Evaluation of Scheimpflug Tomography Parameters in Subclinical Keratoconus, Clinical Keratoconus and Normal Caucasian Eyes

Combined corneal biomechanical and tomographical indices in subclinical and forme fruste keratoconus

PURPOSE

Evaluation of combined corneal tomographic and biomechanical parameters in subclinical/forme fruste keratoconus (ScKC/FFKC).

DESIGN

Cross-sectional observational case-control study.

METHODS INCLUSION CRITERIA

Thirty-one eyes with ScKC (fellow eye of KC with any one sign: keratometry >47 diopters, cylinder >1.5 D, central corneal thickness <500 µm, with/without abnormal topography) or FFKC (fellow eye of KC with normal topography and slit lamp examination) >13 years (cases) and 44 eyes of age-matched 22 healthy subjects (controls).

EXCLUSION CRITERIA

Clinically diagnosed KC, presence of corneal scars, and prior ocular surgery eyes.

STUDY PARAMETERS

Sixteen Pentacam, 15 Corvis ST, and five Sirius parameters were analyzed using paired sample t -test, and a subsample found to be significantly different was used in receiver operating characteristic curve analysis. The Youden index was calculated, and Pearson's correlation analysis was done.

RESULTS

Five Pentacam, three Corvis ST, and two Sirius parameters had an area under curve (AUC) >0.75. Tomographic and biomechanical index (TBI) (cutoff 0.59, 95% specificity, 77% sensitivity), Belin Ambrosio enhanced ecstasia display (cutoff 1.8, 81% specificity, 80% sensitivity), and symmetry index of posterior corneal curvature (cutoff 0.16, 97% specificity, 67% sensitivity) best identified early KC. TBI strongly correlated with maximum Pentacam parameters in both cases and controls. Corvis biomechanical index strongly correlated only in cases, and SP-A1-SD weakly correlated in cases.

CONCLUSION

Upon combined analysis, the average sensitivity and specificity, respectively, of top three parameters (according to AUC) from Pentacam and Corvis ST were 74.1% and 95.4% for posterior elevation and TBI.

TRIAL REGISTRATION

The trial was registered in Clinical Trial Registry of India on January 28, 2022. The Trial Registration Number is REF/2022/01/050638.

Diagnosis of forme fruste keratoconus with scheimpflug photography in Ghanaian patients

AIM

This study aimed to differentiate moderate to high myopic astigmatism from forme fruste keratoconus using Pentacam parameters and develop a predictive model for early keratoconus detection.

METHODS

We retrospectively analysed 196 eyes from 105 patients and compared Pentacam variables between myopic astigmatism (156 eyes) and forme fruste keratoconus (40 eyes) groups. Receiver operating characteristic curve analysis was used to determine the optimal cut-off values, and a logistic regression model was used to refine the diagnostic accuracy.

RESULTS

Statistically significant differences were observed in most Pentacam variables between the groups (p < 0.05). Parameters such as the Index of Surface Variance (ISV), Keratoconus Index (KI), Belin/Ambrosio Deviation Display (BAD_D) and Back Elevation of the Thinnest Corneal Locale (B.Ele.Th) demonstrated promising discriminatory abilities, with BAD_D exhibiting the highest Area under the Curve. The logistic regression model achieved high sensitivity (92.5%), specificity (96.8%), accuracy (95.9%), and positive predictive value (88.1%).

CONCLUSION

The simultaneous evaluation of BAD_D, ISV, B.Ele.Th, and KI aids in identifying forme fruste keratoconus cases. Optimal cut-off points demonstrate acceptable sensitivity and specificity, emphasizing their clinical utility pending further refinement and validation across diverse demographics.

Analysis of Scheimpflug Tomography Parameters for Detecting Subclinical Keratoconus in the Fellow Eyes of Patients with Unilateral Keratoconus in the Eastern Province of Saudi Arabia

Purpose

We compared the characteristics of subtle morphological changes in subclinical keratoconus (KC) and normal corneas using Scheimpflug tomography (Pentacam®) and assessed the efficacy of these parameters for distinguishing KC or subclinical KC from normal eyes.

Patients and Methods

In this multicenter comparative study at Dhahran Eye Specialist Hospital and Al Kahhal Medical Complex in the Eastern Province of Saudi Arabia, we analyzed the Scheimpflug tomography charts of patients with topographically normal eyes and those with unilateral KC. Patients were divided into the normal (NL: patients considered for refractive surgery and with normal topographic/tomographic features, 129 eyes), KC (30 patients with manifest KC in one eye based on biomicroscopy and topographical findings), and forme fruste KC (FFKC: fellow eyes of patients in the KC group that met the NL group criteria) groups. Corneal morphological parameters were analyzed using the area under the receiver operating characteristic (ROC) curves (AUCs).

Results

For distinguishing NL and KC groups, all measured corneal morphological parameters, except for flat keratometry, maximum Ambrósio relational thickness index, and minimum sagittal curvature, had AUCs >0.75. The surface variance index yielded the largest AUC (0.999). For distinguishing NL and FFKC groups, all corneal morphological parameters had AUCs <0.8. Total higher-order aberrations (RMS HOA) yielded the highest AUC, followed by Belin/Ambrỏsio Enhanced Ectasia total deviation (BAD-D), back elevation at the thinnest location, average pachymetric progression index (PPIave), and deviation of Ambrỏsio relational thickness (Da) (AUC 0.74-0.78).

Conclusion

The diagnostic performance of all tested topographic and tomographic parameters measured using Scheimpflug tomography for discriminating subclinical KC was fair at best, with the top parameters being RMS HOA, BAD-D, back elevation at the thinnest location, PPIave, and Da. Distinguishing between subclinical KC and healthy eyes remains challenging. Multimodal imaging techniques may be required for optimal early detection of subtle morphological changes.

