Advances in anterior segment imaging and analysis

Smart decision support system for keratoconus severity staging using corneal curvature and thinnest pachymetry indices

BACKGROUND

This study proposes a decision support system created in collaboration with machine learning experts and ophthalmologists for detecting keratoconus (KC) severity. The system employs an ensemble machine model and minimal corneal measurements.

METHODS

A clinical dataset is initially obtained from Pentacam corneal tomography imaging devices, which undergoes pre-processing and addresses imbalanced sampling through the application of an oversampling technique for minority classes. Subsequently, a combination of statistical methods, visual analysis, and expert input is employed to identify Pentacam indices most correlated with severity class labels. These selected features are then utilized to develop and validate three distinct machine learning models. The model exhibiting the most effective classification performance is integrated into a real-world web-based application and deployed on a web application server. This deployment facilitates evaluation of the proposed system, incorporating new data and considering relevant human factors related to the user experience.

RESULTS

The performance of the developed system is experimentally evaluated, and the results revealed an overall accuracy of 98.62%, precision of 98.70%, recall of 98.62%, F1-score of 98.66%, and F2-score of 98.64%. The application's deployment also demonstrated precise and smooth end-to-end functionality.

CONCLUSION

The developed decision support system establishes a robust basis for subsequent assessment by ophthalmologists before potential deployment as a screening tool for keratoconus severity detection in a clinical setting.

Spectrophotometric Analysis of Different Polymethyl Methacrylate Filters and their Importance in the Implantation of Corneal Rings

PURPOSE

This study evaluated the luminous behavior applied to materials used in intraocular surgeries.

METHODS

Discs of the different products were delivered in 19.00 mm × 3.00 mm. Each sample was fixed on support keeping it perpendicular to the spectrophotometer beam. Later, their analyses were carried out in the air/PMMA ratio. The graphs of individual profiles of the measurements along the length were constructed according to each of the filters from the spectrophotometric analysis. In addition, descriptive statistics of transmittance and absorbance for each wavelength presented were correlated for each filter.

RESULTS

It is possible to observe that the minimum absorption measure was found in the Red Filter, especially in the blue and green light spectrum.

CONCLUSION

Using filters in PMMA materials appears to improve visual quality in corneal implants, especially the red filter, due to greater absorbance of light leading to fewer light scattering phenomena through corneal rings. However, further studies comparing the effects of different filters on Intracorneal rings should be carried out to elucidate this field of study.

Keratoconus epidemiology: A review

Keratoconus is an ectatic corneal disease that affects both men and women, usually at a young age. Risk factors such as eye rubbing, environmental and genetic factors contribute to its pathogenesis. Keratoconus presents a variable prevalence, being as high as 5% of the population in the Middle East. In this review, an English-language search for keratoconus epidemiology was undertaken using the PubMed database. We present and discuss the findings of the most relevant epidemiological studies on keratoconus and describe its characteristics and risk factors, correlating them with its pathogenesis.

Update and Review of Diagnosis and Management of Post-Refractive Surgery Ectasia

ABSTRACT

Post-Refractive Surgery Ectasia is a serious, sight-threatening, and highly - avoided complication seen after the following procedures: Laser in situ Keratomileusis, Photorefractive Keratectomy, Small Incision Lenticule Extraction, Radial and/or Arcuate Keratotomy. Specific risk factors may include age, corneal thickness, degree of refractive error, corneal topographic changes including irregular astigmatism, percent tissue ablation, and residual stromal bed. Biomarkers may be a new option to help indicate who is at greatest risk for ectasia. Visual aids including glasses or contacts lenses are often required to achieve optimal vision. Collagen crosslinking is the only treatment thought to stop progression of ectasia and prevent keratoplasty. Other surgical options may include topography-guided phototherapeutic keratectomy and intrastromal corneal ring segments. Ultimately an "ounce of prevention is a pound of cure" so careful preoperative screening and ultimately offering the safest and most effective treatments for patients is arguably the most important job of the refractive surgeon.

Technologies for anatomical and geometric characterization of the corneal structure and anterior segment: a review

Corneal and anterior segment imaging techniques have become a crucial tool in the clinical practice of ophthalmology, with a great variety of applications, such as corneal curvature and pachymetric analysis, detection of ectatic corneal conditions, anatomical study of the anterior segment prior to phakic intraocular lens implantation, or densitometric analysis of the crystalline lens. From the Placido-based systems that allow only a characterization of the geometry of the anterior corneal surface to the Scheimpflug photography-based systems that provide a characterization of the cornea, anterior chamber, and crystalline lens, there is a great variety of devices with the capability of analyzing different anatomical parameters with very high precision. To date, Scheimpflug photography-based systems are the devices providing the more complete analysis of the anterior segment in a non-invasive way. More developments are required in anterior segment imaging technologies in order to improve the analysis of the crystalline lens structure as well as the ocular structures behind the iris in a non-invasive way when the pupil is not dilated.

Scheimpflug imaging for laser refractive surgery

PURPOSE OF REVIEW

To review the principles and clinical applications of Scheimpflug corneal and anterior segment imaging with special relevance for laser refractive surgery.

