Baseline Findings in the Retrospective Digital Computer Analysis of Keratoconus Evolution (REDCAKE) Project

The Chinese keratoconus (CKC) cohort study

The Chinese keratoconus (CKC) cohort study is a population-based longitudinal prospective cohort study in the Chinese population involving a clinical database and biobanks. This ongoing study focuses on the prevention of KC progression and is the first to involve the effect of gene‒environment interactions on KC progression. The CKC cohort is hospital-based and dynamic and was established in Zhengzhou, China; KC patients (n = 1114) from a large geographical area were enrolled from January 2019 to June 2023, with a mean age of 22.23 years (6‒57 years). Demographic details, socioeconomic characteristics, lifestyle, disease history, surgical history, family history, and visual and social function data are being collected using questionnaires. General physical examination, eye examination, biological specimen collection, and first-degree relative data were collected and analyzed in the present study. The primary focus of the present study was placed on gene, environment and the effect of gene‒environment interactions on KC progression. The follow-up of the CKC cohort study is expected to include data collection at 3 months, 6 months, and 1 year after the initial examination and then at the annual follow-up examinations. The first follow-up of the CKC cohort study was recorded. A total of 918 patients completed the follow-up by June 1, 2023, with a response rate of 82.40%. Aside from the younger age of patients who were followed up, no significant differences were found between patients who were followed up and patients who were not.

Definitions for Keratoconus Progression and Their Impact on Clinical Practice

PURPOSE

There is currently no consensus on which keratoconus need cross-linking nor on how to establish progression. This study assessed the performance of diverse progression criteria and compared them with our clinical knowledge of keratoconus evolution.

METHODS

This was a retrospective, longitudinal, observational study. Habitual progression criteria, based on (combinations of) keratometry (K MAX ), front astigmatism (A F ), pachymetry (P MIN ), or ABCD progression display, from 906 keratoconus patients were analyzed. For each criterion and cutoff, we calculated %eyes flagged progressive at some point (R PROG ), individual consistency C IND (%examinations after progression detection still considered progressive), and population consistency C POP (% eyes with CIND >66%). Finally, other monotonic and consistent variables, such as front steep keratometry (K 2F ), mean radius of the back surface (R mB ), and the like, were evaluated for the overall sample and subgroups.

RESULTS

Using a single criterion (e.g., ∆K MAX >1D) led to high values of R PROG . When combining two, (K MAX and A F ) led to worse C POP and higher variability than (K MAX and P MIN ); alternative criteria such as (K 2F and R mB ) obtained the best C POP and the lowest variability ( P <0.0001). ABC, as defined by its authors, obtained R PROG of 74.2%. Using wider 95% confidence intervals (95% CIs) and requiring two parameters over 95CI reduced R PROG to 27.9%.

CONCLUSION

Previous clinical studies suggest that 20% to 30% of keratoconus cases are progressive. This clinical R PROG value should be considered when defining KC progression to avoid overtreatment. Using combinations of variables or wider margins for ABC brings R PROG closer to these clinical observations while obtaining better population consistency than current definitions.

Fourier analysis on irregular corneal astigmatism using optical coherence tomography in various severity stages of keratoconus

PURPOSE

To investigate the diagnostic capability of Fourier indices in detecting clinical or subclinical keratoconus (KC).

DESIGN

Prospective cross-sectional study METHODS: : The study included 126 eyes with clinical KC (50 KC without any corneal scar, 50 KC with anterior corneal scar, and 26 KC with posterior scar having a history of acute corneal hydrops), 50 with topographic KC (without clinical signs), 50 with pre-topographic KC (normal topography without clinical signs), and 50 controls. Corneal tomographic data were obtained using anterior segment optical coherence tomography (OCT). Fourier analysis decomposed dioptric data from both anterior and posterior corneal surface into spherical, regular astigmatism, asymmetry, and higher-order irregularity components. The discriminating ability of the Fourier indices of pre-topographic KC, topographic KC, and clinical KC from controls were assessed after quantitative Fourier analysis of irregular corneal astigmatism.

RESULTS

Posterior asymmetry and higher-order irregularity components were significantly greater in pre-topographic KC eyes than those in controls (p<0.001 for both), with the highest area under the receiver operating characteristic curve (AUROC) of 0.778 and 0.709, respectively. The same was true for anterior asymmetry, posterior asymmetry, and posterior higher-order irregularity components in topographic KC (AUROC of 0.945, 0.941, and 0.893, respectively), whereas it was >0.948 for all Fourier components in clinical KC.

CONCLUSIONS

Fourier analysis using OCT can evaluate anterior and posterior corneal irregular astigmatism of various KC stages, from very mild to advanced, including severe cases with corneal scar. Irregular astigmatism indices from the posterior corneal surface showed the highest AUROC values in discriminating early KC stages.

Determining the Most Suitable Tomography-Based Parameters to Describe Progression in Keratoconus. The Retrospective Digital Computer Analysis of Keratoconus Evolution Project

OBJECTIVES

To identify the most suitable parameters to describe keratoconus progression.

METHODS

Longitudinal retrospective cohort study. Monotonicity and consistency of over 250 parameters extracted from the Pentacam tomographies (Oculus, Germany) of 743 patients was analyzed. Repeatability was calculated for 69 patients (published elsewhere). The parameters were scored based on their performance for each desired feature and a global ranking was created.

