0.19±0.15 (logMAR), which were all significantly positively correlated with postoperative TA_{3 mm} and HOA_{3 mm}. The mean S-I corneal thickness differences were (44.62±37.74) μm, and the mean N-T was (38.57±32.29) μm. S-I_{2 mm} was significantly positively correlated with J₀ (r=0.31), J₄₅ (r=0.42), HOA_{3 mm} (r=0.37), and HOA_{6 mm} (r=0.48). S-I_{4 mm} and S-I_{8 mm} were significantly positively correlated with HOA_{3 mm} (r=0.30, r=0.40) and HOA_{6 mm} (r=0.46, r=0.35). The X-axis distance between corneal pupillary center and corneal apex was significantly positively correlated with J₄₅ (r=0.29).

CONCLUSIONS

In patients with advanced keratoconus after FBDALK, the unevenly distributed thickness at corneal pupillary area and the misalignment of corneal apex and pupillary center might cause significant regular and irregular astigmatism, which affected the postoperative visual quality.

[Evaluation of mean macular thickness by optical coherence tomography (SD OCT) in black Senegalese subjects]

INTRODUCTION

Our goal was to evaluate the normal macular thickness in Blacks by OCT and to determine socio-demographic and clinical parameters which may influence it.

MATERIALS AND METHODS

This was a multicenter, prospective, descriptive study over 6 months. It included Black adults followed in the ophthalmology departments of Abass Ndao and Aristide-Le-Dantec hospitals in Dakar. Included subjects had corrected visual acuity of 10/10 (0 logMAR) and P2 (+0.1 logMAR), clear ocular media, and no retinal abnormalities. We used the Topcon 3D 2000 OCT to measure the central thicknesses of the cornea (CT) and of the macula (MT), and cup to disc ratio (C/D) in each eye. Socio-demographic, clinical and tomographic data were collected on a survey form and correlated to the MT. The analysis was carried out by the Epi info 7 software. We used the Chi² comparison test with a P value˂0.05.

RESULTS

One hundred and nine patients were included. The mean age was 27.39 years with a male/female ratio of 0.65. The subjects were emmetropic in 54.13% of cases. The mean CT was 519.97μm, the mean C/D was 0.23, and the mean MT was 264.35μm. The P-value (P) was greater than or equal to 0.1 for all the factors studied.

CONCLUSION

MT in our study was lower than that of Whites, and the various parameters studied did not demonstrate a statistically significant influence on MT.

Accuracy of Corneal Thickness by Swept-Source Optical Coherence Tomography and Scheimpflug Camera in Virgin and Treated Fuchs Endothelial Dystrophy

PURPOSE

To assess intraobserver repeatability, intersession reproducibility, and agreement of swept-source Fourier-domain optical coherence tomography (SS-OCT) and the Scheimpflug camera in measuring corneal thickness in virgin and grafted eyes with Fuchs endothelial corneal dystrophy (FECD).

METHODS

Thirty-six control eyes, 35 FECD eyes, 30 FECD with corneal edema eyes, 25 Descemet stripping automated endothelial keratoplasty (DSAEK) eyes, and 29 Descemet membrane endothelial keratoplasty (DMEK) eyes were included. The apical center, pupillary center, and thinnest corneal thickness were determined in 3 consecutive images and repeated 2 weeks later. Repeatability and reproducibility coefficients, intraclass correlation coefficients, and 95% limits of agreement (LOA) between measurements were calculated. Agreement between devices was assessed using Bland-Altman analysis.

RESULTS

Corneal thickness measurements were highly reproducible and repeatable with both systems. SS-OCT showed better repeatability in all corneal locations in the normal, FECD, FECD with edema, DSAEK, and DMEK groups (coefficient of variation ≤0.60%, ≤0.36%, ≤0.43%, ≤1.09%, and ≤0.48%, respectively) than the Scheimpflug (coefficient of variation ≤1.15%, ≤0.92%, ≤1.10%, ≤1.25%, and ≤1.14%, respectively). Between-session 95% LOA for SS-OCT was less than 3% for all groups except for the FECD with edema group, being almost double using the Scheimpflug camera. Differences between instruments were statistically significant in all groups and locations (P < 0.01) except in the DSAEK group (P ≤ 0.51); however, SS-OCT underestimated all measurements.

