Correlation between Guttata Severity and Thickness of Descemet’s Membrane and the Central Cornea

Nanotopography by chromatic confocal microscopy of the endothelium in Fuchs endothelial corneal dystrophy, pseudophakic bullous keratopathy and healthy corneas

AIM

To investigate the interest of chromatic confocal microscopy (CCM) to characterise guttae in Fuchs endothelial corneal dystrophy (FECD).

METHODS

Descemet's membranes (DM) were obtained during endothelial keratoplasty in patients with FECD and pseudophakic bullous keratopathy (PBK). They were compared with healthy samples obtained from body donation to science. Samples were fixed in 0.5% paraformaldehyde and flat mounted. Surface roughness of DMs was quantified using CCM and the AltiMap software that provided the maximum peak (Sp) and valley (Sv) heights, the mean square roughness (Rq) and the asymmetry coefficient (Ssk).

RESULTS

The physiological roughness of healthy samples was characterised by an Rq of 0.12±0.05 µm, which was two times rougher than in PBK (Rq=0.06±0.03 µm), but both were still flat with a symmetrical distribution between peaks and valleys (Ssk close to 0, npeaks=nvalleys), smaller than 1 µm. In FECD, the maximum peak height was 5.10±2.40 µm, up to 5.8 and 8.3 times higher than the control and PBK, respectively. The maximum valley depth was half than the peak (2.28±0.89 µm). The surface with guttae was very rough (Rq=0.45±0.14 µm) and the Ssk=1.84± 0.43 µm, greater than 0, confirms an asymmetric surface with high peaks and low valleys (npeaks>nvalleys). Moreover, the CCM provided quantitative parameters allowing to distinguish different types of guttae from different patients.

CONCLUSIONS

CCM is an innovative approach to describe and quantify different morphologies of guttae. It could be useful to analyse the different stages of FECD and define subgroups of patients.

Applications of Imaging Technologies in Fuchs Endothelial Corneal Dystrophy: A Narrative Literature Review

Fuchs endothelial corneal dystrophy (FECD) is a complex genetic disorder characterized by the slow and progressive degeneration of corneal endothelial cells. Thus, it may result in corneal endothelial decompensation and irreversible corneal edema. Moreover, FECD is associated with alterations in all corneal layers, such as thickening of the Descemet membrane, stromal scarring, subepithelial fibrosis, and the formation of epithelial bullae. Hence, anterior segment imaging devices that enable precise measurement of functional and anatomical changes in the cornea are essential for the management of FECD. In this review, the authors will introduce studies on the application of various imaging modalities, such as anterior segment optical coherence tomography, Scheimpflug corneal tomography, specular microscopy, in vitro confocal microscopy, and retroillumination photography, in the diagnosis and monitoring of FECD and discuss the results of these studies. The application of novel technologies, including image processing technology and artificial intelligence, that are expected to further enhance the accuracy, precision, and speed of the imaging technologies will also be discussed.

Three-Dimensional Assessment of Descemet Membrane Reflectivity by Optical Coherence Tomography in Fuchs Endothelial Corneal Dystrophy

PURPOSE

This study aimed to evaluate Descemet membrane reflectivity using anterior segment optical coherence tomography (AS-OCT) in eyes with Fuchs endothelial corneal dystrophy (FECD).

METHODS

We retrospectively assessed 144 eyes of 88 consecutive participants (41 FECD, 15 pseudophakic bullous keratopathies [BKs], and 32 healthy controls, 63.5 ± 16.5 years). FECD was graded 0 to 3 based on the guttae areas using specular microscopy. The sum of AS-OCT reflectivity of the 3-dimensional volume from 10 μm thickness from the endothelial surface of the cornea and residual stromal area was calculated as D sum (endo) and D sum (stroma) in the central area of 3- and 6-mm diameters, respectively. The D ES ratio was defined as the ratio of D sum (endo) to D sum (stroma). The percentage of the guttae area in the specular images was calculated using MATLAB. D sum (endo) and D ES ratio were compared among FECD, BK, and healthy controls.