RESULTS

Overall, parameters that average a higher number of corneal points performed better than single-point parameters. Zonal keratometries on areas surrounding the maximum curvature point and the steepest front keratometry performed best, followed by front best-fit sphere and mean keratometry of both surfaces. Platform-dependent indices (e.g., Belin-Ambrósio Deviation- or index height decentration-) obtained good scores, but platform-independent LOGIK performed slightly better. Finally, although minimum radius in both surfaces worked competently, minimum pachymetry (PachyMin) performed considerably poorer.

CONCLUSIONS

We presented a list of parameters whose behavior was repeatable, monotonic and consistent, features desirable to describe change. The parameters normally used to follow keratoconus progression may not be the most adequate, as evidenced by the poor performance of PachyMin. Although calculated for a specific Scheimpflug device, most of the best-performing parameters are platform-independent variables, and results may be generalized, pending validation.

Detection of Subclinical Keratoconus With a Validated Alternative Method to Corneal Densitometry

Purpose

To enhance the current standards of subclinical keratoconus screening based on the statistical modeling of the pixel intensity distribution of Scheimpflug images.

Methods

Scheimpflug corneal tomographies corresponding to 25 corneal meridians of 60 participants were retrospectively collected and divided into three groups: controls (20 eyes), subclinical keratoconus (20 eyes), and clinical keratoconus (20 eyes). Only right eyes were selected. After corneal segmentation, pixel intensities of the stromal tissue were statistically modeled using a Weibull probability density function from which parameter α (pixel brightness) was derived. Further, data were transformed to polar coordinates, smoothed, and interpolated to build a map of the corneal α parameter. The discriminative power of the method was analyzed using receiver operating characteristic curves.

Results

The proposed platform-independent method achieved a higher performance in discriminating subclinical keratoconus from control eyes (90.0% sensitivity, 95.0% specificity, 0.97 area under the curve [AUC]) than the standard method (Belin-Ambrósio enhanced ectasia display), which uses only corneal morphometry (85.0% sensitivity, 85.0% specificity, 0.80 AUC).

Conclusions

Analysis of light backscatter at the cornea successfully discriminates subclinical keratoconus from control eyes, upgrading the results previously reported in the literature.

Translational Relevance

The proposed methodology has the potential to support clinicians in the detection of keratoconus before showing clinical signs.

Forecasting Progressive Trends in Keratoconus by Means of a Time Delay Neural Network

Early and accurate detection of keratoconus progression is particularly important for the prudent, cost-effective use of corneal cross-linking and judicious timing of clinical follow-up visits. The aim of this study was to verify whether a progression could be predicted based on two prior tomography measurements and to verify the accuracy of the system when labelling the eye as stable or suspect progressive. Data from 743 patients measured by Pentacam (Oculus, Wetzlar, Germany) were available, and they were filtered and preprocessed to data quality needs. The time delay neural network received six features as input, measured in two consecutive examinations, predicted the future values, and determined the classification (stable or suspect progressive) based on the significance of the change from the baseline. The system showed a sensitivity of 70.8% and a specificity of 80.6%. On average, the positive and negative predictive values were 71.4% and 80.2%. Including data of less quality (as defined by the software) did not significantly worsen the results. This predictive system constitutes another step towards a personalized management of keratoconus. While the results obtained were modest and perhaps insufficient to decide on a surgical procedure, such as cross-linking, they may be useful to customize the timing for the patient’s next follow-up.

Corneal cross-linking versus conventional management for keratoconus: a lifetime economic model

AIMS

To assess the cost-effectiveness of corneal collagen cross-linking (CXL) versus no CXL for keratoconus in the United States (US).

METHODS

A discrete-event microsimulation was developed to assess the cost-effectiveness of corneal cross-linking (CXL, Photrexa + KXL combination product) versus no CXL for patients with keratoconus. The lifetime model was conducted from a US payor perspective. The source for CXL efficacy and safety data was a 12-month randomized, open-label, sham-controlled, multi-center, pivotal trial comparing CXL versus no CXL. Other inputs were sourced from the literature. The primary outcome was the incremental cost per quality-adjusted life year gained. Costs (2019 USD) and effects were discounted 3% annually. The impacts of underlying uncertainty were evaluated by scenario, univariate, and probabilistic analyses.

RESULTS

Starting at a mean baseline age of 31 years and considering a mixed population consisting of 80% slow-progressors and 20% fast-progressors, the CXL group was 25.9% less likely to undergo penetrating keratoplasty (PK) and spent 27.9 fewer years in advanced disease stages. CXL was dominant with lower total direct medical costs (-$8,677; $30,994 versus $39,671) and more QALYs (1.88; 21.80 versus 19.93) compared to no CXL. Considering the impact of reduced productivity loss in an exploratory scenario, CXL was associated with a lifetime cost-savings of $43,759 per patient. CXL was cost-effective within 2 years and cost-saving within 4.5 years.

LIMITATIONS

Limitations include those that are common to similar pharmacoeconomic models that rely on disparate sources for inputs and extrapolation on short-term outcomes to a long-term analytical horizon.

CONCLUSIONS

Keratoconus is a progressive and life-altering disease with substantial clinical, economic, and humanistic consequences. The economic value of cross-linking is maximized when applied earlier in the disease process and/or younger age, and extends to improved work productivity, out-of-pocket costs, and quality of life.