Biochemical Markers and Alterations in Keratoconus

Eccentric Pathology in Keratoconus Exhibits Stiffer Biomechanical Response than Central Pathology

Purpose

To investigate the difference in biomechanical response metrics between central and eccentric pathology and compare axial vs. tangential curvature, as well as zonal vs. single-point values.

Design

Prospective, observational, cross-sectional study.

Participants

The study included 67 eyes of 41 subjects diagnosed with keratoconus (KCN).

Methods

Pentacam tomography and Corvis ST examinations were acquired, and disease severity was defined by maximum curvature, comparing single point of maximum anterior axial curvature (Kmax) vs. magnitude of surrounding 2 mm zonal value (ZKmax) on axial maps, vs. magnitude of steepest 2 mm zone on axial (CSpot_Axi) and tangential (CSpot_Tan) maps located by Cone Location and Magnitude Index (CLMI). Distance between the corneal center and Kmax (Kmax_dist) was compared to radial distance with CLMI (CRad_Axi and CRad_Tan). Single-point Kmax, ZKmax, and CLMI-derived zones were compared with biomechanical metrics via regression analyses, including stiffness parameter at first applanation (SP-A1), deformation amplitude ratio at 2 mm (DA Ratio), integrated inverse radius (IIR), and stress-strain index (SSI). Measurements were analyzed using paired t tests, with t tests between central and eccentric disease, and a significance threshold, P < 0.05.

Main Outcome Measures

Maximum curvature using axial vs. tangential curvature, zonal vs. single-point curvature, and corneal stiffness metrics compared with cone location.

Results

Significantly greater central pathology was found using tangential (58 central and 9 eccentric) vs. axial curvature (28 central and 39 eccentric). ZKmax was significantly different than CSpot_Axi and CSpot_Tan (P < 0.0001). CRad_Axi (1.53 ± 0.41 mm) was significantly greater (P < 0.001) than Kmax_dist (1.33 ± 0.56 mm) and CRad_Tan (0.99 ± 0.34 mm). Kmax (56.09 ± 8.99 diopter [D]) was significantly greater than ZKmax (51.81 ± 7.50 D). Regressions for ZKmax, CSpot_Axi, and CSpot_Tan were significantly negative to SP-A1, stiffness parameter at highest concavity, and SSI, whereas significantly positive to DA Ratio and IIR. Regressions for Kmax_dist, CRad_Axi, and CRad_Tan had significantly positive relationships to SSI and significantly negative relationships to DA Ratio and IIR.

Conclusions

Central pathology has greater frequency with tangential than axial curvature. Corneal stiffness increases as the distance of the cone from the center increases, consistent with the focal nature of KCN. Central stiffness decreases as cone curvature (disease severity) increases. Recommendation is to use zonal values with tangential curvature to evaluate the location of the greatest curvature and changes in curvature over time.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Omics in Keratoconus: From Molecular to Clinical Practice

Keratoconus (KC) is a progressive ocular disorder marked by structural and functional alterations of the cornea, leading to significant visual impairment. Recent studies indicate that these corneal changes are linked to molecular and cellular mechanisms that disrupt and degrade the extracellular matrix. This degradation is influenced by proteinases that contribute to a loss of homeostasis and an imbalance in the antioxidant/oxidative state within the cornea, fostering oxidative stress, inflammation, and apoptosis. Although these biological processes have been identified primarily through molecular biology research, omics technologies have significantly advanced our understanding of the physiological and pathological phenomena associated with KC. Omics studies encompassing genomics, transcriptomics, proteomics, epigenomics, and metabolomics, have emerged as critical tools in elucidating the complex biological landscape of various diseases, including ocular conditions. The integrative application of these studies has demonstrated their potential in personalizing medicine across diverse fields such as oncology, neurology, and ophthalmology. This review aims to describe findings from omics research applied to keratoconus, highlighting the genomic, transcriptomic, proteomic, epigenomic, and metabolomic aspects derived from ocular and other biological samples. Notably, the molecular insights gained from these studies hold promise for identifying biomarkers of keratoconus, which could enhance diagnostic accuracy and therapeutic strategies. The exploration of these biomarkers may facilitate improved management and treatment options for patients, contributing to personalized care in keratoconus management.

Untargeted Tear Proteomics in a Large South-Asian Cohort Reveals Inflammatory Signaling, ECM Remodeling, and Altered Metabolism in Keratoconus

Purpose

Keratoconus (KC), a progressive corneal degenerative disease, is characterized by focal thinning and weakening, and the molecular pathways driving such changes are still being discovered. The progression-related pathologic molecular factors have not been identified in genetic studies from KC, and stage-specific molecular changes remain unknown in prior protein studies. We address this challenge through untargeted mass spectrometry analysis in a large KC cohort.

Methods

The cohort comprised 40 healthy individuals and 107 eyes with varying KC grades from 69 individuals. Quantitative proteomics using iTRAQ labeling coupled with two-dimensional nanoLC-ESI-MS/MS (TripleTOF 5600) was employed followed by validation.

Results

Unbiased LC-MS/MS analysis identified 1104 proteins, with 279 quantified proteins. Thirty-two proteins exhibited significant dysregulation in tear fluids compared to the control, enriched in glycolytic pathways, extra-cellular matrix (ECM) organization, reactive oxygen detoxification, and inflammatory regulation. Cystatin-S, lacritin, glutathione synthetase, and superoxide dismutase were validated to have differential expression across each KC grade.

Conclusions

Our data unveiled novel tear fluid proteins involved in unique biological processes such as neutrophil degranulation, autophagy, metabolic alterations, protein phosphorylation, and more, apart from the ECM modulation and inflammatory pathways. Although the newly identified progressive KC biomarkers will help in disease characterization, identified molecular pathways may serve as novel therapeutic targets.

