Posterior Elevation Values Research Articles

Case-control study of corneal topography and specular microscopy parameters in JIA patients with and without ocular involvement.

To assess corneal topography and specular microscopy values in juvenile idiopathic arthritis-related uveitis (JIA-U). This case-control study included 30 eyes from JIA-U patients, 20 eyes from JIA patients, and 50 eyes from age- and gender-matched healthy subjects. Patients with a history of ocular diseases or intraocular surgery were excluded. Corneal topography maps (Pentacam HR) and specular microscopy images (CellChek SL) were obtained. The measurements of the groups were compared. Keratometric astigmatism was higher in the JIA-U group than in the control group (p = 0.040). Patients with astigmatism greater than 1.50D were more common in the JIA-U group than in the control group (p = 0.026). The JIA-U group had higher anterior and posterior elevation values than the control group (p = 0.006, p = 0.025). The density of endothelial cells, coefficient of variation, and hexagonality did not change across groups (p = 0.465, p = 0.096, p = 0.869). The total number of exacerbations and the duration of anterior chamber inflammation were both positively correlated with posterior elevation (r = 0.600, p 0.001; r = 0.583, p 0.001). The age of diagnosis was found to be negatively correlated with anterior elevation (r = -0.412, p = 0.021). Corneal astigmatism, as well as anterior and posterior elevation values, were all higher in JIA-U patients. Endothelial cell density and morphology, on the other hand, did not differ significantly between groups. Chronic inflammation's impact on stromal remodelling could explain these corneal alterations. The positive correlation between posterior elevation and the number of flares and duration of inflammation represents the importance of early diagnosis and effective treatment.

Long-term evaluation of posterior corneal surface parameters after accelerated corneal cross-linking with a comparison with uncross-linked keratoconic eyes.

To evaluate the 36months changes in posterior corneal surface parameters in keratoconic eyes after accelerated corneal cross-linking and to compare the data with uncross-linked progressive and non-progressive keratoconic eyes. Thirty five cross-linked, 30 uncross-linked progressive, and 30 uncross-linked non-progressive keratoconic eyes were included. Maximum keratometry (Kmax), thinnest pachymetry, minimum radius of curvature back (Rminback), asphericity back, posterior elevation and corneal densitometry, back corneal higher order aberrations (HOAs), back surface deviation (Db), final D, posterior radius of curvature (PRC) and 'B' unit values were recorded at baseline and at the 12, 24, 36months follow-up. Data were analyzed with repeated measures ANOVA and paired t-tests. Kmax and thinnest pachymetry were significantly changed in the cross-linked and progressive uncross-linked groups. Rminback, asphericity back, and HOAs did not change in either group. Total posterior corneal densitometry improved; posterior elevation, Db and B unit worsened in the cross-linked group and did not change in the uncross-linked groups. PRC and final D worsened in the cross-linked and progressive uncross-linked groups, and did not change in the non-progressive group. Despite a decreased Kmax, the posterior corneal surface parameters, posterior elevation values were determined to have significantly worsened in the cross-linked group and this increase was higher than in progressive uncross-linked eyes.

Dynamics of keratoconus progression after a previous successful accelerated crosslinking treatment during and after pregnancy.

To evaluate the effectiveness of previously applied successful accelerated corneal crosslinking (CXL) treatment in keratoconus stabilization during and after pregnancy. Ankara Yildirim Beyazit University, Ataturk Training and Research Hospital, Turkey. Prospective clinical study. Patients with stable keratoconus (after having an accelerated CXL procedure) who became pregnant were included. Uncorrected (UDVA) and corrected distance visual acuity (CDVA), manifest astigmatism (MA), keratometry (K)1, K2, Kmax, central corneal thickness (CCT), thinnest corneal thickness (TCT), and anterior (AE) and posterior elevation (PE) were recorded at baseline (before CXL), before pregnancy (the last visit after CXL), during pregnancy (third trimester), and after pregnancy (the last visit after pregnancy). 24 eyes of 19 patients were included. The mean time between CXL and conception was 12.4 ± 5.1 months. The mean postpartum follow-up period was 27.6 ± 13.3 months. The mean UDVA, CDVA, MA, and PE values did not show any statistically significant differences during and after pregnancy compared with the post-CXL values (P > .05). The mean Kmax flattened significantly after the CXL procedure (P = .011); however, it increased during pregnancy (P = .037, after CXL vs pregnancy) and then decreased back to the prepregnancy level after pregnancy (P = .035, pregnancy vs after pregnancy). The mean K1, K2, AE, CCT, and TCT remained stable during pregnancy and significantly decreased after pregnancy (P < .05). Keratoconus seems to progress during pregnancy in corneas that have previously received successful accelerated CXL treatment. However, this progress was mostly temporary, and generally, regression occurred after delivery.