CONCLUSIONS

SS-OCT provides better reproducible and repeatable measurements of corneal thickness than those obtained with the Scheimpflug camera in patients with FECD or an endothelial transplant. Variations between examinations higher than the 95% LOA observed in our study should raise awareness of changes in the endothelial function.

Repeatability and Intersession Reproducibility of Pentacam Corneal Thickness Maps in Fuchs Dystrophy and Endothelial Keratoplasty

PURPOSE

To assess intrasession repeatability and intersession reproducibility of Pentacam corneal thickness maps in patients with Fuchs endothelial corneal dystrophy (FECD) before and after endothelial transplantation.

METHODS

In this observational diagnostic evaluation, 20 healthy subjects along with 81 consecutive patients were examined. Patients were classified into 4 groups: FECD without corneal edema, FECD with corneal edema, Descemet stripping automated endothelial keratoplasty, and Descemet membrane endothelial keratoplasty. Three consecutive scans of each eye were obtained at 2 different sessions. Raw pachymetry data were used to calculate average values of 4 concentric annular zones, which were also divided into 8 sectors. Repeatability and reproducibility coefficients (CR), coefficient of variation (CV), intraclass correlation coefficient, and 95% limits of agreement were calculated.

RESULTS

The intrasession repeatability CV was ≤1% in the central 6 mm for all groups, with an intraclass correlation coefficient ≥0.97. It was better at the central zone than the periphery in all groups. Intersession reproducibility tended to be worse in the central area than the periphery in FECD without edema (CR ≤ 24.37; CV ≤ 1.48) and FECD with edema (CR ≤ 36.74; CV ≤ 2.03), whereas it was better in the central area in healthy eyes (CR ≤ 20.11; CV ≤ 1.32) and improved after Descemet stripping automated endothelial keratoplasty (CR ≤ 21.93; CV ≤ 1.31) and Descemet membrane endothelial keratoplasty (CR ≤ 30.83; CV ≤ 1.94).

CONCLUSIONS

Pentacam corneal thickness maps showed good repeatability and intersession reproducibility in virgin and grafted corneas with FECD, which makes it a valid tool for monitoring these patients. Central areas showed the highest variability between sessions in diseased groups.

Lenstar® LS 900 vs Pentacam®-AXL: Comparative study of ocular biometric measurements and intraocular lens power calculation

Purpose:

Comparison of biometric measurements and calculation of intraocular lens with a new biometer (Pentacam®-AXL, Oculus, Germany) and a reference biometer (Lenstar LS 900®, Haag-Streit AG, Switzerland), in order to assess the agreement between these two devices.

Setting:

Centro Hospitalar de Leiria, Portugal

Materials and methods:

Prospective, institutional study, in which measurements of axial length, anterior chamber depth from the corneal epithelium and endothelium to the anterior surface of the lens (anterior chamber depth ext and anterior chamber depth int), central corneal thickness and keratometry readings of the flattest and steepest meridians (K1 and K2) were obtained with the two systems. Intraocular lens calculation was also performed, using the Haigis, SRK/T and HofferQ formulas.

Results:

The study sample included 136 eyes of 79 patients. Of these, 42 were women and 37 were men. Statistically significant differences were found (p < 0.05, paired T test) in K1, K2 and central corneal thickness between the 2 biometers. Intraocular lens calculation with the Lenstar® and the Pentacam® with Haigis, SRK/T and HofferQ formulas showed statistically significant differences (p < 0.05 Paired T test).

Conclusion:

Axial length measurements obtained with the Pentacam® and Lenstar® appear to be interchangeable, while measurements of anterior chamber depth, K1 and K2, and central corneal thickness do not appear to be interchangeable between different devices. Statistically significant differences were found in the calculation of intraocular lenses in all formulas used.

Comparative evaluation of Scheimpflug tomography parameters between thin non-keratoconic, subclinical keratoconic, and mild keratoconic corneas

PURPOSE

To evaluate and compare the topographic and topometric parameters, thickness profile data, and data from enhanced elevation maps of thin non-keratoconic, subclinical keratoconic, and mild keratoconic corneas with the Pentacam Scheimpflug corneal tomography and to study the usefulness of different parameters to differentiate keratoconus from topographically normal thin corneas.