The cellular response of lipopolysaccharide-induced inflammation in keratoconus human corneal fibroblasts to RB-PDT: Insights into cytokines, chemokines and related signaling pathways

PURPOSE

Rose Bengal Photodynamic Therapy (RB-PDT) offers dual therapeutic benefits by enhancing corneal stiffness and providing antibacterial activity, presenting significant potential for patients with keratoconus complicated by keratitis. Our purpose was to assess the effect of rose bengal photodynamic therapy (RB-PDT) on the expression of pro-inflammatory cytokines and chemokines, as well as on extracellular matrix (ECM)-related molecules, in lipopolysaccharide (LPS)-induced inflammation of keratoconus human corneal fibroblasts (KC-HCFs). Additionally, the involvement of the mitogen-activated protein kinase (MAPK) and nuclear factor kappa B (NF-κB) signaling pathways which are downstream of the Toll-like receptor 4 (TLR4) pathway were examined.

METHODS

KC-HCFs were stimulated with varying concentrations of LPS (0-10 μg/ml), which was followed by RB-PDT. The expression levels of interleukin-1β (IL-1β), IL-6, IL-8, interferon alpha 2 (IFNA2), IFNB1, intercellular adhesion molecule 1 (ICAM-1), chemokine (C-C motif) ligand 4 (CCL-4), collagen I, collagen V, lysyl oxidase (LOX), transforming growth factor β 1(TGF-β1) were measured using qPCR, ELISA, or western blot. The activation of the NF-κB and MAPK pathways was assessed using qPCR and western blot.

RESULTS

In LPS-induced inflammation of KC-HCFs, the expression of IL-6 was further amplified by the treatment with RB-PDT (p = 0.001). However, the activation of the MAPK and NF-κB pathways did not increase following RB-PDT. Additionally, RB-PDT reduced the transcription of collagen I and collagen V (p≤0.03), while the transcription of LOX and TGF-β1 secretion remained unchanged in KC-HCFs exposed to LPS.

CONCLUSION

In LPS-induced inflammation of KC-HCFs treated with RB-PDT, despite the increased expression of pro-inflammatory cytokines, the activation of the TLR4 signaling pathways is lacking. RB-PDT may have no adverse effects on corneal scar formation of keratoconus corneas in the short term.

Distinct Ocular Surface Microbiome in Keratoconus Patients Correlate With Local Immune Dysregulation

Purpose

Keratoconus (KC) is characterized by irregular astigmatism along with corneal stromal weakness and is associated with altered immune status. Tissue resident microbiomes are known to influence the immune status in other organs, but such a nexus has not been described in ocular conditions. Therefore, we examined the ocular surface microbiome of patients with KC and correlated it to the immune cell and tear molecular factor profiles.

Methods

Sixty-two patients with KC and 21 healthy controls underwent corneal topography analysis and eye examination followed by a collection of Schirmer's strip, ocular surface wash, and ocular surface swabs. Microbiomes were analyzed by extracting DNA from the swabs followed by 16S rRNA gene V3-V4 amplicon sequencing and analyzed using QIIME. Fifty-two molecular factors from Schirmer's strip tear extracts and 11 immune cells from ocular wash were measured using multiplex ELISA and flow cytometry. Alpha diversity, linear discriminant analysis effect size (LEfSe), relative abundance and receiver operating characteristic - area under the curve (ROC-AUC) analysis were performed. Unsupervised clustering at the genus level with clinical parameters, soluble factors, and immune cells was performed.

Results

Fifty-two phyla/class, 132 order, 283 family, and 718 genera were identified in our cohort. Alpha diversity indices were comparable between patients with KC and the healthy controls. Dominant phyla across groups were Actinobacteria, Proteobacteria, Firmicutes, and Bacteroidetes. Alphaproteobacteria increased in KC eyes whereas Actinobacteria, Firmicutes_Bacilli reduced compared with the healthy controls. We found a significant positive correlation of Microbacterium, Cutibacterium, and Brevundimonas genera abundance with keratometry and corneal thickness. Levels of IL-21, IL-9, Fractalkine, and VEGF positively correlated with Tetrasphaera (P < 0.05). β2-microglobulin and CD66bhigh cells correlated with Bacteroides (P < 0.05). CD45+ cells correlated with Escherichia_Shigella (P < 0.02).

Conclusions

We discovered a unique microbiome signature of KC which correlated to disease grades and secreted molecular factors and immune cells. Therefore, the altered microbiome on the ocular surface may drive immune dysregulation in KC and provide scope for potential interventions in the future.

Exploring New Links Among Keratoconus, Hormonal Factors, and Medications: Insights From a Case-Control Study Utilizing the All of Us Database

Purpose

We aimed to identify clinical factors associated with keratoconus (KC) risk in the All of Us database.

Methods

This retrospective matched case-control study utilized patient data from the All of Us Research Program. All patients with a KC diagnosis (n = 572) were enrolled in the study and matched with three controls (n = 1716) based on age ± 1 year, race, ethnicity, and sex. The patients' medical histories, including diabetes, sleep apnea, obesity, smoking, ocular surface disease (encompassing dry eye, eczema, and allergic or atopic conjunctivitis), allergic rhinitis, pregnancy, estrogen-containing medications, tetracyclines, and vitamin C supplementation, were collected using electronic health records. Multivariable odds ratios (ORs) between KC and health history were calculated using the R programming language.

