Corneal elevation indices in normal and keratoconic eyes

Multivariate analysis of refractive state in eyes with keratoconus

OBJECTIVE

To demonstrate a multivariate method of analysis of the short-term variation of refractive state in keratoconus (KC) patients.

METHODS AND ANALYSIS

In this observational study, 19 eyes with KC and 19 healthy control eyes were measured. The study included both male and female participants and the mean age was 23.6 years (range 18-34 years) and 23.2 years (range 22-26 years) for KC and control participants, respectively. Forty consecutive autorefractor measurements were taken for each participant and the short-term variation thereof was analysed using multivariate methods of analysis.

RESULTS AND CONCLUSION

Short-term variation of refractive state is greater in eyes with KC than in healthy control eyes and variation increases with severity of disease. A novel finding was that there was much more ortho-astigmatic and oblique-astigmatic variation seen in KC eyes than in control eyes which had predominately stigmatic variation. Refractive state is described by three components, namely, sphere, cylinder and axis. Although it is multivariate in nature, it is often analysed using univariate statistical methods. In diseases such as KC, where early diagnosis is crucial for a good prognosis, it is necessary that researchers endeavour to investigate the disease from different perspectives to fully understand the nature of the disease. This paper comprehensively demonstrates the multivariate statistical methods of analysis of refractive data. The implementation of this analysis provides insight into the short-term variation of refractive data in healthy and keratoconic eyes, and these findings have not been demonstrated before using univariate statistics.

Immunomodulatory Effect of Human Lactoferrin on Toll-like Receptors 2 Expression as Therapeutic Approach for Keratoconus

Keratoconus (KC) is a corneal disorder whose etiology shares a close relationship with Lactoferrin (LTF) dysregulation and Toll-like Receptors 2 (TLR2) overexpression. This study shows how these two important biomarkers are clinically and molecularly interrelated, increasing knowledge about KC pathophysiology, and opening the door to future therapies. In this prospective clinical study, serum and tear LTF concentrations were quantified in 90 KC patients and 60 controls. A correlation analysis with multiple blood and tear immunoinflammatory mediators, and KC-associated tomographic parameters, was performed. An in vitro study using HEK-BlueTMhTLR2 cell cultures was also conducted to determine the expression and functionality of TLR2 under the influence of LTF treatment. As a result, a LTF decreased was observed in KC patients compared to controls (p < 0.0001), evidencing the strong correlation with TLR2 overexpression at systemic and ocular surface level, with inflammatory mediator upregulation and with KC severity. In stimulated cell cultures, TLR2 expression was decreased using 2 mg/mL of LTF. The levels of secreted embryonic alkaline phosphatase (SEAP) and interleukin-8 (IL-8) were also reduced in supernatants after LTF treatment. As conclusions, the dysregulation of LTF and TLR2 in the ocular surface of KC patients contributes to KC severity by maintaining a detrimental chronic immune−inflammatory state. The immunomodulatory properties of LTF on TLR2 expression suggest its potential as a therapeutic approach for KC.

Anterior segment characteristics in normal and keratoconus eyes evaluated with a new type of swept-source optical coherence tomography

PURPOSE

This study aimed to evaluate and compare the discriminating ability of corneal elevation maps generated using a swept-source optical coherence tomography (SS-OCT) (SS-OCT ANTERION, Heidelberg Engineering, Heidelberg, Germany), which was estimated with different reference surfaces, to distinguish normal corneas from those with keratoconus and keratoconus suspect.

METHODS

A total of 126 eyes of patients, which comprised 43, 37, and 46 keratoconus, keratoconus suspects, and normal controls, respectively, were included in this study. The anterior and posterior elevations at the thinnest point under the best-fit sphere (BFS) and toric-ellipsoid (BFT), respectively, and other corneal parameters were measured using the SS-OCT. In addition, the receiver operating characteristic (ROC) curve analysis and cut-off value were calculated to evaluate the diagnostic ability of the corneal elevation values in differentiating keratoconus and keratoconus suspects from normal eyes.

RESULTS

The mean total keratometric and corneal elevation values were significantly higher in the keratoconus group than in the other groups. Pachymetric parameters exhibited the lowest values for keratoconus. In addition, ROC curve analyses showed a high accuracy of the thinnest point anterior and posterior BFT for both keratoconus and keratoconus suspects and normal controls (area under the ROC were 0.969 and 0.961, respectively). Furthermore, the optimal cut-off point of the posterior elevation at the thinnest point under BFT was 16.44 μm (sensitivity and specificity of 86% and 98%, respectively) for differentiating keratoconus from normal and keratoconus suspect eyes.

CONCLUSIONS

The elevation map using the BFS and BFT references measured with the anterior segment SS-OCT is considered an effective indicator for keratoconus diagnosis. Therefore, the anterior segment SS-OCT can effectively differentiate keratoconus from suspected keratoconus and normal corneas by measuring parameters such as posterior and anterior elevations, pachymetry, and keratometry.

Posterior corneal elevation changes and characteristic analysis 1 year after corneal collagen cross-linking for keratoconus

PURPOSE

To investigate the changes in posterior corneal elevations (PCEs) in the circular areas and local points after corneal collagen cross-linking (CXL) for the treatment of keratoconus.

METHODS

Method 1 divided the cornea into 0-2, 2-4, 4-6, and 6-8 mm regions centering on the apex. Method 2 obtained other 34 PCE values of local point that were identified on the nasal, supra-nasal, sub-nasal, superior, inferior, temporal, supra-temporal, and sub-temporal sides of the circle with diameters of 2, 4, 6, and 8 mm, and the apex and thinnest point.

RESULTS

Method 1 showed a forward displacement of PCE at 1 month after CXL and then a backward displacement at 3 months. In Method 2, the points on the temporal side of 2 mm and 4 mm showed the same trend. The backward displacements of PCE on the temporal side of 2 mm at 6 months and on the temporal side of 4 mm at 12 months after CXL were both statistically different than those at 1 month after CXL (P < 0.05). No significant forward displacement of PCE was found in all local points in different quadrants at 1 year after CXL.

CONCLUSION

The PCEs in circular areas and characteristic points of different diameters in keratoconic eyes after CXL change with time. Local point assessment of the PCE is more clinically significant. In points selected in different quadrants of the cornea, the change in temporal points was more significant after CXL.

The utility of measures of anterior segment parameters of a Pentacam Scheimpflug tomographer in discriminating high myopic astigmatism from keratoconus

The study aimed to evaluate and compare anterior segment parameters between keratoconic eyes and eyes with high myopic astigmatism using Pentacam Scheimpflug tomography. This was a retrospective cross-sectional study that included sixty keratoconic eyes (thirty-two persons) and seventy-three eyes (forty-six persons) with high myopic astigmatism with mean ages 24.72 ± 11.65years and 26.60 ± 10.69years, respectively. Twenty-three parameters from the topographic map and fifteen parameters from the Belin-Ambrosió enhanced ectasia display map of the printouts of a Scheimpflug principle-based Pentacam tomographer were evaluated for their diagnostic accuracy using Receiver Operating Characteristic (ROC) curve. All parameters except cornea volume, anterior chamber volume, and anterior chamber angle indicated a significant difference between high myopic astigmatism and keratoconic eyes. The area under the receiver operating characteristic (AUROC) of eighteen Pentacam parameters was excellent (0.9–1.0) in discriminating keratoconus from high myopic astigmatism, out of which four {anterior minimum sagittal curvature (ant. Rmin), posterior minimum sagittal curvature (post. Rmin), maximum Ambrosió relational thickness (ART max) and total deviation value (D)} indicated excellent (>90%) sensitivity and specificity in addition to the excellent AUROC values. Topographic and Belin-Ambrosió enhanced ectasia display (BAD) maps of a Scheimpflug principle-based Pentacam tomographer are useful in enhancing the diagnosis of keratoconus and may also provide valuable information in effectively screening for keratoconus cases among refractive surgery candidates with high myopic astigmatism.