Revisiting Pentacam Parameters in the Diagnosis of Subclinical and Mild Keratoconus Based on Different Grading System Definitions

Objectives

To retest the performance of Pentacam parameters in the detection of eyes with subclinical keratoconus (KC) and mild KC based on different definitions from the Amsler-Krumeich (AK), Collaborative Longitudinal Evaluation of Keratoconus (CLEK), and ABCD systems.

Materials and Methods

This cross-sectional university-based study comprised 24 eyes with subclinical KC, 144 eyes with mild KC (based on AK in 101 eyes, CLEK in 28 eyes, and ABCD in 15 eyes), and 70 controls. Diagnostic ability of the thinnest point (TP) pachymetry, KISA% index, inferior-superior asymmetry, corneal aberrations, Pentacam indices, front/back elevations, pachymetric progression index, Ambrósio-Relational Thickness (ARTmax), and Belin/Ambrósio Enhanced Ectasia Display scores (Df, Db, Dp, Dt, Da, and D-final) were evaluated.

Results

ARTmax (83.3% sensitivity/74.3% specificity) had the highest ability in distinguishing subclinical KC from normal, followed by TP pachymetry, Dt, and Da. D-final showed excellent sensitivity/specificity in mild KC diagnosis based on AK (98%/100%) and CLEK (97.4%/100%) descriptions. In the mild KC-ABCD group, index of vertical asymmetry accurately detected all eyes with mild KC and 97.1% of the controls.

Conclusion

This study points out the gray zone in the detection of eyes with subclinical and mild KC due to overlapping terminology and grading criteria. Pentacam parameters seem to have modest capability in subclinical KC detection, indicating the necessity for additional diagnostic modalities. However, eyes with mild KC can be diagnosed with high accuracy using Pentacam parameters, although the strongest parameters may vary according to the definition of “mild KC.” Nevertheless, uniform and definitive criteria for subclinical and clinical KC classification are required for a diagnostic and therapeutic consensus in KC.

Could Corneal Densitometry be a Progression Criterion for Subclinical Keratoconus?

Objectives

The objective of this study is to investigate the changes in topometry, tomography, and corneal densitometry in subclinical keratoconus (SK) at the 6-month interval.

Methods

The clinical keratoconus and SK groups included 25 eyes; the control group included 22 eyes from 22 patients. Corneal topographic, tomographic, topometric, and densitometric values obtained using the Pentacam HR imaging system were analyzed.

Results

Posterior elevation (PE), Keratoconus index (KI), index of height asymmetry (IHA), index of height decentration (IHD), Dp, Da, Final D, maximum pachymetric progression index (PPImax), and maximum Ambrósio relational thickness parameters showed significant changes between the baseline and the 6th-month follow-up in SK group (p<0.05 for all values). There were significant changes in all zones except a central layer of 6-10 zone, anterior, and central layer of 10-12 zone between the baseline and the 6th-month follow-up in the SK group (p<0.05, for all values). The changes in mean±standard deviation of KI, IHA, IHD, PPImax parameters, and corneal densitometry values of the posterior layer of 0-2 mm and 2-6 mm zones were significant in the SK group compared to the controls (p<0.05, for all values).

Conclusion

PE, KI, IHA, IHD, and PPImax parameters as well as increasing corneal light backscatter of the posterior central layer might be useful for follow-up of progression of SK. New multimeric parameters created by combinations of topometric, tomographic, and corneal densitometry parameters could be the future of SK follow-up.

Keratoconus Diagnosis: From Fundamentals to Artificial Intelligence: A Systematic Narrative Review

The remarkable recent advances in managing keratoconus, the most common corneal ectasia, encouraged researchers to conduct further studies on the disease. Despite the abundance of information about keratoconus, debates persist regarding the detection of mild cases. Early detection plays a crucial role in facilitating less invasive treatments. This review encompasses corneal data ranging from the basic sciences to the application of artificial intelligence in keratoconus patients. Diagnostic systems utilize automated decision trees, support vector machines, and various types of neural networks, incorporating input from various corneal imaging equipment. Although the integration of artificial intelligence techniques into corneal imaging devices may take time, their popularity in clinical practice is increasing. Most of the studies reviewed herein demonstrate a high discriminatory power between normal and keratoconus cases, with a relatively lower discriminatory power for subclinical keratoconus.

Detection ability of corneal biomechanical parameters for early diagnosis of ectasia

PURPOSE

To assess the detection ability of corneal biomechanical parameters for early diagnosis of ectasia.

METHODS

This retrospective descriptive-analytical study included 134 normal eyes (control group) from 134 healthy subjects and 128 eyes with asymmetric contralateral corneal ectasia with normal topography (ACE-NT, study group) from 128 subjects with definite keratoconus in the opposite eye. Placido-disk-based corneal topography with TMS-4, Scheimpflug corneal tomography with Pentacam HR, and corneal biomechanical assessment with Corvis ST and ocular response analyzer (ORA) were performed. A general linear model was used to compare Corvis ST and ORA biomechanical parameters between groups, while central corneal thickness (CCT) and biomechanically corrected intraocular pressure (bIOP) were considered covariates. Receiving operator sensitivity curve (ROC) analysis was used to determine the cut-off point with the highest sensitivity and specificity along with the area under the curve (AUC) for each parameter.

RESULT

All parameters of Corvis ST and ORA showed a statistically significant difference between the two groups except for the first (P = 0.865) and second (P = 0.226) applanation lengths, and deformation amplitude (P = 0.936). The discriminative analysis of corneal biomechanical showed that the highest accuracy for the classic, new, and combined parameters of Corvis ST was related to HCR (AUC: 0.766), IR & DAR (0.846), and TBI (0.966), respectively. Using ORA, the corneal resistance factor (0.866) had a higher detection ability than corneal hysteresis (0.826).