Results

The study included 2288 participants with an average age of 58.7 years. All included variables showed a significant positive correlation with KC except smoking history, which showed a negative correlation. The most significant correlations were ocular surface disease (OR = 6.04) and obesity (OR = 1.82). Significant positive associations were also identified for tetracyclines and estrogen-containing medications with KC. Smoking was negatively correlated.

Conclusions

In addition to previously known risk factors, patients with a history of increased estrogen exposure and tetracycline usage were more likely to have a KC diagnosis whereas those with a smoking history were less likely.

Translational Relevance

Understanding the risk factors for KC, including estrogen exposure and tetracycline medications, enhances our ability to identify at-risk patients and implement earlier screening, diagnosis, and interventions.

Visual rehabilitation using rigid gas permeable contact lenses after femtosecond laser-assisted minimally invasive lamellar keratoplasty in patients with keratoconus

This study aims to observe the clinical efficacy and safety of rigid gas permeable corneal contact lenses (RGP-CLs) wearing after femtosecond laser-assisted minimally invasive lamellar keratoplasty (FL-MILK) in progressive and advanced keratoconus eyes. Twenty-five patients (27 eyes) fitted with RGP-CLs after FL-MILK were enrolled, and 22 grading-matched keratoconus patients (23 eyes) as a control group. Corneal morphological data, diopter, best corrected vision, corneal endothelium, non-invasive tear film rupture time (NIBUT), corneal perception and comfort questionnaire were analysed before and after wearing RGP-CLs. In the FL-MILK group, the flat K, steep K and Kmax of the corneal anterior surface were decreased by 3.05D, 3.48D and 7.17D respectively after surgery (P = 0.011, 0.004 and 0.007). The central corneal thickness increased by 175.29 μm (P < 0.001). The basic curve of RGP-CLs after surgery was about 0.23 mm flatter than that before surgery (P = 0.013). There was no statistical difference in the best corrected vision and the comfort of wearing RGP-CLs before and after FL-MILK (P = 0.923, 0.391). Compared with the control group, there was no significant difference in vision improvement by RGP-CLs (P = 0.669). During the follow-up, the comfort of wearing RGP-CLs in the two groups was good, and no obvious adverse events were observed. This study showed MILK significantly increases corneal thickness and flattens corneal curvature, achieving good RGP-CLs corrected vision.

Is there a relationship between the keratoconus and the peripapillary choroidal vasculature?

PURPOSE

To evaluate the peripapillary/parapapillary choroidal vascular parameters in the keratoconus (KC) and to determine the relationship between topography parameters and the peripapillary/parapapillary choroidal vascular parameters.

METHOD

Ninety eyes of ninety patients with different stages of KC and 29 eyes of twenty-nine patients without KC were enrolled in the study. Patients with KC were divided into three groups according to the Amsler-Krumeich classification scale. The choroidal vasculature was assessed by choroidal vascular parameters [such as parapapillary choroidal microvascular density (pCMVd) and peripapillary choroidal vascularity index (pCVI)]. These parameters were also evaluated for correlation with other parameters.

RESULT

The retinal nerve fibre layer thickness (RNFLT) of the superior-temporal area and the pCVI were decreased in group 3 compared to the control group (superiror-temporal RNFLT: 122.27 ± 21.43 vs 139.90 ± 21.7, p = 0.01 and pCVI: 67.04 ± 4.14 vs 69.99 ± 4.38, p = 0.04). The superior-temporal RNFLT was decreased in group 3 compared to group 2 (122.27 ± 21.43 vs 141.83 ± 25.58, p = 0.006). There was a negative correlation between pCVI and average simulated keratometry (mean sim K), but this association was weak (r = - 0.29 p = 0.001).

CONCLUSION

This study demonstrated that there may be changes in pCVI in patients with grade 3 KC and that there may be an association between pCVI and mean sim K. As KC grade increases, pCVI may decrease. Furthermore, pCVI may have a negative correlation with mean sim K.

Systemic and Ocular Associations of Keratoconus

Introduction

Keratoconus (KC) is the most prevalent corneal ectasia in the world and its pathogenesis is influenced by both ocular and systemic factors. This review explores the multifaceted associations between keratoconus and systemic health conditions, ocular characteristics, and various other environmental/exogenous factors, aiming to illuminate how these relationships influence the pathophysiology of the disease.

Areas Covered

This review will summarize the fundamental attributes of KC, review and discuss the systemic and ocular association of KC including molecular biomarkers, and provide an organized overview of the parallel alterations occurring within various biological pathways in KC.

Expert Opinion

Despite the substantial volume of research on keratoconus, the precise etiology of the disease remains elusive. Further studies are necessary to deepen our understanding of this intricate disorder and improve its management.

Comparison of long-term outcomes of simultaneous accelerated corneal crosslinking combined with intracorneal ring segment or topography-guided PRK

PURPOSE

To compare long-term outcomes of simultaneous accelerated corneal crosslinking (CXL) with intrastromal corneal ring segments (CXL-ICRS) with simultaneous accelerated CXL with topography-guided photorefractive keratectomy (CXL-TG-PRK) in progressive keratoconus (KC).

SETTING

Kensington Eye Institute and Bochner Eye Institute, Toronto, Canada.

DESIGN

Prospective nonrandomized interventional study.

METHODS

The change in visual and topographical outcomes of CXL-ICRS and CXL-TG-PRK 4 to 5 years postoperatively were compared using linear regression models adjusted for preoperative corrected distance visual acuity (CDVA) and maximum keratometry (Kmax).

