Hypothyroidism is Not Associated with Keratoconus Disease: Analysis of 626 Subjects

Causal Links Between Systemic Disorders and Keratoconus in European Population

PURPOSE

To establish the presence of a causal linkage between prevalent systemic diseases and keratoconus (KC).

DESIGN

Mendelian randomization (MR) analysis.

METHODS

After an exhaustive screening process, genetic variants linked to various systemic diseases were identified as instrumental variables at the genome-wide significance level. Subsequently, MR analyses were conducted to elucidate their potential causal connection with KC (N = 26,742). The encompassed systemic ailments comprise diabetes, hay fever/allergic rhinitis/eczema, obstructive sleep apnea, thyroid dysfunction, aortic aneurysm, major depressive disorder, inflammatory bowel disease (including Crohn's disease and ulcerative colitis), and mitral valve prolapse. Our study adheres to the principles of Strengthening the Reporting of Observational Studies in Epidemiology Using MR guidelines.

RESULTS

Using inverse variance weighting as the primary MR analysis method, our findings revealed that hay fever/allergic rhinitis/eczema (odds ratio, 10.144; 95% CI, 2.441-42.149; P = .001) and ulcerative colitis (odds ratio, 1.147; 95% CI, 1.054-1.248; P = .002) were associated with an increased risk of KC within the largest population under scrutiny. Conversely, the prolonged hyperglycemic state did not exhibit a potentially protective effect in delaying the pathogenesis of KC, and no correlation was observed between the two (odds ratio, 0.320; 95% CI, 0.029-3.549; P = .353). Also, obstructive sleep apnea, thyroid function, aortic aneurysm, major depressive disorder, Crohn's disease, and mitral valve prolapse did not exhibit a causal association with KC (P > .05 for all comparisons).

CONCLUSIONS

This study indicates an increased risk of KC related to hay fever/allergic rhinitis/eczema and ulcerative colitis, with diabetes not providing a protective effect. These findings may potentially contribute some insights to inform clinical interventions.

Ten-year incidence of keratoconus in relation to sex, age, and thyroid gland dysfunction: a nationwide population-based cohort study (2009-2018)

Background

Keratoconus is a corneal ectatic disorder that often leads to visual impairment and may require corneal transplantation. However, its age and gender-based incidence and potential association with thyroid gland dysfunction (TGD) remain poorly understood. This study aims to clarify these aspects and investigate the possible connection between keratoconus and TGD.

Methods

We conducted a nationwide population-based cohort study using data from the Korean National Health Insurance Service database. A retrospective chart review was conducted on 4,059,021 patients aged over 20 without underlying corneal diseases in 2009. The end of the review period was at ten years, or until the onset of keratoconus. To evaluate the association with TGD, multivariate Cox regression analysis was used with adjustment of confounding variables such as sex and age.

Results

During the review period, 2,334 patients developed keratoconus before the 10-year mark. Females exhibited a higher keratoconus incidence (7.101 per 100,000 person-years) compared to males (5.559) (P<0.001). After adjusting for age, the hazard ratio (HR) for keratoconus was 1.295 times higher [95% confidence interval (CI): 1.193-1.406] in females compared to males. Age groups were stratified in 10-year intervals. The highest incidence of keratoconus was observed in the 20 to 29-year age group (10.695 per 100,000 person-years). All other age groups had significantly lower HR values, with the lowest at 50-59 years (0.508, 95% CI: 0.447-0.577). Keratoconus incidence per 100,000 person-years was 6.227 in subjects without TGD, 6.019 in the hypothyroidism group and 8.287 in the hyperthyroidism group, respectively. Although not statistically significant, individuals with hyperthyroidism showed a higher HR (1.290, 95% CI: 0.939-1.771) for keratoconus when compared to those without TGD, after adjusting for age and sex.

Conclusions

This study emphasizes a female predominance in keratoconus incidence and suggests a possible connection between hyperthyroidism and keratoconus. Furthermore, it affirms a higher incidence of keratoconus among young individuals.

Impact of Hypothyroidism on Tomography and Biomechanics in Keratoconus - Cross-Sectional and Longitudinal Assessment within the Homburg Keratoconus Center at the Time of Inclusion and after 1 Year

BACKGROUND AND PURPOSE

The etiology of keratoconus (KC) is probably multifactorial but remains essentially unknown. Previous scientific observations have suggested that hypothyroidism might play a role in the development and progression of KC. The purpose of this study was to analyze the tomographic and biomechanical parameters in KC patients with or without hypothyroidism.

METHODS

Twenty-eight patients with KC and hypothyroidism (HT group) and fifty-six KC patients without thyroid dysfunction (WHT group) with matching gender and age were analyzed. Mean age was 40.3 years (range 14 - 57) in the HT group and 40.3 years (range 14 - 57) in the WHT group. Routine ophthalmic examinations consisted of corneal tomography and biomechanical parameters. We extracted the following KC parameters from the Pentacam (Pentacam HR, Oculus, Wetzlar, Germany): Keratoconus Index (KI), maximum keratometry (Kmax), astigmatism, and thinnest pachymetry (TP). From the ocular response analyzer (ORA, Reichert Ophthalmic Instruments, Depew, NY, USA), we extracted corneal hysteresis (CH), corneal resistance factor (CRF), and KC match index (KMI).

RESULTS

The comparison of the tomographic and biomechanical values from cross-sectional and longitudinal analyses showed no significant differences between the HT and WHT groups.