RESULTS

D sum (endo) in FECD grade 3 was significantly higher than that in healthy control eyes, FECD patients with mild and moderate guttae, and BK (all P ≤ 0.040). The D ES ratio in FECD patients with mild to severe guttae (grade 1-3) was significantly higher than that in healthy control eyes and BK (all P ≤ 0.035). The percentage of the guttae area was significantly correlated with D sum (endo) (R = 0.488, P < 0.001 for 3 mm, R = 0.512, P < 0.001 for 6 mm) and D ES ratio (R = 0.450, P < 0.001 for 3 mm, R = 0.588, P < 0.001 for 6 mm).

CONCLUSIONS

Descemet membrane reflectivity in AS-OCT can be objective biomarkers for assessing guttae and FECD severity from early to end-stage FECD.

Systematic Review of the Diagnostic Criteria and Severity Classification for Fuchs Endothelial Corneal Dystrophy

PURPOSE

There are no defined diagnostic criteria and severity classification for Fuchs endothelial corneal dystrophy (FECD), which are required for objective standardized assessments. Therefore, we performed a systematic literature review of the current diagnosis and severity classification of FECD.

METHODS

We searched the Ovid MEDLINE and Web of Science databases for studies published until January 13, 2021. We excluded review articles, conference abstracts, editorials, case reports with <5 patients, and letters.

RESULTS

Among 468 articles identified, we excluded 173 and 165 articles in the first and second screenings, respectively. Among the 130 included articles, 61 (47%) and 99 (76%) mentioned the diagnostic criteria for FECD and described its severity classification, respectively. Regarding diagnosis, slitlamp microscope alone was the most frequently used device in 31 (51%) of 61 articles. Regarding diagnostic findings, corneal guttae alone was the most common parameter [adopted in 23 articles (38%)]. Regarding severity classification, slitlamp microscopes were used in 88 articles (89%). The original or modified Krachmer grading scale was used in 77 articles (78%), followed by Adami's classification in six (6%). Specular microscopes or Scheimpflug tomography were used in four articles (4%) and anterior segment optical coherence tomography in one (1%).

CONCLUSIONS

FECD is globally diagnosed by the corneal guttae using slitlamp examination, and its severity is predominantly determined by the original or modified Krachmer grading scale. Objective severity grading using Scheimpflug or anterior segment optical coherence tomography can be applied in the future innovative therapies such as cell injection therapy or novel small molecules.

Deep Learning Model for the Detection of Corneal Edema Before Descemet Membrane Endothelial Keratoplasty on Optical Coherence Tomography Images

Purpose

Descemet membrane endothelial keratoplasty (DMEK) is the preferred method for treating corneal endothelial dysfunction, such as Fuchs endothelial corneal dystrophy (FECD). The surgical indication is based on the patients' symptoms and the presence of corneal edema. We developed an automated tool based on deep learning to detect edema in corneal optical coherence tomography images. This study aimed to evaluate this approach in edema detection before Descemet membrane endothelial keratoplasty surgery, for patients with or without FECD.

Methods

We used our previously described model allowing to classify each pixel in the corneal optical coherence tomography images as "normal" or "edema." We included 1992 images of normal and preoperative edematous corneas. We calculated the edema fraction (EF), defined as the ratio between the number of pixels labeled as "edema," and those representing the cornea for each patient. Differential central corneal thickness (DCCT), defined as the difference in central corneal thickness before and 6 months after surgery, was used to quantify preoperative edema. AUC of EF for the edema detection was calculated for Several DCCT thresholds and a value of 20 µm was selected to define significant edema as it provided the highest area under the curve value.

Results

The area under the curve of the receiver operating characteristic curve for EF for the detection of 20 µm of DCCT was 0.97 for all patients, 0.96 for Fuchs and normal only and 0.99 for non-FECD and normal patients. The optimal EF threshold was 0.143 for all patients and patients with FECD.

Conclusions

Our model is capable of objectively detecting minimal corneal edema before Descemet membrane endothelial keratoplasty surgery.

