Keratoconus Screening Research Articles

Research of diagnostic value of corneal biomechanical parameters based on Corvis ST in keratoconus

Objective To compare the corneal biomechanical properties between keratoconic eyes and normal eyes by using corneal visualization Scheimpflug technology (Corvis ST), and to evaluate the diagnostic value of corneal biomechanical parameters based on Corvis ST in keratoconus. Methods A prospective cases-control study was performed.Twenty-four keratoconic eyes from 17 patients and 40 normal eyes (right eye) from 40 participants were enrolled from October to December in Peking University First Hospital.Anterior segment parameters and refractive diopters were obtained with Topography (TMS-4) and mydriatic refraction.Biomechanical parameters were assessed with Corvis ST.Independent sample t-test and Wilcoxon rank sum test were used to compare the parameters of the two groups.The receiver operating characteristic (ROC) curves were plotted to distinguish keratoconus from the normal cornea.Diagnostic efficacies of all parameters were analyzed and some parameters were used as independent variables to establish a Logistic regression model. Results Maximum deformation amplitude of highest concavity (HCDA), maximum corneal velocity during the second applanation (Vout) and distance between both non-deformed peaks (PD) in the keratoconus group were higher than those in the normal control group, and first applanation time (A1T), cord length of first applanation (A1L), cord length of second applanation (A2L), radius value of central concave curvature at highest concavity (HCR) were lower than those in the normal control group, with significant differences between the two groups (all at P 0.05). Many parameters had diagnostic values in keratoconus assessed by ROC analysis.HCR was the most efficient parameter showed by ROC evaluation (area under the curve was 0.927, sensitivity was 95.8%, specificity was 82.5%). The Logistic model were established with two independent variables, HCR (OR=0.205) and central corneal thickness (CCT) (OR=0.970). The forecast model of keratoconus diagnosis was established as follows: Logistic (P)=23.47-1.59×HCR-0.30×CCT.Diagnostic sensitivity and specificity were enhanced by using this model, the sensitivity was 95.8%, and the specificity was 95.0%. Conclusions It is useful to evaluate the corneal biomechanical properties with Corvis ST.HCR is an efficient auxiliary testing index of diagnosis or screening of keratoconus. Key words: Corneal visualization Scheimpflug technology; Keratoconus; Corneal biomechanics

Screening for keratoconus in a refractive surgery population of Upper Egypt

Purpose The purpose of this study was to evaluate the prevalence of keratoconus among candidates of refractive surgery in Upper Egypt. Setting The study was conducted in Sohag University Hospital and Future Center (a private center) for laser in-situ keratomiluesis and refractive surgery in Sohag Governorate, Egypt. Design This is an observational cross-sectional study. Patients and methods Refractive surgery candidates referred for preoperative evaluation before laser in-situ keratomiluesis, photorefractive keratectomy, and phakic intraocular lens implantation in the period from April 2015 to September 2015 were screened for keratoconus using Sirrus Scheimpflug camera. Results The study included 1202 patients, 623 male and 579 female. Keratoconus was detected in 210 (17.5%) patients. Conclusion Prevalence of keratoconus among refractive surgery candidates in Upper Egypt is relatively high, which may reflect an underlying high prevalence in the general population.

Mean Posterior Corneal Power and Astigmatism in Normal Versus Keratoconic Eyes.