CONCLUSIONS

TBI has the best accuracy and the highest effect size for differential diagnosis of normal from ACE-NT eyes with a cut-off point of 0.24.

Refractive and Topographic Parameters of the Belin/Ambrósio Module in Patients with Refractive Defects in Cuenca, Ecuador

Objective:

This study aimed to describe the refractive and topographic parameters of the Belin/Ambrósio module in patients with refractive defects at the Latino clinic in Cuenca, Ecuador, between 2017 to 2021.

Methods:

A descriptive, cross-sectional study was carried out. A database included anonymous cases of patients with refractive defects treated at the ophthalmological consultation of a Latino clinic from January, 2017 to June, 2021 was searched. Data was collected using a form containing study variables. Microsoft Excel and SPSS were used for data collection and analysis using frequencies, percentages, and measures of central tendency.

Results:

The sample consisted of 120 patients; 61.7% were women, and 38.3% were men. Moreover, 70.8% of patients were young adults. The pachymetry mean of the center of the pupil, apex, and position of lowest pachymetry was 521 µm, 520 µm, and 513 µm, respectively. The means of the flattest keratometry, curviest keratometry, and maximum keratometry were 43.30 D, 46.32 D, and 48.01 D, respectively.

Conclusion:

Cases distribution according to anterior and posterior elevation showed pathological values ​​in more than 50% of the studied corneas. According to the average progression index, pathological elevation was found in 18.8% of the cases, and according to the average deviations, 25.4% presented corneal ectasia in different stages.

The false positive rates for detecting keratoconus and potential ectatic corneal conditions when evaluating astigmatic eyes with Scheimpflug Technology

PURPOSE

To quantify the false positive rates for keratoconus (KC) and potential ectatic corneal conditions in highly astigmatism eyes when using published parameters/indices obtained from the Pentacam and Galilei units.

SETTING

Oftalmosalud Instituto de Ojos, Lima, Peru.

DESIGN

Prospective cohort study.

METHODS

67 consecutive eyes with corneal astigmatism > 1.5 D, with a minimum follow ups of 36 months after an uneventful LASIK procedure were included. Indices for KC and other potential ectatic corneal conditions (subclinical KC, forme fruste KC, suspect KC) were obtained using the Pentacam and Galilei Scheimpflug cameras.

MAIN OUTCOME MEASURES

The false positive rates for KC and potential ectatic corneal conditions were measured. Cut off values provided by previous studies and company-based parameters were used to assess the rate of false positivity.

RESULTS

The range of false positive rates for a KC diagnosis depending on the lowest and highest cutoff values were: index of height decentration (61% - 1%), index of surface variance (76% - 0%), Posterior elevation (55% - 0%), maximum Ambrosio Relational thickness (100% - 13%), Belin Ambrosio enhanced ectasia display total deviation value (100% - 4%), Average pachymetric progression index (69% - 3%), Pachymetry at the thinnest point (58% - 1%), CSI Center Surround Index (100%), Differential sector index (51%).

CONCLUSION

The false positive rates for KC and ectatic corneal conditions vary dramatically depending on the cut-off values used. Some indexes used for diagnosis of potential ectatic corneal conditions are inaccurate in normal, highly astigmatic eyes.

An exploratory analysis of forme fruste keratoconus sensitivity diagnostic parameters

PURPOSE

To secondary statistical analysis of the Pentacam or Corvis ST parameters from literatures, and to obtain more sensitive diagnostic parameters for clinical keratoconus (CKC) and forme fruste keratoconus (FFKC), respectively.

METHODS

The parameters and the corresponding area of ROC curve (AUC) in previous studies were extracted and screened to obtain the database of CKC (Data-CKC) and FFKC (Data-FFKC), respectively. Two different importance evaluation methods (%IncMSE and IncNodePurity) of random forest were used to preliminary select the important parameters. Then, based on the partial dependency analysis, the sensitive diagnostic parameters that had promotion to the diagnostic performance were obtained. Data-FFKC was analyzed in the same way. Finally, a diagnostic test meta-analysis on the sensitive parameter of interest was conducted to verify the reliability of the above analysis methods.

RESULTS

There were 88 parameters with 766 records in Data-CKC, 57 parameters with 346 records in Data-FFKC. Based on two importance evaluation methods, 60 important parameters were obtained, of which 20 were further screened as sensitive parameters of keratoconus, and most of these parameters were related to the thinnest point of cornea. The stiffness parameter at first applanation (SPA1) was the only Corvis ST output parameter sensitive to FFKC except the Tomographic and Biomechanical Index and the Corvis Biomechanical Parameter (CBI). A total of 4 records were included in the meta-analysis of diagnostic tests on SPA1. The results showed that there was threshold effect, but no significant heterogeneity (I² = 33%), and the area under the SROC curve was 0.87 (95% CI, 0.84-0.90).

CONCLUSIONS

For the diagnosis of FFKC, the sensitivity of SPA1 is not inferior to the well-known CBI, and may be the earliest Corvis ST output parameter to reflect the changes of corneal biomechanics during keratoconus progression. The elevation parameters based on the typical position of the thinnest point of corneal thickness are of great significance for the diagnosis of keratoconus.