METHODS

The study included 30 eyes with subclinical keratoconus, 30 eyes with mild-stage keratoconus, and 54 healthy eyes with minimal pachymetry ≤500 µm, with a mean age of 21.19 ± 2.97, 21.75 ± 1.93, and 21.5 ± 2.95 years, respectively. The area under the receiver operating characteristic curves was used to analyze the diagnostic significance of the Pentacam parameters.

RESULTS

The anterior and posterior corneal elevations, pachymetric progression, the percentage of thickness increase measurements, overall D value, and topometric indices were statistically significantly higher in subclinical and mild keratoconic corneas than in normal eyes with thin cornea (p < 0.05). All these parameters had sufficient strength (area under the receiver operating characteristic curves >0.90) to differentiate clinical keratoconus. Posterior elevation showed the excellent area under the receiver operating characteristic curves with 100% sensitivity and 100% specificity for this purpose. However, among all parameters studied, the anterior elevation (0.935) showed the excellent area under the receiver operating characteristic curves to differentiate subclinical keratoconus, followed by posterior elevation (0.897), index of height decentration (0.887), and D value (0.882).

CONCLUSION

The parameters derived from the Scheimpflug device, such as corneal elevations and overall D value, can effectively differentiate subclinical and clinical keratoconus from non-keratoconic thin cornea eyes. However, the specificity levels of these parameters were relatively limited in the diagnosis of subclinical keratoconus.

Repeatability of corneal elevation maps in keratoconus patients using the tomography matching method

To assess repeatability of corneal tomography in successive measurements by Pentacam in keratoconus (KC) and normal eyes based on the Iterative Closest Point (ICP) algorithm. The study involved 143 keratoconic and 143 matched normal eyes. ICP algorithm was used to estimate six single and combined misalignment (CM) parameters, the root mean square (RMS) of the difference in elevation data pre (PreICP-RMS) and post (PosICP-RMS) tomography matching. Corneal keratometry, expressed in the form of M, J₀ and J₄₅ (power vector analysis parameters), was used to evaluate the effect of misalignment on corneal curvature measurements. The PreICP-RMS and PosICP-RMS were statistically higher (P < 0.01) in KC than normal eyes. CM increased significantly (p = 0.00), more in KC (16.76 ± 20.88 μm) than in normal eyes (5.43 ± 4.08 μm). PreICP-RMS, PosICP-RMS and CM were correlated with keratoconus grade (p < 0.05). Corneal astigmatism J₀ was different (p = 0.01) for the second tomography measurements with misalignment consideration (−1.11 ± 2.35 D) or not (−1.18 ± 2.35 D), while M and J₄₅ kept similar. KC corneas consistently show higher misalignments between successive tomography measurements and lower repeatability compared with healthy eyes. The influence of misalignment is evidently clearer in the estimation of astigmatism than spherical curvature. These higher errors appear correlated with KC progression.

Aberrant ocular architecture and function in patients with Klinefelter syndrome

Klinefelter Syndrome (KS), the most common chromosomal disorder in men (47,XXY), is associated with numerous comorbidities. Based on a number of isolated case reports, we performed the first systematic and comprehensive evaluation of eye health in KS patients with a focus on ocular structure and vascularization. Twenty-one KS patients and 26 male and 38 female controls underwent a variety of non-invasive examinations investigating ocular morphology (examination of retinal thickness, optic nerve head, and cornea) and function (visual field testing and quantification of ocular vessel density by optical coherence tomography angiography). In comparison to healthy controls, KS patients exhibited a smaller foveal avascular zone and a decreased retinal thickness due to a drastically thinner outer nuclear layer. The cornea of KS patients showed a decreased peripheral thickness and volume. In perimetry evaluation, KS patients required brighter stimuli and gave more irregular values. KS patients show an ocular phenotype including morphological and functional features, which is very likely caused by the supernumerary X chromosome. Thus, KS should not be limited to infertility, endocrine dysfunction, neurocognitive and psychosocial comorbidities. Defining an aberrant ocular morphology and function, awareness for possible eye problems should be raised.