RESULTS

57 eyes of 43 patients with progressive KC who underwent simultaneous accelerated (9 mW/cm 2 , 10 minutes) CXL-ICRS (n = 32) and CXL-TG-PRK (n = 25) were included. Mean follow-up duration was 51.28 (9.58) and 54.57 (5.81) months for the CXL-ICRS and CXL-TG-PRK groups, respectively. Initial mean Kmax was higher in the CXL-ICRS group compared with the CXL-TG-PRK group (60.68 ± 6.81 diopters [D] vs 57.15 ± 4.19 D, P = .02). At the last follow-up, change (improvement) in logMAR uncorrected distance visual acuity (UDVA) compared with that preoperatively was significant with CXL-ICRS (-0.31 ± 0.27, P < .001, which is equivalent to approximately 3 lines) and not significant with CXL-TG-PRK (-0.06 ± 0.42, P = .43). The logMAR CDVA improved significantly with CXL-ICRS (-0.22 ± 0.20, P < .001), but not with CXL-TG-PRK (-0.05 ± 0.22, P = .25). Adjusting for baseline Kmax and CDVA, the improvement in UDVA was significantly greater with CXL-ICRS than with CXL-TG-PRK (-0.27, 95% CI, 0.06-0.47, P = .01). Improvement in CDVA was not significantly different.

CONCLUSIONS

In this cohort of progressive KC with long-term follow-up, UDVA showed more improvement with accelerated CXL-ICRS than with CXL-TG-PRK.

Citation network analysis on keratoconus

OBJECTIVE

The high incidence of keratoconus has caused its management, etiology, and pathogenesis to be controversial topics in the ophthalmology field. This study aims to analyze the relationship between the different publications and authors through citation networks, as well as to identify the research areas and determine the most cited article.

METHODS

The search for publications was carried out through the Web of Science database, using the term "Keratoconus" between 1900 and December 2022. The Citation Network Explorer and CiteSpace software were used for the publication analysis.

RESULTS

9,655 publications were found, with 124,379 citations generated on the network. The year with the highest number of publications was 2021. The most cited publication was "Keratoconus" by Rabinowitz, published in 1998. Cluster function gave five groups of research areas about keratoconus: corneal signs and parameters, cross-linking efficiency and effects, clinical factors, keratoplasty, and treatment.

CONCLUSIONS

The citation network offers an objective and comprehensive analysis of the papers on keratoconus.

Tear Fluid Inflammatory Proteome Analysis Highlights Similarities Between Keratoconus and Allergic Conjunctivitis

Purpose

Keratoconus is characterized by the progressive thinning of the cornea, which leads to a cone-like appearance of the eye over time. Although conventionally defined as a noninflammatory condition, a number of recent studies have associated keratoconus (KC) with allergic conjunctivitis (AC) based on clinical parameters. This study aimed to consolidate this association by performing a proteomic analysis of tear fluid from patients with keratoconus and/or allergic conjunctivitis.

Methods

Of 51 patients, 17 were diagnosed with KC, 17 were diagnosed with AC, and 17 were diagnosed with both KC and AC (combined). Nine of 34 patients with KC had a progressive form of the disease. Tear fluid samples (n = 51, one eye per patient) were collected by the Schirmer's strips. Tear proteins were extracted from the Schirmer's strips. Proteomic profiling of 384 inflammatory proteins was assessed by a multiplex proximity extension assay (Olink Explore 384 Inflammation Panel I).

Results

A total of 384 inflammatory proteins were measured. Two hundred seventy-two of the 384 proteins passed stringent data cleaning and were compared among the patient groups. Compared to the 2 other groups, LGALS9 was upregulated uniquely in KC, whereas FGF19, PDGFB, HPCAL1, OSM, and FCAR were downregulated in KC. Similarly, TNFRSF4 and CCL13 were specifically upregulated in AC, whereas ectodysplasin A receptor (EDAR) was uniquely downregulated in AC.

Conclusions

High-throughput proteomic profiling of tear fluid confirms the association between KC and AC on a molecular level and raise the importance of redefining KC as an inflammatory condition.

Association between Polymorphism rs61876744 in PNPLA2 Gene and Keratoconus in a Saudi Cohort

The genetic etiology of Keratoconus (KC) in Middle Eastern Arabs of Saudi origin is still unclear. A recent genome-wide study identified two significant loci in the region of PNPLA2 (rs61876744) and CSNK1E (rs138380) for KC that may be associated with KC in the Saudi population. In addition, polymorphisms in the apolipoprotein E (APOE) gene, namely, rs429358 and rs7412, responsible for APOE allelic variants ε2, ε3, and ε4, may influence KC via oxidative stress mechanism(s). Thus, we investigated the possible association of polymorphisms rs61876744, rs138380, rs429358, rs7412, and APOE genotypes in KC patients of the Saudi population. This study included 98 KC cases and 167 controls. Polymorphisms rs6187644 and rs138380 were genotyped using TaqMan assays, and rs429358 and rs7412 were genotyped via Sanger sequencing. Although the allele frequency of rs61876744(T) in PNPLA2 was a protective effect against KC (odds ratio (OR) = 0.64, 95% confidence interval (CI) = 0.44-0.93), the p-value (p = 0.020) was not significant for multiple testing correction (p = 0.05/4 = 0.015). However, rs6187644 genotype showed a modestly significant protective effect in the dominant model (OR = 0.53, 95% CI = 0.32-0.88, p = 0.013). Polymorphisms rs138380, rs429358, and rs7412 showed no significant allelic or genotype association with KC. However, the ε2-carriers (ε2/ε2 and ε2/ε3 genotypes) exhibited a greater than 5-fold increased risk of KC, albeit non-significantly (p = 0.055). Regression analysis showed no significant effect of age, gender, and the four polymorphisms on KC. Our results suggest that polymorphism rs6187644 in PNPLA2 might be associated with KC in the Middle Eastern Arabs of Saudi origin but warrant a large-scale association analysis at this locus.