Translational Relevance

Deep learning can help to interpret optical coherence tomography scans and aid the surgeon in decision-making.

Quality of instruments assessing activity and participation of people with muscular dystrophy: A systematic review of participant-reported outcome measures

AIM

To identify the standardized assessment scales for people with muscular dystrophy and investigate the quality/level of evidence of their measurement properties.

METHOD

A systematic review of patient-reported outcome measures was conducted on the MEDLINE, Embase, AMED, DiTA, and PsycINFO databases in August 2020. We included psychometric studies that investigated the validity, reliability, and responsiveness of instruments assessing activity and participation for muscular dystrophy of any type (Duchenne, Becker, limb-girdle, facioscapulohumeral, congenital, and myotonic) or age. Two independent reviewers selected the studies, extracted data, and evaluated the instruments' quality and level of evidence following the COnsensus-based Standards for the selection of health status Measurement INstruments (COSMIN) checklist. The study followed the Preferred Reporting Items for Systematic reviews and Meta-Analysis (PRISMA) 2020 guidelines.

RESULTS

The searches identified 6675 references; a total of 46 studies with 28 condition-specific or general instruments were included. The measurement properties of most instruments had sufficient (68.8%) or indeterminate (25.7%) results according to COSMIN. The quality of evidence of the measurement properties was moderate (23.8%) or low (22.6%) according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE).

INTERPRETATION

There is a lack of high-quality instruments whose psychometric properties are adequately measured. The highest quality instrument is the Muscular Dystrophy Functional Rating Scale. The Motor Function Measure (general instrument), Duchenne Muscular Dystrophy Upper-limb Patient-reported Outcome Measure, North Star Ambulatory Assessment, and Myotonic Dystrophy Type 1 Activity and Participation Scale for Clinical Use (specific) are also recommended.

WHAT THIS PAPER ADDS

There are 28 available instruments for activity and participation of people with muscular dystrophy. The evidence quality is moderate or low because of imprecision and indirectness. The Muscular Dystrophy Functional Rating Scale is the highest quality instrument. The Motor Function Measure is the second most recommended instrument. The Duchenne Muscular Dystrophy Upper-limb Patient-reported Outcome Measure, North Star Ambulatory Assessment, and Myotonic Dystrophy Type 1 Activity and Participation Scale for Clinical Use are also recommended.

Prevalence and severity of cornea guttata in the graft following Descemet Membrane Endothelial Keratoplasty (DMEK)

PURPOSE

The aim of this study was to determine the prevalence and severity of cornea guttata (CG) in grafts after Descemet membrane endothelial keratoplasty (DMEK) and to investigate its impact on various clinical parameters during follow-up.

METHODS

This retrospective study included 664 operations (DMEK and triple-DMEK) on 466 patients. The prevalence and progression of CG after the operation were examined using endothelial specular microscopy images. The severity grade of CG was classified into four grades: G0 without CG, G1 - G3 with increasing severity of CG. Clinical parameters such as central corneal thickness (CCT), visual acuity (VA), endothelial cell density (ECD), pleomorphism and polymegalism were examined during a postoperative follow-up time of 19.6 ± 15.8 months.

RESULTS

Cornea guttata (CG) appeared postoperatively in 124 (18.7%) eyes. 112 (16.9%) could be classified as G1, 9 (1.4%) as G2 and only 3 (0.5%) as G3. The examination of clinical parameters showed significant differences between healthy and low-grade CG (G0/G1) and high-grade CG (G2/G3). A significant deterioration was found in the corrected distance visual acuity (CDVA) (p = 0.02). CCT showed an increase between G0 (534 ± 58 μm) and G2 (549 ± 71 μm)/G3 (558 ± 56 μm) with a p-value of 0.02. Additionally, a significant increase in pleomorphism (p = 0.003) and polymegalism (p = 0.04) was detected.

