Perspective of Future Potent Therapies for Fuchs Endothelial Corneal Dystrophy

Fuchs endothelial corneal dystrophy: an updated review

PURPOSE

The present review will summarize FECD-associated genes and pathophysiology, diagnosis, current  therapeutic approaches, and future treatment perspectives.

METHODS

Literature review.

RESULTS

Fuchs' endothelial corneal dystrophy (FECD) is the most common bilateral corneal dystrophy and accounts for one-third of all corneal transplants performed in the US. FECD is caused by a combination of genetic and non-heritable factors, and there are two types: early-onset FECD, which affects individuals from an early age and is usually more severe, and late-onset FECD, which is more common and typically manifests around the age of 40. The hallmark findings of FECD include progressive loss of corneal endothelial cells and the formation of focal excrescences (guttae) on the Descemet membrane. These pathophysiological changes result in progressive endothelial dysfunction, leading to a decrease in visual acuity and blindness in later stages. The present review will summarize FECD-associated genes and pathophysiology, diagnosis, current therapeutic approaches, and future treatment perspectives.

CONCLUSION

With the characterization and understanding of FECD-related genes and ongoing research into regenerative therapies for corneal endothelium, we can hope to see more significant improvements in the future in the management and care of the disease.

Comparison of Scheimpflug and Anterior Segment Optical Coherence Tomography Imaging Parameters for Japanese Patients With Fuchs Endothelial Corneal Dystrophy With and Without TCF4 Repeat Expansions

PURPOSE

The aim of this study was to investigate the association between cytosine-thymine-guanine trinucleotide repeat (TNR) expansion in TCF4 and the clinical phenotypes of corneal densitometry or anterior segment morphology in Fuchs endothelial corneal dystrophy.

METHODS

This retrospective cross-sectional study included 150 eyes from 75 Japanese consecutive patients with Fuchs endothelial corneal dystrophy. Cytosine-thymine-guanine repeat expansion of leukocyte-derived genomic DNA was analyzed through fragment analysis using polymerase chain reaction and triplet repeat primed polymerase chain reaction. Scheimpflug-based densitometry and anterior segment optical coherence tomography were applied. Corneal densitometry, and corneal and anterior segment morphology parameters were compared between patients with and without TNR expansion of 50 or more (expansion and nonexpansion groups, respectively) using a mixed model.

RESULTS

The average age of the patients was 66.8 ± 13.0 years, and the modified Krachmer grading scale was 1, 2, 3, 4, 5, and 6 for 7, 32, 28, 51, 6, and 18 eyes, respectively. Sixteen patients (21%) exhibited ≥50 TNR expansion. No significant differences in sex, age, history of keratoplasty, modified Krachmer grade, and corneal densitometry in either diameter or depth were observed between the 2 groups. No significant differences in anterior segment morphology, including the anterior chamber depth and anterior chamber angle width parameters, were observed using a univariate mixed model, except for central corneal thickness (P = 0.047). However, according to the multivariate mixed model, repeat expansion was not significantly associated with central corneal thickness (P = 0.27).

CONCLUSIONS

No significant differences in clinical phenotypes were found between Japanese patients having Fuchs endothelial corneal dystrophy with and without TNR expansion.

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.

Corneal Endothelial-like Cells Derived from Induced Pluripotent Stem Cells for Cell Therapy

Corneal endothelial dysfunction is one of the leading causes of corneal blindness, and the current conventional treatment option is corneal transplantation using a cadaveric donor cornea. However, there is a global shortage of suitable donor graft material, necessitating the exploration of novel therapeutic approaches. A stem cell-based regenerative medicine approach using induced pluripotent stem cells (iPSCs) offers a promising solution, as they possess self-renewal capabilities, can be derived from adult somatic cells, and can be differentiated into all cell types including corneal endothelial cells (CECs). This review discusses the progress and challenges in developing protocols to induce iPSCs into CECs, focusing on the different media formulations used to differentiate iPSCs to neural crest cells (NCCs) and subsequently to CECs, as well as the characterization methods and markers that define iPSC-derived CECs. The hurdles and solutions for the clinical application of iPSC-derived cell therapy are also addressed, including the establishment of protocols that adhere to good manufacturing practice (GMP) guidelines. The potential risks of genetic mutations in iPSC-derived CECs associated with long-term in vitro culture and the danger of potential tumorigenicity following transplantation are evaluated. In all, this review provides insights into the advancement and obstacles of using iPSC in the treatment of corneal endothelial dysfunction.