Prevalence and Associations of Keratoconus Among Children, Adults, and Elderly in the Population-Based Ural Eye Studies

PURPOSE

To estimate prevalence and associations of keratoconus in populations in Russia with an age from childhood to seniority.

METHODS

The study population consisted of the cohorts of 3 population-based studies performed in urban and rural areas within the same geographical region in Bashkortostan/Russia: the Ural Children Eye Study (UCES; age = 6-18 y; n = 4890), the Ural Eye and Medical Study (UEMS; age = >40 y; n = 5314), and the Ural Very Old Study (UVOS; age = >85 y; n = 651). Based on Scheimflug imaging, keratoconus was defined by a keratometric reading of ≥48 diopters (D) in any eye.

RESULTS

The mean maximal and minimal corneal refractive power increased from the UCES (43.58 ± 1.50 D and 42.70 ± 1.42 D, respectively) to the UEMS (44.26 ± 1.70 D and 43.61 ± 1.76 D, respectively) and to the UVOS (45.1 ± 1.72 D and 43.98 ± 1.68 D, respectively). Correspondingly, keratoconus prevalence increased from the UCES (42/4890; 0.086%; 95% CI = 0.060, 0.112) to the UEMS (112/5314; 2.11%; 95% CI = 1.72, 2.49) and to the UVOS (42/651; 6.45%; 95% CI = 4.56, 8.34). In the UCES, higher keratoconus prevalence was associated (multivariable analysis) with higher birth order [odds ratio (OR) = 2.34; 95% CI = 1.32, 4.15; P = 0.004], lower birth weight (OR = 0.99; 95% CI = 0.99, 0.99; P < 0.001), and shorter axial length (OR = 0.15; 95% CI = 0.08, 0.30; P < 0.001). In the UEMS, keratoconus prevalence correlated with shorter axial length (OR = 0.15; 95% CI = 0.10, 0.23; P < 0.001), larger corneal volume (OR = 1.17; 95% CI = 1.09, 1.25; P = 0.001), thicker lens (OR = 2.27; 95% CI = 1.06, 5.28; P = 0.04), cortical cataract degree (OR = 1.02; 95% CI = 1.01, 1.04; P = 0.01), and higher stage of age-related macular degeneration (OR = 1.65; 95% CI = 1.09, 2.51; P = 0.02). In the UVOS, keratoconus prevalence correlated with lower educational level (OR = 0.84; 95% CI = 0.71, 0.99; P = 0.04) and lower dynamometric handgrip force (OR = 0.92; 95% CI = 0.88, 0.97; P = 0.003).

CONCLUSIONS

In this study on multiethnic groups from Russia, keratoconus prevalence increased from the pediatric group (0.09%) to the adult group (2.11%) and seniority group (6.45%), correlated mostly with biometric ocular parameters and was in all age groups statistically independent of most systemic parameters.

Ocular surface inflammation and ectatic corneal disorders

PURPOSE OF REVIEW

Inflammatory mediators are a focus of recent corneal ectasia (CE) research and are a profound, modifiable contributor to CE in general and keratoconus (KC) in particular, opening a path to explore new methods of control. As advanced imaging technology and expanded population screening allow for earlier detection, the possibility of early intervention can profoundly change the prognosis of CE.

RECENT FINDINGS

Significant increases in the inflammatory mediators and immune components have been observed in the cornea, tear fluid, and blood of ectasia patients, while inflammation dampeners such as vitamin D and their receptors are reduced. Atopy and allergy have a strong association with KC, known to increase itch factors and stimulate eye rubbing, a risk factor in ectasia pathogenesis. Management of atopy or allergic conditions and topical anti-inflammatories has helped stabilize CE disease.

SUMMARY

Strategies such as monitoring inflammatory factors and using immune or inflammatory modulators, including managing subclinical inflammation, may be clinically beneficial in stabilizing the disease and improving outcomes. The detected factors are biomarkers, but as yet unproven to be sensitive or specific enough to be considered biomarkers for early detection of CE. The establishment of such biomarkers could improve the therapeutic outcome.

How Modifications of Corneal Cross-Linking Protocols Influence Corneal Resistance to Enzymatic Digestion and Treatment Depth

Purpose

The purpose of this study was to determine the effects of the Photoactivated Chromophore for Keratitis Corneal Cross-Linking (PACK-CXL) protocol modifications on corneal resistance to enzymatic digestion and treatment depth.

Methods

Eight hundred one ex vivo porcine eyes were randomly divided into groups of 12 to 86 corneas, treated with various epi-off PACK-CXL modifications, including acceleration (30 > 2 minutes, 5.4 J/cm2), increased fluence (5.4 > 32.4 J/cm2), deuterium oxide (D2O) supplementation, different carrier types (dextran versus hydroxypropyl methylcellulose [HPMC]), increased riboflavin concentration (0.1 > 0.4%), and riboflavin replenishment during irradiation (yes/no). Control group eyes did not receive PACK-CXL. A pepsin digestion assay was used to determine corneal resistance to enzymatic digestion. A phalloidin fluorescent imaging assay was used to determine the PACK-CXL treatment effect depth. Differences between groups were evaluated using a linear model and a derivative method, respectively.

