Comparison of keratometric measurements between color light-emitting diode topography and Scheimpflug camera
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To determine the agreement of measurements between color light-emitting diode corneal topography (Cassini) and Scheimpflug camera keratometry (Pentacam HR).The current retrospective study investigated 117 right eyes of 117 healthy patients before cataract surgery from June 2017 to July 2017. Steep K, flat K, mean K, astigmatism, and axis for both anterior and posterior corneal surface were measured using the two devices. The measured values were converted into J vectors such as J0 and J45. The mean difference for those measurement values were compared between the two instruments, and the agreement was evaluated using the Bland-Altman plot I.There were statistically significant differences in mean K (44.21D [43.34 to 45.34] and 44.30D [43.30 to 45.10] by Cassini and Pentacam [P = 0.004]) and astigmatism (0.90D [0.58 to 1.30] and 0.70D [0.40 to 1.30] by Cassini and Pentacam [P = 0.002]) on the anterior corneal surface and flat K (- 6.21D [- 6.39 to - 6.07] and - 6.30D [- 6.5 to - 6.10] by Cassini and Pentacam [P < 0.001]), mean K (- 6.39D [- 6.54 to - 6.25] and - 6.40D [- 6.60 to - 6.30] by Cassini and Pentacam [P = 0.019]), and astigmatism (0.33D [0.22 to 0.47] and 0.30D [0.15 to 0.40] by Cassini and Pentacam [P = 0.002]) on the posterior corneal surface. The mean difference (= Cassini - Pentacam) with 95% limit of agreement for mean K and astigmatism of the anterior corneal surface were 0.082D (- 0.60 to 0.76) and 0.11D (- 0.73 to 0.95) for measurements obtained by the two instruments, respectively. Regarding keratometric values from the posterior corneal surface, the mean differences for flat K, mean K, and astigmatism were - 0.081D (- 0.42 to 0.26), - 0.030D (- 0.32 to 0.26), and 0.067D (- 0.33 to 0.46), respectively. Intraclass correlation coefficients for steep K, flat K, mean K, and vector J0 were higher than 0.9 in the anterior cornea. Positive correlation in steep K, flat K, mean K, astigmatism, and J0 was found between two devices in both anterior and posterior cornea (P < 0.001).Corneal refractive power and astigmatism tend to be higher when measured using Cassini than Pentacam HR in both anterior and posterior cornea. The two different devices might not be used interchangeably.Retrospectively registered. Registration number: KC17RESI0439 .Keywords:
Scheimpflug principle
To compare the central corneal thickness (CCT) measurements measured by using the Pentacam Scheimpflug system with the CCT measured using ultrasound pachymetry (UP) and to compare the compatibility between the methods in normal, keratoconic, and cross-linked keratoconic corneas.The study included 50 eyes of 50 patients with keratoconus (keratoconus group), 50 eyes of 50 patients with progressive keratoconus who underwent corneal cross-linking treatment (CCL group), and 50 eyes of 50 healthy subjects (control group). Patients in the keratoconus and CCL groups were further classified into mild (mean keratometry [Km] ≤ 47 D) and moderate keratoconus subgroups (47.0 < Km < 52.0 D). CCT values were noted from the Pentacam Scheimpflug and UP.The difference between the Pentacam and UP values was largest in the CCL group (-20.9 0.21.5 μm), followed by the keratoconus and control groups (-10.6 0.20.3 and 0.4 0.6.8 μm). The Pentacam and UP measurements were not comparable in the keratoconus and CCL groups (P = 0.001 and P < 0.001), whereas they were comparable in the control group (P = 0.62). In subgroup analysis, the 2 methods were comparable in the mild keratoconus subgroup (P = 0.12) and not comparable in the moderate keratoconus subgroup and in both mild and moderate subgroups of the CCL group (P = 0.001, P < 0.001 and P < 0.001).Pentacam Scheimpflug tomography and UP can be used interchangeably in normal and mild keratoconic eyes, but not in moderate keratoconic and cross-linked keratoconic eyes. Pachymetry measurements from Scheimpflug must be interpreted with extreme caution with different methods before planning an invasive procedure in these eyes.