Age-related change in corneal biomechanical parameters in a healthy Caucasian population

PURPOSE

To determine the effect of aging on corneal biomechanical parameters measured via ocular response analyzer in a homogenous healthy Caucasian population.

METHODS

A total of 2039 Caucasian adults were consecutively recruited and divided into seven groups according to decades of age. The difference in mean corneal hysteresis (CH), mean corneal resistance factor (CRF), mean Goldmann-correlated intraocular pressure (IOPg), and mean corneal-compensated IOP (IOPcc) between decades of age were investigated. The strength of the correlations between corneal biomechanical parameters, and between each biomechanical parameter and age were evaluated. The effect of age on each corneal biomechanical parameter was analyzed.

RESULTS

Mean age of the participants (1173 female and 866 male) was 43.30 ± 14.64 years. Mean CH, CRF, IOPcc, and IOPg were 11.49 ± 1.89 mmHg, 11.40 ± 2.30 mmHg, 15.01 ± 3.11 mmHg, and 15.72 ± 3.80 mmHg, respectively. There were significant differences in mean CH, CRF, IOPcc, and IOPg between groups (p < 0.001 for all parameters). There was a significant negative correlation between age and CH (r = -0.067 and p = 0.003), and a significant negative correlation between age and CRF (r = -0.053 and p = 0.017). There was a significant positive correlation between age and IOPg (r = 0.25 and p < 0.001), and between age and IOPcc (r = 0.20 and p < 0.001). Linear regression analysis showed that for every 1-year increase CH decreased 0.011 mmHg, CRF decreased 0.004 mmHg, IOPcc increased 0.053 mmHg, and IOPg increased 0.047 mmHg.

CONCLUSIONS

Aging can cause significant changes in corneal biomechanical parameters. Corneal biomechanical parameters were correlated with each other, and each was correlated with aging.

Comparison of central corneal thickness and endothelial cell measurements by Scheimpflug camera system and two noncontact specular microscopes

PURPOSE

To investigate the correlation of Scheimpflug camera system and two noncontact specular microscopes in terms of central corneal thickness (CCT) and corneal endothelial cell morphology measurements.

METHODS

One hundred eyes of 50 healthy subjects were examined by Pentacam Scheimpflug Analyzer, CEM-530 (Nidek Co, Ltd, Gamagori, Japan) and CellChek XL (Konan Medical, California, USA) via fully automated image analysis with no corrections made. Measurement differences and agreement between instruments were determined by intraclass correlation analysis.

RESULTS

The mean age of the subjects was 36.74 ± 8.59 (range 22-57). CCTs were well correlated among all devices, with having CEM-530 the thinnest and CellChek XL the thickest measurements (intraclass correlation coefficient (ICC) = 0.83; p < 0.001 and ICC = 0.78; p < 0.001, respectively). Mean endothelial cell density (ECD) given by CEM-530 was lower than CellChek XL (2613.17 ± 228.62 and 2862.72 ± 170.42 cells/mm², respectively; ICC = 0.43; p < 0.001). Mean value for coefficient of variation (CV) was 28.57 ± 3.61 in CEM-530 and 30.30 ± 3.53 in CellChek XL. Cell hexagonality (HEX) with CEM-530 was higher than with CellChek XL (68.70 ± 4.16% and 45.19 ± 6.58%, respectively).

CONCLUSIONS

ECDs with CellChek XL and CEM-530 have good correlation, but the values obtained by CellChek XL are higher than CEM-530. Measurements for HEX and CV differ significantly and show weak correlation. Thus, we do not recommend interchangeable use of CellChek XL and CEM-530. In terms of CCTs, Pentacam, CEM-530 and CellChek XL specular microscopy instruments are reliable devices.

Torsional and flattening effect on corneal astigmatism after cataract surgery: a retrospective analysis

Background

To evaluate the torsional and flattening effect of steep meridian incisions and influence of posterior corneal astigmatism (PCA) on total corneal astigmatism (TCA) after cataract surgery.

Methods

One hundred thirty-two eyes underwent cataract surgery with steep meridian 2.2 mm microcoaxial and 2.85 mm conventional clear corneal incisions. Eyes were divided into with-the-rule (WTR) astigmatism and against-the-rule (ATR) astigmatism groups depending on the steeper meridian and measured with autokeratorefractor and Pentacam® before surgery, at 1 day, 1 week, 1 and 2 months postoperatively. Polar vector analysis was used to evaluate torsional effect of steep meridian incisions.