Results

PACK-CXL significantly increased corneal resistance to enzymatic digestion compared to no treatment (P < 0.03). When compared to a 10 minute, 5.4 J/cm2 PACK-CXL protocol, fluences of 16.2 J/cm2 and higher increased corneal resistance to enzymatic digestion by 1.5- to 2-fold (P < 0.001). Other protocol modifications did not significantly change corneal resistance. A 16.2 J/cm2 fluence also increased collagen compaction in the anterior stroma, whereas omitting riboflavin replenishment during irradiation increased PACK-CXL treatment depth.

Conclusions

Increasing fluence will likely optimize PACK-CXL treatment effectiveness. Treatment acceleration reduces treatment duration without compromising effectiveness.

Translational Relevance

The generated data help to optimize clinical PACK-CXL settings and direct future research efforts.

Corneal Regeneration Using Gene Therapy Approaches

One of the most remarkable advancements in medical treatments of corneal diseases in recent decades has been corneal transplantation. However, corneal transplants, including lamellar strategies, have their own set of challenges, such as graft rejection, delayed graft failure, shortage of donor corneas, repeated treatments, and post-surgical complications. Corneal defects and diseases are one of the leading causes of blindness globally; therefore, there is a need for gene-based interventions that may mitigate some of these challenges and help reduce the burden of blindness. Corneas being immune-advantaged, uniquely avascular, and transparent is ideal for gene therapy approaches. Well-established corneal surgical techniques as well as their ease of accessibility for examination and manipulation makes corneas suitable for in vivo and ex vivo gene therapy. In this review, we focus on the most recent advances in the area of corneal regeneration using gene therapy and on the strategies involved in the development of such therapies. We also discuss the challenges and potential of gene therapy for the treatment of corneal diseases. Additionally, we discuss the translational aspects of gene therapy, including different types of vectors, particularly focusing on recombinant AAV that may help advance targeted therapeutics for corneal defects and diseases.

Antioxidant and Anti-Inflammatory Effects of Oral Supplementation with a Highly-Concentrated Docosahexaenoic Acid (DHA) Triglyceride in Patients with Keratoconus: A Randomized Controlled Preliminary Study

A prospective, randomized, single-center preliminary study was performed in patients with keratoconus stages I-III (Amsler-Krumeich), who received a high rich docosahexaenoic acid (DHA) (1000 mg/day) supplement for 3 months versus untreated patients. One eye per patient was evaluated. Thirty-four patients were recruited (75% men, mean age 31 years), with 15 randomized to the control group and 19 to the DHA-treated group. Corneal topography variables and plasma biomarkers of oxidative stress and inflammatory status were evaluated. A panel of fatty acids in blood samples was also assessed. There were significant between-group differences in the astigmatism axis, asphericity coefficient, and intraocular pressure in favor of the DHA group. Additionally, between-group significant differences in total antioxidant capacity (TAC), malondialdehyde (MDA), free glutathione (GSH) and GSH/GSSG ratio, as well as reduced values of inflammatory markers, including interleukin (IL)-4, IL-6, and vascular endothelial growth factor (VEGF-A) were found. These preliminary findings support the usefulness of the antioxidant and anti-inflammatory effects of DHA supplementation for targeting underlying pathophysiological mechanisms of keratoconus. Prolonged duration of DHA supplementation may be needed to detect more noticeable clinical changes in corneal topography.

Case-control study of corneal topography and specular microscopy parameters in JIA patients with and without ocular involvement

PURPOSE

To assess corneal topography and specular microscopy values in juvenile idiopathic arthritis-related uveitis (JIA-U).

METHODS

This case-control study included 30 eyes from JIA-U patients, 20 eyes from JIA patients, and 50 eyes from age- and gender-matched healthy subjects. Patients with a history of ocular diseases or intraocular surgery were excluded. Corneal topography maps (Pentacam HR) and specular microscopy images (CellChek SL) were obtained. The measurements of the groups were compared.

RESULTS

Keratometric astigmatism was higher in the JIA-U group than in the control group (p = 0.040). Patients with astigmatism greater than 1.50D were more common in the JIA-U group than in the control group (p = 0.026). The JIA-U group had higher anterior and posterior elevation values than the control group (p = 0.006, p = 0.025). The density of endothelial cells, coefficient of variation, and hexagonality did not change across groups (p = 0.465, p = 0.096, p = 0.869). The total number of exacerbations and the duration of anterior chamber inflammation were both positively correlated with posterior elevation (r = 0.600, p 0.001; r = 0.583, p 0.001). The age of diagnosis was found to be negatively correlated with anterior elevation (r = -0.412, p = 0.021).

CONCLUSION

Corneal astigmatism, as well as anterior and posterior elevation values, were all higher in JIA-U patients. Endothelial cell density and morphology, on the other hand, did not differ significantly between groups. Chronic inflammation's impact on stromal remodelling could explain these corneal alterations. The positive correlation between posterior elevation and the number of flares and duration of inflammation represents the importance of early diagnosis and effective treatment.

Revealing the presence of tear extracellular vesicles in Keratoconus

Extracellular vesicles (EVs) are lipid-bound vesicles that originate from the endosomal system or budded off from the plasma membrane. EVs are involved in cell-cell communication via transporting DNA, RNA, and proteins from one cell to another. Tear EVs (tEVs) have been reported in dry eye, Sjӧgren's Syndrome, and primary open-angle glaucoma. In this study, we sought to investigate the presence of tEVs in relation to keratoconus (KC). Tears were passively collected from the lateral meniscus from 10 healthy (5 males and 5 females) and 9 KC (4 males and 5 females) subjects. Tear samples were processed and analyzed using the ExoView™ R100. Statistical analysis was performed using a Mann-Whitney U non-parametric Student's t-test. All tEVs, in both Healthy and KC subjects, showed a CD9+ dominant tEV cohort independent of sex. A significant decrease in CD63+/CD9+ and CD63+/CD81+/CD9+ was found in the male KC tEVs (p < 0.05), but not in females compared to their healthy counterparts. Neither Healthy nor KC tEVs showed differences in the total number of tEVs, however significant differences were identified between the sexes (p < 0.05), with males having a higher number of tEVs. tEVs diameters ranged from 50 to 200 nm, in both Healthy and KC cohorts, with the majority in the 50-80 nm range suggesting exosome-dominant cohorts. To our knowledge, this is the first time, to date, that tEVs have been isolated and characterized in KCs. While further studies are warranted, the tEVs differences between KC and Healthy subjects suggest a potential role for tEVs in KC pathogenesis.