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To study the biomechanical properties of the corneas of both eyes in patients with evident keratoconus manifestation in one eye.Our study consisted of nine patients with keratoconus and 25 volunteers in the control group. Both eyes of all participants were measured twice with a Pentacam Scheimpflug system: first with the standard Scheimpflug system and subsequently with the original version of the same technique in combination with a new device that can generate experimental artificial intraocular pressure (IOP) elevation. Diagnoses of keratoconus or non-keratoconus were made using the Pentacam Scheimpflug system software (StatSoft, Inc., Tulsa, OK).The artificially elevated IOP caused bulging of the anterior corneal surface in both eyes of keratoconic patients and a small flattening of the cornea in the eyes of the control group. Corneal ectasia, expressed in terms of diopters, during IOP loading in both keratoconic and nominally unaffected eyes was 4.12 D and 1.37 D, respectively. The changes were statistically significant (p < 0.05). Our dynamic study revealed a distinct weakness of the corneal tissue and an inability of keratoconic and contralateral eyes to resist IOP elevation.The IOP loading method permits evaluation of the biomechanical properties of the cornea across its entire surface. All nine contralateral unaffected eyes in patients with a diagnosis of unilateral keratoconus presented weak biomechanical properties and in fact should be considered as forme fruste keratoconus.
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Purpose The aim of this study was to show the usefullness of three different methods of Intraocular Pressure (IOP) measurements: Goldmann Applanation Tonometer, Rebound Tonometer and Ultra High-Speed Scheimpflug Technology. Methods The examined group consisted of 96 patients, 192 eyes (63 females, 33 males of mean age 59,3±19,9 years old). IOP measurements were carried out using Goldmann Applanation Tonometer (GAT), Rebound Tonometer Icare Pro (RT) and Ultra High-Speed Scheimpflug Technology (UHS ST) –“Corvis ST” with pachymetry which automatically took into account of central corneal thickness (CCT) correction. Additionally corneal pachymetry with Pentacam, Oculus were made to considered CCT in GAT IOP value. Statistical analysis was based on the software Statistica 10.0 PL, Statsoft, Poland. Results Mean IOP measured with GAT was 15,6±3,75 mmHg; GAT with CCT correction 15,7±3,7 mmHg; mean IOP measured with RT was 15,6±3,5 mmHg; with UHS ST 16,1±4,0 mmHg. Mean CCT measured with UHS ST was 543,7±52,7 µm; with Pentacam 547,9±54,0 µm. In comparison, there is significant difference between IOP measured with GAT and GAT+CCT, RT versus UHS ST (P<0,001) and no significant between GAT, GAT+CCT versus RT (p>0,5). Central Corneal Thickness was without differences in measurements carried out with UHS ST and Pentacam. All technics showed correlation IOP with CCT (p<0,05; r~0,3). Conclusion Applanation Tonometer and Rebound Tonometer can be equal methods of IOP measurements in contrast to Ultra High-Speed Scheimpflug Technology which give significant different values but can be use to take accurate measurements of Central Corneal Thickness
Scheimpflug principle
Goldmann Applanation Tonometer
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Comparison of Scheimpflug imaging parameters between steep and keratoconic corneas of Caucasian eyes
To compare the keratometric and pachymetric parameters of healthy eyes with those affected by steep cornea and keratoconus (KC) using Scheimpflug camera.Briz-L Eye Clinic, Baku, Azerbaijan.A cross-sectional study.In this study, 49 KC (Amsler-Krumeich stage 1) eyes and 36 healthy eyes were enrolled. A complete ophthalmic evaluation and a Scheimpflug camera scan were performed in every eye included in the study. Tomographic parameters such as parameters from the front and back cornea, maximum keratometry reading (Kmax), corneal volume (CV), anterior chamber volume (ChV), anterior chamber depth (ACD), anterior chamber angle (AC angle), keratometric power deviation (KPD), maximum front elevation (Max FE), and maximum back elevation (Max BE), as well as pachymetric progression indices (PPI), Ambrosio relational thickness (ART), index of surface variance (ISV), index of vertical asymmetry (IVA), center keratoconus index (CKI), index of height asymmetry (IHA), index of height decentration (IHD), and radius minimum (RM) were collected and statistically compared between the two groups.PPI, ART, ISV, IVA, CKI, IHA, IHD, and RM parameter values were significantly different (P<0.05) between the KC and healthy eyes. There were no significant differences in K mean and Q values of the frontal corneal parameters, as well as in Kmax, AC angle, RM, back, and front astigmatism, between stage 1 keratoconic and normal Caucasian eyes with steep cornea. All other parameters such as K mean and Q values of the back corneal parameters, Max FE, Max BE, ACD, ChV, and CV showed significant differences between the groups (P<0.05 for all).Scheimpflug imaging is able to detect corneal morphological differences between stage 1 KC eyes and healthy eyes with steep cornea, in Caucasians.