CONCLUSION

The severity of KC based on tomographical and biomechanical parameters does not seem to depend on the presence of hypothyroidism.

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.

Effect of Thyroxine on Transforming Growth Factor β1, Collagen I, and V Expression in Keratoconus Corneal Fibroblasts and Keratocytes, in Vitro

BACKGROUND

Keratoconus (KC) is a corneal disorder, associated with oxidative stress, hypoxia and as several times discussed, potentially with thyroid gland dysfunction. We aimed to investigate the effect of thyroxine on transforming growth factor β1 (TGF-β1), collagen I and V (Col I and V) expression in human corneal fibroblasts (HCFs) and human keratocytes of KC corneas, in vitro.

METHODS

Primary human KC-keratocytes and normal keratocytes were isolated and cultured as corneal fibroblasts or keratocytes. The effect of 0.1 µg/ml and 1.0 µg/ml thyroxine on TGF-β1, Col I and Col V expression was investigated by qPCR, Western blot, and ELISA. Proliferation assay was performed using BrdU ELISA to observe the 24h effect of 1.0 µg/ml thyroxine on keratocytes, in vitro.

RESULTS

TGFB1 mRNA expression of normal keratocytes increased following 1.0 µg/ml thyroxine stimulation for 24 h (p = .036), without changes in protein expression. Col I protein expression of KC-HCFs increased following 1.0 µg/ml thyroxine stimulation for 24 h (p = .0003). Proliferation of normal and KC keratocytes increased following a 7-day growth period and 24 hours thyroxine administration (p = .018; p = .024).

CONCLUSIONS

Thyroxine may affect the Col I protein expression in KC-HCFs, but not in KC keratocytes, in vitro. Thyroxine administration has no effect on TGF-β1, collagen I and V expression of keratoconus keratocytes. Therefore, an increased thyroxine concentration alone seems not to be causally related to the development of keratoconus.

Is keratoconus associated to thyroid diseases? Assessment of the corneal parameters in patients with congenital hypothyroidism

PURPOSE

To investigate the association between keratoconus and congenital hypothyroidism (CH).

PATIENTS AND METHODS

Patients were enrolled in this study and divided into two groups. The first group comprised 31 subjects (11M:20F) with the mean age of 15.2 ± 3.9 years. affected by CH, and the control group was composed by 19 healthy individuals (8M:11F) aged 14.3 ± 4.6 years. All patients underwent complete ophthalmologic examination with visual acuity assessment, refraction, slit lamp examination, and retinoscopy. Corneal parameters were measured using Scheimpflug camera (Pentacam^® Oculus, Germany). The main outcome measures considered for evaluation were: average corneal curvature (K), central corneal thickness (CCT), anterior elevation and posterior elevation at the thinnest point, corneal volume (CV), anterior chamber depth (ACD), and anterior chamber volume (ACV). Additionally, data from Belin/Ambrosio Enhanced Ectasia Display (BAD) and the high order aberrations were evaluated. Kolmogorov-Smirnov test was used to verify the Gaussian distribution, the comparison between the controls and cases group was performed by Mann-Whitney nonparametric test. A p value less than 0.05 was considered to be statistically significant. The odds ratio was performed in order to quantify the relationship between the congenital hypothyroidism and abnormal values displayed on front BAD.

RESULTS

The significant difference in the refractive status between both groups was observed. As to examined corneal and anterior chamber parameters no statistical differences were detected.

CONCLUSIONS

Congenital hypothyroidism diagnosed and treated since the early postnatal life doesn't induce abnormalities of corneal parameters suggestive for keratoconus.

Corneal Tomographic Analysis Among Patients With Thyroid Gland Dysfunction

PURPOSE

To analyze the corneal tomographic parameters of patients with thyroid gland dysfunction.

METHODS

This case-control study included 100 eyes of 50 patients with thyroid gland dysfunction and 100 eyes of 50 healthy controls. All eyes were examined by Pentacam (Oculus Optikgeräte GmbH). Pentacam parameters were compared between patients with thyroid gland dysfunction and controls. Spearman's correlation coefficient between different Pentacam parameters and the serum level of free thyroxin (T4) and thyroid-stimulating hormone (TSH) was calculated.

RESULTS

Patients with hypothyroidism had significantly higher median values of steep and maximum simulated keratometric readings, central corneal thickness (CCT), and thinnest pachymetry (CTmin) than both patients with hyperthyroidism and controls (P⩽ .05). The median values of the average and maximum pachymetric progression index (PPI), posterior elevation, and back difference elevation were significantly higher in patients with hyperthyroidism than in patients with hypothyroidism and controls (P ⩽ .05). The Ambrósio Relational Thickness (ARTmax) was significantly reduced in patients with hyperthyroidism (P ⩽ .001). Both CCT and CTmin showed a moderately positive correlation with serum TSH level and a moderately negative correlation with serum free T4 level. Patients with non-autoimmune thyroid gland dysfunction had significantly thinner CCT, CTmin, and inferior vertical deviation than the autoimmune group (P ⩽ .05).

CONCLUSIONS

Thyroid gland dysfunction is associated with significant corneal tomographic changes. Patients with hyperthyroidism tend to have thinner corneas and more abnormal tomographic parameters correlating with keratoconus. No significant tomographic changes were found in association with autoimmune thyroid gland dysfunction. The authors recommend screening and regular follow-up of patients with thyroid gland dysfunction for early detection and management of keratoconus. [J Refract Surg. 2021;37(3):192-197.].