Corneal stromal repair and regeneration

The cornea is a specialized, transparent, avascular, immune-privileged, and heavily innervated tissue that affords 2/3rd of refraction to the eye. Ocular injuries, infections, and genetic factors affect corneal function and cause vision impairment. Presently, a variety of laser/non-laser surgeries, immunosuppressants, and/or corneal transplants are predominantly used to revive sight in human patients. The development of novel, precision-guided, and tissue-targeted non-surgical therapies promoting corneal repair and regeneration based on mechanistic understanding is of paramount importance to reduce the impact of global blindness. Research over the past decade revealed that modulation of pathological signaling pathways and factors by a variety of therapeutic delivery methods effectively treats corneal disorders including corneal scar/haze, inflammation, and angiogenesis in various pre-clinical animal models and are primed for human translation. This review discusses recent advances in the areas of corneal repair, restoration, and regeneration. Herein, we provide an overview of evolving approaches and therapeutic modalities that have shown great promise in reviving corneal transparency and function through the use of small drug molecules, gene therapy, nanomedicine, stem cells, trophic factors, exosomes, stromal equivalents, bioengineered stromal scaffolds, tissue adhesives, and 3D bioprinting.

Choroidal thickness assessment in keratoconus patients treated with cross-linking compared to healthy population

PURPOSE

To analyze the choroidal thickness between patients with keratoconus undergoing cross-linking treatment and a healthy population, as well as to determine the factors that influence choroidal thickness.

METHODS

This was an observational, analytical, case-control study that was conducted from February 2021 to June 2021. Choroidal thickness was measured at different locations, including the subfoveal, nasal (1000 μm), temporal (1000 μm), superior (1000 μm) and inferior (1000 μm) locations using a Spectral-domain optical coherence tomography with enhanced depth imaging, which allowed us to obtain horizontal and vertical B-scans centered on the fovea.

RESULTS

This study included 21 patients with keratoconus (mean age, 21.86 ± 5.28 years) and 28 healthy patients (mean age, 24.21 ± 4.71 years). Choroidal thickness was significantly greater in patients with keratoconus than in healthy patients in each of the following measured locations: subfoveal (P < 0.001); nasal (1000 μm) (P < 0.001), temporal (1000 μm) (P < 0.001), superior (1000 μm) (P < 0.001) and inferior (1000 μm) (P < 0.001) locations. Variables such as age (ρ = - 0.09; P = 0.50) and refraction (ρ = 0.14; P = 0.34) were not found to be associated with choroidal thickness. In a stepwise multiple linear regression, the group was the single variable correlated with choroidal thickness (β = 0.88; P < 0.001).

CONCLUSION

Choroidal thickness is thicker in keratoconus patients treated with cross-linking than in the healthy population. This finding could be associated with inflammatory choroidal mechanisms in keratoconus patients, but more studies are needed. Age and refractive error do not seem to influence choroidal thickness.

Nutritional and Metabolic Imbalance in Keratoconus

Keratoconus (KC) is a progressive corneal degeneration characterized by structural changes consisting of progressive thinning and steepening of the cornea. These alterations result in biomechanical weakening and, clinically, in vision loss. While the etiology of KC has been the object of study for over a century, no single agent has been found. Recent reviews suggest that KC is a multifactorial disease that is associated with a wide variety of genetic and environmental factors. While KC is typically considered a disease of the cornea, associations with systemic conditions have been well described over the years. In particular, nutritional and metabolic imbalance, such as the redox status, hormones, metabolites, and micronutrients (vitamins and metal ions), can deeply influence KC initiation and progression. In this paper, we comprehensively review the different nutritional (vitamins and minerals) and metabolic (hormones and metabolites) factors that are altered in KC, discussing their possible implication in the pathophysiology of the disease.

Sex Hormones, Growth Hormone, and the Cornea

The growth and maintenance of nearly every tissue in the body is influenced by systemic hormones during embryonic development through puberty and into adulthood. Of the ~130 different hormones expressed in the human body, steroid hormones and peptide hormones are highly abundant in circulation and are known to regulate anabolic processes and wound healing in a tissue-dependent manner. Of interest, differential levels of sex hormones have been associated with ocular pathologies, including dry eye disease and keratoconus. In this review, we discuss key studies that have revealed a role for androgens and estrogens in the cornea with focus on ocular surface homeostasis, wound healing, and stromal thickness. We also review studies of human growth hormone and insulin growth factor-1 in influencing ocular growth and epithelial regeneration. While it is unclear if endogenous hormones contribute to differential corneal wound healing in common animal models, the abundance of evidence suggests that systemic hormone levels, as a function of age, should be considered as an experimental variable in studies of corneal health and disease.