Accuracy of the posterior corneal elevation values of Pentacam HR from different reference surfaces in early ectasia diagnosis.

Detecting the accuracy of various posterior elevation (PE) indices of Pentacam HR, and correlating them with some possibly related factors or parameters, in a cohort with early keratoconus (KC). A cross sectional study that was conducted at Eye World Hospital, Egypt. One hundred and two corneas were enrolled, including two groups; group 1 (50 corneas) having forme fruste or early KC, and group 2 (52 corneas) for healthy controls. Corneas were scanned using Pentacam HR (Oculus, Wetzlar, Germany). The investigated PE parameters were: PE from best fit sphere (BFS), PE from best fit toric ellipsoid (BFTE), PE from exclusion map of Belin Ambrosio's display (BAD), and PE from difference map of BAD. The four PE values were correlated to age, thinnest corneal thickness "TCT," posterior aberrations, and posterior Q value. All the investigated indices were significantly different in group 1 compared to group 2 (p < 0.001). Accuracy of PE parameters revealed the highest AUROC for PE from BFTE (AUROC = 0.989, and best cutoff > 4 um with sensitivity 96.00% and specificity 96.15%). PE from difference map was the least accurate. Correlation coefficients showed a significant correlation between all the studied PE parameters and some of the posterior aberrations (root mean square of higher order aberrations, vertical coma, and spherical aberrations), besides a significant correlation with posterior Q value. PE indices are sensitive detectors of early ectasia. PE from BFTE had the highest deduced AUROC. Alterations in PE values can significantly alter many posterior corneal aberrations and the posterior Q.

Characteristics of corneal topography in parents of keratoconus patients

Objective: To investigate the corneal topographic characteristics of the parents of patients with keratoconus (KC) and the correlation with their offspring. Methods: Case-control study. Twenty-six patients (49 eyes) with KC, who were 15 males and 11 females, and (18.83±2.74) years old, 48 parents (96 eyes) of patients with KC, who were 23 males and 25 females, and (44.14±1.70) years old, and 44 controls (88 eyes), who were 22 males and 22 females, and (42.81±4.03) years old, were enrolled in Qingdao Eye Hospital. The indexes in the Belin/Ambrósio Enhanced Ectasia Display were acquired with Pentacam topography. The basic indicators were flat K/steep K/maximum K (Kmax) curvature and astigmatism, thinnest pachymetry (TP), and front/back elevation (Ef/Eb); the Belin indexes included deviation of normality of the front/back elevation (Df/Db), deviation of average pachymetry progression/normality of corneal thinnest point/normality of relational thickness (Dp/Dt/Da), overall deviation of normality (Do), minimum/maximum/average pachymetric progression indices (PPImin/PPImax/PPIave), and Ambrósio's average and maximum relational thickness indices (ARTave/ARTmax). All parameters in the groups of parents and controls were compared by Mann-Whitney U test. The ROC curve was used to analyze the differential value of each abnormal index. In addition, the ratio of abnormal indicators in the Belin/Ambrósio Enhanced Ectasia Display was statistically analyzed. Partial correlation analysis was used to find the correlation between the parameters of KC patients and their parents, and binary logistics regression analysis was used to predict the prevalence in children through the parental indicators. Results: Clinical KC was diagnosed in 1 of the 48 parents (2.08%) of patients with KC. There was no statistically significant difference in anterior surface parameters such as K1, K2, Kmax, astigmatism and Ef, but differences in the thickness [522.00 (493.00, 542.75) μm versus 540.00 (523.25, 559.50) μm] and posterior surface elevation value [8.00 (4.00, 11.00) μm versus 5.00 (3.00, 8.00) μm] were statistically significant. Except for Df, the other Belin/Ambrósio indicators such as Do (Z=-4.551, P=0.000), PPImax (Z=-3.959, P=0.000) and ARTave (Z=-4.792, P=0.000) indicated significant difference. The ROC curve analyses showed ARTave had the greatest value in the identification of KC patients (AUC=0.705), PPImax had the best sensitivity (0.845), and Eb had the best specificity (0.837). The ratio of suspicious indicators between the parents' group and the control group was 1.5∶1, and the ratio of pathological indicators was 3∶1. There was a correlation in multiple parameters between KC patients and their parents (all P>0.05). Do/Eb/TP indices of mothers and Do/Kmax indices of fathers were the major influence factors for the disease in the offspring, with a diagnosis rate of 85.6%. Conclusions: The corneal topographic map of the parents of patients with KC showed that the index of the anterior surface was normal, but the thickness was thinner and the posterior surface was higher. According to Belin's analysis, all indicators except Df were abnormal. Moreover, the ratio of suspected and pathological indicators increased. These data suggested that the corneal topography of parents of patients with KC had features of subclinical KC. Compared with the traditional index, ARTave was of the highest value in the identification of subclinical KC. There was a strong correlation between parents of patients with KC and offspring. The Do and Kmax indices of paternal parents and the Do, Eb and TP indices of maternal parents were good predictors of children's disease. (Chin J Ophthalmol, 2020, 56:456-464).