CONCLUSION

Cornea guttata (CG) prevalence after DMEK and triple-DMEK was found to be 18.7%, although most of these cases were classified as low-grade CG and showed no clinical significance. Around 1.9% were classified as high-grade CG and significantly affected several clinical parameters during the follow-up.

Predicting Corneal Improvement after Descemet Membrane Endothelial Keratoplasty for Fuchs Endothelial Corneal Dystrophy

PURPOSE

To develop a model to predict corneal improvement after Descemet membrane endothelial keratoplasty (DMEK) for Fuchs endothelial corneal dystrophy (FECD) from Scheimpflug tomography.

DESIGN

Cross-sectional study.

PARTICIPANTS

Forty-eight eyes (derivation group) and 45 eyes (validation group) with a range of severity of FECD undergoing DMEK.

METHODS

Scheimpflug images were obtained before and after DMEK. Before DMEK, pachymetry map and posterior elevation map patterns were quantified by a special image analysis program measuring tomographic features of edema (loss of regular isopachs, displacement of the thinnest point of the cornea, posterior surface depression). Image-derived novel parameters were combined with instrument-derived parameters, and the relative influences of parameters associated with the change in central corneal thickness (CCT) after DMEK in the derivation group were determined by using a gradient boosting machine learning model. The parameters with highest relative influence were then fit in a linear regression model. The derived model was applied to the validation group. Correlations and agreement were assessed between predicted and observed changes in CCT.

MAIN OUTCOME MEASURES

Predictive power (R ²) and mean difference between predicted and observed change in CCT.

RESULTS

The gradient boosting machine model identified 4 novel parameters of isopach circularity and eccentricity and 1 instrument-derived parameter (posterior surface radius); preoperative CCT was a poor predictor. In the derivation group, the model strongly predicted the change in CCT after DMEK (R ² = 0.80; 95% confidence interval [CI], 0.71-0.89) and the mean difference between predicted and observed change was, by definition, 0 μm. When the same 5 parameters were fit to the validation group, the model performed very highly (R ² = 0.89; 95% CI, 0.84-0.94). When the coefficient estimates from the derivation model were used to predict the change in CCT in the validation group, the predictive power was also high (R ² = 0.78; 95% CI, 0.68-0.88), and the mean difference was 4 μm (predicted minus observed).

CONCLUSIONS

Scheimpflug tomography maps of corneas with FECD can predict the improvement in CCT after DMEK, independent of preoperative corneal thickness measurement. The model could be applied in clinical practice or for clinical research of FECD.

Semiquantitative Criteria in the Eye Bank That Correlate with Cornea Guttata in Donor Corneas

BACKGROUND

Cornea guttata may not be recognized in the eye bank and recent studies have displayed that guttae are transplanted in about 15% of cases in varying severities. The purpose of this study was to establish semiquantitative criteria for the detection of cornea guttata in donor corneas in the eye bank.

METHODS

In this retrospective cohort study, preoperative endothelial pictures of donor corneas were collected and classified according to the post-penetrating keratoplasty cornea guttata grade into three distinct groups: group 1 consists of healthy corneas with no guttae (guttata grade 0); group 2 constitutes corneas with mild asymptomatic cornea guttata (guttata grade +); and group 3 comprises corneas with advanced widespread cornea guttata (guttata grade ++/+++/++++). The preoperative pictures of each group were then individually analyzed using the following five semiquantitative criteria: The number and the area of the cell-depleted surfaces, the presence of less than 50% of the cells having a hexagonal or a circular shape, the presence of cell membrane defects and interruptions, the presence of blebs in the cell membrane, and the presence of groups of cells with a distinct whitish color.

RESULTS

In total, 262 patients were included in this study, with a total number of 1582 preoperative donor corneal endothelial pictures. Out of those pictures, groups 1, 2, and 3 encompassed 995 (62.9%), 411 (26.0%), and 176 (11.1%) pictures, respectively. Three out of the five eye bank criteria were found to correlate with postoperative cornea guttata with a highly significant p value of < 0.001. These three criteria are the presence of less than 50% of the cells having a hexagonal or a circular shape, the presence of cell membrane defects and interruptions and, the presence of blebs. The presence of groups of cells with a distinct whitish color was only a weak predictive factor for cornea guttata (p = 0.069). There was no statistically significant correlation between the number and the area of cell-depleted surfaces and postoperative cornea guttata with a p = 0.181.