Purpose:To compare mean posterior corneal power and astigmatism in normal versus keratoconus affected eyes and determine the optimal cut-off points to maximize sensitivity and specificity in discriminating keratoconus from normal corneas.Methods:A total of 204 normal eyes and 142 keratoconus affected eyes were enrolled in this prospective comparative study. Mean posterior corneal power and astigmatism were measured using a dual Scheimpflug camera. Correlation coefficients were calculated to assess the relationship between the magnitudes of keratometric and posterior corneal astigmatism in the study groups. Receiver operating characteristic curves were used to compare the sensitivity and specificity of the measured parameters and to identify the optimal cut-off points for discriminating keratoconus from normal corneas.Results:The mean posterior corneal power was −6.29 ± 0.20 D in the normal group and −7.77 ± 0.87 D in the keratoconus group (P < 0.001). The mean magnitudes of the posterior corneal astigmatisms were −0.32 ± 0.15 D and −0.94 ± 0.39 D in the normal and keratoconus groups, respectively (P < 0.001). Significant correlations were found between the magnitudes of keratometric and posterior corneal astigmatism in the normal (r=−0.76, P < 0.001) and keratoconus (r=−0.72, P < 0.001) groups. The mean posterior corneal power and astigmatism were highly reliable characteristics that distinguished keratoconus from normal corneas (area under the curve, 0.99 and 0.95, respectively). The optimal cut-off points of mean posterior corneal power and astigmatism were −6.70 D and −0.54 D, respectively.Conclusion:Mean posterior corneal power and astigmatism measured using a Galilei analyzer camera might have potential in diagnosing keratoconus. The cut-off points provided can be used for keratoconus screening.

Advanced anterior segment imaging in keratoconus: a review.

Advances in anterior segment imaging have enhanced our ability to detect keratoconus in its early stages and characterize the pathologic changes that occur. Computerized corneal tomography has elucidated the alterations in shape of the anterior and posterior corneal surfaces and alterations in thickness as the disease progresses. Automated screening indices such as the keratoconus screening index were developed to assist in detecting keratoconus in suspicious cases. In vivo assessment of keratoconic corneas has revealed that compromised corneal biomechanics can now be measured clinically. Optical coherence tomography has demonstrated alterations in corneal epithelial thickness and distribution in keratoconus, has a role in assessing Descemet's membrane detachment in acute corneal hydrops (ACH) and the depth of the demarcation line following corneal collagen cross-linking. In vivo confocal microscopy has exhibited cellular changes that occur in keratoconus and provided insight into cellular events that may be related to the development of neovascularization in ACH.

A Study for Parametric Morphogeometric Operators to Assist the Detection of Keratoconus

The aim of this study is to describe a new keratoconus detection method based on the analysis of certain parametric morphogeometric operators extracted from a custom patient-specific three-dimensional (3D) model of the human cornea. A corneal geometric reconstruction is firstly performed using zonal functions and retrospective Scheimpflug tomography data from 107 eyes of 107 patients. The posterior corneal surface is later analysed using an optimised computational geometry technique and the morphology of healthy and keratoconic corneas is characterized by means of geometric variables. The performance of these variables as predictors of a new geometric marker is assessed through a receiver operating characteristic (ROC) curve analysis and their correlations are analysed through Pearson or Spearman coefficients. The posterior apex deviation variable shows the best keratoconus diagnosis capability. However, the strongest correlations in both healthy and pathological corneas are provided by the metrics directly related to the thickness as the sagittal plane area at the apex and the sagittal plane area at the minimum thickness point. A comparison of the screening of keratoconus provided by the Sirius topographer and the detection of corneal ectasia using the posterior apex deviation parameter is also performed, demonstrating the accuracy of this characterization as an effective marker of the diagnosis and ectatic disease progression.

Can Appropriate Systemic Treatment Help Protect the Cornea in Patients With Rheumatoid Arthritis? A Multidisciplinary Approach to Autoimmune Ocular Involvement.

Purpose:To correlate rheumatologic with ophthalmic and laboratory findings in patients with rheumatoid arthritis (RA) to identify what effect these have on development of ocular disease.Methods:This is a cross-sectional study of 172 eyes of 86 patients with RA. Patients were examined by a group of rheumatologists. Sociodemographic, clinical, and laboratory data were collected. All patients underwent complete ophthalmologic examination including corneal topography and endothelial cell count.Results:There was no significant correlation between RA-negative prognostic indicators (NPIs) and pathologic corneal findings. Patients using disease-modifying antirheumatic drugs (DMARDs) and antimalarial drugs had greater corneal volumes (mean difference 8.51 mm3, 90% confidence interval [CI], 3.98–13.04, P = 0.004; and 2.24, 90% CI, 0.32–4.54, P = 0.048, respectively). Patients using azathioprine had lower endothelial cell counts compared with those using other drugs (mean difference 180 cells/mm2, 90% CI, 69–291, P = 0.008). Patients using biologic DMARDs had better tear osmolarity values (between 280 and 300 mOsm/L) than patients not using them (mean difference 14.3 mOsm/L, P = 0.022). There was no correlation between NPIs of RA and positive keratoconus screening indices (Spearman correlation OD −0.013, P = 0.91; OS −0.033, P = 0.76).Conclusions:There was no clear correlation between RA-NPIs and pathologic corneal findings in our study. DMARDs treatment may help maintain corneal integrity in our patients and prevented collagenolytic manifestations of RA. Other medications such as azathioprine should be used carefully, as endothelial damage may potentially occur.