Anterior and posterior ratio of corneal surface areas: A novel index for detecting early stage keratoconus.

To evaluate the diagnostic ability of the ratio of anterior and posterior corneal surface areas (As/Ps) comparing with other keratoconus screening indices in distinguishing forme fruste keratoconus (FFKC) from normal eyes. In this comparative study, 13 eyes of 13 patients with FFKC, 29 eyes of 29 patients with keratoconus (KC) and 88 eyes of 88 patients with normal subjects were involved. The As/Ps measured by the anterior segment optical coherence tomography (AS-OCT) and other indices measured by AS-OCT and rotating Scheimpflug-based corneal tomography were evaluated. The area under receiver-operating-characteristics (AU-ROC) was calculated to assess the diagnostic ability in discriminating FFKC from normal eyes. The As/Ps, the Belin/Ambrosio display enhanced ectasia total derivation value (BAD-D) and posterior and anterior elevation values showed the AU-ROC 0.9 or more in differentiating FFKC from normal eyes (0.980, 0.951, 0.924 and 0.903, respectively). The sensitivity and specificity were 0.92 and 0.96 for the As/Ps, 1.00 and 0.90 for BAD-D, 0.85 and 0.86 for posterior elevation value, and 0.85 and 0.96 for anterior elevation value, respectively. Among the several indices for keratoconus screening which we evaluated, the As/Ps obtained by AS-OCT had the large AU-ROC with high sensitivity and specificity in detecting FFKC, which was comparable with BAD-D obtained by rotating Scheimpflug-based corneal tomography. The As/Ps may provide information for improving the diagnostic accuracy of KC, even in the initial stage of the disease.

Tomographic and Refractive Characteristics of Pediatric First-Degree Relatives of Keratoconus Patients

To evaluate the tomographic and refractive characteristics of pediatric first-degree relatives of patients with keratoconus. Cross-sectional study. Setting: Department of Ophthalmology at the American University of Beirut Medical, Beirut, Lebanon. Pediatric first-degree relatives of patients with keratoconus. Both eyes of all participants aged between 6 and 18 years were included and studied. Soft contact lens use in the past 2weeks or rigid gas-permeable lens wear within 4weeks, history of prior ocular surgery or infectious keratitis, and unreliable corneal tomography. Masking and Randomization: Two masked cornea and refractive surgeons of different training backgrounds independently evaluated the participants' tomographic outputs. Additionally, the tomographic data were analyzed using Smadja's decision tree. Scheimpflug tomography, manifest refraction, and slit-lamp examination. Anterior curvature indices, posterior elevation values, thinnest pachymetry, and subjective and objective tomographic interpretation. One hundred eighty-three subjects were recruited. Tomographic evaluation after Cohen's kappa coefficient analysis revealed 32 patients as having keratoconus (17.5%), while 35 patients (19.1%) were labeled as keratoconus by objective analysis. There were 11.5%-15.5% of patients with keratoconus aged less than 11 years, 18.0% aged 12-15 years, and 25.5% aged 16-18 years. Their respective steepest anterior curvature and thinnest pachymetry are 44.8 ± 6.5 diopters (D) and 515.9 ± 39.2μm, 47.34 ± 3.4 D and 496.1 ± 37.9μm, and 49.7 ± 6.1 D and 486.0 ± 66.5μm. A total of 37.5% of the keratoconus patients were unilateral as evaluated by tomography alone. The prevalence of keratoconus in pediatric first-degree relatives of diagnosed keratoconus patients is high. Screening in this high-risk group is warranted.