CONCLUSION

Three semiquantitative criteria that can be detected in the eye bank using inverted light microscopy seem to correlate with postoperative cornea guttata: The presence of blebs, the presence of cell membrane defects and interruptions, as well as endothelial pictures with less than 50% of the cells having a hexagonal of circular shape. The presence of groups of cells with a distinct whitish color appears to be a weak predictor of cornea guttata.

Automated Clinical Assessment of Corneal Guttae in Fuchs Endothelial Corneal Dystrophy

PURPOSE

To describe the validation and implementation of an automated system for the detection and quantification of guttae in Fuchs endothelial corneal dystrophy (FECD).

DESIGN

Observational reliability study.

METHODS

Patients with FECD underwent retroillumination corneal photography, followed by determination of the distributions and sizes of corneal guttae by an automated image analysis algorithm. Performance of the automated system was assessed via (1) validation against manual guttae segmentation, (2) reproducibility studies to ensure consistency, and (3) evaluation for agreement with the Krachmer scale. It was then deployed to perform large-scale guttae assessment with anatomic subregion analysis in a batch of 40 eyes.

RESULTS

Compared to manual segmentation, the automated system was reasonably accurate in identifying the correct number of guttae (mean count of 78 guttae per 1 × 1 mm test frame, overestimation: +10 per frame), but had a tendency to significantly overestimate guttae size (mean guttae size 1073 μm², overestimation: +255 μm²). Automated measurements of guttae counts and sizes were reproducible within a 1% discrepancy range across repeat intra-eye assessments. Automated guttae counts, interguttae distances, and density of interguttae gaps lesser than 40 μm (ie, D40 density) were highly correlated with the Krachmer scale (P < .001 for all). Large-scale guttae assessment demonstrated the automated system's potential to selectively identify a region of the corneal endothelium most affected by densely packed guttae.

CONCLUSIONS

Automated guttae assessment facilitates the precise identification and quantification of guttae characteristics in FECD patients. This can be used clinically as a personalized descemetorrhexis zone for Descemet stripping only and/or Descemet membrane transplantation.

Discrepancies in Endothelial Cell Density Values of Human Donor Corneas Resulting From Comparison Between Specular Microscopes and Endothelial Analysis Methods

PURPOSE

The methods for specular microscopy evaluation across eye banks differ, which may result in variability in endothelial cell density (ECD) values that influence the surgeon's decision about donor tissue. A comparison of instruments and analysis methods is conducted in this study.

METHODS

Specular images were captured from 97 donor corneas using both HAI and Konan specular microscopes. A single best quality image of each cornea from each instrument was graded using the respective inherent software and analysis method (HAI: variable frame method; Konan: center method). All raw specular images were standardized for dimensions and regraded in the CellChek system in a blinded fashion. The grading variances and paired t test were performed between instruments in both inherent and standardized analyses. Correlation and Bland-Altman analyses between instruments were also performed.

RESULTS

Using the software inherent within HAI and Konan, the mean ECD readings for the 97 corneas were 2764 ± 583 and 2605 ± 517 cell/mm (P = 0.045), respectively, with a variance of 8.05% (range 0.26%-27.2%). HAI resulted in a higher ECD value in 79 corneas (81.4%). In CellChek software analysis, the mean ECD readings did not differ (2609 ± 514 and 2496 ± 507 cells/mm, respectively, P = 0.127), with a variance of 5.6% (range 0.24%-19.8%).

CONCLUSIONS

There is a slight statistically significant mean difference between the ECD values obtained from the 2 specular microscopes, which is negated by standardization to a single analysis method. Eye banks and surgeons should use caution in making decisions based only on very small differences in ECD between otherwise equivalent corneal donor tissues.