Keratoconus enlargement as a predictor of keratoconus progression

Numerous approaches have been designated to document progression in keratoconus, nevertheless there is no consistent or clear definition of ectasia progression. In this present study, we aim to evaluate Keratoconus Enlargement (KCE) as a parameter to document ectasia progression. We define KCE as an increase of more than 1D in the anterior curvature of non-apical corneal areas. We have designed a longitudinal study in 113 keratoconic eyes to assess keratoconus progression. KCE was compared with variables commonly used for detection of keratoconus progression like Kmax, Km, K2, PachyMin, D-Index, Corneal Astigmatism and PRC of 3.0 mm centered on the thinnest point. The variations of keratometric readings, D-index and ELEBmax showed positive associations with KCE. Evaluating the performance of Kmax, D-index and KCE as isolated parameters to document keratoconus progression we found a sensitivity of 49%, 82% and 77% and a specificity of 100%, 95% and 66% to detect keratoconus progression (p < 0.001 for all). This difference in sensitivity can be explained by the changes in keratoconus outside the small area represented by Kmax. The inclusion of KCE should be considered in the evaluation of keratoconus progression in conjunction with other variables to increase the reliability of our clinical evaluation.

Keratoconus Indices and their Determinants in Healthy Eyes of a Rural Population

Purpose:

To determine the distribution of keratoconus indices in a 5-93-year-old healthy eyes of a rural population in Iran.

Methods:

In this cross-sectional study, multi-stage cluster sampling was applied to select subjects from two villages in the north and southwest of Iran. After obtaining informed consent, all subjects underwent ophthalmologic and optometric examinations. Corneal imaging by the Pentacam was done in subjects above 5 years between 9 a.m. and 2 p.m., at least 3 h after wakeup. All subjects who had abnormal keratoconus indices were excluded. Our main outcome was keratometry-flat (K_f), keratometry-steep (K_s), keratoconus index (KI), and central keratoconus index (CKI).

Results:

The mean ± standard deviation of K_f, K_s, KI, and CKI was 43.12 ± 1.74, 44.25 ± 1.65, 1.02 ± 0.02, and 1.01 ± 0.01, respectively. According to multiple linear regression analysis, the mean index surface variance (ISV) (b: -1.367, P < 0.001), index vertical asymmetry (IVA) (b: -0.012, P < 0.001), KI (b: -0.011, P < 0.001), CKI (b: -0.001, P < 0.001), index height asymmetry (IHA) (b: -0.491, P: 0.005), and index height decentration (IHD) (b: -0.001, P < 0.001) were lower in men compared to women. Moreover, age had an indirect association with ISV (b: -0.030, P < 0.001) and average pachymetric progression index (RPI_avg) (b: -0.001, P < 0.001), and a direct association with KI, CKI, and IHA. Spherical equivalence had an indirect association with KI (b: -0.001, P < 0.001) and RPI_avg (b: -0.004, P < 0.001) and a direct association with CKI (b: 0.001, P < 0.001). Among all variables, sex had the greatest impact on ISV, IVA, KI, IHA, IHD, and minimum sagittal curvature.

Conclusions:

The Keratoconus indices of our study were similar to other studies. Although age, living place, and type of refractive error were associated with some indices, sex was the strongest determinant of Keratoconus indices in a population of healthy eyes.

Corneal and conjunctival alteration of innate immune expression in first-degree relatives of keratoconus patients

PURPOSE

The innate immune toll-like receptors 2 (TLR2) and 4 (TLR4) may play a key role in the physiopathology of keratoconus (KC). Therefore, the aim of this study was to compare TLR2/TLR4 expression in corneal and conjunctival epithelial cells between healthy first-degree relatives of patients with KC and healthy controls as well as KC patients.

METHODS

Case-control study in 72 healthy eyes of 36 control subjects, 53 eyes of 27 first-degree relatives, and 109 eyes with KC (60 patients). All participants were subjected to a clinical, topographic, aberrometric, and tomographic examination with extraction of corneal and conjunctival epithelial cells through scraping. TLR2/TLR4 expression was measured by flow cytometry, and was compared among controls, first-degree relatives, and KC patients. The relationship between TLR expression and epidemiological-clinical variables or topographic-aberrometric-tomographic parameters was also analyzed.

RESULTS

Mean TLR2/TLR4 expression showed a significant gradual increase among groups: controls < first-degree relatives < KC patients. Mean expression of TLR2 in corneal epithelial cells and both TLR2/TLR4 in conjunctival epithelial cells were significantly higher in relatives than in controls (p = 0.026, p < 0.001, and p = 0.031, respectively). Sex, age, allergic disease, eye itching, rubbing, and topographic-aberrometric-tomographic parameters were not associated to TLR2/TLR4 expression in relatives. TLR2 conjunctival expression was independently associated to relatives (OR 1.001; CI 95% 1.000-1.002, p = 0.043) after adjustment by sex, age, and rubbing.

CONCLUSION

TLR2 and TLR4 are overexpressed in corneal and conjunctival epithelial cells of KC relatives compared with controls. Both biomarkers may monitor early ocular changes in first-degree relatives who not show any abnormal clinical-topographic-aberrometric-tomographic parameters.

Sensitivity and Specificity of Belin Ambrosio Enhanced Ectasia Display in Early Diagnosis of Keratoconus

Purpose

Early diagnosis of keratoconus disease (KCN) is the first priority in the preoperative evaluations of refractive surgery (RS).The aim of this study was to investigate the correlation between findings of Belin Ambrosio enhanced ectasia display (BAD) software and conventional corneal imaging (Orbscan and topography) in the early diagnosis of KCN.

Methods

For conducting this cross-sectional study, a total of 1000 eyes were selected from 500 patients that underwent the myopic photorefractive keratectomy surgery and were compared in four study groups during the years 2017-2018. In group 1, all topography, Orbscan, and BAD criteria were normal (65.8%).In contrast, in Group 2, at least one of the topography or Orbscan criteria as well as at least one BAD criterion (12.6%) were abnormal. In Group 3, the eyes had normal Orbscan and topography criteria with at least one abnormal BAD criterion (18.5%). Also, in Group 4, the patients had at least one abnormal Orbscan or topography criterion, but all BAD criteria (3.1%) were normal. Thickness of the thinnest point (TP) of cornea was compared in Pentacam and topography. Data analysis was done by SPSS software (version 21).

Results

BAD criteria were normal in 78.5% of all eyes with normal topography and Orbscan criteria (specificity). BAD criteria were also abnormal in 80.2% of eyes (sensitivity). There was also no significant difference between TP in Orbscan and Pentacam.

Conclusions

BAD criteria had a relatively acceptable sensitivity and specificity, compared with conventional Orbscan and topography criteria. Thus, BAD criteria can be more effective in the early diagnosis of KCN.