Corneal Scheimpflug topography values to distinguish between normal eyes, ocular allergy, and keratoconus in children

To identify and compare keratometric, corneal thickness, and elevation parameters and indices among healthy children, ocular allergy, and keratoconus using the OCULUS Pentacam Scheimpflug topography system. This study included healthy children, children with ocular allergy (OA) without keratoconus, and children with keratoconus (KC). The study design consisted of a prospective evaluation and review of medical records from a Brazilian ophthalmology department. The exclusion criteria were inability to undergo the ocular exam, other ocular diseases, contact lens wear, and topographic corneal ectasia. The effect of each corneal parameter was evaluated using univariate and multivariate logistic regression models adjusted for sex and age, and ROC curves were used to assess the ability each variable to discriminate among groups. A total of 182 subjects were included: healthy children (n = 99), children with OA (n = 32), and children with KC (n = 51). Groups differed in terms of sex, with more males in the OA group (73.2%) and the KC group (67.7%) than in the control group (40.9%). All corneal parameters studied differed significantly between the control and KC groups, and between the OA and KC groups; they also differed significantly between the three groups in terms of astigmatism, q-value, CCT, TP, BAD-D, and ARTmax values. We present the first study to describe and compare corneal tomographic parameters in healthy children, OA, and KC. Keratometry indices, ACD, ARTmax, AETP, and PETP were found to be the most useful for differentiating between healthy and KC children.IBR registry number: CAAE 54921916.9.0000.5404.

Risk Factors for Development of Keratoconus: A Matched Pair Case-Control Study

BACKGROUND

Keratoconus, a progressive ectatic corneal disorder, is believed to be multifactorial in etiology with interaction between genetic and environmental factors. To date, risk factors for the development of the disease are extensively debated and need to be identified since they play a critical role in disease prevention and management. This study aimed to analyze associations between several hereditary and environmental predictors and the development of keratoconus.

PATIENTS AND METHODS

This was a retrospective matched pair case-control study. The study was conducted in Ibn-Alhaitham eye teaching hospital between March 2016 and April 2017. Patients with keratoconus (cases) and their age- and gender-matched controls were asked about childhood and early teenage eye rubbing, ocular trauma, obesity, contact lens wear, smoking and sunlight exposure, family history of keratoconus, parental consanguinity and information related to socio-economic status. Univariable and multivariable conditional logistic regression analyses were used to test the significance of associations.

RESULTS

A total of 166 individuals (83 cases and 83 controls; 60.2% female) were included. On univariable analysis, eye rubbing, family history of keratoconus and parental consanguinity were significant risk factors for keratoconus, whereas all other factors were non-significant. On multivariable analysis, eye rubbing (odds ratio: 4.93; P < 0.01), family history of keratoconus (odds ratio: 25.52; P < 0.01) and parental consanguinity (odds ratio: 2.89; P = 0.02), again, emerged as significant risk factors for disease development.

CONCLUSION

Family history of keratoconus, eye rubbing, and parental consanguinity were significant risk factors for keratoconus development. These results support the evidence for multifactorial etiology, the most important factor being hereditary predisposition.

Tomographically normal partner eye in very asymmetrical corneal ectasia: biomechanical analysis

PURPOSE

To point out the biomechanical changes of the topographically and tomographically normal partner eye (NPE) in patients with very asymmetrical corneal ectasia.

SETTING

Department of Ophthalmology, Saarland University Medical Center in Homburg/Saar, Germany.

DESIGN

Retrospective study.

METHODS

The topographical and tomographical results of the NPE were assessed using the Pentacam HR and the biomechanical corneal properties using the Ocular Response Analyzer (keratoconus match index [KMI], corneal hysteresis [CH], and corneal resistance factor [CRF]) and the Corvis ST (topographic biomechanical index [TBI] and Corvis biomechanical index) and compared those results with a normal control group (CG).

RESULTS

The clinical records of 26 patients recruited from the Homburg Keratoconus Center diagnosed with a very asymmetrical corneal ectasia were reviewed. The NPE (8.5 ± 1.5 mm Hg) showed a significantly more pathological CH (P < .001) compared with the CG. The CRF was also significantly more pathological (P = .04) for the NPE (8.3 ± 1.5 mm Hg) compared with the CG. The NPE (0.62 ± 0.32) showed a nonsignificant (P = .08) more pathological KMI compared with the CG. Nineteen (73.1%) of 26 NPE had a KMI less than 0.72 and were considered pathological. Compared with the CG, the TBI of the NPE (0.19 ± 0.25) did not differ significantly overall (P = .57). However, 5 (19.2%) of 26 eyes had a TBI more than 0.29 and were considered pathological.

CONCLUSIONS

Topographically and tomographically NPEs in very asymmetrical corneal ectasia frequently showed biomechanical changes. This should be considered before planning any type of refractive corneal surgery in such patients.

Analysis of OPD-Scan and Pentacam Parameters for Early Keratoconus Detection

BACKGROUND

PURPOSE: To evaluate Pentacam and OPD-Scan parameters in the early detection of keratoconus.

DESIGN

Retrospective case-control study.

METHODS

Case group included 50 clinically unaffected fellow eyes diagnosed with asymmetric keratoconus showing subtle qualitative changes at the 0.5-D sensitivity OPD-Scan scale, as well as normal anterior and back elevation difference map at Belin/Ambrósio enhanced ectasia display (BAD) at the Pentacam. Control group included 172 normal eyes that underwent Lasik surgery and presented no complications throughout the 2-year follow-up period. OPD-Scan and Pentacam parameters were compared, calculating sensitivity, specificity, and area under the receiver operating characteristic curve (AUC). A multivariate analysis was performed using Pentacam or OPD-Scan variables, and a model using variables of both devices.