Keratoconus patients exhibit a distinct ocular surface immune cell and inflammatory profile

Inflammatory factors have been considered to contribute to keratoconus (KC) pathogenesis. This study aims to determine the immune cells subsets and soluble inflammatory factor profile on the ocular surface of KC patients. 32 KC subjects (51 eyes) across different grades of severity and 15 healthy controls (23 eyes) were included in the study. Keratometry and pachymetry measurements were recorded. Ocular surface immune cells (collected by ocular surface wash) immunophenotyped using flow cytometry include leukocytes, neutrophils, macrophages, natural killer (NK) cells, pan-T cells, gamma delta T (γδT) cells and NKT cells. Tear fluid collected using Schirmer's strip was used to measure 50 soluble factors by multiplex ELISA. Proportions of activated neutrophils, NK cells and γδT cells were significantly increased in KC patients. Significantly higher levels of tear fluid IL-1β, IL-6, LIF, IL-17A, TNFα, IFNα/β/γ, EPO, TGFβ1, PDGF-BB, sVCAM, sL-selectin, granzyme-B, perforin, MMP2, sFasL and IgE, along with significantly lower levels of IL-1α and IL-9 were observed in KC patients. Alterations observed in few of the immuno-inflammatory parameters correlated with grades of disease, allergy, eye rubbing and keratometry or pachymetry measurements. The observation implies a distinct immuno-inflammatory component in KC pathogenesis and its potential as an additional therapeutic target in KC management.

Influence of interleukin 17 A and 17 F polymorphisms in keratoconus

BACKGROUND

Until a few years ago, keratoconus was defined as a noninflammatory degenerative disease. However, recent studies have shown that the altered balance between inflammatory cytokines, proteases, and protease inhibitors, as well as free radicals and oxidants, have a crucial role in the pathogenesis of this disease. The aim of this study is to investigate whether interleukin 17 A G197A (rs2275913) and interleukin 17 F T7488C (rs763780) polymorphisms are associated with keratoconus in patients from a population of the northwestern region of the State of São Paulo, Brazil.

METHODS AND RESULTS

35 patients and 61 controls were enrolled. Genotyping of interleukin 17 A G197A and interleukin 17 F T7488C polymorphisms was carried out using the polymerase chain reaction-restriction fragment length polymorphism technique. Statistical analyses were conducted using the chi-square test, and an odds ratio with a 95% confidence interval was also calculated to evaluate the association between polymorphisms and disease. Evaluating interleukin 17 F T7488C, we found that the TT genotype is associated as a risk factor for keratoconus (P = 0.04; OR = 3.01; CI 1.11-8.14). As for evaluating interleukin 17 A G197A, the allele and genotype frequencies between patients and controls were compared and no statistically significant differences were found.

CONCLUSIONS

Our data showed that the interleukin 17 F T7488C polymorphisms may exert an influence in keratoconus.

Increased epithelial backscatter: A novel finding in subclinical and clinical keratoconus

BACKGROUND

To assess alterations in backscatter from the corneal epithelium, anterior stroma and lens surface in eyes with subclinical, mild and moderate keratoconus (KC).

METHODS

In this single-centre, cross-sectional study involving 24 eyes with subclinical KC, 107 eyes with manifest KC (mild = 40 and moderate = 67 eyes) and 90 controls, line densitometry was performed with Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) to obtain simultaneous backscatter values for the corneal epithelium, anterior stroma and anterior lens surface. Backscatter values and Pentacam parameters were used in subsequent statistical analyses.

RESULTS

Eyes with subclinical, mild and moderate KC had similar epithelial and stromal backscatter (P > 0.05) that was significantly increased compared with the controls (P < 0.05). Although anterior lens surface backscatter did not differ between the control and KC groups (P > 0.05), it was significantly higher in the mild and moderate KC groups than in the subclinical KC group (P < 0.05). In the KC group (n = 131) epithelial backscatter was strongly correlated with stromal backscatter (r = 0.911, P < 0.0001).

CONCLUSIONS

Increased epithelial backscatter and a strong correlation with anterior stromal backscatter in the KC groups were consistent with the epithelium-stroma interaction involved in KC pathogenesis. Single-point backscatter analysis can be used with point clouds to construct epithelial and stromal backscatter maps in Pentacam to aid the detection of KC as a novel feature.

Progressive corneal ectatic disease in pregnancy

Pregnancy influences ocular changes which may exacerbate existing or develop new pathology. This review summarises the existing evidence on the association between pregnancy and progressive keratoconus or iatrogenic keratectasia. Ten online databases were searched systematically. Eligible studies were published in English and reported objective ophthalmic outcomes for women with evidence of (i) a new diagnosis of keratoconus, (ii) keratoconus progression or (iii) iatrogenic keratectasia following refractive surgery; during or within one year of pregnancy. Strength of evidence was assessed using the Oxford Centre for Evidence-Based Medicine levels of evidence. Seventeen articles have reported 33 peripartum women with new-onset or progressive ectasia, evident by signs of corneal hydrops or protrusion (n = 8); steepening on topography imaging (n = 20); a mean decline in best corrected visual acuity by +0.20 logMAR (95% CI -0.01 to +0.40, n = 23); a mean increase in maximum keratometry by 2.18 D (95% CI 1.44 to 2.91, n = 42); a mean decline in spherical equivalent refraction by -1.33 D (95% CI -1.73 to -0.93, n = 41); and a mean increase in astigmatism by -1.61 D (95% CI -2.46 to -0.75, n = 19). Pregnancy is associated with progressive ectasia in some women including those with previously stable keratoconus, or a history of laser-assisted in situ keratomileusis surgery or no history of corneal ectasia. This review highlights the heterogeneity in limited existing evidence, the need for a standardised definition of ectasia progression and further prospective studies for clinical guidelines. Closely monitoring women at risk may assist in early intervention with collagen cross-linking and prevent peripartum vision loss.