Toll-like receptors as diagnostic targets in pellucid marginal degeneration

The main purpose of this study is to evaluate the diagnostic role of Toll-like receptors 2 (TLR2) and 4 (TLR4) expression in corneal and conjunctival epithelial cells of eyes with pellucid marginal degeneration (PMD) compared to keratoconus patients (KC) and control subjects. A prospective case-control study in 29 PMD eyes, 109 KC eyes and 72 healthy eyes was done. All participants were subjected to a clinical, topographic, aberrometric and tomographic exam with extraction of corneal and conjunctival epithelial cells through scraping. The TLR2 and TLR4 expression was measured with flow cytometry. Receiver operating characteristic (ROC) curve analysis was used to determine the most appropriate cutoff point for predicting the risk of PMD and KC. Correlations between TLR2/TLR4 expression and the severity of PMD/KC were evaluated. A TLRs follow-up review was made 19 ± 4 months after to the first review. As result, mean expression of TLR2 and TLR4 in both corneal and conjunctival epithelial cells was significantly higher in eyes with corneal ectasia (PMD and KC) than in control eyes (all p < 0.05). Conjunctival TLR4 expression showed the highest capacity to diagnose the existence of PMD (odd ratio 42.84; 95% confidence interval:6.20-296.20; p < 0.0001) after adjusting by eye rubbing and steeper corneal meridian. Moreover, we found an association between the TLR2/TLR4 overexpression with the severity of the PMD and KC measured by corneal topographic, aberrometric and tomographic quantitative parameters (all p < 0.05). Differences on TLR2/TLR4 expression between study groups were maintained during the follow-up period. In conclusion, the TLR2/TLR4 overexpression in corneal and conjunctival epithelial cells of PMD and KC patients compared to healthy control subjects have demonstrated their role as diagnostic target in both corneal ectatic disorders.

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

Purpose

To evaluate the diagnostic ability of the ratio of anterior and posterior corneal surface areas (As/Ps) comparing with other keratoconus screening indices in distinguishing forme fruste keratoconus (FFKC) from normal eyes.

Methods

In this comparative study, 13 eyes of 13 patients with FFKC, 29 eyes of 29 patients with keratoconus (KC) and 88 eyes of 88 patients with normal subjects were involved.

The As/Ps measured by the anterior segment optical coherence tomography (AS-OCT) and other indices measured by AS-OCT and rotating Scheimpflug–based corneal tomography were evaluated. The area under receiver-operating-characteristics (AU-ROC) was calculated to assess the diagnostic ability in discriminating FFKC from normal eyes.

Results

The As/Ps, the Belin/Ambrosio display enhanced ectasia total derivation value (BAD-D) and posterior and anterior elevation values showed the AU-ROC 0.9 or more in differentiating FFKC from normal eyes (0.980, 0.951, 0.924 and 0.903, respectively). The sensitivity and specificity were 0.92 and 0.96 for the As/Ps, 1.00 and 0.90 for BAD-D, 0.85 and 0.86 for posterior elevation value, and 0.85 and 0.96 for anterior elevation value, respectively.

Conclusions

Among the several indices for keratoconus screening which we evaluated, the As/Ps obtained by AS-OCT had the large AU-ROC with high sensitivity and specificity in detecting FFKC, which was comparable with BAD-D obtained by rotating Scheimpflug–based corneal tomography. The As/Ps may provide information for improving the diagnostic accuracy of KC, even in the initial stage of the disease.

Keratoconus detection using deep learning of colour-coded maps with anterior segment optical coherence tomography: a diagnostic accuracy study

OBJECTIVE

To evaluate the diagnostic accuracy of keratoconus using deep learning of the colour-coded maps measured with the swept-source anterior segment optical coherence tomography (AS-OCT).

DESIGN

A diagnostic accuracy study.

SETTING

A single-centre study.

PARTICIPANTS

A total of 304 keratoconic eyes (grade 1 (108 eyes), 2 (75 eyes), 3 (42 eyes) and 4 (79 eyes)) according to the Amsler-Krumeich classification, and 239 age-matched healthy eyes.

MAIN OUTCOME MEASURES

The diagnostic accuracy of keratoconus using deep learning of six colour-coded maps (anterior elevation, anterior curvature, posterior elevation, posterior curvature, total refractive power and pachymetry map).

RESULTS

Deep learning of the arithmetical mean output data of these six maps showed an accuracy of 0.991 in discriminating between normal and keratoconic eyes. For single map analysis, posterior elevation map (0.993) showed the highest accuracy, followed by posterior curvature map (0.991), anterior elevation map (0.983), corneal pachymetry map (0.982), total refractive power map (0.978) and anterior curvature map (0.976), in discriminating between normal and keratoconic eyes. This deep learning also showed an accuracy of 0.874 in classifying the stage of the disease. Posterior curvature map (0.869) showed the highest accuracy, followed by corneal pachymetry map (0.845), anterior curvature map (0.836), total refractive power map (0.836), posterior elevation map (0.829) and anterior elevation map (0.820), in classifying the stage.

CONCLUSIONS

Deep learning using the colour-coded maps obtained by the AS-OCT effectively discriminates keratoconus from normal corneas, and furthermore classifies the grade of the disease. It is suggested that this will become an aid for improving the diagnostic accuracy of keratoconus in daily practice.

CLINICAL TRIAL REGISTRATION NUMBER

000034587.

Three-year follow-up of intrastromal corneal ring segment implantation in central keratoconus with regular astigmatism: ‘Bow-tie’ shape

Purpose:

To assess the outcomes of implanting Ferrara-type intrastromal corneal ring segments in central ‘bow-tie’-shaped keratoconus over 3 years of follow-up.

Methods:

A total of 20 eyes with central ‘bow-tie’-shaped keratoconus were evaluated before and after implanting Ferrara-type intrastromal corneal ring segments (AJL Ophthalmic, Spain). LogMAR uncorrected distance visual acuity and best corrected distance visual acuity and residual refractive errors analysed using vector analysis were recorded preoperatively, at 6 months, 1 year, and 3 years postoperatively.

Results:

The mean uncorrected distance visual acuity (LogMAR scale) rose from a preoperative 0.75 ± 0.28 to a 6-month postoperative 0.38 ± 0.28 (p < 0.0001). The corrected distance visual acuity, in turn, improved from 0.07 ± 0.06 to 0.05 ± 0.06 (p = 0.0008). Both the uncorrected distance visual acuity and corrected distance visual acuity were stable over the postoperative period in both groups (p > 0.05). None of the eyes lost uncorrected distance visual acuity and corrected distance visual acuity lines over the postoperative follow-up period. The spherical equivalent and the refractive cylinder declined steeply after intrastromal corneal ring segments implantation (p < 0.0001). Both the spherical equivalent and refractive cylinder were stable over the postoperative period. None of the eyes had an increase in maximum or minimum keratometry greater than 0.75D over the postoperative period.

Conclusion:

The planning for intrastromal corneal ring segments insertion proposed in this study reduces the spherical equivalent and refractive cylinder in this type of keratoconus, while improving post-surgery uncorrected distance visual acuity and corrected distance visual acuity. These results remain stable over 3 years of follow-up. Therefore, this procedure could be considered as an effective therapeutic alternative in patients affected by this type of keratoconus.

Pentacam Accuracy in Discriminating Keratoconus From Normal Corneas: A Diagnostic Evaluation Study

OBJECTIVES

This study aims to determine the diagnostic ability of Pentacam indices for keratoconus and identifying the best index for differentiating diseased from normal cases.

METHOD

In this study, 150 keratoconus patients and 150 refractive surgery candidates with a definitive diagnosis of normal healthy corneas were enrolled. Initially, the placido disk topography imaging was performed. The keratoconus and normal corneas were defined based on placido disk topographic data from Rabinowitz-McDonnell. After complete eye examinations for all participants, they underwent Pentacam imaging, and corneal surface topographic indices were extracted. Multiple logistic regression was used to determine the best indices for differentiating diseased from healthy corneas, and the receiver operating curve was calculated to determine the diagnostic capability of each index.

RESULTS

Among the studied indices, the keratoconus index (KI), index of vertical asymmetry (IVA), thinnest point (TP), and maximum keratometry (Kmax) were found capable of detecting keratoconus. Among these, IVA was the best index, with an area under curve (AUC) of 95.24%. The best cutoff point for IVA was 0.20 μm, and its sensitivity and specificity were 87.50% and 96.30%, respectively. Comparison of the AUC of different indices showed that only TP and IVA significantly differed (P=0.002). The combination of KI, IVA, Kmax, and TP indices leads to correct detection in 78% of cases.