RESULTS

Pentacam variables with AUC ≥0.8 were keratoconus index (0.85), index of height decentration (0.81), and overall deviation at BAD (0.8). OPD-Scan variables with AUC ≥0.8 were keratoconus prediction index (0.83), surface asymmetry index (0.83), and total of higher-order trefoil aberration (0.8). In the multivariate analysis, the AUC was 0.85 in the case of OPD-Scan whereas it was 0.89 in the case of Pentacam. When combining all variables from the 2 devices, the AUC was 0.93, with a sensitivity of 82% and a specificity of 94%.

CONCLUSIONS

Several parameters of OPD-Scan and Pentacam can be useful to differentiate cases from normal control eyes, demonstrating even better results when combining parameters of both devices. Anterior corneal indexes were the most important parameters to discriminate both groups.

Simplifying and understanding various topographic indices for keratoconus using Scheimpflug based topographers

Keratoconus (KC) is a progressive ectatic corneal disorder. There are multiple topographic devices and their varied indices used for diagnosis, detecting progression, and deciding management. It is important to understand the repeatablility, intra- test variabililty, and comparability amongst various topographic devices. The Scheimpflug camera-based devices, such as the Pentacam (Oculus, Wetzlar, Germany), Galilei (Ziemer, Biel, Switzerland), and Sirius (Costruzione Strumenti Oftalmici, Florence, Italy) are known to assist in the detection of early keratoconus and subclinical keratoconus. This article reviews the various Scheimpflug camera-based devices in depth, addressing their different indices, diagnostic accuracy, repeatability, and agreement and identifying the strongest parameter of each device. It will guide the practicing clinician by giving practical tips for decision making in the diagnosis and management of keratoconus.

Comparison of refractive outcomes using Scheimpflug Holladay equivalent keratometry or IOLMaster 700 keratometry for IOL power calculation

PURPOSE

This study aims to compare postoperative refractive error results using Pentacam (Oculus Optikgeräte GmbH) Holladay equivalent keratometry readings (EKR) or IOLMaster 700 (Carl Zeiss Meditec AG) keratometry (K) values in IOL power calculation.

MATERIAL AND METHODS

This retrospective study included 54 eyes of 31 patients who underwent cataract surgery. Preoperative biometric measurements of all patients were obtained using IOLMaster 700 followed by Pentacam measurements. IOLMaster 700 K measurements on horizontal (K1) and vertical (K2) axes and EKR measurements on 2 mm (EKR2mm), 3 mm (EKR3mm) and 4.5 mm (EKR4.5 mm) corneal zones were recorded. EKR4.5 mm value and IOLMaster 700 K values were used in Holladay-II, SRK/T, Haigis, and Hoffer-Q formulas to calculate predictive refractive error (PRE). Absolute refractive error (ARE) was calculated as the absolute difference between actual postoperative refractive error (APRE) and PRE values.

RESULTS

Mean age was 72.2 ± 8.3 (51-87) years and mean IOL power was 21.5 ± 2.9 D (18-23 D). There was no significant difference between PRE values when IOLMaster 700 K measurements and EKR4.5 mm K measurements were used in Holladay-II, SRK/T, Haigis, and Hoffer-Q formulas (p = 0.571, p = 0.833, p = 0.165, p = 0.347, respectively). There was no significant difference between APRE and ARE values (p = 0.124). According to mean ARE results, the closest estimate was achieved when the IOLMaster 700 K values were used in the Holladay-II formula (p = 0.271).

CONCLUSION

IOLMaster 700 K measurement and Pentacam EKR4.5 mm measurements can be used interchangeably. IOLMaster 700 K values yielded the most predictive measurement of the refractive result using the Holladay-II formula.

Evaluation of corneal topographic, tomographic and biomechanical indices for detecting clinical and subclinical keratoconus: a comprehensive three-device study

AIM

To evaluate the diagnostic ability of topographic and tomographic indices with Pentacam and Sirius as well as biomechanical parameters with Corvis ST for the detection of clinical and subclinical forms of keratoconus (KCN).

METHODS

In this prospective diagnostic test study, 70 patients with clinical KCN, 79 patients with abnormal findings in topography and tomography maps with no evidence on clinical examination (subclinical KCN), and 68 normal control subjects were enrolled. The accuracy of topographic, tomographic, and biomechanical parameters was evaluated using the area under the receiver operating characteristic curve (AUC) and cross-validation analysis. The Delong method was used for comparing AUCs.

RESULTS

In distinguishing KCN from normal, all parameters showed statistically significant differences between the two groups (P<0.001). Indices with the perfect diagnostic ability (AUC≥0.999) were Sirius KCN vertex of back (KVb), Pentacam random forest index (PRFI), Pentacam index of height decentration (IHD), and Corvis integrated tomographic/biomechanical index (TBI). In distinguishing subclinical KCN from normal, Sirius symmetry index of back (SIb; AUC=0.908), Pentacam inferior-superior difference (IS) value (AUC=0.862), PRFI (AUC=0.847), and Corvis TBI (AUC=0.820) performed best. There were no significant differences between the highest AUCs within keratoconic groups (DeLong, P>0.05).

CONCLUSION

In clinical KCN, all topographic, tomographic, and biomechanical indices have acceptable outcomes in terms of sensitivity and specificity. However, in differentiating subclinical forms of KCN from normal corneas, curvature-based parameters (SIb and IS value) followed by integrated indices (PRFI and TBI) are the most powerful tools for early detection of KCN.

Topographic, elevation, and keratoconus indices for diagnosis of keratoconus by a combined Placido and Scheimpflug topography system

PURPOSE

To determine the accuracy of various corneal parameters in keratoconus diagnosis using Scheimpflug camera combined with Placido disk corneal topography (Sirius, CSO).

