Serum 25-Hydroxy Vitamin D, Vitamin B12, and Folic Acid Levels in Progressive and Nonprogressive Keratoconus

Definition of Progressive Keratoconus: A Systematic Review

PURPOSE

To identify the definitions used for progressive keratoconus in the literature.

METHODS

A systematic literature review aimed to identify the definitions used for "progressive keratoconus" in the published articles. A comprehensive search from January 2018 to May 2023 was conducted across Cochrane Library, PubMed, Taylor & Francis, Web of Science, and other bibliographic databases at Oftalmosalud, Lima, Peru. The inclusion criteria were articles including patients with keratoconus without any previous surgical procedure and containing the definition of "progressive keratoconus" or "keratoconus progression" and a sample size greater than 10 eyes.

RESULTS

A total of 221 articles were included for analysis. The 3 most frequent parameters to define progression included data from anterior curvature, pachymetry, and refraction used in 97.8% (216/221), 37.6% (83/221), and 32.1% (71/221) of the articles, respectively. Specifically, the most frequent criterion used was maximum keratometry (Kmax), used in 85.5% (189/221) of the articles. Progression was assessed between 6- and 12-month follow-up in 64.7% (143/221) of the articles. Data from posterior cornea were used in only 8.1% (18/221) of the studies. None of the studies included data from the corneal epithelium.

CONCLUSIONS

The present study demonstrates the lack of unified criteria to define progression of keratoconus and an underutilization of the technology described. It also shows that the single point Kmax measurement is the most commonly used criterion, followed by a change in refractive astigmatism and thinning at the thinnest pachymetric point.

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.

The Role of Vitamin D3 in Ocular Diseases

Vitamin D3 plays a vital role in numerous physiological processes within the human body, including having a positive effect on eye health. It is renowned for its immunomodulatory, anti-inflammatory, antioxidant, and angiogenic properties. Its deficiency is evolving into a significant global challenge. In order to explain the connection between vitamin D3 and various ocular diseases, 84 relevant studies, mainly from the PubMed database, published in English between 1999 and 2024 were analyzed. Ocular tissues can activate and regulate vitamin D levels, which emphasizes the significance of this nutrient in maintaining eye homeostasis. While there is suggestive evidence for a probable association between vitamin D3 and ocular health, more robust research is needed to establish causation and inform clinical guidelines.

Thyroid gland dysfunction and vitamin D receptor gene polymorphism in keratoconus

OBJECTIVES

To detect the serum level of thyroid hormones, vitamin D and vitamin D receptors (VDR) polymorphism in keratoconus (KC) patients and to identify the association between vitamin D deficiency and thyroid dysfunction in KC.

METHODS

This cross sectional study included 177 KC patients with no thyroid disorders compared to 85 healthy controls with normal corneal tomography. Measurements of thyroid stimulating hormone (TSH), free triiodothyronine (FT3), free tetraiodothyronine (FT4) and serum 25-OH vitamin D were done using Enzyme linked immusoassay (ELISA test). VDR polymorphisms were tested including [Taq I (rs731236), Apa I (rs7975232) and Bsm I (rs1544410)] using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

An increase in frequency of thyroid disorders (P = 0.04), decrease in serum 25(OH) vitamin D level (P < 0.001), Taq 1 and tt genotype (P < 0.001) were significantly distributed in KC patients. A significantly higher serum 25(OH) vitamin D level was reported in TT genotype, while insufficient level was more common in Tt genotype (P < 0.001). A deficient serum 25(OH) vitamin D level was predominant in tt genotype (P < 0.001). A 95% confidence interval was in TSH (1.603, 2.946), FT4 (24.145, 77.06), hypothyroidism (1.062, 67.63), insufficient (2.936, 11.643) and deficient vitamin D (5.283, 28.704) and all were significant risk factors for KC with (P < 0.05).

CONCLUSIONS

Both thyroid disorders and low vitamin D are potential factors for KC development. Studying VDR at the molecular level provides interesting avenues for future research toward the identification of new KC cases.

Comparison of blood levels of vitamin B12, folic acid, riboflavin, and homocysteine in keratoconus and healthy subjects

PURPOSE

To evaluate blood levels of vitamin B12, folic acid, riboflavin, and homocysteine in keratoconus (KC) and healthy subjects.