CONCLUSION

Measuring corneal topographic indices using Pentacam can be helpful in the diagnosis of keratoconus. According to the results of this study, IVA is the best diagnostic index for keratoconus. However, it is recommended to use a combination of Pentacam indices for more accurate differentiation of keratoconus from normal cases.

Involvement of anterior and posterior corneal surface area imbalance in the pathological change of keratoconus

Keratoconus (KC) is an ectatic disorder with a high prevalence rate. However, the exact cause of the disease and possible underlying mechanisms of development remain unclear. In this present study, we aimed to investigate the anterior and the posterior corneal surface area in normal, forme fruste keratoconus (FFKC), and keratoconic eyes (as a reference group) using anterior segment optical coherence tomography (AS-OCT) in order to assess the pathological change of KC. The surface areas of the anterior or posterior cornea, and the anterior-posterior (As/Ps) ratio of corneal surface area, were measured at the central 5.0 mm-, 6.0 mm-, and 7.0 mm-diameter areas via AS-OCT, and a comparison between the normal eyes and FFKC eyes was then performed using the Mann-Whitney U test. The posterior surface area at the central 5.0 mm areas in the FFKC eyes (20.430 mm²) and KC eyes (20.917 mm²) seemed to become larger than that of normal eyes (20.389 mm²) (normal vs FFKC; P = 0.06). Moreover, the As/Ps of the corneal surface area in the FFKC eyes (0.986) and the KC eyes (0.976) was significantly smaller than that of the normal eyes (0.988) (normal vs FFKC; P < 0.01). Anterior and posterior corneal surface area imbalance may reflect keratoconic eyes at the early stage of the disease.

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

Objectives

To evaluate tomographic and topographic parameters in subclinical and clinical keratoconus eyes by comparing them with normal eyes in a young Caucasian population.

Materials and Methods

This cross-sectional study included 88 normal eyes (control group), bilateral data from the preclinical stage of 24 progressive keratoconus eyes (bilateral subclinical keratoconus group), 40 fellow eyes of patients with unilateral keratoconus (fellow eyes group) and 97 eyes with mild keratoconus (clinical keratoconus group). Topographic and tomographic data, data from enhanced elevation maps and keratoconus indices were measured in all study eyes using Scheimpflug tomography. Receiver operating characteristic (ROC) curve analysis was used to assess individual parameters to discriminate eyes of patients with subclinical and clinical keratoconus from control eyes. The sensitivity and specificity of the main effective parameters were evaluated and optimal cut-off points were identified to differentiate subclinical keratoconus and keratoconus from normal corneas.

Results

Comparison of all subclinical and clinical keratoconus eyes from the normal group revealed significant differences in most diagnostic parameters. The ROC curve analysis showed high overall predictive accuracy of several Pentacam parameters (overall D value, anterior and posterior elevations and difference elevations, pachymetry progression index, index of surface variance, index of height decentration and keratoconus index) in discriminating ectatic corneas from normal ones. These outcomes were proportionally less pronounced in all subclinical keratoconus eyes than in the clinical keratoconus eyes. Pachymetric readings were progressively lower in the bilateral subclinical keratoconus eyes and sensitivity and specificity of the analyzed tomographic and topographic parameters were higher than the fellow eyes group when differentiating subclinical keratoconus from healthy corneas.

Conclusion

Scheimpflug tomography parameters such as D value, elevation parameters, progression index and several surface indices can effectively differentiate keratoconus from normal corneas in a Caucasian population. Nevertheless, a combination of different data is required to distinguish subclinical keratoconus.

Clinical Outcomes of Sequential Intrastromal Corneal Ring Segments and an Extended Range of Vision Intraocular Lens Implantation in Patients with Keratoconus and Cataract

Purpose

To evaluate efficacy, safety, and predictability of sequential Ferrara-type intrastromal corneal ring segments (ICRS) and an extended range of vision intraocular lens (IOL) implantation in patients with keratoconus and cataract.

Methods

This study comprised patients with keratoconus and cataract that had ICRS implantation followed 6 months later by extended range of vision IOL implantation. The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and residual refractive errors, analysed using vector analysis, were recorded preoperatively, 6 months after ICRS implantation, and 6 months after IOL implantation, respectively.

Results

The study enrolled 17 eyes (11 patients). The mean UDVA (logMAR scale) was 1.15 ± 0.67 preoperatively, 0.88 ± 0.69 six months after ICRS implantation (P = 0.005), and 0.27 ± 0.18 six months after IOL implantation (P < 0.0001). The CDVA changed from 0.26 ± 0.15 (logMAR) before surgery to 0.17 ± 0.08 six months after Ferrara-type ICRS implantation (P = 0.002) and to 0.07 ± 0.06 six months after IOL implantation (P < 0.0001). The spherical equivalent and the refractive cylinder declined steeply after IOL implantation (P < 0.001). The magnitude of depth of focus was 2.60 ± 1.02 D. There were no statistically significant differences in visual acuity for a defocus range from +0.50 D to −0.50 D (P > 0.1).

Conclusion

Sequential Ferrara-type ICRS and an extended range of vision IOL implantation provided good visual and refractive outcomes, being an effective, safe, and predictable procedure for the treatment of selected cases of patients with keratoconus and cataract. In addition, this approach provides an increase of tolerance to defocus.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Scanning-slit topography in patients with keratoconus

AIM

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.

METHODS

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.

RESULTS

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).

CONCLUSION

The results suggest that scanning-slit topography and pachymetry are accurate methods both for keratoconus screening and for confirmation of the diagnosis.

Identifying more reliable parameters for the detection of change during the follow-up of mild to moderate keratoconus patients

Background

Reaching a consensus on which parameters are most reliable at detecting progressive keratoconus patients with serial topography imaging is not evident. The aim of the study was to isolate the parameters best positioned to detect keratoconus progression using the Pentacam HR® measures based on the respective limits of repeatability and range of measurement.

Method

Using the Pentacam HR®, a tolerance index was calculated on anterior segment parameters in healthy and keratoconic eyes. The tolerance index provides a scale from least to most affected parameters in terms of measurement noise relative to that observed in healthy eyes. Then, based on the "number of increments" from no disease to advanced disease, a relative utility (RU) score was also calculated. RU values close to 1 indicate parameters best positioned to detect a change in keratoconic eyes.

Results

The tolerance index values indicated that 36% of ocular parameters for keratoconic eyes had repeatability limits which were wider than normative limits (worse), but 28% of the ocular parameters were narrower than normative limits (better). Considering only those parameters with a RU greater than 0.95, a small number of parameters were within this range, such as corneal curvature and asphericity indices.

Conclusions

This study demonstrates that measurement error in keratoconic eyes is significantly greater than healthy eyes. Indices implemented here provide guidance on the levels of expected precision in keratoconic eyes relative to healthy eyes to aid clinicians in distinguishing real change from noise. Importantly maximal keratometry (Kmax), central corneal thickness (CCT) and thinnest corneal thickness (TCT) were highlighted as problematic indices for the follow-up of keratoconus in terms of repeatability.

Long-Term Follow-Up of Intrastromal Corneal Ring Segments in Paracentral Keratoconus with Coincident Corneal Keratometric, Comatic, and Refractive Axes: Stability of the Procedure

Purpose

To assess the long-term outcomes of implanting intrastromal corneal ring segments (ICRS) in paracentral keratoconic eyes.

Methods

58 eyes with paracentral keratoconus with coincident refractive, keratometric, and comatic axes were evaluated. Uncorrected (UDVA) and corrected (CDVA) distance visual acuity and refractive errors were recorded before and at all follow-up visits. The postoperative follow-up was 5 years. Patients were divided into two groups: group I (30 years old or younger) and group II (more than 30 years old).