Scanning-slit topography in patients with keratoconus.

To evaluate the anterior and posterior corneal surfaces using scanning-slit topography and to determine the diagnostic ability of the measured corneal parameters in keratoconus. Orbscan II measurements were taken in 39 keratoconic corneas previously diagnosed by corneal topography and in 39 healthy eyes. The central minimum, maximum, and astigmatic simulated keratometry (K) and anterior axial power values were determined. Spherical and cylindrical mean power diopters were obtained at the central and at the steepest point of the cornea both on anterior and on posterior mean power maps. Pachymetry evaluations were taken at the center and paracentrally in the 3 mm zone from the center at a location of every 45 degrees. Receiver operating characteristic (ROC) analysis was used to determine the best cut-off values and to evaluate the utility of the measured parameters in identifying patients with keratoconus. The minimum, maximum and astigmatic simulated K readings were 44.80±3.06 D, 47.17±3.67 D and 2.42±1.84 D respectively in keratoconus patients and these values differed significantly (P<0.0001 for all comparisons) from healthy subjects. For all pachymetry measurements and for anterior and posterior mean power values significant differences were found between the two groups. Moreover, anterior central cylindrical power had the best discrimination ability (area under the ROC curve=0.948). The results suggest that scanning-slit topography and pachymetry are accurate methods both for keratoconus screening and for confirmation of the diagnosis.

Prevalence of keratoconus among patients seeking laser vision correction in Taif area of Saudi Arabia

PurposeTo determine the prevalence of keratoconus among patients seeking laser vision correction (LVC). MethodsRetrospective study of 1374 eyes of 687 patients (335 males, 352 females) who underwent keratoconus screening as a part of routine preoperative evaluation prior to LVC at the Tadawi surgical centre, Taif, Saudi Arabia from January 2014 to June 2015. The diagnosis of keratoconus was based on evaluation of Pentacam derived parameters. ResultsManifest keratoconus was found in 59 subjects (out of 687 subjects) representing a prevalence rate of 8.59%. Of the 687 subjects, 45 subjects (6.55%) had bilateral manifest keratoconus (manifest keratoconus in both eyes or manifest keratoconus in one eyes and sub-clinical in contralateral eye) and remaining 14 patients (2.04%) had unilateral manifest keratoconus (with normal fellow eye). Sub-clinical keratoconus was diagnosed in 65 patients representing a prevalence rate of 9.46%. Of the 687 patients, 20 cases (2.91%) with subclinical keratoconus were bilateral and 45 (6.55%) were unilateral. Overall, 19.70% males (66/335) and 16.48% (58/352) females had either manifest or sub-clinical keratoconus, representing no statistically significant difference in the gender predisposition of the keratoconus disease process (Chi Square test; p = .277). ConclusionHigh prevalence of keratoconus was found among patients seeking LVC. Possible factors contributing to the high prevalence were recognized to be highly selective population (patients seeking LVC for myopia/hyperopia/astigmatism), ethnicity (high prevalence of consanguinity) and geographical location (high altitude) of the study subjects.

Keratoconus Screening With Dynamic Biomechanical In Vivo Scheimpflug Analyses: A Proof-of-Concept Study.