SETTING

Eskişehir Osmangazi University, Eskişehir, Turkey.

DESIGN

Cross-sectional study.

METHODS

100 KC patients (patient group) between the ages of 18 to 35 years and 200 healthy individuals (control group) in the same age range were included in the Eskişehir Osmangazi University Hospital Eye Clinic between October 2019 and March 2020. In all cases, a complete ophthalmologic examination and corneal tomography evaluation with a Pentacam Scheimpflug camera were performed. In blood samples, vitamin B12 and folic acid levels were measured using an electrochemiluminescence immunoassay analyzer, and homocysteine and riboflavin levels were measured using high-performance liquid chromatography. Chi-square tests were used in the analysis of categorical variables, and Mann-Whitney U and Kruskal-Wallis tests were used in the analysis of numerical variables.

RESULTS

Homocysteine (13.0 ± 6.6 vs 12.1 ± 5.4 μmol/L, P = .190), vitamin B12 (313.5 ± 119.4 vs 322.9 ± 128.3 pg/mL, P = .619), and folic acid (7.0 ± 2.7 vs 7.4 ± 2.9 ng/mL, P = .230) levels were not different between KC (100 eyes of 100 subjects) and control (200 eyes of 200 subjects) groups. The mean riboflavin level was 84.0 ± 21.8 μg/L in the patient group and 183.6 ± 74.3 μg/L in the control group, with a significant difference between the 2 groups ( P < .001). Riboflavin levels were below 180 μg/L in 99% (n = 99) of the cases in the KC group and 53.5% (n = 107) in the control group ( P < .001).

CONCLUSIONS

Low blood riboflavin levels in KC patients may be a possible risk factor in the pathogenesis of KC.

Artificial intelligence-based stratification of demographic, ocular surface high-risk factors in progression of keratoconus

Purpose

The purpose of this study was to identify and analyze the clinical and ocular surface risk factors influencing the progression of keratoconus (KC) using an artificial intelligence (AI) model.

Methods

This was a prospective analysis in which 450 KC patients were included. We used the random forest (RF) classifier model from our previous study (which evaluated longitudinal changes in tomographic parameters to predict "progression" and "no progression") to classify these patients. Clinical and ocular surface risk factors were determined through a questionnaire, which included presence of eye rubbing, duration of indoor activity, usage of lubricants and immunomodulator topical medications, duration of computer use, hormonal disturbances, use of hand sanitizers, immunoglobulin E (IgE), and vitamins D and B12 from blood investigations. An AI model was then built to assess whether these risk factors were linked to the future progression versus no progression of KC. The area under the curve (AUC) and other metrics were evaluated.

Results

The tomographic AI model classified 322 eyes as progression and 128 eyes as no progression. Also, 76% of the cases that were classified as progression (from tomographic changes) were correctly predicted as progression and 67% of cases that were classified as no progression were predicted as no progression based on clinical risk factors at the first visit. IgE had the highest information gain, followed by presence of systemic allergies, vitamin D, and eye rubbing. The clinical risk factors AI model achieved an AUC of 0.812.

Conclusion

This study demonstrated the importance of using AI for risk stratification and profiling of patients based on clinical risk factors, which could impact the progression in KC eyes and help manage them better.

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.

Association of keratoconus with serum levels of 25-hydroxyvitamin D and antioxidant trace elements: A systematic review and meta-analysis

The aim of this systematic review and meta-analysis was to summarize and compare the available evidence on the level of vitamin D and antioxidant trace elements between the keratoconus (KC) patients and healthy controls. Seven case-control studies with 830 subjects were found eligible with a systematic search using PubMed, SCOPUS, Web of Science, and EMBASE till November 21, 2021. Data were synthesized with a DerSimonian and Laird random-effects method of meta-analysis. The mean serum vitamin D level was significantly lower in the patients with KC [standardized mean difference (SMD): -0.71; P < 0.001] as compared with the control group. The mean serum vitamin D level decreased more in the progressive patients (SMD: -0.80; P = 0.016) than in the stable patients (SMD: -0.66; P < 0.001) when compared with the control group. The mean serum zinc level was found significantly lower in the patients with KC compared with the control group (SMD: -1.98; P = 0.005). Pooled analysis based on the two studies showed significantly lower mean selenium levels in the KC patients (SMD: -0.34; P = 0.003). Regular evaluation of serum vitamin D, zinc, and selenium levels among the patients with KC at disease onset and future follow-ups could be promising in predicting the progressive disease and disease severity.