METHODS

One hundred and fifteen keratoconic eyes (group1) and a 111 normal eyes (group2) were assessed prospectively between March 2018 and July 2019 for: corneal keratometric indices (K1, K2, sim K, apex curvature) at different corneal rings of both corneal surfaces, central corneal thickness (CCT), thinnest corneal thickness (TL), corneal asphericity (Q), elevation at thinnest point, root mean square (RMS), and root mean square per area (RMS/A) in spherical, aspheric and aspherotoric reference for both corneal surfaces and keratoconus summary parameters; surface asymmetry index of front and back (SIf, SIb respectively), elevation at keratoconus vertex front and back (KVf, KVb respectively), Baiocchi Calossi Versaci front and back index (BCVf, BCVb) and its vector summation (BCV) and convergence radius and cutoff value for each was calculated.

RESULTS

All studied indices were significantly different between the two groups. The highest predictive accuracy "Area under receiver operating characteristic curve (AUROC)" of 0.999 was observed for BCVf, KVb, RMS and RMS/A at 6 mm aspherotoric reference posterior surface. Keratoconus summary indices had high AUROC (0.986, 0.984, 0.948, 0.999, 0.999, 0.998 respectively). Curvature indices had lower AUROC than elevation indices, except for curvature of corneal apex at anterior (0.98) and posterior surface (0.99). Higher AUROC was noted with elevation at thinnest point especially at aspherotoric reference surface.

CONCLUSION

Sirius topography showed high predictive accuracy in detection of keratoconus. Elevation indices and keratoconus summary parameters have the highest diagnostic ability.

Subclinical keratoconus detection with three-dimensional (3-D) morphogeometric and volumetric analysis

PURPOSE

To assess the efficacy of morphogeometric and volumetric characterization of the cornea based on three-dimensional (3-D) modelling in diagnosis of subclinical keratoconus (KC).

METHODS

Cross-sectional study. Ninety-three eyes with subclinical KC with a best spectacle-corrected distance visual acuity ≥20/20 (grade zero KC according to the RETICS classification) and 109 control eyes were included. Computer-based 3-D corneal morphogeometric model was generated using raw topographic data. Distance-, area- and volume-based parameters were used for statistical analysis. Distance parameters included deviation of anterior (D_apexant )/posterior (D_apexpost ) apices and minimum thickness points (D_mctant , D_mctpost ) from corneal vertex, and D_apexant -D_apexpost difference. Areal variables were derived from anterior (A_ant ) and posterior (A_post ) corneal surfaces, sagittal plane passing through corneal apices (A_apexant , A_apexpost ) and thinnest point (A_mctant , A_mctpost ). Total corneal volume (V_total ) and volumetric distribution (with 0.1mm steps) centred to thinnest corneal point (VOL_mct ) and anterior (VOL_aap )/posterior (VOL_pap ) apices comprised the volume-based parameters.

RESULTS

In the subclinical KC group, all D values, D_apexant -D_apexpost difference, A_ant , A_post and A_apexant values were higher (p < 0.001), while A_apexpost , A_mctpost , V_total , VOL_mct , VOL_aap and VOL_pap values were lower when compared to the control group (p < 0.001). Regression analysis-based formula correctly classified 96.8% of the eyes with subclinical KC and 94.5% of the normal ones (p < 0.0001).

CONCLUSIONS

Eyes with subclinical KC seem to represent asymmetrically displaced anterior and posterior corneal apex, corneal thinning and volume loss. 3-D morphogeometric and volumetric parameters and differentiation formula can be incorporated into topography software to detect subclinical KC with high sensitivity and specificity in clinical practice.

Evaluation of corneal topography and tomography in fellow eyes of unilateral keratoconus patients for early detection of subclinical keratoconus

Purpose:

To analyse topographic and tomographic changes in fellow eyes of unilateral keratoconus patients by comparing them with normal eyes.

Methods:

This five-year retrospective observational comparative case study included 15 advanced keratoconus eyes of unilateral keratoconus (KCN group), 15 normal fellow eyes of unilateral keratoconus (Fellow eye group) and 34 eyes of normal refractive surgery candidates (Normal group). Topographic and tomographic data, data from enhanced elevation maps, and keratoconus indices were measured in all study eyes using Pentacam. Receiver operating characteristic (ROC) curves were used to evaluate the area under the curve (AUC), sensitivity and specificity of each parameter and identify cut-off points in discriminating between the fellow and normal eyes.

Results:

Corneal thickness at the apex (CTA, P = 0.001) and at the thinnest point (CTT, P < 0.001), corneal volume (CV, P = 0.007), Belin/Ambrosio Enhanced Ectasia Display (BAD) - thinnest point (Dt, P = 0.002) and thinnest point displacement (Da, P = 0.002) were significantly lower in the fellow group compared to eyes of normal subjects. On ROC curve analysis, the most efficient distinguishing indices between the fellow group and normal controls were BAD - overall D value (AUC = 0.859), Dt (AUC =0.827), Da (AUC = 0.789) followed by pachymetric progression index maximum (AUC = 0.741).

Conclusion:

BAD-D value and pachymetric progression index could be useful in detecting the earliest form of subclinical keratoconus. However, every single parameter alone is not enough to detect early changes; a combination of different data is required to distinguish subclinical keratoconus.

A Case of Early Keratoconus Associated with Eye Rubbing in a Young Child

INTRODUCTION

Keratoconus usually presents during puberty and is considered rare in young children.

METHODS

Case report with clinical findings and computerized corneal tomography.

RESULTS

We report the case of an 8-year-old girl with early bilateral keratoconus who presented with allergic conjunctivitis and persistent eye rubbing. Although our patient did not exhibit steep keratometry, early cones and inferotemporal thinnest corneal thicknesses were detected in both eyes using Scheimpflug imaging (Oculus GmbH Pentacam, Wetzlar, Germany). Belin/Ambrósio total D values were 1.85 on the right and 2.11 on the left. Improvement in best-corrected visual acuity was noted after treatment of allergic eye disease, and corneal tomographic findings remained stable 4 months after initial consult.