Results

The mean UDVA (logMAR) rose from a preoperative 0.83 ± 0.31 to a five-year postoperative 0.42 ± 0.33 (P < 0.0001). The mean CDVA varied from 0.16 ± 0.17 to 0.11 ± 0.18 (P = 0.0003). Both the UDVA and CDVA were stable over the postoperative period in both groups (P > 0.05). The spherical equivalent and the refractive cylinder declined steeply after ICRS implantation in both groups (P < 0.001), and were stable over the postoperative period (P > 0.05). The keratometric values were also stable over the postoperative follow-up.

Conclusion

Ferrara-type ICRS implantation in keratoconus that meets the characteristics of the sample under study reduces the refractive error at the same time as it improves postoperative UDVA and CDVA six months after surgery and that these results remain stable over five years of follow-up.

Assessing Progression of Keratoconus and Cross-linking Efficacy: The Belin ABCD Progression Display

Several methods have been described to both evaluate and document progression in keratoconus and to show efficacy of cross-linking, however, there are no consistent generally accepted parameters. Modern corneal tomography, including both anterior and posterior elevation and pachymetric data can be used to screen for ectatic progression, be employed to detect earlier change and additionally to show efficacy of new treatment modalities, such as crosslinking.

To describe specific quantitative values that can be used as progression and efficacy determinants, the normal noise measurements of the three parameters used in the ABCD keratoconus classification (corneal thickness at the thinnest point, anterior and posterior radius of curvature taken from the 3.0 mm optical zone centered on the thinnest point), were determined. Values were obtained from both a normal population and a known keratoconic population. The 80 and 95% one-sided confidence intervals for all three parameters were surprisingly small, suggesting that they may perform well as progression and efficacy determinants.

How to cite this article

Belin MW, Meyer JJ, Duncan JK, Gelman R, Borgstrom M, Ambrósio Jr R. Assessing Progression of Keratoconus and Cross-linking Efficacy: The Belin ABCD Progression Display. Int J Kerat Ect Cor Dis 2017;6(1):1-10.

Corneo-scleral contact lenses in an uncommon case of keratoconus with high hyperopia and astigmatism

PURPOSE

To analyse the visual quality achieved by fitting corneo-scleral contact lenses (CScL) in an uncommon case of bilateral keratoconus, high hyperopia and astigmatism.

METHODS

A 45-year-old man presented for eye examination due to the unsatisfactory quality of his vision wearing soft toric contact lenses. He presented high hyperopia and astigmatism with bilateral keratoconus. He was fitted with CScL to correct his irregular astigmatism and ocular aberrations. A diagnostic trial set was used in the fitting process and he was assessed according to standardised fitting methodology. Visual acuity, corneal topography, biometry and ocular aberrations were evaluated. The follow-up period was 1year.

RESULTS

The best spectacle-corrected visual acuity was 20/32 with +8.00/-4.50×30° for the right eye (RE) and 20/25 with +7.75/-2.25×120° for the left eye (LE). After CScL fitting, visual acuity was improved to 20/20 and 20/16 for the RE and LE, respectively. The patient wore these contact lenses an average of 13h a day. The total high order aberrations decreased by approximately 79% in the RE (2.37-0.50μm) and 47% in the LE (1.04-0.55μm) after CScL fitting. Visual quality and wearing time were maintained after 1year wearing CScL. In addition, no adverse ocular effects were found during this period.

CONCLUSION

The present case report describes how the patient had CScL fitted successfully for management of keratoconus with high hyperopia and astigmatism. They provided optimal visual quality, along with prolonged use times and no adverse effects to the cornea.

Normative values and contralateral comparison of anterior chamber parameters measured by Pentacam and its correlation with corneal biomechanical factors

PURPOSE

To evaluate the normative values of anterior chamber parameters measured by Pentacam and corneal hysteresis (CH) and corneal resistance factor (CRF) measured by Ocular Response Analyzer (ORA) and their relationship.

METHODS

In an observational cross-sectional study, patients aged 18-35 years were included. Exclusion criteria were history of any intraocular or corneal disease, anomaly or surgery; hyperopic spherical refraction more than +3, and myopic spherical refraction less than -5.00 diopters (D) or cylindrical refraction more than 2.00 D. ORA was used to measure CH and CRF. Corneal volume (CV), anterior and posterior Q value (QA and QP), anterior and posterior elevation (AE and PE), central corneal thickness (CCT), corneal thinnest thickness (CTT), anterior chamber depth (ACD), anterior chamber volume (ACV) and anterior chamber angle (ACA) were measured with Pentacam.

RESULTS

This study evaluated 506 eyes of 253 cases (182 females) with a mean age of 28.43 ± 6.36 years. The average CH and CRF were 10.07 ± 1.61 and 10.33 ± 1.68 mmHg. CH and CRF were not correlated with PQ, AQ, AE and PE. CH and CRF were significantly correlated with CCT (r = 0.499, p < 0.0001 and r = 0.591, p < 0.0001 respectively), CTT (r = 0.469, p < 0.0001 and r = 0.593, p < 0.0001 respectively) and CV (r = 0.443, p < 0.0001 and r = 0.526, p < 0.0001 respectively).

CONCLUSION

A significant positive correlation was found between CH and CRF, and CCT, CTT and CV. This study also provided data about wide range normative values of corneal parameters.

Pupillary Offset in Keratoconus and its Relationship with Clinical and Topographical Features

PURPOSE

To evaluate the change in the location of pupillary center with corneal tomography in keratoconic patients, and determine the correlation of pupillary offset with clinical and topographical features of keratoconus.

METHODS

Ninety-one eyes of the 54 patients with keratoconus in different stages and 39 eyes of 39 refractive surgery candidates with normal corneas were included in our study. Ocular aberrations and the pupillary offset parameters (x-offset and y-offset) over a 5 mm (undilated) pupil were measured with a Sirius corneal tomographer. A correlation analysis among the pupillary offset parameters and the possible determinative variables (topographical and tomographical parameters, corneal aberrations and best corrected visual acuity) was performed.

RESULTS

The mean pupillary offset was significantly greater in the keratoconic eyes compared with the controls (p = 0.003), and the difference was mostly due to the y-offset (p = 0.03). There was no significant difference between the groups in the mean horizontal pupillary offset value (p = 0.07). Both the vertical and the total pupillary offset values correlated significantly (p < 0.0001) with the keratoconus stage (r = 0.58 and r = 0.51, respectively). They also correlated with the corneal aberrations, and negatively correlated with the visual acuity.

CONCLUSIONS

The pupillary offset seems to correlate with the clinical and topographic features of keratoconus. It may be important to quantify its magnitude and direction in order to ensure correct centralization of the corneal procedures.

Accuracy of machine learning classifiers using bilateral data from a Scheimpflug camera for identifying eyes with preclinical signs of keratoconus

PURPOSE

To describe the topographic and tomographic characteristics of normal fellow eyes of unilateral keratoconus cases and to evaluate the accuracy of machine learning classifiers in discriminating healthy corneas from the normal fellow corneas.

SETTING

Department of Ophthalmology, Semmelweis University, Budapest, Hungary.

DESIGN

Retrospective case-control study.

METHODS

Patients with bilateral keratoconus (keratoconus group), clinically and according to the keratoconus indices of the Pentacam HR Scheimpflug camera; normal fellow eyes of patients with unilateral keratoconus (fellow-eye group); and eyes of refractive surgery candidates (control group) were compared. Tomographic data, topographic data, and keratoconus indices were measured in both eyes using the Scheimpflug camera. Receiver operating characteristic (ROC) analysis was used to assess the performance of automated classifiers trained on bilateral data as well as individual parameters to discriminate fellow eyes of patients with keratoconus from control eyes.