Vitamin D, the Vitamin D Receptor, Calcitriol Analogues and Their Link with Ocular Diseases

The global prevalence of eye diseases continues to grow, bringing with it a reduction in the activity levels and quality of life of patients, and partial or complete blindness if left untreated. As such, there is considerable interest in identifying more effective therapeutic options and preventive agents. One such agent is vitamin D, known to have a range of anti-cancer, anti-angiogenic, anti-inflammatory and anti-oxidative properties, and whose deficiency is linked to the pathogenesis of a range of cardiovascular, cancer, and inflammatory diseases. This review presents the current stage of knowledge concerning the link between vitamin D and its receptor and the occurrence of eye disease, as well as the influence of analogues of calcitriol, an active metabolite of vitamin D. Generally, patients affected by various ocular disorders have vitamin D deficiency. In addition, previous findings suggest that vitamin D modulates the course of eye diseases and may serve as a marker, and that its supplementation could mitigate some disorders. However, as these studies have some limitations, we recommend further randomized trials to clarify the link between vitamin D and its activity with eye disease.

Vitamin D and Ocular Diseases: A Systematic Review

The contributory roles of vitamin D in ocular and visual health have long been discussed, with numerous studies pointing to the adverse effects of vitamin D deficiency. In this paper, we provide a systematic review of recent findings on the association between vitamin D and different ocular diseases, including myopia, age-related macular degeneration (AMD), glaucoma, diabetic retinopathy (DR), dry eye syndrome (DES), thyroid eye disease (TED), uveitis, retinoblastoma (RB), cataract, and others, from epidemiological, clinical and basic studies, and briefly discuss vitamin D metabolism in the eye. We searched two research databases for articles examining the association between vitamin D deficiency and different ocular diseases. One hundred and sixty-two studies were found. There is evidence on the association between vitamin D and myopia, AMD, DR, and DES. Overall, 17 out of 27 studies reported an association between vitamin D and AMD, while 48 out of 54 studies reported that vitamin D was associated with DR, and 25 out of 27 studies reported an association between vitamin D and DES. However, the available evidence for the association with other ocular diseases, such as glaucoma, TED, and RB, remains limited.

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.

Tear Proteomics in Keratoconus: A Quantitative SWATH-MS Analysis

Purpose

To elucidate dysregulated proteins in keratoconus (KC) to provide a better understanding of the molecular mechanisms that lead to the development of the disease using sequential window acquisition of all theoretical mass spectra (SWATH-MS) as a protein quantification tool of the tear proteomic profile.

Methods

Prospective cross-sectional study that includes 25 keratoconic eyes and 25 healthy eyes. All participants underwent a clinical, tomographic, and aberrometric exam. Tear sample was collected using Schirmer strips and analyzed by liquid chromatography with tandem mass spectrometry. SWATH-MS was used as a quantification tool of the tear proteomic profile. The expression of the quantified proteins was compared between groups, and the biological and molecular functions of the dysregulated proteins as well as their functional relationships were studied by in silico analysis.

Results

A total of 203 proteins were quantified in tear samples of patients with KC and control participants, of which 18 showed differential expression between groups (P < 0.05). An increase in the expression of 7 proteins and a decrease in the expression of 11 proteins were observed. Protein–protein interactions and gene ontology analysis showed the involvement of these dysregulated proteins in structural, inflammatory-immune, iron homeostasis, oxidative stress, and extracellular matrix proteolysis processes.

Conclusions

Tear protein quantification has revealed the dysregulation of proteins involved in biological processes previously associated with KC. Among them, iron homeostasis should be highlighted as a relevant pathway in the KC pathophysiology, and it should be taken into account in the development of therapeutic targets to cope with tissue damage derived from iron accumulation and toxicity.