This proof-of-concept study was designed to analyze the ability of in vivo biomechanical corneal analyses with the corneal visualization Scheimpflug technology (CorvisST; Oculus Optikgeräte, Wetzlar, Germany) to differentiate between normal eyes and eyes with manifest keratoconus after strictly eliminating the potential confounding factors intraocular pressure (IOP) and central corneal thickness (CCT). In this retrospective, cross-sectional study, after pairwise matching for CCT and IOP, 29 normal eyes and 29 keratoconic eyes (one eye from each patient) were selected as study population. Older CorvisST parameters and the new Corvis Biomechanical Index (CBI), including several biomechanical and one tomographic parameter, as well as an adjusted CBI (aCBI) (including only biomechanical parameters), were compared regarding their discriminative ability between both groups. None of the CorvisST parameters of the former software version demonstrated statistically significant differences between normal and keratoconic eyes. On the other hand, the CBI and aCBI reached accuracies of 0.91 and 0.93, respectively, to discriminate between CCT- and IOP-matched normal and keratoconic eyes (CBI: [AUC/sensitivity/specificity]: 0.961/0.90/0.93; aCBI: [AUC/sensitivity/specificity]: 0.986/0.93/0.93). This study demonstrated that the concept of keratoconus screening with the CorvisST is effective in differentiating keratoconic from non-keratoconic eyes. The next steps will be testing the indices in subclinical keratoconus cases and hopefully combining biomechanical analyses with already established topography and tomography indices to further improve current keratoconus screening. [J Refract Surg. 2017;33(11):773-778.].

Keratoconus Screening Indices and Their Diagnostic Ability to Distinguish Normal From Ectatic Corneas

To compare the diagnostic ability of 3 Scheimpflug devices in differentiating normal from ectatic corneas. Comparison of diagnostic instrument accuracy. This study included 42 normal, 37 subclinical keratoconic, and 51 keratoconic eyes seen in a tertiary eye care institute. Keratoconus screening indices were evaluated using the Pentacam (Oculus, Wetzlar, Germany), Galilei (Ziemer, Biel, Switzerland), and Sirius (Costruzione Strumenti Oftalmici, Florence, Italy). Sensitivity, specificity, and area under receiver operating characteristic curve (AUC) were calculated. Highest sensitivity (100%) to diagnose keratoconus was seen for 6 parameters on Pentacam and 1 on Galilei. None of the indices in Sirius reached 100% sensitivity. For subclinical keratoconus, the highest sensitivity (100%) was seen for 2 parameters on Pentacam but for none of them on Galilei and Sirius. All parameters were strong enough to differentiate keratoconus (AUC> 0.9). On comparing the best parameters of all 3 machines, the AUC of the Belin/Ambrosio enhanced ectasia total derivation (BAD-D) and the inferior-superior value (ISV) of Pentacam were statistically similar to that of the keratoconus prediction index (KPI) and keratoconus probability (Kprob) of Galilei (P= .27) and 4.5mm root mean square per unit area (RMS/A) back of Sirius (P= .55). When differentiating subclinical from normal corneas, BAD-D was similar to the surface regularity index (SRI) of Galilei (P= .78) but was significantly greater than the 8mm RMS/A back of Sirius (P= .002). Keratoconus indices measured by all 3 machines can effectively differentiate keratoconus from normal corneas. However, new cutoff values might be needed to differentiate subclinical from normal corneas.

Intereye asymmetry in bilateral keratoconus, keratoconus suspect and normal eyes and its relationship with disease severity

Background/AimTo describe the intereye asymmetry in patients with keratoconus (KC), keratoconus suspect (KCS) and normal participants, and to evaluate the relationship between asymmetry and disease severity.MethodsIn this prospective observational comparative...

Interpretation of keratoconus indices

SummaryWe provide an overview on the dedicated keratoconus indices of Pentacam (Scheimpflug‐based tomographer), CASIA SS‐1000 (anterior segment optical coherence tomographer), TMS‐5 (Scheimpflug and Placido tomo‐/topographer) and Ocular Response Analyzer (pneumotonometer which features measurement of biomechanical properties). We demonstrate how modern keratoconus screening software modules such as the Belin‐Ambrósio Enhanced Ectasia Display (BAD) or the ectasia screening of the CASIA/TMS‐5 work in comparison to the classical McDonnell/Rabinowitz and Smolek/Klyce/Maede indices, and we point out the differences between metric keratoconus indices and classificators. We will also discuss the diagnostic capacity of the devices and indices/classificators in detail.