RESULTS

Keratometry, elevation, and keratoconus indices values were significantly higher and pachymetry values were significantly lower in keratoconus eyes than in fellow eyes of unilateral keratoconus cases (P < .001). These fellow eyes had significantly higher keratometry, elevation, and keratoconus index values and significantly lower pachymetry values than control eyes (P < .001). Automated classifiers trained on bilateral data of index of height decentration had higher accuracy than the unilateral single parameter in discriminating fellow eyes of patients with keratoconus from control eyes (area under ROC 0.96 versus 0.88).

CONCLUSION

Automatic classifiers trained on bilateral data were better than single parameters in discriminating fellow eyes of patients with unilateral keratoconus with preclinical signs of keratoconus from normal eyes.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Correlation between visual function and refractive, topographic, pachymetric and aberrometric data in eyes with keratoconus

AIM

To analyze the relationship between two visual functions and refractive, topographic, pachymetric and aberrometric indicators in eyes with keratoconus.

METHODS

Corrected distance visual acuity (CDVA), and letter contrast sensitivity (CS) were correlated with refraction, corneal topography, pachymetry, and total corneal wavefront data prospectively in 71 eyes with keratoconus. The topographic indices assessed were simulated keratometry for the flattest and steepest meridians (SimK1 and SimK2), posterior steeper K (Ks), elevation value in best-fit sphere (BFS) maps, squared eccentricity (Є(2)), aspheric asymmetric index (AAI), pachymetry, thickness progression index (TPI), the amount of pachymetric decentralization (APD), and GalileiTM-keratoconus indices.

RESULTS

The mean CDVA (expressed as logMAR) were 0.25±0.21. The mean CS was 1.25±0.46. The spherical refraction correlated well with CDVA (r=-0.526, P<0.001). From topographic indices, SRI correlated with CS (r=-0.695), and IAI with CS (r=-0.672) (P<0.001 for all). Root mean square (RMS) was 4.3±1.81 µm, spherical aberration (SA) was -0.4±0.67 µm, vertical and horizontal coma were -2.1±1.47 and -0.4±0.72 µm. All wavefront data (except horizontal coma), AAI, Є(2) and maximum BFS correlated significantly with the visual function (P≤0.001 for all).

CONCLUSION

In this study, CS is more affected than CDVA as a visual function. The quantity and quality of vision is significantly correlated with well-known and new topographic indices. There is not a significant correlation between visual function and pachymetric parameters. The significantly correlated indices can be used in staging keratoconus and to follow the outcome of a treatment.

The distribution of orbscan indices in young population

Purpose

To determine the distribution of anterior eye biometry indices, such as keratometry pachymetry, anterior chamber depth (ACD), pupil diameter, and corneal diameter, as measured by Orbscan instrument in a young Iranian population.

Methods

A cross-sectional study was conducted, and subjects were selected through multistage cluster sampling from the students of Mashhad University of Medical Sciences. Objective and subjective refraction were performed followed by Orbscan imaging.

Results

A total of 1330 subjects were selected, 1121 of which participated in the study. After applying the exclusion criteria, the final analysis was performed on the data of 1051 subjects. The mean age of the participants was 26.1 ± 3.2 years (19–34 years old). The mean ± SD and 95% confidence interval (CI) of maximum keratometry, minimum keratometry, pupil diameter, corneal diameter, ACD, and central corneal thickness was 44.5 ± 1.7 (44.4–44.6), 43.1 ± 1.6 (43.0–43.2), 4.3 ± 0.9 (4.3–4.4), 11.7 ± 0.4 (11.7–11.7), 3.7 ± 0.3 (3.6–3.7), and 550.5 ± 35 (548.4–552.6), respectively. After adjusting for age and the mean spherical equivalent (MSE), maximum keratometry, minimum keratometry, central corneal thickness, and the thinnest pachymetry were statistically significantly higher in female subjects (P < 0.001) whilst the corneal diameter and ACD were higher in male subjects (P < 0.001). The pupil diameter and ACD showed statistically significant changes with age (P < 0.001). The MSE was only correlated with maximum keratometry and ACD (P < 0.001).

Conclusion

In this study, the distribution of Orbscan measurements for the anterior segment parameters was reported in a large sample of the young Iranian population. Age, gender, and refractive error may affect the orbscan measurements.

A Novel scoring system for distinguishing keratoconus from normal eyes

PURPOSE

To evaluate the accuracy of a novel scoring system in differentiation of keratoconus (KC) eyes from normal eyes using a Scheimpflug camera system tomography.

SETTING

Marmara University Hospital, Istanbul, Turkey and Birinci Eye Hospital, Istanbul, Turkey.

DESIGN

Retrospective case-control study.

METHODS

The study included 624 keratoconus eyes and 512 healthy eyes. Thirty nine significant parameters obtained from the Scheimpflug imaging system (Pentacam-Oculus Optikgeräte GmbH, Wetzlar, Germany) were studied. The cut-off value and area under receiver operating characteristic (AUROC) curve analysis for each studied parameter were established in the previous study. Minus three and plus three standard deviations of the cut-off value were scored after multiplication of AUROC for each parameter. The sum of all scores (TKS; Total Keratoconus Score) was compared between keratoconus and normal eyes.

RESULTS

Average TKS value was -29.57±5.65 (Range from -43.11 to -7.09) in normal eyes and 36.23±24.3 (Range from -16.82 to 97.45) in keratoconus eyes (p<0.001). Receiver operating characteristic curve analyses showed perfect predictive accuracy for TKS (ROC 1.0 (95% CI: 0.999-1.0)). The TKS distinguished the keratoconus group from the normal group with 99% sensitivity and 99% specificity at the best cut-off point of -12.45.

CONCLUSIONS

The new scoring system measured by the Scheimpflug imaging system provides perfect discrimination of keratoconus from normal corneas.

Comparison between corneal elevation maps using different reference surfaces with Scheimpflug-Placido topographer

The purpose of this study was to compare the anterior and posterior elevation measurements using different reference surfaces (spheric, aspheric, and aspherotoric) with Scheimpflug-Placido topography in simple myopic and keratoconus patients. 600 eyes of 600 patients undergoing screening for keratorefractive surgery (500 simple myopic, 100 keratoconus stage 1 and 2) in Sohag refractive center, Egypt, were examined by Scheimpflug-Placido topography (Sirius, CSO, Italy) for both the anterior and posterior corneal elevation maps using the spheric, aspheric, and aspherotoric reference surfaces. 100 keratoconic eyes showed higher discriminating power using the aspherotoric reference surface in both the anterior and posterior elevation maps. The use of aspherotoric reference surface gives more data for eyes with keratoconus and its use is more informative in screening.

Anterior segment characteristics in normal and keratoconus eyes evaluated with a combined Scheimpflug/Placido corneal imaging device

Purpose

To assess the anterior segment parameters of keratoconus (KC) eyes at different stages of the disease by a new Scheimpflug camera combined with Placido disk corneal topography (Sirius, CSO, Italy) in a sample of the Iranian population.

Methods

A total of 225 eyes of 225 individuals comprising 41 suspect KC, 40 mild KC, 71 moderate KC, 48 severe KC and 25 normal eyes were assessed for the following parameters: corneal thickness at the apex (CTA), thinnest corneal thickness (TCT), anterior chamber depth (ACD), corneal volume (CV), corneal keratometry (K), corneal asphericity (Q), and corneal elevation in the anterior and posterior surface. Also, the Zernike coefficients for the corneal aberrations including total root mean square (RMS), RMS Coma, RMS spherical aberration (SA), RMS Astigmatism, Baiocchi Calossi Versaci front index (BCV_f), and BCV back index (BCV_b) were noted for all eyes. Data was analyzed using analysis of variance (ANOVA) and post hoc Bonferroni test for comparison of the means of the five groups. P-value was considered significant if it was <0.05.