Phase 2, Randomized, Open-Label Parallel-Group Study of Two Dosing Regimens of Netarsudil for the Treatment of Corneal Edema Due to Fuchs Corneal Dystrophy

Background: This phase 2 study evaluated the therapeutic potential of netarsudil to reduce corneal edema and to improve vision in patients with Fuchs corneal dystrophy (FCD). Methods: Patients (N = 40) with baseline central corneal thickness (CCT) of ≥600 μm and best-corrected visual acuity (BCVA) of 70-20 letters (20/40-20/400 Snellen equivalent) were randomized 1:1 to receive netarsudil once a day (QD) or twice a day (BID) for 8 weeks. Primary endpoint was mean CCT change from baseline at week 4. Results: Netarsudil QD and BID significantly reduced CCT at week 4 [mean change (standard error of mean), 28.4 (7.99) μm, P = 0.0021; and 20.1 (8.75) μm, P = 0.0335, respectively]. Five (12.5%) patients achieved complete resolution of corneal edema at week 4. BCVA improved by 3.2 (2.76) letters with QD and 1.5 (2.84) letters with BID, and 10 (25%) patients [5 with QD (P = 0.0078) and 5 with BID (P = 0.0096)] gained ≥10 letters at week 4. Improvements in CCT and vision were observed at week 2 and persisted at week 8, without significant differences between the 2 doses at any time point. Netarsudil QD significantly improved visual acuity and glare factor scores on the Visual Function and Corneal Health Status (V-FUCHS) questionnaire at weeks 4 and 8 (mean change, -0.4 to -0.3; P ≤ 0.0200). Netarsudil was well tolerated. Reticular edema developed in one (2.5%) patient with BID, which resolved with treatment discontinuation. Conclusions: Netarsudil QD led to significant reductions in corneal edema as well as improvements in vision and patient-reported symptoms of glare and visual impairment in patients with FCD. Clinical Trial Registration Number: NCT04498169.

Correlation Between Angle Parameters and Central Corneal Thickness in Fuchs Endothelial Corneal Dystrophy

PURPOSE

To evaluate the correlation between anterior chamber parameters and central corneal thickness (CCT) or peripheral corneal thickness (PCT) in patients with Fuchs endothelial corneal dystrophy (FECD) using anterior segment optical coherence tomography.

METHODS

This case-control study included 20 eyes from 20 patients with FECD and 31 eyes from 31 patients with healthy corneas. CCT was measured as an indicator of FECD severity. Anterior chamber angle parameters, including trabecular-iris angle (TIA500) and angle opening distance (AOD500), were measured as an indicator of peripheral anterior chamber morphology. We also analyzed PCT and lens vault (LV). The relationships between CCT or PCT and anterior chamber parameters were also analyzed in patients with FECD.

RESULTS

Patients with FECD had a larger CCT (593.9 ± 54.6 μm vs. 533.0 ± 25.4 μm, P < 0.001), smaller TIA500 (21.8 ± 9.9 vs. 32.5 ± 11.2 degrees, P = 0.002), smaller AOD500 (0.21 ± 0.11 vs. 0.34 ± 0.18 mm, P = 0.002), and greater LV (0.60 ± 0.27 vs. 0.40 ± 0.29 mm, P = 0.02) than control subjects. In patients with FECD, CCT was negatively correlated with the angle parameters TIA500 (R = 0.29, P = 0.009) and AOD500 (R = 0.19, P = 0.03). There were no significant correlations between PCT and TIA500 (R = 0.008, P = 0.29) or AOD500 (R = 0.007, P = 0.29). There were also no significant correlations between CCT and LV (R = 0.02, P = 0.55).

CONCLUSIONS

Larger CCT was significantly associated with narrower anterior chamber angle width, but not with LV. We showed that the severity of FECD is associated with angle chamber morphology.

Diseases of the corneal endothelium

The corneal endothelial monolayer and associated Descemet's membrane (DM) complex is a unique structure that plays an essential role in corneal function. Endothelial cells are neural crest derived cells that rest on a special extracellular matrix and play a major role in maintaining stromal hydration within a narrow physiologic range necessary for clear vision. A number of diseases affect the endothelial cells and DM complex and can impair corneal function and vision. This review addresses different human corneal endothelial diseases characterized by loss of endothelial function including: Fuchs endothelial corneal dystrophy (FECD), posterior polymorphous corneal dystrophy (PPCD), congenital hereditary endothelial dystrophy (CHED), bullous keratopathy, iridocorneal endothelial (ICE) syndrome, post-traumatic fibrous downgrowth, glaucoma and diabetes mellitus.

REVIEW: Current understanding of the pathogenesis of Fuchs' endothelial corneal dystrophy

Fuchs' endothelial corneal dystrophy (FECD) is the most prominent reason for corneal-endothelial transplantations across the globe. The disease pathophysiology manifests through a combination of various genetic and non-heritable factors. This review provides a comprehensive list of known genetic players that cause FECD, and discusses the prominent pathological features that participate in disease progression, such as channel dysfunction, abnormal extracellular matrix deposition, RNA toxicity, oxidative stress, and apoptosis. Although current practices to correct visual acuity involve surgical intervention, this review also discusses the scope of various non-surgical therapeutics to remedy FECD.