Results

A decrease in astigmatic polar value (AKP) (+0) was observed in both keratometric and total astigmatism (TA) after 1 and 2 months, although the decrease was only statistically significant in TA (p < 0.05). The AKP(+45) was more significant in the conventional group than the microcoaxial group at 2 months postoperatively (p < 0.05, respectively). There was a significant correlation between corneal thickness of the superior quadrant and PCA in the WTR group (p = 0.028). In eyes with anterior corneal astigmatism smaller than 0.55D of WTR astigmatism and PCA greater than 0.35D of WTR astigmatism showed greater shifting of steep axis and also increment of refractive cylinder powers.

Conclusions

In eyes with superior corneal thickness greater than 714.5 μm and PCA greater than 0.35D of WTR astigmatism, steep meridian incision may cause a significant torsional effect and off-steep meridian change, contributing to an increment of postoperative residual manifest astigmatism after cataract surgery.

Reproducibility and repeatability of central corneal thickness measurement in healthy eyes using four different optical devices

Aim

The aim of the study is to compare the measurements of central corneal thickness (CCT) performed by two examiners with four different methods at different times inter- and intra-individually.

Methods

Thirty healthy people were included in the study. In these measurements, an optical low-coherence reflectometry (OLCR), an optic coherence tomography (OCT), a specular microscopy (SM), and a corneal topography (CT) were used. Two examiners performed the measurements in a consecutive manner. After 1–7 days of the first measurements, the second measurements were performed again consecutively. The mean of three measurements was taken in each session for all devices.

Results

In OCT measurements, there was a significant difference between two examiners in both sessions (p < 0.001), while no significant differences were found between two examiners in first and second sessions in SM, CT, and OLCR measurements. When each examiner’s measurements were compared to two sessions, there were no significant differences (p > 0.05, for all) except the SM measurements of the first examiner (p = 0.041). When the first measurements of two examiners were compared, the smallest values were of OCT. At the first session of two examiners, there was a significant difference between OCT and CT measurements, and between OCT and OLCR (p < 0.001, p = 0.002 for the first examiner and p < 0.001 for the second examiner, respectively).

Conclusion

Our study showed that CCT measurements made by CT and OLCR methods were almost same and highly correlated for both the examiners’ measurements. CCTs measured by OCT were on average 30 μm thinner than CT and OLCR.

Central Corneal Thickness Measurement Using Ultrasonic Pachymetry, Rotating Scheimpflug Camera, and Scanning-slit Topography Exclusively in Thin Non-keratoconic Corneas

Purpose:

To evaluate the agreement among Pentacam, Orbscan and ultrasound (US) pachymetry for measurement of central corneal thickness (CCT) in thin corneas with normal topographic pattern.

Methods:

We included 88 eyes of 44 refractive surgery candidates with thinnest pachymetric readings of 500 micrometers (μm) or less on Orbscan, a normal topographic pattern, no sign of keratoconus, and best corrected visual acuity (BCVA) of 20/20. Pentacam, Orbscan and US were performed in one session by the same examiner. Exclusion criteria were history of ocular surgery, topographic abnormalities suggesting forme fruste keratoconus or keratectasia, and recent contact lens wear.

Results:

The difference in CCT measurements by US pachymetry and Orbscan II [using an acoustic factor (AF) of 0.92] ranged from −34 to +34 μm. The difference between the thinnest point and central readings measured by US reached 16 μm with Orbscan II (AF: 0.92) and 2 μm with Pentacam. Mean differences between the employed devices were 0.2 μm for Pentacam versus US (P = 0.727), 30.1 μm for uncorrected Orbscan versus US (P < 0.001), 10.4 μm for Orbscan II (AF = 0.92) versus US (P < 0.001), and 0.2 μm for Orbscan II (AF = 0.94) versus US (P = 0.851).

Conclusion:

In normal thin corneas, Pentacam demonstrated better agreement with US pachymetry as compared to corrected Orbscan readings. Results achieved by Orbscan were better consistent with US pachymetry using an AF of 0.94. We speculate that a dynamically graded AF in reverse proportion to CCT constitutes a better approach for correcting Orbscan measurements.