Results

The TCT, CTA and posterior corneal elevation were significantly different between all comparison groups (P < 0.05). ACD values showed inconsistent differences between groups. Mean value of CV in comparing normal eyes vs suspect KC group, normal eyes vs mild KC, and normal eyes vs moderate KC revealed statistically significant change (P < 0.05). Also, weak non-significant positive correlation was demonstrated between K and CV (r = 0.08). There were statistically significant differences in total RMS, RMS coma, BCV_f, and BCV_b for most groups (P < 0.05).

Conclusion

Posterior corneal elevation, corneal thickness and high order aberrations are important indices that need to be considered to diagnose different grades of keratoconus.

Predictive Ability of Galilei to Distinguish Subclinical Keratoconus and Keratoconus from Normal Corneas

Purpose:

To determine the predictive ability of different data measured by the Galilei dual Scheimpflug analyzer in differentiating subclinical keratoconus and keratoconus from normal corneas.

Methods:

This prospective comparative study included 136 normal eyes, 23 eyes with subclinical keratoconus, and 51 keratoconic eyes. In each eye, keratometric values, pachymetry, elevation parameters and surface indices were evaluated. Receiver operating characteristic (ROC) curves were calculated and quantified by using the area under the curve (AUC) to compare the sensitivity and specificity of the measured parameters and to identify optimal cutoff points for differenciating subclinical keratoconus and keratoconus from normal corneas. Several model structures including keratometric, pachymetric, elevation parameters and surface indices were analyzed to find the best model for distinguishing subclinical and clinical keratoconus. The data sets were also examined using the non-parametric “classification and regression tree” (CRT) technique for the three diagnostic groups.

Results:

Nearly all measured parameters were strong enough to distinguish keratoconus. However, only the radius of best fit sphere and keratometry readings had an acceptable predictive accuracy to differentiate subclinical keratoconus. Elevation parameters and surface indices were able to differentiate keratoconus from normal corneas in 100% of eyes. Meanwhile, none of the parameter sets could effectively discriminate subclinical keratoconus; a 3-factor model including keratometric variables, elevation data and surface indices provided the highest predictive ability for this purpose.

Conclusion:

Surface indices measured by the Galilei analyzer can effectively differentiate keratoconus from normal corneas. However, a combination of different data is required to distinguish subclinical keratoconus.

Comparison of Scheimpflug imaging parameters between steep and keratoconic corneas of Caucasian eyes

Purpose

To compare the keratometric and pachymetric parameters of healthy eyes with those affected by steep cornea and keratoconus (KC) using Scheimpflug camera.

Setting

Briz-L Eye Clinic, Baku, Azerbaijan.

Design

A cross-sectional study.

Methods

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.

Results

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).

Conclusion

Scheimpflug imaging is able to detect corneal morphological differences between stage 1 KC eyes and healthy eyes with steep cornea, in Caucasians.

Assessing progression of keratoconus: novel tomographic determinants

Several methods have been described in the literature to both evaluate and document progression in keratoconus, but there is no consistent or clear definition of ectasia progression. The authors describe how modern corneal tomography, including both anterior and posterior elevation and pachymetric data can be used to screen for ectatic progression, and how software programs such as the Enhanced Reference Surface and the Belin-Ambrosio Enhanced Ectasia Display (BAD) can be employed to detect earlier changes. Additionally, in order to describe specific quantitative values that can be used as progression determinants, the normal noise measurement of the three parameters (corneal thickness at the thinnest point, anterior and posterior radius of curvature (ARC, PRC) taken from the 3.0 mm optical zone centered on the thinnest point), was assessed. These values were obtained by imaging five normal patients using three different technicians on three separate days. The 95 % and 80 % one-sided confidence intervals for all three parameters were surprisingly small (7.88/4.03 μm for corneal thickness, 0.024/0.012 mm for ARC, and 0.083/0.042 mm for PRC), suggesting that they may perform well as progression determinants.

Variability of different reference bodies in normal, keratoconus, and collagen crosslinked corneas

PURPOSE

To evaluate the reproducibility of different Scheimpflug imaging-derived reference bodies in normal, keratoconus (KC), and crosslinked (CXL) eyes.

METHODS

In this prospective, observational study, 40 participants populated the control group (CG), while 33 and 34 patients formed the KC group and the CXL group, respectively. One eye was randomly selected when both were eligible. Elevation measurements were obtained using Scheimpflug camera, by applying the following reference bodies: the best fit sphere (BFS), the best fit toric ellipsoid (BFTE), the best fit toric ellipsoid with fixed eccentricity of 0.4 (BFTEF), the best fit ellipsoid (BFE), and the best fit torus, by 2 operators in 2 sessions. The variability of different reference bodies' parameters was assessed using intraclass correlation coefficient (ICC).

RESULTS

Differences between operators were nonsignificant for all reference bodies' parameters in all study groups (p&gt;0.1). Regarding CG, BFS for both operators and BFTE for operator 1 presented the best intrasession repeatability (majority of ICCs &gt;0.90), while average interobserver reliability was recorded for the majority of reference bodies' parameters. Regarding KC and CXL groups, BFS, BFTEF, and BFE reference bodies demonstrated the best intrasession and interobserver reproducibility (majority of ICCs &gt;0.90) for both groups. Steep and flat radius parameters presented the best overall reproducibility, with the majority of ICCs for all reference bodies ranging above 0.90, in all study groups.

CONCLUSIONS

High variability was encountered for most reference surfaces. Ellipsotoric surfaces presented acceptable repeatability in KC and post-CXL corneas.

Sensitivity and specificity of posterior and anterior corneal elevation measured by orbscan in diagnosis of clinical and subclinical keratoconus

PURPOSE

To determine the sensitivity and specificity of anterior and posterior corneal elevation parameters as determined by Orbscan II (Bausch and Lomb, Rochester, NY, USA) in discriminating between (sub) clinical keratoconus (KCN) and normal corneas.

METHODS

This prospective case-control study included 28 eyes with subclinical KCN, 65 with clinical KCN and 141 normal corneas. Anterior and posterior corneal elevation was measured and compared in the central 5-mm corneal zone using Orbscan II.

RESULTS

Receiver operating curves (ROC) curve analyses for posterior corneal elevation showed predictive accuracy in both KCN and subclinical KCN with an area under the curve (AUC) of 0.97 and 0.69, respectively while optimal cutoff points were 51 μm for KCN and 35 μm for subclinical KCN. These values were associated with sensitivity and specificity of 89.23% and 98.58%, respectively, for KCN; and 50.00% and 88.65% for subclinical KCN. ROC curve analyses for anterior corneal elevation showed predictive accuracy in both KCN and subclinical KCN with AUC of 0.97 and 0.69, respectively while optimal cutoff points were 19 μm for KCN and 16 μm for subclinical KCN. These values were associated with sensitivity and specificity of 93.85% and 97.16%, respectively, for KCN; and 60.71% and 87.94% for subclinical KCN.

CONCLUSION

Anterior and posterior corneal elevation data obtained by Orbscan II can well discriminate between KCN and normal corneas, however the reliability of their indices is lower in differentiating subclinical KCN from normal cases.

Correlation of the KISA% index and Scheimpflug tomography in 'normal', 'subclinical', 'keratoconus-suspect' and 'clinically manifest' keratoconus eyes

PURPOSE

To analyse tomographic changes in eyes classified as 'normal', 'keratoconus-suspect' and 'clinically manifest keratoconus' based on the established KISA% definition of Rabinowitz and Rasheed and to develop the category of 'subclinical keratoconus eyes' to expand the classification into a 'subtopographic' range.

