Spectrum of Darkness, Agent of Light: Myopia, Keratoconus, Ocular Surface Disease, and Evidence for a Profoundly Vitamin D-dependent Eye

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.

Association between serum vitamin D and refractive status in United States adolescents: A cross-sectional study

Purpose

We performed this study to determine the relationship between serum vitamin D levels and refractive status in adolescents aged 12-19 years.

Methods

Cross-sectional study using the National Health and Nutrition Examination Survey (NHANES) database from 2001 to 2006. We used weighted multivariate linear regression models to assess the association between serum vitamin levels and adolescent refractive status and then built a smooth curve fitting to investigate their internal non-linear relationships. Finally, subgroup analysis was performed according to gender, and the threshold effect of serum vitamin D levels on spherical equivalent degree was analyzed using a two-piecewise linear regression model.

Result

A total of 5,901 adolescents aged 12 to 19 years were included in this study. After adjusting for all confounding factors, the multiple linear regression model showed no significant correlation between adolescent spherical equivalent degree and serum vitamin D [0.0019 (-0.0018, 0.0046)]. However, smooth curve fitting analysis showed an inverted U-shaped curve relationship between spherical equivalent degree and serum vitamin D levels in adolescents (turning point: 58.1 nmol/L). In analyses by gender subgroup, this inverted U-shaped relationship was found to be more pronounced in female adolescents (turning point: 61.6 nmol/L).

Conclusion

Our results suggest that the correlation between refractive status and serum vitamin D in adolescents differs by gender. When serum vitamin D concentrations were <61.6 nmol/L in female adolescents and <53.2 nmol/L in male adolescents, the spherical equivalent degree showed a positive correlation with serum vitamin D levels. However, there was no significant correlation when adolescent vitamin levels exceeded this threshold.

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.

Observations on Refractive Status and Risk Factors for Visual Impairment in Children with Disabilities

Vision integrates all the senses and plays a fundamental role in the acquisition of different skills and the general development of a child. Recently, refractive errors and visual impairment have become serious health problems among children. Background and Objectives: The aim of this study was to identify the prevalence of refractive errors and visual impairment in children with disabilities. Moreover, this study aimed to explore the risk factors for visual impairment in children with respect to vitamin D levels, parental smoking, and the use of spectacles. Materials and Methods: We retrospectively analyzed 161 children aged 5–16 years old, divided into two groups: a group of 80 children with disabilities and a control group consisting of 81 clinically healthy children. All the children underwent refraction measurements, visual acuity testing, and plasmatic vitamin D level dosing, measured in ng/mL. Results: Refractive errors and visual impairment were found to have a higher prevalence in the group of children with disabilities than in the control group. Moreover, the plasma level of vitamin D was lower in the group of children with special health needs. Conclusions: Given the present results, children with disabilities should undergo special eye examinations as soon as possible to ensure the quality of their socio-academic lives.