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To examine the repeatability of measurements obtained using a noncontact Scheimpflug-based tonometer (Corvis ST) and investigate potential differences in these parameters between healthy and keratoconic (KC) corneas.Forty-five keratoconic eyes and 103 healthy eyes were examined using biomicroscopy, corneal tomography and the Corvis ST (CST).Intraocular pressure and central corneal thickness (CCT) were highly repeatable (intraclass correlation [ICC] > 0.70, coefficient of variation [CV] < 0.20). Deformation amplitude (DA) and applanation-1 time (A1T) were fairly repeatable (ICC > 0.60, CV < 0.20). There was no association between DA and age, sex, or ethnicity in healthy eyes. There was a greater mean DA in the KC group compared with 46 age-matched healthy eyes (KC 1.37 ± 0.21 mm, healthy 1.05 ± 0.11 mm, P < 0.001). Multivariate analysis showed DA in KC was predicted by IOP, CCT, and the steepest simulated keratometry value (P = 0.03, P = 0.03, P = 0.001 respectively, R(2) = 0.75). A subgroup analysis of healthy and KC eyes with comparable mean CCT and IOP highlighted a statistically significant difference in mean DA (KC 1.25 ± 0.08 mm, thin healthy 1.13 ± 0.09 mm, P = 0.006). Receiver-operating characteristic analysis showed an area under the curve of 0.77 (95% CI 0.61-0.93, P = 0.006) but no ideal cutoff value for DA.Key parameters assessed by the CST are repeatable. Keratoconus is associated with greater DA than in healthy eyes, even when controlled for CCT and IOP. Deformation amplitude may be a useful adjunct in keratoconus assessment and monitoring, but cannot solely discriminate between healthy and keratoconic corneas.
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Scheimpflug principle
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To evaluate the alteration in anterior chamber parameters with the progression of keratoconus using a rotating Scheimpflug camera.Inonu University, Turgut Ozal Medical Center, Ophthalmology Department, Malatya, Turkey.Two hundred sixteen eyes of 123 patients diagnosed with keratoconus and 224 eyes of 112 normal subjects were evaluated with a Pentacam Scheimpflug camera (Oculus Inc.). Keratoconic eyes were divided into 3 groups according to mean keratometer (K) readings: mild (K = less than 47.0 diopters [D]), moderate (K = 47.0 to 52.0 D), and severe (K = 52.0 D or higher). The following parameters were obtained: thinnest corneal thickness (TCT), anterior chamber depth (ACD), corneal volume (CV), anterior chamber angle (ACA), and anterior chamber volume (ACV).One hundred twenty-nine eyes had mild keratoconus, 59 had moderate keratoconus, and 35 had severe keratoconus. There were no statistically significant differences between the keratoconus group and control group in age, sex, or eye distribution (P>.05). With the progression of the disease, TCT and ACD were statistically different between all groups (P<.05). There were statistically significant differences in ACA and CV measurements between the mild keratoconus and severe keratoconus groups (P<.05). Also, CV readings were significantly different between the control group and all keratoconus groups (P<.05), although there was no significant difference in ACA measurements (P>.05). Despite a progressive increase in the ACV with disease progression, the differences between groups were not statistically significant (P>.05) except between the severe keratoconus group and the control group (P<.05).Anterior segment parameters of the eye showed significant alterations with the progression of keratoconus.