Measurement of central corneal thickness by ultrasonic pachymeter and oculus pentacam in patients with well-controlled glaucoma: hospital-based comparative study

Background

The measurement of central corneal thickness (CCT) plays an important role in the diagnosis and treatment of glaucoma and many corneal diseases.

Objective of the study

To compare the measurement of CCT by ultrasonic pachymeter with that measured by oculus pentacam in both normal subjects and patients with well-controlled glaucoma.

Patients and methods

In 173 eyes of both controls and patients with open-angle glaucoma (normal intraocular pressure) attending Ibn Al Haitham Teaching Eye Hospital, CCT was measured by oculus pentacam and then by ultrasound pachymeter at the same morning by the same technicians.

Results

The results showed no significant difference in CCT readings measured by the two devices in both glaucoma and control groups (glaucoma group: 547.29±49.32 µm with pentacam vs 547.66±45.24 µm with ultrasound pachymeter; control group: 551.02±36.28 µm with pentacam vs 541.25±34.96 µm with ultrasound pachymeter). P-values were >0.05 in both groups (statistically not significant).

Conclusion and recommendation

Ultrasonic pachymeter and oculus pentacam can be used interchangeably in measuring CCT, and we recommend a nontouch method (in this study, pentacam Scheimpflug camera) for measuring CCT during assessment of patients with glaucoma or any ocular disease or surgery.

Reliability of Pentacam HR Thickness Maps of the Entire Cornea in Normal, Post-Laser In Situ Keratomileusis, and Keratoconus Eyes

PURPOSE

To measure the repeatability and reproducibility of Pentacam HR system thickness maps for the entire cornea in normal, post-laser in situ keratomileusis (post-LASIK), and keratoconus (KC) eyes.

DESIGN

Reliability study.

METHODS

Sixty normal subjects (60 eyes), 30 post-LASIK subjects (60 eyes), and 14 KC patients (27 eyes) were imaged with the Pentacam HR system by 2 well-trained operators. For pachymetry the cornea was divided into 4 zones: a central zone (2-mm diameter) and concentric pericentral zone (2-5 mm), transitional zone (5-7 mm), and peripheral zone (7-10 mm). The 3 concentric zones were subdivided into 8 sectors. Intraobserver repeatability and interobserver reproducibility of entire corneal thickness maps were tested by the repeatability and reproducibility coefficients, intraclass correlation coefficients, coefficient of variation, and 95% limits of agreement.

RESULTS

From central to peripheral zones, the precision of corneal thickness measurements became gradually smaller. Central zone repeatability and reproducibility were the best in the normal, post-LASIK, and KC groups. The peripheral superior sectors showed poorer repeatability and reproducibility for all subjects. The intraobserver repeatability and interobserver reproducibility for all zones were ≤19.3 μm, ≤22.1 μm, and ≤20.7 μm, in the normal, post-LASIK, and KC groups, respectively. The intraobserver and interobserver coefficients of variation for all zones were ≤1.3%, ≤1.6%, and ≤1.6% for all 3 groups.

CONCLUSIONS

Pentacam HR system pachymetry of the entire cornea provided good precision in normal, post-LASIK, and KC corneas. Thickness measurements in the peripheral cornea should be interpreted with caution in abnormal corneas after surgery or with diseases.

Evaluation of Central Corneal Thickness Using Corneal Dynamic Scheimpflug Analyzer Corvis ST and Comparison with Pentacam Rotating Scheimpflug System and Ultrasound Pachymetry in Normal Eyes