METHODS

Tomographic and topographic analyses of 670 eyes performed with a rotating Scheimpflug imaging system (Pentacam(®), Oculus Inc., Wetzlar, Germany) were retrospectively analysed. Based on the KISA% keratoconus classification system, eyes were assigned to a 'normal', 'keratoconus-suspect' or 'manifest keratoconus' group. In addition, a new group of 'subclinical keratoconus eyes' was analysed, comprising unsuspicious fellow eyes of patients with keratoconus. T-tests, Wilcoxon rank-sum test, receiver operating characteristics (ROC) and robust regression analyses were performed to correlate tomographic parameters with the increasing KISA% index.

RESULTS

KISA%-grouped keratoconus eyes showed robust tomographic changes. By adding the subclinical group, although the concurrent topography was unchanged, we were able to demonstrate statistically significant changes for almost all tomographic parameters (parameters with highest sensitivity/specificity: ART_max, [0.69/0.69], BAD_D [0.66/0.66]). The highest coefficient of determination (R(2)) with the KISA% index was demonstrated for Ele_f_max (R(2) = 0.70), Ele_f_TP (R(2) = 0.69), Ele_b_TP (R(2) = 0.69) and BAD_D (R(2) = 0.68).

CONCLUSION

We recommend the use of the expanded KISA% index (eKISA% index) as the basis for the definition of keratoconus and normal groups in future keratoconus research projects.

Comparative analysis of anterior segment parameters in normal and keratoconus eyes generated by scheimpflug tomography

Purpose. To assess and compare the anterior and posterior corneal surface parameters, keratoconus indices, thickness profile data, and data from enhanced elevation maps of keratoconic and normal corneas with the Pentacam Scheimpflug corneal tomography and to determine the sensitivity and specificity of these parameters in discriminating keratoconus from normal eyes. Methods. The study included 656 keratoconus eyes and 515 healthy eyes with a mean age of 30.95 ± 9.25 and 32.90 ± 14.78 years, respectively. Forty parameters obtained from the Pentacam tomography were assessed by the receiver operating characteristic curve analysis for their efficiency. Results. Receiver operating characteristic curve analyses showed excellent predictive accuracy (area under the curve, ranging from 0.914 to 0.972) for 21 of the 40 parameters evaluated. Among all parameters indices of vertical asymmetry, keratoconus index, front elevation at thinnest location, back elevation at thinnest location, Ambrósio Relational Thickness (ARTmax), deviation of average pachymetric progression, deviation of ARTmax, and total deviation showed excellent (>90%) sensitivity and specificity in addition to excellent area under the receiver operating characteristic curve (AUROC). Conclusions. Parameters derived from the topometric and Belin-Ambrósio enhanced ectasia display maps very effectively discriminate keratoconus from normal corneas with excellent sensitivity and specificity.

Safety and Visual Outcome of Visian Toric ICL Implantation after Corneal Collagen Cross-Linking in Keratoconus: Up to 2 Years of Follow-Up

Purpose. To evaluate the long-term safety and clinical outcome of phakic Visian toric implantable collamer lens (ICL) insertion after corneal collagen cross-linking (CXL) in progressive keratoconus. Methods. This was a retrospective study of 30 eyes (19 patients), with progressive keratoconus, who underwent sequential CXL followed by Visian toric ICL implantation after 6 months. Results. At baseline, 6 eyes had stage I, 14 eyes stage II, and 10 eyes stage III keratoconus graded by Amsler-Krumeich classification. At 6 months after CXL, only K (steep) and K (max) decreased significantly from baseline, with no change in visual acuity or refraction. Flattening in keratometric readings was stable thereafter. There was significant improvement in mean uncorrected distance visual acuity (1.57 ± 0.56 to 0.17 ± 0.06 logMAR, P < 0.001) and mean corrected distance visual acuity (0.17 ± 0.08 to 0.11 ± 0.05 logMAR, P < 0.001) at 12 months after ICL implantation that was maintained at the 2-year follow-up. Mean cylinder power and mean spherical equivalent (SE) also decreased significantly after ICL implantation. A small hyperopic shift in SE (+0.25 D) was observed at 2 years that did not alter visual outcomes. Conclusions. Visian toric ICL implantation following CXL is an effective option for improving visual acuity in patients with keratoconus up to 2 years.

Non-topography-guided PRK combined with CXL for the correction of refractive errors in patients with early stage keratoconus

PURPOSE

To evaluate the safety and clinical outcome of combined non-topography-guided photorefractive keratectomy (PRK) and corneal collagen cross-linking (CXL) for the treatment of mild refractive errors in patients with early stage keratoconus.

METHODS

A retrospective, nonrandomized study of patients with early stage keratoconus (stage 1 or 2) who underwent simultaneous non-topography-guided PRK and CXL. All patients had at least 2 years of follow-up. Data were collected preoperatively and postoperatively at the 6-month, 1-year, and 2-year follow-up visit after combined non-topography-guided PRK and CXL.

RESULTS

Seventy-nine patients (140 eyes) were included in the study. Combined non-topography-guided PRK and CXL induced a significant improvement in both visual acuity and refraction. Uncorrected distance visual acuity significantly improved from 0.39 ± 0.22 logMAR before combined non-topography-guided PRK and CXL to 0.12 ± 0.14 logMAR at the last follow-up visit (P <.001) and corrected distance visual acuity remained stable (0.035 ± 0.062 logMAR preoperatively vs 0.036 ± 0.058 logMAR postoperatively, P =.79). The mean spherical equivalent decreased from -1.78 ± 1.43 to -0.42 ± 0.60 diopters (D) (P <.001), and the mean cylinder decreased from 1.47 ± 1.10 to 0.83 ± 0.55 D (P <.001). At the last follow-up visit mean keratometry flat was 43.30 ± 1.75 vs 45.62 ± 1.72 D preoperatively (P = .03) and mean keratometry steep was 44.39 ± 3.14 vs 46.53 ± 2.13 D preoperatively (P = .02). Mean central corneal thickness decreased from 501.74 ± 13.11 to 475.93 ± 12.25 µm following combined non-topography-guided PRK and CXL (P < .001). No intraoperative complications occurred. Four eyes developed mild haze that responded well to a short course of topical steroids. No eye developed infectious keratitis.

CONCLUSIONS

Combined non-topography-guided PRK and CXL is an effective and safe option for correcting mild refractive error and improving visual acuity in patients with early stable keratoconus.

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

Purpose

To assess the correlation between keratoconus severity and intereye asymmetry of pachymetric data and posterior elevation values and to evaluate their combined accuracy in discriminating normal corneas from those with keratoconus.

Methods

This study included 97 patients: 65 subjects with bilateral normal corneas (NC) and 32 with keratoconus (KC). Central corneal thickness (CCT), thinnest corneal thickness (ThCT) and posterior elevation (PE) at the thinnest point of the cornea were measured in both eyes using Scheimpflug imaging. Intereye asymmetry and its correlation with keratoconus severity were calculated for each variable. The area under the receiver operating characteristic curve (AUROC) was used to compare predictive accuracy of different variables for keratoconus.

Results

In normal eyes, intereye differences were significantly lower compared with the keratoconus eyes (p<0.001, for CCT, ThCT and PE). There was a significant exponential correlation between disease severity and intereye asymmetry of steep keratometry (r² = 0.55, p<0.001), CCT (r² = 0.39, p<0.001), ThCT (r² = 0.48, p<0.001) and PE (r² = 0.64, p<0.001). After adjustment for keratoconus severity, asymmetry in thinnest pachymetry proved to be the best parameter to characterize intereye corneal asymmetry in keratoconus. This variable had high accuracy and significantly better discriminating ability (AUROC: 0.99) for KC than posterior elevation (AUROC: 0.96), ThCT (AUROC: 0.94) or CCT (AUROC: 0.92) alone.

Conclusions

There is an increased intereye asymmetry in keratometry, pachymetry and posterior corneal elevation values in keratoconic patients compared to subjects with normal corneas. Keratoconus patients with more severe disease are also more asymmetric in their disease status which should be taken into account during clinical care.