Keratometric, Pachymetric, and Surface Elevation Characterization of Corneas With Fuchs Endothelial Corneal Dystrophy Treated With DMEK.

To characterize pachymetric, keratometric, and surface elevation parameters in pseudophakic eyes with Fuchs dystrophy that underwent Descemet membrane endothelial keratoplasty (DMEK) and to compare these characteristics with those in normal pseudophakic eyes. Postoperative corneal tomography with a median follow-up of 20 months was evaluated using the Pentacam tomographer on 46 DMEK eyes. Results were compared with data from an age-matched cohort of 46 normal eyes. Parameters included curvature analysis, keratometry values, corneal thickness (CT), pachymetric progression index, Ambrósio relational thickness, posterior elevation, and D-index values. Bonferroni correction was used for multiple comparisons. CT at the apex (mean difference 41 μm; 95% confidence interval 28-54) and CT at the thinnest point (46 μm; 33-60) were statistically significantly lower in the DMEK group (P < 0.001), whereas pachymetric progression index average (0.47; 0.32-0.62), Ambrósio relational thickness maximum (172; 126-228), IHD (0.096; 0.005-0.014), and the global D-index (1.03; 0.51-1.56) were significantly higher in eyes with DMEK (P < 0.001). The mean CT along the vertical and horizontal meridians was significantly lower in the DMEK group within the central 5 mm. A quarter and one half of the DMEK eyes had a CT of less than 500 μm at the apex or at the thinnest point, respectively. Resolution of corneal edema after DMEK was associated with a thinner-than-normal central cornea, steeper pachymetric progression from the thinnest point to the periphery, and some high-end outliers for posterior elevation values. Caution should be exerted in planning corneal refractive surgery for residual refractive errors.

Anterior Segment Parameters in Patients With Wilson Disease.

To investigate anterior segment parameters in patients with Wilson disease (WD). In this cross-sectional study, 22 patients with WD (study group) and 22 healthy subjects (control group) were enrolled. Each participant underwent a comprehensive ophthalmic assessment including best-corrected visual acuity, slit-lamp biomicroscopy, fundus examination, and intraocular pressure. Anterior segment parameters were measured by the Sirius anterior segment analyzer system (Costruzione Strumenti Oftalmici, Florence, Italy). Mean central corneal thickness was 522 ± 47 μm in the study group and 568 ± 37 μm in the control group (P < 0.001). Mean flat keratometry was 42.4 ± 1.7 diopter (D) in the study group and 41.5 ± 1.16 D in the control group (P = 0.011); mean steep keratometry was 43.4 ± 2.0 and 42.4 ± 1.4 D in the study and control groups, respectively (P = 0.025). The anterior corneal elevation value was 5.5 ± 3.2 μm in the study group and 4.08 ± 2.2 μm in the control group (P = 0.029); the mean posterior corneal elevation value was 15.1 ± 6.0 and 10.1 ± 4.1 μm in the study and control groups, respectively (P = 0.002). The mean anterior chamber depth was 2.97 ± 0.3 μm in the study group and 3.16 ± 0.3 μm in the control group (P = 0.01); the mean horizontal visible iris diameter was 11.9 ± 0.4 and 12.2 ± 0.4 μm in the study and control groups, respectively (P = 0.001). This study indicates that patients with WD have differences in the anterior segment parameters including central corneal thickness, keratometric values, anterior and posterior elevations, horizontal visible iris diameter, and anterior chamber depth when compared with healthy controls.

Corneal elevation in a large number of myopic Chinese patients.

To establish a normative database for corneal elevation in Chinese myopic patients who underwent refractive surgery, and analyze the association of corneal elevation with sex, age, and ocular parameters. A total of 3000 eyes in 1500 patients were evaluated with the Pentacam. Anterior and posterior elevations were measured at the apex and thinnest point. Normative thresholds were defined according to the Tukey method. Univariate and multivariate analyses were performed to assess the association of corneal elevation with sex, age, and ocular parameters. Normal upper limits for corneal elevation in adult Chinese were 4.95μm, 5.25μm, 6.2μm, and 11.0μm at the anterior apex, anterior thinnest point, posterior apex, and posterior thinnest point, respectively. Thinner corneal pachymetry at the apex and greater anterior corneal astigmatism tended to show greater anterior corneal elevation values. Younger age, greater anterior corneal astigmatism, lower anterior and posterior keratometry, and shallower anterior chamber depth resulted in greater posterior corneal elevation values. Locally derived thresholds may offer higher sensitivity and specificity when screening eyes for myopic refractive surgery, and keratoconic and post-orthokeratology eyes. Anterior and posterior corneal elevation at the apex and thinnest point were associated significantly with anterior corneal astigmatism, showing a positive correlation.