Purpose. To assess the repeatability and reproducibility of central corneal thickness (CCT) measurements by corneal dynamic Scheimpflug analyzer Corvis ST in normal eyes and compare the agreement with Pentacam rotating Scheimpflug System and ultrasound pachymetry. Methods. 84 right eyes underwent Corvis ST measurements performed by two operators. The test-retest repeatability (TRT), within-subject coefficient of variation (CoV), and intraclass correlation coefficient (ICC) were used to evaluate the intraoperator repeatability and interoperator reproducibility. CCT measurements also were obtained from Pentacam and ultrasound pachymetry by the first operator. The agreement between the three devices was evaluated with 95% limits of agreement (LoA) and Bland-Altman plots. Results. Corvis ST showed high repeatability as indicated by TRT ≤ 13.0 μm, CoV < 0.9%, and ICC > 0.97. The interoperator reproducibility was also excellent. The CoV was <0.9%, and ICC was >0.97. Corvis ST showed significantly lower values than Pentacam and ultrasound pachymetry (P < 0.001). The 95% LoA between Corvis ST and Pentacam or ultrasound pachymetry were −15.8 to 9.5 μm and −27.9 to 12.3 μm, respectively. Conclusions. Corvis ST showed excellent repeatability and interoperator reproducibility of CCT measurements in normal eyes. Corvis ST is interchangeable with Pentacam but not with ultrasound pachymetry.

[Influence of corneal pachymetric changes on functional results after cataract surgery]

BACKGROUND

In the early postoperative period following uncomplicated cataract surgery, the correlation of corrected distance visual acuity (CDVA) and the increase in corneal thickness and anterior chamber depth (ACD) are investigated.

PATIENTS AND METHODS

A total of 54 cataract patients with a mean age of 70 ± 8.4 years were included in this prospective study. Surgery was carried out on one eye of each patient according to the study protocol. Refraction, CDVA and ACD were evaluated 1 day and 1 week postoperatively and compared with the pachymetry results measured with the Pentacam.

RESULTS

The mean postoperative CDVA significantly improved from 0.31 ± 0.24 logMAR to 0.18 ± 0.22 logMAR after one day and up to 0.06 ± 0.13 logMAR one week after surgery (p < 0.05). The mean spherical equivalent was - 0.52 ± 0.69 D after one day and - 0.50 ± 0.82 D one week after surgery and showed only minimal differences compared to the mean target refraction of - 0.39 ± 0.70 D. Postoperative corneal thickness showed a significant increase compared to the preoperative results (p < 0.05) on both visits: the mean difference was 33.26 ± 50.20 µm (- 17 to 315 µm) on the first day and 20.22 ± 23.15 µm (- 10 to 99 µm) one week after surgery. Up to 7 days postoperatively the increase in corneal thickness and CDVA showed only moderate or no correlations (r = 0.465 vs. r = 0.072, respectively). Regarding pachymetry and ACD values, no or only low correlations were found.

CONCLUSION

The significant increase in corneal thickness on the first and seventh day shows no to moderate correlation to the CDVA. Nevertheless, a good and early rehabilitation of visual acuity following uncomplicated cataract surgery is possible. Intraocular pressure measurement can lead to false high results due to an increase in corneal thickness.

Corneal thickness profile and posterior corneal astigmatism in normal corneas

PURPOSE

To analyze the influence of corneal thickness profile on posterior corneal astigmatism (PA).

DESIGN

Prospective, observational study.

SUBJECTS

We included 418 normal subjects (213 men and 205 women) ranging in age from 6 to 93 years (49.0 ± 23.4 years, mean ± standard deviation) in this study.

METHODS

Anterior and posterior corneal topography were evaluated using 3-dimensional anterior segment optical coherence tomography. Pericentral corneal thickness (PCT) in each quadrant (superior, inferior, nasal, and temporal) was measured, and average PCT in the vertical (superior + inferior) and horizontal (nasal + temporal) directions was calculated. Posterior corneal astigmatism was calculated as (1) assumed PA based on the anterior corneal curvature measurement and the keratometric index and (2) actual PA derived from the direct measurement of posterior corneal curvature.

MAIN OUTCOME MEASURES

Corneal thickness distribution and the difference between assumed and actual PA.

RESULTS

The PCT was significantly greater in the vertical (546.0 ± 31.8 μm) than in the horizontal direction (542.6 ± 31.7 μm) (P < 0.0001), and the difference between them was significantly correlated with subject age (r = 0.518, P < 0.0001). The difference between assumed and actual PA significantly correlated with the discrepancy between vertical and horizontal PCT (r = 0.819, P < 0.0001), as well as subject age (r = 0.533, P < 0.0001).

CONCLUSIONS

Corneal thickness is greater in the vertical than in the horizontal direction, making the PA more against-the-rule pattern than calculated on the basis of the anterior corneal curvature measurement only. Such discrepancy is more prominent in older patients.