RECENT FINDINGS

Computerized Scheimpflug imaging has been used for corneal and anterior segment tomography (CASTm) in different commercially available instruments. Such approach computes the three-dimensional image of the cornea and anterior segment, enabling the characterization of elevation and curvature of the front and back surfaces of the cornea, pachymetric mapping, calculation of the total corneal refractive power and anterior segment biometry. CASTm represents a major evolution for corneal and anterior segment analysis, beyond front surface corneal topography and single point central corneal thickness measurements. This approach enhances the diagnostic abilities for screening ectasia risk as well as for planning, evaluating the results, managing complications of refractive procedures, and selecting intraocular lens power, type, and design. In addition, dynamic Scheimpflug imaging has been recently introduced for in-vivo corneal biomechanical measurements and has also been used for anterior segment imaging of femtocataract surgery.

SUMMARY

Scheimpflug imaging has an important role for laser refractive surgery with different applications, which continuously improve due to advances in technology.

Intrasubject repeatability in keratoconus-eye measurements obtained with a new Scheimpflug photography-based system

PURPOSE

To evaluate in keratoconus eyes the intrasubject repeatability of anterior and posterior corneal curvature and of other anterior segment anatomic measurements obtained with a new topography system combining Scheimpflug-photography and Placido-disk technology.

SETTING

Vissum Corporation, Alicante, Spain.

DESIGN

Evaluation of technology.

METHODS

All keratoconus eyes had a comprehensive ophthalmologic examination including analysis with the Sirius system. Three consecutive measurements were obtained to assess the intrasubject repeatability of the following parameters: anterior and posterior corneal curvature and shape factor, white-to-white (WTW) corneal diameter, central and minimum corneal thickness, and anterior chamber depth (ACD). The within-subject standard deviation (S(w)) and intraclass correlation coefficient (ICC) were calculated.

RESULTS

This study comprised 61 eyes of 61 patients ranging in age from 14 to 64 years. For anterior and posterior corneal curvatures and power vector components, the S(w) was 0.29 mm or less in all cases. The ICC was above 0.990 in all cases except the flattest curvature of the posterior corneal surface at 3.0 mm, which was 0.840 (moderate agreement), and the posterior power vector J0, which was 0.665 (poor agreement), 0.752, and 0.758 (moderate agreement) for 3.0 mm, 5.0 mm, and 7.0 mm, respectively. In shape factor measurements, the S(w) was 0.12 or less in all cases and the ICC ranged between 0.989 and 0.999. Pachymetry, ACD, and WTW had ICC values very close to 1.

CONCLUSION

The new topography system provided repeatable measurements of corneal shape and other anatomic parameters in eyes with keratoconus.

FINANCIAL DISCLOSURE

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

Predictive value of optical coherence tomography in graft attachment after Descemet's membrane endothelial keratoplasty

PURPOSE

To evaluate the predictive value of early anterior segment optical coherence tomography (AS-OCT) on graft adherence or detachment after Descemet's membrane endothelial keratoplasty (DMEK).

DESIGN

Retrospective study of prospectively collected data at a tertiary referral center.

PARTICIPANTS

A total of 87 eyes of 87 patients of a consecutive series of 142 DMEK surgeries.

METHODS

Anterior segment OCT was performed within the first hour after DMEK and at 1 week, 1 month, 3 months, and 6 months, and for each time interval detachments were classified as "none," ≤ 1/3 detachment, >1/3 detachment of the total graft surface area, or "complete" detachment. Throughout the study, no rebubbling procedures were performed.

MAIN OUTCOME MEASURES

Graft adherence at various postoperative time intervals.

RESULTS

One-hour AS-OCT scans were more accurate at predicting the final 6-month graft adherence status than those at 1 week or 1 month. Grafts showing complete attachment or <1/3 detachment at 1 hour remained stable or improved in 73% of the cases at 1 week, 82% at 1 month, 86% at 3 months, and 90% at 6 months. All grafts attached at 1 week remained attached at 6 months. Graft detachments of >1/3 at 1 hour showed reattachment at 6 months in 25% of the cases, whereas 67.5% of the cases showed a persistent detachment of >1/3 at 6 months and 12.5% showed a complete detachment.

CONCLUSIONS

The 1-hour AS-OCT scan showed the best predictive value on 6-month graft adherence status. The combined information of the 1-hour and 1-week AS-OCT scans may facilitate decision making about surgical reintervention after DMEK.

Topometric and Tomographic Indices for the Diagnosis of Keratoconus

Purpose

To compare topometric (front surface curvature) and tomographic (3D corneal shape) indices for diagnosing keratoconus.

Methods

Pentacam data from one eye randomly selected of 200 normals (N) and 177 keratoconus (KC) were analyzed. Tomographic and topometric indices were tested. Receiver operating characteristic (ROC) curves were calculated, along with pairwise comparisons.

Results

All tested variables had significant differences among N and KC (Mann-Whitney, p < 0.001). Most accurate tomographic indices had higher AUC than best topometric ones (DeLong, p < 0.05). Belin-Ambrosio D (BAD-D) had AUC of 1.00 (sensitivity 100.0%; specificity 98.5%).

Conclusion

Tomographic data was superior than topometric data to detect keratoconus. The BAD-D was an enhanced approach for detecting keratoconus.

How to cite this article

Correia FF, Ramos I, Lopes B, Salomão MQ, Luz A, Correa RO, Belin MW, Ambrósio R Jr. Topometric and Tomographic Indices for the Diagnosis of Keratoconus. Int J Kerat Ect Cor Dis 2012;1(2):92-99.