Correlation of basic indicators with stages of keratoconus assessed by Pentacam tomography.

To evaluate the diagnostic efficiency of basic indicators and find characteristic indicators for keratoconus (KC) at adjacent stages, and to assess the progression pattern of KC. One hundred and eight (41 subclinical, 40 moderate, and 27 severe) keratoconic patients (108 eyes) and 105 myopic patients (105 eyes) as controls were recruited in this prospective, comparative case series study. Pentacam topography was performed. Receiver-operating-characteristic curves were used to get the characteristic indicators. The most efficient distinguishing index between the subclinical KC and the controls was posterior elevation value (PEV, AUC=0.882), with the highest specificity being 93.8%. Corneal thickness (AUC=0.852) and posterior inferior-superior value (I-S) ranked second and third (AUC=0.776). When KC became moderate, PEV remained to be of the highest diagnostic efficiency (AUC=0.988), followed by the anterior elevation value (AUC=0.986) and other parameters of anterior surface. The diagnostic value increased significantly in the anterior curvature indices (all AUC>0.900) and appeared in the anterior best fitting sphere radius (AUC=0.919) when KC developed into the severe stage. In the subclinical stage of KC, PEV, thickness, and posterior I-S had important diagnostic values, and elevation values remained most efficient when KC developed to the moderate stage. The anterior curvature indices were most characteristic when KC became severe. KC first appeared in the inferior cornea of posterior surface, but the feature of protrusion formed at the moderate stage.

Longitudinal Evaluation of Posterior Corneal Elevation after Laser Refractive Surgery Using Swept-Source Optical Coherence Tomography

To investigate the change in posterior corneal elevation up to 1 year after myopic femtosecond-assisted LASIK and photorefractive keratectomy (PRK). Prospective, longitudinal, comparative study. Patients undergoing femtosecond-assisted LASIK or PRK. Corneal imaging was performed using swept-source optical coherence tomography at baseline and at each postoperative follow-up. A 2-way analysis of variance model with repeated measures and a linear mixed effect model were used to compare the differences in posterior corneal elevation between LASIK and PRK at different points after adjusting for the preoperative spherical equivalent (SEQ), central corneal thickness (CCT), thinnest corneal thickness (TCT), residual bed thickness (RST), and ablation depth (AD). The changes in posterior corneal elevation 1 month, 3 months, 6 months, and 12 months after surgery. Ninety-eight eyes of 49 patients (mean age 35.2 ± 8.5 years) (62 LASIK, 36 PRK) were included. The mean change in posterior corneal elevation values after LASIK and PRK were 4.88±0.47 μm versus 3.67±0.48 μm (B-1), 2.42±0.56 μm versus 3.00±0.47 μm (B-3), 3.76±0.46 μm versus 2.76±0.46 μm (B-6), and 2.92±0.46 μm versus 2.72±0.46 μm (B-12), respectively. Significant differences in posterior corneal elevation after LASIK were found from month 1, to month 3, to month 6, to month 12 (P ≤ 0.001), whereas posterior corneal elevation did not change significantly from month 3, to month 6, to month 12 (P ≥ 0.373) after PRK. LASIK and PRK eyes showed significant differences at months 3 and 12 (P ≤ 0.023). A similar pattern was observed for the changes in posterior corneal elevation after LASIK and PRK after adjusting for the effect of SEQ, CCT, TCT, RST, and AD. The adjusted forward displacements of the posterior corneal surface were statistically significant throughout the study period after both refractive surgeries (P < 0.05). The findings of our study suggested that there was a mild but significant forward protrusion of the posterior cornea after femtosecond laser-assisted LASIK and PRK. The posterior cornea fluctuated during the first postoperative year after LASIK, whereas it stabilized as early as 3 months after PRK.