Keratoconus Screening in Primary Eye Care – A General Overview

Keratoconus early detection (screening) and diagnosis requires an in-deep corneal analysis with different techniques; slip lamp assessment, corneal topography and corneal tomography are the most commonly accepted to detect clinical signs and assess anterior and posterior corneal surface and global corneal pachymetry. However, keratoconus early detection and definitive diagnosis are two different clinical procedures that require a different approach and goals. The aim of this review is to provide some general information about different corneal assessment technology, useful in keratoconus patient assessment; highlighting the differences in the adequate investigation techniques to its detection in primary eye care clinic and to conduct the definitive diagnosis (usually in a cornea specialist clinic). Information of most extensively available commercial devices and the advantages and disadvantages of their use in keratoconus early detection and diagnosis are described. In conclusion, corneal topography (Placido-based keratographers) plays a significant role in keratoconus detection, especially in primary eye care clinics. However, corneal tomography (with different slit scanning and/or rotational imaging devices) including posterior corneal surface assessment and global corneal pachymetry investigation, is critical in definitive keratoconus diagnosis.

Rotating Scheimpflug Imaging Indices in Different Grades of Keratoconus.

Purpose. To evaluate accuracy of various Keratoconus (KC) screening indices, in relation to Topographic Keratoconus (TKC) grading. Setting. Al Watany Eye Hospital, Cairo, Egypt. Methods. Data of 103 normal (group 1) and 73 KC eyes (group 2), imaged by Pentacam (branded as Allegro Oculyzer), were analysed. Group 2 was divided into 2a: 14 eyes (TKC = 1, early KC), 2b: 25 eyes (TKC = 1 to 2 or 2, moderate KC), and 2c: 34 eyes (TKC = 2 to 3 up to 4, severe KC). Participants were followed up for six years to confirm diagnosis. Area under the receiver operating characteristic curve (AUROC) was calculated for evaluated curvature, elevation, and pachymetry indices with various reference shapes at different diameters. Results. When comparing normal to KC eyes, ten indices had significantly higher AUROC. Only five of them had significantly higher AUROC in early KC compared to normal corneas: Pachymetry Progression Index- (PPI-) Maximum (Max), Ambrósio's Relational Thickness- (ART-) Max, PPI-Max minus PPI-Minimum (Min), central corneal thickness (CCT), and diagonal decentration of thinnest point from the apex (AUROC = 0.690, 0.690, 0.687, 0.683, and 0.674, resp.). Conclusion. Generally, ten pachymetry and elevation-based indices had significantly higher AUROC. Five indices had statistically significant high AUROC when comparing early KC to normal corneas.

Moria One-Use Plus sub-Bowman’s keratomileusis head: a useful tool in the refractive surgeon’s armamentarium

Patients and methods A total of 500 eyes of 250 patients underwent laser in situ keratomileusis (LASIK) surgery using the One-Use Plus sub-Bowman’s keratomileusis head for the creation of an ultrathin LASIK flap. During the follow-up at 1, 6, 12, and 24 months, both uncorrected visual acuity (UCVA) and best-corrected visual acuity were recorded. A keratoconus screening corneal topography was carried out during the last follow-up visit. Results A total of 500 eyes of 250 myopic patients were included in this study. There were 115 male patients and 135 female patients. The mean age was 27.5 years (range: 18–44 years). The mean preoperative refractive error was −5.0 diopter sphere (DS) (range: −3 to −9 DS). The mean cylindrical error was −2.5 diopter cylinder (DC) (range: −0.75 to −4.5 DC). The mean UCVA was 0.07 (range: 0.01–0.3), and it improved to 1.0 (range: 0.8–1.25) on day 1 postoperatively. At the end of the follow-up, the mean UCVA was 1.0 and the mean best-corrected visual acuity was 1.0. The mean stromal residual bed thickness was 362 μm (range: 304–466 μm), and the mean central flap thickness was 102 μm (range: 82–120 μm). Complications were perilimbal bleeding in 15 eyes and fine irregular stromal edge cuts at the sides of the hinge in 10 eyes. There were no epithelial defects, no epithelial heaping or sliding, no irregular stromal bed surface cuts, no free caps or button holes, or incomplete flaps. Diffuse lamellar keratitis occurred in one eye of one patient, and no slipped flaps, macrostriae or microstriae, or epithelial downgrowth was seen during the follow-up period. At the end of the follow-up period none of our patients had topographic evidence of keratoconus. Conclusion The One-Use Plus sub-Bowman’s keratomileusis head is a safe and effective method for creating an ultrathin LASIK flap and allows the surgeon to treat higher errors of refraction while maintaining a higher safety margin by leaving more residual stromal tissue.