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Purpose: To evaluate the relationship between biomechanical parameters measured with a dynamic Scheimpflug analyzer and glaucoma. Patients and Methods: Cross-sectional observational data of 47 eyes of 47 consecutive subjects with medically controlled primary open-angle glaucoma and 75 eyes of 75 healthy subjects examined with a dynamic Scheimpflug analyzer (Corvis ST) were retrospectively investigated. Eight biomechanical parameters were compared between eyes with and without glaucoma using multivariable models adjusting for intraocular pressure (IOP), central corneal thickness, age, and axial length. Results: In multivariable models, glaucoma was negatively correlated with A1 time ( P <0.001, coefficient=−0.5535), A2 time ( P =0.008, coefficient=−0.1509), radius ( P =0.011, coefficient=−0.4034), and whole eye movement ( P <0.001, coefficient=−0.0622). Negative correlation between glaucoma and 3 parameters (A1 time, A2 time, and radius) consistently indicate larger deformability of the cornea and negative correlation between glaucoma and whole eye movement indicate smaller eye movement, in glaucoma eyes. There were significant correlations of many biomechanical parameters with other baseline factors (8 parameters with IOP, 2 with central corneal thickness, 4 with age, and 7 with axial length). Conclusions: Eyes with medically controlled glaucoma were more deformable than healthy eyes, which may increase the risk of optic nerve damage through an underestimation of IOP and biomechanical vulnerability of the globe. Many parameters showed a significant correlation with baseline factors, suggesting the importance of adjustment for these confounding factors when evaluating the correlation between biomechanical parameters and ocular diseases. These results suggest the relevance of measuring biomechanical properties of glaucoma eyes for accurate IOP measurement and risk assessment.
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Objective To compare the corneal biomechanical properties of the corneas of keratoconic eyes and normal eyes using corneal visualization Scheimpflug technology (Corvis ST),and to investigate the role of corneal biomechanical parameters in the diagnosis of keratoconus.Methods Ninety keratoconic eyes from 65 patients and 90 normal eyes from 90 participants were enrolled in this comparative study.Based on the Amseler-Krumeich keratoconus stages,the keratoconic eyes were divided into a mild group (46 eyes),moderate group (23 eyes) and severe group (21 eyes).Tomography and biomechanical parameters of all eyes were obtained with the Pentacam and Corvis ST,respectively.All parameters were compared between the keratoconic and normal groups.The correlation between deformation amplitude and anterior segment parameters was also analyzed.An independent t test,Wilcoxon rank sum test,ANOVA,nonparameter test were used.The receiver operating characteristic (ROC) curves were plotted to distinguish keratoconus from the normal cornea.Results The tomography and biomechanical parameters of the keratoconic eyes were significantly different from those of normal eyes except for the anterior chamber angle,first applanation length,highest concavity time,and peak distance.The deformation amplitude (area under the curve:0.865)was the best predictive parameter,with a sensitivity of 84.5％,specificity of 75.6％ and cut-off point of 1.14 mm.The diagnostic efficiency of the deformation amplitude increased with an increase in the severity of keratoconus.In both the normal and keratoconic groups,the deformation amplitude was negatively correlated with intraocular pressure,central corneal thickness,and corneal volume at 3 mm.The respective r values of the deformation amplitudes of the normal and keratoconic groups in regard to:intraocular pressure,-0.707 and-0.213 ; central corneal thickness,-0.219 and-0.357 ;and corneal volume at 3 mm,-0.212 and-0.27.All P values were ＜0.05.Conclusion Corvis ST offers an alternative method for measuring corneal biomechanical properties.The deformation amplitude has a high sensitivity for the diagnosis of keratoconus.The negative correlations with intraocular pressure and central corneal thickness deserve clinical attention.
Key words:
Biomechanics; Keratoconus ; Corneal visualization Scheimpflug technology ; Deformation amplitude
Scheimpflug principle
Corneal pachymetry
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