CONCLUSION

This is a case of early diagnosed keratoconus in a young patient. Diagnosis of this condition in young children is challenging, as these patients are less likely to report visual complaints, and clinical examination is usually unremarkable. Keratoconus screening should be considered in children with atopy and eye rubbing behavior regardless of age, even in those with no other associated pathology and with negative family history.

Corneal Indices Determined with Pentacam in Possible Candidates for Corneal Refractive Surgery

Objective:

To describe the level of correlation of clinical refractive variables with corneal indices in Pentacam Scheimpflug tomography, demonstrate the usefulness of the study of corneal indices in the diagnosis of keratoconus (KC), and identify the corneal indexes with the greatest influence on the diagnosis of KC.

Methods:

A descriptive, retrospective, and cross-sectional study was conducted in 69 patients (138 eyes) with refractive disorders, possible candidates for corneal refractive surgery, at the Exilaser Ophthalmological Center, Cuenca, Ecuador, from March to August 2019. Corneal indices were studied using Pentacam. Statistical correlation methods, Levene’s test, Fisher’s exact test, Cramérs’ V coefficient, and multiple correspondence analyses were used.

Results:

The variables refractive cylinder and central keratometry had a direct correlation with the corneal indices (p<0.001). An inverse correlation was obtained between central pachymetry and corneal indices (p<0.001). A high level of dependence on central KC index (CKI) (Cramér V = 0.785) and KC index (KI) (Cramér V = 0.775) was obtained with the diagnosis of KC.

Conclusion:

Pentacam is a valuable tool in the analysis of corneal indices for the diagnosis of KC, given its high level of correlation with clinical refractive variables. The selection of candidates for refractive surgery, even when there is no diagnosis of KC, is strengthened with the analysis of the corneal indices. The indices with the most intense level of dependence with the diagnosis of KC are, in order, the following indices: CKI, KI, vertical asymmetry, minimum radius, and variation of the surface.

The prevalence of keratoconus in children with allergic eye disease in an Egyptian population

PURPOSE

To determine the prevalence of keratoconus (KC) among children with ocular allergy.

METHODS

A cross-sectional study was conducted on all children presenting with ocular allergic disease from September 2017 to September 2018. All study participants were subjected to history taking (a specially designed questionnaire), routine ophthalmological examination, and corneal tomography.

RESULTS

A total of 79% of the study patients had vernal keratoconjunctivitis (VKC) while the remaining had perennial allergic conjunctivitis (10%), seasonal allergic conjunctivitis (9%) and atopic keratoconjunctivitis (2%). Manifest KC was seen in 7% of cases, suspect KC was found in 27% of cases, and 66% had no evidence of KC. For the manifest KC, 56% had clinical signs, while 44% were diagnosed by tomography. For the purpose of statistical analysis, the cohort was divided into group KC (manifest or suspicious KC) and group non-KC (no KC). The mean age was 11.2 years in group KC, and 9 years in group non-KC (p < 0.001). The mean duration of allergic symptoms was 3.75 years in group KC, and 2.5 years in group non-KC (p = 0.001). The mean duration of eye rubbing was 2.5 years in group KC, and 0.83 years in group non-KC (p = 0.02). Systemic atopy was present in 35.3% of group KC, and in 12.5% in group non-KC (p = 0.005).

CONCLUSION

The overall prevalence of KC was 34%. Risk factors for the development of KC in patients with ocular allergy were age, duration of symptoms specially eye rubbing, systemic atopy and VKC. Tomographic diagnosis of KC can be present in absence of clinical signs.

A predictive model for early diagnosis of keratoconus

BACKGROUND

The diagnosis of keratoconus in the early stages of the disease is necessary to initiate an early treatment of keratoconus. Furthermore, to avoid possible refractive surgery that could produce ectasias. This study aims to describe the topographic, pachymetric and aberrometry characteristics in patients with keratoconus, subclinical keratoconus and normal corneas. Additionally to propose a diagnostic model of subclinical keratoconus based in binary logistic regression models.

METHODS

The design was a cross-sectional study. It included 205 eyes from 205 patients distributed in 82 normal corneas, 40 early-stage keratoconus and 83 established keratoconus. The rotary Scheimpflug camera (Pentacam® type) analyzed the topographic, pachymetric and aberrometry variables. It performed a descriptive and bivariate analysis of the recorded data. A diagnostic and predictive model of early-stage keratoconus was calculated with the statistically significant variables.

RESULTS

Statistically significant differences were observed when comparing normal corneas with early-stage keratoconus/ in variables of the vertical asymmetry to 90° and the central corneal thickness. The binary logistic regression model included the minimal corneal thickness, the anterior coma to 90° and posterior coma to 90°. The model properly diagnosed 92% of cases with a sensitivity of 97.59%, specificity 98.78%, accuracy 98.18% and precision 98.78%.

CONCLUSIONS

The differential diagnosis between normal cases and subclinical keratoconus depends on the mínimum corneal thickness, the anterior coma to 90° and the posterior coma to 90°.

Ten years experience of corneal collagen cross-linking : An observational study of 6120 cases

PURPOSE

To study the effect of corneal collagen cross-linking (CXL) using riboflavin and ultraviolet rays on cases of corneal ectasia in keratoconus cases, post-laser-assisted in situ keratomileusis ectasia, and pellucid marginal degeneration and to present its long-term results over many years.