Evaluation of intereye corneal asymmetry in patients with keratoconus. A scheimpflug imaging study.

PurposeTo assess the correlation between keratoconus severity and intereye asymmetry of pachymetric data and posterior elevation values and to evaluate their combined accuracy in discriminating normal corneas from those with keratoconus.MethodsThis study included 97 patients: 65 subjects with bilateral normal corneas (NC) and 32 with keratoconus (KC). Central corneal thickness (CCT), thinnest corneal thickness (ThCT) and posterior elevation (PE) at the thinnest point of the cornea were measured in both eyes using Scheimpflug imaging. Intereye asymmetry and its correlation with keratoconus severity were calculated for each variable. The area under the receiver operating characteristic curve (AUROC) was used to compare predictive accuracy of different variables for keratoconus.ResultsIn normal eyes, intereye differences were significantly lower compared with the keratoconus eyes (p<0.001, for CCT, ThCT and PE). There was a significant exponential correlation between disease severity and intereye asymmetry of steep keratometry (r2 = 0.55, p<0.001), CCT (r2 = 0.39, p<0.001), ThCT (r2 = 0.48, p<0.001) and PE (r2 = 0.64, p<0.001). After adjustment for keratoconus severity, asymmetry in thinnest pachymetry proved to be the best parameter to characterize intereye corneal asymmetry in keratoconus. This variable had high accuracy and significantly better discriminating ability (AUROC: 0.99) for KC than posterior elevation (AUROC: 0.96), ThCT (AUROC: 0.94) or CCT (AUROC: 0.92) alone.ConclusionsThere is an increased intereye asymmetry in keratometry, pachymetry and posterior corneal elevation values in keratoconic patients compared to subjects with normal corneas. Keratoconus patients with more severe disease are also more asymmetric in their disease status which should be taken into account during clinical care.

Contribution of reference bodies in diagnosis of keratoconus.

To evaluate the contribution of reference bodies for elevation maps in diagnosis of keratoconus (KC) and forme fruste keratoconus (FFK). Study groups included (1) 80 eyes with KC, (2) 55 eyes with FFK, and (3) 95 eyes as control eyes. The maximum elevation value at the central 5 mm of the posterior cornea (MEL) and the elevation value at thinnest corneal point (TEL) were evaluated for their diagnostic capacity using receiver operating characteristic curves under the following reference bodies: sphere, ellipsoid, toric ellipsoid, and torus, with autodiameter and fixed 8-mm-diameter settings. Moreover, characteristic parameters for each reference body and the root mean square (RMS) were evaluated for their diagnostic capacity. Significant differences were detected in TEL, MEL, and RMS parameters among groups, for almost all reference bodies. The highest predictive accuracy (KC group, >99.97%; FFK group, >90.9%) was estimated for the TEL and MEL parameters using the toric ellipsoid (8 mm) reference body with a fixed eccentricity of 0.4. Moreover, the RMS parameter demonstrated sufficient diagnostic capacity (KC group, 99.95%; FFK group, 85.1%). The cutoff points for the TEL parameter were found to be 7 and 3 μm in the KC group and the FFK group, respectively; for the MEL parameter, they were 11 and 6 μm, respectively; and for the RMS parameter, they were 6.87 and 7.19 μm, respectively. The posterior corneal elevation values and the RMS parameter can effectively discriminate KC from normal corneas, although measured values and cutoff points depend on the selection of reference body. Moreover, the use of a toric ellipsoid reference body, with a fixed eccentricity of 0.4, seems to be an effective tool even in diagnosis of FFK.

Scheimpflug imaged corneal changes on anterior and posterior surfaces after collagen cross-linking.

To compare the anterior and posterior corneal parameters before and after collagen cross-linking therapy for keratoconus. Collagen cross-linking was performed in 31 eyes of 31 keratoconus patients (mean age 30.6±8.9y). Prior to treatment and an average 7mo after therapy, Scheimpflug analysis was performed using Pentacam HR. In addition to corneal thickness assessments, corneal radius, elevation, and aberrometric measurements were performed both on anterior and posterior corneal surfaces. Data obtained before and after surgery were statistically analyzed. In terms of horizontal and vertical corneal radius, and central corneal thickness no deviations were observed an average 7mo after operation. Corneal higher order aberration showed no difference neither on anterior nor on posterior corneal surfaces. During follow-up period, no significant deviation was detected regarding elevation values obtained by measurement in mm units between the 3.0-8.0 mm-zones. Corneal stabilization could be observed in terms of anterior and posterior corneal surfaces, elevation and higher order aberration values 7mo after collagen cross-linking therapy for keratoconus.