Screening for Keratoconus With New Dynamic Biomechanical In Vivo Scheimpflug Analyses.

To improve keratoconus (KC) screening with new in vivo biomechanical Scheimpflug analyses. After adjusting for intraocular pressure and corneal thickness, predefined static and new dynamic Scheimpflug curve analyses [Pentacam HR and Corvis ST (CST); Oculus] of 87 normal eyes, 27 subclinical KC eyes, 42 suspected KC, and 65 manifest KC eyes were reviewed retrospectively. A t test (for a normal distribution), Wilcoxon matched-pairs test (if not normally distributed), and receiver operating characteristics were used to test for statistically significant differences between these groups. In addition, new dynamic curve analyses were performed to analyze corneal dynamics throughout the entire response to the CST air puff impulse. Comparing normal and KC-suspect eyes, the parameters A1 length, A2 length, radius of the inward-bended cornea, and deflection length at the highest concavity revealed statistically significant differences. In addition, the newly calculated "applanation length level" and "deflection length level" demonstrated consistently increasing differences with increasing statistical significance between normal eyes and those with advancing KC stages. However, when comparing normal and subclinical KC eyes, none of the analyzed parameters demonstrated statistically significant differences. In vivo biomechanical analyses (CST) at their current state only marginally improve KC screening protocols. Newly generated parameters such as the applanation length level and deflection length level might further improve early KC screening.

Efficacy of axial and tangential corneal topography maps in detecting subclinical keratoconus

To investigate and compare the efficacy of axial and tangential corneal topography maps obtained using the Orbscan IIz scanning-slit device to distinguish differences in eyes with subclinical keratoconus from normal eyes. LV Prasad Eye Institute, Hyderabad, India. Retrospective cross-sectional study. Axial and tangential maps of the anterior and posterior corneal surfaces were obtained in eyes of patients with subclinical keratoconus (normal fellow eye of an eye with clinically diagnosed keratoconus). The following measurements were obtained from each map and compared between the 2 groups: location of the corneal apex in millimeters relative to the corneal vertex, dioptric power at the corneal apex and corneal vertex, corneal irregularity indices at 3.0 mm and 5.0 mm, anterior-posterior apex ratio, and inferior-superior dioptric asymmetry value. Maps were obtained in 71 eyes (71 patients) with subclinical keratoconus and 76 normal eyes (76 patients). The tangential posterior apex curvature was significantly steeper than the axial posterior apex curvature in both groups (P < .001). The anterior-posterior apex ratio on the tangential map demonstrated the highest area under the receiver operating characteristic (ROC) curve of 0.992 (cutoff ≥-6.97, sensitivity 98.6%, specificity 98.7%) followed by the posterior irregularity index in the 5.0 mm zone with an area under the ROC curve of 0.938 (cutoff ≥0.4, sensitivity 98.6%, specificity 84.2%) in differentiating subclinical keratoconus eyes from normal eyes. The anterior-posterior apex ratio on the tangential map and 5.0 mm irregularity index of the posterior corneal surface were highly sensitive and specific for early detection of subclinical keratoconus. Tangential corneal topography maps should be considered in preoperative subclinical keratoconus screening. No author has a financial or proprietary interest in any material or method mentioned.