METHODS

This study was conducted throughout 10 "years" experience in corneal collagen CXL, including 6120 cases. The study consists of two parts: a retrospective and a prospective part. All patients in the retrospective part were operated by epi-off, while in the prospective part, the epi-on procedure was used. Also, other machines were used as Peschke Vario, Peschke Phoenix, and different types of riboflavin. The results were analyzed using SPSS.

RESULTS

The study showed stabilization ectasia in 95% of cases using our standard protocol, and this was proved by topography, pachymetry, refraction, and visual acuity. The effect of CXL was continued in 20% of cases, over a period of 3-5 years, some cases needed to repeat CXL due to the progression of corneal ectasia after cross-linking, in six eyes, that were rubbing their eyes and/or hormonal disturbance.

CONCLUSION

Corneal collagen cross-linking CXL is an effective method to prevent the progression of corneal ectasia, whether primary or post-laser-assisted in situ keratomileusis, and the effect was stable over the years of study.

Keratometric indices for detecting the type of keratoconus: a combined discriminant analysis

BACKGROUND

This study sought to determine the diagnostic ability of anterior, posterior and total keratometric indices in discriminating keratoconus (KCN) stages 1 to 4 from normal corneas.

METHODS

Anterior and posterior simulated keratometry (sim-Ksteep and sim-Kflat), maximum keratometry (Kmax), Kmax y co-ordinate, anterior and posterior radii of curvature centred on the thinnest point (ARC-3 mm and PRC-3 mm), and anterior, posterior, and total asphericity (Q-value) measured by Pentacam were extracted from electronic medical records of 200 KCN and 200 normal cases. Stepwise leave-one-out cross-validation and areas under receiver operating characteristic curves (AUROC) were used to detect the best set of indices for differentiating normal from low-grade (stages 1-2, Kmax ≤ 53.00 D) and high-grade (stages 3-4, Kmax > 53.00 D) KCN.

RESULTS

Mean age in KCN and normal groups was 33.10 ± 7.48 and 32.24 ± 9.00 years (p = 0.332), respectively. In the low-grade KCN group, PRC-3 mm (AUROC = 0.986), Kmax (AUROC = 0.979), and Kmax y co-ordinate (AUROC = 0.824) performed best, and the difference in AUROC between PRC-3 mm and Kmax was not significant (p = 0.153). In the high-grade KCN group, Kmax (AUROC = 1.000), PRC-3 mm (AUROC = 0.998), posterior Ksteep (AUROC = 0.970), posterior Q-value (AUROC = 0.940), and posterior Kflat (AUROC = 0.894) performed best, and there was no significant difference in AUROC values between Kmax and PRC-3 mm (p = 0.307) or between posterior Ksteep and posterior Q-value (p = 0.113).

CONCLUSIONS

Among the studied keratometric indices, PRC-3 mm and Kmax appear to have the best ability for detecting mild to severe KCN. The next best factors which showed good discrimination ability were Kmax y co-ordinate in low-grade cases and posterior Ksteep and Q-value in high-grade cases.

Correlation of corneal elevations measured by Scheimpflug corneal imaging with severity of keratoconus

Purpose

To evaluate the correlation of corneal elevation and difference elevation with severity of keratoconus.

Methods

Anterior and posterior corneal elevations with both conventional and enhanced best-fit spheres (using rotating Scheimpflug camera) were measured. Front and back difference elevation were extrapolated from difference map of Belin/Ambrỏsio Enhanced Ectasia Display of the Scheimpflug system. Data from corneal elevations and difference elevations were correlated with maximum keratometry, minimal corneal thickness, and severity of keratoconus as assessed by Amsler-Krumiech classification of keratoconus.

Results

Ninety eyes of 55 keratoconus patients of different clinical stages were evaluated. There was a significant positive correlation between keratoconus severity and corneal elevations (anterior and posterior elevation as measured with both conventional and enhanced best-fit spheres) and also between keratoconus severity and corneal elevation differences (P < 0.001 and r > 0.625 for all). Maximum keratometry (Kmax), mean keratometry (Kmean), and all corneal elevations and difference elevations were highly correlated (P < 0.001 and r > 0.840 for all). A significant negative correlation was found between minimum corneal thickness and all corneal elevations and difference elevations (P < 0.001 and r < 0.711 for all). Receiver operating characteristic (ROC) curve analyses showed that anterior and posterior difference elevations have the best predictive accuracy for grading keratoconus severity.

Conclusion

Evaluation of corneal elevation and difference elevation data obtained from Scheimpflug corneal imaging is useful for grading severity of keratoconus.

Pentacam® Corneal Tomography for Screening of Refractive Surgery Candidates: A Review of the Literature, Part I

Corneal tomography and Scheimpflug imaging are frequently used to analyze the corneal surface, especially in the field of cataract and refractive surgery. The Pentacam system is one of the most commonly used commercially available systems for this purpose. Through a rotating Scheimpflug camera, the system is capable of creating a three-dimensional map of the cornea. These advances in tomography have simultaneously enhanced the ability of clinicians to screen surgical candidates and detect subtle corneal changes in diseases such as keratoconus. However, there remains a need to enhance diagnosis in order to recognize mild and early forms of corneal ectasia. As iatrogenic ectasia and keratoconus are dreaded complications of refractive surgery, it is imperative to screen patients appropriately prior to surgery. The Pentacam is one of many systems utilized in the screening process, but the literature has not identified specific protocol nor parameters that are capable of carrying out this process appropriately. Post-operative keratoconus continues to occur despite the advances in technology seen in corneal imaging. Therefore, clear indices for screening are required in order to diagnose early forms of keratoconus and other corneal diseases that may exclude the seemingly asymptomatic patient from undergoing refractive surgery. This article aims to summarize the indices available on the Pentacam system and to identify the most accurate parameters for screening of the refractive surgery candidate.