Anterior segment parameters of rabbits with rotating Scheimpflug camera

Rabbit is one of the most commonly used experimental animals for corneal studies due to similarity of size to human cornea and ease of manipulation. In this study, we assessed anterior segment parameters of the healthy rabbit eyes with Pentacam HR (Oculus, Wetzlar, Germany). Six-month-old, approximately 2.5-3 kg weighted, 30 female New Zealand rabbits were used in the study. Right eye of the each rabbit was imaged with Pentacam HR under intramuscular ketamine hydrochloride (Ketalar; Eczacibasi, Turkey) anesthesia (50 mg/kg). After the imaging, the rabbits with blinking errors, which results in low-quality images, were excluded from the study. Keratometric readings, central corneal thickness (CCT), anterior chamber depth (ACD), and anterior and posterior elevation values, and lens density were noted. In this study, the flattest and the steepest keratometric values were found as 43.34 ± 1.86, 42.7 ± 2.0, and 43.9 ± 1.9 diopters, respectively. The mean CCT and ACD of rabbits were found as 388 ± 39 μm and 2.08 ± 0.16 mm, respectively. Mean of the anterior and posterior elevation at thinnest point was found as 1.29 ± 4.28 and 3.91 ± 6.17 μm, respectively. Keratometric readings and anterior and posterior elevation values of rabbits were similar to human; however, corneal thickness and anterior chamber depth (ACD) values were lower than humans.

Anterior and Posterior Corneal Changes after Crosslinking for Keratoconus

To evaluate anterior and posterior changes in corneal topography and tomography after corneal crosslinking (CXL) in eyes with progressive keratoconus. Scheimpflug analyses (Pentacam, Oculus) of 20 eyes with keratoconus performed before and after corneal CXL were included into retrospective analysis. Mean follow-up was 2 years. Changes in topographic, tomographic, and pachymetric values were statistically analyzed applying analysis of variance. Further, the distance and direction between the anterior maximum keratometry (K(max)) and the apex as well as the distance and direction between the thinnest point in corneal thickness (TPCT) and the corneal apex before and after CXL were studied. Two years after CXL, a statistically significant reduction of the keratometry at the flat meridian (-0.8 D, p < 0.05), the steep meridian (-0.5 D, p < 0.05), the "index of surface variance" (-5.3, p < 0.05), and the "index of highest decentration" (-0.05, p < 0.05) could be demonstrated. While the elevation of the front surface at the apex decreased (-1.5 μm, p < 0.05), the back elevation at the apex (+2 μm, p < 0.05) increased. Although not reaching statistical significance, the maximum front and back elevation demonstrated the same trend; while maximum front elevation data remained stable (-0.3 μm, p = 0.961), maximum back elevation data increased (+6.7 μm, p = 0.122). The corneal thickness at the apex (-22.0 μm, p < 0.001) and the TPCT (-20.0 μm, p < 0.001) decreased, leading to an increase of the corneal thickness progression from the corneal apex to the periphery. The position of K(max) and TPCT remained stable. Corneal topography proved to be useful in the follow-up for CXL because of significant changes in the keratometry. Increasing posterior elevation values, despite a stabilized anterior corneal surface, might be a sign of ongoing ectatic changes in the posterior corneal surface.

Comprehensive anterior segment normal values generated by rotating Scheimpflug tomography

To identify normal values for tomographic parameters that are considered useful in screening patients for refractive surgery. Private center, Albany, New York, USA. Database study. A Pentacam HR Scheimpflug system was used to examine 1 randomly selected eye of patients to determine normal values of 21 parameters considered the most clinically applicable for surgical screening. Normality of data was evaluated using the Kolmogorov-Smirnov test. Statistical analyses were performed using the Student t test to compare means and the 2-paired sample Wilcoxon signed-rank test. Results are displayed in 95.0% and 97.5% confidence intervals (CIs). The study evaluated 341 adults. High-end outliers at the 97.5% CI were 46.1 diopters (D) for flat keratometry (K), 47.4 D for steep K, 3.4 D for astigmatism, 3.8 μm for anterior chamber depth, 4 μm for front apical elevation, 5 μm for front elevation at the thinnest point, and 12 μm for front elevation in the central 4.0 mm. Respective posterior elevation values were 7 μm, 13 μm, and 25 μm, with a progression index maximum of 1.53 and mean of 1.19, difference between apical and thinnest pachymetric reading of 7 μm, a maximum K of 48.2 D, and an inferior-superior ratio of 1.44 D. Low-end outliers were a maximum Ambrósio relational thickness of 335 and a mean of 425, minimum pachymetry of 479 μm, thickness at the apex of 481 μm, and central 4.0 mm corneal volume of 6.31 mm(3). Scheimpflug-derived corneal tomography identified key refractive surgery parameters that may be useful in screening refractive surgical patients.