Quantitative analysis of iris parameters in keratoconus patients using optical coherence tomography

To investigate the relationship between quantitative iris parameters and the presence of keratoconus. Cross-sectional observational study that included 15 affected eyes of 15 patients with keratoconus and 26 eyes of 26 normal age- and sex-matched controls. Iris parameters (area, thickness, and pupil diameter) of affected and unaffected eyes were measured under standardized light and dark conditions using anterior segment optical coherence tomography (AS-OCT). To identify optimal iris thickness cutoff points to maximize the sensitivity and specificity when discriminating keratoconus eyes from normal eyes, the analysis included the use of receiver operating characteristic (ROC) curves. Iris thickness and area were lower in keratoconus eyes than in normal eyes. The mean thickness at the pupillary margin under both light and dark conditions was found to be the best parameter for discriminating normal patients from keratoconus patients. Diagnostic performance was assessed by the area under the ROC curve (AROC), which had a value of 0.8256 with 80.0% sensitivity and 84.6% specificity, using a cutoff of 0.4125 mm. The sensitivity increased to 86.7% when a cutoff of 0.4700 mm was used. In our sample, iris thickness was lower in keratoconus eyes than in normal eyes. These results suggest that tomographic parameters may provide novel adjunct approaches for keratoconus screening.

Comparison of objective and subjective refractive surgery screening parameters between regular and high-resolution Scheimpflug imaging devices

To compare objective and subjective metrics from regular and high-resolution Scheimpflug devices (Pentacam) to determine their equivalence and interchangeability for refractive surgery screening. Emory Vision at Emory University, Atlanta, Georgia, USA. Retrospective comparative case series. Eyes of consecutive screened refractive surgery patients were evaluated with high-resolution and regular Scheimpflug devices. Objective parameters evaluated included keratometry (K) values, central corneal thickness (CCT), and device-generated keratoconus screening indices. Masked expert reviewers subjectively graded images as normal, suspicious, or abnormal. One hundred eyes of 50 patients were evaluated. The mean K values were not significantly different (anterior K: high resolution 1.21 diopters [D] ± 1.13 (SD) versus regular 1.15 ± 1.16 D, P = 0.73; posterior K: 0.34 ± 0.23 D versus regular 0.35 ± 0.23 D, P = .67). The mean CCT was significantly thinner in the high-resolution group (514.7 ± 26.6 μm versus 527.6 ± 27.6 μm (P < .0001) with limits of agreement of -12.9 to +17.5 μm. Most keratoconus screening indices were more suspicious with the high-resolution device than with the regular device except the indices of height asymmetry and height deviation. Subjectively, 60% of cases received the same score, high resolution was more suspicious in 28% of cases, and regular was more suspicious in 12% of cases; there was only slight subjective agreement between technologies (κ = 0.26 to 0.31). Regular and high-resolution Scheimpflug imaging devices generated different objective values and significantly different subjective interpretations with poor inter-reviewer agreement. The high-resolution device provided a more conservative overall output. For refractive surgical screening, the 2 devices are not interchangeable. Proprietary or commercial disclosures are listed after the references.

Independent Population Validation of the Belin/Ambrósio Enhanced Ectasia Display: Implications for Keratoconus Studies and Screening

ABSTRACT With advances in technology and imaging, finding diagnostic criteria that are both sensitive and specific for keratoconus while using the latest corneal imaging modalities is paramount. The Belin/Ambrósio enhanced ectasia display final ‘D’ index, tested on an independent population, illustrated excellent false positive rates for refractive screening while eliminating 99% of keratoconus corneas. A false positive rate of 0% is achieved with a final ‘D’ of 2.69, meeting the more stringent criteria for treatment studies. How to cite this article Villavicencio OF, Gilani F, Henriquez MA, Izquierdo L Jr, Ambrósio RR Jr, Belin MW. Independent Population Validation of the Belin/Ambrósio Enhanced Ectasia Display:Implications for Keratoconus Studies and Screening. Int J Kerat Ect Cor Dis 2014;3(1):1-8.