Diagnosis of Subclinical Keratoconus Using Posterior Elevation Measured With 2 Different Methods

To compare the efficacy of posterior corneal elevation, measured by 2 methods, in discriminating subclinical keratoconus from normal corneas. In 30 consecutive patients with subclinical keratoconus, and 37 candidates for refractive surgery, posterior corneal elevation was measured using Pentacam's rotating Scheimpflug camera (Oculus, Wetzlar, Germany) with the standard method [maximal elevation above the best fit sphere (BFS)] and with the enhanced-BFS (E-BFS) method (difference in elevation measured above the E-BFS and that measured above the BFS). Using cutoff points selected a priori (≥ 29 and ≥ 12 µm, respectively, for the standard and E-BFS methods) the sensitivity, specificity, and overall accuracy, determined through the area under the receiver operating characteristic curves, were assessed for each method and then compared. Mean posterior elevation values were statistically higher (P < 0.001) in corneas with subclinical keratoconus than in normal corneas, using either the standard (38 ± 15.9 µm vs. 20.3 ± 7.1 µm) or the E-BFS (15 ± 9.5 µm vs. 7.8 ± 5.5 µm) methods. Sensitivity and specificity rates were slightly higher with the standard method than with the E-BFS method (sensitivity, 73.3% vs. 60%; specificity, 86.5% vs. 83.8%), but neither difference was statistically significant (P > 0.05). The overall accuracy of the tests was similar (P = 0.19): the area under the curve was 0.80 for the standard and 0.72 for the E-BFS method. Posterior corneal elevation measured using either standard or E-BFS method has similar efficacy in discriminating corneas with subclinical keratoconus from normal corneas. As a single parameter, posterior elevation can be considered quite effective with either method, but it cannot be used alone to identify patients with subclinical keratoconus.

Corneal Changes in Progressive Keratoconus After Cross-linking Assessed by Scheimpflug Camera

To evaluate corneal changes after corneal cross-linking (CXL) in progressive keratoconus with Scheimpflug imaging. This prospective analysis included 40 eyes from 22 patients with progressive keratoconus. Corneal CXL was performed in 25 eyes (CXL group) and 15 fellow eyes served as controls (control group). Uncorrected (UDVA) and corrected distance visual acuity (CDVA), thinnest corneal thickness (ThCT), posterior elevation, and Holladay equivalent keratometry values (K1, K2) were determined with Pentacam (Oculus Optikgeräte GmbH) before and 1 year after CXL. Area under the receiver operator characteristic (ROC) curve and multivariable general estimating equation models were used to determine the most sensitive parameters of corneal changes. Manifest sphere (-2.55±3.21 to -1.48±2.39 diopters [D], P=.02), UDVA (0.23±0.25 to 0.31±0.25, P<.001), and CDVA (0.58±0.28 to 0.72±0.19, P=.019) improved significantly in the CXL group. Significant decreases were found in ThCT (472.53±33.18 to 440.53±38.67 μm, P<.001), posterior elevation (68.33±28.69 to 22.67±16.21, P<.001), and keratometry values (K1 [45.06±4.55 to 43.51±4.67 D, P<.001], K2 [48.39±5.41 to 46.71±5.67 D, P<.001]) in the CXL group. These parameters remained stable in controls (P>.05). According to ROC analysis, posterior elevation change was the most characteristic parameter of corneal change after CXL (area under the curve=0.99). General estimating equation model showed that CXL (P=.001) and initial ThCT (P=.007) were significant predictors of decrease in posterior elevation with a significant negative interaction of initial ThCT on CXL effect (P=.005). Posterior elevation is a sensitive parameter to monitor corneal remodeling after CXL. Corneal CXL showed augmented effect on corneal protrusion in eyes with thinner corneas.